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Journal Cover International Journal of Heat and Mass Transfer
  [SJR: 1.749]   [H-I: 137]   [225 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
   Published by Elsevier Homepage  [3175 journals]
  • Review of pool boiling enhancement with additives and nanofluids
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Gangtao Liang, Issam Mudawar
      Enhancement of nucleate pool boiling by modifying fluid properties has drawn considerable attention in recent years. This paper provides a comprehensive review of published literature concerning enhancement methodologies of surfactant and polymer additives, and nanofluids. Each method is discussed in detail in terms of measured impact on the nucleate boiling heat transfer coefficient and critical heat flux (CHF), mechanisms proposed for any heat transfer enhancement, and predictive models. It is shown that adding surfactant to base liquid shifts the nucleate boiling region of the boiling curve towards lower surface superheats, thereby promoting earlier boiling incipience and increasing the nucleate boiling heat transfer coefficient, but the heat transfer merits of polymer addition are polymer specific. Despite significant enhancement in CHF with most nanofluids, there are many contradictory findings concerning influence of nanofluids on nucleate boiling heat transfer coefficient. These contradictions are the result of many complex influences of base liquid, nanoparticles, and initial surface roughness. Despite the potential heat transfer benefits of nanofluids, there are several serious practical concerns that must be considered carefully before deploying nanofluids in practical cooling applications.

      PubDate: 2018-04-15T05:27:49Z
       
  • Review on the measurement and calculation of frost characteristics
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Mengjie Song, Chaobin Dang
      As a common physical phenomenon, frost deposition is inevitable and always has significant negative effects on several industry fields, such as aerospace, aviation, and heating, ventilation, air conditioning, and refrigeration. To accurately predict and control a frosting–defrosting cycle, there is a need to understand the interrelated heat, mass, and momentum transport phenomena within the frost and at the air–frost interface, which is a moving boundary condition. Consequently, during the past several decades, there has been a continuous effort to advance the understanding and modeling of frost formation on cold surfaces on the basis of experimental, semi-empirical, theoretical, and numerical approaches. To provide an overview of the analytical tools for scholars, researchers, product developers, and policy designers, a review and a comparative analysis of the available literature on frosting characteristics, correlations, and mathematical models are presented in this study. The mechanisms of the frost formation process and its influence will be first introduced, followed by the presentation of methods for the measurement of the frost layer thickness and the frosting rate. Then, the frost characteristics, including the accumulation, the density, the thermal conductivity and morphology, and the heat and mass transfer coefficients, will be summarized. The existing gaps in the research works on frost will be identified, and recommendations will be offered as per the viewpoint of the present authors. Finally, the conclusions of this study will be given.

      PubDate: 2018-04-15T05:27:49Z
       
  • A new rate-transient analysis model for shale gas reservoirs coupled the
           effect of slip flow and surface diffusion
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Yanan Miao, Xiangfang Li, Yunjian Zhou, John Lee, Zheng Sun, Yucui Chang, Shan Wang, Chenhong Hou
      Forecasting production in shale gas reservoirs accurately has been of growing interest in the industry. Horizontal wells with multiple fractures are commonly utilized to develop shale reservoirs, which indicates that the dominant flow regime observed will be linear flow for several years. Until now, it has been widely recognized that the rate-transient data analysis is the most efficient approach to estimate rate, where it appears as a straight line on the plot of normalized pressure vs. square root of time in linear flow. However, the traditional square-root-of-time plot may result in overestimation of reservoir properties and will not allow us to forecast production with confidence in shale gas reservoirs. In this paper, a new analytical methodology is put forward to analyze the rate-transient data from fractured wells in shale gas reservoirs producing at a constant flowing-pressure, which incorporates both slip flow/Knudsen diffusion of bulk gas and surface diffusion of adsorbed gas directly into the model. These flow mechanisms cannot be well described by traditional models. Depending on flow discrepancies from conventional reservoirs, the modified pseudo-pressure and pseudo-time equations to account for these critical transport mechanisms are constructed. In addition, a new procedure for rate-transient data analysis applying the proposed model is presented in details, which is reliable and easy to utilize. The novel approach is validated against numerically simulated cases and field observations. Comparisons between the new approach and traditional method are conducted by a number of test cases. The results demonstrate that the newly developed model dramatically eliminates the inaccuracy of production forecast and provides a more reliable estimated ultimate recovery (EUR). This work should provide an efficient guidance to assist analysts in evaluating hydrocarbon production accurately in shale gas reservoirs.

      PubDate: 2018-04-15T05:27:49Z
       
  • Tribological behaviour of the steel/bronze friction pair (journal bearing
           type) functioning with selective mass transfer
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Filip Ilie
      The use of lubricants in the friction pairs that accelerate oxidation processes at the same time with their heating lead to mechanical destruction, as well as to a catalytic and electrochemical effect of the friction surfaces. Also, the current tendency to separate oxidation products and stabilize them in a meta-stable state leads to the same effect. As a result, experimental tests on friction pairs (steel/bronze, journal bearing type), has confirmed that it is useful to be done quickly thermodynamic unstable processes both inside the lubricant (here glycerine) and on the surfaces of the friction pairs, at the beginning of the friction process. This supposes, that in operating conditions unfold physical-chemical processes that are friction favorable, such as polymerized, formation of active substances at the contact surfaces, the formation of colloids and of other compounds with low resistance to tangential stress (shear). The friction in such conditions takes place with the selective mass transfer (SMT), and it is used there where the friction of the mixed layers and adhesion is not safe enough, or the friction pairs durability is not assured. SMT uses the positive effect of friction through the physical-chemical processes that take place in the contact areas of the friction pairs and allows the transfer of some elements of the materials from one surface to the other, forming a thin, superficial layer, with superior properties at minimal friction and wear. The purpose of this paper is to analyze the physical-chemical parameters and the suitable processes for initiation and achieving the selective mass transfer (IASMT) for the steel/bronze pair, which in optimal conditions, forms on the contact surfaces, a thin layer (tribofilm), in whose structure predominate copper. Also, are presents some studies and research concerning the tribological behavior of the surfaces of a friction pair with contact on the surface (journal bearing) which operates with SMT tested on the sliding bearing tribometer.
      Graphical abstract image

      PubDate: 2018-04-15T05:27:49Z
       
  • A computational and experimental study of thermal energy separation by
           swirl
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): B. Kobiela, B.A. Younis, B. Weigand, O. Neumann
      When compressed air is introduced into a tube in such a way as to generate a strong axial vortex, an interesting phenomenon is observed wherein the fluid temperature at the vortex core drops below the inlet value, while in the outer part of the vortex, the temperature is higher than at inlet. The most familiar manifestation of this phenomenon is known as the Ranque-Hilsch effect, and several alternative explanations for it have been proposed. In this study, we present an analysis of the heat transfer mechanism underlying this phenomenon, based on consideration of the exact equation governing the conservation of the turbulent heat fluxes. The outcome is a model that explicitly accounts for the dependence of the heat fluxes on the mean rates of strain, and on the gradients of mean pressure. These dependencies, which are absent from conventional closures, are required by the exact equation. To verify the model, an experimental investigation of flow in a swirl chamber was conducted, and the measurements were used to check the model’s performance as obtained by three-dimensional numerical simulations. Comparisons between predictions and measurements demonstrate that the new model yields predictions that are distinctly better than those obtained using conventional closures.

      PubDate: 2018-04-15T05:27:49Z
       
  • Experimental investigation of hydronic air coil performance with
           nanofluids
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Roy Strandberg, Debendra Das
      The objective of this study is to experimentally characterize and compare the performance of a nanofluid comprised of Al2O3 nanoparticles with 1% volumetric concentration in a 60% ethylene glycol/40% water (60% EG) solution to that of 60%EG in a liquid to air heat exchanger. The test bed used in the experiment was built to simulate a small air handling system typical of that used in HVAC applications. Previously established empirical correlations for thermophysical properties of fluids were used to determine the values of various parameters (e.g. Nusselt number, Reynolds number, and Prandtl number). The testing shows that the 1% Al2O3 nanofluid generates a marginally higher rate of heat transfer than the 60% EG under certain conditions. At Re = 3000, the nanofluid produced a rate of heat transfer that was 2% higher than that of the 60% EG. The empirically determined Nusselt number associated with the convection in the coil tubing for the nanofluid follows the behavior predicted by the Dittus-Boelter correlation (R2 = 0.97), while the empirically determined Nusselt number for the 60% EG follows the Petukhov correlation similarly (R2 = 0.97). Pressure loss and hydraulic power for the nanofluid were higher than for the base fluid over the range of conditions tested. The exergy destroyed in the heat exchange and fluid flow processes were between 9% and 12% lower for the nanofluid than the base fluid over the tested range of Reynolds numbers.

