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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 242  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3163 journals]
  • Implementation of a new thermal model and static calibration of a
           wedge-shaped hot-film probe in a constant-temperature mode
    • Authors: M. Krause; U. Gaisbauer; E. Kraemer; A.D. Kosinov
      Pages: 1 - 9
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): M. Krause, U. Gaisbauer, E. Kraemer, A.D. Kosinov
      Wedge-shaped hot-films are a promising alternative to hot-wires for supersonic free flow disturbance measurements if hot-wires cannot be used due to harsh flow conditions. Up to the present, wedge hot-films could not serve as quantitative tools because of an insufficient modelling of the substrate’s influence on the thermal balance. The present paper shows a static calibration of a wedge-shaped hot-film sensor that is based on a combination of an analytical, a numerical and an experimental approach. The substrate’s impact was analysed by the help of CFD simulations and modelled by a newly introduced substrate factor. The obtained sensitivities were discussed and qualitatively explained compared with standard hot-wires. A quantitative comparison of experimentally detected mass flux fluctuations proved the wedge hot-film data to match similar hot-wire results very well. The presented approach has the potential to upgrade hot-films of various shapes to tools for quantitative fluctuation measurements.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.002
      Issue No: Vol. 126 (2018)
       
  • Detailed parametric investigations on drag and heat flux reduction induced
           by a combinational spike and opposing jet concept in hypersonic flows
    • Authors: Min Ou; Li Yan; Wei Huang; Shi-bin Li; Lang-quan Li
      Pages: 10 - 31
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Min Ou, Li Yan, Wei Huang, Shi-bin Li, Lang-quan Li
      In the current study, the flow field behavior induced by a novel combinational opposing jet and spike concept has been investigated numerically. A comprehensive analysis on the selections of the turbulence model and the height of the first grid point off the wall (Δx) has been conducted firstly. Then, this paper mainly focuses on the influences of the nozzle diameter (d 0), the length-to-diameter ratio of the aerospike (L/D) and the jet pressure ratio (PR) on the flow field structures, the aerodynamic drag and heat properties. The results show that when d 0 is 2 mm, adding the opposing jet to the single spiked blunt body has no help in modifying the high drag and heat environment. However, the combinatorial thermal protection system has a great contribution to reduce the drag and heat when d 0 is 4 mm, with 45% and 38% drop on the wall Stanton number (St) and drag coefficient (Cd) respectively. The values of the wall heat flux, the static pressure and the drag coefficient decrease apparently when L/D increases from 1.0 to 1.5, while the drop rates of these indexes seem not so obvious when L/D rises from 1.5 to 2.0. Meanwhile, the introduction of the opposing jet creates a recirculation zone upstream the spike head, and there is a recirculation zone emerges downstream the aerodisk as well when L/D increases to 2.0. Both of the recirculation zones have alleviated the high temperature the aerodisk sustained significantly.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.013
      Issue No: Vol. 126 (2018)
       
  • Surface tension driven flow forming aluminum oxide microtubes
    • Authors: Isabela T. Coutinho; A.A.R. Neves; G. Sombrio; J.A. Souza
      Pages: 32 - 38
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Isabela T. Coutinho, A.A.R. Neves, G. Sombrio, J.A. Souza
      Aluminum oxide microtubes decorated with metallic nanoparticles were produced through thermal oxidation method by using metallic aluminum microwire above its melting point, i.e., in the liquid phase. The obtained translucent aluminum oxide microtubes have 66 µm of internal diameter, with a wall thickness of ∼2 µm while the patterned Al metallic nanoparticles have diameter in the range 50–200 nm. Structural characterization indicated that the microtube wall is formed by amorphous oxide phase which coexist with crystallized metallic one. Heat treatment at T = 1050 °C leads to the crystallization into Al2O3 phase. During the fabrication process, a thin oxide layer was formed first on the molten liquid surface establishing a solid oxide tube with a liquid inner core. The formation and growth of a spherical droplet, at the microwire’s end, draw the molten aluminum inner core, acting as a driving force for the liquid mass transfer movement and microtube formation. The capillary effect and surface tension driven flow effect plays an important role towards the microtube formation.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.026
      Issue No: Vol. 126 (2018)
       
  • The interfacial dynamics of the micrometric droplet diameters during the
           impacting onto inclined hot surfaces
    • Authors: Deendarlianto; Yasuyuki Takata; Arif Widyatama; Akmal Irfan Majid; Ardi Wiranata; Adhika Widyaparaga; Masamichi Kohno; Sumitomo Hidaka; Indarto
      Pages: 39 - 51
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Deendarlianto, Yasuyuki Takata, Arif Widyatama, Akmal Irfan Majid, Ardi Wiranata, Adhika Widyaparaga, Masamichi Kohno, Sumitomo Hidaka, Indarto
      The interfacial dynamics of the micrometric size liquid droplets during impact onto inclined hot surfaces have been experimentally studied. The inclination angles were varied at 15°, 30°, and 45° from horizontal for surface temperatures were decreasing from 500 °C to 100 °C. The droplet diameters tested were 500 μm and 700 μm. The tested material was stainless steel-grade 304 (SUS 304) with varying surface roughness ranging from Ra 0.04 up to Ra 10. The interfacial dynamics during the impact onto inclined hot surfaces were investigated by using a high-speed video camera with the frame speed of 15,000 fps. The objectives of this study are to provide insight into the dynamic behaviors of contact angles and dependence of importance parameters at various surface temperatures. It was found that depending on the surface temperature the droplet evaporation and its bouncing process play an important role on the droplet detachment mechanisms from the inclined surface. Three transient regions of the interfacial evolution during the micrometric droplets impacting onto oblique hot surface were identified. Moreover, the contribution of the important physical parameters, such as, advancing and receding contact angles on the interfacial dynamics are presented.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.023
      Issue No: Vol. 126 (2018)
       
  • Study on gas-droplet heat and mass transfers in oscillating flows
    • Authors: Qiang Li; Wenjing Yang
      Pages: 52 - 60
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Qiang Li, Wenjing Yang
      A numerical study on the dynamics of evaporating droplets in oscillatory flows is performed by using an Eulerian-Eulerian model including two-way couplings. The diluted liquid fuel-gas two-phase flow is assumed to be laminar. The droplet is assumed to be spherical during its lifetime and its thermal conductivity is also assumed to be infinite. Heat and mass transfer of this two-phase flow is characterized by analyzing the effects of acoustic fields on the two-phase temperatures, droplet diameter and concentration, spray evaporation rate and vaporizing species mass fraction. Results show that acoustic forcing can substantially influence the dynamics of the two-phase flow. The presence of droplet clustering as a consequence of acoustic forcing affects the two-phase flow in two aspects. The first is the oscillation of the two-phase flow parameter which roots in the periodic variation of droplet concentration. The second is the enhancement of the droplet evaporation rate at all conditions. The maximal relative increase in spray evaporation rate can be up to 72.9% in the parameter range studied. The mechanism for the enhancement of droplet evaporation rate is the optimal distribution of the heat in the liquid phase whose direct cause is droplet clustering. The enhancement of evaporation rate is highly dependent on the acoustic oscillation amplitude; however, there is no significant relationship between the acoustic oscillation frequency and the evaporation rate. Additionally, the oscillation amplitudes of the two-phase flow parameters are found to decrease with the growth of acoustic forcing frequency. It is made clear that the evaporation of droplets has a negligible effect on the occurrence of droplet clustering despite its marked influence on the two-phase flow through the reduction of the droplet relaxation timescale. Increasing the droplet initial concentration is also found to be beneficial for the enhancement of droplet evaporation rate.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.008
      Issue No: Vol. 126 (2018)
       
  • Simulation on a gravity-driven dripping of droplet into micro-channels
           using the lattice Boltzmann method
    • Authors: Hangyu Chen; Jinya Zhang; Yongxue Zhang; Zhichao Wei
      Pages: 61 - 71
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Hangyu Chen, Jinya Zhang, Yongxue Zhang, Zhichao Wei
      Micro-channels are prevalent extensively in microelectronic devices and heat-exchange equipment. In this study, a single-component multiphase (SCMP) pseudo-potential lattice Boltzmann model is employed to investigate the dripping of a droplet driven by gravity into micro-channels in two-dimensional coordinates. The model has capabilities that make it applicable to cases with high density ratios, low viscosities, and tunable surface tension. Tests on static droplets verify these capabilities and exhibit the effect of different parameters. Four typical deformation processes are identified: free falling, attachment, flowing, and dripping. Furthermore, the effects of different parameters, such as wettability of walls, are compared. And the critical values of dimensionless numbers are investigated. The results quantificationally shows that the critical break-up number (Ca) is increasing and the critical dripping number (Bo) is decreasing with the increase of fluid–solid strength on walls.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.04.151
      Issue No: Vol. 126 (2018)
       
