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  • A thermal non-equilibrium approach on thermo-solutal natural convection due to the lateral flux of heat and solute on enclosure walls: Multi-solutions and oscillations
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-27
    P. Bera, Sarita Pippal, Arshan Khan

    In this paper, we address the influence of the thermal non-equilibrium state on double-diffusive convection in a porous enclosure, subject to constant heat and solute fluxes at the vertical walls, while other walls of the enclosure are adiabatic. For this, Darcy model has been adopted. The governing equations are solved numerically by the ADI method and analytically by using parallel flow assumption valid for the slender enclosure. A comparative study has been made in between buoyancy aiding flow(i.e., buoyancy ratio, ) and buoyancy opposed flow(i.e., buoyancy ratio, ). It was found that same as LTE (local thermal equilibrium) state particular oscillations and multiple solutions have also been observed on considering local thermal non-equilibrium (LTNE) state between the fluid and solid phase, for a certain range of interphase heat transfer coefficient (H) and conductivity ratio of fluid and solid (), when both buoyancy forces are opposite in nature (buoyancy ratio, ). The range of the interval for buoyancy ratio, , (in which multiple solutions exists) increases on increasing the value of H as well as , while the range of the interval for buoyancy ratio, , (in which oscillation exits) vary in a subtle way. In general, same as LTE state, here also is found to be a subset of for most of the values of H as well as considered in this study. Apart from this, in case of buoyancy aiding flow, the enhancement of aspect ratio (A) enhances the heat transfer rate for both the phases, up to a threshold value of A, beyond that threshold value the impact of the same is negligible, while acts in other way.

    更新日期:2018-09-28
  • Dropwise condensation on superhydrophobic nanostructure surface, Part I: Long-term operation and nanostructure failure
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-26
    Jian Xie, Jinliang Xu, Xiang Li, Huan Liu

    Dropwise condensation heat transfer (DWC) on superhydrophobic nanograsses surface (NGS) was investigated for long-term operation. For DWC of pure water-vapor on fresh NGS, two heat transfer regimes are identified: higher heat transfer coefficients with droplet jumping, and constant heat transfer coefficients with droplet rolling. The one-week operation not only deteriorates heat transfer performance, but also changes jumping or rolling mode to sliding mode. The condensation heat transfer coefficients are apparently decreased from first to third day, but they approach a limit value since the third day. In order to identify if the single-molecule-layer of polymer (SML) modified on nanograsses was destroyed, DWC on a smooth single-molecule-layer of polymer surface (SSML) was tested to display stable heat transfer with drop sliding for one-week operation, concluding no failure of the polymer layer. The collapse and breakage of nanograsses were observed to explain the decayed heat transfer versus time on NGS. Compared with SSML, the NGS has smaller droplet departure size but lower heat transfer coefficients, indicating positive and negative effects after introducing nanostructures. Three nanostructure failure mechanisms are proposed. This work suggests a new research field of the nanoscale fluid-wall interaction.

    更新日期:2018-09-27
  • Novel designs of charring composites based on pore structure control and evaluation of their thermal protection performance
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Weijie Li, Jun Liang, Jingran Ge

    To improve the thermal protection performance of the charring composites in reentry vehicles subjected to the challenged aerothemodynamic environment, we design six kinds of charring ablators based on the pore structure control. At the same time, a thermal-fluid-chemical coupled ablation model is developed for evaluating the designed ablators’ performances. Based on this model, the coupled thermal-fluid-chemical responses of an existing composite with homogeneous pores’ distribution are calculated to validate the developed model. After that, the numerical results of the pore structure controlled charring composites indicate that a charring ablator with a reasonable pores’ distribution will have better thermal protection performance, especially in which the initial pores’ content rise at the locations near the ablator’s bondline and in the middle of the thickness. This study will be a guidance for the design of charring composites for thermal protection application in reentry vehicles in a quantitative and efficient manner.

    更新日期:2018-09-26
  • Experimental investigation on the effects of rotation and the blowing ratio on the leading-edge film cooling of a twist turbine blade
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Hai-wang Li, Feng Han, Yi-wen Ma, Hai-chao Wang, Zhi-yu Zhou, Zhi Tao

    An experimental investigation has been performed to investigate the effects of the rotation and blowing ratio on the film cooling effectiveness distributions of the leading-edge regions of a twist gas turbine blade using a thermochromic liquid crystal (TLC) technique. The experiments were carried out at three rotating speeds, including 400 rpm (positive incidence angle), 550 rpm (zero incidence angle), and 700 rpm (negative incidence angle). The averaged blowing ratio ranged from 0.5 to 2.0. CO2 was used as the coolant to ensure that the coolant-to-mainstream ratio was equal to 1.56. The Reynolds number, based on the mainstream velocity of the turbine outlet and the rotor blade chord length, was 6.08 × 104. The effects of the rotating speed and the blowing ratio were analyzed based on the film cooling effectiveness distribution. The results show that rotating speed plays an indispensable role in determining the film cooling effectiveness of distributions on the leading edge. The position of the stagnation line moves from the pressure side (PS) to the suction side (SS) via an increase in rotating speed. Under the same blowing ratio, the area-averaged film cooling effectiveness increases monotonously with an increase in rotating speed. Under the same rotating speed, the area-averaged film cooling effectiveness increases with the increase in blowing ratio. More details about the effects of the rotation speed and blowing ratio on the spanwise averaged film cooling effectiveness of the leading-edge region are shown in this study.

    更新日期:2018-09-26
  • Thin reaction zones in highly turbulent medium
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    V.A. Sabelnikov, R. Yu, A.N. Lipatnikov

    A big database (23 cases characterized by Damköhler number less than unity) created recently in 3D Direct Numerical Simulation (DNS) of propagation of a statistically one-dimensional and planar, dynamically passive reaction wave in statistically stationary, homogeneous, isotropic turbulence is analyzed. On the one hand, the DNS data well support the classical Damköhler expression, i.e., square-root dependence of a ratio of turbulent and laminar consumption velocities on the turbulent Reynolds number. On the other hand, contrary to the common interpretation of the Damköhler theory and, in particular, to the concept of distributed burning, the DNS data show that the reaction is still localized to thin zones even at Da as low as 0.01, with the aforementioned ratio of the consumption velocities being mainly controlled by the reaction-zone-surface area. To reconcile these apparently inconsistent numerical findings, an alternative regime of propagation of reaction waves in a highly turbulent medium is analyzed, i.e., propagation of an infinitely thin reaction sheet is theoretically studied, with molecular mixing of the reactant and product being allowed in wide layers. In this limiting case, an increase in the consumption velocity by turbulence is solely controlled by an increase in the reaction-sheet area. Based on physical reasoning and estimates, the area is hypothesized to be close to the mean area of an inert iso-scalar surface at the same turbulent Reynolds number. This hypothesis leads to the aforementioned square-root dependence. Thus, both the DNS data and the developed theory show that a widely accepted hypothesis on penetration of small-scale turbulent eddies into reaction zones is not necessary to obtain the classical Damköhler scaling for turbulent consumption velocity.

