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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 294  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3161 journals]
  • Verification of thermoelectric magnetohydrodynamic flow effects on
           dendritic tip kinetics by in-situ observations
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Rijie Zhao, Jianrong Gao, Andrew Kao, Koulis Pericleous Magnetohydrodynamic flows can be driven by Lorentz forces acting on thermoelectric currents. Their effects on tip velocities of Pd dendrites solidifying from an undercooled melt under magnetic field intensities of up to 6 T were investigated by in-situ observations using a high-speed camera. At low undercoolings, the tip velocities are depressed by magnetic fields of low and high intensities, but recover under an intermediate magnetic field intensity. At high undercoolings, the tip velocities are also depressed, but their recovery is shifted to a higher magnetic field intensity. These observations on Pd dendrites support and extend the findings obtained in previous studies on Ni and Fe dendrites, and fully verify the convection effects on dendritic growth due to three thermoelectric magnetohydrodynamic flow patterns as predicted in recent numerical simulations.Graphical abstractGraphical abstract for this article
       
  • Experimental investigation of microbubble generation in the venturi nozzle
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Chang Hun Lee, Hong Choi, Dong-Wook Jerng, Dong Eok Kim, Somchai Wongwises, Ho Seon Ahn We studied the effect of varying the entry and exit angles of Venturi nozzles on the formation of microbubbles in Venturi nozzle-type microbubble generators. We 3D-printed nozzles with five entry angles (15, 22, 30, 38 and 45°) and five exit angles (15, 22, 30, 38 and 45°). For the visualization experiment, we inserted the nozzles into a cover case made of aluminum and transparent acrylic. We measured the pressure drop and the air flow rate with respect to the entry and exit angles, determined the diameters of the bubbles using a digital camera, and analyzed bubble breakage by observing the behavior of the bubbles using a high-speed camera. We confirmed that the exit angle (not the entry angle) is dependent on the pressure drop and found that the air flow rate did not vary linearly with the fluid flow rate, as expected according to Bernoulli's theorem. Instead, it tended to remain constant or decrease as the fluid flow rate increased due to the abnormal flow. The sizes of the bubbles decreased as the exit angle increased, except in cases where the outlet angle was greater than 30° at high flow rates (260–300 LPM). We observed a change in bubble size with respect to exit angle. According to our visualization, the bubbles were broken by the flow separation at the beginning of the divergence at the exit.
       
  • Mass transfer measurements and flow separation behavior in a 90°
           short elbow
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yuya Ikarashi, Nobuyuki Fujisawa The mass transfer distribution and flow separation behavior in a 90° short elbow (radius to diameter ratio 1.0) were investigated experimentally in the Reynolds number range Re = (3–15) × 104. The mass transfer distribution in the 90° short elbow showed two high peaks on both sides of the elbow centerline of the inner elbow wall at lower Reynolds numbers (Re = (3–5) × 104). In order to characterize this phenomenon, velocity measurements were carried out using particle image velocimetry (PIV) to explain the flow separation in the short elbow, followed by the flow reattachment in the downstream. A comparative study of the mass transfer distribution and the flow fields on and near the inner wall indicated that the high mass transfer is highly responsible for the flow separation, where the turbulence intensity increased and contributed to the high mass transfer on the inner elbow wall. By increasing the Reynolds number, the flow separation region decreased in size and it came closer to the elbow centerline, which resulted in a lower mass transfer coefficient on the inner elbow wall at higher Reynolds numbers.
       
  • Turbulent heat transfer optimization for solar air heater with variation
           method based on exergy destruction minimization principle
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Hui Xiao, Junbo Wang, Zhichun Liu, Wei Liu In this paper, a heat transfer optimization approach is brought in with focusing on exergy destruction to properly deal with the trade-off between irreversibility of heat transfer process and pump power consumption in turbulent flow for solar air heater. Thus, the exergy destruction minimization principle is mathematically extended to three dimensional turbulent flow and governing equations are derived with variation method. Successively, the optimized flow field for solar air heater is obtained at Re = 12,000 by applying SST k–ω turbulence model. Furthermore, with detail analysis of velocity and temperature distribution, it is found that the longitudinal swirl flow is generated through this optimization approach. Besides, within the scope of this study, the total heat transfer exergy destruction and average absorber temperature are maximally decreased by about 65% and 30 K respectively in the test section compared with the plain duct. And the maximum Nusselt number and friction factor are increased to 1.81 and 3.13 times over plain duct respectively. These results indicate that the optimization approach is effective for improving the thermal-hydraulic performance of solar air heater. Finally, the inclined vortex plate is designed to realize this kind of optimized flow field successfully. This work will promote technique developments of solar air heater.
       
  • Fluctuation nucleation rate at limiting stretchings
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): P.A. Pavlov, V.E. Vinogradov The dynamics of an initially critical bubble after a small (as small as is wished) perturbation of its radius has been examined. Dependences of the radius, the vapor pressure and the rate of change of the bubble radius on the time from the perturbation instant have been obtained. As a result, a new formula for the specific nucleation rate in stretched and superheated liquids has been deduced with the help of the well-known theory of fluctuation nucleation. To check the formula suggested, experiments were conducted on the superheating of Freon 11 and dodecane in the pressure range from −10 MPa to +1 MPa. A satisfactory agreement between calculation and experiment has been obtained, which gives grounds to suggest using the comparatively simple formula obtained in the practice of calculating the dynamics of explosive boiling-up.
       
  • On the individual importance of temperature and concentration fluctuations
           in the turbulence-radiation interaction in pool fires
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): G.C. Fraga, F.R. Centeno, A.P. Petry, P.J. Coelho, F.H.R. França This paper presents a study of resolved-scale turbulence-radiation interaction (TRI) effects in large-scale methanol and ethanol pool fires. A broad investigation of the magnitude of the phenomenon when assuming the participating medium as gray or as non-gray is first conducted, followed by an analysis of the individual importance of turbulent fluctuations of temperature and species concentrations in the prediction of the mean radiation field. For these purposes, transient data generated by large eddy simulation are compared to results of independent radiative transfer calculations initialized with mean temperature and medium composition fields. A new methodology is proposed to isolate the influence of each fluctuating scalar on the overall TRI. In all test cases, turbulence-radiation interaction was found to increase the region of radiation loss, leading to differences between 60% and 80% in the radiant fraction of the flame compared to solutions neglecting turbulent fluctuations. When treating the media as non-gray, TRI effects were globally more significant, even though in some parts of the domain simulations employing the gray assumption yielded larger deviations in the mean radiative heat source due to TRI. By isolating the contributions of fluctuations of temperature and fluctuations of species concentrations, the latter resulted in mean radiation fields very similar to the ones obtained by neglecting all scalar fluctuations, while the former, although being closer to the solution considering full TRI effects, still showed differences as high as 60% relative to that solution. These findings indicate that temperature fluctuations are more important to the turbulence-radiation interaction phenomenon, but fluctuations in medium composition need to be taken into account in order to obtain reliable predictions of the mean radiative heat transfer.
       
  • Numerical study on the flow and heat transfer characteristics in a dimple
           cooling channel with a wedge-shaped vortex generator
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Jae Sung Yang, Myunggeun Jeong, Yong Gap Park, Man Yeong Ha This study numerically investigates the detailed flow structure and heat transfer characteristics of a newly designed dimple cooling channel. The proposed surface geometry is a general dimple structure combined with a wedge-shaped vortex generator on the upstream dimple. The main purpose of the surface geometry is to enhance the flow mixing and heat transfer in the flow-recirculating region that is generated by the dimple cooling channel. Direct numerical simulations were carried out with a Reynolds number of 2800 and Prandtl number of 0.71 in the cooling channel. The main design parameter is the width ratio between the cooling channel and vortex generator (W*). When W* increases, the heat transfer on the surface is enhanced because of the main counter-rotating vortex downstream of the computational domain. In the case of W* = 0.4411, the volume goodness factor increases to approximately 30% compared to the general dimple cooling channel.
       
  • Non-Fourier transient thermal analysis of biological tissue phantoms
           subjected to high intensity focused ultrasound
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Pragya Gupta, Atul Srivastava The present study is concerned with the numerical analysis of the non-Fourier heat transfer phenomena in biological tissue samples subjected to high intensity focused ultrasound (HIFU). Due to the inherent non-homogeneous nature of biological samples, the well-known Pennes bioheat equation (PBHTE) is not strictly suitable for correctly predicting the temperature distribution in the tissue medium subjected to HIFU. In this respect, thermal wave model of bioheat transfer (TWMBT), which takes into account the finite propagation speed of thermal front, plays an important role in describing the observed wave-like behavior of heat transfer in biological tissue medium. The temperature profiles obtained from TWMBT show the presence of oscillations during the process of diffusion of thermal wave after reaching its maximum peak, depending upon the corresponding relaxation time. Results show that the thermal dosage with finite value of relaxation time gives lesser heat-affected area compared to the dosage calculated by considering the infinite propagation of thermal front as in the case of the conventional Fourier model. These observations make the present study important as otherwise, the target area is prone to remain under insufficiently heated conditions.
       
  • Numerical simulation of the movement of water surface of dam break flow by
           VOF methods for various obstacles
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Alibek Issakhov, Medina Imanberdiyeva In this paper, the movement of the water surface is numerically simulated when a dam is broken by the volume of fluid (VOF) method. The mathematical model is based on the Navier-Stokes equations and uses the LES turbulent model, describing the flow of an incompressible viscous fluid and the equation for the phase. These equations are discretized by the finite volume method. Numerical PISO algorithm was chosen for numerical solution of this equation system. The movement of the water surface is captured by using the VOF method, which leads to a strict mass conservation law. The accuracy of the 3D model and the chosen numerical algorithm were tested using several laboratory experiments on dam break problem. In each of the problems, the obtained results were compared with the experimental data and several calculations by other authors and in each of the test problems, the developed model showed results close to the experimental data. Comparison of simulation results with experimental data for various turbulent models was also performed. And also a three-dimensional model of dam break flow on uneven terrain was developed. And also two combined problems were performed which are more close to real conditions, with the help of these problems, flooding zones and flooding time were identified that would help in evacuating people from dangerous zones.
       
  • A useful case study to develop lattice Boltzmann method performance:
           Gravity effects on slip velocity and temperature profiles of an air flow
           inside a microchannel under a constant heat flux boundary condition
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Annunziata D'Orazio, Arash Karimipour Mixed convection heat transfer of air in a 2-D microchannel is investigated numerically by using lattice Boltzmann method. The effects of buoyancy forces on slip velocity and temperature profiles are presented while the microchannel side walls are under a constant heat flux boundary condition. Three states are considered as no gravity, Gr = 100 and Gr = 500. At each state, the value of Knudsen number is chosen as Kn = 0.005, Kn = 0.01 and Kn = 0.02 respectively; while Reynolds number and Prandtl number are kept fixed at Re = 1 and Pr = 0.7. Density-momentum and internal energy distribution functions are used in order to simulate the hydrodynamic and thermal domains in LBM approach. Develop the ability of LBM to simulate the constant heat flux boundary condition along the microchannel walls in the presence of slip velocity and buoyancy forces is proved for the first time at present work. The new and interesting results are achieved such as generating a rotational cell through the fluid flow due to buoyancy forces which leads to see the negative slip velocity at these areas.
       
  • Anisotropic corrections for the downwelling radiative heat transfer flux
           from various types of aerosols
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Zhouyi Liao, Mengying Li, Carlos F.M. Coimbra Comprehensive Monte Carlo simulations are used to correct deviations in the atmospheric downwelling longwave (DLW) radiative flux calculated by isotropic scattering assumptions. The widely used δ-M approximation is validated for low to medium values of aerosol loading. For very high aerosol loading conditions, the δ-M approximation incurs an error. Here we propose scaling corrections for extreme loading conditions routinely found in selected urban areas in Asia, but also in other continental and coastal areas susceptible to large-scale wildfire pollution (Western USA) or dust storms (Mediterranean regions and Northern Africa). The scaling rules are expressed as functions of the normalized aerosol optical depth t∗ and the scattering asymmetry factor eg. An exponential relationship between the DLW deviation that assumes isotropic scattering and t∗ is found, and the corresponding fitting coefficients are correlated for different types of aerosols (sample internal mixing, urban, continental and marine aerosols). The δ-M approximation is sufficiently accurate when aerosol optical depths (AOD) at the ground level are smaller than 0.5. For AOD beyond this threshold, the proposed scaling rule corrections should be used for estimation of downwelling thermal radiative fluxes. The effects of moisture content on aerosol composition and on DLW radiative fluxes are also investigated for all conditions of interest.
       
  • On the transient thermal response of thin vapor chamber heat spreaders:
           Governing mechanisms and performance relative to metal spreaders
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Gaurav Patankar, Justin A. Weibel, Suresh V. Garimella Vapor chambers can offer a passive heat spreading solution for thermal management in electronics applications ranging from mobile devices to high-power servers. The steady-state operation and performance of vapor chambers has been extensively explored. However, most electronic devices have inherently transient operational modes. For such applications, it is critical to understand the transient thermal response of vapor chamber heat spreaders and to benchmark their transient performance relative to the known behavior of metal heat spreaders. This study uses a low-cost, 3D, transient semi-analytical transport model to explore the transient thermal behavior of thin vapor chambers. We identify the three key mechanisms that govern the transient thermal response: (1) the total thermal capacity of the vapor chamber governs the rate of increase of the volume-averaged mean temperature; (2) the effective in-plane diffusivity governs the time required for the spatial temperature profile to initially develop; and (3) the effective in-plane conductance of the vapor core governs the range of the spatial temperature variation, and by extension, the steady-state performance. An experiment is conducted using a commercial vapor chamber sample to confirm the governing mechanisms revealed by the transport model; the model accurately predicts the experimental measurements. Lastly, the transient performance of a vapor chamber relative to a copper heat spreader of the same external dimensions is explored as a function of the heat spreader thickness and input power. The mechanisms governing the transient behavior of vapor chambers are used to explain the appearance of key performance thresholds beyond which performance is superior to the copper heat spreader. This work provides a foundation for understanding the benefits and limitations of vapor chambers relative to metal heat spreaders in transient operation and may inform the design of vapor chambers for improved transient performance.
       
  • Quench of molten copper and eutectic mixture in natural seawater
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yu-You Chang, Ben-Ran Fu, Chin Pan The interaction of molten materials with coolant is of significant fundamental interest and is of paramount importance for nuclear safety and material processing as well. This study explores the quenching of melts of copper spheres and a eutectic mixture of bismuth trioxide and tungsten trioxide (BTOP) in de-ionized water and natural seawater through visualization using a high-speed video camera. The results show no fragmentation in the case of molten copper owing to its high surface tension, while the quench of BTOP in de-ionized water and seawater results in extensive fragmentation. The fragmentation in seawater is characterized by a greater fraction of larger debris than that in the de-ionized water. Moreover, the examination of the debris quenched in seawater using scanning electron microscopy reveals a rougher surface, which demonstrates intensive interactions between the BTOP melts and the seawater owing to the complex ions there.
       
