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Journal Cover International Journal of Heat and Mass Transfer
  [SJR: 1.749]   [H-I: 137]   [190 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
   Published by Elsevier Homepage  [3043 journals]
  • Heat transfer and pressure drop in the transitional flow regime for a
           smooth circular tube with twisted tape inserts and a square-edged inlet
    • Authors: J.P. Meyer; S.M. Abolarin
      Pages: 11 - 29
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): J.P. Meyer, S.M. Abolarin
      The purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics in the transitional flow regime of twisted tape inserts in a circular tube. Experiments were conducted in a circular tube with an internal diameter of 19.0 mm and a length of 5.27 m, and twisted tape inserts with twist ratios of 3, 4 and 5. A square-edged geometry was used at the tube inlet and it was experimentally operated with water flowing through it while the tube was heated with a constant heat flux. The experiments were conducted at three different heat fluxes of 2, 3 and 4 kW/m2. The experimental set-up was operated between Reynolds numbers of 400 and 11400, and the Prandtl numbers varied between 2.9 and 6.7. Two methods were used to identify the transition points of the different heat fluxes and twist ratios. The first method used the standard deviation of the temperature measurements, and the second method used three linear curve fits on a log–log scale. The curve fits made it possible for correlations to be developed for the non-dimensionalised heat transfer coefficients and friction factors, which took twist ratio, heat flux and Reynolds number into consideration. For the same heat flux, it was found that the Colburn j-factors increased as the twist ratios decreased, and transition started earlier. When the twist ratio was kept constant and the heat flux was varied, higher heat fluxes delayed the transition from laminar to transitional flow. The friction factors were found to increase as the twist ratio decreased. When both the twist ratio and the Reynolds number were kept constant, an increase in heat flux was found to decrease the friction factor.

      PubDate: 2017-10-11T03:05:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.103
      Issue No: Vol. 117 (2017)
       
  • A mesoscopic model for transient mass transfer of volatile organic
           compounds from porous walls of different structures
    • Authors: Yan Su; Tiniao Ng; Yinping Zhang; Jane H. Davidson
      Pages: 36 - 49
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Yan Su, Tiniao Ng, Yinping Zhang, Jane H. Davidson
      Transient mass diffusion and convection of volatile organic compounds (VOCs) from walls is an important issue for air quality in buildings. In the present work, a new model of these processes that captures mass transport within the wall structure is presented and applied for a ventilated enclosure. Porous wall structures composed of two solid phases (one carrying the VOC and one inert) and one fluid phase air are generated by the Controllable Structure Generation Scheme (CSGS) based on discrete Gaussian quadrature space and velocity. Mesoscopic scale parallel non-dimensional lattice Boltzmann method (P-NDLBM) simulations are performed for relevant ranges of wall porosity, Reynolds and Schmidt numbers for a two-dimensional enclosure with a top inlet and bottom outlets. The effect of the wall structure on mass transfer in the enclosure is investigated for two wall structures: type (A) a wall with randomly immersed particles, and type (B) a shape-separated wall structure. Results include transient VOC concentration and streamlines in the porous wall and the enclosure for a vary of porosities and diffusivities for each phase. The pore structure and porosity of the wall have significant impact on mass transfer. Type (B) structures are more favorable for rapid mass transfer within the wall.

      PubDate: 2017-10-11T03:05:39Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.131
      Issue No: Vol. 117 (2017)
       
  • Thermohydraulics of a metal foam-filled annulus
    • Authors: M.P. Orihuela; F. Shikh Anuar; I. Ashtiani Abdi; M. Odabaee; K. Hooman
      Pages: 95 - 106
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): M.P. Orihuela, F. Shikh Anuar, I. Ashtiani Abdi, M. Odabaee, K. Hooman
      This paper offers numerical and experimental analysis of forced convection through an annulus filled with aluminium foam. Effects of flow rate and foam pore density on the performance of the heat exchanger were investigated. Specifically, 5 and 20 pore per inch (PPI) aluminium metal foams were tested at three different airflow rates; 20, 85 and 150 standard litre per minute. In parallel, the problem has been simulated numerically. Once validated against experimental data, numerical simulations were conducted to add to the level of details obtained from experiments. The thermal study was done by analysing the temperature field throughout the porous volume and determining the thermal entrance length. This parameter, the thermal entrance length, establishes a reliable design criteria for metal foam-filled heat exchangers, since it marks the length beyond which heat transfer does not significantly increase while the pressure drop keeps growing.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.009
      Issue No: Vol. 117 (2017)
       
  • Influence of source conditions and heat losses on the upwind back-layering
           flow in a longitudinally ventilated tunnel
    • Authors: P. Salizzoni; M. Creyssels; L. Jiang; A. Mos; R. Mehaddi; O. Vauquelin
      Pages: 143 - 153
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): P. Salizzoni, M. Creyssels, L. Jiang, A. Mos, R. Mehaddi, O. Vauquelin
      We study experimentally the dynamics of a back-layering flow developing below the ceiling of a longitudinally ventilated tunnel, and induced by the presence of a steady source of buoyancy at the tunnel floor. Our aim is to identify the dependence of the longitudinal extent of the back-layering flow upwind of the source (and therefore against the tunnel ventilation velocity) as a function of the parameters characterising the buoyant release at the source and of those characterising the thermal losses at the tunnel ceiling. To this end purpose we performed experiments in two different reduced scale models, using helium and hot air as buoyant fluids. Based on the experimental results, we develop a semi-empirical model for the prediction of the (non-dimensional) extent of the back-layering flow. This can be expressed as a function of three non-dimensional parameters. The first one is the tunnel Richardson number Ri, expressing the ratio between the buoyancy effects induced by the source and the inertia effects of the tunnel ventilation. The second is its critical value Ri c, obtained by imposing the so-called critical ventilation velocity, preventing the formation of a back-layer flow upstream of the source. The third parameter, referred to as λ T ∗ , characterises the heat losses at the tunnel walls. The variability of the conditions imposed at the source, namely the momentum flux related to the injection of buoyant fluid, have negligible influence on the critical condition and therefore on the extent of the back-layering flow (which depends therefore on the buoyancy flux at the source, only). In contrast, the heat losses play instead a major role, which results in a relevant reduction of the back-layering flow that can be five times shorter than in the adiabatic case.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.017
      Issue No: Vol. 117 (2017)
       
  • Transient forced convection from an infinite cylindrical heat source in a
           saturated Darcian porous medium
    • Authors: Paolo Conti; Daniele Testi; Walter Grassi
      Pages: 154 - 166
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Paolo Conti, Daniele Testi, Walter Grassi
      This paper deals with the problem of an infinite cylindrical heat source embedded into a saturated porous medium and subject to a cross-axial Darcian flow. Only forced convection is considered. We derived the transient dimensionless solution through a combined analytical – numerical method consisting of four steps: (a) a preliminary dimensional analysis of the constitutive equations of the problem in order to find the dimensionless groups governing the solution; (b) the identification of the validity range of the model as a function of the just-mentioned dimensionless groups; (c) the numerical resolution of the problem; (d) the synthesis of the numerical results in a general dimensionless form. Specifically, we provide several dimensionless maps of the 2D thermal field evolution for six different orders of magnitude of the Péclet number ( 10 - 3 – 10 2 ) . The evolution of the temperature of the heat source is fully illustrated and discussed through plain dimensionless criteria. Then, we discuss the time, space and fluid velocity scales in which the solution is practically equivalent to the ones given by a linear heat source and a purely conductive model. We conclude that the present model has to be employed to evaluate the temperature in proximity of the heat source when the reference Péclet number is greater than 0.5. On the contrary, the linear model can be successfully used for radial distances 5–10 times greater that the heat source radius, depending on the reference Péclet number.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.012
      Issue No: Vol. 117 (2017)
       
  • Novel air-cooled condenser with V-frame cells and induced axial flow fans
    • Authors: Lei Chen; Lijun Yang; Xiaoze Du; Yongping Yang
      Pages: 167 - 182
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Lei Chen, Lijun Yang, Xiaoze Du, Yongping Yang
      The thermo-flow performances of air-cooled condensers (ACCs) are basically deteriorated under wind conditions, so it is of great concerns to propose the measures against the adverse wind effects on air-cooled condensers. In this work, a novel reconstruction of ACCs combined the V-frame condenser cells with the induced axial flow fans, and a modified layout of the novel ACCs for a specific wind direction are proposed based on the direct dry cooling system in a 2× 600 MW power plant. The CFD approach with a validation is applied to the performance investigation of the novel ACCs. The variable fields, mass flow rate, inlet air temperature and turbine back pressure for both the conventional and novel layouts of ACCs under different wind conditions are obtained and compared. The results show that the mass flow rates of the novel ACCs increase conspicuously compared with the conventional ACCs both in the absence and presence of winds. The flow distortions through the induced axial flow fans are greatly restrained and the inlet air temperature of the novel ACCs decreases, which lead to the improved thermo-flow performances of ACCs and reduced turbine back pressure of power generating unit.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.139
      Issue No: Vol. 117 (2017)
       