    更新日期:2018-09-26
  • 更新日期:2018-09-26
  • Modeling Leidenfrost drops over heated liquid substrates
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Long Qiao, Zhong Zeng, Haiqiong Xie, Hao Liu, Liangqi Zhang

    To simulate Leidenfrost drops over a heated liquid pool (namely the liquid-substrate-based (LSB) Leidenfrost drops), a model of evaporation phase change contained within a three-fluid system is developed based on the ternary Cahn-Hilliard equations. In the numerical simulation, an axisymmetric model employing a hybrid LB-FD (lattice Boltzmann-finite difference) method is established, and the model and code are validated by two classical problems, i.e. lens spreading and drop evaporation. Then, the dynamics of LSB Leidenfrost droplets is unveiled numerically, and the results firstly present the distribution of evaporation flux, temperature and velocity near the LSB Leidenfrost drop. Meanwhile, this study also addresses the influence of several important parameters (including vapor Stefan number, vapor Prandtl number, drop Bond number, drop Ohnesorge number, releasing height and pool depth) on the evolution of drop volume and the configuration of quasi-equilibrium Leidenfrost system.

    更新日期:2018-09-26
  • Analytical solutions of fluid flow and heat transfer in a partial porous channel with stress jump and continuity interface conditions using LTNE model
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Qi Li, Pengfei Hu

    Forced convection heat transfer is analytically performed in a channel partially filled with porous media located at two inner walls under local thermal non-equilibrium (LTNE) condition. A constant heat flux is imposed at the channel walls. The Brinkman extended Darcy model is applied in the porous region and the stress jump and continuity conditions are employed at the interface. Exact solutions are obtained for velocity, pressure drop, the fluid and solid temperatures and Nusselt number. The effects of pertinent parameters on the fluid flow and heat transfer are conducted. Furthermore, the solution for the Nusselt number is compared to that by applying the local thermal equilibrium (LTE) assumption and the validity of the LTE is examined. It is shown that by applying LTNE model for different solid to fluid effective thermal conductivity ratios (K) and Biot numbers (Bi), the variations of Nusselt number with hollow ratio include three types of curves, which are: a maximized Nusselt number occurs at a small optimum hollow ratio, Nusselt number monotonically decreases by increasing hollow ratio and a minimized Nusselt number occurs at a small hollow ratio, respectively. For high K, a small critical value of S at which the Nusselt number reaches to LTE Nusselt number occurs and it lowers with the increase of Bi number and the decrease of Darcy number; while for low K, the LTNE Nu number versus hollow ratio is almost the same with LTE Nu number and therefore the LTE is valid. The stress jump at the interface is found to have negligible effect on the Nusselt number and the pressure drop, except in a high Darcy number with a low stress jump coefficient where the calculation of pressure drop need to account for the stress jump effect at the interface and the Nusselt numbers for both LTE and LTNE models slightly differs from the case of stress continuity interface condition.

    更新日期:2018-09-26
  • Contact line dynamics of two-dimensional evaporating drops on heated surfaces with temperature-dependent wettabilities
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Xuemin Ye, Xiangshan Zhang, Minglan Li, Chunxi Li, Shuai Dong
    更新日期:2018-09-26
  • A finite particle method with particle shifting technique for modeling particulate flows with thermal convection
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Z.L. Zhang, K. Walayat, C. Huang, J.Z. Chang, M.B. Liu

    Particulate flows with thermal convection are very challenging to simulate numerically due to the existence of constantly moving boundaries and complex heat-fluid coupling effects. Meshfree and particle methods have special advantages in modeling complex fluid flows with moving boundaries. However, previous works based on meshfree modeling mainly focused on either particulate flows only with momentum exchange or natural thermal convection. In this paper, a finite particle method integrated with particle shifting technique (FPM-PST) is developed for modeling particulate flows with thermal convection. FPM is an improved smoothed particle hydrodynamics (SPH) method with better accuracy while extremely irregular particle distribution may lead to ill-conditioned corrective matrix and terminate the simulation. PST can achieve regular particle distribution through shifting highly disordered particles while current PST is based on conventional SPH of poor accuracy. A number of numerical examples demonstrated that FPM-PST is a novel approach for modeling thermal particulate flows with good performance in accuracy and stability. It has better accuracy than the conventional SPH and can obtain comparable results with those from other sources. The unphysical voids can also be avoided by FPM-PST. From the FPM-PST simulations, it is observed that at relatively low Reynolds numbers thermal convection between hotter or colder particles and the fluid causes significant increase or decrease in the drag force acting on particles, while the thermal convection has little influence on the particle motion at relatively high Reynolds numbers.

    更新日期:2018-09-26
  • Cell transport and suspension in high conductivity electrothermal flow with negative dielectrophoresis by immersed boundary-lattice Boltzmann method
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Qinlong Ren, Fanlong Meng, Cho Lik Chan

    The cell transport and suspension using AC electrokinetics is essential for cell patterning and other biomedical applications in microfluidics. To avoid the undue cellular stress and irreversible damage to cells caused by low conductivity media, direct manipulations of cells in physiological solution of high electrical conductivity without dilution becomes significant. The driving mechanism of alternating current electrothermal (ACET) flow makes it attractive for pumping the physiological conductivity solution and transporting cells through the electrohydrodynamic (EHD) force. In addition, negative dielectrophoresis (nDEP) force is induced on a cell when its electrical conductivity is lower than that of solution media. In this paper, the effectiveness of ACET flow and negative DEP force in high conductivity solution is novelly used simultaneously to achieve a successful long-range cell transport and suspension in the microfluidic chamber. An immersed boundary-lattice Boltzmann method (IB-LBM) is developed to investigate the cell transport and suspension mechanism with respect to AC voltage magnitude, electrical conductivities of cell and solution, cell initial position, and cell size. It is found that a sufficient DEP force is indispensable for stabilizing the cell transport process and anchoring cells by overcoming the cell-cell interaction. Based on this, the design of a lab-on-a-chip device to generate a large DEP force is essential for future research to realize an efficient AC electrokinetic-based cell transport and suspension in physiological fluids.

    更新日期:2018-09-26
  • Numerical simulation of enhancing shale gas recovery using electrical resistance heating method
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    Yudou Wang, Bo Liao, Li Qiu, Diansheng Wang, Qingzhong Xue

    Gas production from shale gas reservoirs can be enhanced by increasing the temperature of the reservoirs due to the increased desorption of the adsorbed gas. However, limited techniques are currently available for practically introducing heat into such low permeability reservoirs. This paper investigates the feasibility of an electrical resistance heating method to promote shale gas production by increasing the temperature of the reservoirs. To achieve our research goal, a mechanistic numerical model is developed to describe electrical field, temperature field, and pressure field. To capture gas flow in a shale gas reservoir, non-linear flow, diffusion and adsorption/desorption which are all dependent on temperature are incorporated into a dual continuum media model. In our study, the gas production enhancement by electrical heating with two parallel horizontal electrode wells is evaluated using this model. We then assess impacts of the thermal properties of the formation, electrode length, electrical power, Langmuir volume and starting time of heating on gas production. The results indicate that the electrical heating method using two parallel horizontal electrodes can be an efficient method to enhance shale gas production. The heat capacity and conductivity of the formation have significant impacts on gas production. Reservoirs with low conductivity and low heat capacity tend to produce more gas due to heating. Meanwhile, shale gas reservoirs with high Langmuir volume also tend to yield more gas due to heating for. To maximize gas production, electrical power should be optimized based on the properties of shale gas reservoir and heating equipment. Longer electrodes heat more formations of the reservoir and thus lead to higher gas production by using the electrical heating method. In order to efficiently enhance shale gas production, electrical heating should start later in gas production, instead of earlier.