  • Progress on numerical simulation of yield stress fluid flows (Part I):
           Correlating thermosolutal coefficients of Bingham plastics within a porous
           annulus of a circular shape
    • Authors: Karim Ragui; Abdelkader Boutra; Rachid Bennacer; Youb Khaled Benkahla
      Pages: 72 - 94
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Karim Ragui, Abdelkader Boutra, Rachid Bennacer, Youb Khaled Benkahla
      The main purpose of our work is to show the impact of some pertinent parameters; such Lewis and solutal Rayleigh numbers as well as the buoyancy and the aspect ratios; on a viscoplastic materials’ double-diffusive convection which occurs within an SiC annulus; contained between a cold “and less concentric” outer circular cylinder and a hot “and concentric” inner one, to come out with innovative correlations what predict the mean transfer rates into such annulus. To do so, the physical model for the momentum conservation equation is made using the Brinkman extension of the classical Darcy equation. The set of coupled equations is solved using the finite volume method and the SIMPLER algorithm. To handle the cylinder shape in Cartesian coordinates; the Cartesian Cut-Cell approach was adopted. Subsequently, inclusive correlations of overall transfers within such viscoplastic porous annulus are set forth as a function of the governing parameters; which foresee with ±2 to ±3% the numerical predictions. Noted that the validity of the computing code was ascertained by comparing its results with experimental data and numerical ones; already available in the literature.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.010
      Issue No: Vol. 126 (2018)
       
  • Linear stability of thermal-bioconvection in a suspension of gyrotactic
           micro-organisms
    • Authors: Moli Zhao; Yue Xiao; Shaowei Wang
      Pages: 95 - 102
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Moli Zhao, Yue Xiao, Shaowei Wang
      By utilizing a randomly swimming model, a linear stability analysis is applied to investigate the stability of bioconvection in a horizontal suspension layer of motile gyrotactic micro-organisms with heated from below. The micro-organisms under consideration are orientated by a balance between a gravitational torque, due to them being bottom heavy, and viscous torque arising from local fluid velocity gradients. The obtained eigenvalue problem containing thermal Rayleigh number and bioconvection Rayleigh number is solved numerically using one-term Galerkin method. The case of non-oscillatory instability is analyzed, the relationship among thermal Rayleigh number, bioconvection Rayleigh number, Lewis number, critical wavenumber and the shape of microorganisms are discussed. We point out that the heating from below makes the layer more unstable. When increasing the value of thermal Rayleigh number to 1750, the suspension becomes unstable itself, which imply that bioconvection Rayleigh number has nothing to do with the stability of this system. We also find that Lewis number has no effect on critical value of thermal Rayleigh number, but has a great influence on critical bioconvection Rayleigh number. The increasing cell eccentricity enlarges the critical value of bioconvection Rayleigh number, which means that the suspension is more stable.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.030
      Issue No: Vol. 126 (2018)
       
  • Flow boiling of R134a in an open-cell metal foam mini-channel evaporator
    • Authors: Wuhuan Gao; Xianghua Xu; Xingang Liang
      Pages: 103 - 115
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Wuhuan Gao, Xianghua Xu, Xingang Liang
      Open-cell metal foam mini-channel evaporator (OMFME) is proposed to enhance heat transfer in electronics cooling. In present study, flow boiling in an OMFME is investigated using R134a. The OMFME has nine channels, which are 507 μm in width and 1097 μm in depth. Comparing with a mini-channel evaporator (ME) with the same footprint area, the heat transfer coefficient (HTC) is enhanced up to 1.5 times and the dry out is delayed. Flow patterns are presented and compared with an existed flow patterns map. HTCs generally increases with the quality, the heat flux and it is slightly influenced by the mass flow rate. Nucleate boiling and evaporation in the porous fins are the two heat transfer mechanisms in different quality range. A correlation is presented to calculate frictional pressure drop.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.04.125
      Issue No: Vol. 126 (2018)
       
  • Thermal performance enhancement of vapor chamber by coating mini-channel
           heat sink with porous sintering media
    • Authors: Songkran Wiriyasart; Paisarn Naphon
      Pages: 116 - 122
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Songkran Wiriyasart, Paisarn Naphon
      This paper have been investigated on the thermal performance enhancement of air cooling vapor chamber by coating mini-channel heat sink inside with porous sintering wick sheet. The results obtained from experiments are considered and compared with without porous sintering wick sheet. The effects of power input, amount of filled working fluid into the vapor chamber and mass flow rate of air on the cooling performance and thermal resistance characteristics are considered. It can be found that the porous sintering wick sheet has significant effect on the increment of the capillary force which results in higher heat transfer rate. Therefore, the thermal performance of air cooling vapor chamber with porous sintering wick sheet inside mini-channel shows 20% maximum higher than that without porous sintering wick sheet. In addition, the increasing of power in put and cooling air mass flow rate have significantly increased thermal performance of the vapor chamber. The passive cooling device with vapor chambers is favorable technique that can enhanced thermal performance and reduce heat accumulate on the electronic component.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.020
      Issue No: Vol. 126 (2018)
       
  • Separation of heat transfer components from impinging methane diffusion
           flames
    • Authors: Vinay C. Raj; Pramod Kuntikana; S. Sreedhara; S.V. Prabhu
      Pages: 123 - 138
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Vinay C. Raj, Pramod Kuntikana, S. Sreedhara, S.V. Prabhu
      The high heat transfer rates from impinging flame jets and plumes are extensively used in many industrial applications. Comprehensive literature review suggests that the characterization of flame impingement is done primarily by the measurement of heat flux onto the target surface. The use of in-situ probes limits the spatial resolution of the measurement. For a diffusion flame, radiation cannot be neglected and it is therefore necessary to determine the convective and radiative heat flux components to quantify the thermal boundary condition to the impingement surface. For determining the heat transfer characteristics of impinging diffusion flames, the target surface is impinged by a methane diffusion flame from the bottom and is simultaneously cooled from the top by air jets of different Reynolds number. At steady state, one dimensional energy balance across the impingement surface provides an equation with the three unknowns being the heat transfer coefficient of the flame jet, the reference temperature and the emissivity of the gas/flame. By keeping the flame jet impingement conditions same and varying the air jet impingement on the top surface, five different forms of the energy balance equation is obtained. A minimization technique, that makes use of the Nelder-Mead algorithm, is developed to solve for the over-determined system of equations. The obtained results are compared with the slope method that determines the effective heat transfer coefficient and the reference temperature. The impingement surface is modeled in FLUENT and the experimentally obtained heat transfer coefficient of the flame jet, the reference temperature and the emissivity of the gas/flame is provided as the boundary condition to numerically determine the surface temperature. For validation purpose, the impingement surface material and thickness is changed and the experimentally obtained and numerically determined wall temperatures are compared. It is demonstrated that the minimization technique is capable of separating the convective and radiative heat transfer components from impinging diffusion flames.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.014
      Issue No: Vol. 126 (2018)
       
  • Experimental investigation and radial basis function network modeling of
           direct evaporative cooling systems
    • Authors: Kadir Kavaklioglu; Mehmet F. Koseoglu; Oguz Caliskan
      Pages: 139 - 150
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Kadir Kavaklioglu, Mehmet F. Koseoglu, Oguz Caliskan
      Radial basis function network method is used for modeling a direct evaporative cooling system. Air dry exit temperature, air pressure drop across the cooler and cooler efficiency are predicted using these models. The inputs are pad thickness, air inlet speed, air dry inlet temperature, relative humidity at the inlet and feed water temperature. The data for the models are taken from the experiments performed specifically for this purpose. Model validation is performed using twofold cross validation method. A grid search is used to determine optimal network parameters, such as, optimum number of radial basis elements and spread parameter. Validated models are tested against ordinary least squares models for the output variables. The results indicate that it is feasible to apply radial basis function networks to model direct evaporative coolers.
      Graphical abstract image

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.022
      Issue No: Vol. 126 (2018)
       