  • Instabilities of thermocapillary flows between counter-rotating disks
           under microgravity conditions
    • Authors: Qi-Sheng Chen; Meng He; Peng Zhu; Kai-Xin Hu
      Pages: 183 - 187
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Qi-Sheng Chen, Meng He, Peng Zhu, Kai-Xin Hu
      Instabilities of thermocapillary flows between counter-rotating disks under microgravity conditions are investigated by linear stability analysis. The basic-state and perturbation equations are solved using the Chebyshev-collocation method. For small Prandtl number liquids (Pr ≤ 0.01), bifurcation of thermocapillary flows between counter-rotating disks is found to be a 3D oscillatory state for the Coriolis number τ ≤ 100, except at certain Coriolis number where the most unstable perturbation is 3D stationary state. The critical capillary Reynolds number is a function of Prandtl number, Coriolis number and aspect ratio. Energy analysis shows that the perturbation energy consists of the viscous dissipation, the work done by surface tension and the interaction between the perturbation flow and the basic flow, respectively. For small Prandtl number liquids (Pr ≤ 0.01), the perturbation energy mainly comes from the interaction between the perturbation and the basic flow, which suggests that the instability mechanism is hydrodynamic. The interaction between the perturbation and the basic flow in the azimuthal direction becomes negative when a moderate rotation is applied on the disks, and the moderate rotation can stabilize the thermocapillary flows for small Prandtl number liquids.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.137
      Issue No: Vol. 117 (2017)
       
  • Design and characterization of an additive manufactured hydraulic oil
           cooler
    • Authors: Brandon J. Hathaway; Kunal Garde; Susan C. Mantell; Jane H. Davidson
      Pages: 188 - 200
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Brandon J. Hathaway, Kunal Garde, Susan C. Mantell, Jane H. Davidson
      A hydraulic oil cooler was fabricated from an aluminum alloy by selective laser melting. The plate-fin tube bank has special features, including non-circular, internally finned tubes, and external angled fins to allow flexibility in the printing process. The study demonstrates the capability to additively manufacture commercial-scale heat exchangers with intricate features. Heat transfer and pressure drop performance are characterized in a wind tunnel over a range of oil- and air-side flow rates for inlet temperatures representing high limits for a commercial hydraulic excavator. The data and results of a computational fluid dynamic model provide insight on the impact of features that are dictated by the manufacturing process on thermal and hydraulic performance.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.013
      Issue No: Vol. 117 (2017)
       
  • Direct nanofluids configuration optimization based on the evolutionary
           topology optimization method
    • Authors: Chao Bai; Guanmin Zhang; Yan Qiu; Xueli Leng; Maocheng Tian
      Pages: 201 - 210
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Chao Bai, Guanmin Zhang, Yan Qiu, Xueli Leng, Maocheng Tian
      Nanofluids performance counts on nanoparticle configuration. The evolutionary topology optimization algorithm is applied in this work for direct nanoparticle configuration optimization. The initial random distribution of nanoparticles inside base fluid is found to well simulate practical nanofluids. The optimized nanofluids configuration proves to be continuous strips assembled by nanoparticles with width comparable to size of nanoparticles and length comparable to size of heat-transferring system. System overall thermal resistance is significantly reduced by the optimized nanoparticle configuration. Future nanofluids should be fabricated with strip-shaped nanoparticles in order to perform better.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.135
      Issue No: Vol. 117 (2017)
       
  • Analysis of a remote phosphor layer heat sink to reduce phosphor operating
           temperature
    • Authors: Indika U. Perera; Nadarajah Narendran
      Pages: 211 - 222
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Indika U. Perera, Nadarajah Narendran
      The remote phosphor method has provided significant improvement in overall LED lighting system efficiency by reducing the number of photons absorbed at the LED chip. However, increased demand for higher light output from smaller light engines has resulted in high radiant energy and heat densities on the phosphor layer. The problem is exacerbated by the phosphor conversion efficiency decreasing with increased operating temperature in the remote phosphor layer. A higher operating temperature can negatively affect performance in terms of luminous efficacy, color shift, and life. In cases such as this, the system’s performance can be improved through suitable thermal management that reduces the phosphor layer temperature. In this study, we present the first investigation to experimentally quantify the operating temperature and optical performance effects of using a dedicated phosphor layer heat sink solution as a thermal management strategy to reduce phosphor layer operating temperature. The effects of heat sink geometry and material parameters on phosphor layer operating temperature and optical performance were investigated. The experimental results showed a decrease in phosphor layer operating temperature with an increase in phosphor layer heat sink interface area, while the total radiant power decreased. Ray-tracing simulations identified the low surface reflectance of the heat sink interface area as the cause of this decrease in radiant power. A finite element model was developed from the experimental results to understand the decrease in phosphor layer operating temperature with increased heat sink interface area. This simulation work was used in identifying the causes affecting observed optical and thermal performance in the short-term experiments. The study also investigated the long-term performance of phosphor layer heat sinks and the findings are reported.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.016
      Issue No: Vol. 117 (2017)
       
  • Turbulent heat transfer and friction factor of nanodiamond-nickel hybrid
           nanofluids flow in a tube: An experimental study
    • Authors: L. Syam Sundar; Manoj K. Singh; Antonio C.M. Sousa
      Pages: 223 - 234
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): L. Syam Sundar, Manoj K. Singh, Antonio C.M. Sousa
      Turbulent heat transfer and friction factor of nanodiamond-nickel (ND-Ni) hybrid nanofluids flow in a horizontal tube has been investigated experimentally. The ND-Ni nanoparticles were synthesized using in-situ growth and chemical co-precipitation method and characterized by XRD, TEM and VSM. The hybrid nanofluids were prepared by dispersing ND-Ni hybrid nanoparticles in distilled water. The thermal conductivity and viscosity enhancements were observed as 29.39% and 23.24% at 0.3% volume concentration of hybrid nanofluid at 60°C compared to distilled water. The heat transfer and friction factor experiments were conducted at different Reynolds numbers (3000–22,000) and particle volume concentrations (0.1% and 0.3%). The Nusselt number enhancement of 0.3% volume concentration of hybrid nanofluid is 35.43% with a friction factor penalty of 1.12-times at a Reynolds number of 22,000 compared to distilled water data. The obtained experimental Nusselt number of hybrid nanofluids was compared with other kind of hybrid nanofluids available literature. New Nusselt number and friction factor correlations were proposed based on the experimental data.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.109
      Issue No: Vol. 117 (2017)
       
  • Numerical simulation of mass transfer and fluid flow evolution of a
           rectangular free jet of air
    • Authors: Ivan Di Venuta; Ivano Petracci; Matteo Angelino; Andrea Boghi; Fabio Gori
      Pages: 235 - 251
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Ivan Di Venuta, Ivano Petracci, Matteo Angelino, Andrea Boghi, Fabio Gori
      The paper presents Large Eddy Simulations (LES) of mass transfer and fluid flow evolutions of a submerged rectangular free jet of air in the range of Reynolds numbers from Re = 3400 to Re = 22,000, with the Reynolds number, Re, defined with the hydraulic diameter of the rectangular slot, of height H. The numerical simulations are 3D for Re = 3400 and 6800, while 2D for Re = 10,400 and 22,000 to reduce computational time costs. The average and instant LES numerical simulations are compared with the concentration visualizations, obtained with the Particle Image Velocimetry (PIV) technique, and the fluid dynamics variables, velocity and turbulence, measured with the PIV technique and the Hot Film Anemometry (HFA). In the numerical simulations, the Schmidt number is equal to 100 to compare the air concentration in the PIV experiments, while the turbulence on the exit of the slot is equal to the value measured experimentally, and ranging between 1% and 2%. The average 2-3D LES simulations are in agreement with the concentration and the fluid dynamics experimental results in the Undisturbed Region of Flow (URF) and in the Potential Core Region (PCR), while the vortex breakdown is captured only by the 3D LES approach. As far as the instant flow evolution is concerned, the 2-3D LES simulations reproduce the Negligible Disturbances Flow (NDF), where the jet height maintains constant, and the Small Disturbances Flow (SDF), where the jet height oscillates, with contractions and enlargements, but without the vortex formation. Average and instant velocity and turbulence numerical simulations on the centreline are in good agreement to the experimental PIV measurements.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.030
      Issue No: Vol. 117 (2017)
       
