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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 333  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3185 journals]
  • Effect of thermocapillary instability on liquid film breakdown
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): E.A. Chinnov, E.N. Shatskiy, V.V. Semionov The film of water flowing down along a vertical surface with a heater was studied experimentally at Re = 10–50. The initial temperature of the water film varied from 15 to 70 °C and heat fluxes on the heater varied from 0 to 6.5 W/cm2. Simultaneous measurements of the film thickness and surface temperature carried out. The effect of development of thermocapillary instability type A on wave amplitudes, deformation of the liquid film surface, and formation of the first stable dry spot on the heater was investigated. It is shown that when the longitudinal temperature gradients reach values larger then 7–10 K/mm formation of thermocapillary structures begins. At the leading edge of the heater, X/mm 
       
  • Influences of confinement on subatmospheric water vaporization phenomena
           in a vertical rectangular channel
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Florine Giraud, Brice Tremeac The influence of confinement on water vaporization phenomena occurring close to the triple point in a vertical rectangular channel of 0.2 m × 0.5 m is investigated. The influence of the driving pressure, the operating pressure and the filling ratio on flow boiling and on time-averaged overall heat transfer depending on the channel thickness is introduced and discussed. It is shown that three main different phenomena at the top of the bubbles occurred depending on the confinement number and on water vaporization production rate: dendrites, evaporation waves and curved interface. Entrainment of droplets by the vapour flow was also observed for the highest confinement number investigated (Co = 0.69). These different phenomena observed impact the heat transfer leading to higher performances for a confinement number of 0.69 compared to confinement number of 0.35 and 0.23 for rate of vapour production obtained at high driving pressures and low filling ratio but also for operating conditions obtained at low driving pressure and high filing ratio.
       
  • A mathematical study of bubble dynamics in superheated sodium chloride
           solution
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Liang Hao A mathematical study of bubble growth in the superheated binary solution with a non-volatile solute is conducted by solving the momentum, energy and species equations around the bubble. Additionally, the two-characteristic-parameter correlation (TCPC) model is used to identify the thermodynamic conditions at the bubble-solution interface. By considering a single bubble and ignoring the interactions between the bubbles, the bubble growth characteristics in the NaCl solution are analyzed in detail, and the effects of NaCl concentration and operating conditions on bubble growth are discussed. It is observed that the non-volatile solute of NaCl slows down the bubble growth process in the entire duration of the growth period due to the extension of delay time and reduction of the driving forces with increase of solute concentration. The effects of solute concentration on bubble growth cannot be entirely eliminated by modifying the operating conditions to give the same degree of superheat by compensating the boiling point elevation (BPE). The increase of solute concentration near the bubble at moderate or high superheated conditions has non-negligible influence on bubble growth. A revised Mikic-Rohsenow-Griffith (MRG) formula by considering the solute effect and the increase in solute concentration near the bubble surface is proposed to predict the bubble growth in salt solutions. The predictions from the revised formula agree well with the complete simulations of bubble growth at various salt concentrations.
       
  • Anisotropic thermal conductivity under compression in two-dimensional
           woven ceramic fibers for flexible thermal protection systems
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Rodrigo Penide-Fernandez, Frederic Sansoz Flexible thermal protection materials made from two-dimensional woven ceramics fibers are of significant interest for hypersonic inflatable aerodynamic decelerators being developed by NASA for future missions on Mars and other planets. A key component of the thermal shield is a heat-resistant outer ceramic fabric that must withstand harsh aero-thermal atmospheric entry conditions. However, a predictive understanding of heat conduction processes in complex woven-fiber ceramic materials under deformation is currently lacking. This article presents a combined experimental and computational study of thermal conductivity in 5-harness-satin woven Nextel 440 fibers, using the hot-disk transient plane source method and computational thermo-mechanical modeling by finite-element analysis. The objective is to quantify and understand the effect of compressive strain on anisotropic heat conduction in flexible two-dimensional ceramic materials. We find, both experimentally and theoretically, that thermal conductivity of woven fabrics rises in both in-plane and out-of-plane directions, as the transverse load increases. Air gap conduction and fiber-to-fiber contacts are shown to play a major role in this behavior. Our finite-element simulations suggest that the thermal conductivity anisotropy is strong because heat transfer of air confined between fibers is reduced compared to that of free air. The proposed modeling methodology accurately captures the experimental heat conduction results and should be applicable to more complex loading conditions and different woven fabric materials, relevant to extreme high temperature environments.Graphical abstractGraphical abstract for this article
       
  • Molecular dynamics simulation on evaporation enhancement of water and
           aqueous nano-films by the application of alternating electric field
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Hao-Han Zhang, Bing-Bing Wang, Zhi-Ming Xu, Xing-Can Li, Wei-Mon Yan In this work, molecular dynamics simulation has been adopted to investigate the influence of square-wave alternating electric field on the evaporation of pure water and aqueous nano-films. The evaporation of the films with 3360 water molecules and 0, 1.11 and 2.18 mol L−1 NaCl on a hot gold (1 0 0) surface was analyzed. The results showed that both the evaporation of water and aqueous films were enhanced by applying the alternating electric field. Compared with the liquid films at the absence of the electric field, the maximum evaporation rates increased 1.71, 1.70 and 1.66 times for water film and aqueous films with 1.11 and 2.18 mol L−1 NaCl for the frequency of 500 GHz, respectively. The reasons were inferred that the water film subjected to the time-varying electrical force resulted in increasing of the rotational and translational kinetic energy of water molecules. Thus applying the alternating electric field accelerated the temperature rise of the water film and enhanced thermal volume expansion of the water film. In addition, the interaction between water molecules became weaker and the water molecules escaped from the water film more easily. The MD simulation also showed that the evaporation enhancement was more significant for the alternating electric field parallel to the films surface than in the perpendicular direction.
       
  • Turbulence dissipation & its induced entrainment in subsonic swirling
           steam injected in cocurrent flowing water
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Afrasyab Khan, Mohd Sobri Takriff, Masli Irwan Rosli, Nur Tantiyani Ali Othman, Khairuddin Sanaullah, Andrew Ragai Henry Rigit, Ajmal Shah, Atta Ullah, Muhammad Umar Mushtaq Subsonic swirling steam induced turbulence, its dissipation, and entrainment inside the concurrent flowing water has been investigated on an experimental basis. Pressure fluctuations of dissimilar amplitudes have been observed which have been attributed to the vortices and hence instances for entrainment on a spatial basis. The extent of turbulence dissipation has been measured by the rate of decrement of the smallest pressure fluctuation of amplitude 0.04 bars. It has been observed that the turbulence dissipation along radial direction rises from 2.3 to 6.3 fluctuations/cm with rising in the inlet pressure of steam & till 12.5 fluctuations/cm in case of rising in rpm of the swirler. On a temporal scale, the turbulence dissipation varies from 0.7 fluctuations/sec at initial conditions which rise till 1.9 fluctuations/sec with the rise in inlet pressure of steam & 3.7 fluctuations/sec in case of rising in rpm of the swirler. Effect of rising in compressibility & rpm on sheer layer transformation into vortices imparted in terms of spatial dislocation along the axial axis, which ranges from 64–66% to 35–41% respectively. The extent of entrainment has found to be influenced by an increase in the compressibility, the rpm of the swirler and the surrounding water inlet pressure, which has been represented by the number of occurrences of the vortices across radial and axial directions. Effects imparted by the given conditions on fluctuations, entrainment, and non-dimensionalized flux has also been investigated.
       
  • Fractal description of fouling deposits in boiling heat transfer modelling
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): T. Dupuy, T. Prusek, F. Oukacine, M. Lacroix, A. Kaiss, J.P. Clerc, M. Jaeger A novel methodology is developed for predicting the thermal impact of fouling in Steam Generators (SG). The originality of this methodology is to resort to fractal and statistical theories to depict the porous structure of the deposits. The proposed Statistical Fractal methodology (SF) accounts for the heat transfer driven by the liquid-vapor phase change inside the deposits. It simulates the complex intricate networks of sinuous open pores of different scales, with liquid inflows (capillaries) and vapor outflows (steam-chimneys). The multi-layered representation of fouling deposits allows to mimic aging mechanisms such as densification which occur during SG operation.The SF predictions are consistent with experimental data. The deposit thickness and the profile of porosity are found to be the most influential fouling properties on the heat exchange. The methodology is capable to simulate the experimentally observed heat transfer enhancement for thin and porous deposit as well as the heat exchange decline for thick and dense deposit.
       