  • A pore structure based real gas transport model to determine gas
           permeability in nanoporous shale
    • Authors: Wenhui Song; Jun Yao; Jingsheng Ma; Yang Li; Wencheng Han
      Pages: 151 - 160
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Wenhui Song, Jun Yao, Jingsheng Ma, Yang Li, Wencheng Han
      Gas flows in the forms of multiple transport mechanisms in shale nanoporous media with complex pore structure and different pore types. Laboratory pressure pulse decay technique is often applied to measure gas permeability but the current gas permeability interpretation model is mostly based on the homogeneous macro scale model while the influence of pore structure on real gas transport is neglected. In this study, a novel pore structure based real gas transport model is proposed to determine gas permeability in nanoporous shale combining laboratory pressure pulse decay technique with pore network simulation. The laboratory pressure pulse decay process is simulated in a virtual system based on the similarity principle which contains upstream vessel, downstream vessel, and core sample. The core sample is constructed by a series of connected pore networks and the sizes of pores and throats in each location of the pore network are randomly assigned according to laboratory measured pore size distribution. Gas transport mechanisms inside the core sample consider viscous flow, Knudsen diffusion, surface diffusion and real gas effect. At each time step, the upstream vessel pressure decreases and the downstream vessel pressure increases until the upstream vessel pressure and downstream vessel pressure become equal. The simulated pressure drop versus time curve is obtained and is applied to fit the laboratory measured pressure drop data by repeating core sample construction and pressure pulse decay process. The proposed model is applied to measure gas permeability of Sichuan basin, Longmaxi formation shale core sample. The results indicate that the predicted value based on the proposed model matches well with the experimental measured pressure drop data. The proposed model is used to study the influences of test gas type and pore size on gas permeability. When the average organic pore radius is less than 20 nm, helium tested permeability overestimates at least 40% of the methane permeability.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.012
      Issue No: Vol. 126 (2018)
       
  • Evaporation modes of LiBr, CaCl2, LiCl, NaCl aqueous salt solution
           droplets on aluminum surface
    • Authors: G.V. Kuznetsov; D.V. Feoktistov; E.G. Orlova; S.Y. Misyura; V.S. Morozov; A.G. Islamova
      Pages: 161 - 168
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): G.V. Kuznetsov, D.V. Feoktistov, E.G. Orlova, S.Y. Misyura, V.S. Morozov, A.G. Islamova
      The evaporation of droplets of the LiBr, CaCl2, LiCl and NaCl aqueous salt solutions were studied experimentally and their evaporation characteristics were compared to droplets of distilled water. The geometrical parameters of droplets (contact angle, height, and diameter) were measured using three methods of data processing: tangential methods (T) and the Young-Laplace method (Y-L). Scattering of the measured data does not depend on the processing method selected for large contact angles. However, in the case of small contact angles, the Y-L method exhibited the smallest measurement error. An optical method allowed for measuring the contact angle of salt solutions droplets just prior to crystallization. The experiments have shown that crystalline hydrates grow near the contact line and distort the droplet profile. The contact angles of salt solution droplets were found to depend on time in a non-linear manner. Typical evaporation modes of the studied aqueous salt solutions are detected: 1 – increasing the contact diameter; 2 – pinning the droplet; 3 – formation of salt crystals (NaCl) or crystalline hydrates (LiBr, CaCl2 and LiCl).
      Graphical abstract image

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.040
      Issue No: Vol. 126 (2018)
       
  • Numerical investigations of impingement cooling performance on flat and
           non-flat targets with dimple/protrusion and triangular rib
    • Authors: Qi Jing; Di Zhang; Yonghui Xie
      Pages: 169 - 190
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Qi Jing, Di Zhang, Yonghui Xie
      Jet impingement is an efficient cooling method and has been widely adopted in electronic device and turbine blade. Well-designed structures including dimples and protrusions arranged in the flow path can alter flow fields in ways that provide a favorable trade between total pressure loss and increased heat transfer. In this paper, impingement cooling performances are numerically investigated for three different target shapes and various surface arrangements of dimple/protrusion and triangular rib. Within the Re range of 10,000–50,000, the detailed flow patterns, heat transfer and friction characteristics are obtained. Compared with flat channels, concave and V-shape targets produce more complex flow patterns. The adoption of dimple/protrusion improves the local and overall heat transfer. The Nu/Nu 0 of 1.31 is achieved by sparse protrusion arrangement in concave and V-shape channels, while the f/f 0 is only 0.96. The rib-dimple/protrusion arrangement improve the local Nu while significantly deteriorating the overall heat transfer. Comprehensively considering the quantity of heat flux Q, the Coefficient of Performance, Nu/Nu 0 and f/f 0, an excellent cooling performance has been achieved by protrusion arrangement in non-flat channels.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.009
      Issue No: Vol. 126 (2018)
       
  • Heat transfer characteristics of a natural circulation separate heat pipe
           under various operating conditions
    • Authors: Ye Bai; Liang Wang; Shuang Zhang; Ningning Xie; Haisheng Chen
      Pages: 191 - 200
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Ye Bai, Liang Wang, Shuang Zhang, Ningning Xie, Haisheng Chen
      In order to determine the heat transfer performance and the mechanisms of separate heat pipe (SHP) under various operating conditionscovering two-phase states and transcritical states, experimental investigation was carried out in this study. The effect of charging mass, cold bath temperature, heat load and height between evaporator and condenser on heat pipe was analyzed and the thermal resistance was calculated to characterize the heat transfer performance. Results showed that the increase of head load, the decrease of height difference and the increase of condenser temperature led to increases in thermal resistance. Appropriate charging mass was seen to be the most important factor in terms of optimum heat transfer performance, whereas too much or too little charging mass led to the subcooling or superheating in the evaporator, which was found to have a direct impact on heat transfer performance.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.04.130
      Issue No: Vol. 126 (2018)
       
  • Influence of channel scale on the convective heat transfer of CO2 at
           supercritical pressure in vertical tubes
    • Authors: Chen-Ru Zhao; Zhen Zhang; Pei-Xue Jiang; Rui-Na Xu; Han-Liang Bo
      Pages: 201 - 210
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Chen-Ru Zhao, Zhen Zhang, Pei-Xue Jiang, Rui-Na Xu, Han-Liang Bo
      Channel scales vary from several centimeters to several micrometers in various industrial applications that conduct convective heat transfer at supercritical pressures. The heat transfer performance reveals relatively different features even under similar Reynolds number and thermphysical property conditions. The authors investigated the influence of the channel scale on the supercritical convective heat transfer based on the experimental results conducted on vertical tubes with inner diameters of 0.27 mm and 2.0 mm. Numerical simulations using several low Reynolds number k-ε turbulence models were also discussed to evaluate the performance of turbulence models when modelling supercritical heat transfer in tubes of various scales. The results exhibited significant heat transfer deterioration due to flow acceleration effect in the 0.27 mm tube at a heat flux to mass flux ratio of about 0.2, whereas the 2.0 mm tube at a similar inlet Reynolds number and heat flux to mass flux ratio exhibited great heat transfer enhancement due to the buoyancy effect. The heat transfer deterioration in the 0.27 mm tube can be explained by its relation to the redistributed mean velocity profiles and the relatively small energy-containing scale while relatively large dissipation scale as compared to those in the 2.0 mm tube.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.04.080
      Issue No: Vol. 126 (2018)
       
  • Thermal conductivity of hybrid nanofluids: A critical review
    • Authors: Muhammad Usman Sajid; Hafiz Muhammad Ali
      Pages: 211 - 234
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Muhammad Usman Sajid, Hafiz Muhammad Ali
      Innumerable studies are conducted on nanofluids containing single type nanoparticles and attributes of such colloidal mixture have been well elucidated and prospected. Furtherance in nano-composites has entitled production of hybrid nanomaterials (nanoparticles) and remarkable researchers are exploring hybrid nanofluid characteristics. The cardinal objective of this study is to provide a comprehensive review on thermal conductivity of hybrid nanofluids by overviewing experimental, numerical and ANN (artificial neural networking) studies. Assorted factors that affect thermal conductivity such as nanoparticle type, concentration of nanoparticles, types of base fluid, size of nanoparticle, temperature, addition of surfactant, pH variation and sonication time are analyzed in present paper. Additionally, synthesis of hybrid nano-composites, preparation of hybrid nanofluids, approaches for stability measurement and enhancement, methods of thermal conductivity measurement and reasons for thermal conductivity enhancement are discussed. Miscellaneous empirical correlations developed by researchers for thermal conductivity prediction of hybrid nanofluids are also compiled and presented. Results suggest that enhancing temperature and concentration increases thermal conductivity and proper selection of hybrid nanoparticles plays a prime role in attaining stability of hybrid nanofluids.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.021
      Issue No: Vol. 126 (2018)
       
  • Analysis of the interfacial instability and the patterns of rollover in
           multi-component layered system
    • Authors: Wei Sha; Jingjie Ren; Han Zhang; Yaofen Bo; Mingshu Bi
      Pages: 235 - 242
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Wei Sha, Jingjie Ren, Han Zhang, Yaofen Bo, Mingshu Bi
      Rollover was always observed in multi-component system. The effect of initial buoyancy ratio on interfacial instability and the patterns of rollover in two-layer stratified system were researched by means of experiment and simulation. The results indicated that the heat accumulated in bottom layer would be balanced by the cold liquid above the interface as the interface descended. Under lower buoyancy ratio, the interface was easily penetrated by the floating flow along the sidewall, and then W-type field of solute can be observed. With the increase of initial buoyancy ratio, bottom liquid could accumulate more energy, but it was difficult to float directly to the liquid surface. Meanwhile the Y-type and Hourglass-type profiles were presented successively. Therefore it cannot be arbitrarily concluded that the rollover pattern under higher buoyancy ratio was more dangerous in multi-component layered system.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.042
      Issue No: Vol. 126 (2018)
       