  • Experimental measurements of the high-temperature oxidation of carbon
           fibers
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Francesco Panerai, Thom Cochell, Alexandre Martin, Jason D. White We carried out laboratory experiments to study the decomposition of carbon fibers at high temperature and studied the material used in charring carbon phenolic ablators for planetary probe heatshields. Porous plug samples were exposed to controlled rates of molecular oxygen, carbon dioxide, and carbon monoxide at furnace-heated flow-tube reactor temperatures between 700 and 1500 K and pressures between 2000 and 6200 Pa. We used calibrated mass spectroscopy to make time-resolved quantitative measurements of decomposition products of the gases downstream of the test sample. Absolute and differential pressure measurements were used to determine the high-temperature permeability of the material and to monitor changes during material decomposition, and we characterized the microstructure of the porous sample using scanning electron microscopy. We found substantial carbon fiber oxidation for O2 flows, resulting in increasing CO/CO2 production ratios with increasing temperature. The CO2 was shown to react with carbon fibers following a Boudouard reaction at temperatures above 1200 K.
       
  • Multi-component droplet evaporation model incorporating the effects of
           non-ideality and thermal radiation
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Bin Fang, Longfei Chen, Guangze Li, Lei Wang Currently, sophisticated fuel formulation and high temperature combustion in gas turbine and internal combustion engines make it important to investigate the effects of mixture non-ideality and radiation absorption on fuel droplet evaporation. In this study, an improved evaporation model by considering activity coefficients (AC) and external thermal radiation was established to simulate the evaporation process of multi-component non-ideal fuel droplets, and droplet suspension experiment was performed to validate the proposed model. It was found that the accuracy of simulated results was enhanced by considering activity coefficients and radiation absorption, and both effects were dependent on ambient temperature. The effect of activity coefficient was significant at low temperature (503 K), under which the droplet evaporation rate in the initial period was obviously faster than that at later stage. Consequently, the droplet lifetime decreased by about 8% at low temperature when activity coefficient was taken into consideration. At high temperature (703 K), however, the effect of activity coefficient or non-ideality on the droplet evaporation rate turned out to be insignificant. The radiation had a strong influence on evaporation at high temperature with the droplet lifetime decreasing 48% when ambient temperature increased from 503 K to 703 K. There seemed to be a critical diameter, under which the effect of radiation became negligible. It is also demonstrated that the component concentration gradients existed inside the non-ideal droplets in the initial period because of relatively low mass diffusion rate. As time elapsed, the gradients gradually disappeared due to the fact the components with large activity coefficient nearly completely evaporated.
       
  • Flow visualization of R1234ze(E) in a 0.643 mm microchannel tube
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Houpei Li, Pega Hrnjak This paper presents the discussion of regimes of two-phase flow of R1234ze(E) in a 24-port microchannel tube with average hydraulic diameter of 0.643 mm, obtained by visualization. The experiment is conducted in the same facility in the previous work for R32 (Li and Hrnjak, 2019). The conditions cover mass flux from 50 to 225 kg m−2 s−1. The inlet saturation temperature is 30 °C. The two-phase flow is generated by adding heat in several steps to refrigerant initially subcooled at the entrance of test line. As vapor quality increases at a fixed mass flux, the flow is firstly plug/slug, then transitional, and finally is annular flow regime at high quality. When mass flux is 50 kg m−2 s−1, no annular flow observed in the tube. The vapor quality of boundary between two flow patterns decreases as mass flux increases. The annular flow starts at x = 0.85 (G = 100 kg m−2 s−1) and x = 0.63 (225 kg m−2 s−1). The transitional flow starts at x = 0.8 (G = 50 kg m−2 s−1) and x = 0.3 (225 kg m−2 s−1). Comparing to R32 and R134a, flow patterns of R1234ze(E) transition at lower quality due to the lower vapor density and thus higher vapor velocity. Three flow pattern maps in literature are compared to the results and they have limited agreement with our observations. The plug/slug flow behaves as homogeneous. The velocity at interface between liquid slug and vapor plug is close to the homogeneous velocity. The vapor plug length fraction also agrees to the homogeneous void fraction. The length of vapor plug increases dramatically as vapor quality increases at fixed mass flux. The length of liquid slug first increases and then unchanged as quality increases. The video supports that there are liquid droplets formed from the liquid slug and liquid ring collision.
       
  • Investigation on heat transfer of in-tube supercritical water cooling
           accompanying out-tube pool boiling
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Haicai Lv, Qincheng Bi, Xinyu Dong, Zanjian Zhang, Ge Zhu Heat transfer of in-tube supercritical fluid cooling accompanying out-tube pool boiling was investigated. A smooth horizontal circular tube with an inside-diameter of 20 mm was submerged in a water pool at atmospheric pressure. Test parameters of in-tube were as follows: Pressure: 23–28 MPa, mass flux: 600–1000 kg·m−2·s−1, fluid temperature: 400–725 K, and the temperature difference between bulk and wall: 300–374 K. A thermal amplification system based on out-tube pool boiling was used to improve the measurement accuracy of local heat duty near pseudocritical region. According to the experiment, the transition from nucleate boiling to film boiling in the pool occurred near the pseudo-critical fluid region. Sharp variation on thermo-physical properties led to the peak value of heat transfer coefficient in the pseudo-critical region. The pool boiling heat flux increased gradually to 1.19 MW·m−2 near the pseudocritical point. Based on the experimental data, a modified Gnielinski equation was adopted to predict the heat transfer coefficient of in-tube supercritical fluid cooling with out-tube pool boiling. The thermophysical property ratio of the wall to the bulk as well as the effect of buoyancy were taken into consideration in the new correlation. The predicted correlation has an error of less than 20% to the experimental data.
       
  • Numerical investigation of the laminar natural convection heat transfer
           from the equilateral triangular cluster of three horizontal spheres
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Ze-Yuan Liu, Yang Chu, Jie Liu, Wen-Qiang Lu Natural convection heat transfer from the equilateral triangular cluster of three horizontal spheres in air has been investigated numerically over the range of 10≤Gr≤105. An extended model is used for the partially symmetric cluster in the three-dimensional condition, which is proposed initially by Bejan et al. (1995). The accuracy of the extended model has been validated by the single sphere. The comprehensive results consist of isothermal and streamline contours, the local drag coefficients as well as the local and average Nusselt number distributions with the different Grashof numbers. There is a thicker thermal boundary in the center clearance of the cluster due to the interaction of the three adjacent surface for all Grashof numbers, which weakens the heat transfer and deteriorates into the decreasing of local Nusselt number along the polar angle, while the negative velocity gradient has a similar effect. Then the correlation equation of the average Nusselt number in the range of 10≤Gr≤105 has been proposed. Compared with the single sphere, the average Nusselt number of the cluster changes from 64.69% to 92.45% of that of the single sphere due to the stronger buoyancy force and the larger temperature gradient with the increasing Grashof number.
       
  • Predicting the effective thermal conductivity of silica/clay mineral
           nanocomposite aerogels
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Fatemeh Pashaei Soorbaghi, Mehrdad Kokabi, Ahmad Reza Bahramian The crucial effect of the morphology of nanocomposite aerogel on its effective thermal conductivity caused the presence of comprehensive theoretical investigation. Classic unit cell model provided an analytical relationship between microstructure and thermal conductivity of pristine silica aerogels, but the predicted results showed more than 250% deviation from the experimental results. In this work, the classic unit cell model was modified for nanocomposite aerogel by considering the effect of phonon scattering, secondary porosity, and clay mineral presence. The modified classic unit cell model (MCUM) acted as a powerful tool in the analysis of thermal conductivity mechanism of silica/clay mineral nanocomposite aerogels. Clay mineral was utilized to improve thermal radiation insulation properties of nanocomposite aerogels. Experimental results revealed that addition of 7 wt% clay mineral to silica aerogel led to a 55% reduction in thermal radiation heat transport at 700 °C. MCUM showed good agreement with experimental results with a less than 10% deviation for neat and nanocomposite aerogel.Graphical abstractGraphical abstract for this article
       
  • Experimental investigation of thermal performance of the oscillating heat
           pipe for the grinding wheel
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Ning Qian, Yucan Fu, Yuwen Zhang, Jiajia Chen, Jiuhua Xu A massive amount of heat is generated during the high-efficiency grinding process, which leads to a serious burnout problem that limits the increase of the material removal rate. The oscillating heat pipe (OHP) can augment the heat transfer in the grinding zone to avoid the burnout. An oscillating heat pipe grinding wheel that is a combination of a grinding wheel and OHPs was proposed in this paper. Aimed to determine geometric dimensions and operating parameters of the OHP, experimental investigations were carried out to study effects of working fluid, inner diameter, and heat flux on the heat transport capability of OHPs. The dynamics of flow change and coupled effects of geometric dimensions and thermophysical properties of working fluids were further analyzed by visualization. The OHP filled with acetone shows an advantage in heat transfer. Within the critical diameter range, a large inner diameter is better for the thermal performance. As heat flux increases, changes of flow pattern and motion modes from bubbly flow to annular flow and from oscillation to circulation enhance the thermal performance. The inner diameter of 3 mm and acetone as the working fluid are preferred for better cooling effects.
       
  • Quench subcooled-jet impingement boiling: Staggered-array jets enhancement
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Sang Gun Lee, Massoud Kaviany, Jungho Lee In quench subcooled-jet boiling, an effective cooling of large surface area is achieved with jet arrays. Here a stainless-steel plate initially superheated at 900 °C is cooled with seven hexagonally arranged water [1 atm, 20 °C (80 °C subcooling)] jets (7j), and with varying jet separation distance (with a jet Reynolds number ReD = 5000). Using high-definition visualization synchronized with the surface thermal characterization based on the inverse-conduction analysis allows calculation of the spatial and temporal variations of the local and average heat flux (q) and heat transfer coefficient (h). The local and temporal peaks in q and h occur under the jets with enhancements in the regions of their interactions. We compare these results with the prior two jets (2j) and single jet (1j) results (with ReD = 15,000). For a jet separation of four nozzle diameter (S/Dn = 4), the 7j behavior is close to the single jet (1j), while with larger separation extra h peaks occur and the cooling becomes more effective (larger cooling area, but with smaller area-averaged heat transfer coefficient 〈h〉). For S/Dn = 10, the 7j enhanced cooling effectiveness is smaller than the 2j effectiveness, suggesting using similar total liquid flow rate, fewer jets are preferred. The cooling effectiveness enhancement for the S/Dn = 6 arrangement is the highest, reaching 50% and covering a large high-h area, and over a long elapsed time.
       
  • Experimental investigation on interfacial oscillation of direct contact
           condensation of steam jet in water pipe flow
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Qiang Xu, Xiaona Chu, Haiyang Yu, Weizhi Liu, Tian Yao, Liejin Guo Interfacial oscillation associated with direct contact condensation of steam jet in water pipe flow is of high significance for industrial processes. In this paper, experimental study is conducted to reveal the mechanisms of the interfacial oscillation in steam jet condensation in subcooled water flow in a vertical pipe. The interfacial behavior of the jet plume is acquired by high speed camera, and the entire interface in both space and time simultaneously is quantitatively analyzed with digital image processing technology. Bubbling regime occurs at subsonic conditions, where an undulated bubble plume forms with one or more large bubbles falling off intermittently. Jetting regime happens at transonic or supersonic conditions, where a quasi-stable jet plume is observed with numerous uncondensed tiny bubbles continuously shedding off from the end of the jet plume. Distinct waveforms of the radial interface position in both space and time simultaneously are recognized for the two typical condensation regimes. The interfacial unsteadiness reaches a maximum near the sonic point and then drops in the supersonic region, which exhibits similar trend with pressure oscillation induced by condensing jet in a qualitative sense. The results confirm that the pressure oscillation is highly relevant to the motion of the jet interface and it should be induced by the interfacial oscillation. The spatial growth rate of the interface unsteadiness along the jet decreases steadily as steam mass flux increases from subsonic to sonic point and it almost does not vary in the supersonic region. The Kelvin-Helmholtz instability mechanism is more important near the nozzle exit, while in other region the Kelvin-Helmholtz instability is of the same importance as the Rayleigh-Taylor instability.
       
  • An experimental study on the thermal effects of duty-cycled plasma
           actuation pertinent to aircraft icing mitigation
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yang Liu, Cem Kolbakir, Haiyang Hu, Xuanshi Meng, Hui Hu An experimental study was performed to evaluate the effectiveness of utilizing the thermal effects induced by duty-cycled dielectric barrier discharge (DBD) plasma actuation for aircraft icing mitigation. The experimental study was carried out in the unique Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT) with a NACA0012 airfoil model embedded with DBD plasma actuators exposed under a typical glaze icing condition. During the experiments, the DBD plasma actuators were operated in two different modes for a comparative study, i.e., in duty-cycled actuation mode vs. in conventional continuous actuation mode as the comparison baseline. While the anti-/de-icing performances of the DBD plasma actuators under different actuation modes were revealed clearly based on the snapshot images acquired by using a high-speed imaging system, an infrared (IR) thermal imaging system was also used to map the corresponding surface temperature distributions over the ice accreting airfoil surface in order to characterize the thermal effects induced by the plasma actuations. It was found that, with the same power input, the plasma actuation in duty-cycled mode would have a higher instantaneous voltage during the “on” periods, resulting in much stronger thermal effects for an improved anti-/de-icing performance, in comparison to the case in the continuous actuation mode. The thermal effects induced by the duty-cycled plasma actuation were found to be further enhanced by increasing of the modulating frequency of the duty cycles, which is a very promising approach to further improve the anti-/de-icing performance of DBD plasma actuation. The findings derived from the present study could be used to explore/optimize design paradigm for the development of novel DBD-plasma-based anti-/de-icing strategies tailored specifically for aircraft icing mitigation.
       
  • Heat transfer enhancement of turbulent channel flow using dual
           self-oscillating inverted flags: Staggered and side-by-side configurations
           
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yujia Chen, Yuelong Yu, Di Peng, Yingzheng Liu This study experimentally determined the flapping dynamics of dual self-oscillating inverted flags placed inside turbulent channel flows in side-by-side and staggered configurations and their ability to enhance wall heat removal. Three clearance-distance to channel-width ratios (Gc/W = 0.19, 0.31, and 0.5) and three streamwise-distance to channel-width ratios (Gy/W = 0, 2, and 4) were used to examine distinct flag behaviors. A single flag mounted to the heated wall with various gap clearances was chosen as the benchmark. The flags’ time-varying motions were recorded by a high-speed camera system. Three dynamic regimes were identified on the basis of the flags’ dimensionless stiffness and the channel flow’s Reynolds number: the biased mode, the flapping mode, and the deflected mode. Temperature sensitive paint (TSP) measurements demonstrated that the best cooling enhancement, with a local Nusselt number ratio of over 1.6, was achieved for the single flag system at Gc/W = 0.19. Adding another inverted flag to the side-by-side configuration at Gc/W = 0.19 further enhanced the heat removal performance on both channel walls, and the flapping period increased by nearly 50%. However, placing two side-by-side flags close to each other (Gc/W = 0.31) led to chaotic flapping motions, resulting in diminutive augmentation in heat transfer and an appreciable penalty in pressure drop. In the staggered configuration at Gy/W = 2 and 4, the two inverted flags synchronously flapped with a stable phase difference, and the flapping periods were similar to those of the single flag. The peak Nusselt number ratio was 1.9 for Gy/W = 2, which was attributed to the concerted influence of the staggered inverted flags. The system with staggered flags placed close to the heated wall had a higher thermal enhancement factor than the system with flags mounted in tandem along the channel centerline.
       