  • Amelioration of the pool boiling heat transfer performance via
           self-assembling of 3D porous graphene/carbon nanotube hybrid film over the
           heating surface
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Nurettin Sezer, Shoukat Alim Khan, Muammer Koç This study investigates the boiling heat transfer enhancement of 3D porous graphene/carbon nanotube hybrid surface formed via self-assembling. Experimentally, colloidal suspensions of functionalized carbon nanotubes and graphene oxide (at 1:10 wt ratio) and only graphene oxide in water are prepared via sonication using three weight concentrations; 0.00005%, 0.0005%, and 0.005%. Boiling tests are conducted for each prepared fluid using a custom-made boiling apparatus. After boiling tests, Scanning Electron Microscopy analysis is carried out over the heating surfaces in order to observe the deposition behavior of the suspended nanoparticles. For wettability analysis, the contact angle of sessile water droplets on the heating surfaces are measured using the goniometry method. The boiling performance of the heating surface formed by self-assembling of graphene oxide/functionalized carbon nanotube outperforms the self-assembled graphene oxide-only surface with greater critical heat flux and heat transfer coefficient values at all the tested concentrations. A decent interfacial contact of graphene sheets and carbon nanotubes improves surface capillarity and thermal activity. The highly porous surface improves the nucleation site density, bubble departure diameter, and frequency of departure. All these factors contribute enhancement of heat transfer coefficient and critical heat flux.
       
  • Research on the solution method for thermal contact conductance between
           circular-arc contact surfaces based on fractal theory
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Yang Liu, Qingyu Meng, Xinxin Yan, Siyao Zhao, Jiyuan Han A thermal contact conductance (TCC) prediction model between circular-arc rough contact surfaces is established. The self-similarity and continuity of rough surfaces are characterised by using the Weierstrass–Mandelbrot (W–M) function. Then, the model of contact mechanics is established. In addition, the contact force and deformation of the contact surfaces at different states are calculated by considering the three deformation processes of elastic, elastic–plastic, and complete plastic. Thus, a numerical method for calculating the predicted TCC is provided. The global contact stress and TCC distribution caused by the change in the contact azimuth angle are analysed. Simultaneously, the fractal parameters of the circular-arc contact surfaces and the TCC calculation during the experiment are introduced. The effects of different materials, external contact temperature, contact-surface roughness and contact pressure on the TCC are analysed. The experimental results agree well with the simulation calculations, which validate the accuracy of the simulation results. We find that a ‘temperature waterfall’ phenomenon occurs between the circular-arc contact surfaces. As the external contact temperature and contact pressure increase, the ‘softening’ phenomenon of asperities occurs, resulting in an increase in the TCC. Meanwhile, the TCC decreases with the increase in the surface roughness, and it is cross-impacted by the material properties. This study provides a basis for TCC prediction in engineering practice.Graphical abstractGraphical abstract for this article
       
  • Air inlet angle influence on the air-side heat transfer and flow friction
           characteristics of a finned oval tube heat exchanger
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Linghong Tang, Xueping Du, Jie Pan, Bengt Sundén In this study, the influence of various air inlet angles on the heat transfer and flow friction characteristics of a 2-row plain finned oval tube heat exchanger is analyzed by experimental and numerical methods. The experimental results show that an air inlet angle 45° provides the best heat transfer performance, and an air inlet angle 90° provides the smallest pressure drop, while an air inlet angle 30° provides the worst heat transfer performance associated with the largest pressure drop. The 3-D numerical simulation results indicate that with the decrease of the air inlet angle, the uniformity of the air velocity distribution in the z-direction of the heat exchanger becomes worse. The heat transfer characteristics at different air inlet angles are analyzed from the prospective of the field synergy principle and the effect of the air velocity distribution uniformity. The overall heat transfer performance is also evaluated by the JF factor under the same air mass flow rate. The results show that the air inlet angle 45° offers the best overall heat transfer performance, next is the air inlet angle 60°, while the air inlet angle 30° has the worst overall heat transfer performance.
       
  • Thermal conductivity of molybdenum disulfide nanotube from molecular
           dynamics simulations
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Han Meng, Dengke Ma, Xiaoxiang Yu, Lifa Zhang, Zhijia Sun, Nuo Yang Single layer molybdenum disulfide (SLMoS2), a semiconductor possesses intrinsic bandgap and high electron mobility, has attracted great attention due to its unique electronic, optical, mechanical and thermal properties. Although thermal conductivity of SLMoS2 has been widely investigated recently, less studies focus on molybdenum disulfide nanotube (MoS2NT). Here, the comprehensive temperature, size and strain effect on thermal conductivity of MoS2NT are investigated. Thermal conductivity is obtained as 16 Wm−1 K−1 at room temperature, and it has a ∼T−1 dependence on temperature from 200 to 400 K and a ∼Lβ dependence on length from 10 to 320 nm. Interestingly, a chirality-dependent strain effect is identified in thermal conductivity of zigzag nanotube, in which the phonon group velocity can be significantly reduced by strain. This work not only provides feasible strategies to modulate the thermal conductivity of MoS2NT, but also offers useful insights into the fundamental mechanisms that govern the thermal conductivity, which can be used for the thermal management of low dimensional materials in optical, electronic and thermoelectrical devices.
       
  • Analysis of temperature and concentration polarizations for performance
           improvement in direct contact membrane distillation
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Zhengfei Kuang, Rui Long, Zhichun Liu, Wei Liu Regarding numerical simulation of the direct contact membrane distillation (DCMD) based on computational fluid dynamics, the variation of mass flowrate and concentration along the flow direction has merely been considered. To relieve such issues, a refined model coupling Navier-Stokes equations and species transportation equations is employed to illustrate the flow, heat and mass transfer characteristics in the flat sheet DCMD process. The potential of attaching baffles to the feed/permeate channel shell to improve the DCMD performance has been investigated under the laminar and turbulent flow, respectively. Modified channels were designed to have regularly distanced baffles with various shapes at different characteristic lengths. The heat transfer coefficient, mass transfer coefficient, temperature polarization coefficient, concentration polarization coefficient, mass flux, thermal efficiency and power consumption of the original and modified modules are calculated and compared. Results reveal that a structural modification could promote the temperature polarization phenomenon and restrain the concentration polarization phenomenon, thus to improve the module water production. However, the presence of baffles contributes to extra power consumption. At a feed flow Reynolds number of 358, for module with semi-circle shaped baffle at the characteristic length of 1 mm, the water production is increased by 28.3%, meanwhile the hydraulic energy consumption is increased by 3.32-fold. Under the laminar flow, the water production can be significantly improved by attaching baffles in the channel shells, which is not appealing under the turbulent flow due to the huge augment in hydrodynamic loss.
       
  • Analytical layered solution of radiation and non–Fourier conduction
           problems in optically complex media
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Guillaume Lambou Ymeli, Hervé Thierry Tagne Kamdem, Réné Tchinda, Myriam Lazard The analytical layered solution for radiative transfer through participating optically complex media is developed. The angular processing of radiation is based on double spherical harmonics method (DPN) which split up the radiative intensity into two stream components before expanding in Legendre polynomial basis. The proposed layered radiative solution assumes that the optically complex media is a set of thin layers dealing with homogeneous properties. Therefore, the analytical solution for radiative transfer is performed and then coupled to the finite volume method (FVM), to solve the non – linear hyperbolic thermal conduction problems, formulated thanks to Cattaneo–Vernotte flux. In developing the FVM, the Roe′s corrections of interface fluxes is adopted in order to enhance the performances of the method. The accuracy of the proposed model for dealing with inhomogeneous radiation/conduction problems is investigated by considering participating media such as slab, solid or hollow spheres, with temperature – dependent thermal conductivity. The effects of different parameters, known as scattering albedo, graded index function, thermal conductivity, boundary emissivity and the conduction–radiation parameter on both temperature and heat flux distributions for purely radiation, steady and transient states are studied. Results of the present work compare well with those available in the literature with maximum relative error less than 1%. These results show that the listed parameters have a significant effect on both temperature profiles and hyperbolic sharp wave front. It also comes from this study that the proposed layered approach is an efficient, robust, and accurate method for radiative flow analysis in inhomogeneous media while the Roe′s correction of interface fluxes in FVM is suitable to accommodate thermal wave front in non – Fourier analysis.
       