  • A mathematical model for heating and evaporation of a multi-component
           liquid film
    • Authors: S.S. Sazhin; O. Rybdylova; C. Crua
      Pages: 252 - 260
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): S.S. Sazhin, O. Rybdylova, C. Crua
      A new model for heating and evaporation of a multi-component liquid film, based on the analytical solutions to the heat transfer and species diffusion equations inside the film, is suggested. The Dirichlet boundary condition is used at the wall and the Robin boundary condition is used at the film surface for the heat transfer equation. For the species diffusion equations, the Neumann boundary conditions are used at the wall, and Robin boundary conditions are used at the film surface. The convective heat transfer coefficient is assumed to be constant and the convective mass transfer coefficient is inferred from the Chilton-Colburn analogy. The model is validated using the previously published experimental data for heating and evaporation of a film composed of mixtures of isooctane/3-methylpentane (3MP). Also, it is applied to the analysis of heating and evaporation of a film composed of a 50%/50% mixture of heptane and hexadecane in Diesel engine-like conditions.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.020
      Issue No: Vol. 117 (2017)
       
  • Numerical modeling and analysis of the thermal behavior of NCM lithium-ion
           batteries subjected to very high C-rate discharge/charge operations
    • Authors: Ti Dong; Peng Peng; Fangming Jiang
      Pages: 261 - 272
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Ti Dong, Peng Peng, Fangming Jiang
      Lithium-ion batteries are easily overheated during discharge/charge operations with large current output/input. Traditional battery tests are difficult to pinpoint the internal thermal mechanism for an overheated battery. In this study, it is proposed a model to investigate the thermal behavior of the charge and discharge processes of lithium-ion battery with very high C-rate. The model combines an electrochemical-thermal (ECT) coupled module and a thermal abuse module. The whole successive process of the cell operation including charge/discharge, battery material exothermic reactions, and even thermal runaway within a cell, is fully described, by a single model. Predictions of individual LiNixCoyMnzO2 (NCM) lithium-ion cell high C-rate (up to 8C) discharge/charge processes compare well with experimental data. A detailed analysis is conducted to evaluate the influence of external heat release condition and charge/discharge C-rate on the thermal behavior of batteries during and after very high C-rate (>8C) charge/discharge operations. Results indicate: (1) the very large output/input current leads to the early-coming of cut-off voltage, terminating the discharge/charge operation; (2) compared with the very high C-rate charge operation, the discharge operation of the same C-rate is easier to cause battery overheat, leading to the occurrence of battery thermal runaway; (3) the high C-rate charge operation with cut-off voltage control fault is very dangerous as it can cause very fast heat generation and eventually possible thermal runaway; (4) favorable heat release condition or effective and active thermal control may be the key to the thermal control and restraining thermal runaway of lithium-ion batteries.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.024
      Issue No: Vol. 117 (2017)
       
  • Transient simulation of coupled heat and moisture flow through a
           multi-layer porous solid exposed to solar heat flux
    • Authors: L. Škerget; A. Tadeu; C.A. Brebbia
      Pages: 273 - 279
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): L. Škerget, A. Tadeu, C.A. Brebbia
      The present paper reports the simulation of unsteady coupled moisture and heat transport through a multi-layer porous solid. The governing partial-differential transport equations are written and solved simultaneously for the continuous driving potentials, i.e. relative humidity and temperature. The coupled equations are solved numerically using a singular boundary integral representation of the governing equations. The multi-layer porous solid building elements under study are submitted to convective heat and mass exchange with the surrounding environment and exposed to solar heat flux. The integral equations are discretized using mixed-boundary elements and a multidomain method also known as the macro-elements technique (Brebbia, 1984 [1], Popov et al., 2007 [2]). The numerical model uses quadratic approximation over space and linear approximation over time for all field functions, which provides highly accurate numerical results.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.010
      Issue No: Vol. 117 (2017)
       
  • Experimental investigation of thermal and electrical conductivity of
           silicon oxide nanofluids in ethylene glycol/water mixture
    • Authors: Yufeng Guo; Tongtong Zhang; Dongrui Zhang; Qi Wang
      Pages: 280 - 286
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Yufeng Guo, Tongtong Zhang, Dongrui Zhang, Qi Wang
      In this paper, the thermal conductivity and electrical conductivity of SiO2 nanofluids using mixture of ethylene glycol (EG) and water (H2O) as the base fluid are investigated. The two-step method was used to prepare SiO2-EG/H2O nanofluids with a mass concentration of 0.3%. The variations in thermal conductivity and electrical conductivity as functions of EG concentration (0–100%, v/v) and temperature (25–45 °C) are present. Experimental results showed that the thermal conductivity and electrical conductivity of SiO2-EG/H2O nanofluids both decreased as the EG content percentage increases in the EG/H2O mixture. At a specific EG content percentage, thermal conductivity and electrical conductivity both increased with the increase in temperature. To better evaluate the enhancement performance of SiO2-EG/H2O nanofluids, the relative electrical conductivity was introduced and studied explicitly. The mechanism of electrical conductivity enhancement in SiO2-EG/H2O nanofluids was analyzed in detail. Meanwhile, the ratio of thermal conductivity and electrical conductivity was also discussed.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.091
      Issue No: Vol. 117 (2017)
       
  • Triple diffusive mixed convection along a vertically moving surface
    • Authors: P.M. Patil; Monisha Roy; S. Roy; E. Momoniat
      Pages: 287 - 295
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): P.M. Patil, Monisha Roy, S. Roy, E. Momoniat
      This paper presents a numerical investigation on steady triple diffusive mixed convection boundary layer flow past a vertical plate moving parallel to the free stream in the upward direction. The temperature of the plate is assumed to be hotter compared to the surrounded fluid temperature. Sodium chloride and Sucrose are chosen as solutal components which are added in the flow stream from below with various concentration levels. The concentrations of NaCl-Water and Sucrose-Water are considered to be higher near the wall compared to the concentrations of NaCl-Water and Sucrose-Water within the free stream. The coupled nonlinear partial differential equations are transformed using the non-similarity variables and solved numerically by an implicit finite difference scheme with quasi-linearization technique. The effects of Richardson numbers, velocity ratio parameters, ratio of buoyancy parameters and Schmidt numbers of both the solutal components on the fluid flow, thermal and species concentration fields are investigated. Results indicate that 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 4.36% and 64.56% for NaCl and Sucrose, respectively.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.106
      Issue No: Vol. 117 (2017)
       
  • A direct solution for radiative intensity with high directional resolution
           in isotropically scattering media
    • Authors: Zhifeng Huang; Qiang Cheng; Chun Lou
      Pages: 296 - 302
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Zhifeng Huang, Qiang Cheng, Chun Lou
      Radiative intensity with high directional resolution can provide fruitful information inside radiative systems, which is very useful for inverse analysis. In this work, a direct solution for radiative intensity with high directional resolution in isotropically scattering media enclosed by diffuse boundaries is developed. First, linear equations about radiative intensity at the boundaries (outgoing directions) and source terms in the media are established based on the integral form of the Radiative Transfer equation (RTE). Then, after directly solving the established equations and with the obtained radiative intensity and source terms, radiative intensity at any position with high directional resolution is readily calculated by summation operation. The proposed method is validated by comparing the calculated directional radiative intensity with that of the iterative Distributions of Ratios of Energy Scattered Or Reflected (iterative-DRESOR) method as well as the reverse Monte Carlo (RMC) method, both in one-dimensional and three-dimensional cases. The computing time comparison shows that the proposed method has a distinct advantage for calculating radiative intensity with high directional resolution compared with the reverse Monte Carlo method.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.101
      Issue No: Vol. 117 (2017)
       
  • Active control of evaporative solution deposition by means of modulated
           gas phase convection
    • Authors: H.M.J.M. Wedershoven; K.R.M. Deuss; C. Fantin; J.C.H. Zeegers; A.A. Darhuber
      Pages: 303 - 312
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): H.M.J.M. Wedershoven, K.R.M. Deuss, C. Fantin, J.C.H. Zeegers, A.A. Darhuber
      In solution processing, functional materials are dissolved or dispersed in a solvent and deposited typically as a thin liquid film on a substrate. After evaporation of the solvent, a dry layer remains. We propose an ‘active’, non-contact technique for evaporative pattern formation that does not require any substrate modification. It is based on an array of nozzles, some of which introduce a dry carrier gas in the air space above the liquid film. By spatially modulating the solvent vapor saturation above the liquid, patterns in the dry layer thickness can be induced in a controlled fashion. In this manuscript we study pattern formation due to a single pixel of such a nozzle array, by means of quantitative experiments and numerical simulations.
      Graphical abstract image

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.123
      Issue No: Vol. 117 (2017)
       