  • Influences of the perforation on effective transport properties of gas
           diffusion layers
    • Authors: Wen-Zhen Fang; Yu-Qing Tang; Li Chen; Qin-Jun Kang; Wen-Quan Tao
      Pages: 243 - 255
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Wen-Zhen Fang, Yu-Qing Tang, Li Chen, Qin-Jun Kang, Wen-Quan Tao
      In this paper, the through-plane and in-plane effective transport properties, including permeability, diffusivity and thermal conductivity, of the perforated gas diffusion layer (GDL) are predicted using multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) based on stochastic reconstructed microstructures. When predicting effective thermal conductivities of GDL, the effect of anisotropic conductive property of fibers is considered. The effective transport properties of dry perforated GDL are fitted as a function of perforation diameter and porosity. It is found that the permeability and effective diffusivity of GDL increase with perforation diameter and porosity while the effective thermal conductivity decreases. The two-phase LBM is adopted to simulate water distributions in perforated GDLs, and dependences of effective transport properties on saturation are then obtained. The results show that: the existence of the perforation significantly affects the water transport in hydrophobic perforated GDLs if its diameter is larger than the average pore size of GDL. The effective permeability and diffusivity of GDL decrease while effective thermal conductivity increases with saturation. The effective transport properties of perforated GDLs change less significantly with saturation than those of non-perforated GDL if the water droplet intruding into the perforation is displaced, while change more rapidly with saturation if the water droplet remains inside the perforation.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.016
      Issue No: Vol. 126 (2018)
       
  • A comparative study of passive control on flow structure evolution and
           convective heat transfer enhancement for impinging jet
    • Authors: Xuzhi Du; Zhigang Yang; Zheyan Jin; Chao Xia; Di Bao
      Pages: 256 - 280
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Xuzhi Du, Zhigang Yang, Zheyan Jin, Chao Xia, Di Bao
      The present study experimentally and numerically investigated the passive control on flow structure evolution and convective heat transfer enhancement for impinging jet. Four different impinging jets, including a baseline circular jet (CJ) and three passive controlled jets, i.e., an elliptic jet (EJ), a circular-chevron jet (CCJ) and an elliptic-chevron jet (ECJ), were comparatively analyzed by utilizing the Particle Image Velocimetry (PIV) technique, infrared (IR) thermography and large eddy simulation (LES) over a wide range of jet-to-wall distances ( H / D ) at the jet Reynolds number ( Re ) of 20,000. The results showed that, unlike CJ which presented a general shedding of axisymmetric toroidal vortices, EJ showed highly deformed toroidal structures accompanied with the axis switching effect, both CCJ and ECJ exhibited the well-organized counterrotating streamwise vortex pairs developing from the chevron notches. All the three passive controlled strategies were found to induce a stronger mixing and fluctuating activity near around the stagnation region, especially for ECJ (i.e., the passive–passive controlled device) which showed the highest turbulence level approaching the target wall due to the double-passive enhancement. Moreover, compared with the baseline jet CJ, all the passive controlled jets achieved a significant heat transfer improvement in the vicinity of the stagnation point, particularly for ECJ which presented the highest heat transfer enhancement of about 41% at H / D = 5 . Whereas both CCJ and ECJ were found to exhibit a less-than-ideal heat transfer performance at a small H when the heat transfer uniformity was specifically considered, due to the anisotropic thermal imprint distributions.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.01.061
      Issue No: Vol. 126 (2018)
       
  • An iterative finite-element algorithm for solving two-dimensional
           nonlinear inverse heat conduction problems
    • Authors: Mattia Bergagio; Haipeng Li; Henryk Anglart
      Pages: 281 - 292
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Mattia Bergagio, Haipeng Li, Henryk Anglart
      It is often useful to determine temperature and heat flux in multidimensional solid domains of arbitrary shape with inaccessible boundaries. In this study, an effective algorithm for solving boundary inverse heat conduction problems (IHCPs) is implemented: transient temperatures on inaccessible boundaries are estimated from redundant simulated measurements on accessible boundaries. A nonlinear heat equation is considered, where some of the material properties are dependent on temperature. The IHCP is reformulated as an optimization problem. The resulting functional is iteratively minimized using a conjugate gradient method together with an adjoint (dual) problem approach. The associated partial differential equations are solved using the finite-element package FEniCS. Tikhonov regularization is introduced to mitigate the ill-posedness of the IHCP. The accuracy of the implemented algorithm is assessed by comparing the solutions to the IHCP with the correct temperature values, on the inaccessible boundaries. The robustness of our method is tested by adding Gaussian noise to the initial conditions and redundant boundary data in the inverse problem formulation. A mesh independence study is performed.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.04.104
      Issue No: Vol. 126 (2018)
       
  • Review on flow boiling of refrigerants R236fa and R245fa in mini and micro
           channels
    • Authors: Stanislawa Sandler; Bartosz Zajaczkowski; Zbigniew Krolicki
      Pages: 591 - 617
      Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part A
      Author(s): Stanislawa Sandler, Bartosz Zajaczkowski, Zbigniew Krolicki
      Flow boiling in mini and micro channels is considered to be one of the most efficient cooling solutions for mobile devices and electronic components. Cooling systems relying on flow boiling should be able to work efficiently in a wide range of operating conditions including saturation temperature. Employing refrigerants characterized by low saturation pressures assure lightweight structure of the cooling system even at high operating temperatures. Therefore, this article focuses on two low-pressure refrigerants R236fa and R245fa (refrigerants which are characterized by low saturation pressures corresponding to high saturation temperatures) with special emphasis on the influence of saturation temperature on flow boiling characteristics. It presents a detailed review on the most recognized heat transfer models during flow boiling and an experimental database on R236fa and R245fa covering channel hydraulic diameters ranging from 0.1 to 3 mm, mass fluxes from 42 to 2500 kg/m2/s, and wall heat fluxes varying between 6.5 and 422.7 kW/m2. The covered vapor qualities range from −0.09 to 1.14 (which translates into subcooled, saturated and superheated flows) and reference saturation temperatures vary between 14 and 120 °C. Subcooling at the heat exchanger inlet changes from 0 to 19 K. The amassed experimental data are compared with the results obtained from 24 theoretical models on flow boiling. The models follow additive, asymptotic, Nusselt-type and phenomenological approaches. The accuracy of the models is assessed on the basis of Mean Absolute Percentage Error MAPE and standard deviation σ SD . The additive models of Saitoh et al. with MAPE = 27.4 % and σ SD = 43.8 % , Chen with MAPE = 28.6 % and σ SD = 35.8 % and an Nusselt-type correlation of Sun and Mishima with MAPE = 28.4 % and σ SD = 43.4 % exhibit the best accuracy. The amassed database allowed determination of the range of experimental conditions that need further scientific investigation. Review on heat transfer models together with results of comparison between the models and experimental data allowed identification of the most problematic aspects of modeling flow boiling in mini and micro channels.

      PubDate: 2018-05-28T02:49:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2018.05.048
      Issue No: Vol. 126 (2018)
       
  • Bubble breakup and coalescence models for bubbly flow simulation using
           interfacial area transport equation
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Hang Liu, Takashi Hibiki
      This paper provides the state-of-the-art critical review on the modeled source and sink terms of the one-group interfacial area transport equation. The reviewed source and sink terms include models developed by Wu et al., Hibiki and Ishii, Hibiki et al., Yao and Morel, Park et al., Hibiki et al., Kataoka et al., Nguyen et al., Shen and Hibiki and Hazuku et al. The present critical review assesses major issues in modeling the one-group source and sink terms. Important conclusions are that the existing source and sink terms are not well-validated for developing and transient flows and the applicability of the source and sink terms to high pressure conditions such as prototypic nuclear reactor conditions has not been well-discussed. In view of these, coefficients of the source and sink terms in Hibiki and Ishii’s model have been modified for their application to prototypic nuclear reactor conditions. In addition, approximated area-averaged source and sink terms due to turbulent diffusion and lateral migration are derived by area-averaging local source and sink terms due to turbulent diffusion and lateral migration developed by Kataoka et al. The role of the area-averaged source and sink terms due to turbulent diffusion and lateral migration on the interfacial area transport should be tested in a future study. This paper also overviews important model validation challenges to be addressed in a future study. The challenging model validation should address the model performance for various test sections and flow conditions. They are (1) the effect of channel size (small (or micro/mini)-to-large channels) on the interfacial area transport, (2) the scalability of the interfacial area transport equation to prototypic nuclear reactor conditions, (3) the effect of covariance due to phase distribution on the interfacial area transport, (4) the effect of inlet conditions on the interfacial area transport, (5) the applicability of the interfacial area transport equation to transient and developing flow conditions, and (6) the applicability of the interfacial area transport equation to various flow channels including a rod bundle.