    更新日期:2018-09-26
  • Experimental investigation on the Leidenfrost phenomenon of droplet impact on heated silicon carbide surfaces
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-25
    ZeFeng Wang, Jinbiao Xiong, Weiyi Yao, Wenhai Qu, Yanhua Yang
    更新日期:2018-09-26
  • The coordination distribution analysis on the series schemes of heat exchanger system
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Jiangfeng Guo, Xinying Cui, Xiulan Huai, Keyong Cheng, Haiyan Zhang

    The influences of series schemes on the heat exchanger system are investigated using matrix analysis method in the present work. The performance of heat exchanger system can be improved by arranging the series schemes without an obvious increase of pressure drop or heat transfer area. The matrix analysis indicates that the series scheme has important effect on the parameter distribution over the heat exchanger system. The heat transfer can be enhanced by improving the distributed coordination between heat transfer coefficient and temperature difference besides increasing their values. The better distributed coordination between heat transfer coefficient and temperature difference corresponds to the better uniformity of heat transfer rate over the heat exchanger system, which is favorable to safety running of system. The matching performance improvement between the entransies of hot and cold fluids could lead to the better distributed uniformity of entransy dissipation over the heat exchanger system, which results in the reduction of the total entransy dissipation finally. The present work might provide a new approach to the optimization and layout of heat exchanger system for the fluids with drastic changes of properties.

    更新日期:2018-09-25
  • Characterization of transport limitations in SAPO-34 adsorbent coatings for adsorption heat pumps
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Jens Ammann, Bruno Michel, Patrick W. Ruch

    Adsorption heat pumps have become an increasingly viable technology to use waste heat or renewable thermal energy for heating and cooling. The power density of this emerging technology is limited by the rate of heat and/or mass transfer in the adsorption heat exchanger (AdHEX) which drives investment costs. This work presents an experimental analysis of the mass and heat transfer during water sorption on SAPO-34 coatings to determine the limiting transport mechanism in state-of-the-art AdHEX. Isochoric temperature swings were carried out and evaluated using a recently introduced method to determine the relative importance of heat and mass transport impedances. Coatings with thicknesses between 60 and 460 µm were investigated and in all cases the sorption dynamics were limited by mass transport. Ragone plots were used to characterize the power and energy trade-off during thermal cycling of SAPO-34 in water vapor to identify the pareto-optimal cycle time for a specific coating thickness. With the knowledge of the rate-limiting mechanism, the overall transport rates of adsorbent coatings can systematically be improved to enhance transport rates in next-generation AdHEX.

    更新日期:2018-09-25
  • Modeling heat capacity of ionic liquids using group method of data handling: A hybrid and structure-based approach
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Alireza Rostami, Abdolhossein Hemmati-Sarapardeh, Abdorreza Karkevandi-Talkhooncheh, Maen M. Husein, Shahaboddin Shamshirband, Timon Rabczuk

    Ionic liquids (ILs) are a significant class of chemicals with applications in solar cells, sensors, capacitors, batteries, plasticizers and thermal fluids. These compounds have attracted wide attention due to their low vapor pressure, tunable viscosity, non-flammability, wide liquid region phase diagrams and substantial chemical and thermal stability. Moreover, ILs structures can be easily modified leading to highly tunable physicochemical properties, which widen the application of these compounds. Heat capacity of ILs is an essential property for heat transfer evaluation as well as the estimation of widely used thermodynamic properties. Establishing a generalized and accurate model for predicting the heat capacity of ILs is valuable for their further development. In this manuscript, a hybrid group method of data handling (GMDH) was employed to establish a model estimating the ILs heat capacities. The database employed is an all-inclusive source of data taken from NIST standard, which includes the heat capacities of 56 ILs as a function of temperature and four structural parameters. About 80% of the database was assigned for building the model, and the remainder was used for evaluating the model performance. Statistical parameters and graphical techniques revealed that the model developed in this study is very accurate, with an R2 value of 0.982 and an average absolute percent relative error (AAPRE) of 1.84%. Moreover, the sensitivity analysis showed that the chemical structure of the cation has the highest impact on the heat capacity of ILs.

    更新日期:2018-09-25
  • Turbulent molten pool analysis of tandem GMA automotive steel sheet welding
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Kyungbae Park, Hunchul Jeong, Sungjin Baek, Dong-Yoon Kim, Moon-Jin Kang, Jungho Cho

    In this research, a three-dimensional turbulent weld pool simulation technique of tandem gas tungsten arc welding (GMAW) in a lap joint fillet is described and compared to a conventional laminar flow simulation. Basically, four governing equations are adopted for continuity, namely, continuity, Navier-Stokes, energy, and the popular volume of fluid equations. According to the basic theory of an arc weld pool, all known characteristics such as the arc heat input, arc pressure, electromagnetic force, and Marangoni flow are applied to the analysis model as a body force term or boundary conditions. A conventional arc weld pool analysis usually adopts a laminar flow; however, its results have shown a weld bead shape that is quite different from an experiment of a tandem GMA lap joint fillet welding of an automotive steel sheet. Therefore, the authors suggest the use of a k-εturbulent analysis model and show that its results coincide with the experiment results.

    更新日期:2018-09-25
  • A generalized thermal conductivity model for nanoparticle packed bed considering particle deformation
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Lin Zizhen, Huang Congliang, Li Yinshi

    Theoretically understanding the thermal conductivity of the nanoparticle packed beds (NPBs) is critical for designing high-performance thermal insulation materials. Currently, the classical effective medium assumption (EMA) model, Nan model, just show their good prediction at a high porosity of NPBs (≥0.75). Herein, we propose a generalized model of the thermal conductivity that almost covers the whole porosity range by considering the effect of the nanoparticle deformations on the thermal contact resistance (). It has been demonstrated that our model matches the experimental results great well. It is also found that at high porosity is dominated by the phonon diffusive scatterings (), while it is determined by the phonon ballistic scatterings () at a low porosity. More interestingly, can determine the porosity at which the lowest thermal conductivity of NPBs appears. This work opens a new way to design the desired thermal insulation materials.

    更新日期:2018-09-25
  • Impact of an oscillating guide vane on the thermo-hydraulic fields in a square cavity with single inlet and outlet ports
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Yang-Cheng Shih, J.M. Khodadadi, Shih-Wei Nien, Yi Zeng, Xuan-Long Huang

    This study reports on a numerical investigation of the impact of an oscillating rigid plate guide vane on the transient behavior of thermo-hydraulic fields within a square cavity with single inlet and outlet ports. The computational fluid dynamics software ANSYS® FLUENT was employed to perform the numerical simulations. The numerical analysis focused on the effect of the frequency and amplitude of an oscillating rigid guide vane on modification of the transverse throughflow, internal flow re-distribution, re-arrangement of multiple rotating vortices and the ensuing heat transfer performance. According to the numerical results, it is shown that for a combination of the Strouhal number and amplitude of inclination angle of the guide vane, the instantaneous Nusselt number that is a measure of the thermal performance of the system exhibits cyclical changes once the respective periodic state was reached. Moreover, the cycle-averaged and peak-to-peak Nusselt number increases with the increase of the amplitude of oscillations as the frequency of oscillation is fixed. For a fixed amplitude of oscillation, the cycle-averaged and peak-to-peak Nusselt number decreases as the frequency increases. Instantaneous variations of the dimensionless pressure drop of the cavity also exhibited periodic oscillations. Enhancement of heat transfer due to oscillations of the guide vane was accompanied with the expense of increasing the pressure drop.