      PubDate: 2018-04-15T05:27:49Z
       
  • Innovative analytic and experimental methods for thermal management of
           SMD-type LED chips
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Hosung Jang, Jae Hwa Lee, Chan Byon, Byeong Jun Lee
      In this study, we propose innovative analytic and experimental methods for thermal management of SMD-type LED chips: a geometry optimization algorithm of natural convective heat sinks together with a novel technique for estimation of the LED surface temperature. An analytic algorithm for the optimal design of the LED heat sink is proposed. By using this algorithm, the optimal fin configuration and corresponding thermal performance of the heat sink can be readily predicted according to the inputted base plate dimensions, ambient condition, heat dissipation rate, and LED chip distributions. In addition, a novel experimental technique for an accurate measurement of the LED junction temperature is proposed based on infrared thermometry and an isothermal chamber with an observation hole. The LED junction temperature is also measured using T3ster method, and the results are compared with those from the aforementioned infrared thermometry and analytic procedure. The proposed analytic and experimental results are shown to agree with each other well. The present analytic model is well validated by experimental results, and can be widely utilized for designing the cooling system related to various LED products.

      PubDate: 2018-04-15T05:27:49Z
       
  • Thermodynamic optimization for an air-standard irreversible Dual-Miller
           cycle with linearly variable specific heat ratio of working fluid
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Zhixiang Wu, Lingen Chen, Yanlin Ge, Fengrui Sun
      This paper establishes an air-standard irreversible Dual-Miller cycle (DMC) model with the specific heat ratio (SHR) of working fluid (WF) linearly varying with its temperature. Because the specific heat (SH) of WF varies with combustion reaction in actual internal combustion engine (ICE), the SHR of WF should be a function of temperature but not a constant. In order to accurately reflect the practical characteristics of DMC engine, performance of DMC with linearly variable SHR, and with heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses (IILs) is analyzed and optimized by applying finite-time thermodynamics. Analytical formulae of the power output ( P ), efficiency ( η ), entropy generation rate (EGR) and ecological function ( E ) are derived. Relationships among P , η , E and compression ratio are obtained via numerical calculations. Effects of the design parameters, cycle temperatures and linearly variable SHR of WF on P , η and E are investigated. Performance differences among the DMC and its simplified cycles, including Otto cycle (OC), Dual cycle (DDC) and Miller cycle (OMC) are compared. Performance characteristics of the DMC with different optimization objective functions (OOFs) are analyzed. The results indicate that the maximum power output ( MP ), maximum efficiency ( MEF ) and maximum ecological function ( ME ) of the DMC are superior to those of OC, DDC and OMC, and optimizing E is the best compromise between optimizing P and optimizing η . The presented results may be helpful to optimize the performance of practical DMC engines.

      PubDate: 2018-04-15T05:27:49Z
       
  • Buoyancy-driven flow of nanofluids in an inclined enclosure containing an
           adiabatic obstacle with heat generation/absorption: Effects of periodic
           thermal conditions
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Sameh E. Ahmed, Hillal M. Elshehabey
      The buoyancy-driven heat transfer enhancement and fluid flow of nanofluids inside inclined enclosures in the presence of heat generation/absorption effect are investigated in this paper. The bottom and top walls of the enclosure are thermally insulated, while both side walls are considered to have sinusoidal distributions of thermal boundary conditions. Two cases are considered; an enclosure containing a cold obstacle and the other one contains a cold circular cylinder. The governing equations are converted to dimensionless forms and then solved using Galerkin finite element method. Effects of the key-parameters, namely, Rayleigh number, nanoparticle volume fraction, cavity inclination angle, heat generation/absorption parameter, amplitude parameter, phase angle, size and position of the inner shapes on the contours of streamlines and isotherms as well as average Nusselt number are examined. It is found that an enclosure with a square obstacle enhances the heat transfer rate with a higher rate comparing with the circular cylinder case. Also, Considering an inclined cavity gives rate of heat transfer greater than the horizontal/vertical cavity. In addition, regardless the inner shape, the average Nusselt number is an increasing function of nanoparticle volume fraction, amplitude parameter and phase angle.

      PubDate: 2018-04-15T05:27:49Z
       
  • Approximate, analytical procedure for rectangular annular fins by
           accommodating the Cauchy–Euler equation
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Antonio Campo, Agustín M. Delgado-Torres
      An approximate, analytical treatment is presented for the rectangular annular fin by transforming the complicated modified Bessel equation of zero order into a rudimentary Cauchy-Euler equation. The essential step in the computational procedure revolves around a simple manipulation of the radial coordinate that sets up a variable coefficient in the third term of the modified Bessel equation of zero order. In the third term, the radial variable will be replaced by the mean radius of the inner and outer radius, whereas the radial variable prevails in the first and second terms. This action paves the way to the easier Cauchy-Euler equation. For a collection of rectangular annular fins of interest in engineering applications, approximate, analytical temperature distributions and heat transfer rates (via the fin efficiency) written in terms of two binomials demonstrate excellent quality levels in all cases. Additionally, relative error distributions are presented in detailed manner using as the baseline cases the classical exact, analytical temperature distributions and heat transfer rates expressed in terms of the complicated modified Bessel functions of first and second kind.

      PubDate: 2018-04-15T05:27:49Z
       
  • Quantitative measurements of nanoscale thin frost layers using surface
           plasmon resonance imaging
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Chan Ho Jeong, Dong Hwan Shin, Vinaykumar Konduru, Jeffrey S. Allen, Chang Kyoung Choi, Seong Hyuk Lee
      This study reports the presence of a nanoscale thin frost layer. During the frosting process, the surface plasmon resonance (SPR) imaging method can be used to overcome conventional optical limits and quantify this layer. The research outlined here also provides quantitative thickness measurement of the thin frost layer via a proposed calibration method based on the measured SPR intensity. The SPR system established in this study consists of a 50 nm gold-coated BK7 cover glass, a prism, a light source, a polarizer, a lens and a filter for the collimated light of a 600 ± 5 nm wavelength, and a CCD camera. The SPR angle of the ice phase is 72°, which corresponds to the ice refractive index of 1.307. The gold-glass specimen is cooled from room temperature (23 ± 1 °C) to −4.0 ± 0.8 °C by using a thermoelectric cooler to maintain the relative humidity of 20 ± 3% (at the room temperature). As a result, it is found that the nanoscale thin frost layer between the frozen condensates exists on the surface. Also, the present study yields the spatial distribution of reflectance that is associated with the frost layer thickness, indicating that the local information about thin frost layer thickness can be obtained through this SPR imaging method. It is found that the SPR imaging method enables successful capture of the depthwise spatial variations of the thin frost layer, showing that the frost layer was grown over time as a result of the de-sublimation of water vapor.

      PubDate: 2018-04-15T05:27:49Z
       
  • Heat transfer and fluid flow characteristics of a pair of interacting dual
           swirling flame jets impinging on a flat surface
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Parampreet Singh, Subhash Chander
      Experimental and numerical studies have been conducted to investigate the flow field and heat transfer characteristics of a pair of dual interacting swirling flames impinging on a flat surface. Commercial computational fluid dynamics (CFD) code (FLUENT®) has been used to simulate the interacting isothermal swirling impinging jets. Inverse heat conduction procedure (IHCP) has been used to calculate the impingement heat fluxes from the surface temperatures captured by Infra-red camera. Effect of separation distance (H/Dh = 2.5, 4, 6 and 8) and inter-jet spacings (S/Dh = 4, 6, 8 and 10) have been studied at various Reynolds numbers (Re(o) = 7000, 9000, 11000, 13,000 and Re(i) = 700, 1000, 1300) under stoichiometric conditions. Strong interactions between adjacent dual swirling flames result in high heat transfer due to increased mixing and turbulence in the interaction region. The inner non-swirling flames are seen to deflect towards interacting side due to asymmetric interactions. Numerical simulation predicted this deflection to be primarily due to large recirculation bubble developed from asymmetric interactions. Tilted cross-flow, emerging from interaction region has been observed due to momentum exchange taking place between cross-flow and swirling flames (jets). Area weighted average of local heat flux and relative deviation from averaged value has been calculated at various H/Dh and S/Dh. High average heat fluxes are obtained at smallest H/Dh and S/Dh. It has been concluded that for a system of burners considered for the present study, H/Dh = 2.5 and S/Dh = 8 is the optimum configuration on the basis of minimum relative deviation.