  • The extended Reynolds analogy for the Couette problem: Similarity
           parameters
    • Authors: A.A. Abramov; A.V. Butkovskii
      Pages: 313 - 318
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): A.A. Abramov, A.V. Butkovskii
      We consider the extended Reynolds analogy for the Couette problem. That is, we study the relation between the shear stress and the energy flux transferred to the boundary surface at different velocities and temperatures. We use the direct simulation Monte Carlo (DSMC) method. We show that for all considered plates’ velocities and temperatures the extended Reynolds analogy for a monatomic gas at any fixed Knudsen number depends on the plates’ velocities and temperatures only via the Eckert number (up to statistical fluctuations). Additionally, we generalize an extended Reynolds analogy. For a monatomic gas in the transitional flow regime we show that the generalized Reynolds analogy up to statistical fluctuations depends only on Knudsen number for all considered Eckert numbers. For a gas at any Knudsen number as well as for liquid we show that the sum of the Reynolds analogies for the upper and lower plates in the Couette problem is exactly one.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.011
      Issue No: Vol. 117 (2017)
       
  • A hierarchical manifold microchannel heat sink array for high-heat-flux
           two-phase cooling of electronics
    • Authors: Kevin P. Drummond; Doosan Back; Michael D. Sinanis; David B. Janes; Dimitrios Peroulis; Justin A. Weibel; Suresh V. Garimella
      Pages: 319 - 330
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Kevin P. Drummond, Doosan Back, Michael D. Sinanis, David B. Janes, Dimitrios Peroulis, Justin A. Weibel, Suresh V. Garimella
      High-heat-flux removal is necessary for next-generation microelectronic systems to operate more reliably and efficiently. Extremely high heat removal rates are achieved in this work using a hierarchical manifold microchannel heat sink array. The microchannels are imbedded directly into the heated substrate to reduce the parasitic thermal resistances due to contact and conduction resistances. Discretizing the chip footprint area into multiple smaller heat sink elements with high-aspect-ratio microchannels ensures shortened effective fluid flow lengths. Phase change of high fluid mass fluxes can thus be accommodated in micron-scale channels while keeping pressure drops low compared to traditional, microchannel heat sinks. A thermal test vehicle, with all flow distribution components heterogeneously integrated, is fabricated to demonstrate this enhanced thermal and hydraulic performance. The 5mm×5mm silicon chip area, with resistive heaters and local temperature sensors fabricated directly on the opposite face, is cooled by a 3×3 array of microchannel heat sinks that are fed with coolant using a hierarchical manifold distributor. Using the engineered dielectric liquid HFE-7100 as the working fluid, experimental results are presented for channel mass fluxes of 1300, 2100, and 2900kg/m2 s and channel cross sections with nominal widths of 15μm and nominal depths of 35μm, 150μm, and 300μm. Maximum heat flux dissipation is shown to increase with mass flux and channel depth and the heat sink with 15μm×300μm channels is shown to dissipate base heat fluxes up to 910W/cm2 at pressure drops of less than 162kPa and chip temperature rise under 47°C relative to the fluid inlet temperature.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.015
      Issue No: Vol. 117 (2017)
       
  • Mixed convection of nanofluids in a three dimensional cavity with two
           adiabatic inner rotating cylinders
    • Authors: Fatih Selimefendigil; Hakan F. Öztop
      Pages: 331 - 343
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Fatih Selimefendigil, Hakan F. Öztop
      In this study, mixed convection of nanofluids in a three dimensional cavity with two inner adiabatic rotating circular cylinders were analyzed by using finite element method. Vertical surfaces are kept at constant temperature while other walls and rotating cylinder surfaces were taken as adiabatic. The three dimensional cavity was filled with water and various types of nanoparticles (Cu, Al2O3 and TiO2). The water-Cu nanofluid provided the highest heat transfer rate and at the highest value of Rayleigh number, 4 % higher average heat transfer rate is obtained when compared to other particles. When cylinders rotate, depending on the rotational direction either enhancement or deterioration of average Nusselt number is observed. For the highest value of rotational speed of the cylinders, 8.5 % discrepancy between the average Nusselt number is observed for the nanofluid with Cu and Al2O3 nanoparticles. For Cu-water nanofluid at the highest volume fraction as compared to base fluid, 38.10 % of enhancement in the average heat transfer is obtained. A correlation for the average Nusselt number in polynomial form was developed which is a function of Rayleigh number and angular rotational speed of the cylinders.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.116
      Issue No: Vol. 117 (2017)
       
  • Investigations of film-cooling effectiveness on the squealer tip with
           various film-hole configurations in a linear cascade
    • Authors: Feng-na Cheng; Jing-zhou Zhang; Hai-ping Chang; Jing-yang Zhang
      Pages: 344 - 357
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Feng-na Cheng, Jing-zhou Zhang, Hai-ping Chang, Jing-yang Zhang
      An experimental investigation is performed to study the effect of film-hole configurations on the blade tip film cooling performance in a five-blade linear cascade. Six film-hole configurations are taken into consideration under four typical blowing ratios. In Type-A, Type-B and Type-C, the film holes are arranged in a single row along the middle-camber line with different hole-to-hole pitches. Type-D, Type-E and Type-F have the same film-hole number of 13 as Type-B. For Type-D, the film holes are also arranged in a row, but they are located close to the suction-side squealer. For Type-E, the film holes are arranged in two rows. For Type-F, two rows of 8 holes are concentrated at the leading edge, and the rest 5 holes are arranged in a line at the middle chord region of the blade tip. Besides, some numerical simulations are conducted to provide detailed coolant jet trajectory. The results show that film-hole arrangement has a great impact on the tip film-cooling effectiveness. The coolant issuing from middle-camber holes are suctioned by the vortex structures inside squealer cavity to flow towards the pressure side, producing good film coverage at the local zone between the middle-camber line and pressure-side squealer for Type-A, Type-B and Type-C. For Type-F, as more film holes are concentrated at the leading edge, the film coverage on the front tip surface is well improved compared to the other film-hole arrangements. Under the same coolant usage, Type-F obtains the most favorable film cooling performance except for the trailing edge, and Type-C produces wider film coverage extending to trailing edge.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.100
      Issue No: Vol. 117 (2017)
       
  • Effective thermal conductivity of polymer composites: Theoretical models
           and simulation models
    • Authors: Siping Zhai; Ping Zhang; Yaoqi Xian; Jianhua Zeng; Bo Shi
      Pages: 358 - 374
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Siping Zhai, Ping Zhang, Yaoqi Xian, Jianhua Zeng, Bo Shi
      Polymer composites of highly effective thermal conductivity (ETC) are commonly used in various industries, for renewable energy systems and Electronic Systems. Owing to the low thermal conductivity (TC) of polymers, inserting particles with ultra-high TC into the polymer matrix makes it possible for polymer composites to possess high ETC. The ETC of polymer composites is determined by several factors, including the particle and matrix properties and microscopic structures. Modelling methods are powerful tools to understand how these factors influence the ETC of polymer composites. Modelling methods can be combined with experimental data and can be used to qualitatively and quantitatively analyse the impact of various factors on the ETC. Moreover, modelling methods can be used asa guide for the choice and design of particle-filled composites for engineering applications. Herein, we review the recent research on ETC models of polymer composites. First, the classical theoretical models of ETC for polymer composites are introduced. Then, novel theoretical and simulation models are described. We focus on the influence of the theoretical models and the simulation models of polymer composites at multiple scales. Finally, we conclude and give an outlook regarding the ETC models of polymer composites.
      Graphical abstract image

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.067
      Issue No: Vol. 117 (2017)
       
  • Spatial orientation as a factor in flow boiling heat transfer of cooling
           liquids in enhanced surface minichannels
    • Authors: Kinga Strąk; Magdalena Piasecka; Beata Maciejewska
      Pages: 375 - 387
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Kinga Strąk, Magdalena Piasecka, Beata Maciejewska
      This paper presents the results of flow boiling heat transfer in an asymmetrically heated rectangular minichannel oriented with seven inclination angles: 0°, 30°, 60°, 90°, 120°, 150°, and 180° relative to the horizontal plane. The liquid flowing in the minichannel, Fluorinert FC-72, HFE-7100 or HFE-7000 (3M), was heated by a thin plate. The plate had an enhanced surface on the side that was in contact with the fluid. The enhanced surface was obtained by vibration-assisted laser surface texturing. Infrared thermography was used to determine changes in the temperature on the outer smooth side of the plate. Two-phase flow patterns were observed through a glass panel. Local heat transfer coefficients between the heated plate and the cooling liquid flowing in a minichannel were calculated with the Trefftz method. The method approximates the unknown solution of differential equation by a linear combination of functions that exactly satisfy the differential equation. The results are presented as images of the two-phase flow structures, relationships between the temperature plate and the distance from the channel inlet, the heat transfer coefficient values and the distance from the channel inlet or the channel orientation and as boiling curves for selected working fluids and orientations of the test module. They are discussed separately for the subcooled and for the saturated boiling regions.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.019
      Issue No: Vol. 117 (2017)
       