    更新日期:2018-09-25
  • Nucleate boiling heat transfer model based on fractal distribution of bubble sizes
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Baojin Qi, Ya Wang, Jinjia Wei, Yonghai Zhang, Ting Yu

    Scientifically and accurately predicting the distribution of the bubble sizes on the heating surface is a key step to improve the calculation accuracy of the boiling heat transfer model. In the present study, an ingenious nucleate boiling heat transfer model was developed on the basis of random fractal function of the bubble sizes distribution, and renormalization group theory was introduced to solve this distribution function. Compared to the previous correlations, the distribution function of bubbles for various sizes can be obtained by solving this random fractal distribution function with renormalization group method. Furthermore, the process of increasing the fractal dimension from 1 to 2 was first proposed in this paper to match the whole evolution of the heated liquid from natural convection to nucleate boiling, to transition boiling, and finally to film boiling. Therefore, the present model can reveal the nature of nucleate boiling more comprehensively and deeply. Through comparison, it can be found that the image of bubble distribution obtained from the random fractal model was very similar to the experimental photographs statistically, and the predictions heat transfer were in good agreement with the experimental data when the superheat ΔT is higher than 10 °C, and the deviation is less than 20%.

    更新日期:2018-09-25
  • Study on the characteristics of GDL with different PTFE content and its effect on the performance of PEMFC
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Tao Chen, Shihua Liu, Jiwei Zhang, Mengnan Tang

    The content of Polytetrafluoroethylene (PTFE) is the key factor to determine the hydrophobicity and heat transfer characteristics of the gas diffusion layer (GDL), which directly affects the performance of the proton exchange membrane fuel cell (PEMFC). The PTFE content of GDL materials changes due to the complex and variable working conditions and the accumulation of working hours in fuel cells. In order to study the effect of PTFE content and external load on the thermal conductivity of GDL materials, a new method based on Fiber Bragg Grating (FBG) sensing technology was proposed to measure the thermal conductivity of GDL materials. The thermal conductivity of GDL materials with different PTFE content was measured by FBG temperature sensor, and the effect of different PTFE content on the performance of fuel cell was studied. The experimental results show that the hydrophobicity of GDL material increases with the increase of PTFE content, and different PTFE content of GDL materials have different effects on the performance of PEMFC. The difference of thermal conductivity of GDL material with different PTFE content can be measured by using FBG sensing measurement technology, which reflects the change of GDL material properties due to the difference of PTFE content in the GDL material. The results of this study provide guidance for the method of detecting the change of internal material characteristics of PEMFC.

    更新日期:2018-09-25
  • Some features of solving an inverse problem on identification of material properties of functionally graded pyroelectrics
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    A. Vatulyan, S. Nesterov, R. Nedin

    In the paper, we propose an approach to solving an inverse problem of identifying material characteristics of a functionally graded thermo-piezoelectric body. The operator reciprocity equations of the first kind are obtained in order to solve the problem formulated on the basis of the iterative process. As an example, the inverse problem of thermo-electroelasticity for a pyroelectric rod is investigated. We have carried out the computational experiments on restoration of the rod characteristics with various laws of inhomogeneity including those modeling layered and functionally graded coatings.

    更新日期:2018-09-25
  • A fractal model of effective thermal conductivity for porous media with various liquid saturation
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-24
    Xuan Qin, Jianchao Cai, Peng Xu, Sheng Dai, Quan Gan
    更新日期:2018-09-25
  • Physical absorption of CO2 and H2S from synthetic biogas at elevated pressures using hollow fiber membrane contactors: The effects of Henry’s constants and gas diffusivities
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-22
    Puttipong Tantikhajorngosol, Navadol Laosiripojana, Ratana Jiraratananon, Suttichai Assabumrungrat
    更新日期:2018-09-25
  • Dynamic evolution of the CO2-brine interfacial area during brine imbibition in porous media
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-22
    Lanlan Jiang, Bohao Wu, Yu Liu, Tetsuya Suekane, Dayong Wang

    Explicit knowledge on the two-phase interface evolution during CO2 dissolving in brine provides accurate predictions on the subsurface behavior of long-term CO2 storage. In this research, the interfacial areas of CO2-unsaturated brine were dynamically measured during multiphase flow using 3D quantitative analyses. The two-phase interfaces during brine imbibition were divided into three terms based on their attributes, i.e., ganglia, cluster and singlet. The evolution terms of the interfaces were interesting, as their fates showed wide evolution patterns due to the diverging effects of the Reynolds number (fluid velocity × length scale/fluid viscosity) and gravity. The brine bypassed the CO2, and the interface evolved with the development of a priority path under a heterogeneity impact. Relying on the approach of the slice-averaged and volumetric measurement, the effects of forces and heterogeneity on the CO2-unsaturated brine interface were evaluated on different directions. Linear regression of the clouded data points exploited the validity of the power-law distribution from number of trapped cluster to frequency of interfacial area, and the max interfacial areas and variance decreased, while the mean interfacial area increased with brine saturation. Slice-averaged CO2-brine interfacial areas normalized by volume or geometric surface area decreased linearly with the brine saturation at different Reynolds numbers.

    更新日期:2018-09-25
  • Effective and uniform cooling on a porous micro-structured surface with visualization of liquid/vapor interface
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-22
    Hyunwoo Noh, Junseon Yoo, Jin-Oh Kim, Hyun Sun Park, Don Koan Hwang, Dong-Pyo Kim, Moo Hwan Kim

    This study examines cooling efficiency, uniformity, and bubble dynamics on a porous surface. We use infrared (IR) thermometry to visualize results of temperature fields and liquid/vapor interfacial dynamics. Porous and non-porous micro-structured surfaces are prepared using soft-lithography and a ceramic precursor, allylhydropolycarbosilane (AHPCS). The surface cavities promote nucleation, and the heat transfer coefficient on the porous surface is approximately 30% higher than that on the non-porous surface. Additionally, the porous surface exhibits a more uniform temperature field with lower spatial and temporal variations than the non-porous surface. Bubble dynamics is visualized via an IR camera through the bottom side of the test specimens using the IR transparent characteristics of the substrate and micro-structures. The porous surface reveals higher nucleation site density and contact line density and lower equivalent bubble diameter when compared with those of the non-porous surface, and this is consistent with more effective and uniform cooling on the porous surface.