      PubDate: 2018-04-15T05:27:49Z
       
  • Mixing improvement induced by the combination of a micro-ramp with an air
           porthole in the transverse gaseous injection flow field
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Lang-quan Li, Wei Huang, Li Yan, Shi-bin Li, Lei Liao
      A new injection strategy combined with a micro-ramp and an air porthole is proposed in this paper, and the properties of the transverse gaseous injection flow field with such injection strategy have been investigated simultaneously. The numerical approach employed in the current study has been validated against the two-dimensional and three-dimensional experimental data in the open literature, and it can be used with confidence to investigate the influence of the air porthole aspect ratio and the distance between the air porthole and the fuel orifice on the transverse injection flow field with the combination of a micro-ramp and an air porthole. The obtained results predicted by the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model show that the mixing performances of the transverse gaseous injection flow fields vary under different conditions, and a transverse injection flow field with short mixing length, low stagnation pressure loss and ideal fuel penetration depth has been achieved by adding the combination of an optimized micro-ramp with a proper air porthole, i.e. Case 6–8, and its mixing length decreases considerably by 14.26 mm on the basis of Case c, even shorter than the mixing length of Case a by 2.86 mm. However, its total pressure loss increases when compared with Case c, and its stagnation pressure loss is 2.7 percent smaller than Case a. Further, the hydrogen distribution on the flat plate of Case 6–8 is much less than that of Case a and Case b. Additionally, it is found that the mixing enhancement mechanism of the air jet is different from that of the micro-ramp. The micro-ramp enhances the mixing process between the fuel and air by inducing large-scale vortices, while the air porthole enhances the mixing process by seeding lots of air into the fuel boundary layer, as well as fuel plume.

      PubDate: 2018-04-15T05:27:49Z
       
  • Numerical and experimental investigation on thermal shock failure of
           Y2O3-coated CVD ZnS infrared windows
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Xing Liu, Jiaqi Zhu, Jiecai Han
      Infrared transparent windows on aircraft and missiles can be subjected to extreme aerothermodynamics, which can cause thermal shock failure. Finite element analysis and oxygen–propane flame jet impingement tests were performed to investigate the thermal shock failure of an yttrium oxide-coated chemical vapor deposition (CVD) ZnS infrared window. Good agreement was achieved between the simulation and experimental results, which indicated that thermal shock failure occurs under high temperature differences and thermal stresses. The temperature and stress in the samples increased rapidly in a few seconds and then trended to be stable. The center area of the window surface failed most easily because the maximum temperature and stress both occurred in this area. No delamination of the Y2O3 films occurred during the thermal shock, which indicated good adhesion between the Y2O3 films and CVD ZnS substrate. In the experiment, the center area of the specimen surface was damaged in the form of pits and line cracks.

      PubDate: 2018-04-15T05:27:49Z
       
  • Cascade-like and cyclic heat transfer characteristics affected by
           enclosure aspect ratios for low Prandtl numbers
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Bin Wang, Tien-Mo Shih, Xiwen Chen, Richard Ru-Gin Chang, Chen-Xu Wu
      For low Prandtl-number fluids, heat-transfer characteristics under the influence of the aspect ratio for buoyancy-driven recirculating flows in rectangular enclosures (with left hot, right cold, top/bottom insulated walls) behave differently from those for high-Pr fluids. At Ra = 10 6 and Pr = 0.025 , as the enclosure widens, time-averaged and hot-wall-spatially-averaged heat transfer first decreases, then cascades downward. Locally, heat transfer peaks at a few locations, and these peaks travel cyclically as time elapses. For completeness, the present study serves as a sequel of a previous high-Pr investigation.

      PubDate: 2018-04-15T05:27:49Z
       
  • Effect of non-condensable gas on pressure oscillation of submerged steam
           jet condensation in condensation oscillation regime
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Weichao Li, Zhaoming Meng, Jianjun Wang, Zhongning Sun
      The pressure oscillation is an important characteristic of direct contact condensation of steam in subcooled water. Many experimental works have been performed on pure steam submerged jet condensation. However, the effect of non-condensable gas content on the characteristics of the pressure oscillation is not yet fully understood. So, present paper aims to investigate the effect of air mass fraction on the characteristics of the pressure oscillation. Experimental results show that: for pure steam jets, the pressure oscillation dominant frequency decreases with the rise of water temperature and nozzle diameter. While it increases with the rise of steam mass velocity, which is consistent with the most of previous research results. The pressure oscillation intensity increases with the rise of water temperature, steam mass velocity and nozzle diameter. For air-steam mixture gas jets, the effect of water temperature and steam mass velocity on pressure oscillation characteristics is the same as pure steam jets. The pressure oscillation dominant frequency rapidly decreases with the rise of air mass fraction. However, air mass fraction has a complex effect on pressure oscillation intensity. As the air mass fraction increases, the pressure oscillation intensity rapidly increases at first, then slowly decreases and then slowly increases. In addition, new correlations for pressure oscillation dominant frequency and intensity are developed. The predicted results agree well with the experimental results.

      PubDate: 2018-04-15T05:27:49Z
       
  • Novel measurement of receding wicked liquid responsible for critical heat
           flux enhancement
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Hong Hyun Son, Namgook Kim, Sung Joong Kim
      In-situ hydrodynamic behavior of wicked liquid comes from interfacial dynamics at triple contact line, resulting in receding motion around expanding dry spot. We here introduce a new and creative technique of wicking experiment adopting an external pressure source equivalent to bubble nucleation pressure in order to investigate the receding behavior of wicked liquid. On the various types of surface morphology including smooth, nanostructure, nanoporous, and microstructure, it was clearly observed that wicked liquid receded from expanding dry area except for a smooth surface. The receding velocity was slower at microstructure, nanoporous, and nanostructure, in order. Clearly this result provides a hydrodynamic evidence of smaller dry area size and contact line length on microscale structure than on nanoscale structure. Moreover, the diameter of dry area showed a linear relation with CHF enhancement that indicates smaller diameter of dry area is more effective to delay irreversible expansion of dry spots. This novel observation is expected to provide reliable analysis of contact line dynamics with CHF enhancement on wicking-dominant surfaces.

      PubDate: 2018-04-15T05:27:49Z
       
  • Nanofluid flow and heat transfer in a microchannel with interfacial
           electrokinetic effects
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Qingkai Zhao, Hang Xu, Longbin Tao
      The behaviour of microchannel flow of a nanofluid between two parallel flat plates in the presence of the electrical double layer (EDL) is investigated in this paper. The problem is formulated based on the Buongiorno nanofluid model with the electrical body force due to the EDL being considered in the momentum equation. As one of the highlights of the present investigation, the unphysical assumption introduced in previous studies often leading to the discontinuities of flow field that the electrostatic potential in the middle of the channel has to be equal to zero is eliminated. In addition, the inappropriate assumption that the pressure constant is treated as a known condition is also rectified. The new model is developed with the governing equations being reduced by a set of dimensionless quantities to a set of coupled ordinary differential equations. Based on the analytical approximations, the influences of various physical parameters on the flow field and temperature field, and the important physical quantities of practical interests are analysed and discussed in detail.