  • Conjugate heat and species transport in an air filled ventilated enclosure
           with a thermo-contaminated block
    • Authors: Neha Gupta; A.K. Nayak; Sumit Malik
      Pages: 388 - 411
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Neha Gupta, A.K. Nayak, Sumit Malik
      The flow visualization, thermal and solutal effects in a ventilated enclosure around a thermo-contaminated square block is numerically modeled. Simulations are performed for different locations and different sizes of the thermo-contaminated block with inlet and outlet port along the vertical walls where coolant air is supplied and contaminated air is flush out. The block is maintained with higher temperature and species concentration compared to the injected cold fluid. The walls are assumed as impermeable and adiabatic to heat and solute. The heat and species transfer rate along the surface of the block is compared for different values of Richardson number, Reynolds number, buoyancy ratio and block positions. Cooling efficiency inside the enclosure and average fluid temperature is calculated for different physical flow parameters to find the most suitable size and position of the block in order to obtain the maximum heat and mass transfer rate inside the enclosure. It is found that maximum cooling inside the enclosure is obtained when thermo-contaminated block is placed near the outlet port.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.028
      Issue No: Vol. 117 (2017)
       
  • Phase-field modeling on laser melting of a metallic powder
    • Authors: Ji-Qin Li; Tai-Hsi Fan; Takashi Taniguchi; Bi Zhang
      Pages: 412 - 424
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Ji-Qin Li, Tai-Hsi Fan, Takashi Taniguchi, Bi Zhang
      Laser-based manufacturing process such as selective laser melting, sintering, and direct deposition using metallic powders plays an important role in additive manufacturing technology. As spatial resolution increases, there is a great need to advance the design, quantitative analysis, and optimization of relevant thermal fluid processes at the powder level. In this paper, a theoretical model is developed to characterize melting and Marangoni flow dynamics within a pure metal powder heated by a moving Gaussian laser beam. Phase field formulation is developed to simulate the solid-liquid phase transition along with the thermocapillary effect at the free surface, which drives the molten flow within the powder and thus influences heat transfer behaviors. The formulation, simplification, and computational results for two-dimensional cases are demonstrated and discussed in detail.
      Graphical abstract image

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.001
      Issue No: Vol. 117 (2017)
       
  • Lattice Boltzmann method based study of the heat transfer augmentation
           associated with Cu/water nanofluid in a channel with surface mounted
           blocks
    • Authors: Rasul Mohebbi; Hassan Lakzayi; Nor Azwadi Che Sidik; Wan Mohd Arif Aziz Japar
      Pages: 425 - 435
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Rasul Mohebbi, Hassan Lakzayi, Nor Azwadi Che Sidik, Wan Mohd Arif Aziz Japar
      The study of the forced convection in a channel has many practical applications. In this paper, the forced convection heat transfer from surface mounted blocks attached to the bottom wall of a horizontal channel with nanofluid is numerically studied by the second-order lattice Boltzmann method (LBM). The effects of Reynolds numbers and geometrical parameters of the blocks in different aspect ratios on the flow field and temperature distribution for various volume fractions of nanofluid (φ =0, 0.01, 0.03 and 0.05) are analyzed. Also, the influence of these parameters is investigated on the local and average Nusselt numbers. It is concluded that heat transfer in channels can be enhanced by using the block on the walls and adding nanoparticles. There is a maximum value of 39.04% increase in average heat transfer coefficient for all the examined cases compared to the base fluid (i.e., water).

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.043
      Issue No: Vol. 117 (2017)
       
  • Free-standing planar thin-film thermoelectric microrefrigerators and the
           effects of thermal and electrical contact resistances
    • Authors: Yu Su; Jianbiao Lu; Baoling Huang
      Pages: 436 - 446
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Yu Su, Jianbiao Lu, Baoling Huang
      Thermoelectric microrefrigerators provide an attractive solid-state solution for on-chip thermal management of microelectronics due to their unique advantages. Here we propose a free-standing planar design of thermoelectric microrefrigerator based on thin film technologies to address the high-performance on-chip cooling and compatibility with microelectronics fabrication. By combining theoretical modeling, numerical simulations and experiments, we conducted a comprehensive investigation of the steady-state and transient performances of the proposed microrefrigerators and various factors that might influence their performance, such as contact resistances, element geometries, convection and radiation, have been explored. Both thermal and contact resistances are found to be important for the cooling performance of the proposed microrefrigerators while they play different roles on the cold and hot sides of a refrigerator. The influence of contact resistances on the design strategies of a microrefrigerator is also discussed. It is demonstrated that microrefrigerators based on IC-compatible low-cost SiGe thin films can potentially achieve a cooling temperature more than 20K with a response time shorter than 40ms near room temperature, rendering them competitive against the state-of-the-art microrefrigerators based on toxic conventional heavy metal thermoelectrics such as Bi2Te3 and Sb2Te3.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.023
      Issue No: Vol. 117 (2017)
       
  • Heat transfer characteristics of urea-water spray impingement on hot
           surfaces
    • Authors: Yujun Liao; Panayotis Dimopoulos Eggenschwiler; Roman Furrer; Moyu Wang; Konstantinos Boulouchos
      Pages: 447 - 457
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Yujun Liao, Panayotis Dimopoulos Eggenschwiler, Roman Furrer, Moyu Wang, Konstantinos Boulouchos
      This study presents an investigation of the heat transfer characteristics of the urea-water spray (UWS) impingement on a stainless steel plate under typical diesel exhaust flow conditions. The rear side temperature of the spray-impinged plate has been measured by infrared thermography with high temporal and spatial resolution. The spray impinged side temperature and heat flux distributions have been computed by solving the 3D inverse heat conduction in the plate with the sequential function specification method. Measurements show that the instantaneous plate temperature determines the heat transferred during the spray impingement. Based on the plate temperature, different regimes (film boiling, transition boiling and nucleate boiling) have been identified. At high plate temperatures, film boiling and Leidenfrost effect are prevailing and the heat transferred from the plate to the liquid is low. With decreasing plate temperatures, the critical heat flux regime is approached and the heat transferred increases substantially. At lower plate temperatures, nucleate boiling occurs limiting the heat transferred to low values. The critical heat flux and temperature found for UWS are reported and in good agreement with the trend in previous studies for water.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.031
      Issue No: Vol. 117 (2017)
       
  • Experimental investigation of thermally driven meniscus instability in
           capillary tubes
    • Authors: John Polansky; Tarik Kaya
      Pages: 458 - 464
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): John Polansky, Tarik Kaya
      An experimental study of evaporating meniscus instability was performed for five capillary tube diameters ranging from 0.3 to 1.2 mm and three different volatile fluids (n-pentane, ethanol and acetone). By heating the tubes above the meniscus, the meniscus was observed to destabilize, unless the capillary tube suffered a mechanical failure due to the excess heat load. The onset of instability was recorded as a meniscus height measurement. The temperature difference across the meniscus, or superheat, at the onset of instability was calculated using the measured height and a previously validated mathematical model. Of the menisci destabilized, the superheat values varied non-linearly with capillary tube diameter. The smaller capillary tubes required higher superheats for instability. Comparison of the calculated superheats with previously developed stability criteria proved unsuccessful. An empirical relation was observed when the instability heights were scaled by the capillary geometry. Additional comparison was drawn between the capillary tubes and channels, and it was found that tubes require a larger superheat to destabilize as compared to a channel of comparable geometry.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.014
      Issue No: Vol. 117 (2017)
       
  • Numerical study of falling film flow on a horizontal rotating tube
    • Authors: Shi Lin; Zheng Zhang; Xi Liu; Kunyu Zhuang; Xuelai Li
      Pages: 465 - 473
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Shi Lin, Zheng Zhang, Xi Liu, Kunyu Zhuang, Xuelai Li
      In this paper, a CFD simulation of falling film on a horizontal rotating tube is illustrated. The objective of this simulation is to explore the influence of various parameters on this kind flow. The simulation results show that in a certain range, the offset angle of the liquid column increases with the increase of the rotational speed, which agrees well with the experimental values. Compared to a stationary tube, the liquid film thickness at the left side of the liquid column is thinner but the right gets larger when the tube is rotating counterclockwise. And the liquid film velocity at the left side of the liquid column is equivalent to the linear superposition of the velocity at the standstill and the rotational velocity denoted by ω. Rotation has a great influence on the velocity distribution at the right side of liquid column. Increasing the rotational speed and the diameter, decreasing the inlet velocity and the inlet hole diameter will make the offset angle of the liquid film larger. The high temperature reduces the offset angle of the liquid column, and the gradient of the liquid column offset angle to temperature becomes smaller. When the temperature is above 65 °C, the effect of temperature on the offset angle of liquid column is negligible. When ω = 200 rpm, the offset angle increases first and then decreases with the increase of the inlet height, but when ω = 300 rpm, the offset angle increases with the increase of the inlet height.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.005
      Issue No: Vol. 117 (2017)
       