  • Wave characteristics of vertical upward adiabatic annular flow in pipes
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Peng Ju, Yang Liu, Xiaohong Yang, Mamoru Ishii Annular flow exists in many engineering applications, such as refrigerators, oil extraction, nuclear reactors and so on, due to its high heat and mass transfer efficiencies. Annular flow is characterized by liquid film on the wall and gas core at the center of the flow duct. The interface between the gas and liquid is composed of many different waves that play important role in mass, momentum and energy transfers between gas and liquid phases. Here three important parameters regarding wave characteristics, namely, wave velocity, base film thickness and wave height have been studied. For wave velocity, correlation has been proposed by two methods which are derived from liquid interfacial velocity and interfacial shear stress, respectively. For correlations of base film thickness and wave height, they are proposed in similar forms as that of average film thickness previously developed by the authors. These newly proposed correlations are functions of gas and liquid Weber numbers, and are simpler and more straightforward to use as compared to the existing ones. The newly proposed wave velocity, base film thickness and wave height correlations, respectively, have mean absolute percentage errors of 9.56%, 14.6% and 12.1% compared to current databases. They have shown an improved prediction accuracy compared to the other correlations in the literature.
       
  • Generation of micron-sized droplet streams by high frequency electric
           fields
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Krishnadas Narayanan Nampoothiri, M.S. Bobji, Prosenjit Sen Generation and transfer of micron-sized droplets are of significant interest for several applications such as electronics cooling, lab-on-chip, microscale printing, etc. We report generation of microscale droplet streams when a larger droplet is exposed to high frequency (>10 kHz) electric fields using dielectric covered coplanar electrodes. Generation of these droplet streams is found to be a function of the actuation frequency and voltage. Our experiments rule out electrospray as the relevant mechanism. Experiments further reveal that the droplet streams are formed due to (1) Evaporation of the larger droplet due to Joule heating; and (2) Enhanced localized condensation on nucleation sites originating from the leakage currents at high electric fields. The condensed droplets are dragged along with the convection current of the larger droplet, leading to the observation of streams. A computational model is used to solve for the convection velocities which is compared with the experimental high-speed videos. The stream velocity is found to increase with the applied field, which is attributed to the smaller size of the condensed droplet at higher electric fields. Capability to generate microscale droplets and transfer them to other substrates is desired in current microfluidic platforms for various applications. This study reports a viable technique and presents critical information for its design.Graphical abstractGraphical abstract for this article
       
  • Numerical investigation on thermal-hydraulic characteristics of NaK in a
           helical wire wrapped annulus
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Hao Qin, Chenglong Wang, Mingjun Wang, Dalin Zhang, Wenxi Tian, G.H. Su, Suizheng Qiu The wire wrapped on an annulus can act as a structural stabilizer and heat transfer promoter, which is a promising heat transfer augmentation device. The thermal-hydraulic characteristics of NaK in a helical wire wrapped annulus is numerically investigated using structured mesh, with the conjugate heat transfer between the solid and liquid domain being taken into consideration. The sensitivity analysis of the turbulent model and turbulent Prandtl number are conducted. The flow and temperature fields of the coolant are obtained, which show a fully mixing and uniformity. As a cost, the temperature distribution of the solid domain is observed to be non-uniform. The heat transfer is strengthened due to the enhancement of the synergy between the velocity and temperature field. The correlations of the heat transfer coefficient and friction factor are provided. The thermal-hydraulic performance ratio of annulus with and without wrapped wire is 0.92–0.99, suggesting a satisfactory performance. Besides, the average heat flux on the helical wire surface is only 5% of that of loaded on the outer smooth wall of the inner sleeve. This paper may contribute to the thermal-hydraulic design of the liquid metal cooled and helical wire wrapped annulus.
       
  • Solid sorption heat pipe coupled with direct air cooling technology for
           thermal control of rack level in internet data centers: Design and
           numerical simulation
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Yang Yu, Liwei Wang The utilization of direct/indirect free cooling (natural cold source) method for data center (DC) cooling and thermal management system has great potential in reducing electric energy consumption. Integrating heat pipe indirect and passive heat transfer method with active vapor-compression refrigeration technique is considered as a promising and alternative solution. The proposal of solid sorption heat pipe is expected to alleviate the drawbacks of heat transfer limits in both conventional heat pipe and thermosyphon. Here, a novel dual-mode thermal control system coupled solid sorption heat pipe with direct air convection scheme for rack level cooling of DC is designed and three-dimensional calculation models are set up to simulate the flow and temperature fields for DC room level and rack level, respectively. Experimental results of solid sorption heat pipe with NaBr show that the maximum axial heat flux with different filing amount and different inclination angle are 913.3 kW/m2 and 559.7 kW/m2, respectively. The parameterized simulation results for rack level cooling of DC illustrate that when flow rate of supply air is 2 m/s and heat dissipation of single server reaches 1000 W, this novel dual-mode thermal management scheme could reduce the peak temperature of server from 75.8 °C to 68.8 °C. A case study based on typical DC scale further elaborates that the dual-mode thermal control oriented to rack level is feasible for energy-saving of DC cooling system.Graphical abstractSSHP unit and the novel dual mode thermal control system oriented to rack level cooling.Graphical abstract for this article
       
  • A two-phase simulation for analyzing thermohydraulic performance of
           Cu–water nanofluid within a square channel enhanced with 90° V-shaped
           ribs
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Mehdi Bahiraei, Nima Mazaheri, Yaghoub Hosseini, Hossein Moayedi A numerical investigation is conducted by implementing a two-phase model based on the mixture theory with the aim of assessing the attributes associated with the thermohydraulic performance of the Cu–water nanofluid through a square channel equipped by the 90° V-shaped ribs. The ribs are attached on the top and bottom walls of the channel with different rib heights and rib pitches. It is observed that the average heat transfer coefficient significantly enhances with the volume fraction increment such that it enhances around 22.7% with increasing the volume fraction from 1 to 2% at rib pitch of 100 mm and rib height of 2.5 mm. The presence of the ribs considerably intensifies the flow mixing and disrupts the thermal boundary layer by means of generating the four counter-rotating vortices. In addition, employing the ribs with greater heights as well as smaller pitches augments the heat transfer coefficient as well as Nusselt number, such that the Nusselt number increases about 28.3% when the rib height increases from 2.5 to 7.5 mm in the condition in which the rib pitch is 50 mm. The Figure of Merit (FoM), which shows the fraction of the convective heat transfer coefficient ratio to the pumping power ratio for the case of using the nanofluid compared to the water, is much higher than 1, which demonstrates the benefit of employing the nanofluid rather than the water. Furthermore, increasing the volume fraction results in a greater FoM, which manifests the greater merit of using the nanofluid at higher concentrations.
       
  • The effect of electrode energy balance on variable polarity plasma arc
           pressure
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 145Author(s): Bin Xu, Shinichi Tashiro, Fan Jiang, Manabu Tanaka, Shujun Chen The plasma arc evolution and the physical mechanism associated with variable polarity plasma arc (VPPA) remain unclear, slowing down its process development and optimization. In this work, we revealed its increasing phenomenon in the initial segment of electrode negative (EN) phase through the experimental measurement of VPPA pressure. The current increasing enlarged the pressure difference between EN and electrode positive (EP) phase. A unified numerical simulation model was developed coupling tungsten electrode, constricting nozzle, plasma arc and workpiece for clarifying the mechanism of pressure evolution. In this model, the electrical conductivity of gas adjacent to melting region in tungsten electrode is considered to be superior than that of gas adjacent to solid region. Through the evolution of temperature field and energy transfer, the electrode was gradually cooled mainly by thermionic electron emission at the initial segment of EN phase, because of which the current attachment shrank to the electrode tip. Thus, the electromagnetic force depending on the current density increased in EN phase, leading to an increase in the plasma arc pressure. Our results clarified aspects of energy balance physics behind VPPA, which is critical for its development.
       
  • In-tube condensation heat transfer characteristics of CO2 with N2 at near
           critical pressure
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Wonkeun Baik, Rin Yun The condensation heat-transfer coefficient and pressure drop for pure CO2 and CO2 + N2 mixtures were investigated under the near-critical condition, which simulates the CO2 transporting conditions under Carbon Capture, Transportation, and Storage (CCS). The experimental apparatus consists of a test section, heat exchangers, mass flow meters, temperature sensors, a magnetic gear pump, and a differential pressure transducer. The test section made with a copper tube was assembled with Polyvinyl Chloride (PVC) pipe to form a double tube. The condensation temperature and mole fraction of N2 of the CO2 mixtures ranged from 20 °C to 30 °C, and 1 to 5%, respectively. The mass flux was changed from 500, 600 and 700 kg·m−2s−1. The average heat transfer coefficient of the CO2 + N2 mixtures decreased by 2.23 to 15.9% based on the average heat transfer coefficient of pure CO2, and the pressure drop decreased by 53.4 to 77.3% at the condensation temperature of 25 °C with increase of the mole fraction of N2.
       