      PubDate: 2018-04-15T05:27:49Z
       
  • Total hemispherical apparent radiative properties of the infinite V-groove
           with specular reflection
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Rydge B. Mulford, Nathan S. Collins, Michael S. Farnsworth, Matthew R. Jones, Brian D. Iverson
      Multiple reflections in a cavity geometry augment the emission and absorption of the cavity opening relative to a flat surface in a phenomenon known as the cavity effect. The extent of the cavity effect is quantified using apparent absorptivity and apparent emissivity. Analysis of complicated thermal systems is simplified through application of apparent radiative properties to cavity geometries. The apparent radiative properties of a specularly-reflecting, gray, isothermal V-groove have been derived analytically, but these results have not been validated experimentally or numerically. Additionally, the model for apparent absorptivity of an infinite V-groove subjected to partial illumination in the presence of collimated irradiation is not available. In this work, the following existing models for a specularly-reflecting V-groove are collected into a single source: (1) the apparent absorptivity of a diffusely irradiated V-groove, (2) the apparent emissivity of an isothermal V-groove and (3) the apparent absorptivity of a V-groove subject to collimated irradiation with full-illumination. Further, a new analytical model is developed to predict the apparent absorptivity of an infinite V-groove subject to collimated irradiation with partial-illumination. A custom, Monte Carlo ray tracing solver is used to predict the apparent radiative properties for all cases as a means of numerical verification by comparing the ray tracing data with the results from the new model in this work and the previously existing models. For diffuse irradiation, the analytical model and ray tracing data show excellent agreement with an average discrepancy of 4.4 × 10−4, verifying the diffuse-irradiation analytical model. Similar agreement is found for collimated irradiation, where the full and partial illumination models indicate average discrepancies of 4.9 × 10−4 and 4.6 × 10−4 when compared with ray tracing data.

      PubDate: 2018-04-15T05:27:49Z
       
  • The research on the heat source characteristics and the equivalent heat
           source of the arc in gaps
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Kai Liu, Fan Yang, Shaohua Wang, Bing Gao, Chong Xu
      The discharging process causes the multiple physical field coupling problem, which make it complicated to analyze the heat effect of discharging arc. The heat effect of the arc can be divided two parts including the heat effect of the arc column and the heat effect on the cathode surface. Therefore, this paper proposes an equivalent heat source to be equivalent to the two parts heat effect of the arc and simplifies the process for thermal analysis of the arc. Firstly, this paper analyzes the heat source characteristics of the arc based on MHD model. According to the heat source characteristics of the arc, this paper proposes respectively using ellipsoid heat source and Gaussian surface heat source to be equivalent to the two parts of the heat effect of the arc. Then the equivalent heat source is used to calculate the temperature distribution of tip-plane electrode under discharging. Comparing with the numerical results in MHD model, the error between the two models is within 0.5%, which proofs that the equivalent heat source can be used to equivalent to the heat effect of the arc. Moreover, this paper discusses the method to determine the parameters of the equivalent heat source. Finally, an experiment is carried out to verify the accuracy of the MHD model and the equivalent heat source of the arc.

      PubDate: 2018-04-15T05:27:49Z
       
  • Effect of CNT coating on the overall thermal conductivity of
           unidirectional polymer hybrid nanocomposites
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): M.K. Hassanzadeh-Aghdam, M.J. Mahmoodi, J. Jamali
      The role of carbon nanotube (CNT) coating on the carbon fiber (CF) surfaces in the effective thermal conductivities of the unidirectional polymer hybrid nanocomposites is investigated by a newly presented multi-stage micromechanical method. The constructional feature of the hybrid nanocomposite is that randomly oriented CNTs grown on the CF surfaces. For simulating, a new version of the semi-empirical Halpin-Tsai (H-T) model is appropriately coupled with an analytical unit cell micromechanical model developed in the present research. The model captures the influences of the CNTs random dispersion, waviness, length, diameter, volume fraction and the CNT/polymer interfacial thermal resistance and also the CF cross-section shape parameters. The predicted results for the thermal conductivities of fibrous composites and polymer nanocomposites containing CNTs are verified with the available experimental data and a very good agreement is found. The results show that the longitudinal thermal conductivity of CF-reinforced hybrid nanocomposites is not affected by the CNTs coating. However, the nanocomposites transverse thermal conductivities are significantly enhanced over those of the conventional fibrous composites without the CNTs coating. An improvement in the nanocomposites transverse thermal conducting behavior can be observed with (i) increasing the CNTs volume fraction and length (ii) using straight CNTs and (iii) forming a perfect bonding interface.

      PubDate: 2018-04-15T05:27:49Z
       
  • Thermal diode using controlled capillary in heterogeneous nanopores
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Tadeh Avanessian, Gisuk Hwang
      The development of a compact, efficient, reliable thermal diode is crucial to improve advanced thermal management efficiency and controllability, and to enable brand new applications such as thermal logic gates and computers. In this study, we examine a nanoscale and efficient capillary-controlled thermal diode mechanism in Ar-filled Pt-based heterogeneous nanoporous structures, using Grand Canonical Monte Carlo (GCMC) simulation combined with Non-Equilibrium Molecular Dynamics (NEMD) simulation at the temperature range of 70–150 K and the pressure of 1.66 atm. Results show that the large thermal conductivity contrast between the controlled adsorption and capillary states using the structural heterogeneity (nanopillars on only one surface) and/or material heterogeneity (two different materials for nanogap surfaces) allows for the maximum thermal rectification ratio, Rmax  ∼ 140 with minimal hysteresis under the cyclic operating temperatures −40 K < ΔT < +40 K. It is also found that the material heterogeneity is equivalent to the structural heterogeneity for minimizing the hysteresis in adsorption-capillary transition, but the heat flux across the nanogap with the material heterogeneity reduces due to weaker Ar-solid interaction. The coupled structural-material heterogeneity for the capillary-driven thermal diode is also discussed. The obtained results pave pathways for advanced thermal management systems such as thermal transistors, thermal logic gates, and computers.

      PubDate: 2018-04-15T05:27:49Z
       
  • Experimental study on boiling heat transfer of a self-rewetting fluid on
           copper foams with pore-density gradient structures
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Leping Zhou, Wei Li, Tengxiao Ma, Xiaoze Du
      Light-weight and high-surface-area metal foams used in phase change heat transfer may suffer flow resistance from the porous matrix and cause boiling deterioration. To alleviate the flow resistance, metal foams with pore-density gradient was proposed and significant enhancement of pool boiling heat transfer was achieved for fluids such as water and refrigerants. In this work, a self-rewetting fluid (aqueous n-butanol solution) was used for boiling on copper foams with pore-density gradient structures formed by using several layers of foam covers. The experimental results show that, comparing with the one-layer foam, the bubble departure phenomenon was substantially attenuated due to the largely increase of pore density and hence the bubble moving resistance when using a two- or three-layer foam structure. However, the increase of pore density can enhance the pool boiling of water when the foam thicknesses are the same due to more active cavity sites being formed in a denser metal foam. While the enhancement for the solution is not obvious especially for that in the foam structure with higher pore density and heat transfer deterioration may emerge at high heat fluxes, the boiling heat transfer of the solution can generally be enhanced by using the 110 ppi foam and its gradient structures as compared to the polished surface. This provides new insight into enhancing the boiling heat transfer utilizing both the surface properties formed in the pore-density gradient structure and the unique interfacial properties of the self-rewetting fluids.

      PubDate: 2018-04-15T05:27:49Z
       
  • Numerical simulation of natural convection in a horizontal enclosure: Part
           I. On the effect of adiabatic obstacle in middle
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Jae Ryong Lee
      In this study, an effect of a three-dimensional obstacle of natural convection in a horizontal enclosure was discussed. Geometry which was taken into account was horizontal enclosure with unit aspect ratio and length of π along spanwise direction. The enclosure was heated from the bottom wall, and then was cooled down from above. An obstacle was located in the middle of the enclosure to examine its effect. A three-dimensional solution was obtained using Chebyshev spectral multi-domain methodology for different Rayleigh number at which the thermal behavior was evolved from a steady state to a chaotic pattern. As the geometry was elongated in conjunction with periodic boundary conditions to allow lateral freedom for the convection cells, longitudinal geometry along spanwise direction was discretized through a Fourier series expansion with a uniform mesh configuration. An adiabatic obstacle played a different role in determining the thermal behavior: No-slip condition of the surface of the obstacle disturbed the overall plume behavior in terms of the momentum transfer, whereas the adiabatic boundary condition did not influence significantly in terms of energy transfer. At a low Rayleigh number, thermal behavior in three-dimensional enclosure showed steady invariant solution along spanwise direction which is identical to two-dimensional result. With increasing buoyant force, spanwise invariance of longitudinal roll cell was collapsed and three-dimensional mode was obtained following flow regime transition. After undergoing periodically oscillatory phase, a chaotic flow transition occurred. At a high Rayleigh number, three-dimensional thermal plume oscillates freely in elongated geometry and consequently yields higher heat transfer rate. In addition, the thermal flow field was captured by visualizing the three-dimensional vortical structure. The chaotic three-dimensional flow behavior was quantitatively examined by obtaining the turbulent statistics.