  • Simultaneous wick and fluid selection for the design of
           minimized-thermal-resistance vapor chambers under different operating
           conditions
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Kalind Baraya, Justin A. Weibel, Suresh V. Garimella The thermal resistance of a vapor chamber is primarily governed by conduction across the evaporator wick and the saturation temperature gradient in the vapor core. The relative contributions of these two predominant resistances can vary dramatically with vapor chamber operating conditions and geometry. In the limit of very thin form factors, the contribution from the vapor core thermal resistance dominates the overall thermal resistance of the vapor chamber; recent work has focused on working fluid selection to minimize overall thermal resistance in this limit. However, the wick thermal resistance becomes increasingly significant as its thickness increases to support higher heat inputs while avoiding the capillary limit. It therefore becomes critical to simultaneously consider the contributions of the wick and vapor core thermal resistances in the development of a generalized methodology for vapor chamber working fluid selection. The current work uses a simplified thermal-resistance-network-based vapor chamber model to explore selection of working fluids and wick structures that offer the minimum overall thermal resistance as a function of the vapor chamber thickness and heat input. An illustrative example of working fluid selection, for cases with and without the contribution of wick thermal resistance, is first used to demonstrate the potential significance of the wick thermal resistance on fluid choice. This influence of the wick on working fluid selection is further explained based on the wick properties (effective pore radius, permeability, and effective thermal conductivity). The ratio of effective pore radius to wick permeability is found to be the most critical wick parameter governing the overall vapor chamber resistance at thin form factors where minimizing the wick thickness is paramount; the wick conductivity becomes an equally important parameter only at thicker form factors. Based on this insight, a new approach for vapor chamber design is demonstrated, which allows simultaneous selection of the working fluid and wick that provides minimum overall thermal resistance for a given geometry and operating condition.
       
  • Correlations for the Graetz problem in convection – Part 1: For round
           pipes and parallel plates
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Ted D. Bennett A general correlation is proposed for the laminar Graetz problem associated with convection in round pipes and parallel plate ducts. The general correlation for the average Nusselt number can be expressed under conditions of either constant wall temperature or constant wall heat flux. Additionally, closed form expressions for the local Nusselt number can be derived from the general correlation. New correlations are found to be within ±1.5% of exact solutions to the Graetz problem for round pipes and parallel plates, and are contrasted with existing correlations in the literature.
       
  • Evaporation of ethanol films wicking on structured, porous coatings
           deposited on copper plates
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Chen Feng, Sanjeev Chandra Porous copper coatings were deposited on copper plates by flame spraying. Wire mesh masks were placed on the substrate while spraying to create channels in the coatings. Pores increased the capillary pressure of liquid flowing through the coating while channels increased permeability. Coated copper strips were suspended vertically with their bottom edges touching an ethanol reservoir so that liquid wicked upwards due to capillary force and evaporated. The copper strips were heated electrically and their temperature recorded as the heater power was varied. The rate of ethanol evaporation was measured by recording the change in weight of the liquid reservoir and the height of the liquid film measured from photographs. Raising surface temperature increased liquid evaporation rate and reduced the film height. Surface dry-out occurred when the mass evaporation rate became greater than the maximum wicking rate for a given surface. Increasing the effective porosity of the coating enhanced the maximum mass flow rate through it. For high porosity surfaces the liquid began to boil before dry-out occurred. An analytical model of liquid film rise was developed to predict film height, film thickness, and the rate of evaporative cooling as a function of surface temperature.
       
  • Uncertainty and sensitivity analysis of SST turbulence model on hypersonic
           flow heat transfer
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yatian Zhao, Chao Yan, Xiaoyong Wang, Hongkang Liu, Wei Zhang Due to the lacking of knowledge and incomplete information about the closure coefficients in Menter Shear Stress Transport (SST) turbulence model, numerical predictions of hypersonic flow heat transfer possess some uncertainties. The objective of this work is to investigate the uncertainty and identify the key parameters contributing most to the uncertainty in hypersonic aeroheating predictions. In the current study, the nine closure coefficients in SST turbulence model are treated as uncertainty variables represented with intervals, meanwhile stochastic expansion based on non-intrusive polynomial chaos (NIPC) expansion is utilized to represent and propagate the uncertainties, afterwards the Sobol indices evaluated by the polynomial chaos expansion coefficients are used to rank the relative contribution of each closure coefficient. Totally, 110 CFD evaluations are adopted to quantify the uncertainty and sensitivity in hypersonic flow heat transfer. Specifically, uncertainty and sensitivity analysis are performed for hypersonic flow over the double-ellipsoid model and the X-33 flight vehicle. The numerical results show that heat flux is more sensitive to uncertainty of closure coefficients compared to pressure. For the SST model, the coefficients which contribute most to uncertainty in hypersonic flow heat are σω1, κ and a1. While a1 is one of the dominant source of heat flux and pressure in the shock region near the wall.
       
  • Effect of burners configuration on performance of heat treatment furnaces
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Niki Rezazadeh, Hamzeh Hosseinzadeh, Binxin Wu In order to obtain the most uniform temperature of the load, heat transfer in heat treatment furnaces used in the steel industry was studied. Different two-equation turbulence models were compared with experimental results. The Realizable k-ε model, predicts the load center line temperature better than the other two models, and it agrees closer to the experimental data. Also, by considering the radiation effect in the numerical simulation, the results were improved by 33% compared with experimental data. Finally, from different configurations of the burners studied and the results showed that the best temperature uniformity would be achieved for the configuration when the burners were located in a three down-three up arrangement.
       
  • Numerical investigation of magnetohydrodynamic natural convection heat
           transfer and entropy generation in a rhombic enclosure filled with
           Cu-water nanofluid
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Shantanu Dutta, Navneet Goswami, Arup Kumar Biswas, Sukumar Pati The present work analyses magnetohydrodynamic natural convection heat transfer and entropy generation in rhombic enclosures filled with Cu-water nanofluids. Numerical simulations were executed for varying Rayleigh number (Ra) in the range 103–106, Hartmann number (Ha) in the range 0–100 and inclination angles of the enclosure (30°, 45° and 60°) considering three different volume fractions of the nanofluid (1%, 3% and 5%). The results indicate that at low Ra, the heat transfer rate remains invariant with the variation in Ha. At high Ra (≥105), the presence of the magnetic field is more perceptible implying that the reduction in heat transfer rate with the increase in magnetic field intensity is far more significant. The heat transfer rate enhances with the increase in inclination angle for all Ha for Ra =103 and 104. However, at high Ra (=105 and 106) the trend becomes contrasting due to the interplay of buoyancy and Lorentz forces. There exists an operating range of Ha in the convection regime wherein the efficacy of the nanofluid in augmenting the heat transfer rate is negated when compared to the corresponding performance of the base fluid. The concomitant thermal identity resulting due to the combined interactions of Hartmann number and volume fraction of the nanofluid have been presented. The entropy generation rate decreases with the increase in Ha for all values of Ra and inclination angles of the enclosure.
       
  • A superheat degree driven liquid-vapor phase-change lattice Boltzmann
           model
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Anjie Hu, Dong Liu This paper proposes a phase-change pseudo-potential lattice Boltzmann model based on the bubble dynamic theory. To maintain the stability of the liquid during the phase change process, the phase change of the model is driven by the superheat degree in the interface area instead of the thermodynamic temperature in the equation of state (EOS). The presented model is verified by the simulations of liquid film evaporation and is applied to the simulation of the bubble growth in superheated fluid and on the wall. The simulation results show that the simulation density ratio over 100 can be reached. The influence of the bubble curvature on the superheat degree in the bubble can also be reflected with the proposed model.
       
  • Numerical simulation of ash particles deposition in rectangular heat
           exchange channel
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Zhimin Han, Zhiming Xu, Xiaoyan Yu, Aodi Sun, Yanfeng Li The flue gas of the coal-fired boiler is composed of a great number of fly ash particles. Such particles may easily form ash deposition on the heating surface of the heat exchanger when recovering the wasted heat energy from the flue gas. Here, we study the deposition of gas-side fly ash particles on the heating surface in a three-dimensional rectangular heat transfer channel by a numerical simulation method. First, the critical deposition velocity is calculated using the user-defined function (UDF) and the deposition process of the ash particles are simulated using the discrete phase model (DPM). Then, the rationality of the proposed method is verified by comparing the simulation results with the experimental data. In addition, we investigate the effects of the inlet velocities and particle diameters on the deposition efficiency of each wall of the rectangular channel. The results show that the particle deposition efficiency of different locations of the channel, i.e., the floor, the two sidewalls, and the ceiling, may be varied by the changing the particle diameter and the flow velocity. Moreover, we show that for a large particle, the ceiling and sidewalls, respectively, the first and second lowest particles deposition efficiency, while the floor exhibits the largest particles deposition efficiency.
       
  • Flat plate film cooling with linear and curved round-to-diffusion shaped
           slots using PSP measurement technique
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Izhar Ullah, Chao-Cheng Shiau, Je-Chin Han This paper experimentally examines the effect of hole shape and coolant trajectory on film cooling effectiveness by using PSP measurement technique. Three different density ratios DR = 1, DR = 1.5, and DR = 2 were tested with five blowing ratios ranging from M = 0.5–1.5 with an increment of 0.25. Three different hole geometries (round to slot, round to annulus, and round to annulus2) were used with linear and projectile trajectories. Results obtained agreed with the general trend of shaped holes. In terms of hole shape, the slot-shaped hole resulted in better performance as compared to annulus shaped holes. Particularly, the slot-shaped hole with projectile trajectory results in 30–35% increase in effectiveness as compared to its linear trajectory slot-shaped counterpart. This design is found to have lowest discharge coefficient, but it works best at DR = 2. A correlation was also developed for single row different exit shaped holes helping the designers to calculate the spanwise effectiveness at different conditions.
       
  • Effects of pin and wire electrodes on flow boiling heat transfer
           enhancement in a vertical minichannel heat sink
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Jinxin Zhang, Xiaoping Luo, Zhenfei Feng, Feng Guo In this paper, electrohydrodynamic (EHD) enhancement of flow boiling heat transfer in a vertical minichannel heat sink was investigated experimentally. The pin and wire electrodes are used to create different kinds of non-uniform electric fields. Flow boiling experiments of refrigerant R-141b under electric fields are conducted under various applied voltages. The results show that the application of pin and wire electrodes can promote the Onset of Nucleate Boiling (ONB) and effectively enhance heat transfer coefficient. For the pin and wire electrodes, the EHD enhancement effect increases with the increase of applied voltage. At the same heat flux, heat transfer enhancement for pin electrode is higher than that for wire electrode at low applied voltage (U ≤ 400 V), but is lower than that for wire electrode at high applied voltage (U ≥ 550 V). Moreover, the obtained maximum enhancement ratio for pin and wire electrodes could reach 1.72 and 1.80, respectively. The influence area of pin electrode is limited, whereas the influence area of wire electrode is the entire electrode length at U ≥ 400 V. Based on the simulation and experiment results, the enhancing mechanism of EHD on flow boiling heat transfer in minichannel was discussed.
       
  • Numerical analysis of irreversible processes in a piston-cylinder system
           using LB1S turbulence model
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Siti Nurul Akmal Yusof, Yutaka Asako, Mohammad Faghri, Lit Ken Tan, Nor Azwadi bin Che Sidik, Wan Mohd Arif bin Aziz Japar A numerical analysis for the irreversible processes in an adiabatic piston-cylinder system was conducted using the Lam & Bremhorst low Reynolds number turbulence model (LB1) modified for compressible flows by Sarkar and Balakrishnan (LB1S model). Two-dimensional compressible momentum equation and energy equation which includes the substantial derivative of pressure and the viscous dissipation terms were solved numerically to obtain the state quantities of the system. The computations were performed for a single compression process with constant piston velocity, up=-10 m/s and for cyclic compression and expansion processes with sinusoidal velocity variation. The selected rotation speed ranges from 1000 to 50,000 rpm. The computations were performed for 10 cycles. It was found that the sinusoidal piston velocities have effects on the state quantities of the piston-cylinder system and it experienced an irreversible process when the piston moved with a finite velocity. For the case of single compression process, the flow was laminar when the piston velocity was below 10 m/s. In the cyclic processes, the flow was turbulent when the rotation speed is in the range from 2000 to 50,000 rpm. However, for the case of 2000 rpm, the flow was laminar only at the first cycle. This is due to the turbulent viscosity that is lower than dynamic viscosity (1.862×10-5 Pa s). It was found increasing the rotation speed will increase the value of the turbulent viscosity. In the cyclic processes for the cases N = 1000, 10,000 and 50,000 rpm, the internal energy increased by 0.003%, 0.028% and 0.289% of the compression work in each cycle, respectively.
       
  • Fingering instability analysis for thin gravity-driven films flowing down
           a uniformly heated/cooled cylinder
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Chicheng Ma This paper focuses on fingering instability of a thin liquid film flowing down a vertical uniformly heated/cooled cylinder under the influence of gravity. Thin film model is applied to derive the evolution equation and linear stability analysis in three dimensional setting is investigated. According to the evolution equation, the height of the thin film flowing down a cylinder depends on two parameters, the Marangoni number and the dimensionless cylinder radius. Travelling wave solutions are constructed, and the influence of the Marangoni number, the thickness of the precursor film and the radius of the cylinder are taken into consideration. Fully three dimensional simulations are also given based on finite element method with the help of open source software Freefem++. Numerical simulations demonstrate that the Marangoni effect enhances long-wave instability while the thickness of the precursor film suppresses fingering instability. The dimensionless radius has a significant destabilizing influence on the flow while the scaled radius R
       
  • Two-phase flow and heat transfer in a self-developed MRI compatible LN2
           cryoprobe and its experimental evaluation
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Xin Zhang, S.M.Chapal Hossain, Qiang Wang, Bensheng Qiu, Gang Zhao Cryosurgery is a new alternative surgical treatment compared with other traditional methods. However, it is hampered to standard cancer treatment due to some limitations. One is difficult to accurately monitor the extent of frozen tissue of internal organs during treatment. Another is insufficient freezing effect in the edge of the frozen region which leads to recurrence and metastasis of tumors. The approach of magnetic resonance imaging (MRI) is used to overcome such type of drawbacks during cryosurgery. The reason is that MRI could be explored to guide the puncture process and also monitor the developed frozen region throughout the cryoablation. Also, the iceball monitoring approaches could help to reduce the cell death of non-cancerous tissues. However, none of the studies enunciated the MRI compatible liquid nitrogen (LN2) cryoprobe based cryosurgery system to demonstrate the thermal evaluation during the treatment of carcinoma tissue. In this study, we established the MRI compatible LN2 cryoprobe based cryosurgery system to accurately destroying cancerous tissue while minimizing the destruction of healthy tissue. An unsteady two-phase flow and coupled heat transfer model was used to analyze the dynamics of the temperature fields developing in biological tissue during cryosurgery. The 3.0-T MRI system was applied to monitor the iceball propagation and detect the artifacts caused by the cryoprobe in cryosurgery. In vitro experiment was performed in porcine liver and further used in MRI approach. The results revealed that the ice ball diameter was approximately 4 cm determined by MRI approach after 500 s freezing both in phantom and porcine liver cases. Cell killing experiment with 0.1% (w/v) Fe3O4 nanoparticles was also conducted to overcome the edge effect and enlarge the effective killing region of entire iceball, found that there was no additional damage to the surrounding unfrozen tissue. All these methodologies show that the developed cryoprobe could be a potential to be adopted in MRI guided cryosurgeries that could be precisely watched the frozen propagation inside the diseased tissue. These findings may further promote the cryosurgery to be a more effective thermal treatment.
       