  • Heat transfer efficiency of Al2O3-MWCNT/thermal oil hybrid nanofluid as a
           cooling fluid in thermal and energy management applications: An
           experimental and theoretical investigation
    • Authors: Amin Asadi; Meisam Asadi; Alireza Rezaniakolaei; Lasse Aistrup Rosendahl; Masoud Afrand; Somchai Wongwises
      Pages: 474 - 486
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Amin Asadi, Meisam Asadi, Alireza Rezaniakolaei, Lasse Aistrup Rosendahl, Masoud Afrand, Somchai Wongwises
      The main objective of the present study is to assess the heat transfer efficiency of Al2O3-MWCNT/thermal oil hybrid nanofluid over different temperatures (25–50 °C) and solid concentrations (0.125%–1.5%). To this end, first of all, the stability of the nano-oil has been studied through the Zeta potential analysis. Then, the dynamic viscosity and thermal conductivity of the nanofluid have been experimentally investigated. It was found that the nanofluid showed Newtonian behavior over the studied range of temperatures and solid concentrations. The dynamic viscosity showed increasing trend as the solid concentration increased. It is found that the minimum increase in dynamic viscosity is at the temperature of 50 °C in all the studied solid concentrations except 0.5% and 1%. As for the thermal conductivity, it showed increasing trend as the temperature and solid concentration increased. The maximum enhancement was at the temperature of 50 °C and solid concentration 1.5% by approximately 45%. Based on the experimental data, two new highly precise correlations to predict the dynamic viscosity and thermal conductivity of the studied nanofluid have been proposed. Moreover, the heat transfer efficiency of the nanofluid has been evaluated based on different figures of merit. It is revealed that using this nanofluid instead of the base fluid can be beneficial in all the studied solid concentrations and temperatures for both the internal laminar and turbulent flow regimes except the solid concentrations of 1 and 1.5% in internal turbulent flow regimes. The effect of adding nanoparticles on pumping power and convective heat transfer coefficient has also been theoretically investigated.
      Graphical abstract image

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.036
      Issue No: Vol. 117 (2017)
       
  • A parametric study on thermal performance of microchannel heat sinks with
           internally vertical bifurcations in laminar liquid flow
    • Authors: Han Shen; Chi-Chuan Wang; Gongnan Xie
      Pages: 487 - 497
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Han Shen, Chi-Chuan Wang, Gongnan Xie
      The optimal position of internal vertical bifurcation integrated with a microchannel heat sink (MHS) is investigated numerically in the present research. The corresponding rectangular smooth microchannel is compared with those with internal vertical bifurcation. The optimal position along the streamwise direction for interval distances is studied in detail. The corresponding temperature fields, flow fields, pressure drop and thermal characteristics are presented through verified computational model. The numerical simulation indicates that a clear inflection point of pressure gradient may prevail with the presence of internal vertical bifurcation. It is also found that the microchannel heat sink with a small distance between the tail end of internal vertical bifurcation and the outlet of microchannel shows the best thermal performance instead of those with setting the tail end of internal bifurcation at the outlet of microchannel. The proposed optimal design of internal vertical bifurcation shows improved thermal performance without any pressure drop penalty.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.025
      Issue No: Vol. 117 (2017)
       
  • Wall-mounted perforated cubes in a boundary layer: Local heat transfer
           enhancement and control
    • Authors: Fermin Mallor; Carlos Sanmiguel Vila; Andrea Ianiro; Stefano Discetti
      Pages: 498 - 507
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Fermin Mallor, Carlos Sanmiguel Vila, Andrea Ianiro, Stefano Discetti
      A passive convective heat transfer enhancement device based on perforated obstacles is proposed. The perforation crosses the obstacle from the flow-facing side to the rear side. In this configuration a jet is delivered from the obstacle perforation, thus changing the topology of the wake behind the obstacle. Measurements of the convective heat transfer over a flat plate equipped with perforated wall-mounted cubes are carried out using infrared thermography. Flow fields measurements are performed with Particle Image Velocimetry to address the effect of the perforation (and of the jet issuing from it) on the wake topology and on the heat transfer distribution. A modal analysis is carried out with Proper Orthogonal Decomposition to extract the coherent structures organization and the modifications induced by the perforation of the obstacle. When comparing the results of the perforated cubes with those of a solid cube, it can be observed that perforated obstacles offer a simple solution to obtain a localized increase of the convective heat transfer when the perforation crosses the obstacle creating a jet directed towards the wall. This is obtained at the expenses of a reduced space-averaged heat transfer rate due to a ’lift-up’ of the recirculation bubble past the obstacle, which postpones the flow reattachment and reduces the velocity of the reattaching flow. Nevertheless, in case of large perforation angles (thus jet issuing with larger angle with respect to the streamwise direction) this penalty is significantly reduced, providing a local gain in terms of heat transfer rate with almost the same overall heat transfer performances as a solid obstacle.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.027
      Issue No: Vol. 117 (2017)
       
  • Characterization of molten pool behavior and humping formation tendency in
           high-speed gas tungsten arc welding
    • Authors: Xiangmeng Meng; Guoliang Qin; Zengda Zou
      Pages: 508 - 516
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Xiangmeng Meng, Guoliang Qin, Zengda Zou
      The humping defect which easily forms in high-current and high-speed gas tungsten arc welding (GTAW) severely deteriorates the homogeneity of weld properties. However, the complicated and multi-coupled transport phenomena in molten pool make the quantitative characterization of humping formation tendency difficult. In this paper, dimensionless groups containing characteristic heat and fluid-flow variables of molten pool are determined based on Buckingham π-theorem. These groups with clear physical implication correspond to important and peculiar molten pool behaviors during humping formation, and they can be combined to evaluate humping formation tendency. Scaling analysis is then employed to study the molten pool behaviors in high-speed GTAW, in which the analytical equations between characteristic molten pool variables and process variables are formulated. The scaling laws are well verified and calibrated by numerical data from a numerical heat transfer and fluid flow model. The dimensionless groups and scaling equations show an explicit relation between process variables and humping formation tendency. The proposed methodology has low computational intensity, and can be easily applied to give a quantitative description of humping formation tendency at different welding parameters and to predict humping formation.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.124
      Issue No: Vol. 117 (2017)
       
  • SPH-FDM boundary for the analysis of thermal process in homogeneous media
           with a discontinuous interface
    • Authors: Bing Bai; Dengyu Rao; Tao Xu; Peipei Chen
      Pages: 517 - 526
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Bing Bai, Dengyu Rao, Tao Xu, Peipei Chen
      A SPH-FDM boundary method is proposed for the analysis of thermal process in homogeneous media with a discontinuous interface in this study, in which the smoothed particle hydrodynamics (SPH) method is used in the inner computational domain; and the finite difference method (FDM) is used as the function approximation near the boundary. This mixed method not only can improve the calculation accuracy under the first-type boundary conditions (i.e., Dirichlet), but also can convert the second- and third-type boundary conditions (i.e., Neumann and Robin) into the first-type boundary conditions in solving heat conduction problems of homogeneous media. As a result, a second-order accuracy can be achieved in the entire solution domain. The proposed SPH-FDM boundary method is applicable to the analysis of heat conduction in various media, including the problems with discontinuous interface in the computational domain and the solidification of materials with a moving phase transition boundary. Numerical results show that the proposed SPH-FDM boundary method overcomes the difficulties of the conventional SPH method in dealing with the second- and third-type boundary conditions and has a very high calculation accuracy.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.004
      Issue No: Vol. 117 (2017)
       
  • Numerical simulation of natural convection in open-cells metal foams
    • Authors: D. Chiappini
      Pages: 527 - 537
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): D. Chiappini
      The aim of this work is to present results obtained through a multi-physics solver used to numerically determine the thermal behaviour of an open-cells metal foam in the case of natural convection. Particular attention is addressed to the right geometry definition in order to capture the intrinsic foam characteristics, thus, the elementary cell used for describing the unitary metal foam one is the tetrakaidecahedron. In addition, in order to improve its isotropy, a random deformation on the basic structure has been introduced. This feature allows to locally deviate flow paths with obvious benefits in terms of heat exchange, with reducing preferential paths arising while packing the elementary cell over the volume. This mesh generation approach is coupled with a hybrid solver based on the lattice Boltzmann framework for the fluid-dynamics field reconstruction and on finite volume method for solving the energy equation so to retrieve temperature evolution. For the first time, high order differencing scheme are used in temperature discretization with obvious benefits in computational accuracy. Numerical results are compared with a set of experimental data available for a range of Rayleigh numbers and for different foam geometries. The agreement between numerical and experimental data is satisfactory with positive outcomes for future model developments.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.022
      Issue No: Vol. 117 (2017)
       