      PubDate: 2018-04-15T05:27:49Z
       
  • Non-uniform ground-level wind patterns in a heat dome over a uniformly
           heated non-circular city
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Yifan Fan, Yuguo Li, Shi Yin
      Urban heat island-induced circulation, or urban heat dome flow, significantly influences urban thermal environments and air quality in calm wind conditions with stable stratification. An urban heat dome is characterized by convergent inflow at the ground level, divergent outflow at the upper level and upward flow over the city center in calm conditions. We report a new city-shape effect on heat dome flow patterns in a laboratory modeling experiment. For a circular city, both the inflow at the lower level and the outflow at the upper level are axisymmetric. For a square urban area, a non-uniform flow pattern was observed with four dominant diagonal inflows at the ground level and four dominant side outflows (perpendicular to city edges) at the upper level, indicating that the inflow changes direction as it rises over the urban area. The experiments were carried out in two water tank models with stable stratification, using thermal image velocimetry and particle image velocimetry. “Cell-like” and “stripe-like” eddy structures were identified over the modeled urban area, depending on the mean flow speed. To the best of our knowledge, this study reveals for the first time that in calm conditions the shape of an urban area may significantly affect the winds within a city, and thus the local heat transfer coefficients, urban air temperature and urban haze distribution will not be uniform under such conditions. Results on the eddy structures and mean flow fields can provide insights for theoretical analysis on heat transfer models in future studies.
      Graphical abstract image

      PubDate: 2018-04-15T05:27:49Z
       
  • Numerical analysis and optimization study on shell-side performances of a
           shell and tube heat exchanger with staggered baffles
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Xinting Wang, Nianben Zheng, Zhichun Liu, Wei Liu
      With a view to possessing the characteristics of the simple fabrication of the shell and tube heat exchanger with segmental baffles (STHX-SG) and the helical flow of the shell and tube heat exchanger with continuous helical baffles (STHX-CH), a shell and tube heat exchanger with staggered baffles (STHX-ST) is proposed in this work. The baffles of the STHX-ST are arranged according to a certain rule that the adjacent baffles are staggered by a constant clockwise or counterclockwise angle in sequence. Comparisons of the heat transfer performance and pressure drop among the STHX-SG, STHX-CH, and STHX-ST are firstly carried out. Results show that the comprehensive performance of the STHX-ST is superior the STHX-SG and STHX-CH. The parametric studies about the baffle cut δ and staggered angle β are conducted for the STHX-ST. Moreover, the multi-objective optimization is carried out to obtain the optimal solutions using the genetic algorithm further. The relationships between the design variables (the baffle cut δ, staggered angle β, and number of baffles n) and objective functions (the heat transfer rate Q and pressure drop Δp) are characterized by the artificial neural networks. The STHX-ST, at the δ = 0.45, β = 79°, and n = 11, is determined as the optimal solution according to the TOPSIS selection. Meanwhile, it is proved that the STHX-SG, a special STHX-ST at the β = 180°, is not always the best choice from the view of heat transfer enhancement. The STHX-ST can provide a preferable and meaningful solution for more efficient energy utilization in industrial applications.

      PubDate: 2018-04-15T05:27:49Z
       
  • A simplified energy dissipation based model of heat transfer for
           post-dryout flow boiling
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Jarosław Mikielewicz, Dariusz Mikielewicz
      A model for post dryout mist flow heat transfer is presented based on considerations of energy dissipation in the flow. The model is an extension of authors own model developed earlier for saturated and subcooled flow boiling. In the former version of the model the heat transfer coefficient for the liquid single-phase convection as a reference was used, due to the lack of the appropriate model for heat transfer coefficient for the mist flow boiling. That issue was a fundamental weakness of the former approach. The purpose of present investigation is to fulfil this drawback. Now the reference heat transfer coefficient for the saturated flow boiling is that corresponding to vapour flow the end of the mist flow. The wall heat flux is based on partitioning and constitutes of two principal components, namely the convective heat flux for vapour flowing close to the wall and two phase flow droplet–vapour in the core flowing. Both terms are accordingly modelled. The results of calculations have been compared with some experimental correlations from literature showing a good consistency.

      PubDate: 2018-04-15T05:27:49Z
       
  • Numerical modeling of flow film boiling in cryogenic chilldown process
           using the AIAD framework
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Jianye Chen, Ruirui Zeng, Xiaobin Zhang, Limin Qiu, Junlong Xie
      Flow film boiling plays a dominant role in cryogenic chilldown process, which involves complicated heat transfer and flow regime transition. Nevertheless, existing researches about flow film boiling with cryogenic fluids are relatively limited. In this study, a Computational Fluid Dynamics (CFD) model based on a wall heat flux partition algorithm is built. The AIAD framework implemented in the two-fluid model is employed to appropriately calculate the drag force on the liquid-vapor interfaces. The CFD model is validated by the satisfactory coincidence between the simulated heat fluxes and experimental data in literature. Accordingly, the two-phase interaction on the flow regime and heat transfer is further investigated. The results reveal that the vapor film beneath the bulk liquid becomes thinner due to the drag force on the liquid-vapor interface. In addition, FFT analysis on the pressure drop shows that dominant frequency of the interfacial waves in the tube mainly locates around 2.8 Hz. The normalized intensity indicates that fluctuation becomes more violent with the increase of superheat and inlet liquid flow rate. Finally, comparison between correlations and experimental data indicates that a correlation of heat transfer coefficient considering both film boiling effect and forced convective flow effect needs to be proposed.

      PubDate: 2018-04-15T05:27:49Z
       
  • Evaporation-induced receding contact lines in partial-wetting regime on a
           heated substrate
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Abbasali Abouei Mehrizi, Hao Wang
      The moving contact line is a nanoscale joint providing critical boundary conditions for the liquid interface in a wetting system. Our understanding about the partial-wetting contact line is highly limited which is especially true when the situation is complicated by phase change that is ubiquitous in nature and technologies. In this work we explored evaporation-induced receding contact lines in partial wetting regime by means of two modes of atomic force microscopy scanning. By means of tapping mode scanning, the intrinsic meniscus profile was found to be linear down to the apparent contact line without bending in profile, which greatly facilitates the modeling about the intrinsic meniscus. The local angle on the contact line systematically varied with the moving speed, which fact is against the widely used constant assumption in hydrodynamic models. Using the tapping mode scanning and also force curve method with either soft or stiff probes, a layer of nano thin film was detected on the substrate beyond the contact line. The nano film thickness slightly decreased with the distance away from the contact line, and finally reached a constant that was the adsorbed i.e. non-evaporating film thickness if the tests were in a vapor chamber. We further investigated advancing contact lines in open air, and still detected the nano thin film in front of the contact line as a precursor. The nano thin film can provide extra evaporation area, which could rationalize the abnormal ultrahigh evaporation flux observed in recent experiments on nanoscale menisci. Guidance is provided for the calculation of partial-wetting contact line evaporation.

      PubDate: 2018-04-15T05:27:49Z
       
  • Assessment of a new method for determining the relationship between
           effective diffusivity and moisture concentration – Exemplified by
           autoclaved aerated concrete of four density classes
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Halina Garbalińska, Marcin Stasiak, Magdalena Bochenek, Grzegorz Musielak
      The main purpose of the study was to assess the usability of a new calculation technique for determining the relationship between effective moisture diffusivity and moisture concentration. Four types of autoclaved aerated concrete, differing in their densities, were chosen as model porous media. The drying curves and the moisture distribution for samples that had different drying times were determined experimentally. The results obtained were used in a numerical procedure to give an estimation of the diffusion coefficient. The dependence of the coefficient on the moisture concentration was approximated by a polygonal chain. An entirely satisfactory correlation with experimental data was obtained by the application of an eight-segment polygonal chain. It was found that the diffusion coefficient was a decreasing function with respect to the moisture concentration in the low moisture content range. It reached a minimum and then increased together with the moisture concentration. It was also concluded that the greater the density of the tested porous material the lower its effective diffusivity.