  • Probabilistic simulation of advection-reaction-dispersion equation using
           random lattice Boltzmann method
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Ali Akbar Hekmatzadeh, Ali Adel, Farshad Zarei, Ali Torabi Haghighi Mass transfer is subject to numerous sources of uncertainties due to scarcity of observational data. In this research, a numerical procedure was developed for the probabilistic study of a two-dimensional advection-dispersion problem, while considering chemical reactions. Innovatively, the lattice Boltzmann method was coupled with the concept of random field theory for the probabilistic simulations. The effects of various coefficients of variations (COV) and a number of autocorrelation distances were considered for the stochastic parameters, including dispersion coefficient, pore velocity, and the reaction term. The results indicated that the introduced probabilistic framework can be employed to effectively describe the effects of uncertainties in parameters related to the advection-dispersion equation. Moreover, it was deduced that the mass travel time and the time-concentration curves were influenced significantly by the variations of COV and autocorrelation distance for pore velocity. Interestingly, the mass transfer in the transverse direction increased (through the dispersion phenomenon) with a rise in the values of COV for longitudinal pore velocity. However, different values of COV and autocorrelation distances for the dispersion coefficient and the reaction term caused small alterations in the mass travel time and time-concentration curve.
       
  • An experimental method to quantify local air-side heat transfer
           coefficient through mass transfer measurements utilizing color change
           coatings
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Min Che, Stefan Elbel This paper presents a visualization method to quantify local air-side heat transfer coefficient (HTC). It is challenging to measure local air-side HTC with good accuracy, especially for complicated geometries and real heat exchangers. The present method relies on measuring convective mass transfer and applying the analogy between heat and mass transfer. It is based on the chemical interaction between a pair of coating material and tracer gas. The coating material absorbs tracer gas and changes its color. Therefore, a visualization procedure is developed to correlate color change on the surface to the local mass transfer coefficient. In this research, the coating formulation, coating methods, and surface topography are evaluated to make sure the analogy between heat and mass transfer is valid. The experimental results of the flat plate in laminar flow show that the standard uncertainty of the local heat transfer coefficient is 15%. Furthermore, the results also show good agreement compared with the analytical Blasius solution except in the vicinity of the leading and trailing edges. Because of these promising results, it seems feasible to use this method to acquire local air-side HTC through a visualization approach for more complicated geometries.
       
  • Effects of mixed surfactants on heat transfer performance of pulsed spray
           cooling
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Ni Liu, Zhixiang Yu, Yong Liang, Hua Zhang Pulsed spray cooling is a new type of cooling technique which can make full use of working medium and achieve better heat transfer effect. In this study, the effects of surfactants on pulsed spray cooling were investigated experimentally in a closed pulsed spray cooling system. The optimal pulsed spray parameters were determined to be 450 ms spray cycle and 60% duty cycle. Under this condition, the heat transfer performance of surfactant FS-31was studied. The results show that the mean surface temperature and the heat transfer coefficient of FS-31 are 50.01 °C and 1.55 W/cm2·K at the concentration of 100 ppm. Furthermore, the effects of mixed surfactants of AOS-FS-31, CTAB-FS-31 and CTAB-AOS on the heat transfer performance of pulsed spray cooling were studied. The results show that the mixed surfactants of AOS-FS-31 has a significant enhancement on the heat transfer performance of pulsed spray cooling due to the synergistic effect between anionic and nonionic. The mean surface temperature and the heat transfer coefficient can reach 48.03 °C and 1.75 W/cm2·K.
       
  • Numerical study on the effectiveness of precursor isolation using N2 as
           gas barrier in spatial atomic layer deposition
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Dongqing Pan Spatial atomic layer deposition (ALD) is capable to increase film deposition rate dramatically by eliminating the need of traditional pulse/purge steps in ALD process. Numerical simulations offer valuable information on spatial ALD system design and development. In this paper, a numerical study of inline spatial ALD process with a large gap (36 mm) is presented to investigate the effectiveness of precursor isolation using N2 flow as gas barrier in two different geometric designs, namely, top and bottom purge configurations. Bottom purge configuration is shown more effective in preventing precursor intermixing than top design. Higher N2 injecting flow rate and higher relative purging pressure are beneficial to construct an effective gas barrier in spatial ALD system. Evenly assigned precursor dosing pressure is advantageous to further prevent material intermixing. Transient material distributions in the flow field, contour plots of species, velocity field, and material tracelines have confirmed the effective gas barrier built by N2. Precursor intermixing molar fraction is shown as low as 0.0045%, and the intermixing molar concentration is as low as 9.105 × 10−5 mol/m3. The study provides invaluable information in determining geometric and process parameters for system design, and the effectiveness of precursor isolation using N2 as gas barrier in spatial ALD with a large gap is validated.
       
  • An experimental study on explosive boiling of superheated droplets in
           vacuum spray flash evaporation
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Wenzhong Gao, Qiaye Qi, Jiahao Zhang, Guangming Chen, Dawei Wu Spray flash evaporation is an effective desalination method, which increases specific surface area of salty water by liquid atomization, thereby improving desalination performance and maximising low-grade heat source utilization. During evaporation, explosive boiling phenomenon occurs inside superheated droplets on a heated surface. In order to understand the mechanism of explosive boiling, spray flash evaporation of distilled water and 3.5 wt% salty water in a high vacuum vessel was observed visually. Meanwhile, a parametric study was carried out to scrutinize the impacts of the variation of ambient pressure, heat flux, and surface superheat degree. The experiment data indicates that nucleate site is located in the upper layer of a droplet due to internal superheated liquid and Marangoni convection. In different operating conditions, bubble fragmentation process or crown fragmentation process happens at nucleate site. The fragmentation time of pure water, which is mainly influenced by heat flux and surface superheat degree, shrinks with higher heat flux and higher surface superheat degree. The fragmentation time of 3.5 wt% salty water decreases with ambient pressure drops and superheat degree increments.
       
  • An investigation on effective thermal conductivity of hybrid-filler
           polymer composites under effects of random particle distribution, particle
           size and thermal contact resistance
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Ich Long Ngo, Viet Anh Truong The thermal conductivity (TC) of polymer composites with randomly distributed hybrid fillers is investigated numerically and theoretically. The effective thermal conductivity (ETC) of such composites is examined under various effects, such as the TC ratios, volume fraction (VF), and particle distribution, particle size, and particularly thermal contact resistance (TCR). The contribution of particle distribution to the ETC were explained comprehensively, which is as a function of projected area and effective length of hybrid fillers. Results indicated that the optimal ETC was affected significantly by particle distribution and particle size at high VF, high TC, low TCR, and largely total particle size of hybrid fillers. However, particle distribution and particle size show not to affect considerably to the value of the optimal TC ratio between two fillers. Particularly, it was confirmed that the TC is generally enhanced when more particles are stacked and concentrated along the thermal flow direction regardless of the effects of TCR. In addition, modified Hashin-Shtrikman model by Ngo's study again shows a good TC prediction even with the TCR effect. These results are very good in practical optimization process to achieve the maximum ETC of composites, thus total cost of composite synthesis can be reduced significantly.
       
  • Development and design optimization of novel polymer heat exchanger using
           the multi-objective genetic algorithm
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Ukmin Han, Heeseung Kang, Hongyoung Lim, Jeongwan Han, Hoseong Lee Recently, there has been great attention to find new materials of a heat exchanger to replace aluminum which has been typically used for a long time as a basic material of heat exchangers. In this context, polymeric materials are considered as candidates due to their characteristics of lightweight and excellent corrosion resistance. Despite substantial benefits of polymeric materials, there is a critical issue as used for the heat exchanger, which is the low heat transfer performance due to their extremely low thermal conductivity. In this study, to overcome this limitation, a novel polymer heat exchanger is proposed with the new heat flow design. The finless teardrop-shaped tube bundle polymer heat exchanger is newly designed and its thermal-hydraulic performances are investigated with experiments and simulations. Then, the geometries of the novel polymer heat exchanger are optimized to maximize the thermal and hydraulic performance by using the online approximation-assisted optimization technique.
       
  • Tuning substrate geometry for enhancing water condensation
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Yong Jin, Mohammed Albaity, Yusuf Shi, Noreddine Ghaffour, Peng Wang Water condensation is an important phase change phenomenon whose applications range from power generation to water desalination. In the present study, we compared condensation occurring on two different substrates (namely square and strip) and demonstrated the effect of substrate geometry on water condensation. It is found that condensation on different regions of the same substrate is dramatically different due to different local vapor flux. In general, the condensation rate is linearly proportional to vapor flux while average vapor flux can be improved by creating geometrical discontinuity (strip substrate) within rigid substrates. Experimental result of water collection confirms that the condensation rate is increased by around 40% on the strip substrate compared to the square substrate. This study demonstrates that water condensation can be enhanced by rationally tuning the geometry of the condensation substrate. Performance of water condensation of a specific substrate can be predicated by simulating the vapor flux over the substrate.
       