  • Significantly enhanced convective heat transfer through surface
           modification in nanochannels
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Pranay Chakraborty, Tengfei Ma, Lei Cao, Yan Wang The subject of convective heat transfer in micro-/nano-scale channels is of utmost importance for the effective cooling of small-scale electronic devices with high power density. The overall heat convection in these channels largely depends on interfacial (wall-fluid) thermal transport. In this work, we demonstrate that a carefully designed surface topology can enhance heat dissipation in nanochannels. Specifically, we found that both uniformly and randomly distributed surface roughness can substantially increase the overall heat transfer between the wall and fluid in the nanochannels. Moreover, we reveal that depositing a coating layer, of which the vibrational density of states bridge those of the walls and the flowing fluid, can significantly enhance wall-fluid interfacial heat transfer. This work reveals the critical effect of surface topology and material choice of the channel wall on heat dissipation in nanochannels, which is important for the cooling of small-scale devices.
       
  • Effects of thermocapillarity on the dynamics of an exterior coating flow
           of a self-rewetting fluid
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Rong Liu, Xue Chen, Xun Wang The effects of thermocapillarity on the dynamics of an exterior coating flow of a self-rewetting fluid on a vertical fibre are investigated theoretically. Whereas surface tension decreases linearly with temperature for most fluids, the surface tension of a self-rewetting fluid exhibits a well-defined minimum. We developed an evolution equation for the interface in the framework of the long wave approximation. Linear stability analysis and numerical simulations on the nonlinear evolution have been performed to investigate the effects of thermocapillarity for axisymmetric disturbances. The results showed that thermocapillarity plays different roles in the stability and dynamics depending on the value of difference between the temperature at the interface, Θ¯i, and the temperature corresponding the minimum of the surface tension, Θ0. The results of linear stability analysis showed that the thermocapillarity is destabilizing or stabilizing as Θ¯i-Θ0 is negative or positive. At the nonlinear stage, for Θ¯i-Θ00 the thermocapillarity weakens the tendency of formation of beads due to the Rayleigh-Plateau mechanism.
       
  • Steam condensate behavior and heat transfer performance on
           chromium-ion-implanted metal surfaces
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Kiwook Kim, Ji Hwan Jeong Aluminum, copper, nickel, and stainless steel 304 (SUS304) are widely used to construct heat exchangers. In this work, test specimens made of these metallic materials were irradiated with chromium ions. The static and dynamic contact angles of water droplets on the test specimens were measured to examine changes in the surface characteristics. Condensate behavior was visually observed and condensation heat transfer performance was experimentally measured. Filmwise condensation occurred on the surfaces of all the specimens that had no ion implantation. After these specimens were irradiated with chromium ions, filmwise condensation or dropwise condensation was induced depending on the ion irradiation conditions. When the substrates were irradiated with chromium ions at an ion energy level of 100 keV and an ion dose of 3 × 1016 ions/cm2, dropwise condensation occurred regardless of material. When the specimens were irradiated at an ion energy level of 70 keV, dropwise condensation, filmwise condensation, or both occurred depending on the substrate material. The condensation heat transfer coefficient of the surface where dropwise condensation occurred appeared to be more than 3.2 times larger than the theoretical value according to Nusselt’s film theory in the subcooling region below 9.5 K.
       
  • Experimental and theoretical studies on the droplet temperature behavior
           of R407C two-phase flashing spray
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Zhi-Fu Zhou, Meng-Yuan Hu, Hui Xin, Bin Chen, Guo-Xiang Wang Flashing spray is a common phenomenon in many industrial fields. A rapid droplet temperature change in flashing spray is an important feature, which distinguishes this phenomenon from other traditional sprays. This study provides first-hand droplet temperature data of an R407C flashing spray, which serves as a substitute for R22, by conducting systematic experiments. A coupled droplet evaporation model is also introduced to predict the droplet temperature of flashing spray, rather than CFD simulation, for the first time considering the coupling of heat and mass transfer between a droplet surface and its surrounding region of influence. Experimental result shows that droplet temperature first decreases rapidly with axial distance, and then a gradual decrease in the downstream until its minimum value is reached. A hot core is observed near the nozzle exit, where the droplet temperature is higher at the spray center than in its periphery region. Droplet radial temperature distribution becomes uniform in the far spray field. The interaction of heat and mass transfer between the droplet surface and its surrounding region of influence is revealed using a coupled evaporation model. That is, the vapor mass fraction and temperature of the influence region undergo increase and decrease with evaporating time, respectively. Therefore, the coupled evaporation model presents better performance than a one-way evaporation model in predicting droplet minimum temperature. This predictive result agrees well with the experimental data. The minimum temperature of a predictive droplet is independent of the initial diameter and velocity of this droplet.
       
  • Effect of self-rewetting fluids on the liquid/vapor phase change in a
           porous media of two-phase heat transfer devices
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Riadh Boubaker, Souad Harmand, Safouene Ouenzerfi This paper presents an experimental study of the phase change phenomenon in a porous medium. The tested working fluids are pure water and butanol aqueous solutions with different concentrations. In contrast to ordinary fluids, the surface tension of self-rewetting fluids exhibits a positive gradient beyond a certain temperature value. The experimental results indicate that the use of self-rewetting fluids (water/butanol) as working fluid significantly improves the performance of the capillary evaporator by decreasing the casing temperature. To explain the heat transfer enhancement mechanism, the phase change phenomenon is visualized for the two working fluids. It is shown that as the applied power increases, the shape of the vapor pocket that developed within the porous wick also increases for pure water until it reaches a stable shape. With respect to self-rewetting fluids, the shape of the vapor pocket decreases with increasing applied power allowing more efficient mass and heat transfers. Wettability, capillary pressure and Marangoni forces are the factors related to surface tension and contact angle that seem to be responsible for this heat transfer improvement for self-rewetting fluids.
       
  • A simple model for the quench front propagation in a highly superheated
           particle bed
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): D.Y. Yeo, H.C. NO In this paper, a simple and fast-running model for the quenching of a particulate bed is suggested assuming two-step quenching: downward quench front propagation step and upward quench front propagation step. Most of the existing models are based on the assumption that the quenching rate is only hydraulically limited. However, the model suggested in this paper assumes that the quenching rate can be also thermally limited by the large thermal energy of a particulate bed in addition to the hydraulic limit of quenching. It turns out that the suggested model well predicted the decreasing trend of heat flux with increasing bed temperature. Also, it was found out that the effect of particle size on the heat removal during the quenching can be smaller than one expected from the flooding-limit based model. RMSE of the current model was 15% in comparison with 38% of Ginsberg’s model.
       
  • Theoretical modeling of a phase change heat transfer problem with a
           pre-melted or pre-solidified region
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Mohammad Parhizi, Ankur Jain Heat transfer problems involving phase change occur in a wide variety of engineering applications. Except a few simple cases, most phase change problems do not have an exact solution, and a number of approximate analytical methods have been developed. This paper presents a theoretical solution for a one-dimensional phase change problem that includes a pre-melted or pre-solidified length between the region of interest and a time-dependent temperature boundary condition. Such a scenario can occur in multiple engineering applications when the heating or cooling process is intermittent in time. The theoretical approach involves iteratively solving the coupled problem involving thermal conduction and phase change, utilizing a perturbation-based method for the phase change problem with a time-dependent boundary condition. The resulting theoretical solution compares well with numerical simulations. Results are used for analyzing the effect of geometry, thermal properties and other parameters on the nature of heat transfer and phase change in this problem of much technological importance. These insights may be helpful in analyzing and optimizing heat transfer in several applications such as phase change based cooling of Li-ion cells during intermittent operation.
       
  • Heat transfer and pressure drop characteristics of CO2 mixtures in a
           pipeline under the seawater condition
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Wonkeun Baik, Wonjun Lee, Rin Yun Captured CO2 from CO2 emission sources contains impurities such as N2, CH4, H2O, O2 and Ar, and these are transported with the CO2 in pipelines under supercritical condition. The aim of this study is to experimentally investigate the effects of impurities in CO2 + N2 and CO2 + CH4 on the in-tube heat transfer and pressure drop under seawater environmental conditions during pipeline transportation. The experimental apparatus consisted of a test section, heat exchangers that were connected to two chillers, and a magnetic gear pump. The test section was made by a cooper tube that was inserted into a Polyvinyl Chloride (PVC) pipe to form a double-tube. The operational temperature and pressure of the CO2 mixture ranged 25–55 °C and 80–100 bar, respectively. The mass flux was varied by 300, 500, and 700 kg m−2 s−1. The mole fraction of CO2 in the CO2 mixtures was varied from (1.00–0.95). When the CO2 mole fraction decreased from 1.00 to 0.95, the maximum heat transfer coefficients of CO2 + N2 and CO2 + CH4 decreased by 4157 and 1224 W m−2 K−1, respectively, and the average pressure drop of CO2 + CH4 increased by 29.87%.
       
  • A theoretical and experimental study of typical heterogeneous ice
           nucleation process on auto windshield under nocturnal radiative cooling
           and subfreezing conditions
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Xuzhi Du, Zhigang Yang, Zheyan Jin, Yuyu Zhu, Zhiwei Zhou In the present study, we theoretically and experimentally investigated a typical and practical heterogeneous ice nucleation process on auto windshield under nocturnal radiative cooling and subfreezing conditions. During the experiment, a general class A passenger car was placed outdoors in a subfreezing environment (i.e., 44.14° N, 126.45° E) during nights in January, with a purpose to produce a nocturnal radiative cooling condition for supercooling the windshield to trigger the ice nucleation. The results revealed a distinctive three-stage frosting process: (I) inhomogeneous occurrence of incipient ice nucleation; (II) small-sized ice crystals grew into large-sized ones primarily based on the incipient nucleation sites, together with a continual formation of new nucleation sites and a merging between large-sized and small-sized crystals; (III) large-sized ice crystals coalesced into large-scale groups, tending to make a full ice coverage. Unlike the classical three-period frosting process, the present study exhibited an absence of the drop-wise condensation but with a presence of dendritic crystals nearly parallel to the supercooled surface. Besides, the incipient ice nucleation was first initiated on the upper part of the windshield, which then propagated downward with a further heat loss of the windshield due to the continual nocturnal radiation. Meanwhile, the probable presence of surface roughness or contamination was much more likely to trigger an earlier initiation of incipient heterogeneous ice nucleation. Additionally, the arrival of saturation point, rather than the nominal supersaturation state (i.e., the condensation nucleation point), could be expected to approximately mark the initiation of icing under a practical engineering condition. Higher relative humidity tended to induce an earlier occurrence of ice nucleation and produce a larger surface coverage.
       
  • Heat transfer enhancement in microchannel heat sink with bidirectional rib
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Guilian Wang, Nan Qian, Guifu Ding The heat transfer and flow characteristics of the microchannel heat sink (MCHS) with bidirectional ribs (BRs) are experimentally and numerically studied in the present paper. The BR, composed of vertical rib (VR) and spanwise rib (SR), can interrupt the thermal boundary layer and induce recirculation in both vertical and spanwise directions. Its cooling effectiveness is compared with that of the widely-used VR and SR for the Reynolds number ranged from 100 to 1000. The results show that the Nussalt number of the microchannel with BRs (BR-MC) is up to 1.4–2 and 1.2–1.42 times those of microchannels with VRs (VR-MC) and SRs (SR-MC), respectively. This implies that the BR can strengthen the heat transfer more sufficiently. Meanwhile, the utilizing of BR gives rise to the larger pressure drop penalty due to its broader obstruction areas. In addition, the higher relative rib height of VR (eVR) and relative rib width of SR (eSR) are revealed to enhance the heat transfer but induce pressure drop in the BR-MC. The thermal enhancement factor can keep larger than 1 when eVR 
       
  • Internal flow near the triple line in sessile droplets of binary mixtures
           during evaporation at different ambient temperatures
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Leping Zhou, Yang Yang, Xiaoze Du, Yongping Yang The internal flow of an evaporating droplet is mainly influenced by capillary flow and Marangoni flow, which are affected by many factors including ambient temperature in the gas phase. For binary droplets, the internal flow near the triple line is of critical importance for understanding their evaporation characteristics. In this work, the internal flow near the triple line in evaporative sessile droplets of binary mixtures, including methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, and 1-heptanol of the same mass which were added to deionized water, at different ambient temperatures was experimentally investigated. An evanescent-wave based fluorescence microscope which has a depth of illumination field of about 360 nm was used to obtain the depinning times and near-wall average velocities of the samples. The relationship between the near-wall velocity V and the time t was described by V ∼ (tf − t)−1 for droplets without vortex, and changed to quadratic-functions due to the coexistence of the vortex and depinning phenomena. For droplets without vortex, an equation was derived for quantitatively describing the relationship between the near-wall velocity and the ambient temperature.
       
  • Unsteady mixed convection in a square enclosure with an inner cylinder
           rotating in a bi-directional and time-periodic mode
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Hui Yang, Wei Zhang, Zuchao Zhu This work first numerically investigated the mixed convection in a cold square enclosure with an inner hot circular cylinder at Ra = 106. The cylinder rotates about its center in a time-periodic and bi-directional mode, thus the fluid is driven by both the viscous shear stress from the cylinder surface and buoyancy from density variation. Our objective is to explore the effect of cylinder rotation on the unsteady thermal and flow characteristics, and to determine the propagation of thermal and flow perturbations within the enclosure. Numerical results reveal that the cylinder rotation weakens the mean heat transfer but imposes notable perturbation on the local heat transfer on both solid walls. At large α and P, the perturbation is the most significant as reflected by the pronounced temporal fluctuation of heat transfer rate on the solid walls and remarkable distortion of circulating vortices. The perturbation propagates from the cylinder into the whole fluid domain and results in phase lag between the variation histories of characteristic quantities, and the fluctuating amplitude of Nusselt number on the enclosure surface can be much larger than that of the cylinder. The thermal field is the most perturbed in the region close to the cylinder at small P, while it also exhibits a large fluctuation close to the top wall of the enclosure at large P due to the unsteady circulating flow.
       
  • Composite fouling characteristics of CaCO3 and CaSO4 in plate heat
           exchangers at various operating and geometric conditions
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Kang Sub Song, Junyub Lim, Sungho Yun, Dongwoo Kim, Yongchan Kim In a water heating system, such as a district heating and hot water supply system, the composite fouling of CaCO3 and CaSO4 characterizes the actual usage environment. In this study, the composite fouling characteristics of CaCO3 and CaSO4 in plate heat exchangers were measured and analyzed at various concentrations, flow velocities, temperatures, and chevron angles. Moreover, based on the measured data, empirical correlations for the fouling resistance, fouling period, and pressure drop ratio at an asymptotic state, are developed as a function of concentration, Re, temperature, and chevron angle. The correlations for the fouling resistance, fouling period, and pressure drop ratio at the asymptotic state yield satisfactory predictions with mean absolute errors of 7.1%, 4.6%, and 2.0%, respectively. In addition, the sensitivities of the operating and geometrical parameters on the composite fouling characteristics are analyzed using modified regression coefficients.
       