      PubDate: 2018-04-15T05:27:49Z
       
  • Triple diffusive mixed convection from an exponentially decreasing
           mainstream velocity
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): P.M. Patil, Monisha Roy, A. Shashikant, S. Roy, E. Momoniat
      Current paper deals with the numerical study on steady triple diffusive mixed convection boundary layer flow for exponentially decreasing external flow velocity in presence of suction/injection. Such exponentially decreasing external flows have specific applications in diverging channel flows. The temperature of the vertical surface is assumed to be higher compared to the surrounded fluid temperature. In the triple diffusive flow, the solutal components are chosen as Sodium chloride and Sucrose and the components are added in the flow stream from below with various concentration levels. The concentrations of NaCl-Water and Sucrose-Water are assumed to be lower within the free stream compared to the species concentrations of NaCl-Water and Sucrose-Water near the wall. The coupled nonlinear partial differential equations governing the flow, thermal and species concentration fields are transformed using the non-similarity variables and solved numerically by an implicit finite difference scheme with quasi-linearization technique. The effects of wall suction/injection, Richardson number, decelerating parameter, ratio of buoyancy parameters and Schmidt numbers of both the solutal components on the fluid flow, thermal and species concentration fields are analyzed and discussed. Results indicate that the thickness of the momentum boundary layer is lower for suction compared to injection for the buoyancy opposing flow. The decelerating parameter has significant impact on the flow fields. Also, the species concentration boundary layer thickness decreases with the increase of Schmidt numbers and that increases with the ratio of buoyancy parameters for both the species components. Overall, the mass transfer rate is found to increase with Schmidt numbers approximately 10 % and 64 % for NaCl and Sucrose, respectively.

      PubDate: 2018-04-15T05:27:49Z
       
  • Water droplet impacting on overheated random Si nanowires
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Manuel Auliano, Maria Fernandino, Peng Zhang, Carlos Alberto Dorao
      Micro and nanostructured surfaces can significantly improve the heat transfer capability and shift the Leidenfrost temperature of impacting droplets. In this study, the effect of overheated random Si Nanowires on impacting water droplets is presented. The cooling performance was studied in term of droplet evaporation time and surface temperature while the boiling dynamics was observed through high-speed visualization. The Si Nanowires can increase almost twice the Leidenfrost temperature compare to the similar case of plain Si surface. At the same time, the heat transfer is enhanced by widening the transition boiling region about 150 K. In this regime, the film liquid lift-off behavior is observed in the range of the We numbers studied.

      PubDate: 2018-04-15T05:27:49Z
       
  • A comparison study on the thermal effects in DBD plasma actuation and
           electrical heating for aircraft icing mitigation
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Yang Liu, Cem Kolbakir, Haiyang Hu, Hui Hu
      A comparison study of a novel method of utilizing thermal effects induced by Dielectric-Barrier-Discharge (DBD) plasma actuation (i.e., DBD plasma-based method) and a conventional electrical heating method for aircraft icing mitigation was performed in an Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT). A NACA0012 airfoil/wing model embedded with an AC-DBD plasma actuator and a conventional electrical film heater over the airfoil surface was tested under a typical aircraft icing condition. While a high-speed imaging system was used to record the dynamic ice accretion and transient surface water transport processes over the airfoil surface, an infrared (IR) thermal imaging system was also utilized to map the corresponding surface temperature distributions over the airfoil surface simultaneously to quantify the unsteady heat transfer and phase changing process over the ice accreting airfoil surface. It was found that, with the same power input, the DBD plasma-based method showed at least equivalent effectiveness, if not better, in preventing ice accretion over the airfoil surface, in comparison to the conventional electrical heating method. Further optimization of the DBD plasma-based method with a duty-cycle modulation was found to have a much better anti-/de-icing performance, in comparison to the conventional electrical heating method. The findings derived from the present study demonstrated the potential of a new class of anti-/de-icing strategy by leveraging the thermal effects induced by DBD plasma actuation for aircraft in-flight icing mitigation.

      PubDate: 2018-04-15T05:27:49Z
       
  • Direct and inverse approaches for analysis and optimization of fins under
           sensible and latent heat load
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Ranjan Das, Balaram Kundu
      An inverse methodology is introduced by differential evolution (DE) search algorithm to determine optimal dimensions of a wet fin for a given volume for to maximize heat transfer rate. The DE optimization method is first employed to explore multiple combinations of geometrical fin parameters satisfying a constraint volume. The pertinent rates of heat transfer are computed using a forward analysis based on the differential transform method. In this study for a fixed fin volume, a same value of heat transfer rate in wet fins can be acquired for multiple values of surface areas, and also, even a given surface area can yield multiple values of heat transfer rates. Hence, the local temperature distribution acts as an important factor in selecting a unique set of fin dimensions towards maximizing the rate of heat transfer. The evaluation of sensitivity coefficients reveals that among various geometric parameters, the fin thickness plays an influential role significantly to govern the heat transfer rate.

      PubDate: 2018-04-15T05:27:49Z
       
  • MHD mixed convection of viscoplastic fluids in different aspect ratios of
           a lid-driven cavity using LBM
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): GH.R. Kefayati, H. Tang
      In this paper, a two-dimensional simulation of mixed convection in an enclosure with differentially heated sidewalls in the presence of a uniform magnetic field has been performed for different aspect ratios of the enclosure while the enclosure is filled with a viscoplastic fluid. The viscoplastic fluid has been simulated by the exact Bingham model without any regulations. Lattice Boltzmann Method (LBM) has been applied to solve the problem. Heat transfer, fluid flow, and yielded/unyielded zones are investigated for certain pertinent parameters of the Reynolds number (Re = 100, 500, and 1000), the Hartmann number (Ha = 0, 2, and 5), the Bingham number (Bn = 1, 5, and 10), the aspect ratio (AR = 0.25, 1, and 4), and Eckert number (Ec = 0, 10 - 4 , 10 - 3 , and 10 - 2 ) when the Grashof and prandtl numbers are fixed at Gr = 10 4 and Pr = 1; respectively. Results show that the increase in the Reynolds number augments the heat transfer and changes the extent of the unyielded section. Furthermore, for fixed studied parameters, an increase in the Bingham number decreases the heat transfer while enlarging the unyielded section. The rise of the aspect ratio alters the size and position of the unyielded/yielded zones. As Hartmann number rises, the heat transfer drops gradually and the unyielded parts increase significantly. The change of the magnetic field angle alters the heat transfer and the unyielded/yielded regions in the cavity. It was observed that the viscous dissipation and the joule heating parts in the energy equation based on the practical values of Eckret numbers have marginal effects on heat transfer and yielded/unyielded sections.

      PubDate: 2018-04-15T05:27:49Z
       
  • Conjugate natural convection heat transfer in an open-ended square cavity
           partially filled with porous media
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Sheng Chen, Wei Gong, Yuying Yan
      Conjugate natural convection heat transfer in an open-ended square cavity, which is partially filled with porous media, is a useful research prototype to deepen our insight into many important practical applications, such as solar energy collectors. But surprising, until now there is no open literature on it. In addition, for traditional numerical approaches, it is a great challenge to model conjugate problems on fluid-porous interfaces. In the present work, firstly we develop a new lattice Boltzmann (LB) approach to overcome such difficulty. The present LB model is validated by three benchmark tests. With the aid of this LB approach, we investigate the effects of thickness of porous layer, fluid-to-porous thermal conductivity ratio and permeability of porous layer on conjugate natural convection heat transfer in an open-ended porous-partially-filled square cavity, for the first time. It is found that these factors all influence the patterns of flow field and temperature field significantly. Especially, there exist some critical values. A small offset from them will cause a substantial change of heat and mass transfer. Sometimes the change trends are completely reversed. The present results may provide useful theoretical guides for the relevant practical applications.