    更新日期:2018-09-25
  • Modelling sorption equilibria and kinetics in numerical simulations of dynamic sorption experiments in packed beds of salt/zeolite composites for thermochemical energy storage
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-22
    Christoph Lehmann, Olaf Kolditz, Thomas Nagel

    Composite materials consisting of a salt-impregnated porous host matrix constitute a way to combine the high energy storage density of hygroscopic salts with the fast kinetics of the carrier material. Depending on its pore structure the carrier can furthermore prevent or inhibit leakage of the salt solution. It has been shown experimentally that by impregnation with CaCl2 the heat storage density of zeolite Ca-X can be increased by 53 % to 270 kWh m−3, which confirms the potential of this material class. In transforming this potential into technical heat storage solutions, numerical simulations can support the design process by bridging the gap between material characterization, process specification and reactor design. Such simulations rest, among others, on suitable constitutive relations. For the equilibria and kinetics of salt/zeolite composite sorbents those relations are still missing in the literature. In this work, we present an axisymmetric model of the mass and heat transport through a packed bed of composite sorbent pellets accounting for radial effects such as increased bed void fraction near the sorption chamber walls. Special focus is laid on the modelling of the sorption equilibria and kinetics of CaCl2/zeolite Ca-X composites of various salt loadings. The developed sorption equilibrium model for arbitrary salt loadings of the CaCl2/zeolite Ca-X is based on isotherm measurements of only one composite sample and one sample of pure zeolite Ca-X thereby enabling reduced experimental effort for the equilibrium characterization. The linear driving force kinetics is calibrated using data from dynamic sorption experiments on zeolite Ca-X and used to predict the dynamic sorption behaviour of CaCl2/zeolite Ca-X composites. We found a good predictive capability of the unmodified kinetics model for high inlet humidities—i.e., the practically most relevant cases where the composite plays its strengths. Contrarily, for low inlet humidities, the used kinetics model strongly overestimates the sorption rate, which indicates the presence of additional kinetic inhibition mechanisms under such conditions.

    更新日期:2018-09-25
  • Identification of nucleate boiling as the dominant heat transfer mechanism during confined two-phase jet impingement
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Matthew D. Clark, Justin A. Weibel, Suresh V. Garimella

    Thermal management of high-power electronics requires cooling strategies capable of dissipating high heat fluxes while maintaining the device at low operating temperatures. Two-phase jet impingement offers a compact cooling technology capable of meeting these requirements at a low pressure drop. Generally, confined impingement geometries are used in electronics cooling applications, where the flow is constrained between the hot surface and orifice plate. Understanding the primary heat transfer mechanisms occurring as boiling takes place on the surface during jet impingement is important, specifically under such confined conditions. In this study, heat transfer from a copper surface is experimentally characterized in both confined jet impingement and pool boiling configurations. The dielectric liquid HFE-7100 is used as the working fluid. For the jet impingement configuration, the jet issues through a single 2 mm-diameter orifice, at jet exit velocities of 1, 3, 6, and 9 m/s, into a confinement gap with a spacing of 3 jet diameters between the orifice and heat source. Additional orifice-to-target spacings of 0.5, 1, and 10 jet diameters are tested at the lowest (Vj = 1 m/s) and highest (Vj = 9 m/s) jet velocities. By incrementing the heat flux applied to the surface and observing the steady-state response at each flux, the single-phase and two-phase heat transfer performance is characterized; all experiments were carried through to critical heat flux conditions. The jet impingement data in the fully boiling regime either directly overlap the pool boiling data, or coincide with an extension of the trend in pool boiling data beyond the pool boiling critical heat flux limit. This result confirms that nucleate boiling is the dominant heat transfer mechanism in the fully boiling regime in confined jet impingement; the convective effects of the jet play a negligible role over the wide range of parameters considered here. While the presence of the jet does not enhance the boiling heat transfer coefficient, the jet does greatly increase single-phase heat transfer performance and extends the critical heat flux limit. Critical heat flux displays a linear dependence on jet velocity while remaining insensitive to changes in the orifice-to-target spacing.

    更新日期:2018-09-25
  • 更新日期:2018-09-25
  • Comments on “‘Combined effects of magnetohydrodynamic and temperature dependent viscosity on peristaltic flow of Jeffrey nanofluid through a porous medium: Application to oil refinement’ by W.M. Hasona, A.A. El-Shekhipy and M.G. Ibrahim, International Journal of Heat and Mass Transfer, 2018, 126: 700–714”
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-20
    M.A. Elogail

    Dear Editor of International Journal of Heat and Mass Transfer,In this letter, I attempt to draw your attention to the fact that the above work that have been published in your highly respectful journal by Hasona et al. (2018) is not original. As the main idea upon which their results have been established is basically plagiarized from another published work and not genuine as the authors claimed. The investigation has been done recently for the first time in the peristaltic literature by Elogail and Elshekhipy (2018). In addition, in the coming few pages, I prove that all the results obtained in Hasona et al. work are significantly incorrect. Also, I elaborate on some of the numerous mistakes in their paper with suggested corrections for your knowledge, as it worth attracting the reader’s attention for such misleading study. Taking into account all the above, I wrote these comments.

    更新日期:2018-09-21
  • Flow boiling heat transfer in mini channel with serrated fins: Experimental investigation and development of new correlation
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Tao Wen, Hongbo Zhan, Dalin Zhang

    Extensive studies have been conducted on flow boiling heat transfer in mini or micro channels with square and circular configurations. Few investigations, however, have focused on a channel configuration featuring serrated fins. Therefore, the present study experimentally investigated the flow boiling heat transfer characteristics of refrigerant R134a in two mini channels with serrated fins. The equivalent diameters are 1.28 mm with 11 channels and 1.59 mm with 9 channels. Quantitative experiments were conducted under a mass flux of 60–308 kg/(m2.s), heat flux of 6–48 kW/m2, saturation pressure of 0.27–0.45 MPa and vapour quality of 0–1. Flow patterns during flow boiling in the channel were also captured and analysed. Results indicated that in the low vapour quality region, the local heat transfer coefficient increases with both heat flux and saturation pressure. However, the influence of mass flux is related to heat flux. The flow pattern in this region starts with dispersed bubbly flow and develops to vigorous bubbly flow. Slug flow and annular flow are then observed along the flow direction of the refrigerant. In contrast, in the high vapour quality region, the influence of heat flux and saturation pressure seem to vanish and higher refrigerant mass flux corresponds to a greater heat transfer coefficient. The annular flow continues in this region with intermittent dry-out, which leads to a sharp decrease in the heat transfer coefficient. As the existing empirical correlation for calculating flow boiling heat transfer coefficient fails to give a reasonable prediction for the present experimental data, a new correlation was proposed with a mean absolute relation deviation of 15.0% for all 1429 data points. The present experimental data and new proposed correlation can provide meaningful guidance for the design of a mini channel two phase heat exchanger with serrated fins.