  • Field synergy analysis on flow and heat transfer characteristics of
           nanofluid in microchannel with non-uniform cavities configuration
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Fang Li, Wenhui Zhu, Hu He Microchannel cooling technology using nanofluid is one of the effective ways to solve the rapid heat dissipation in a limited space for high power density device. In this work, the field synergy and heat transfer performance of nanofluid in the microchannel with non-uniform internal spoiler cavities configuration based on conjugate heat transfer and homogenous model were investigated. The heat transfer enhancement mechanism of nanofluid in this complex microchannel was discussed through the analysis of field synergy angle, field synergy factor, and flow and heat transfer characteristics. It was found that the flow and heat transfer performance of the nanofluid in the microchannel can be well explained by the field synergy principle. The nanofluid heat transfer enhancement phenomenon could be attributed to the improvement of the field synergy of the thermal boundary layer under the axial thermal conductive effect. In addition, the field synergy analysis of nanofluid in complex microchannel revealed that the heat transfer enhancement was affected by the combination of perturbation effect, the axial thermal conduction effect and the thermal boundary redevelopment.
       
  • An experimental investigation of the melting process of an ice bead on the
           smooth and micro-grooved surfaces under a hot shear flow
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Miaomiao Chen, Zhigang Yang, Zheyan Jin In the present study, we experimentally investigated the melting process of an ice bead on the smooth and micro-grooved surfaces under a hot shear flow. One smooth silicon surface and three micro-grooved silicon surfaces were fabricated and tested. A parameter study of the substrate surface temperature and the air flow speed was conducted. During the experiment, an ice bead was first formed from a freezing water droplet on a cold substrate surface. Then, the ice bead was exposed to a hot shear flow and its melting process was recorded by a CCD camera and an infrared camera simultaneously. As for the micro-grooved surfaces, the direction of the hot shear flow was parallel to the micro-grooves. The results showed that the melting process of the ice bead on the smooth and micro-grooved surfaces under a hot shear flow could be divided into three categories. The air flow speed, the surface temperature, and the type of the surface had a significant influence on which category the melting process of the ice bead belonged to. Besides, the presence of the micro-grooves was found to apparently affect the wetting length, the removable time, and the temperature along the centerline of the ice bead. In general, the micro-grooved surfaces were found to be more favorable for the ice bead melting process than the smooth surface.
       
  • Influence of AlSi10Mg particles microstructure on heat conduction during
           additive manufacturing
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Panding Wang, Hongshuai Lei, Xiaolei Zhu, Haosen Chen, Daining Fang Powder-based metallic additive manufacturing (AM) technology is opening new avenues to fabricate highly complex components from metallic powders. However, most of the powder-scale modeling methods are limited to single track process and ideal particle microstructure. Nevertheless, the presence of hollow particles significantly influences the heat conduction during AM processing and experimental quantification of the heat conduction between hollow particles is extremely challenging. Herein, we have used X-ray micro-computed tomography (μCT) to reconstruct 3D structures of AlSi10Mg particles. The morphology, location and distribution of intact and hollow particles are studied to analyze their role in AM processing. Based on X-ray tomography images, two 3D image-based finite element models of statistically representative particles with imperfect geometry are reconstructed and compared to simulate the thermal conduction in the powder bed. Simulation results shows that thermal conduction is governed not only by cell topology but also by cavities in particles induced by powder production. The calculation results are consistent with the Serial-Parallel Model, which is based on the reconstruction geometry model and statistical results. The results reveal that the presence of cavities in particles significantly influences the thermal conduction and, consequently, reduces the sintered density during selective laser sintering (SLS).Graphical abstractGraphical abstract for this article
       
  • An experimental study on the flow and heat transfer of an impinging
           synthetic jet
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Yang Xu, Chanhee Moon, Jin-Jun Wang, Oleg G. Penyazkov, Kyung Chun Kim This study experimentally investigated the combined effects of the wall temperature (Tw0) and the orifice-to-wall distance (H/D) on the flow and heat transfer characteristics of an impinging synthetic jet. Thermographic phosphor thermometry (TPT) was used to measure the wall surface temperature, and the quantitative flow velocity was obtained using time-resolved particle image velocimetry (PIV). A cavity-diaphragm actuator was employed to generate a round synthetic jet to impinge onto a heated wall that was coated with Mg4FGeO6:Mn (MFG) for use as a temperature sensor. Three orifice-to-wall distances (H/D = 10, 15, and 20) and three wall temperatures (Tw0 = 60 °C, 90 °C, and 120 °C) were tested for comparison, whereas the the operating conditions of the incident synthetic jet were kept constant. It was found that the maximum temperature drop at the stagnation point could reach approximately 50°C although the orifice-to-wall distance was relatively large in this study, which indicated a good cooling performance of the synthetic jet. The penetration of the wall shear layer played an important role on the cooling performance of the impinging synthetic jet. For a heated wall with high Tw0, the enhanced buoyancy and thermal boundary layer resulted in the formation of a strong wall shear layer, which was more difficult for the impinging synthetic jet to affect or penetrate. For a large H/D, the vortex rings of the synthetic jet lose coherence completely before impacting the wall. Thus, they have no ability to penetrate the wall’s shear layer to interact with it directly. As a result, the cooling performance of the impinging synthetic jet gradually decreased as both Tw0 and H/D increased. In particular, the maximum cooling effect by the synthetic jet impingement can achieve 64% of the theoretical maximum.Graphical abstractGraphical abstract for this article
       
  • Numerical investigations on flow and heat transfer of swirl and
           impingement composite cooling structures of turbine blade leading edge
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Fan Wu, Liang Li, Jiefeng Wang, Xiaojun Fan, Changhe Du In this paper, four swirl and impingement composite cooling structures are established to deeply study the flow and heat transfer characteristics, where the swirl nozzles and impingement nozzles are reasonably arranged. Numerical simulation is conducted by solving the Reynolds Averaged Navier-Stokes (RANS) equations with the standard k-ω model. Meanwhile, numerical results are compared with the cooling behaviors of swirl cooling and impingement cooling under the same condition. Results revealed that the pressure distribution of four composite cooling structures is quite different from that of swirl cooling and impingement cooling. Hence, the nozzle mass flow ratio distribution of composite cooling structures displays a large fluctuation with the variation of the nozzle location, which has an influence on the flow and heat transfer characteristics. Moreover, the heat transfer characteristics of swirl and impingement composite cooling combine the advantages of impingement cooling and swirl cooling, where there both exists extremely high local heat transfer regions and uniform heat transfer regions. As for composite cooling 3 and composite cooling 4, the alternate locations of impingement nozzles and swirl nozzles could effectively increase the band-shaped high heat transfer area. Meanwhile, the low heat transfer area caused by the continuous arrangement of impingement nozzles is reduced. Among four composite cooling structures, the composite cooling 4 has the highest average heat transfer coefficient and the minimum pressure loss. The globally average heat transfer of composite cooling 4 is 3.49% lower than swirl cooling but is 19.12% higher than impingement cooling. Its total pressure loss is 4.29% lower than swirl cooling and is slightly lower compared with impingement cooling.
       
  • Large eddy simulation of film cooling flow from round and trenched holes
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Rui Hou, Fengbo Wen, Yuxi Luo, Xiaolei Tang, Songtao Wang The thermal and flow fields of round and trenched holes in the flat-plate model are investigated using large eddy simulation (LES) after validated against the experimental results. The focus is on understanding the influence of the trenched hole on downstream vortex structures at blowing ratios M = 0.5 and 1.0, which may benefit its effective application in cooling design. At M = 1.0, the transverse trench increases turbulent fluctuations and augments the complexity of vortex structures. Dynamic mode decomposition analysis is employed to extract the primary vortex structures. The dominant vortices of the trenched hole include K-H vortices and hairpin-like vortices near the centerline. This series of hairpin-like vortices present a larger spatial size than the hairpin vortex downstream of the round hole. Besides, they correspond to the downstream counter-rotating vortex pair in the mean flow field, which is detrimental to the local film cooling effectiveness. At lower blowing ratio M = 0.5, the previous spatially large hairpin-like vortices are replaced by a smaller one which alternatively appears on both sides of the centerline. In the mean flow field, each branch of the CVP is caught between two anti-CVPs. The suppression of adjacent vortices guarantees the attachment of coolant to the surface.
       