  • Subcooled water quenching on a super-hydrophilic surface under atmospheric
           pressure
    • Authors: Jun-young Kang; Gi Cheol Lee; Moo Hwan Kim; Kiyofumi Moriyama; Hyun Sun Park
      Pages: 538 - 547
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Jun-young Kang, Gi Cheol Lee, Moo Hwan Kim, Kiyofumi Moriyama, Hyun Sun Park
      The goal of this work is (i) to evaluate the cooling rate on a super-hydrophilic surface asa function of the subcooled degree ΔT sub of the liquid coolant, (ii) to analyze the contact heat transfer q″c of the liquid-solid contact, and (iii) to investigate the mechanism of microbubble emission boiling (MEB). We fabricated a super-hydrophilic surface by anodic oxidation of a zirconium vertical rod, so called completely wettable surface (CWS), which had surface microstructures with super-hydrophilicity. The CWS results in a decrease of the cooling time t cool as compared with the Bare Zirconium surface (BZS) results under small ΔT sub (t cool ∼50% decrease for ΔT sub =0, 15, and 40K, respectively). However, its surface effect is limited in the case of large ΔT sub (t cool ∼within 5% for ΔT sub =60 and 75K). The fast quench on the CWS under ΔT sub, explained by the increase in minimum film-boiling temperature T MFB and rewetting velocity U, is due to the liquid-solid contact. We evaluate the contact area A c and volumetric absorption rate of the liquid dV/dt by conducting liquid absorption experiments. The increase in A c and dV/dt contribute to an increase in q″c, by forming the liquid film at the liquid-solid contact spot. The orders of the time scale between capillary-wicking and liquid-solid contact are comparable. Destabilization of the large vapor bubble is caused by an increase in q″c, which is a major reason for MEB generation, and this mechanism enables the q″ to be significantly high on the CWS under subcooled quenching.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.006
      Issue No: Vol. 117 (2017)
       
  • Forced convection heat transfer from the biomimetic cylinder inspired by a
           harbor seal vibrissa
    • Authors: Hyo Ju Kim; Hyun Sik Yoon
      Pages: 548 - 558
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Hyo Ju Kim, Hyun Sik Yoon
      The present study investigates the forced convection heat transfer around a biomimetic elliptic cylinder inspired by a harbor seal vibrissa (HSV). This study is an original research to find the effect of the unique geometry of HSV on the forced convection around the biomimetic cylinder. We carried out large eddy simulation (LES) to investigate the flow and heat transfer around the vibrissa shaped cylinder for the Reynolds number (Re) of 500 and Prandtl number (Pr) of 0.7. The circular and elliptic cylinders are considered for the purpose of the comparison. The time histories of the surface-averaged Nusselt number showed that the HSV provided the stable behavior of the heat transfer by the significant suppression of its fluctuation. This characteristic of the heat transfer is comparable to the unique ability of the HSV to suppress the lift fluctuation and to role as a detecting device to capture the water movement induced by prey fish. The three-dimensional (3D) geometry of the HSV formed the spanwise variation of the Nusselt number, resulting in the sinusoidal profiles with a maximum and a minimum at the saddle and the node, respectively. This spanwise variation of the Nusselt number is identified by the flow structures. The nearly undetectable vortices in the wake at the node leads to the very weak secondary heat transfer by the recirculation in the near-wake. Thus, the minimum of the Nusselt number appears at the node. Otherwise, the saddle forms the large vortices in the near-wake and improve the heat transfer in this region, forming the maximum of the Nusselt number.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.10.053
      Issue No: Vol. 117 (2017)
       
  • Investigation of heat and mass transfer characteristics during energy
           discharge in an energy storage unit using hollow fiber membranes
    • Authors: Dechang Wang; Zhen Liu; Shaohong Zhang; Xiaoliang Tian; Yanhui Li
      Pages: 559 - 570
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Dechang Wang, Zhen Liu, Shaohong Zhang, Xiaoliang Tian, Yanhui Li
      A novel concentration difference energy accumulator was evaluated. This accumulator was framed by hollow fiber membranes as the water vapor transfer channels. This was the membrane energy accumulator (MEA). A mathematical model was created to simulate the heat and mass transfer in the crystal dissolving process of the energy discharging stage. In addition, the model was experimentally validated. Based on the simulation results, the heat and mass transfer characteristics of the MEA in the crystal dissolving process were analyzed. The results of the simulation and experiments proved the feasibility of the MEA. The energy storage capacity of the MEA was a minimum of 25% greater than that of a traditional concentration difference energy accumulator. The effectiveness of the MEA was confirmed.
      Graphical abstract image

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.125
      Issue No: Vol. 117 (2017)
       
  • One-dimensional model of a closed low-pressure adsorber for thermal energy
           storage
    • Authors: M. Schaefer; A. Thess
      Pages: 571 - 583
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): M. Schaefer, A. Thess
      The energy transition from fossil to renewable energy requires the development and integration of efficient energy storages. For thermal energy storage, concepts based on adsorption are promising. One key challenge is to overcome limitations of the storage performance by the heat and mass transfer. Against this background, a closed low-pressure adsorber with zeolite 13X honeycomb adsorbent is studied numerically to identify the limiting factors. The focus of the study is on the adsorption process with the heat extraction limited to the end of the zeolite honeycomb arrangement. A detailed model which takes effects of rarefied gas flow (e.g. slip) as well as cooling effects by the inflowing vapour into account is derived. The model is applied to study the mass transport, heat transport and adsorption over a broad range of relevant geometry and process parameters. The simulations demonstrate that the adsorption process is not limited by the mass transport and isobaric conditions can be assumed in most of the studied cases. In addition, special effects of rarefied gas flow are found to be negligible. Regarding the heat transport, the convective cooling by the vapour is found only to be significant for a very short initial time period. Further analysis show that the process is mainly limited by the heat transport. Only for short channels and wide channel diameters the process becomes limited by the adsorption.

      PubDate: 2017-10-18T10:35:05Z
      DOI: 10.1016/j.ijheatmasstransfer.2017.09.095
      Issue No: Vol. 117 (2017)
       
  • Flow and heat transfer characteristics over a square cylinder with corner
           modifications
    • Authors: Tehmina Ambreen; Man-Hoe Kim
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Tehmina Ambreen, Man-Hoe Kim
      In the present study, the effect of corner modifications on fluid flow and heat transfer characteristics across a square cylinder has been analyzed numerically in an effort to improve thermohydraulic parameters. Two-dimensional simulations have been carried out for laminar flow across a square cylinder with sharp, round, chamfered and recessed corners for Reynolds number range 55–200. Corner variations have been made for dimension c/D=0.125, where c and D indicate corner size and cylinder diameter respectively. When compared with the sharp-cornered cylinder, the results illustrated that corner modifications lead to significant drag reduction, however, the penalty in terms of Strouhal number increment is comparatively low. Deflected flow from upstream modified corners promotes flow separation from downstream corners in contrast to the sharp-cornered cylinder results in narrow wake width with intense fluid circulations, farther vortex shedding location and consequently reduced pressure drag as well as improved heat transfer coefficients. Recirculating fluid inside the upstream corner cut of recessed corners additionally contributes towards drag increment as compared to other corner configurations. Results also indicate that upstream corners modifications are more influential in amelioration of thermohydraulic characteristics as compared to downstream corners. Moreover, a new correlation for the average Nusselt number has been developed as a function of Reynolds number.

      PubDate: 2017-10-11T03:05:39Z
       
  • Significance of particle concentration distribution on radiative heat
           transfer in circulating fluidized bed combustors
    • Authors: Cihan Ates; Nevin Gorkem Kulah
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Cihan Ates, Nevin Selçuk, Gorkem Kulah
      In this study, effect of particle concentration distribution on radiative heat transfer in circulating fluidized bed combustors (CFBCs) is investigated. The aim is to identify how important it is to include axial and radial variations of particle concentration along the splash and dilute zones in radiative heat transfer calculations and to determine the predictive accuracy of simple 0D and 1D approximations for particle concentration distribution in the riser by benchmarking their predictions against a semi-empiric 2D axisymmetric model developed for a wide range of operating conditions and systems. Input data required for the radiation model are provided from measurements carried out in a 150 kWt cylindrical Circulating Fluidized Bed Combustor (CFBC) test rig burning low calorific value Turkish lignite with high volatile matter/fixed carbon (VM/FC) ratio in its own ash. Radiative transfer equation (RTE) is solved for 2-D axisymmetric cylindrical enclosure which contains gray, absorbing, emitting gas mixture with gray, absorbing, emitting, anisotropically scattering particles bounded by diffuse, gray/black walls. Incident heat fluxes and source terms along the riser are predicted by the Method of Lines (MOL) solution of Discrete Ordinates Method (DOM) with Leckner’s correlations for combustion gases, geometric optics approximation for particles and normalized Henyey-Greenstein for the phase function. Comparisons reveal that 0D and 1D representations of particle concentration distribution lead to overprediction of incident heat fluxes in both splash and dilute zones, where discrepancy of 0D model is larger. Similarly, errors in source term predictions introduced by simplifying the particle concentration distribution via deploying 0D and 1D models are found to be significantly large. These findings indicate that rigorous evaluation of particle concentration distribution is essential for accurate prediction of radiative heat transfer in CFBCs despite its high CPU requirements.