      PubDate: 2018-04-15T05:27:49Z
       
  • Slag adhesion on the refractory sensor for molten steel level measurement
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Qing He, Zhi Xie
      A novel principle for molten steel level measurement in tundish by using temperature gradient was proposed in our previous work. A refractory sensor was inserted into the tundish to sense the temperature distribution of the slag and the molten steel. However, during the lifting process, the slag usually adhered to the refractory sensor, impairing the temperature readings of the CCD camera. While in contrast, molten steel was never found adherent to the sensor. In order to study the mechanism of this phenomenon, slag/molten steel adhesion on the sensor was analyzed in view of dynamics. Dynamic differential equations were established based on a one dimensional axisymmetric model. Steady-state solution of the equations was obtained in an analytical form. For the transient solutions, the differential equations were transformed into a heat conduction problem and were computed via the thermal module of the finite element software ANSYS. It is found that the adhesive thickness of the slag/molten steel on the sensor depends on the lifting velocity of the sensor, the viscosity and the density of the slag/molten steel. Because of the differences in density and viscosity, the adhesive thickness of the molten steel is very small, while the adhesive thickness of the slag is noticeable and increases with the decrease of its temperature. Experimental data at the steel plants is used to validate the theoretical analysis.

      PubDate: 2018-04-15T05:27:49Z
       
  • Role of differential vs Rayleigh-Bénard heating at curved walls for
           efficient processing via entropy generation approach
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Pratibha Biswal, Tanmay Basak
      The present study deals with the finite element based numerical simulations of heat transfer and entropy generation rates during natural convection for fluid saturated porous media in enclosures involving curved walls (case 1: lower curvature and case 2: higher curvature) with various thermal boundary conditions. The differential heating (isothermally hot left wall and cold right wall and adiabatic horizontal walls) and Rayleigh-Bénard heating (isothermally hot bottom wall and cold top wall involving adiabatic left and right walls) are considered. The locations and magnitudes of the entropy generation due to heat transfer ( S θ ) and fluid friction ( S ψ ) are presented and discussed based on the spatial distributions of isotherms and streamlines, respectively. The magnitudes of local entropy generation ( S θ , S ψ ), total entropy generation ( S total ) and average heat transfer rates ( Nu r ‾ and Nu t ‾ ) are significantly lesser for the Rayleigh-Bénard heating compared to the differential heating for all the cases involving all Da m and Pr m . The Rayleigh-Bénard heating is the optimal strategy for all Da m and Pr m involving both the concave cases except for 10 - 3 ⩽ Da m ⩽ 10 - 2 , Pr m = 10 and case 1 (concave) domain. The Rayleigh-Bénard heating is also the optimal strategy compared to the differential heating involving the convex cases at 10 - 5 ⩽ Da m ⩽ 10 - 4 whereas the differential heating is the optimal heating strategy for Da m ⩾ 10 - 3 involving both Pr m for the convex cases.

      PubDate: 2018-04-15T05:27:49Z
       
  • In situ characterization of enhanced thermal performance by periodic
           nanostructures on the surface of a microchannel
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Jiwon Yu, Seok-Won Kang, Tae-Soon Kwon, Debjyoti Banerjee
      In situ formation of nanofins (i.e. isolated and dispersed precipitation of nanoparticles) on flow conduits induces changes to the surface morphology for heat exchange, increasing effective surface area and enhancing their cooling performance. Furthermore, the existence of these nanostructures has a significant influence on heat transfer, as opposed to the thermo-physical properties (e.g. thermal conductivity) of cooling fluids enhanced by addition of nanoparticles. This study conducted an in situ analysis exploring the effects of nanoscale surface modifications on forced convective heat transfer and thermal performance. A numerical heat transfer analysis, based on the conductive/convective heat transfer between a fin base and deionized water (DIW), was performed with the assumption that periodic nanostructures existed on the heated microchannel surface. Predictions of enhanced thermal performance (between 37% and 143%) from the resultant increase in the effective heat transfer area were validated for flows over these nanostructures (artificial nanofins) fabricated by SFIL (step and flash imprint lithography) inside a microchannel. Polydimethylsiloxane microchannels are bonded to a silicon wafer containing thin-film thermocouple arrays deposited onto artificial nanofins, which had been fabricated a priori for the in situ characterization of thermal performance. It was found that the convective heat transfer Nusselt number (Nu) increased from 61% to 110%. Additionally, a theoretical analysis of the pressure drop was also successfully achieved for a comprehensive understanding of the heat transfer characteristics at the fluid-wall interface of a microchannel.

      PubDate: 2018-04-15T05:27:49Z
       
  • New friction factor and Nusselt number equations for turbulent convection
           of liquids with variable properties in circular tubes
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Houjian Zhao, Xiaowei Li, Xinxin Wu
      Large temperature differences between the wall and bulk fluid in heat exchangers will result in significant property variations in the cross section. Most existing equations use correction factors such as ( μ w / μ b ) n or ( Pr w / Pr b ) m to take account of property variation effects on heat transfer coefficients and friction factors. The exponents, n or m obtained by regression analysis of experimental data are not consistent in the literature. They are also different for heating and cooling conditions. In the current investigation, velocity and temperature distributions of turbulent convection with variable properties in circular tubes are analyzed using classical turbulent boundary layer theory. The viscosity variation effects on velocity and temperature fields are simplified to the effects on the critical point between the linear and the logarithmic distribution regions. New friction factor and Nusselt number equations for turbulent convection of liquids with variable properties are obtained. The new equations show accurate predictions of experimental data for both heating and cooling conditions and for different kinds of liquids. The new equations show that viscosity variation effects on friction factor decrease with the increasing of Reynolds number, while its effects on Nusselt number almost keep constant with the increasing of Reynolds number.

      PubDate: 2018-04-15T05:27:49Z
       
  • Effect of nano-structure coating on thermal performance of thermosyphon
           boiling in micro-channels
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Shuang-Fei Li, Yi-Ying Bao, Ping-yang Wang, Zhen-hua Liu
      A novel micro-channel thermosyphon technology for passively cooling 3D stacked chips was provided, and the thermosyphon boiling characteristics in vertical and inclined micro-channels with two open ends which simulate the specific stacked structure of actual 3D chip were experimentally carried out. In order to improve the heat transfer of micro-channel thermosyphon by surface treatment technology, four kinds of nanoparticles (CuO, Cu, Al2O3, SiO) were added to the base fluid to make nano-structure coatings on the heater surfaces by using a long time pool boiling treatment. Then, micro-channel thermosyphon boiling experiments were carried out with four kinds of working liquids: two kinds of pure fluids (deionized water and R113) and two kinds of moist fluids (deionized water+surfactant and R113+surfactant). The gaps and heights of micro-channels tested were in the range of 30–60 μm and 30–90 mm, respectively. Experimental results show that nano-structure coatings can significantly enhance both the maximum heat flux and heat transfer coefficient of thermosyphon boiling in micro-channels, and exist both the optimal nanoparticle kind and nanoparticle concentration in the base fluids. The experimental results provided some meaningful technology support for 3D stacked chip cooling.

      PubDate: 2018-04-15T05:27:49Z
       
  • Evaluation of the WSGG model against line-by-line calculation of thermal
           radiation in a non-gray sooting medium representing an axisymmetric
           laminar jet flame
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Felipe R. Centeno, Rogério Brittes, Luís G.P. Rodrigues, Felipe R. Coelho, Francis H.R. França
      This paper presents an evaluation of the weighted-sum-of-gray-gases (WSGG) model in the computation of the radiative heat transfer in an axisymmetric gas system composed of H2O, CO2 and soot by comparison with line-by-line (LBL) integration. The test cases consider temperature and species concentrations fields that are representative of a laminar diffusion jet flame of ethylene diluted with H2O. Different approaches are considered in the application of the WSGG model, including the use of WSGG coefficients obtained for different ratios between the mole concentrations of H2O and CO2, and the superposition between the coefficients of H2O/CO2 and soot. The WSGG coefficients for H2O and CO2 are based on HITEMP2010 database, while for soot they are based on the consideration of linear spectral dependence of its absorption coefficient. The spatial integration of the radiative transfer equation is carried out with the discrete ordinates method. The results in the paper show that, although the ratio between the mole concentrations of H2O and CO2 varies locally in the flame, using WSGG coefficients for a constant ratio, but equivalent to the global average ratio in the flame, can provide satisfactory solutions in comparison to the LBL integration. Moreover, the superposition method between the WSGG coefficients of combined H2O/CO2 and of soot proved accurate considering both moderate and high concentrations of soot. The paper provides algebraic relations for the temperature and concentration fields, which can be used for the evaluation of other gas models in future studies.