  • Surrogate model for convective flow inside electromagnetically levitated
           molten droplet using magnetohydrodynamic simulation and feature analysis
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Xiao Xiao, Robert W. Hyers, Douglas M. Matson Containerless processing of molten metals using electromagnetic levitation techniques is an important approach for material research, and the induced convection inside an electromagnetically levitated molten metal droplet is both difficult to measure experimentally and a key control parameter. This work proposed a surrogate model based on parametric numerical experiments of magnetohydrodynamic simulations of the ISS-EML facility, characterizing and quantifying the convective flow due to electromagnetic positioning power as a function of melt thermophysical properties. Feature mapping methods integrated with feature selection is used to construct an optimized formula in explicit form for the data fitting which maintains both of physical interpretability and mathematical tractability. The trained surrogate model is then applied for selected industrial important metals and alloys as examples that show the generalization ability of the model and how it can be utilized to quantify the induced convection and characterize internal flow patterns.
       
  • Corresponding principle of critical heat flux in flow boiling
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): B.H. Yan, C. Wang, R. Li An equation of state is a thermodynamic equation relating fluid properties which describe the state of matter under a given set of physical conditions. Considering there are some connections between the properties of different fluids, we believe there are some corresponding relations between the critical heat flux (CHF) of different fluids. A corresponding principle was developed to predict the critical heat flux with the experimental data obtained with modeling fluids. A series of scaling criteria were developed on the basis of fluid similarity and molecular thermodynamics, which is totally different from the conventional scaling methods based on experimental data and empirical correlations. The prediction error of this principle is much lower than conventional prediction methods. The average and maximum error of the corresponding principle is about 10%.
       
  • Internal natural convection around a sphere in a rectangular chamber
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Daehoon Lee, Hosung Jang, Byeong Jun Lee, Wonjoon Choi, Chan Byon In this study, a three-dimensional internal natural convection heat transfer between a cuboidal enclosure and a spherical surface placed in the enclosure, is investigated numerically. The effects of enclosure shape and Rayleigh number on the flow and heat transfer characteristics are analyzed for concentric and eccentric positions of sphere, respectively. The numerical results show that there exists a critical Rayleigh number beyond which the Nusselt number decreases as the temperature difference increases. This is attributable to the fact that the thermal diffusivity and kinematic viscosity of air both increases as the temperature increases, resulting in reduction of Rayleigh number with the temperature increases. Based on the numerical results, a correlation for predicting Nusselt number is proposed as a function of Rayleigh number and the enclosure shape for concentric and eccentric cases, respectively.
       
  • Combined effects of alcohol and electrolyte on mass transfer from single
           carbon-dioxide bubbles in vertical pipes
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yohei Hori, Yutaka Hirota, Kosuke Hayashi, Shigeo Hosokawa, Akio Tomiyama Mass transfer rates, kL, of single carbon-dioxide (CO2) bubbles rising through vertical pipes filled with alcohol-electrolyte mixed aqueous solutions were measured to investigate the combined effects of alcohol and electrolyte on kL. 1-octanol and 1-heptanol, which are known to adsorb to the interface and behave like surfactant, were used. Sodium chloride (NaCl) was used for the electrolyte. The surface tension, σ, decreased with increasing the NaCl concentrations, CN, while keeping the alcohol concentration, CA, constant. Three combinations of CA and CN having the same values of σ were selected for the experimental conditions to avoid the effect of σ. The pipe diameters, D, were 12.5 and 18.2 mm. A wide range of bubble diameter covered various bubble shapes, i.e. ellipsoidal, cap, semi-Taylor and Taylor bubbles. The conclusions obtained are as follows: (1) the combination of CA and CN for the same σ does not affect the aspect ratios of ellipsoidal bubbles and the lengths, L, of Taylor bubbles, (2) the Sherwood numbers, Sh, of bubbles in alcohol-NaCl mixed aqueous solutions depend on the combination of CA and CN due to the change in the Schmidt number, Sc, even at the same σ for all the tested combinations of concentrations of impurities, and (3) the modified Sherwood number, ShD, of contaminated Taylor bubbles is well correlated in terms of the bubble Reynolds number, Sc, the dimensionless group for surfactant properties and L/dT, where dT is the transition bubble diameter at the transition from the ellipsoidal-cap bubble regime to the transition regime.
       
  • Local instantaneous heat transfer around a single elongated bubble in
           inclined pipes
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): A. Fershtman, L. Shemer, D. Barnea The instantaneous convective heat transfer rate resulting from the passage of a single elongated bubble propagating in an inclined pipe with a constant translational velocity is examined experimentally for various pipe inclinations and liquid flow rates. Local instantaneous heat transfer rates in the upper and lower parts of the pipe were determined using wall temperature measurements by an IR camera. The ensemble-averaged values of the heat transfer rate are presented as a function of the distance from either the bubble tip or bottom. Optical sensors synchronized with the IR camera were used for this purpose. Possible mechanisms that govern the enhancement of the heat transfer rate during the passage of an elongated bubble are discussed.
       
  • Accurate measurement of nanofluid thermal conductivity by use of a
           polysaccharide stabilising agent
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): R. Ebrahimi, D. de Faoite, D.P. Finn, K.T. Stanton Measuring the thermal conductivity of low viscosity fluids such as aqueous nanofluids is challenging due to the formation of convection currents. In the current work, a modification of the transient hot-wire thermal conductivity measurement technique was investigated to address this problem. The polysaccharide agar was used as a gelling agent to prevent the formation of convection currents, thereby enabling measurement of thermal conductivity. The experimental method was validated by comparison of experimentally measured thermal conductivity values with published reference values over a range of temperatures for two reference fluids stabilised by agar: water and an ethylene glycol/water solution. The precision of thermal conductivity measurements was found to be significantly improved by use of this gelling agent. These findings indicate that agar, or a similar gelling agent, can be used to enable accurate measurement of the thermal conductivity of aqueous fluids. This measurement technique was utilised to accurately measure the thermal conductivity enhancements of copper and alumina aqueous nanofluids with low nanoparticle concentrations, over a range of temperatures. The thermal conductivities of these nanofluids were found to be within ±2% of those predicted by the Maxwell model.
       
  • Effects of carbon steel surface oxidation on critical heat flux in
           downward-face pool boiling
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Kai Wang, Nejdet Erkan, Haiguang Gong, Koji Okamoto In this study, a downward-face pool boiling critical heat flux (CHF) experiment was performed using a carbon steel plate soldered to a copper base. The results of the experiment were analyzed and compared with those of a carbon steel and copper block experiment previously conducted at the same test facility. After polishing the surface using sandpaper, heat was applied to the surface by cartridge heating until CHF was attained. Due to the oxidation of the carbon steel, the surface changed gradually during boiling. The boiling cycle was repeated several times, and the CHF variations were observed. Detailed images of the heating surface behavior during boiling acquired by two synchronized high-speed cameras with different heat fluxes were analyzed. It was found that the more oxidized the surface became, the fewer bubbles were generated and the higher the CHF became; however, the bubble film departure frequency remained the same in all conditions. The contact angle and microscope surface images of the oxidation material were also obtained, and it was determined that the combined effect of the increase in wettability and decrease in nucleation site density was likely the reason that the CHF increased. This gradual oxidation process could be beneficial in actual situations since it can increase the upper limit of in-vessel retention external reactor vessel cooling.
       
  • Temperature drop and gelatinization characteristics of waxy crude oil in
           1000 m3 single and double-plate floating roof oil tanks during storage
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Min Wang, Xinyu Zhang, Qianqian Shao, Jingfa Li, Bo Yu Single and double-plate floating roof oil tanks are two types of widely used floating roof oil tanks in petrochemical industry. However, the differences in flow and hear transfer characteristics of waxy crude oil inside these two tanks have been studied insufficiently. Finite volume method is employed in this research to study the temperature drop and gelatinization processes of waxy crude oil as well as the differences in single and double-plate floating roof tanks. Based on a comprehensive consideration of the atmosphere, soil, floating roof oil tank as well as the tank structure and the variations of the waxy crude oil state and rheological behavior, general physical and mathematical models are established. In the model, wax precipitation and gelatinization processes of waxy crude oil are described by the enthalpy-porous media method. Non-Newtonian behavior is described by the Power law equation. Turbulent natural convection is described by the LES method. SIMPLE algorithm is employed to couple pressure and velocity. Taking 1000 m3 single and double-plate floating roof oil tanks as examples, the evolution of oil temperature and flow behavior is studied and the variations of the gel oil thickness and heat flux are analyzed. Moreover, the differences between these two tanks are also discussed. Results show that due to the structure difference of the tank roof, the temperature drop rates are 0.018 °C/h and 0.007 °C/h respectively in single and double-plate floating roof tanks in the case of this research. Secondly, for the growth of gel oil on tank bottom, in double-plate floating roof tank, gel oil thickness keeps growing and fluctuating, while in single-plate tank, the original gelled oil layer disappears firstly and then increases gradually. Thirdly, although for both tanks, tank roof is the main part of heat dissipation towards the atmosphere, the maximum heat fluxes are respectively over 2.0 kW and 0.4 kW for single and double-plate floating roof tanks, and the total average heat fluxes respectively are 1.49 kW and 0.59 kW.
       
  • Kinetic simulation of the non-equilibrium effects at the liquid-vapor
           interface
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): A.Ph. Polikarpov, I.A. Graur, E.Ya. Gatapova, O.A. Kabov Phase change phenomena at microscale is important for novel cooling microsystems with intensive evaporation, so the development of reliable models and simulations are challenging. The vapor behaviors near its condensed phase are simulated using the non-linear S-model kinetic equation. The pressure and temperature jumps obtained numerically are in good agreement with the analytical expressions derived from the appropriate Onsager-Casimir reciprocity relations. The results of the evaporation flux are close to those given by the Hertz-Knudsen-Schrage formula, only when the values of the pressure and temperature at the upper boundary of the Knudsen layer are used. Comparison with recently measured temperature jumps are provided and disagreement with some experiments are discussed.
       
  • Experimental and numerical study of the film cooling performance of the
           suction side of a turbine blade under the rotating condition
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Haichao Wang, Zhi Tao, Zhiyu Zhou, Feng Han, Haiwang Li The film cooling performance of the suction side of a turbine blade is experimentally and numerically investigated under the rotating condition. Experiments were performed on a 1.0-stage turbine. In the experiments, the effects of density ratio (0.96 and 1.52) and blowing ratio (0.2–1.0) were studied. The rotational effects were studied by comparing results of three mainstream rotating Reynolds numbers (3528, 4410 and 5292). Three hole positions of 1/4, 1/2 and 3/4 of the total blade height were set on three blades to confirm the mainstream influence. The jets of the holes at 1/4 and 3/4 of the blade height deflect to the mid-span of the blades. The film protection at both hole positions is damaged by the mainstream vortices, resulting in a lower cooling effectiveness. Moreover, as proven by the flow field, the passage vortex influence can be strengthened by the rotation. Thus, as the rotating Reynolds number increases the film cooling performance worsens. An optimal blowing ratio, 0.6, for the mid-span hole film cooling exists. Different from the flat plate film cooling, the film deflection occurs in the blade film cooling and decreases as the blowing ratio. At last, the high density ratio can improve the film cooling performance.
       
  • Reconsideration of correlation for condensation outside a vertical tube in
           the presence of noncondensable gas
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Kentaro Kanatani A correlation of the condensation heat transfer coefficient (HTC) on the exterior surface of a vertical tube in the presence of noncondensable gas is reconsidered taking into account temperature variation of the tube and the coolant. We derive a heat transfer model of the condenser tube by employing energy conservation and the HTCs of the outside and inside of the tube. For the condensation HTC, two different suction factors are examined. We estimate a correction factor of the condensation HTC by fitting a numerical solution of the model into experimental data. As a result, it is shown that the correction factor depends on the suction parameter. Furthermore, we show that the correction factor inevitably diverges at no subcooling because of the heat and mass transfer analogy (HMTA). To resolve this problem, we propose a simplified expression for the condensation HTC without HMTA. Finally, a double layer model, where the concentration boundary layer around the condensing surface is composed of viscous and diffusive sublayers, is developed as a generalization of the two suction factors. The variation of the correction factor against the suction parameter can be explained by the double layer model.
       
  • Measurement of two-dimensional heat transfer and flow characteristics of
           an impinging sweeping jet
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Sang Hyouk Kim, Hyun Dong Kim, Kyung Chun Kim This study experimentally explores the two-dimensional heat transfer characteristics of an impinging sweeping jet generated from a feedback–channel-type fluidic oscillator. The results were compared to those of a steady square jet. A phosphor thermometry technique was used to measure the surface temperature field on an aluminum plate for different Reynolds numbers and jet-to-wall spacing. A two-dimensional planar Particle Image Velocimetry (PIV) measurement of the sweeping impinging jet was also conducted to couple the flow characteristics and heat transfer performance. The local Nusselt number distributions on the flat plate were evaluated by converting the temperature fields. The heat transfer performance of the sweeping jet is much higher than that of the steady jet because the sweeping motion of the jet induces significant turbulent flow and clearly improves the thermal transport near the impingement plate. However, when the jet-wall spacing becomes greater than 5, the heat transfer performance of the sweeping jet drastically decreases due to the reduced impinging velocity, and the heat transfer of the steady square jet surpasses that of the sweeping jet. In the ensemble averaged velocity fields, two main jet streams are ejected to the plate like oblique impinging jets near the sidewalls of the exit because the jet flow is attached to sidewall one or the other for more than 70% of an oscillation period. There was high similarity between the ensemble averaged velocity profiles and the Nusselt number profiles.
       
  • Experimental investigation on ice accretion on a rotating aero-engine
           spinner with hydrophobic coating
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Mei Zheng, Zhiqiang Guo, Wei Dong, Xiaofeng Guo Ice accretion on aero-engine inlets is a serious threat to the inflight safety. As an important part of the engine inlet components, the rotating spinner has special icing phenomena compared with the stationary ones. An experimental study is conducted to investigate the ice accretion on a rotating aero-engine spinner in the icing wind tunnel. A full-scale engine spinner model is used in the experiments operated under different conditions. The hydrophobic nanoparticle-polymer composite coating is applied to cover on the aluminum-based spinner and then to examine its anti-icing performance. The dynamic icing processes and the final ice shapes on the rotating spinner surface are captured. The experimental results reveal that the ice growth and ice shape are basically determined by the airflow temperature and slightly affected by the rotating speed when the airflow velocity and icing cloud parameters are constant. The ice fracture and shedding are greatly dependent on the rotating speed when the icicle length is large enough. The freezing delay on the hydrophobic coating is inconspicuous and there is even no effect on the ice growth. However, the ice shedding on the coating happens, especially in the mixed icing condition with a higher rotating speed, demonstrating its icephobicity. Meanwhile, the dynamic icing processes and the effects of the airflow velocity and rotating speed on the ice growth are analyzed based on the mechanism of the supercooled droplet impingement characteristics, heat and mass transfer, force analysis on the rotating surface. The surface wettability is introduced to evaluate the freezing delay and icephobicity on the hydrophobic coating.
       