  • RANS-based numerical simulation of the turbulent free convection
           vertical-plate boundary layer disturbed by a normal-to-plate circular
           cylinder
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Evgueni M. Smirnov, Alexander M. Levchenya, Varvara D. Zhukovskaya
       
  • Optimal design and thermal modelling for liquid-cooled heat sink based on
           multi-objective topology optimization: An experimental and numerical study
           
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Hao Li, Xiaohong Ding, Fanzhen Meng, Dalei Jing, Min Xiong This work suggests a design method of liquid-cooled heat sink based on topology optimization. First, a multi-objective optimization problem is developed in order to manage the tradeoff between the minimization of fluid power dissipation and the maximization of heat exchange. The novel cooling channels with clear topology information are generated under both single-uniform and the multiple-non uniform heat source conditions. The effects of initial guess, weighting factor, and Reynolds number on the Pareto optimal solutions are discussed. Next, a full scale 3D conjugate heat transfer numerical model is built to test the flow and thermal performances of the heat sinks. The results show that the optimized cooling channel can achieve a lower thermal resistance and a higher Nusselts number in comparison to the conventional parallel channel, which means the optimal channel can remove more heat energy while the pumping power supply is minimum. Finally, both traditional parallel and topology optimized channel are manufactured by CNC machine and the high performance of the optimally designed heat sink is validated by conducting experimental tests.Graphical abstractThis work presents a method of designing liquid-cooled heat sink based on topology optimization. First, a multi-objective optimization problem is developed in order to manage the tradeoff between the minimization of fluid power dissipation and the maximization of heat exchange. The novel cooling channels with clear topology information are generated under both uniform single heat and the non-uniform multiple heat load conditions. The effects of initial guess, weighting factor, and Reynolds number on the Pareto optimal solutions are discussed. Next, a full scale 3D conjugate heat transfer numerical simulation model is built to test the flow and thermal performances of the heat sinks. The results show that the optimized cooling channel can achieve a lower thermal resistance and a higher Nusselts number in comparison to the conventional parallel channel. Lastly, the high performance of TO design is validated by conducting experimental tests.Graphical abstract for this article
       
  • Thermodynamic property surfaces for various adsorbent/adsorbate pairs for
           cooling applications
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Tahmid Hasan Rupam, Md. Amirul Islam, Animesh Pal, Anutosh Chakraborty, Bidyut Baran Saha This study focuses on comparative analysis of five different adsorbent/adsorbate pairs regarding thermodynamic property fields based on some well-established mathematical modelling. The thermodynamic property fields such as enthalpy (h), entropy (s) are expressed in terms of temperature, pressure and adsorbed quantity. Moreover, the isosteric heat of adsorption for pairs having a common adsorbent with the three different refrigerants were compared to investigate the effect of adsorbate molecules on the isosteric heat of adsorption. T-s diagrams are analyzed for all the five pairs for different cooling conditions: 5 °C, 10 °C and 15 °C. This information along with the isotherms and kinetics data find immense importance in the computation of energy balances of the adsorbed phase. These results are crucial for rigorous design and analysis of adsorption cooling systems.Graphical abstractGraphical abstract for this article
       
  • A new modified Levenberg-Marquardt algorithm for identifying the
           temperature-dependent conductivity of solids based on the radial
           integration boundary element method
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Kai Yang, Geng-Hui Jiang, Hai-Feng Peng, Xiao-Wei Gao In this paper, combination of radial integration boundary element method (RIBEM) with complex variable and Levenberg-Marquardt algorithm (LMA) is firstly proposed to identify temperature-dependent conductivity in the inverse heat conduction problem. To obtain the simulative temperature, radial integration boundary element method is used to solve the transient nonlinear heat conduction problem with temperature-dependent conductivity. What’s more, RIBEM with complex variable, which transforms the real variables into complex ones in boundary element method, makes it possible to perform complex variable derivative method (CVDM) in LMA. Furthermore, because of the introduction of CVDM, the sensitivity coefficient matrix can be calculated accurately and efficiently, and then the identification of unknown variable can be achieved admirably in the inverse heat problem. Finally, different initial guess value and measurement errors are considered, respectively, and various numerical examples are presented to fully demonstrate the accuracy and feasibility of the proposed method in identifying temperature-dependent conductivity.
       
  • Heterogeneous anisotropic conductive heat transfer in composite conical
           shells: An exact analysis
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Babak Erfan Manesh, Mohammad Mohsen Shahmardan, Hossein Rahmani, Mahmood Norouzi In present paper, problem of anisotropic heat conduction in heterogeneous composite conical shells is solved analytically. Arbitrary values for fiber angle (ranging from zero to 90 degrees) cause anisotropy for the heat conduction problem in composite conical shells. In our analysis, heat convection between conical shell and ambient flow is taken into account. In addition, an external source of radiative heat transfer is modeled. Herein, the heat conduction problem is assumed to be heterogeneous which is due to dependence of the conductivity coefficient on temperature. Kirchhoff transformation followed by an integral transform method are used to solve present heterogeneous heat conduction problem. Green’s functions are applied to find the solution of final ordinary differential equations. Verification of the present analytical solution is obtained through comparing the analytical results with those of a second order finite difference method. Good agreement between the analytical and numerical results has been found. In order to evaluate the capability of our analytical solution in solving real industrial problems, the temperature distributions in a typical pressure vessel and a pin fin are calculated.
       
  • Prediction of thermal conductivity in dielectrics using fast,
           spectrally-resolved phonon transport simulations
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Jackson R. Harter, S. Aria Hosseini, Todd S. Palmer, P. Alex Greaney We present a new method for predicting effective thermal conductivity (κeff) in materials, informed by ab initio material property simulations. Using the Boltzmann transport equation in a self-adjoint angular flux formulation, we performed simulations in silicon at room temperatures over length scales varying from 10 nm to 10 μm and report temperature distributions, spectral heat flux and thermal conductivity. Our implementation utilizes a Richardson iteration on a modified version of the phonon scattering source. In this method, a closure term is introduced to the transport equation which acts as a redistribution kernel for the total energy bath of the system. This term is an effective indicator of the degree of disorder between the spectral phonon radiance and the angular phonon intensity of the transport system. We employ polarization, density of states and full dispersion spectra to resolve thermal conductivity with numerous angular and spatial discretizations.
       
  • A continuum framework for modeling liquid-vapor interfaces out of local
           thermal equilibrium
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Anirban Chandra, Pawel Keblinski, Onkar Sahni, Assad A. Oberai Continuum numerical methods modeling liquid-vapor phase change processes typically assume local thermal equilibrium at the liquid-vapor interface – continuity of temperature at phase interfaces, and a relation between interfacial saturation pressure and temperature based on phase co-existence curves. Several standard macroscopic problems have been solved accurately by adhering to this assumption. However, in micro-scale and certain non-standard macro-scale applications, significant jumps in temperature are observed at liquid-vapor interfaces during phase change, and vapor pressure can be far from equilibrium values. In this paper, we present a locally discontinuous arbitrary Lagrangian Eulerian finite element formulation with temperature discontinuities at interfaces. A penalty-based approach is used to weakly enforce the temperature jump condition. Furthermore, we use kinetic-theory-based Schrage relationship to evaluate the rate of phase change. We apply our methodology to solve the problem of flowing vapor in a planar heat pipe. The flow rates predicted by our continuum simulations are in excellent agreement with recently published molecular dynamics simulation results of the same problem. Interestingly, accounting for temperature discontinuities leads to only a slight improvement in the prediction of mass fluxes as compared to the case when temperature continuity is assumed. This is in contrast to the large improvement in the prediction of temperature profiles and is a consequence of a weak dependence of the evaporation/condensation rates on the vapor temperature.
       