      PubDate: 2018-06-18T19:52:16Z
       
  • Combined effects of magnetohydrodynamic and temperature dependent
           viscosity on peristaltic flow of Jeffrey nanofluid through a porous
           medium: Applications to oil refinement
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): W.M. Hasona, A.A. El-Shekhipy, M.G. Ibrahim
      Viscosity is an essential parameter of fluid physical properties for assaying the heat transfer when designing a nanofluid system. For this purpose, this article investigates the effect of temperature dependent viscosity on the peristaltic flow of Jeffrey nanofluid in an asymmetric channel. For peristaltic literature, this model is progressed for the first time. This model of nonlinear partial differential equation is reformulated under the assumption of long wavelength and low Renolds number, and solved semi-analytically with the aid of multi-step differential transform method (Ms-DTM). Semi-analytical solutions have been evaluated for the pressure gradient as well as the distributions of velocity, temperature and nanoparticles concentration. Moreover, numerical integration is also operated to assess the expressions for pressure rise. Two cases of temperature dependent viscosity are deliberated. Case (I), all non-dimensional parameters that are functions of viscosity, have been regarded as constant within the flow. Case (II), these acknowledged parameters are then supposed to vary with temperature. We have made a detailed comparison between the two cases, and unrealistic results have been found, although case (II) accepts the experimental results. Excellent agreements are found between the semi-analytical results of the present paper and the existing published results, by taking ( β = 0 ) and Da = ∞ . In case (II), decrement in variable viscosity parameter β cause to enlarge the temperature of fluid. As the molecules of oil, the increase in temperature acquire it more energy and make them moves more freely, which is the main idea of crude oil refinement, where crude oil is converted and refined into more desirable products such as petroleum naphtha, gasoline, kerosene and heating oil.

      PubDate: 2018-06-18T19:52:16Z
       
  • Constructal optimization for line-to-line vascular based on entropy
           generation minimization principle
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Hannan Shi, Zhihui Xie, Lingen Chen, Fengrui Sun
      Constructal optimizations of the first to fifth order line-to-line vascular channels (LVCs) with convective heat transfer are carried out in this paper by taking minimum entropy generation rate (EGR) and minimum entropy generation number (EGN) as the optimization objectives, respectively. The angles of the LVCs are taken as the optimization variables, and the fixed vascular channel areas and total volumes of LVCs are taken as the constraints. The optimal constructs corresponding to minimum EGR and minimum EGN are obtained, respectively. The influences of the mass flow rate (MFR) on the optimal results are analyzed. The results show that the EGR of the LVCs decreases when the angle freedom increases with the constant dimensionless MFR, which is more obvious when the order increases. When the order increases, the EGR increases but the EGN decreases. Both the EGR and the EGN increase with the increase of the dimensionless MFR. The results obtained herein can provide some thermal design and management guidelines for the applications of LVCs.

      PubDate: 2018-06-18T19:52:16Z
       
  • Determination of the thermal cycle during flash lamp annealing without a
           direct temperature measurement
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): L. Rebohle, M. Neubert, T. Schumann, W. Skorupa
      Flash lamp annealing (FLA) is a modern annealing technique which, starting from microelectronics, has spread over new application areas like flexible electronics, photovoltaics or thin film deposition. Because of the short annealing time in the range of milliseconds and below, FLA allows the suppression of unwanted processes like diffusion, the annealing of temperature-sensible substrates, and the saving of process time and energy. In addition, it is predestined for roll-to-roll applications. However, the determination of the thermal cycle during FLA is challenging. The existing methods for a direct temperature measurement, mostly based on pyrometry, are elaborate and have to solve the problem to detect thermal radiation against the background of the intense flash light. An alternative way is simulation, but now an extended knowledge about the flash and the material system to be flashed is needed. In this work we describe a methodology to determine the thermal cycle during FLA without the need for a direct temperature measurement. This methodology is based on an optical-thermodynamic simulation and calibration experiments which can be implemented with reasonable effort under certain assumptions. The simulation considers not only the properties of the flash and the sample, but also the reflectivity of the chamber walls. Finally, the pros and cons of this methodology are shortly discussed.

      PubDate: 2018-06-18T19:52:16Z
       
  • Thermal performance characteristics of a pulsating heat pipe at various
           nonuniform heating conditions
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Dong Soo Jang, Hyun Joon Chung, Yongseok Jeon, Yongchan Kim
      A pulsating heat pipe (PHP) is an excellent cooling device based on the phase change of a working fluid. However, the performance of the PHP can be degraded by nonuniform heating conditions in the evaporator section. The objective of this study is to investigate the thermal performance characteristics of a PHP at various nonuniform heating conditions. The thermal performance of the PHP is measured by varying the dimensionless heat difference from 0 to 0.3, heat input from 30 to 100 W, and filling ratio from 50% to 70%. As a result, the optimal filling ratios for the best PHP performance and reliability are determined to be 50%, 60%, and 70%, at the dimensionless heat differences of 0, 0.2, and 0.3, respectively. In addition, the thermal resistance and evaporator temperature difference of the PHP increase with an increase in the dimensionless heat difference owing to the decreased driving force. Finally, contour maps for the effective thermal conductivity are proposed to provide design guides of PHPs.

      PubDate: 2018-06-18T19:52:16Z
       
  • Flow boiling of water and emulsions with a low-boiling disperse phase in
           minichannels
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): B.M. Gasanov
      The paper presents the results of an experimental investigation of heat transfer at flow boiling of water and n-pentane/water and freon-11/water emulsions in a horizontal minichannel with a hydraulic diameter of 1.1 mm. The flow conditions of two-phase flows have been visualized at the exit from an evaporator with the use of high-speed video filming. At bubble and slug flow conditions of a two-phase flow the mean coefficient of heat transfer from the channel wall to emulsions has proved to be higher than to water. The results of a synchronous measurement of variations in the liquid temperature at the channel inlet and outlet and the excess pressure in the system at the instability of a two-phase flow have been examined.

      PubDate: 2018-06-18T19:52:16Z
       
  • Optimization of skin cooling by computational modeling for early
           thermographic detection of breast cancer
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Yan Zhou, Cila Herman
      The purpose of this study is to enhance the early detection of breast cancer using dynamic infrared (IR) imaging by optimizing thermostimulation with cooling stress to improve thermal contrast. A 2D hemispherical breast model was built to compute steady-state and transient surface temperature profiles for tumors of different size (10–30 mm), depth (6.6–26.6 mm) and location (15°–90°). Larger tumors and tumors closer to the skin surface leave sufficiently large thermal signatures (∼0.6 °C) to be detected by steady state IR imaging. Smaller and deeper tumors in the middle and bottom portion of the gland, with thermal contrasts below 0.1 °C, require dynamic imaging with thermostimulation (cooling) to achieve satisfactory thermal contrast for IR detection. In this paper, we consider cooling times of 15–25 min and cooling temperatures of 5–15 °C to optimize thermal contrast. Cooling penetration depths during the cooling phase for constant temperature cooling at 5 °C, 10 °C and 15 °C were analyzed. To achieve the maximum thermal contrast for deeper and smaller tumors, the tissue should be cooled 5–15 min, and in the maximum thermal contrast of the thermal recovery phase appears after 20–45 min. Effects of tumor size and depth on maximum thermal contrast were analyzed systematically to provide recommendations and guidelines for clinical applications. Thermal signatures computed in this study provide valuable data for inverse reconstruction algorithms that allow the measurement of tumor properties, such as the metabolic heat generation rate.

      PubDate: 2018-06-18T19:52:16Z
       
  • Numerical study of steam condensation inside a long, inclined, smooth tube
           at different saturation temperatures
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): S.M.A. Noori Rahim Abadi, M. Mehrabi, Josua P. Meyer
      In this study, the effects of the inclination angle on the heat transfer coefficients and on pressure drops were investigated numerically, during the process of development of heat condensation inside a long smooth tube, at different saturation temperatures. The simulation model included a smooth tube with a diameter of 18 mm and a length of 7.2 m. The imposed inclinations varied between −60° (downward flow) to +60° (upward flow). Moreover, the saturation temperatures varied between 40 °C and 70 °C. The flow field was assumed to be three-dimensional, unsteady, and turbulent. The Volume of Fluid (VOF) multiphase flow method was utilised to solve the governing equations comprising mass, momentum, energy, and turbulence equations, along with phase change rates. The simulation results were in good agreement with the experimental data. The results showed that the condensation heat transfer coefficient first increased and then decreased along the length of the tube. Furthermore, it was noted that the condensation heat transfer coefficient and pressure drop decreased when the steam saturation temperature increased.