    更新日期:2018-09-21
  • Effect of evaporator tilt on a loop heat pipe with non-condensable gas
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Huanfa Wang, Guiping Lin, Xiaobin Shen, Lizhan Bai, Dongsheng Wen

    The coupling effect of non-condensable gas (NCG) and evaporator tilts on the steady state operation of a loop heat pipe (LHP) was investigated both experimentally and theoretically in this work. Nitrogen was injected quantitatively into an ammonia-stainless steel LHP to simulate NCG, and the steady state characteristics of the LHP were studied under three typical evaporator tilts. According to the experimental results, the main conclusions below can be drawn. (1) The temperature is the highest under adverse tilt and the lowest under favorable tilt no matter whether there is NCG in LHP. (2) The existence of NCG could cause the increase of temperature under all three typical evaporator tilts, but the temperature increment caused by NCG seems to be relatively small under adverse tilt. (3) The increments of the temperature caused by NCG display different patterns under different tilts. Theoretical analysis was conducted to explain the results: the temperature under the coupling effect of NCG and evaporator tilt was determined by the energy balance between the heat leak from evaporator to compensation chamber and the cooling capacity of returning subcooled liquid. With the increase of heat load, the augmentation of heat leak caused by NCG and the enhancement of subcooled liquid cooling effect were incongruent. The coupling effect of NCG and evaporator tilts should be considered in the terrestrial application of LHP.

    更新日期:2018-09-21
  • 更新日期:2018-09-21
  • Spatio-temporal identification of heat flux density using reduced models. Application to a brake pad
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    S. Carmona, Y. Rouizi, O. Quéméner

    The identification of the spatio-temporal variations of a heat flux density field is addressed in this paper. The developed technique combines the use of reduced models (BERM method) with an iterative method of conjugate gradient descent, for which the gradient is estimated by the adjoint method. The application relates to the identification of the heat flux received by a brake pad in a braking situation, for which the mechanical deformation and the phenomena of wear cause the appearance of hot spots that one seeks to locate. The use of two different Branch bases, one for the temperature field and the other for the heat flux, enable to identify rapidly the time-space variation of the heat flux, without any hypothesis on the spatial form on it.

    更新日期:2018-09-21
  • Local end-wall heat transfer enhancement by jet impingement on a short pin-fin
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    S. Schekman, M.D. Atkins, T. Kim

    A short pin-fin array has been used to improve the internal cooling characteristics at the trailing edge of some gas turbine blade designs. In such a cooling scheme, the pin-fin array that is sandwiched by the turbine blade’s inner surfaces, experiences a uniform-like coolant stream. The local elevation of internal heat transfer especially on the end-walls (i.e., inner blade surfaces) at the trailing edge is achieved predominantly by horseshoe vortex-type secondary flows whose fluidic behavior has been well established. A modification to this cooling scheme has been made by introducing a blockage upstream, causing multiple jets to impinge on the pin-fins – the blockage jets. Previous studies on the internal cooling scheme employing the blockage jets have assumed that the end-wall flow topology is similar to that formed by the horseshoe vortex-type secondary flows due to similar local heat transfer distributions. However, there is no detailed and sufficient acknowledgement made of the lack of an approaching boundary layer. Therefore, the present study experimentally investigates local heat transfer around a single short pin-fin subjected to a fully turbulent jet impingement simulating the blockage jet impingement and demonstrates that the end-wall flow topology loosely resembles that formed by a horseshoe vortex system and is strictly different, depending on the distance between the jet exit and the pin-fin, relative to the length of the jet’s potential core.

    更新日期:2018-09-21
  • Passive production of synthesis gas from liquid methanol using a packed bed of porous material particles
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Kunito Okuyama, Kanoko Ichimi, Masato Takazawa, Asami Natori, Mikako Tanaka

    The passive production of synthesis gas from liquid methanol using a packed bed of porous material particles supporting a catalyst is investigated. Heating of the upper portion of a vertical tube packed with the porous particles where the bottom is immersed in liquid methanol is expected to cause steady upward fluid flow due to capillary action enhanced by evaporation. The emergence of a dry region and a resulting increase in temperature can produce synthesis gas due to catalytic reaction, which then flows out of the top end of the tube. In the proposed process, the capillary force, which is dependent on the local liquid content in the porous bed, is balanced locally with the gravitational force and the viscous forces acting on the liquid and vapor. The distributions of the liquid content, flow rates, pressures, and temperatures of liquid and vapor along the tube axis are calculated using a one-dimensional model based on the mass, force, and energy balances for each phase. The experimental results indicate the validity of the process, that is, the induction of steady fluid flow, the emergence of a dry region, temperature increase to the reaction level, and the products of the reacted gases. The behavior of liquid-vapor flow induced by phase-change in a packed bed and the factors that characterize the process and affect the performance are discussed.

    更新日期:2018-09-21
  • Cascaded lattice Boltzmann method based on central moments for axisymmetric thermal flows including swirling effects
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Farzaneh Hajabdollahi, Kannan N. Premnath, Samuel W.J. Welch

    A cascaded lattice Boltzmann (LB) approach based on central moments and multiple relaxation times to simulate thermal convective flows, which are driven by buoyancy forces and/or swirling effects, in the cylindrical coordinate system with axial symmetry is presented. In this regard, the dynamics of the axial and radial momentum components along with the pressure are represented by means of the 2D Navier-Stokes equations with geometric mass and momentum source terms in the pseudo Cartesian form, while the evolutions of the azimuthal momentum and the temperature field are each modeled by an advection-diffusion type equation with appropriate local source terms. Based on these, cascaded LB schemes involving three distribution functions are formulated to solve for the fluid motion in the meridian plane using a D2Q9 lattice, and to solve for the azimuthal momentum and the temperature field each using a D2Q5 lattice. The geometric mass and momentum source terms for the flow fields and the energy source term for the temperature field are included using a new symmetric operator splitting technique, via pre-collision and post-collision source steps around the cascaded collision step for each distribution function. These result in a particularly simple and compact formulation to directly represent the effect of various geometric source terms consistently in terms of changes in the appropriate zeroth and first order moments. Simulations of several complex buoyancy-driven thermal flows and including rotational effects in cylindrical geometries using the new axisymmetric cascaded LB schemes show good agreement with prior benchmark results for the structures of the velocity and thermal fields as well as the heat transfer rates given in terms of the Nusselt numbers. Furthermore, the method is shown to be second order accurate and significant improvements in numerical stability with the use of the cascaded LB formulation when compared to other collision models for axisymmetric flow simulations are demonstrated.

    更新日期:2018-09-21
  • 更新日期:2018-09-21
  • Optimized inlet geometry of a laidback fan-shaped film cooling hole – Experimental study of film cooling performance
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Marc Fraas, Tobias Glasenapp, Achmed Schulz, Hans-Jörg Bauer

    The orientation of an internal coolant channel with respect to the external hot gas flow has a major impact on film cooling performance. Previous studies reported a considerable decrease of cooling performance with perpendicular coolant crossflow for a state-of-the-art laidback fan-shaped film cooling hole. The objective of this experimental study is to investigate the extent to which cooling performance in such a setup can be improved by using an optimized cooling hole inlet geometry. For this purpose, three geometries with different cooling hole inlets are investigated. Results are compared to a baseline geometry with a sharp-edged cylindrical inlet. A test rig is used which enables compliance with all relevant non-dimensional parameters. High-resolution infrared measurements are conducted and heat transfer as well as cooling effectiveness are evaluated for up to 50 cooling hole diameters downstream of the cooling hole exit.Results show that the cooling hole inlet geometry tremendously affects cooling performance. Diffuser aerodynamics are altered for all investigated geometries with a modified inlet. This leads to a more symmetrical pattern of the film cooling jet for two of the investigated geometries. As a consequence, film cooling effectiveness is increased compared to the baseline case. The disadvantages of a perpendicular coolant flow in terms of effectiveness are entirely eliminated. Additionally, heat transfer coefficients are lowered. An overall evaluation reveals that the heat flux into the wall is significantly reduced for the proposed optimized cooling hole geometries.