  • Numerical study of a liquid drop on an inclined surface with
           solidification
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Truong V. Vu, Cuong T. Nguyen, Quan H. Luu Drop deformation and solidification on an inclined surface appears in many engineered and industrial applications. In this paper, we thus present a front-tracking-based simulation of the deformation and solidification process of a liquid drop on a plate tilted at an angle ϕp in the range of 10°–80°. The plate temperature is kept fixed at a value below the liquid-solid phase change temperature of the drop liquid while the drop is assumed to stick to the surface. The drop experiences some oscillating deformation, and when it reaches almost a steady state shape the solidification process starts undergoing volume expansion (ρsl = 0.9). Increasing ϕp from 10° to 80° causes the liquid drop to experience more oscillations with larger amplitudes. The increase in ϕp makes the solidification process last longer and results in a more asymmetric solidified drop with an increase in the tip shift Δxt [i.e. Δxt/d = 0.1278(ϕp/ϕref) + 0.014 with d, apparent diameter of the liquid drop, and ϕref = 90°, reference angle]. However, varying ϕp in this range has a very minor effect on the height and the conical tip angle ϕt at the top of the solidified drop (i.e. Hs/d ≈ 0.784 and ϕt/ϕref ≈ 1.33). With the presence of the plate inclination (ϕp = 60°), the drop oscillates more strongly when increasing either the drop wetting angle ϕ0 (from 50° to 130°) or the Bond number Bo (from 0.1 to 3.2). These increases in ϕ0 and Bo also result in an increase in the solidification time τs and Δxt. In contrast, the tip angle is less affected by ϕ0 and Bo. Further investigations on ρsl and the growth angle ϕgr show that the solidified drop is more asymmetric with a decrease in ρsl from 1.0 to 0.8 while ϕgr varied from 0° to 28° induces no change in Δxt. Accordingly, the numerical results confirm that the plate angle and the initial liquid drop shape have strong impact on the asymmetry of the solidified drop, and volume expansion and the growth angle strongly affect the conical tip angle.
       
  • A new model of regression rate for solid fuel scramjet
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Hao Zhang, Ningfei Wang, Zhiwen Wu, Wanzhi Han, Rui Du A new theoretical model has been developed to calculate the regression rate of solid fuel scramjet (SF-Scramjet). This model obtains the local regression rate by calculating the local heat flux on the fuel surface, which is obtained by a standard wall function. A two-dimensional, axisymmetric, turbulent, one-reaction model which used the new method was developed to study the solid fuel regression rate for SF-Scramjet numerically with a flight environment of 25 km and a Mach number of 6. The quasi-steady state numerical method has been adopted to calculate the regression rate at different times. Experiments were carried out on the ground dedicated connected-pipe static test facility under the same boundary conditions to verify the correctness of the model. The results demonstrate that the numerical results agree well with the experimental results in the first few seconds. In the next few seconds of combustion, the numerical results of the regression rate gradually deviate from the experimental results. This may be due to the gradual accumulation of errors in the quasi-steady method.
       
  • Coupled unsteady computational fluid dynamics with heat and mass transfer
           analysis of a solar/heat-powered adsorption cooling system for use in
           buildings
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Wahiba Yaïci, Evgueniy Entchev In recent years, considerable interest has been given to the application of solar-powered cooling technology for use in buildings. Solar cooling systems look like to be a suitable substitution to the traditional vapour-compression electrical-driven machines. Solar systems have the advantage of using harmless working fluids, especially water. They also have the capacity to decrease the peak loads for electricity utilities and can contribute to a substantial reduction of the harmful CO2 emissions, which produce the notorious greenhouse effect that in turn is responsible for global warming and its devastating consequences. Amongst cooling technologies, low-temperature, solar-powered adsorption chillers/heat pumps are arising as a sustainable alternative to electrical vapour-compression systems.This study aims at examining the impact of design and operating factors on an adsorption cooling system’s performance in a residential application. An unsteady Computational Fluid Dynamics (CFD) combined with a heat and mass transfer model of the adsorption cooling system using adsorbent/water pair, was created in order to predict the following: (1) Flow behaviour; (2) Pressure; (3) Temperature; and (4) Water adsorption distributions. For possible adsorbents, both silica gel and zeolite 13X were considered; however, it is worth mentioning that silica gel was used at a lower working temperature range, as required by the operation. This makes silica gel an efficient option for solar/heat driven residential cooling applications. For the CFD model implemented equations, two geometries found in literature were employed for validation. Validation of the unsteady simulation results with experimental data found in literature showed favourable agreements. In a parametric study, various computation cases underwent simulation over the duration of the adsorption mode, which considered the following set of factors: heat transfer fluid (HTF) velocity (v); adsorbent bed thickness (lbed); heat exchanger tube thickness (b); and adsorbent particle diameter (dp) in order to perform a detailed investigation for main geometrical and operating parameters’ influence upon system performance. Results obtained from CFD disclosed the significance of v, lbed and dp whereas b was found having relatively minor modifications within the system performance. Additionally, the development of CFD combined with heat and mass transfer model serves as an effective tool for both simulation and optimisation of adsorption cooling systems as well as for performance predicting purposes.
       
  • Experimental study of methane hydrate dissociation in porous media with
           different thermal conductivities
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Xiao-Yan Li, Yi Wang, Xiao-Sen Li, Yu Zhang, Zhao-Yang Chen Methane hydrate dissociation is an endothermic reaction. Therefore, one of important factors for methane hydrate dissociation is the heat transfer rate. In order to study the heat transfer characteristics of porous media on methane hydrate dissociation, experiments of methane hydrate dissociation using depressurization are conducted in porous media with different thermal conductivities, including quartz sand (0.926 W/(m·K)), white corundum (28.82 W/(m·K)) and silicon carbide (41.9 W/(m·K)). Experimental results show that, during the depressurization stage (DS), the temperature difference among different positions in quartz sand is larger than that in white corundum and silicon carbide. Since the heat transfer rate of quartz sand is smallest among three kinds of sand. A low temperature zone at the center of the reactor is observed in quartz sand compared to white corundum and silicon carbide. During the constant pressure stage (CPS), as the thermal conductivity of porous media increases, the temperature rising rate increases, and the duration of the CPS decreases. The dissociation rate of methane hydrate is controlled by the heat transfer rate of sediments during the CPS. The minimum gas production rate is obtained from the experimental in quartz sand, and the maximum gas production rate is obtained from the experiment in silicon carbide. This result indicates that the dissociation rate of hydrate increased with the increase of the thermal conductivity of porous media. Meanwhile, the overall rate constants (koverall) for different runs are calculated to quantify the dissociate rate of methane hydrate during the CPS. As the thermal conductivities of porous media increase, the overall rate constant of methane hydrate dissociation increases. The results of this study are important for understanding the effects of thermal conductivity of porous media on hydrate dissociation in actual field. Furthermore, it can also be used for the validation of numerical simulation in future.
       
  • Experimental investigation of droplet entrainment and deposition in
           horizontal stratified wavy flow
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Byeonggeon Bae, Taeho Kim, Kyungdoo Kim, Jae Jun Jeong, Byongjo Yun An experimental study of the local droplet parameters for an atmospheric horizontal stratified wavy flow was conducted in a horizontal circular pipe with an inner diameter of 40 mm and a length of 5.5 m. The local distributions of the droplet fraction, droplet velocity, droplet diameter, and droplet mass flux in the cross section of the pipe were measured using single optical fiber probes at four locations with length-to-diameter ratios of 17.5, 55.0, 80.0, and 105.0 from the inlet of the test section. The average droplet mass flow rate along the axial direction of the flow channel was also obtained from the droplet parameters. The combination of the droplet entrainment and deposition rate models of Schimpf et al. was evaluated for droplet mass flow rates obtained from five different experiments including the present experiment in the horizontal stratified flow. However, its prediction accuracy was not good for the present and REGARD data. Finally, new droplet entrainment and deposition rate models for the horizontal stratified flow were proposed based on those five experiments. The applicable ranges of the proposed models are 65,500–571,400 and 170–11,000 for the gas (Reg) and liquid (Rel) Reynolds numbers, respectively.
       
  • Interface diffusion-induced phonon localization in two-dimensional lateral
           heterostructures
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Yuxiang Ni, Honggang Zhang, Song Hu, Hongyan Wang, Sebastian Volz, Shiyun Xiong We report that the interface composition diffusion, which often occurs in the synthesis of two-dimensional lateral heterostructures, can significantly suppress the thermal transport property. Our molecular dynamics simulations show that the thermal conductivity of graphene/h-BN lateral heterostructures can be largely tuned by varying the interface composition diffusion length. The underling mechanism is explained by Anderson localization of phonons, which is corroborated by the exponential decay of the phonon transmission with composition gradient length. Phase breaking interactions are shown to delocalize the modes at elevated temperatures. The findings in this work suggest that composition graded interfaces can be used to tune the thermal transport of heterostructures via phonon localization, which is important for their applications in electronics, thermoelectrics and thermal insulators.
       