      PubDate: 2018-06-18T19:52:16Z
       
  • Condensation heat transfer characteristics of low-GWP refrigerants in a
           smooth horizontal mini tube
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Qiang Guo, Minxia Li, Haoxiang Gu
      In this paper, a comprehensive study on heat transfer coefficient (HTC) and pressure drop of the two-phase condensation for R1234ze(E), R290, R161 and R41 were obtained in a smooth horizontal tube with 2 mm inner diameter, for these refrigerants being considered as environmentally friendly working fluid candidates in refrigeration and air conditioning systems. HTCs of R32 and R134a were also investigated as a baseline in this study. Condensation temperatures were from 35 °C to 45 °C. The mass flux ranged from 200 kg/m2·s to 400 kg/m2·s and the heat flux from 8 to 30 kW/m2. The results show that with the increasing saturated temperature and heat flux, the condensation heat transfer coefficients decrease, the HTCs of R161 are the highest while those of R1234ze(E) are the lowest at the same working condition. The pressure drop decreases while the saturation temperature rises. The predicted values of HTCs by 7 models were compared with experimental data. The results show that although different models are suitable for different refrigerants, Koyama et al.’s model is prevailing over other models for most refrigerants. On the basis of Koyama et al.’s model, a modified ϕ v correlation with Weber number was taken into consideration and the revised model shows an improved prediction accuracy.

      PubDate: 2018-06-18T19:52:16Z
       
  • Design and analysis of a gas heating/cooling sorption refrigeration system
           with multi-salt solid sorbent of CaCl2 and MnCl2
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): J. Gao, L.W. Wang, P. Gao, G.L. An, H.T. Lu
      Multi-salt sorbents were reported with better performance than single salt sorbents because they could reduce the sorption hysteresis phenomena, but such type of sorbents have not been utilized in the refrigeration systems. In this paper, a gas heating/cooling sorption refrigeration system with multi-salt sorbent of CaCl2/MnCl2 is designed and analyzed, and the results show the maximum SCP gets to about 330 W kg−1. The system is proposed for refrigerated truck transport and it makes the structure much simpler than the previous two-stage refrigeration system because only one sorption bed is required. The critical conditions, such as low heat transfer coefficient of exhaust gas and cooling air as well as high cooling temperature in hot summer, are considered. The sorption bed with a tri-pass structure for exhaust gas is compared with the tetra-pass design, and it shows better performance for that the pressure drop of the modularized sorption bed is only about 380 Pa when the air flow rate is 600 m3 h−1, and the engine performance won’t be affect if such a bed is installed at the outlet of exhaust pipe of the truck. The heat transfer performance of the bed with tri-pass for exhaust gas is analyzed by the experimental system set up in the lab, and it has a heat transfer rate of about 60 kW/m3 sorption bed during the desorption process, which is about 2.3 times that of the conventional liquid heating/cooling system. The preliminary test results show that the volumetric refrigeration capacity gets to about 19 kW m−3, increasing by almost 30% when compared with the liquid heating/cooling system.

      PubDate: 2018-06-18T19:52:16Z
       
  • An investigation on convective heat transfer performance around
           piezoelectric fan vibration envelope in a forced channel flow
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Xin-Jun Li, Jing-zhou Zhang, Xiao-ming Tan
      An experimental and numerical investigation is performed in the current study to further explore the convective heat transfer performance by a vertically-oriented piezoelectric fan in the presence of channel flow. The effects of velocity ratio and fan tip-to-heated surface clearance are taken into considerations. It is illustrated that the presence of channel flow has an innegligible influence on the vibration amplitudes of the piezoelectric fan under large channel flow velocities. In the presence of channel flow, the vortical structures at the edges of vibrating fan are certainly suppressed, especially under large velocity ratios. On the other hand, the vortical streaming flow mixes with the channel flow to form a long stripe of vortical structure downstream of the fan vibration envelope. Under small velocity ratios, the impingement role of streaming flow along fan tip is still dominated and simultaneously the channel flow passing through the vibration envelope is effectively pulsated. Therefore, combined flows generally produce heat transfer enhancement around the fan vibration envelope related to the pure vibrating fan, especially at a small non-dimensional tip-to-surface gap. While under large velocity ratios, the impingement role of streaming flow induced by a vibrating fan is seriously weakened by the strong channel flow. The convective heat transfer produced by combined flows in the fan vibration envelope is generally reduced in comparison with pure piezoelectric fan. Related to the pure channel flow, the combined flows effectively improve the convective heat transfer, especially downstream of the fan vibration envelope.

      PubDate: 2018-06-18T19:52:16Z
       
  • Constructal design of a semi-elliptical fin inserted in a lid-driven
           square cavity with mixed convection
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): A.L. Razera, R.J.C. da Fonseca, L.A. Isoldi, E.D. dos Santos, L.A.O. Rocha, C. Biserni
      The present study is focused on the geometric optimization, according to Constructal Design, of a semi-elliptical morphing fin, i.e. a fin that can vary its dimensions, inserted into a lid-driven square cavity under mixed convection. The fluid flow is considered incompressible, two-dimensional, laminar and at the steady state. Conservation equations of mass, momentum and energy are solved numerically by means of the Finite Volume Method. Moreover, buoyancy forces are modeled with Boussinesq approximation. The main purpose here is to maximize the dimensionless heat transfer rate between the heated fin and the surrounding flow for different Reynolds (ReH  = 10, 102 and 103) and Rayleigh (RaH  = 103, 104, 105 and 106) numbers keeping constant the Prandtl number (Pr = 0.71). The studied domain has two constraints (areas of fin and cavity) and one degree of freedom given by the aspect ratio between the height and length of the fin (H 1/L 1), which is evaluated in three different surfaces of the cavity and four different area fractions of the fin. Results showed that the optimal configurations presented a gain in the thermal performance on the order of 40% in relation to other geometries. Finally, it is worth to mention that the optimal shapes here discovered are highly influenced by Reynolds and Rayleigh numbers.

      PubDate: 2018-06-18T19:52:16Z
       
  • Evolution to chaotic natural convection in a horizontal annulus with an
           internally slotted circle
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): M. Zhao, D.M. Yu, Yuwen Zhang
      The characteristics of transition from laminar to chaotic natural convection in a two-dimensional horizontal annulus with an internally slotted circle is analyzed using Lattice Boltzmann method (LBM). The aim of this paper is to identify the route(s) to chaos, and to illustrate the dynamical response of the flow with the change of the control parameter (Ra). The results obtained for a range of the Rayleigh number, Ra, from 5 × 103 to 2 × 106 at Pr = 0.71, and the slot degree, S f, from 0.1 to 0.4. The numerical results show that slot ratio, slot configuration, and Rayleigh number are influential to oscillation phenomenon in this model; the flow inside the annulus may be: (1) a stable base-two-cells regime, (2) a multi-cellular flow with four-stable-symmetrical-secondary cells regime, (3) a multi-cellular flow with four-oscillatory-secondary cells regime, and (4) an asymmetrical oscillation regime. The results also show that the oscillatory flow undergoes several bifurcations and ultimately evolves to a chaotic flow after the first bifurcation. In addition, certain features of nonlinear dynamical systems like bifurcation, self-sustained oscillations are also observed. The simulation results also show that slot degree S f is relevant to oscillations. Furthermore, with the larger slotted ratio, the flow is more unstable, and the configuration with top and bottom slot seems to be the most unstable among the given four models.

      PubDate: 2018-06-18T19:52:16Z
       
  • Quantitative analysis of anti-freezing characteristics of superhydrophobic
           surfaces according to initial ice nuclei formation time and freezing
           propagation velocity
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Junghan Kim, Jaehyeon Jeon, Dong Rip Kim, Kwan-Soo Lee
      In order to quantitatively analyze the anti-freezing characteristics of superhydrophobic and bare surfaces, the freezing delay properties of the surfaces were experimentally investigated under various operating conditions by placing sessile droplets on their surface. The freezing delay time was calculated using the experimental results and analyzed by employing a stochastic method. The formation time of initial ice nuclei and freezing propagation velocity at a macroscopic level were proposed as measures of surface anti-freezing characteristics. The anti-freezing properties of the bare and superhydrophobic surfaces were analyzed using the proposed quantitative measures. Consequently, the tendency of quantitative results was consistent with that of the qualitative ones according to the changes of the operating conditions (air inlet velocity, relative humidity, and surface temperature). Moreover, the superior anti-freezing performance of the superhydrophobic surface was quantitatively confirmed by the initial ice nuclei formation time, which was delayed by 22–92%, and the freezing propagation velocity, which decreased by 17–30%.