    更新日期:2018-09-21
  • Parameterising continuum models of heat transfer in heterogeneous living skin using experimental data
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Sean McInerney, Elliot J. Carr, Matthew J. Simpson

    In this work we consider a recent experimental data set describing heat conduction in living porcine tissues. Understanding this novel data set is important because porcine skin is similar to human skin. Improving our understanding of heat conduction in living skin is relevant to understanding burn injuries, which are common, painful and can require prolonged and expensive treatment. A key feature of skin is that it is layered, with different thermal properties in different layers. Since the experimental data set involves heat conduction in thin living tissues of anesthetised animals, an important experimental constraint is that the temperature within the living tissue is measured at one spatial location within the layered structure. Our aim is to determine whether this data is sufficient to reliably infer the heat conduction parameters in layered skin, and we use a simplified two-layer mathematical model of heat conduction to mimic the generation of experimental data. Using synthetic data generated at one location in the two-layer mathematical model, we explore whether it is possible to infer values of the thermal diffusivity in both layers. After this initial exploration, we then examine how our ability to infer the thermal diffusivities changes when we vary the location at which the experimental data is recorded, as well as considering the situation where we are able to monitor the temperature at two locations within the layered structure. Overall, we find that our ability to parameterise a model of heterogeneous heat conduction with limited experimental data is very sensitive to the location where data is collected. Our modelling results provide guidance about optimal experimental design that could be used to guide future experimental studies.

    更新日期:2018-09-21
  • The effect of fin oscillation in heat transfer enhancement in separated flow over a backward facing step
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-20
    Saurav Kumar, S. Vengadesan

    Two-dimensional laminar fluid flow and heat transfer characteristics have been investigated numerically for a oscillating fin mounted on the top wall of backward facing step with constant bottom wall temperature. OpenFOAM is used to solve the governing equation of mass, momentum and energy conservation with the appropriate boundary conditions. Air is used as a working fluid with constant thermo-physical property (Pr = 0.71). It is found that the oscillating fin is the most effective method with highest average Nusselt number and lowest pressure drop, to enhance the mixing and heat transfer when it is compared to the different types of stationary fin arrangement. Further, the effect of frequency (which is directly proportional to the amplitude of velocity) and oscillation have been investigated and found that the average Nusselt number increases with the increase in velocity amplitude. It is also observed that the change in average Nusselt number is negligible with the increase in the amplitude of oscillation for a constant velocity amplitude. A correlation is also presented to express the effectiveness of the fin (ηf) in terms of ratio (Kv) of velocity amplitude (Vo) to the flow velocity (Uf) and is observed to follow the power law with constant exponent as ηf=cKv0.3.

    更新日期:2018-09-21
  • Review of pool boiling enhancement by surface modification
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-21
    Gangtao Liang, Issam Mudawar
    更新日期:2018-09-21
  • Influence factors of the evaporation rate of a solar steam generation system: A numerical study
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-19
    Jinxin Zhong, Congliang Huang, Dongxu Wu, Zizhen Lin
    更新日期:2018-09-20
  • Flow patterns of vertically upward and downward air-water two-phase flow in a narrow rectangular channel
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-20
    Vikrant Siddharudh Chalgeri, Ji Hwan Jeong

    Considering the importance of two-phase flows in narrow rectangular channels and their use in various applications, the hydrodynamics of a co-current air-water two-phase flow in a vertical narrow rectangular channel has been studied. Experiments have been carried out and flow regime maps for vertical upward and vertical downward flows have been plotted based on measured data sets. Flow regimes were identified and classified based on visual observation and void fraction data. Flow visualization was performed using a high speed camera, while a void fraction analysis was done using the electrical impedance method and a digital image analysis. Four different flow patterns were identified for the vertical upward flow and seven flow patterns were identified for the vertical downward flow. The flow regime map for the vertical upward flow was compared with previous studies and also with the flow regime map obtained for the vertical downward flow in this study.

    更新日期:2018-09-20
  • An analysis of the droplet support fiber effect on the evaporation process
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-20
    Christian Chauveau, Madjid Birouk, Fabien Halter, Iskender Gökalp

    This paper presents an analysis of the effect of the droplet support fiber on the droplet evaporation process. This effect is evaluated for a droplet evaporating in a hot environment at atmospheric pressure using the experimental results of the present study and those in the literature. Selected published results are acquired using similar test conditions and experimental setups as the present data. The only main difference between these studies is the droplet support fiber diameter which varies between 14 µm and 225 µm. The ambient temperature explored in these studies ranges from room temperature up to 973 K. n-Heptane is selected because it is the most common fuel used in these studies. The main findings are that the cross-fiber technique, which uses 14 µm fiber diameters, induces no noticeable heat transfer into the droplet and consequently does not interfere with the evaporation process. In contrast, the classical fiber technique, which uses relatively larger fibers, greatly enhances the droplet evaporation rate as a consequence of increased conduction heat transfer through the fiber. A correlation is proposed to quantify the level of this increase as a function of ambient temperature and the fiber cross-sectional area, df2.

    更新日期:2018-09-20
  • 更新日期:2018-09-20
  • 更新日期:2018-09-20
  • An analytical technique for the optimal designs of tube-in-tank thermal energy storage systems using PCM
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-19
    Yuhang Fang, Jianlei Niu, Shiming Deng

    Latent heat thermal energy storage (LHTES) using phase change material (PCM) has many application potentials, in view of the fact that it has higher thermal energy storage capacity than the sensible heat thermal energy storage such as stratified water storage (SWS). However, the stored thermal energy in an LHTES system is not all effective in discharging due to the additional heat transfer resistance between PCM and heat transfer fluid (HTF). An LHTES system could have a higher effective storage capacity than an SWS system only if it is well designed. The optimal design of an LHTES system could be realized only after the effective energy storage ratio, Est, is analyzed in the design stage. In comparison to the laborious computational analysis method, in this work, we developed an analytical technique from the effectiveness-NTU theory to calculate the required heat transfer length and predict Est of the basic unit in any tube-in-tank LHTES system. The technique was first compared with the numerical simulation method we reported earlier, and then used to find the optimal design under various constraints. It was shown that heat transfer enhancement in PCM could effectively improve the effective storage capacity of an optimal design. However, the maximum Est was limited by the thermal resistance in HTF when the enhancement in PCM was over a certain threshold. It was demonstrated that the use of HTF in a low-Re turbulent region could enhance heat transfer in HTF and achieve an Est as high as that in a laminar region while obtaining a higher discharging rate if heat transfer in PCM was well enhanced. This analysis provided quantitative guidelines on designing optimal tube-in-tank LHTES systems.