  • Physical properties measurement and performance comparison of membranes
           for planar membrane humidifiers
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Chen-Yu Chen, Yu-Hsuan Chang, Chun-Han Li, Chih-Chang Chang, Wei-Mon Yan The research and development of humidifiers is important to proton exchange membrane fuel cell systems. The water exchange membrane is a key component to the planar membrane humidifier. In this work, two types of low-cost membrane, the pervaperation (PV) membrane and the reverse osmosis (RO) membrane, are selected as the research targets. Their physical properties and humidification performance are tested and compared with the Nafion®-212 membrane. The ex-situ tests indicate that the order of air permeability is RO membrane > Nafion® 212 membrane > PV membrane, and the order of water vapor permeability is RO membrane ∼ Nafion® 212 membrane > PV membrane. From the in-situ tests, the order of humidification performance is Nafion® 212 membrane > RO membrane > PV membrane at all air flow rates. The DPATs with the RO and PV membranes are roughly 1–2 °C and 2–3 °C higher than that with the Nafion® 212 membrane, respectively. The highest WRRs obtained at 30 L/min with the Nafion® membrane, RO membrane and the PV membrane are about 53%, 48% and 42%, respectively. The Nafion® membrane is most energy-efficient because it has the highest COP. Moreover, the PV and RO membranes are equally energy-efficient when considering both the water transfer performance and the power loss.
       
  • Experimental and numerical analysis of the heat transfer in a packed bed
           exposed to the high thermal radiation flux
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Gustavo Ruiz, Nicolás Ripoll, Nataliia Fedorova, Ana Zbogar-Rasic, Vojislav Jovicic, Antonio Delgado, Mario Toledo This paper investigates temperature profiles and heat fluxes in a packed bed heated by radiation that simulates solar energy flux. For this purpose, the discrete element method (DEM) was used along a heat transfer model (conduction and radiation mechanism). Short-range model is proposed for considering thermal radiation in a discrete elements system, which represents an easy-to-implement and low-computational-cost alternative. As results of the simulations, thermal profiles through the packed bed were obtained, as well as the accompanying heat flux. Experiments were performed in a packed bed of inert ceramic particles (alumina spheres). A radiant porous burner was placed at the bottom of the packed bed to simulate an imposed concentrated solar heat flux. Numerical results show good agreement with experimental data. In addition, the thermal profiles, obtained by the heat transfer model in DEM, were compared with the results obtained by discretizing the conservation of energy equation of the solid phase using finite differences, showing a correlation between the power and temperatures reached. It is concluded that the radiation model proposed provides the basis to continue with the study of granular materials at high temperature, where radiation is the dominant mechanism.
       
  • A coupled wicking and evaporation model for prediction of pool boiling
           critical heat flux on structured surfaces
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Han Hu, Justin A. Weibel, Suresh V. Garimella Boiling is an effective heat transfer mechanism that is central to a variety of industrial processes including electronic systems, power plants, and nuclear reactors. Micro-/nano-structured surfaces have been demonstrated to significantly enhance the critical heat flux (CHF) during pool boiling, but there is no consensus on how to predict the structure-induced CHF enhancement. In this study, we develop an analytical model that takes into consideration key mechanisms that govern CHF during pool boiling on structured surfaces, namely, capillary wicking and evaporation of the liquid layer underneath the bubble. The model extends existing wicking-based CHF theories by introducing the competing evaporation mechanism. The model reveals a wicking-limited regime where CHF increases monotonically with the wicking flux, and an evaporation-limited regime where additional increases in the wicking flux do not significantly affect CHF. The model predictions are shown to agree with experimental CHF data from the literature for boiling of water on surfaces structured with square micropillar arrays. A parametric study is performed for such micropillared surfaces and has identified the optimal structure based on the competition between wicking and evaporation, capillary pressure and viscous resistance, and conduction and liquid-vapor interfacial resistance.
       
  • Measurement model for near-infrared radiative properties of open-cell
           metallic foams based on transmittance spectra
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Meng Liu, Qing Ai, Hai-Chao Yin, Xin-Lin Xia, He-Ping Tan Considering the existence of edge effect caused by the cut surface of struts or sintering points will affect the actual radiative transfer process in metallic foams, a three-layer structure model is constructed to obtain their spectral radiative properties. Using the double-thickness model for reference, the real spectral radiative properties of metallic foams are calculated based on transmittance spectra. To verify the feasibility of this method, transmittance spectra of nickel foams with different cell sizes and thicknesses are measured by FTIR spectrometer system in the near infrared band. Through comparing extinction coefficients obtained by traditional single-layer structure model and the three-layer structure model proposed in this paper, it is found that extinction coefficient will be underestimated by the latter method, while the deviation can reach 13% for 20ppi nickel foam and 8% for 40ppi nickel foam. Then absorption coefficient and scattering coefficient are calculated by a prediction model with parameters corrected. Based on this method, temperature influence on extinction coefficient of nickel foam is studied from 293 K to 773 K and it is found that extinction coefficient decreases with temperature in the researched band while the maximum changing rate is 2.1% in the researched band.
       
  • Experimental and theoretical study of two-phase flow in wide microchannels
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Ivan S. Vozhakov, Fedor V. Ronshin Experimental and theoretical studies of the two-phase flow regimes in a wide microchannel with the height of 164 μm were performed. The ranges of parameters of the formation of the main flow regimes are determined: jet, bubble, churn, stratified, and annular. The pressure drop in single-phase and two-phase flows was measured. Using a flat flow model, we performed a theoretical study of the pressure drop and compared it with experimental data. Regular waves were experimentally detected in film flow regimes. The formation of waves on a liquid film was investigated, and characteristic wavelengths were measured. As for the theory, the study of linear stability of the stratified two-phase flow regime in a wide microchannel was performed. The comparison of numerical and experimental results indicated the validity of the proposed approach for modeling waves in film regime in wide microchannels.
       
  • Numerical investigation of the effect of moisture on buoyancy-driven low
           turbulence flow in an enclosed cavity
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Draco Iyi, Reaz Hasan This paper reports a numerical investigation of low turbulence buoyancy-driven flow of moist air and heat transfer inside a rectangular cavity with differentially heated vertical walls. The variations of the flow, temperature and moisture inside the cavity has been analysed together with heat transfer coefficients for a range of mass fraction of water vapour and temperature gradients between the vertical walls of the cavity. The accuracy of the numerical methodology was also scrutinised by conducting a rigorous validation study of benchmark experimental data for the average Nusselt number for similar buoyancy driven cavity flow.The results of this investigation showed that during the natural convection process, the change in moisture content in the moist air has a significant influence on the flow and temperature fields inside the enclosure and the variation of the vertical wall temperature gradients have also shown to affect the moisture concentration inside the cavity. The percentage change in the average heat transfer varied significantly depending on the mass fraction of moisture in the air and the temperature gradient between the vertical walls. The results also showed a 3.5% increase in the average heat transfer for every 0.02 kg/kg increment in the mass fraction of water vapour. The findings from the study are significance to scientists and practitioners who are responsible for moisture management in enclosed space at the design threshold and for optimisation of energy used in buildings.
       
  • Heat transport and storage processes in differential scanning calorimeter:
           Computational analysis and model validation
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Václav Kočí, Jiří Maděra, Anton Trník, Robert Černý Experimental results provided by differential scanning calorimetry (DSC) can be affected by systematic errors, which are difficult to identify and quantify correctly by the end-users, as a DSC device is commonly used as a gray box. The signal delay due to thermal inertia and the effects of sample size or heating rate present the most common sources of uncertainties. In this paper, a 3-D computational model of a differential scanning calorimeter is constructed, calibrated and validated. Five reference standards are used for both experimental and computational calibration, resulting in a very good agreement (R2 > 0.999794) of the computational model with experimental outputs. Model is validated using two different materials and processes. The analysis of melting of aluminum, as one of the standards not used at the calibration, shows a maximum difference of 0.279 mW·mg−1 at the peak top, which is well within the accuracy limits. The application of the model for the determination of effective specific heat capacity of quartz, as a representative of commonly studied materials which are though not standardized for DSC, reveal a good agreement with both the measured data and the results of independent experiments reported by several other investigators. The main advantage of the model consists in the detailed analysis and separation or quantification of particular heat evolving/consuming mechanisms in both the DSC device and the studied materials. Therefore, contrary to the empirical calibration, it can identify exactly the physical sources of measurement uncertainties. The raw experimental data provided by the DSC device can then be corrected in a straightforward way and the systematic errors can be eliminated.
       
  • Unsteady flow and heat transfer past a stretching/shrinking sheet in a
           hybrid nanofluid
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Iskandar Waini, Anuar Ishak, Ioan Pop The unsteady flow and heat transfer past a stretching/shrinking sheet in a hybrid nanofluid is studied. The governing equations of the problem are transformed to the similarity equations by using similarity transformation technique. The problem is solved numerically using the boundary value problem solver (bvp4c) in Matlab software. The plots of the skin friction coefficient and the local Nusselt number as well as the velocity and temperature profiles for selected parameters are presented. It is found that dual solutions exist for a certain range of the unsteadiness parameter. A temporal stability analysis is performed to determine the stability of the dual solutions in a long run, and it is reveals that only one of them is stable while the other is unstable.
       
  • A simplified model for fast estimating infrared thermal radiation of
           low-altitude under-expanded exhaust plumes
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Qinglin Niu, Debin Fu, Shikui Dong, Heping Tan In this paper, a fast estimating method of thermal infrared radiation signatures for low-altitude exhaust plumes was proposed. In engineering application, it is essential to predict the thermal radiation effect of the plume as soon as possible. A simple numerical model was established considering thermal, species formation, entrainment and radiating effects. In this methodology, the mixing region was treated as a hot, under-expanded, reacting and isotonic flow. The reacting flows were simulated by solving the governing equations with finite rate kinetics and conservation matching relations. A single-line-group (SLG) model with Curtis-Godson approximation was utilized to evaluate radiative properties of radiating species. A line-of-sight (LOS) method was used to compute the spectral radiation intensity. This computational model was verified against the Atlas-II’s reference data within the wavelengths of 2–6 μm. The simulation analyzed combustion flows and infrared thermal effects of a typical exhaust plume along flight trajectory points. Results show that the current model can dramatically improve the computational efficiency by 100–1000 times by comparing with the commonly used method. According to this model, the plume’s range and an appropriable cutoff temperature for thermal radiation calculations are easy to obtain. Infrared radiation phenomena accord with the experimental observations. As a main outcome, this simple model can provide a time-saving and range-unlimited method for the infrared radiation signature prediction of a low-altitude plume in engineering application.
       
  • Three-dimensional liquid-vapor interface reconstruction from high-speed
           stereo images during pool boiling
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Carolina Mira-Hernández, Justin A. Weibel, Pavlos P. Vlachos, Suresh V. Garimella A technique for reconstruction of liquid-gas interfaces based on high-speed stereo-imaging is applied to the liquid-vapor interfaces formed above a heated surface during pool boiling. Template matching is used for determining the correspondence of local features of the liquid-vapor interfaces between the two camera views. A sampling grid is overlaid on the reference image, and windows centered at each sampled pixel are compared with windows centered along the epipolar line in the target image to obtain a correlation signal. The three-dimensional coordinates of each matched pixel are determined via triangulation, which yields the physical world representation of the liquid-vapor interface.Liquid-vapor interface reconstruction is demonstrated during pool boiling for a range of heat fluxes. Textured mushroom-like vapor bubbles that are fed by multiple nucleation sites are formed close to the heated surface. Analysis of the temporal attributes of the interface distinguishes the transition with increasing heat flux from a mode in which vapor is released from the surface as a continuous plume to one dominated by the occurrence of intermittent vapor bursts. A characteristic morphology of the vapor mushroom formed during vapor burst events is identified.This liquid-vapor interface reconstruction technique is a time-resolved, flexible and non-invasive alternative to existing methods for phase-distribution mapping, and can be combined with other optical-based diagnostic tools, such as tomographic particle image velocimetry. Vapor flow morphology characterization during pool boiling at high heat fluxes can be used to inform vapor removal strategies that delay the occurrence of critical heat flux during pool boiling.
       
  • Thermal performance of radially rotating trapezoidal channel with
           impinging jet-row
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Shyy Woei Chang, Kuo-Ching Yu The detailed Nusselt number distributions and Fanning friction factors of the rotating trapezoidal channel cooled by a row of six in-lined impinging jets were measured. The channel orientation relative to the rotating axis was 45 degrees and the six lateral jets issued from a plenum chamber were aimed at the centerline of the apex wall of the trapezoidal channel. The experimental conditions in terms of channel Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers were 5000–17500, 0–0.3 and 0–0.088, respectively. Also the rotational impact on the mass flow rate through each nozzle was examined. The coupled and isolated effects of Coriolis force and rotating buoyancy on the thermal performance of the rotating channel were illustrated using a selective set of test results. Due to the Coriolis-force effect on the radially outward crossflow and the impinging jets, the airflow rates issued from the jets 1–3 and 5–6 were respectively increased and decreased from the non-rotating values. With the different degrees of Ro impact on the leading, apex and trailing walls of the rotating trapezoidal channel, the Coriolis force effect on the heat transfer distribution was spatially asymmetric. The present “cavity-like” channel hub configuration significantly undermined the fluency of the spent flow to incur weak convection region adjacent to the sealed channel hub. But the Coriolis force effect considerably improved the heat convection over the channel hub region. All the Nusselt number ratios between the rotating (Nu) and non-rotating (Nu0) channels followed the general pattern of hub-to-tip decay. While the rotating buoyancy effect impaired the heat transfer performance, its impact was systematically weakened when the relative strength of Coriolis force enhanced. Two sets of empirical correlations that permitted the evaluations of the regionally averaged Nusselt number over the leading, apex and trailing walls and the overall Fanning friction factors were devised to assist the development of an internal cooling scheme of a gas turbine rotor blade.
       
  • Visualization investigation of the effects of nanocavity structure on pool
           boiling enhancement
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Sihui Hong, Siqiang Jiang, Yanxin Hu, Chaobin Dang, Shuangfeng Wang Boiling heat transfer can be greatly enhanced through careful control of the physiochemical characteristics of contact surfaces. In this work, by utilizing the electrodeposition method, we prepared enhanced metallic surfaces with 3D cubic Cu2O crystals and dendritic copper branch nanostructures. Their static contact angles are 127° and 139°, respectively. Additionally, incipience temperature overshoot at the onset of nucleate boiling decreased to only 4.4 K and 2.9 K from 15.3 K, and the maximum heat transfer coefficients for the conditioned surfaces were improved by 311.4% and 389.2%, respectively. Based on comparative analysis, the effects of nanocavity structure on bubble dynamics and heat transfer mechanisms are explicitly clarified. We determined that deep nanoscale cavities with interconnected branch structures are the key factor for facilitating appreciable capillary force and low seepage resistance to maintain efficient boiling heat transfer. Slender bubbles generated from dendritic structured surfaces effectively mitigate bubble coalescence and delay local vapor film coverage, thereby overcoming the defect of heat transfer deterioration under high heat flux. A surface with a 3D dendritic nanostructured layer can withstand a heat flux up to q = 73.53 W/cm2 without drying out.Graphical abstractWith visualization experiments of pool boiling on 3D nanostructured surfaces, bubble dynamics and heat transfer characteristics are both investigated. The dendritic nanostructured surface can not only reduce the initial temperature overshoot to 2.9 K at ONB, but also withstand more than 1.61 times the heat flux of the flat surface. The proposed high-performance and cost-effective nanostructured surface enables a reliable hydrophobic surface to be applied in electronics cooling, nuclear engineering, chemical, and petrochemical industries, etc.Graphical abstract for this article
       
  • A 3D thermal LB model on non-orthogonal grid and its application for
           natural convection in irregular domains
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Xun Zhou, Bo Dong, Weizhong Li, Cong Chen In this paper, a 3D thermal LB model on non-orthogonal grid is derived, as well as the corresponding boundary treatment method for irregular boundary. Numerical validation is then performed by modeling natural convection in a 3D annulus. It is proved that the thermal flow structure in the annulus is accurately predicted with less grids. After that, present method is applied to study natural convection in a 3D cavity with inclined side walls. Two opposite inclined walls on the left and right sides are kept at different constant temperatures, while the remained four walls of the cavity are either adiabatic (Type 1) or own linear temperature variations (Type 2). It is found out that natural convection in the inclined cavity exhibits distinct 3D features under Type 2 thermal boundary setting, yet it can be viewed as a 2D process under Type 1 condition. Moreover, a large Prandtl number (Pr = 10.0) can generally suppress the 3D effect stemmed from thermal boundary setting. The aforementioned results indicate that present model and boundary treatment method are reliable to deal with 3D natural convection in irregular domains.
       