      PubDate: 2018-06-18T19:52:16Z
       
  • Flow pattern transition and destabilization mechanism of thermocapillary
           convection for low Prandtl number fluid in a deep annular pool with
           surface heat dissipation
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Li Zhang, You-Rong Li, Chun-Mei Wu, Qiu-Sheng Liu
      In order to understand clearly the flow pattern transition and the destabilization mechanism of thermocapillary convection for low Prandtl number fluids in a deep annular pool with surface heat dissipation, we carried out a series of three-dimensional numerical simulations by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are respectively fixed at 0.5 and 1.0. Prandtl number of the working fluid is 0.011. Because the total heat dissipation coefficient on the free surface for low Prandtl fluids is small, Biot number is varied from 0 to 1.0. Results indicate that thermocapillary convection experiences the transitions from axisymmetric steady state flow into three-dimensional steady flow, and then into three-dimensional oscillation flow with the increase of Marangoni number. The critical Marangoni number of flow pattern transition decreases slightly with the increase of Biot number, and the maximum temperature and velocity fluctuations appear near the lower part of outer wall. The azimuthal temperature fluctuation on the free surface gradually shrinks to the inner wall, and the temperature fluctuation region decreases. However, it remains almost unchanged near the bottom of the annular pool, but the fluctuation amplitude increases.

      PubDate: 2018-06-18T19:52:16Z
       
  • Nanofluid heat transfer augmentation and exergy loss inside a pipe
           equipped with innovative turbulators
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): M. Sheikholeslami, M. Jafaryar, S. Saleem, Zhixiong Li, Ahmad Shafee, Yu Jiang
      Exergy variations for forced convection of nanofluid through a pipe equipped with twisted tape turbulators have been simulated via Finite volume method. Roles of height ratio, pitch ratio and Reynolds number on variation of nanofluid hydrothermal treatment, second law efficiency ( η II ) and exergy loss ( X d ) were presented. Suitable formulas for ( X d ) and ( η II ) are provided. Results reveal that exergy drop reduces with enhance of Reynolds number and height ratio. Second law performance rises with augment of height ratio while it reduces with augment of pitch ratio.

      PubDate: 2018-06-18T19:52:16Z
       
  • Natural convection in a square enclosure with different positions and
           inclination angles of an elliptical cylinder Part I: A vertical array of
           one elliptical cylinder and one circular cylinder
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Seong Hyun Park, Yeong Min Seo, Man Yeong Ha, Yong Gap Park
      This paper numerically investigates the two-dimensional natural convection in a square enclosure with a vertical array of a hot elliptical cylinder and a hot circular cylinder with Rayleigh numbers in the range of 10 4 ⩽ Ra ⩽ 10 6 . An immersed boundary method was used to capture the wall boundary of the cylinders. The effects of the position and inclination angle ϕ of the elliptical cylinder were investigated. When the Rayleigh number increases to Ra = 106, the numerical solutions reach an unsteady state for all cases of the lower elliptical cylinder and the cases of the upper elliptical cylinder except at ϕ = 90 ° . The transition of the flow regime from unsteady state to steady state depends on the flow direction and the space between the upper cylinder and top wall of the enclosure due to the changes in the inclination angle of the elliptical cylinder. At Ra = 106 in the case of upper elliptical cylinder at ϕ = 0 ° , the time- and surface-averaged Nusselt numbers for the walls of the enclosure increase by about 1.99% compared to the case of two circular cylinders. The thermal performance and flow stability were influenced by the position and inclination angle of the elliptical cylinder.

      PubDate: 2018-06-18T19:52:16Z
       
  • Natural convection of Al2O3/H2O nanofluid in an open inclined cavity with
           a heat-generating element
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Igor V. Miroshnichenko, Mikhail A. Sheremet, Hakan F. Oztop, Nidal Abu-Hamdeh
      Free convection of alumina-water nanofluid in a tilted open cavity with a heat-generating solid element has been studied. The considered topic allows understanding an opportunity of nanofluids for cooling of the heat-generating elements in open cavities. Upper border is supposed to be open where nanofluid penetrates into the cavity. Simulation has been performed using the Oberbeck–Boussinesq equations formulated in non-dimensional stream function, vorticity and temperature. Finite difference method of the second order accuracy has been applied. The effects of cavity inclination angle (0≤γ≤π/2), heater location (0.1≤δ≤0.7, where δ is the dimensionless distance between the heater and left wall) and nanoparticles volume fraction (0≤ϕ≤0.04) have been analyzed. It has been found that the considered parameters allow minimizing average heater temperature. The cavity inclination angle of π/3 characterizes the heat transfer enhancement (average Nusselt number has the maximum value), while the heater average temperature has the minimum value. At the same time, a proximity of the heater to the cavity wall characterizes non-essential cooling of the heat-generating element. The most effective cooling of the heat-generating element occurs for central heater location with cavity inclination angle of π/3. The considered alumina-water nanoparticles do not allow to intensify the cooling process for the heater element.

      PubDate: 2018-06-18T19:52:16Z
       
  • Effects of film cooling hole locations on flow and heat transfer
           characteristics of impingement/effusion cooling at turbine blade leading
           edge
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Junfei Zhou, Xinjun Wang, Jun Li, Yandong Li
      In order to investigate the effects of the film cooling hole locations on the flow and heat transfer characteristics of the impingment/effusion cooling, the film cooling holes are established on a concave target channel with three inclined angle (0°, 30°, 60° between film cooling hole axis and jet hole axis). The film cooling holes are both in-line and staggered arranged with jet holes when the inclined angle is 30° and 60° and only staggered arranged when the inclined angle is 0°. The film extraction flow distributions, static pressure development, total pressure drop, overall averaged Nusselt number and combined thermal performance are compared among different cases. The development of vortex and cross flow inside the target channel in different cases are studied and compared. The span averaged Nusselt number, Nusselt number contour on the target surface and Nusselt number distribution at several cross sections are studied and compared. Results show that the location of the film cooling holes affects the flow distributions of the film extraction air and the flow development inside the target channel. The heat transfer performance inside the target channel is affected by the impinging effect and the development of the cross flow and vortices.

      PubDate: 2018-06-18T19:52:16Z
       
  • Dynamic of plumes and scaling during the melting of a Phase Change
           Material heated from below
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Santiago Madruga, Jezabel Curbelo
      We identify and describe the main dynamic regimes occurring during the melting of the PCM n-octadecane in horizontal layers of several sizes heated from below. This configuration allows to cover a wide range of effective Rayleigh numbers on the liquid PCM phase, up to ∼ 10 9 , without changing any external parameter control. We identify four different regimes as time evolves: (i) the conductive regime, (ii) linear regime, (iii) coarsening regime and (iv) turbulent regime. The first two regimes appear at all domain sizes. However the third and fourth regime require a minimum advance of the solid/liquid interface to develop, and we observe them only for large enough domains. The transition to turbulence takes places after a secondary instability that forces the coarsening of the thermal plumes. Each one of the melting regimes creates a distinct solid/liquid front that characterizes the internal state of the melting process. We observe that most of the magnitudes of the melting process are ruled by power laws, although not all of them. Thus the number of plumes, some regimes of the Rayleigh number as a function of time, the number of plumes after the primary and secondary instability, the thermal and kinetic boundary layers follow simple power laws. In particular, we find that the Nusselt number scales with the Rayleigh number as Nu ∼ Ra 0.29 in the turbulent regime, consistent with theories and experiments on Rayleigh-Bénard convection that show an exponent 2 / 7 .

      PubDate: 2018-06-18T19:52:16Z
       
  • Analysis of mixed convection flow in an inclined lid-driven enclosure with
           Buongiorno’s nanofluid model
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Qiang Yu, Hang Xu, Shijun Liao
      The laminar mixed convection flow in an inclined lid-driven cavity filled with a nanofluid is investigated in the presence of internal heat generation. The two sidewalls of the enclosure are sinusoidally heated while the top and bottom walls are insulted. The Buongiorno’s model that incorporates the effects of Brownian motion and thermophoresis is applied to describe the nanofluid behaviours. Parametrical studies are given on the regimes of the complex flow, temperature and concentration fields. The developed equations are nondimensionalized and then solved numerically by the newly developed wavelet-homotopy technique. Comparisons with previously studies in literature are presented and found to be in excellent agreement. The results of this work indicate that the Grashof number, the slipping parameters, the nanoparticles related parameters, the inclination, the boundary coefficients including amplitude ratios of temperature and concentration, as well as the phase deviation have significant effects on characteristics of the cavity flow.