      PubDate: 2018-04-15T05:27:49Z
       
  • Experimental study of augmented flow boiling in a dielectric fluid due to
           backward and forward facing stepped microchannels
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Le Gao, Sushil H. Bhavnani
      This study explores the thermal performance of novel backward-facing-step and forward-facing-step structures in microchannel heat sinks. Tests are conducted at mass fluxes of 444–1776 kg/m2 s and inlet subcoolings of 5–20 °C using FC-72 as the coolant. The effects of step change on boiling curve, flow pattern, pressure drop and heat transfer coefficient are discussed in this paper. The saw-toothed steps enhance the heat transfer performance by greater than 30% across the entire range of input parameters tested, with a peak enhancement of 100% at the highest mass flux. Pressure drop penalties range from 30% to 70% for the range of parameters tested. The forward-facing configuration leads to a larger bubble population in the channels, causing more effective mixing. These microchannel structures offer the promise of improved thermal performance without the complex fabrication processes associated with nanostructured or re-entrant geometries.

      PubDate: 2018-04-15T05:27:49Z
       
  • Similarity-solution-based improvement of γ-Reθt model for
           hypersonic transition prediction
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Yutian Wang, Yiwen Li, Lianghua Xiao, Bailing Zhang, Yinghong Li
      The improvement of γ-Reθt model for hypersonic transition prediction is conducted based on the compressible similarity solutions. The Wilcox’s correlation of vorticity Reynolds number and momentum thickness Reynolds number adopted in the original γ-Reθt model is not suitable for hypersonic boundary layer. The new correlation is obtained from similarity solutions of compressible boundary layer equations, which includes parameters such as Mach number and temperature of boundary edge and wall temperature. Then the new correlation as well as several modifications are applied to improve the γ-Reθt model for hypersonic transition prediction. Four test cases are selected to assess the performance of the improved γ-Reθt model, including a wide range flows from two-dimensional flat plate and double ramp to three-dimensional X-51A forebody and scramjet intake. The predicted pressure coefficient and Stanton number are consistent with the available experimental data, which validate the transition prediction capacity of the improved γ-Reθt model in different hypersonic conditions. For complex scramjet intake, the predicted results by the improved γ-Reθt model show a good agreement with experimental data, especially in the interior region, which demonstrates that the improved γ-Reθt model can be an effective tool for the design and optimization of hypersonic vehicles.

      PubDate: 2018-04-15T05:27:49Z
       
  • Numerical analysis of heat transfer and fluid flow in multilayer
           deposition of PAW-based wire and arc additive manufacturing
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Xingwang Bai, Paul Colegrove, Jialuo Ding, Xiangman Zhou, Chenglei Diao, Philippe Bridgeman, Jan roman Hönnige, Haiou Zhang, Stewart Williams
      A three-dimensional numerical model has been developed to investigate the fluid flow and heat transfer behaviors in multilayer deposition of plasma arc welding (PAW) based wire and arc additive manufacture (WAAM). The volume of fluid (VOF) and porosity enthalpy methods are employed to track the molten pool free surface and solidification front, respectively. A modified double ellipsoidal heat source model is utilized to ensure constant arc heat input in calculation in the case that molten pool surface dynamically changes. Transient simulations were conducted for the 1st, 2nd and 21st layer depositions. The shape and size of deposited bead and weld pool were predicted and compared with experimental results. The results show that for each layer of deposition the Marangoni force plays the most important role in affecting fluid flow, conduction is the dominant method of heat dissipation compared to convection and radiation to the air. As the layer number increases, the length and width of molten pool and the width of deposited bead increase, whilst the layer height decreases. However these dimensions remain constant when the deposited part is sufficiently high. In high layer deposition, where side support is absent, the depth of the molten pool at the rear part is almost flat in the Y direction. The profile of the deposited bead is mainly determined by static pressure caused by gravity and surface tension pressure, therefore the bead profile is nearly circular. The simulated profiles and size dimensions of deposited bead and molten pool were validated with experimental weld appearance, cross-sectional images and process camera images. The simulated results are in good agreement with experimental results.

      PubDate: 2018-04-15T05:27:49Z
       
  • Experimental investigation of heat transfer characteristics and wall
           pressure distribution of swirling coaxial confined impinging air jets
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Burak Markal
      In the present study, swirling coaxial confined impinging turbulent air jets issuing from a novel designed nozzle is studied experimentally. Heat transfer characteristics and pressure distribution on the impingement plate are analyzed. Experiments have been conducted at different dimensionless nozzle-to-plate distances (H/D = 0.5, 1.0, 1.5, 2.0 and 2.5) and dimensionless flow rates (Q∗  = 0.25, 0.50 and 0.75) for a constant total flowrate of 1.33 × 10−3 m3 s−1 (80 L/min). The results show that the flowrate ratio improves the uniformity of the heat transfer through the impingement surface and increases the average Nusselt number. Also, the intensity of convective heat transfer is shown to enhance significantly with decreasing nozzle-to-plate distance. With regards to the pressure distribution, subatmospheric regions occur on the impingement plate. Contribution of swirl is also compared against the pure circular impingement jet condition (Q∗  = 0.0).

      PubDate: 2018-04-15T05:27:49Z
       
  • (Semi-)analytical solution of Luikov equations for time-periodic boundary
           conditions
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): R. Pečenko, N. Challamel, T. Colinart, V. Picandet
      The paper addresses the problem of coupled heat and moisture transfer in porous materials with the time-periodic boundary conditions applied. The solution of Luikov equations [1], which describe coupled heat and moisture transfer, is presented. Laplace transform is used, where some terms of the inverse Laplace transform ought to be solved by Gaussian quadrature, meaning that the solution is semi-analytical. The time-periodic boundary conditions are applied to simulate the humidity and temperature oscillations of natural environment. Therefore, the proposed solution is appropriate to evaluate the distribution of moisture and temperature within the porous material exposed to everyday natural cycles. The paper presents convergence tests, validation of semi-analytical solution and application to different building materials are presented in the paper.

      PubDate: 2018-04-15T05:27:49Z
       
  • Mathematical model for thermal behavior of lithium ion battery pack under
           overcharge
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Chuang Qi, Yanli Zhu, Fei Gao, Kai Yang, Qingjie Jiao
      An overcharge model of lithium ion battery pack was built by coupling the electrochemical model with thermal abuse model. The pack consists of three fully-charged batteries, each of which has a capacity of 10 Ah, using Li[Ni1/3Co1/3Mn1/3]O2 as the positive electrode. The three batteries in the pack were juxtaposed, and only the middle one was overcharged. The influences of current, convection coefficient and gap between batteries on the thermal runaway propagation were studied. The results of temperature and voltage obtained from the models were validated experimentally, and they were agreed well with the experimental data with the relative error within 6%. The results showed that the onset temperature of thermal runaway of the charged battery increased with an increase in the current, while the temperatures for the other two decreased. The temperature rate of the charged battery changed little when the convection coefficient was greater than 40 W/m2 K. The clamp of lithium ion battery pack had an important effect on the thermal runaway propagation. The occurrence of thermal runaway propagation was depended on whether there was the existence of clamp when the battery gap exceeded 5 mm.

      PubDate: 2018-04-15T05:27:49Z
       
  • Direct simultaneous reconstruction for temperature and concentration
           profiles of soot and metal-oxide nanoparticles in nanofluid fuel flames by
           a CCD camera
    • Abstract: Publication date: September 2018
      Source:International Journal of Heat and Mass Transfer, Volume 124
      Author(s): Guannan Liu, Dong Liu
      A reconstruction model based on inverse radiation analysis is presented to determine the temperature and concentration distributions of soot and metal-oxide nanoparticles in nanofluid fuel sooting flames using radiative intensities received by a CCD camera. The combined method consisting of the least-square QR decomposition (LSQR) algorithm and one dimensional searching was adopted to solve the inverse problem. Influences of ray number, wavelength combination, measurement error and metal-oxide nanoparticle concentration on the reconstruction accuracy were studied in details. The reconstructed results illustrated that the temperature distribution and soot concentration fields can be accurately retrieved, even with the measurement signal to noise ratio (SNR) as low as 39 dB, whereas the metal-oxide nanoparticle concentration field estimation process was more easily influenced by the measurement error and the practical metal-oxide nanoparticle concentrations. The proposed reconstruction method here is effective and robust for simultaneously retrieving the temperature distribution and concentration fields of soot and metal-oxide nanoparticles, even with noisy data.

      PubDate: 2018-04-15T05:27:49Z
       
 
 
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