  • Research on heat transfer of submersible motor based on fluid network
           decoupling
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yongming Xu, Mengmeng Ai, Yang Yang A heat transfer model of submersible motor based on partition decoupling is proposed. Due to the special circulation system of the fluid in the submersible motor, the internal inner flow field represents a repeatability alone the axial direction. In addition, the relationship between the velocity and pressure of the internal fluid inside the gap, the inner cavity of the shaft and the oil splashing holes of the bearing are also determined, which can determine the boundary conditions of the end of the single motor Then the global motion fluid field is decomposed into local flow field, which simplifies the thermal model of the global fluid field of the submersible motor. Taking a submersible motor as an example, the temperature distribution of each component and the flow state of the internal motor are calculated, and the influence of the latter on the temperature field is analyzed. Finally, the validity of the method is verified by comparing the calculated results with the experimental data. The research results provide a theoretical basis for analyzing the global fluid field and thermal effect of other motors with special fluid structure.
       
  • Modeling condensation on structured surfaces using lattice Boltzmann
           method
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Yaroslav Vasyliv, Dennis Lee, Ted Tower, Richard Ng, Vicky Polashock, Alexander Alexeev A single component, two-phase lattice Boltzmann model based on the Shan-Chen pseudopotential model is coupled to a continuum-based thermal energy solver. The model is verified using the Stefan problem and Nusselt’s falling film. We then use the model to simulate 2D drop-wise condensation of a saturated vapor on hydrophobic structured surfaces. We report the normalized condensed mass and condensation rate as we vary the spacing between structures, numerical interface thickness, and structure topology. For a non-dimensional spacing of s=6.4, a primary droplet engulfs each post after a non-dimensional thermal diffusion time of t∗≈1.1 (square), t∗≈0.59 (semi-circular), and t∗≈2.38 (equilateral). The growth of this thermally resistant primary droplet is fed by coalescing satellite droplets characterized by low heat transfer resistance. These small satellite droplets continuously nucleate, grow and merge into the primary droplet resulting in condensation rates four to seven times greater than the film-wise condensation rate. These small droplets only appear to form when the ratio of numerical interface thickness w to structure length L is sufficiently small (w/L
       
  • ( C N T - Fe 3 O 4 / H 2 O ) +hybrid+nanofluid+for+improvements+in+heat+transfer+for+flow+in+an+asymmetric+channel+with+dilating/squeezing+walls&rft.title=International+Journal+of+Heat+and+Mass+Transfer&rft.issn=0017-9310&rft.date=&rft.volume=">A novel coupling of ( C N T - Fe 3 O 4 / H 2 O ) hybrid nanofluid
           for improvements in heat transfer for flow in an asymmetric channel with
           dilating/squeezing walls
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Fitnat Saba, Naveed Ahmed, Umar Khan, Syed Tauseef Mohyud-Din Hybrid nanofluid is an advanced version of a nanofluid, which significantly boosts the heat transport mechanisms. Therefore, this can be considered a new alternative source to the traditional ways (involving certain fluids or nanofluids) of heating or cooling. The main concern of this manuscript is to scrutinize the flow field and heat transfer phenomena, for the flow of a hybrid (CNT-Fe3O4/H2O) nanofluid, inside an asymmetric long channel, whose porous walls exhibit embracing or parting motion. The equations, corresponding to the mass, momentum and energy conservations, have been modeled accordingly and after this, by making use of similarity transformations, a relevant set of nonlinear ordinary differential equations have been successfully achieved. In order to devise a numerical solution of the consequent equations, shooting method coupled with Runge–Kutta–Fehlberg algorithm have been employed. Furthermore, a graphical aid, to interpret the influential behaviors of various emerging entities on the velocity and temperature distributions, have also been provided. The dispersion of CNTs in (Fe3O4/H2O) nanofluid, have a considerable impact on the flow, temperature and heat transport properties, and these variations can be clearly visible at the both walls. Moreover, it has been observed that the SWCNTs, in most of the cases, seem to have a greater impact on the temperature profile as well as on the heat transport phenomenon.
       
  • Review of single-phase and two-phase nanofluid heat transfer in
           macro-channels and micro-channels
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Gangtao Liang, Issam Mudawar This paper provides a comprehensive review of published literature concerning heat transfer benefits of nanofluids for both macro-channels and micro-channels. Included are both experimental and numerical findings concerning several important performance parameters, including single-phase and two-phase heat transfer coefficients, pressure drop, and critical heat flux (CHF), each being evaluated based on postulated mechanisms responsible for any performance enhancement or deterioration. The study also addresses issues important to heat transfer performance, including entropy minimization, hybrid enhancement methodologies, and nanofluid stability, as well as the roles of Brownian diffusion and thermophoresis. Published results point to appreciable enhancement in single-phase heat transfer coefficient realized in entrance region, but the enhancement subsides downstream. And, while some point to the ability of nanofluids to increase CHF, they also emphasize that this increase is limited to short duration boiling tests. Overall, studies point to many important practical problems associated with implementation of nanofluids in cooling situations, including clustering, sedimentation, and precipitation of nanoparticles, clogging of flow passages, erosion to heating surface, transient heat transfer behavior, high cost and production difficulties, lack of quality assurance, and loss of nanofluid stability above a threshold temperature.
       
  • R14 flow condensation heat transfer performance: Measurements and modeling
           based on two-phase flow patterns
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Qinglu Song, Gaofei Chen, Hanwen Xue, Yanxing Zhao, Maoqiong Gong An experimental investigation on flow condensation heat transfer characteristics of tetrafluoromethane (R14) in a horizontal smooth tube with inner diameter of 4 mm was carried out. Experiments were implemented at mass fluxes from 200 to 650 kg/(m2 s), saturation pressures from 1 to 3 MPa and heat fluxes from 8.3 to 28.2 kW/m2 over the entire range of vapor quality. The effects of saturation pressure, mass flux, heat flux and vapor quality were analyzed and discussed. In addition, R14 experimental data were compared with fifteen well-known flow condensation heat transfer correlations. Based on the comparison result and experimental data, an improved flow pattern-based heat transfer correlation was proposed and predicted R14 experimental data well with a mean absolute relative deviation of 6.26%. Finally, 1370 data points from nine published literature were adopted to evaluate the predictive ability of this new model. It achieves a satisfactory predicting result with a mean absolute relative deviation of 20.04% and 77.61% of the experimental data within the deviation bandwidth of ±30%.
       
  • Thermal convection in horizontal rectangular enclosures at moderate
           Rayleigh numbers: Effect of sidewall conductance and aspect ratio
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): U. Madanan, R.J. Goldstein Moderate Rayleigh number thermal convection for horizontal rectangular enclosure is experimentally studied for 1.85×106⩽Ra⩽1.04×1011. The best fit for the investigated range of Rayleigh numbers is found to be Nu=0.067Ra0.330 when a sidewall material of very low thermal conductivity is employed. The effect of sidewall conductance and aspect ratio on the Nu-Ra relationship is also scrutinized.
       
  • RANS study of steady and pulsed gaseous jets into a supersonic crossflow
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Zhao-bo Du, Wei Huang, Li Yan, Lang-quan Li, Zheng Chen, Shi-bin Li The mixing process plays an important role in the combustion realization of the scramjet engine. In the current study, the steady jet, as well as pulsed jets with different wave shapes namely sine, square and triangle waves, is investigated in order to achieve adequate fuel/air mixing. Flow field properties are studied numerically based on grid independency analysis and code validation. The vortex structures, as well as the flow field parameters such as mixing efficiency, total pressure recovery coefficient, fuel penetration depth and mixing length, are deeply analyzed for different jet-to-crossflow pressure ratios. The obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation SST κ-ω turbulence model show that the grid scale makes only a slight difference to wall pressure profiles for all cases studied in this article. Compared with the steady jet, the pulsed jets with different wave shapes are beneficial for the mixing efficiency improving of the transverse jet, and the pulsed jets have special advantages on reducing the total pressure loss and mixing length but not for improving the fuel penetration depth. When the jet-to-crossflow pressure ratio is high, the performance of pulsed jets is better, and different wave shapes in the pulsed jet result in different vortex structures. This should be studied and discussed deeply in the near future.
       
  • Simulation of convection heat transfer of magnetic nanoparticles including
           entropy generation using CVFEM
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Tawfeeq Abdullah Alkanhal, M. Sheikholeslami, A. Arabkoohsar, Rizwan-ul Haq, Ahmad Shafee, Zhixiong Li, I. Tlili An investigation has been conducted to study Lorentz effect on nanomaterial behavior within a permeable space including innovative numerical technique namely CVFEM. Iron oxide has been mixed with H2O and porous domain was filled with this nanomaterial. The impacts of the flow and geometric variables on entropy generation along with the heat transfer have been examined. The simulations have been carried out with wide ranges of the magnetic force, permeability and Rayleigh numbers. The outcomes indicate that the Darcy term has inverse relationship with temperature of hot surface. Stronger convection mode and lower exergy loss appear when buoyancy forces augment. Entropy generation goes up with growth of Hartmann number.
       
  • Experimental investigation on natural convection and thermal
           stratification of IRWST using PIV measurement
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Weian Du, Yusheng Liu, Hongsheng Yuan, Shouxu Qiao, Sichao Tan Passive Residual Heat Removal Heat Exchanger (PRHR HX) immerged in the In-containment Refueling Water Storage Tank (IRWST) plays an important role in removing the core decay heat under non-Loss of Coolant Accident (LOCA) accident. In the initial stage of the Passive Residual Heat Removal System (PRHRS) activating, the natural convection is the main way to exchange heat between the secondary side of the PRHR HX with IRWST. However, it is almost impossible to acquire the thermohydraulic performance in IRWST since the influence of the natural convection and thermal stratification in IRWST happens simultaneously. In this paper, Hierarchical Two-Tiered Scaling (H2TS) method is employed to get scaling criteria based on control equations. Anda visualized water tank with five C-shape electrical heating tubes was scaled-down and applied to investigate the thermohydraulic performance for IRWST of CAP1400 Nuclear Power Plants (NPPs). Particle Image Velocimetry (PIV) measurement was used to investigate the evolution of the flow field of total twenty-five surfaces in three axial directions under three steady- and two variable-heating conditions. Meanwhile, three thermocouple bundles were adopted to acquire temperature data in three regions. The experimental results show that the temperature deviation in the same height of the IRWST is flattened by plenty of vortexes. As a result, local circulation and the temperature difference is less than 1 °C. While the thermal stratification along the vertical direction is obvious, the distribution of flow field and temperature demonstrate that a “dead zone” exists in bottom of the IRWST. Besides, a “thermal interface” region forms in the lower middle region as hot and cold fluid mixing. An obvious upwelling flow is observed near the PRHR HX heating rod bundle from flow fields of three axial directions. At the same time, the maximum height of the upwelling flow decreases with time increasing. On the one hand, the natural convection is induced by the thermal stratification. What is more, the thermal stratification will impair the scale and strength of natural convection, which will intensify the thermal stratification conversely.
       
  • Mesoscale understanding of capillarity driven two-phase flow in a packed
           bed architecture
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Saurabh Bhardwaj, Amaresh Dalal, Partha P. Mukherjee Understanding the displacement dynamics in capillarity driven two-phase flow in packed bed architectures is of fundamental importance. In this work, the role of mesoscale physics due to the underlying capillarity-wettability interaction on the two-phase flow in a sphere-packed architecture is presented. The influence of different pore surface wettability, porosity and pressure gradient on the two-phase flow behavior has been studied. The mesoscale study exhibits interesting pattern formations due to the invasion of a non-wetting fluid and surface adherence owing to the underlying wettability-capillarity characteristics. The emergence of finger like invasion pattern in a hydrophobic architecture is observed while a stable fluid front predominates in a hydrophilic structure. This study further reveals that a hydrophilic architecture is prone to elevated saturation limit for the invading fluid, while a larger pressure gradient can promote pronounced finger-like patterns.Graphical abstractGraphical abstract for this article
       
  • Heat and mass transfer on rectangular and annular finned surfaces of heat
           exchangers operating under frosting conditions
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Teresa Benítez, S.A. Sherif, J. Benítez The analysis of the process of frost formation on a cold surface exposed to humid air yields a system of differential equations. In this study, the orthogonal collocation method is used to help solve the system of equations resulting from the flow of humid air over heat exchanger fins maintained at a temperature below both the dew-point temperature of water vapor in air and the freezing point. The temporal dependence of the frost growth creates a moving boundary that is addressed using a front-fixing method. This proposed method allows solving for important variables such as frost thickness, temperature distribution, and heat flux through the frost layer. Model results were found to agree closely with available experimental data. In all data sets modeled, it was found that super saturation at the frost-air interface must be included in the model to accurately predict frost growth.
       