  • A compact and lightweight liquid-cooled thermal management solution for
           cylindrical lithium-ion power battery pack
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Yongxin Lai, Weixiong Wu, Kai Chen, Shuangfeng Wang, Chuang Xin Battery thermal management (BTM) is indispensable to the battery pack of electric vehicles (EVs) for safety. Among different types of BTM technologies, liquid cooling shows its superiority with high heat transfer coefficient and low power consumption. However, the previous works paid little attention to the compactness and weight ratio of liquid-cooled BTM system, which is vital to the specific energy of battery pack. In this study, a compact and lightweight liquid-cooled BTM system is presented to control the maximum temperature (Tmax) and the temperature difference (ΔT) of lithium-ion power battery pack. In this liquid-cooled solution, one thermal conductive structure (TCS) with three curved contact surfaces is developed to cool cylindrical battery. The influences of mass flow rate (mf), inner diameter (d), contact surface height (h) and contact surface angle (α) of the TCS are investigated through numerical study. It is found that for the 5C discharge rate process of battery, Tmax can be maintained within 313 K when mf is larger than 1 × 10−4 kg/s. A weight sensitive factor is defined to evaluate the influences of d, h and α on ΔT and the weight of TCS. It is found that d is the most important parameter that influences the weight. h is the secondary parameter, and α is the parameter with the minimal impact on the weight. Then the values of d, h, and α are designed to reduce the weight of TCS while maintaining its cooling performance. The designed TCS can control Tmax under 313 K with ΔT as 4.137 K. Compared to the original TCS, ΔP, ΔT and the weight are respectively reduced by 80%, 14% and 46% for the designed TCS. Furthermore, the performance of liquid-cooled system with parallel TCSs is discussed. The flow distribution among parallel TCSs is improved through designing the positions of the inlet and the outlet, which enables that Tmax and ΔT of battery pack is similar to the ones of a single battery. The present study facilitates the guideline for compact and lightweight design of liquid-cooled battery thermal management system.
       
  • Forced convection condensation of R134a in three-dimensional conical pin
           fin tubes
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): J.Y. Ho, K.C. Leong, T.N. Wong This paper investigates the forced convection condensation heat transfer performance of R134a in circular tubes with three-dimensional conical pin fin structures. Five conical pin fin tubes of different circumferential fin pitch (pc) and longitudinal fin pitch (pl) were fabricated by Selective Laser Melting (SLM) with the aim of enhancing the internal forced convection condensation of R134a. Experiments were performed to characterize the condensation heat transfer coefficients (href) and pressure drops (ΔP) across these enhanced tubes. These experiments were conducted at the refrigerant mass fluxes (mref) of 50 kg/m2·s to 200 kg/m2·s, average vapor qualities (xave) from 0.2 to 0.8 and saturation pressure (Psat) of 13.4 bar. The effects of xave, mref, pc and pl on href and ΔP were determined and the results were compared against a commercial Al tube, a plain tube fabricated by SLM and two SLM fabricated enhanced tubes with dome-shaped fins. It was found that href of the conical pin fin tubes increases with increasing xave and mref and these values are also significantly higher than those of the plain tubes. Both pl and pc were found to significantly affect the href values of the conical pin fin tubes whereas the ΔP values were affected only by the change in pc. An efficiency index (η1) is defined to evaluate the thermal-hydraulic performances of the enhanced tubes. The experimental results show that all the conical pin fin tubes demonstrated higher η1 than the dome-shaped fin tubes. Based on the boundary layer approach, a semi-empirical model is developed to predict the Nusselt numbers of the conical pin fin tubes. Reasonably accurate predictions were achieved with an overall mean absolute error (MAE) of 10.5%.
       
  • Numerical simulation of reactive gas-particle flow in a solar jet spouted
           bed reactor for continuous biomass gasification
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Houssame Boujjat, Sylvain Rodat, Srirat Chuayboon, Stéphane Abanades Solar steam gasification of beech wood biomass in a novel solar conical jet spouted bed reactor was studied. A 3D numerical model of the reactive two-phase gas-particle flow was developed and the model was experimentally validated. The cavity-type solar reactor was operated in both direct and indirect heating configurations at a constant wall temperature of 1200 °C with a biomass feeding rate that varied from 1.2 g/min to 2 g/min. Experiments showed that directly heating the particles increases the H2 yield and the carbon conversion efficiency. The Computational Fluid Dynamics (CFD) model was developed to thoroughly investigate the biomass conversion process inside the conical jet spouted bed subjected to direct or indirect solar irradiations. The desired vigorous cyclic flow pattern of the biomass particles was accurately predicted by the model with peak particles velocity of 2 m/s in the spout region. The maximum temperature reached by the indirectly-irradiated particles is about 1200 °C while it is above 1500 °C when considering directly-irradiated particles. Direct heating thus increases both particles gasification rates and carbon conversion efficiency. Furthermore, simulations reveal that the reaction zone temperature is 100 °C higher for the direct heating configuration. This promotes the H2 formation at the expense of CH4. The steam oxidant concentration, gas products distribution and particles trajectories inside the cavity were also investigated to identify improvement strategies for enhancing the phase mixing and the gas/solid residence time.Graphical abstractGraphical abstract for this article
       
  • Study of fully-developed turbulent flow and heat transfer in a rotating
           wavy-walled duct
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Abhishek G. Ramgadia, Arun K. Saha Finite volume based computations of fully developed flow and heat transfer through rotating wavy-walled ducts using large eddy simulation (LES) has been carried out. The shear improved Smagorinsky model (SISM) is employed to model the unresolved turbulent fluctuations. The wavy-walls of the duct are described by the sine function y=2asin2(πx/L). The geometrical ratios Hmin/Hmax and L/a are kept fixed to 0.2 and 8 respectively. The effect of rotation on the fluid flow and heat transfer characteristics are presented. All the computations are at a Reynolds number of 5000 and the rotation number is varied in the range, 0–0.5. It has been observed that the pressure drop across the wavy-walled duct varies with increasing rotation number. It is also found out that with rotation, the heat transfer increases on the trailing wall while the leading wall shows the opposite trend. Both Nusselt number and pressure drop for the wavy-walled duct is observed to be less than the corresponding values in ribbed duct geometry.
       
  • Buoyancy effect on the mixed convection flow and heat transfer of
           supercritical R134a in heated horizontal tubes
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Ran Tian, Mingshan Wei, Xiaoye Dai, Panpan Song, Lin Shi Thermal non-uniformity in the horizontal mixed convection heat transfer of fluids at the supercritical pressure is a major issue that must be addressed in a trans-critical organic Rankine cycle. However, the heat transfer mechanism is not fully understood. To further investigate the mechanisms of the buoyancy effect and property variations in a horizontal supercritical flow, mixed convection with supercritical pressure R134a is studied numerically herein using the AKN turbulence model. When the buoyancy effect is weak, the difference in the turbulent kinetic energy with ktop 
       
  • Mass transfer intensification strategies for liquid–liquid extraction
           with single drop investigations
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Javad Saien, Farnaz Jafari Process intensification of liquid–liquid extraction based on single drop studies is discussed. Design, simulation and optimization of this process, usually adopts with swarm of drops, and depends on individual drops behavior as well as the relevant influential parameters. Improving mass transfer performance with optimized operating conditions or using additives like salts and nanoparticles are distinctive concerns. Accordingly, as a systematic study, the hydrodynamic and mass transfer behavior of drops as well as effects of operating parameters are considered. Due to the importance of subject, the behavior of nanoparticles for improving extraction process, with or without external fields, is highly regarded. Furthermore, the promising techniques/materials of reactive extraction, microfluidic extraction, ionic liquid solvents, their combination and coupling heat and mass transfer are considered. The content will bring greater clarity to select additives and to employ suitable conditions. Indeed, drop intensification methods, in relation to the drop breakage/coalescence, build the high performance industrial scale operations.
       
  • Experimental investigations on the interfacial characteristics of
           steam-air mixture sonic jets in subcooled water
    • Abstract: Publication date: December 2019Source: International Journal of Heat and Mass Transfer, Volume 144Author(s): Weichao Li, Zhongning Sun, Zhaoming Meng, Guangming Fan, Jianjun Wang Interfacial characteristics of steam-air mixture sonic jets are recorded and processed using image processing technique. Interfacial shape, radius, fluctuation height, fluctuation velocity and fluctuation acceleration are analyzed. Four typical interfacial shapes including expansion-contraction, double expansion-contraction, expansion-contraction-divergence and expansion-divergence are observed and a three-dimensional interfacial shape map is developed. Gas dynamic effect is notable in the axial region of the near field. The interfacial radius increases linearly with the axial distance in the far field. The spreading rate increases with the rise of air mass fraction and its value is in the range of 0.12–0.27. The interfacial fluctuation height is proportional to the axial distance both in the near field and far field. The spreading coefficient is in the range of 0.03 ± 0.008. In general, both interfacial fluctuation velocity and acceleration increase with the axial distance. The growth rate decreases rapidly in the near field and then increases slightly again in the far field. The maximum velocity and acceleration of interface fluctuation are estimated to be around 6 m/s and 20,000 m/s2, respectively.
       
 
 
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