      PubDate: 2017-10-11T03:05:39Z
       
  • Numerical analysis of the flow and heat transfer in cylindrical clothing
           microclimates – Influence of the microclimate thickness ratio
    • Authors: M.S. Santos; Oliveira J.B.L.M. Campos T.S. Mayor
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): M.S. Santos, D. Oliveira, J.B.L.M. Campos, T.S. Mayor
      Clothing microclimates, i.e. the space between the skin and the clothing, can play a central role in the heat and mass exchanges from or to the body. This is especially true for protective clothing, where microclimates are generally thicker and natural convection is more likely to occur. We used a computational fluid dynamics approach to perform numerical studies of fluid flow and heat transfer across cylindrical clothing microclimates for Reynolds number of 3900. Transient simulations were performed for three different values of microclimate thickness to diameter ratio (0.05, 0.10 and 0.25), considering a two-dimensional cross-section of a human limb surrounded by a porous fabric and exposed to cool external air ( 10 ° C ). The obtained local heat transfer along the skin shows that increasing the microclimate thickness ratio from 0.05 to 0.25 decreases the convective heat fluxes by up to 100 % in the upstream regions of the microclimate, and increases them up to 190 % in the downstream regions. This asymmetry, which indicates an increasingly important role of natural convection as the microclimate thickness ratio is increased, is often overlooked in space-averaged approaches due to the opposite changes in the different regions of the microclimate. Local variations in temperature along the outer fabric and in convective fluxes along the skin were significant, reaching up to 14 K and 90%, respectively. The critical thickness ratio above which natural convection should not be ignored was found to be 0.1 (e.g. corresponding to a microclimate thicknesses of 11 mm or 8 mm, around an upper arm or forearm, respectively).

      PubDate: 2017-10-11T03:05:39Z
       
  • Heat transfer characteristics of the integrated heating system for cabin
           and battery of an electric vehicle under cold weather conditions
    • Authors: Jae-Hyeong Seo; Mahesh Suresh Patil Chong-Pyo Cho Moo-Yeon Lee
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Jae-Hyeong Seo, Mahesh Suresh Patil, Chong-Pyo Cho, Moo-Yeon Lee
      The objective of this study is numerically to investigate the heat transfer characteristics of the integrated heating system considering the temperature of cabin and battery of an electric vehicle under the cold weather conditions. The integrated heating system consists of a burner to combust fuel, an integrated heat exchanger for CHE (coolant heat exchanger) and AHE (air heat exchanger). The heat transfer characteristics like the overall heat exchanger effectiveness, the heat transfer rate, the temperature distribution and the fluid flow characteristics like the pressure drop, velocity distribution of the investigated integrated heating system were considered and analyzed by varying the inlet mass flow rates and the inlet temperatures of the cold air and water, respectively. The average Nusselt numbers for the cold air side and the water side were increased 28.4% and 9.5%, respectively, with the increase of the cold air side Reynolds numbers from 15,677 to 72,664 and the water side Reynolds numbers from 4330 to 11,912. The numerical results showed good agreement within ±9.0% of the existed data and thus confirmed that the present model was valid. In addition, the proposed integrated heating system could be used as the thermal management of the cabin and the battery system of the electric vehicle under the cold weather conditions.

      PubDate: 2017-10-11T03:05:39Z
       
  • The effect of natural convection in a liquid layer and the thermal
           inhomogeneity of vapor on the stability of a vapor film on a flat
           horizontal heater
    • Authors: V.V. Konovalov; T.P. Lyubimova
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): V.V. Konovalov, T.P. Lyubimova
      The linear stability of a vapor film, formed on the surface of a flat horizontal heater in a subcooled film boiling regime under conditions of terrestrial gravity, is studied. The study is aimed to estimate the role of natural convection in a liquid cooled from above, which is influenced by an additional flow caused by the redistribution of matter in the phases, in the process of stabilization of a stationary base state with a balanced heat flux at the interface between the two media. A modification of the conventionally used model of convective heat transfer (Newton–Rikhman’s law) is proposed. The calibration of the presented model, which is characterized by a dependence of the local coefficient of convective heat transfer on the rate of phase transition, is carried out on the basis of the experimental data available in the literature. The modified model allows to avoid the underestimation of the critical value of the heat flux in the subcooled liquid, at which a complete suppression of the Rayleigh–Taylor instability by a phase transition is achieved. In addition, it is demonstrated that the inhomogeneity of thermophysical properties of vapor and heat transfer by radiation at the boundaries of the vapor layer exert, respectively, stabilizing and destabilizing effects under the condition of a significant overheating of the heater surface.

      PubDate: 2017-10-11T03:05:39Z
       
  • A reassessed model for mechanistic prediction of bubble departure and lift
           off diameters
    • Authors: Mazzocco Ambrosini; Kommajosyula Baglietto
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): T. Mazzocco, W. Ambrosini, R. Kommajosyula, E. Baglietto
      Heat transfer models in multiphase flow with wall boiling rely on closure relations for bubble departure and lift-off diameters. The approach proposed in this paper reassesses the physical representation of each term of the force balance model, eliminating inconsistent assumptions and redundant calibration, leading to a more general methodology to predict lift-off and departure diameters. The validation against available datasets shows improved applicability when compared to existing models. The mechanistic model proposed in this work is expected to be implemented in CFD codes, to improve predictive performance of heat partitioning models.

      PubDate: 2017-10-11T03:05:39Z
       
  • Experimental study on sorption and heat transfer performance of NaBr-NH3
           for solid sorption heat pipe
    • Authors: L.W. Wang; G.L.
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Y. Yu, L.W. Wang, G.L. An
      NaBr is considered as one of the typical low temperature salts employed for solid sorption refrigeration. The novel concept of solid sorption heat pipe (SSHP) which integrates heat and mass transfer with solid-gas sorption technology is expected to fulfill the continuous heat transfer and alleviate the drawbacks of both conventional heat pipe and thermosyphon. In this paper, an experimental system for both sorption/desorption unit and heat transfer unit is designed and the experiments of non-equilibrium sorption/desorption performances of NaBr-NH3 and heat transfer performances of SSHP with different molar amounts and inclination angles are carried out, respectively. The test results of sorption/desorption unit demonstrate that the increase of desorption quantity becomes very slow when the heating temperature reaches up to 75 °C and above, and with the increase of condensing pressure, the mass of ammonia desorbed from the ammoniate NaBr becomes less. The investigations of SSHP with 3 mol sorbates show that the heat transfer quantity increases significantly with the heating temperature reaches to 55 °C and above, in which the relatively higher desorption rate can be obtained. The largest value of heat transfer quantity per unit molar ammonia for 3 mol sorbates is close to that of 5 mol under the condition of heating temperature of 90 °C and cooling temperature of 20 °C. When the angle of inclination changes from 90° to 45°, the heat transfer capacity of SSHP declines more significantly compared with that of the angle from 45° to 0°.
      Graphical abstract image

      PubDate: 2017-10-11T03:05:39Z
       
  • Numerical study on mass transfer from a composite particle settling in a
           vertical channel
    • Authors: Junjie Zhaoli; Guo
      Abstract: Publication date: February 2018
      Source:International Journal of Heat and Mass Transfer, Volume 117
      Author(s): Junjie Hu, Zhaoli Guo
      A two-dimensional study of mass transfer from a circular composite particle settling in a vertical channel is conducted with the lattice Boltzmann method. The particle is composed of two materials, one insoluble while the other soluble in the ambient fluid. In the problem, mass transfer, particle motion and fluid flow are closely coupled, where the concentration at the particle surface and particle properties vary with mass transfer. It is observed that mass transfer follows a Schmidt number independent scaling law of [ t / ( t ν Sc ) ] - 1.5 (t is the physical time, t ν is the momentum diffusion time scale and Sc is the Schmidt number), which is quite different from the pure diffusion of a stationary particle, ∼ ( t / t α ) - 0.5 ( t α is the mass diffusion time scale). An analysis of the concentration and flow pattern around the particle suggests that the scaling law for a settling particle is related to both diffusion distance and convection distance, while it is only relevant to the diffusion distance in the case of a stationary particle. For a settling particle, mass transfer is enhanced by two mechanisms due to convection, i.e., the concentration around the particle surface transported to the downstream of the particle by the fluid flow and the interface of mass transfer stretched with the particle motion, which are absent in the case of a stationary particle. Thus, the rate of mass transfer in the case of a settling particle is much higher than that for a stationary particle.

      PubDate: 2017-10-11T03:05:39Z
       
 
 
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