  • Hydrodynamic dispersion due to a variety of flow velocity profiles in a
           porous-walled microfluidic channel
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Morteza Dejam A reduced-order model for the advective-dispersive mass transfer due to a variety of flow velocity profiles in a porous-walled microfluidic channel is developed in this study. The fluid flow in the microfluidic channel is described by a generalized class of the Poiseuille equation proposed by Amatore et al. (2009), which includes the bluntness parameter for exhibiting the level of bluntness of the velocity profile. This flow formulation represents all the traditional velocity profiles for the purely pressure-driven (Poiseuille) flow, the combined pressure-driven and electro-osmotic flows, and the purely electro-osmotic flow (EOF) in the microfluidic channel. The resulting reduced-order model delivers the mass transfer coefficients, including the hydrodynamic dispersion and the effective advection coefficients, which are functions of the Peclet number and the bluntness parameter. The results reveal that the hydrodynamic dispersion decreases when the flow varies from the pressure-driven to the electro-osmotic. In other words, the smaller the bluntness parameter the smaller the hydrodynamic dispersion. The diffusive, transient, and advective mass transfer regimes can be identified from the ratio of the hydrodynamic dispersion coefficient in the porous-walled microfluidic channel to the one in the nonporous-walled microfluidic channel. It is found that the mass transfer between the microfluidic channel and the porous medium should be included in determination of the hydrodynamic dispersion coefficient due to a variety of flow velocity profiles in a porous-walled microfluidic channel for the transient and the advective regimes. The results also show that the smaller the bluntness parameter the slower the mass transfer. Furthermore, the mass transfer in a porous-walled microfluidic channel is slower than the mass transfer in a nonporous-walled microfluidic channel.Graphical abstractGraphical abstract for this article
       
  • Anti-freezing of air-cooled heat exchanger with rolling-type windbreaker
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Xiaoru Yang, Huimin Wei, Ruonan Jin, Lijun Yang, Xiaoze Du, Yongping Yang On cold days with even high wind speeds, the excessive cooling capacity of ambient air may result in a freezing risk for air-cooled heat exchanger. In this work, an anti-freezing approach is proposed based on the air flow control by pulling-down adjustment of rolling-type windbreakers, to ensure that the lowest outlet water temperature of each sector in air-cooled heat exchanger is not less than 0 °C. The coupled heat transfer models of natural draft dry cooling system with steam condenser are developed and experimentally validated. The opening degrees of rolling-type windbreakers and air mass flow rates for various sectors are obtained, and the outlet water temperature of each sector with rolling-type windbreakers is calculated. The correlating equations of the opening degree with wind speed at various ambient temperatures are also fitted. The results show that the opening degree of rolling-type windbreaker for each sector varies widely with the ambient temperature and wind speed. At the ambient temperature of −5 °C, only the windbreakers of windward sectors are regulated. While at −10 °C and −15 °C, the windbreakers of lateral and leeward sectors should also be adjusted. The configuration and regulation of rolling-type windbreakers can realize the anti-freezing of air-cooled heat exchanger with the low cost and high energy-efficiency.
       
  • Study on the movement and deposition of particles in supercritical water
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Dongliang Ma, Tao Zhou, Bing Li, Xiang Feng, Hailong Zhang The movement and deposition of fine particles in supercritical water is closely related to the safe operation of supercritical water reactors and supercritical thermal power units. When deposition of corrosion particles occurs, it will affect the heat exchange of the pipe wall and cause the wall temperature to rise rapidly. It will seriously threaten the safe and stable operation of supercritical water reactors or supercritical thermal power units. In this paper, the ANASYS numerical software was used to simulate the movement of fine particles in supercritical water. The effects of parameters such as heating power, inlet temperature, inlet velocity, average particle diameter, and asymmetry of heating on the influence of fine particles in the supercritical water were investigated. The results show that with the increase of inlet temperature, the peak value of particle deposition concentration gradually approaches the inlet section of the pipe. With the increase of inlet velocity, the peak value of particle concentration gradually moves to the outlet of the pipe. The heating of the pipe has a certain inhibitory effect on the concentration and deposition of particles. The simulation result of the particles deposition has been compared and verification with the existing experimental data. The verification results show that the particle deposition concentration distribution characteristics obtained by the simulation and the experimental data are consistent. It facilitates the mechanism analysis of the movement and deposition characteristics of the fine particles in the supercritical water. It is conducive to the safe design of supercritical water reactors.
       
  • Critical heat flux on heterogeneous fractal surfaces with micro-pin-fins
           in pool boiling – Part II: Model establishment and analysis
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Jie Zhou, Baojin Qi, Jinjia Wei The heterogeneous fractal surfaces can achieve higher critical heat flux (CHF) than that with the uniformly distributed surfaces, which is reported in Part Ⅰ. In order to explain the phenomenon and understand the trigger mechanism of CHF, a theoretical model of CHF for the heterogeneous structure surfaces is proposed based on the bubble coalescence caused by the hydrodynamic instability and the wall dryout induced by the liquid supply impediment. The continuous expansion and coalescence of the dry spots lead to the formation of the vapor blanket covering the whole surface, which triggers the occurrence of critical phenomenon. The CHF is obtained according to the arrangement of the vapor columns on the heating surface. Both the distribution of the heterogeneous structure and the subcooling of liquid affect the bubble behaviors and liquid supply, which result in an optimal structure distribution to reach the highest CHF under different subcoolings. Compared with the uniform distribution, the width of smooth region surrounding the bubble increases with the increase of heat flux and bubble diameter on the fractal structure, which can effectively provide liquid replenishment at high heat fluxes and achieve higher CHF. The CHFs calculated from this model agree well with the experimental results, and the vapor column arrangement is consistent with the bubble distribution observed from the experimental phenomenon. Moreover, the model can also be used to calculate the CHF of the uniformly distributed heterogeneous surfaces and the homogeneous microstructure surfaces with good precision, which verifies the correctness and extensive applicability of the model.Graphical abstwwractGraphical abstract for this article
       
  • Experimental and numerical studies on convective heat transfer of
           supercritical R-134a in a horizontal tube
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Y.L. Cui, H.X. Wang, Y.T. Wang Experimental studies on convective heat transfer characteristics of supercritical R-134a flowing in a horizontal tube with an inner diameter 8 mm were conducted in the range of mass flux 500–1000 kg m−2 s−1, heat flux 20–100 kW m−2 s−1 and pressure 4.3–4.8 MPa. Local wall temperatures and convective heat transfer coefficients of the top and bottom surfaces of the test tube were obtained, and their variational trends with increasing heat flux and mass flux were discussed within the experimental range. To have a quantitative and more comprehensive analysis of convective heat transfer behaviors of supercritical fluids as compared with the conventional methods, two new field synergy analytical methods designated as TCEH and FCEH respectively were developed, motivated by the two basic concepts of the field synergy principle respectively, i.e., the analogy of convective heat transfer to conductive heat transfer and the three general criteria associated with convective heat transfer enhancements. Numerical simulations were performed within the identical parameter ranges, and the effects of buoyancy, heat flux and mass flux on convective heat transfer were analyzed using these two new methods. Finally some new insights into supercritical convective heat transfer were obtained.
       
  • A novel approach for modelling thermal energy storage with phase change
           materials and immersed coil heat exchangers
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): M.Y. Abdelsalam, M.F. Lightstone, J.S. Cotton A novel modelling approach is presented for a thermal energy storage system with immersed coil heat exchangers. The energy store consists of a water tank in which rectangular phase change material (PCM) modules are submerged. The immersed coil heat exchangers are placed at the bottom and top sections of the tank for charging and discharging, respectively. This design promotes thermal mixing inside the tank when charged from the bottom coil and discharged from the top coil. In addition, the location of the coil heat exchangers favorably limits the heat transfer when charged through the top coil or discharged through the bottom coil giving rise to the thermal diode effect. PCMs can offer large storage capacity since they store large amounts of thermal energy in the form of latent heat of phase change (solid-liquid). This paper proposes a simplified physics-based numerical model of the heat transfer and phase change in the thermal storage tank. The model discretizes the storage tank one-dimensionally into three fully-mixed control volumes; two control volumes surrounding the immersed coil heat exchangers and one control volume in the middle of the tank including the PCM modules. All the heat transfer dynamics between the control volumes, the heat exchangers and the PCM modules are considered. Experimental validations, using a full-scale test facility, are carried out for systems with and without PCMs under various operation scenarios and the results are found to agree well within the experimental uncertainties. Such model potentially provides high computational efficiency that is desirable in simulating the performance of storage systems under long-term operations.
       
  • Interferometric study of the heat and mass transfer during the mixing and
           evaporation of liquid oxygen and nitrogen under non-uniform magnetic field
           
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Shi-Ran Bao, Rui-Ping Zhang, Yangyiming Rong, Xiao-Qin Zhi, Li-Min Qiu Improving the separation efficiency and reducing the energy consumption in air separation units is of great importance to the development of petrochemical, iron and steel industries. A new method was proposed to improve the efficiency of cryogenic distillation by comprehensive utilizing of the boiling point and magnetic differences of oxygen and nitrogen. Laser interferometry system was designed and constructed to validate the effect of non-uniform magnetic field on the mass and heat transfer process between liquid oxygen and nitrogen. One-dimensional continuous wavelet transform was used to extract the two-dimensional concentration distribution from the interference patterns. Results have revealed 4 stages during the mass transfer process, including liquid oxygen filling stage, stratified diffusion stage, stable evaporation stage and unstable bubbling stage. The time for the stratified diffusion under magnetic field was maintained longer than that without magnetic field. The high gradient magnetic medium, which filled between the magnet poles, can further enhance the effect of magnetic field. With 0.5 g steel wools, the mole fraction of oxygen decreased by 30% at 120 min from the beginning of mass transfer compared to that without medium and decreased by 38% compared with that without magnetic field. The stratified diffusion and the bubbling phenomenon revealed in the experiments will provide a basis for the further development of the magnetically enhanced air separation units.
       
  • Correlations for the Graetz problem in convection – Part 2: For ducts of
           arbitrary cross-section
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 135Author(s): Ted D. Bennett A general correlation is proposed for the laminar Graetz problem associated with convection in ducts of arbitrary cross-section. The correlation assumes knowledge of fully developed transport constants, specifically the product of fully developed friction factor and Reynolds number, and the fully developed value of Nusselt number, whose values are particular to the duct geometry and wall condition. The new correlation is suitable for ducts having a convective surface equal to the wetted perimeter, and for ducts having a wall condition of either constant temperature or constant heat flux. For the majority of solutions to the Graetz problem found in the literature for various duct geometries, the new correlation is generally found to be within ±5% of first principle calculations.
       
  • Effective properties of a thermoelectric composite containing an elliptic
           inhomogeneity
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 135Author(s): K. Song, H.P. Song, M. Li, P. Schiavone, C.F. Gao In this paper we use complex variable methods to develop the effective properties of a thermoelectric composite containing an elliptic inhomogeneity. We provide closed-form representations of the effective electric conductivity, the Seebeck coefficient, the thermal conductivity and the thermoelectric figure of merit for a square area containing the elliptic inhomogeneity. In addition, we present explicit expressions for and a discussion of the effective properties of the composite in the particular case of a circular inhomogeneity. In this case, we find that the effective figure of merit can exceed more than 6.4% of that of each constituent for a precise ratio of material parameters. Consequently, our analysis provides a new approach for improving the performance of thermoelectric devices and the design of thermoelectric composites.
       
  • Effect of nanofluid formation methods on behaviors of boiling bubbles
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 135Author(s): Hanwook Park, Sang Joon Lee, Sung Yong Jung Understanding the boiling heat transfer characteristics of nanofluid suspensions containing nanoparticles is one of the challenging issues in the heat transfer research field. The addition of nanoparticles modifies both the surface characteristics and the thermo-physical properties of the suspension, including thermal conductivity, viscosity, and surface tensions. One of the critical features is the stability of nanoparticle suspension, which is strongly related to the formulation method of nanofluids. In this study, to investigate the effect of several formation methods, the pool-boiling bubble behaviors of Al2O3 nanofluid, with varying nanofluid formation methods, were systematically analyzed using an X-ray imaging system. The changes in the wettability of Al2O3 nanofluid suspensions and the variations of boiling bubble characteristics were analyzed to determine the relationship between boiling-bubble behaviors and examine the effects of heating the substrate. Before the heating substrate, the bubble generating ratio was increased by 1.4 times, when the concentration of Nanofluid 3 increased from 0.05 wt% to 1 wt% with adopting the electrostatic stabilization method and high-speed rotating procedure. On the other hand, at the end of heating process, the bubble generating ratio was decreased by 0.78 times for the same concentration change. Once the nanoparticle sedimentation occurred, the trend of wettability and bubble behaviors of nanofluids changed based on the surface modification, regardless of the nanofluid formation method. An increase in the Al2O3 nanofluid concentration results in a deterioration of the heat transfer characteristics, and the formulation method is not related to the boiling heat transfer performance when nanoparticles are deposited.
       
  • Simultaneous prediction of dryout heat flux and local temperature for thin
           film evaporation in micropillar wicks
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Geoffrey Vaartstra, Zhengmao Lu, Evelyn N. Wang Porous wicks are of great interest in thermal management because they are capable of passively supplying liquid for thin film evaporation, a promising method to reliably dissipate heat in high performance electronics. While dryout heat flux has been well-characterized for many wick configurations, key design information is missing as many previous models cannot determine the distribution of evaporator surface temperature. Temperature gradients are inherent to the passive capillary pumping mechanism since the shape of the liquid/vapor interface is a function of the local liquid pressure, causing spatial variation of permeability and heat transfer coefficient (HTC). Here, we present a comprehensive modeling framework for thin film evaporation in micropillar wicks that can predict dryout heat flux and local temperature simultaneously. Our numerical approach captures the effect of varying interfacial curvature across the micropillar evaporator to determine the spatial distributions of temperature and heat flux. Heat transfer and capillary flow in the wick are coupled in a computationally efficient manner via incorporation of parametric studies to relate geometry and interface shape to local permeability and HTC. This model predicts notable variations of HTC (∼30%) across the micropillar wick, highlighting the significant effects of interfacial curvature. Further, we are able to quantify the tradeoff associated with enhancing either dryout heat flux or HTC by optimizing geometry. Our model provides all of the information needed to guide the design and optimization of micropillar wicks by resolving evaporator temperature distributions in addition to dryout heat flux.
       
  • Bubble nucleation over patterned surfaces with different wettabilities:
           Molecular dynamics investigation
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 136Author(s): Wenjing Zhou, Yang Li, Mingjie Li, Jinjia Wei, Wenquan Tao The bubble nucleation of liquid argon over patterned surfaces with different wettabilities is investigated by using molecular dynamics (MD) simulations. In order to study effects of different wall temperatures on bubble nucleation process, bubble nucleation positions and bubble dynamics behaviors are observed. Simulation results show that at low wall temperatures bubble nucleation tends to occur over the hydrophobic part of the wall. With increasing wall temperature, the bubble nucleus gradually changes its position from the hydrophobic to hydrophilic part. When the wall temperature increases to a certain value, bubble nuclei first appear on both the hydrophobic and hydrophilic parts. By analyzing heat flux and change trend of argon state points, differences in bubble nucleation process at different wall temperatures are explained. Moreover, the effect of area fraction of hydrophobic part on bubble nucleation temperature is investigated. It is found that there exists an optimal area fraction which makes the bubble nucleation temperature the lowest.
       
  • Microencapsulation of solid cores to prepare double emulsion droplets by
           microfluidics
    • Abstract: Publication date: June 2019Source: International Journal of Heat and Mass Transfer, Volume 135Author(s): Wei Gao, Yongping Chen We herein present an effective microfluidic method based on facile glass capillary assembly for encapsulating solid cores to prepare double emulsions. Visualization experiments are conducted to verify the effectiveness of the presented microfluidic device. It is indicated that, via the presented microfluidic device, solid cores can be controllably encapsulated into every generated double emulsion droplets under wide operating range of flow rate. The number of the encapsulated solid cores can be well manipulated by adjusting the flow rate of different phases. Particularly, by employing multiple injection microchannels, multiple kinds of solid cores can be encapsulated into a single droplet in different combinations. This microfluidic methods show good applicability to generate both solid-in-oil-in-water (s/o/w) and solid-in-water-in-oil (s/w/o) double emulsion droplets. We believe that the current microfluidic methods are capable to extend the application of microencapsulation in microcapsule preparation, drug detection, food delivery, single cell analysis, and synthesis of nanomaterials, etc.
       
 
 
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