      PubDate: 2018-06-18T19:52:16Z
       
  • Investigation on the temperature dependence of filling ratio in cryogenic
           pulsating heat pipes
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Xiao Sun, John Pfotenhauer, Bo Jiao, Luis Diego Fonseca, Dongyang Han, Zhihua Gan
      The pulsating heat pipe (PHP) is an efficient two-phase heat transfer device. Its heat transfer performance and internal working fluid flow patterns are affected by a variety of parameters. The filling ratio (FR) is one of the most important parameters, and it is usually regarded as a temperature-independent constant during the operation of the PHP. In this study, the fact that the FR is temperature dependent is pointed out, recognizing that the specific volumes of the liquid working fluid and vapor working fluid change with temperature. FR lines on a T-v diagram are used to analyze the trend of the FR with temperature. Also the influence of the variation of the FR on the heat transfer performance is discussed with the experimental data obtained from a hydrogen-filled PHP and a helium-filled PHP. For a cryogenic PHP, the optimal FR is close to the critical FR, and different initial FRs cause the PHP to either reach a dry-out limit or reach a liquid convection limit. Moreover, the temperature dependence of the FR for room temperature fluids can be ignored.

      PubDate: 2018-06-18T19:52:16Z
       
  • Effect of fin shape on the thermal performance of nanofluid-cooled micro
           pin-fin heat sinks
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Tehmina Ambreen, Man-Hoe Kim
      The study presents the combined effects of using nanofluid and varying fin cross-sectional shape on the heat transfer characteristics of a micro pin-fin heat sink by employing discrete phase model (DPM). Three fins configurations of the square, circular and hexagon cross-section with constant fin diameter and height have been analyzed for the inline arrangement of 17 × 34 fins. Aqueous nanofluid containing spherical shaped particle dispersions of TiO 2 has been simulated for the particle concentration and size of 4.31 vol% and 30 nm respectively. Constant heat flux (192 W) boundary condition at the base of heat sink has been considered for the range of Reynolds number 250 ≤ Re ≤ 550. The influence of fin shape on the thermal efficiency of the heat sink has been analyzed by evaluating heat sink base temperature, Nusselt number, convective heat transfer coefficient distribution and temperature contours along the surface of the heat sink. Additionally the velocity streamlines and contours have also displayed to elaborate the fluid flow attributes. Results demonstrate that under identical flow conditions, the nanofluid cooled circular fins displayed most efficient thermal performance followed by the hexagon and square fins. While the water cooled square fins depicted lowest heat transfers characteristics. The best thermal performance of the circular fins is the response of the delayed flow separation along the smooth surface of fins and the subsequent uniform flow distribution along the whole sink. For all the cases, upstream fin rows played a primary contribution in flow distribution and hence thermal characteristics of the heat sink.

      PubDate: 2018-06-18T19:52:16Z
       
  • Thermal characteristic and analysis of closed loop oscillation heat
           pipe/phase change material (CLOHP/PCM) coupling module with different
           working media
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Jiateng Zhao, Jie Qu, Zhonghao Rao
      Aimed to understand the thermal characteristic of closed loop oscillation heat pipe/phase change material (CLOHP/PCM) coupling module filled with different working media for thermal energy storage and thermal management application, experimental investigation on the heat charge and discharge process of the coupling module under different conditions was carried out. The main result shows that the CLOHP filled with self-rewetting fluid (SRWF) and not placed horizontally has better thermal transfer performance relative to the water case as the heat load is low. But, the CLOHP filled with water has better thermal transfer performance than the SRWF case in horizontal condition especially under low heat load. The rise speed of temperature in the heating section increases when the phase transition completes. The highest temperature of the PCM locates in the middle region. Standard deviation (STD) of PCM temperature keeps relative stable for a long time and then increases rapidly and the rise speed has a positive correlation with the heat load. The uniformity of PCM temperature has been greatly improved for those three cases compared to that without working medium. During the discharge process, the fluctuation occurs only when the temperature of evaporation exceeds about 60 °C.

      PubDate: 2018-06-18T19:52:16Z
       
  • Parametric study on the hydrocarbon fuel flow rate distribution and
           cooling effect in non-uniformly heated parallel cooling channels
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Yuguang Jiang, Jiang Qin, Khaled Chetehouna, Nicolas Gascoin, Wen Bao
      Advanced aero-engines with higher flying Mach number, like SCRamjets, offer good solution to the hypersonic propulsion. However, the thermal boundary condition of the engine cooling channels is normally non-uniform, which may cause fuel mal-distribution. Serious fuel cooling capacity waste and even over-temperature may occur. To ensure the reasonable flow distribution and wall temperature, a parametric study of the cooling channel geometries is conducted under non-uniform thermal boundary condition. A 3D numerical model considering the flow and heat transfer under supercritical pressure in parallel cooling channels is developed and validated. The results indicate that the flow distribution and cooling effect both improve with the reasonable design of the channel geometry. Higher aspect ratio (AR) improves the flow distribution and cooling effect. The variations of rib thickness and total channel flow area show greater impact on the heat transfer performance than on the flow distribution. At last, the results of channel geometry optimization are validated under different heat flux distributions. It can be concluded that the channel geometry optimization in this work improves the flow distribution and lowers the wall temperature, which provides reference for the design of cooling channels in aero-engines like SCRamjets.

      PubDate: 2018-06-18T19:52:16Z
       
  • A renovated Buongiorno’s model for unsteady Sisko nanofluid with
           fractional Cattaneo heat flux
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Ming Shen, Lili Chen, Mengchen Zhang, Fawang Liu
      A renovated Buongiorno’s model with fractional differential equation is proposed to investigate the heat and mass transfer characteristics of Sisko nanofluid over a continuously moving flat plate. The fractional Cattaneo heat flux is introduced to describe the anomalous heat transport of Sisko nanofluid considering the influences of Brownian diffusion and thermophoresis. The governing boundary layer equations of continuity, momentum, energy and concentration are reduced by dimensionless variable and solved numerically. The quantities of physical interest are graphically presented and discussed in detail. It is found that the renovated model with Caputo time fractional derivatives is more capable to explain the abnormal thermal conductivity enhancement, which is also able to describe the influence of memory on the nanofluid behavior. Results indicate that the heat and mass transfer ability of Sisko nanofluid is reduced by the temperature fractional derivative parameter in both cases of shear thinning and shear thickening. Moreover, the rise of temperature fractional derivative parameter results in a significant increase of the average Nusselt number and a slight decrease of the average Sherwood number.

      PubDate: 2018-06-18T19:52:16Z
       
  • Experimental investigation of the effects of mass fraction and temperature
           on the viscosity of microencapsulated PCM slurry
    • Abstract: Publication date: November 2018
      Source:International Journal of Heat and Mass Transfer, Volume 126, Part B
      Author(s): Krzysztof Dutkowski, Jacek Jan Fiuk
      The use of microencapsulated phase change materials (mPCM) is one of the most efficient ways of storing thermal energy. Microencapsulated phase change slurry (mPCM slurry) is formed when the microencapsulated phase change material is dispersed into the carrier fluid. The mPCM slurry can be used as a heat transfer medium. This paper details an experimental study that was performed to investigate rheological properties of microencapsulated phase change slurry (Micronal® DS 5039 X – water). Six samples of mPCM slurry were prepared with different mass ratios of mPCM to water, namely: 10:90, 30:70, 50:50, 70:30, 90:10, 100:0 (pure Micronal® DS 5039 X). The dynamic viscosity-shear rate curves were obtained for spindle speeds from 0.01 to 100 rpm (shear rate 0.0132–132.00 s−1 respectively). The steady state measurement of viscosity was carried out when the slurry reached constant temperatures, namely: 10.0; 15.0, 17.5, 20.0, 22.5, 25.0, 27.5, 30.0, 40.0 and 50.0 °C. The dynamic viscosity of slurries increases with the mPCM concentration in dispersion rises. Only the sample of 10% mPCM may be considered as a Newtonian fluid within the test range (shear rate 0.0132–132.00 s−1). Increasing the shear rate ultimately causes viscosity to decrease down to the Newtonian plateau, where it seems to be constant. The higher the temperature of the slurry, the lower the shear rate value, after which the viscosity characteristic becomes linear or constant. The same principle applies to mass ratio. In vicinity of the melting point (about 25 °C) the phase change process of mPCM slurry does not influence the viscosity-shear rate characteristic behavior when steady state conditions are preserved. The non-steady state condition was also examined, more specifically, the temperature of the sample was increased continuously at a steady pace from 16 °C to 29 °C. This stage took 17 min with each data point collected at 15 s intervals. During a non-steady state temperature increase, near melting point, the viscosity of the slurry clearly departed from those values observed in steady states. It can therefore be concluded that around the melting point temperature, the phase change process of mPCM slurry influences the viscosity.

      PubDate: 2018-06-12T03:08:17Z
       
 
 
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