    更新日期:2018-09-20
  • Ice formation modes during flow freezing in a small cylindrical channel
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-19
    Aakriti Jain, Ankur Miglani, Yonghua Huang, Justin A. Weibel, Suresh V. Garimella
    更新日期:2018-09-20
  • Validation of numerical models for cryogenic-liquid pool spreading and vaporization on solid ground
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-18
    Le-Duy Nguyen, Myungbae Kim, Byungil Choi, Kyungyul Chung

    Accidental spills of cryogenic liquids create vaporizing pools spreading over the ground that can result in pool fires, explosions, or hazardous vapor clouds. Various integral models have been developed for simulating the spread and vaporization of cryogenic liquid pools. The spreading law of a constant Froude number (CFN1), which was originally derived for floating pools on water, has been assumed to be accurate for pools spreading on land in some models. This assumption is controversial and has not been validated. In addition, although the gas accumulation over spreading pools (GASP2) model has been well developed, further validation is required. An attempt was made to fill these gaps. This study aimed to propose and validate numerical models, i.e., a model incorporating the spreading law of a constant Froude number (CFN model) and simplified GASP models for indoor spills. The results were compared to the experimental data of cryogenic liquid pools spreading on solid ground. A good agreement between the predictions obtained from the simplified GASP models and the measured data was shown. Conversely, the CFN model yielded unrealistic results. Then, a modified CFN model was proposed and validated. The validations suggested that the modified CFN and simplified GASP models successfully simulated the behavior of cryogenic liquid pools spreading on solid ground.

    更新日期:2018-09-20
  • Phonon backscatter, trapping, and misalignment effects on microscale thermal conductance below the Casimir limit
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-18
    Francis G. VanGessel, Peter W. Chung

    At nanometer to micron length scales, there exists a strong competition between intrinsic and extrinsic scattering mechanisms that can curtail the free flight of phonons and ultimately affect the thermal transport. Despite significant progress in showing the ability to reach behaviors significantly below the Casimir limit, little appears to be understood about the competition between these scattering sources. In this investigation, we propose a simple one-parameter geometry that simultaneously modulates backscattering and trapping effects to enable directed study of these different means of controlling phonons. The geometry is a simple sequence of chambers offset from one another by a defined distance. We use the geometry to study the effects of phonon backscatter, trapping, and corner-turning on the thermal conductance in Si nanowires (NWs). We employ a full Brillouin zone Boltzmann Transport Equation (BTE) method to determine spatially-varying phonon densities in the geometry. Significantly greater impact is seen due to backscatter than any other means of arresting phonon flow. By creating a geometry that maximizes backscatter, a roughly 8-fold reduction in thermal conductance below the Casimir limit can be achieved at room temperature which is a factor of four smaller than the nearest reported value in the literature. The geometry is also useful for systematic investigation of other means of controlling phonons and affecting thermal transport; particularly, we investigate diffuse versus specular boundary scattering and the induced misalignment between the phonon flow and thermal flux due to the shape of the geometry. These effects combine to offer new insights into fundamental phonon behaviors and possible routes to phonon control.

    更新日期:2018-09-20
  • An experimental study on the effects of frosting conditions on frost distribution and growth on finned tube heat exchangers
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-18
    Long Zhang, Yiqiang Jiang, Jiankai Dong, Yang Yao, Shiming Deng
    更新日期:2018-09-20
  • Sensitivity analysis and application of machine learning methods to predict the heat transfer performance of CNT/water nanofluid flows through coils
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-18
    Alireza Baghban, Mostafa Kahani, Mohammad Alhuyi Nazari, Mohammad Hossein Ahmadi, Wei-Mon Yan
    更新日期:2018-09-20
  • Experimental investigation of condensation heat transfer and pressure drop of R-134a flowing inside dimpled tubes with different dimpled depths
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Kanit Aroonrat, Somchai Wongwises

    An experimental investigation is conducted to determine the effect of dimpled depth on the condensation heat transfer coefficient and pressure drop of R-134a flowing inside dimpled tubes. The test condenser is a double tube heat exchanger where the refrigerant flows inside and water flows in the annulus. The inner tube is a 1500 mm long and 8.1 mm inside diameter. The experiments are carried out for one smooth tube and three dimpled tubes having dimpled depth of 0.5, 0.75, and 1.0 mm. For each test tube, several test runs are performed over mass flux range of 300–500 kg/m2s, heat flux range of 10–20 kW/m2, and condensing temperature range of 40–50 °C. The experimental results reveal that the dimpled tube presents the significant heat transfer enhancement and pressure drop penalty. The tube with the highest dimpled depth yields the highest heat transfer enhancement and pressure drop penalty up to 83% and 892% higher than those of the smooth tube, respectively. Additionally, the overall performance of dimpled tube is evaluated in term of efficiency index. The new correlations including the effect of dimpled depth, dimpled pitch, and helical pitch on the Nusselt number and friction factor of R-134a in dimpled tube are developed.

    更新日期:2018-09-18
  • Experimental research on condensation of R134a and R404A refrigerants in tubular mini-channels during impulsive instabilities. Part II
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Waldemar Kuczynski

    The following paper presents the results of experimental research on the condensation of R134a and R404A refrigerants in tubular mini-channels during impulsive hydrodynamic instabilities. The first part includes an analysis of the influence of impulsive instabilities on the development of the condensation phase-change of R134a and 404A refrigerants in horizontal tubular mini-channels. The second part will present results of research on the same type of instabilities during the decay of the condensation phase-change process of R134a and 404A refrigerants. This research was conducted using the same set of investigated mini-channels with internal diameters of D = 0.63–3.30 mm. Special attention was paid to the possible occurrence of characteristic instabilities during condensation in mini-channels, so-called capillary blocking.

    更新日期:2018-09-18
  • Effects of magnetic field on the pool boiling heat transfer of water-based α-Fe2O3 and γ-Fe2O3 nanofluids
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Shi-Yan Li, Wen-Tao Ji, Chuang-Yao Zhao, Hu Zhang, Wen-Quan Tao

    Pool boiling experiments of water-based α-Fe2O3 and γ-Fe2O3 nanofluids with different concentrations (0.005–0.100 g/L) were conducted at atmospheric pressure. Two kinds of magnetic field induced by two neodymium magnets were also applied to investigate the effects of magnetic field on the pool boiling of nanofluids. It demonstrated that the magnetic field could change the local concentration of nanofluids and produce an extra pressure on the bubble boundary. The extent of the effects was not only dependent on the intensity and distribution of magnetic field, but also the magnetism and concentration of nanoparticles. For the 0.050 g/L γ-Fe2O3 nanofluid in the presence of magnetic field induced by two mutually exclusive magnets, an enhancement in boiling heat transfer coefficient up to 28% was obtained. The results of the experiments indicated the feasibility to control the pool boiling performance of magnetic nanofluids by external magnetic field.

    更新日期:2018-09-18
  • Experimental research on condensation of R134a and R404A refrigerants in mini-channels during impulsive instabilities. Part I
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Waldemar Kuczynski

    The following paper presents the results of experimental research on the condensation of R134a and R404A refrigerants in horizontal tubular mini-channels during impulsive hydrodynamic instabilities. Due to the complexity of the problem, it will be presented in two parts. The first part covers the results of experimental research on the influence of impulsive instabilities during the development of condensation of R134a and R404A refrigerants in mini-channels. The second part will cover the decay of condensation for similar conditions. The paper also provides a definition and conditions of the initiation and propagation of impulsive instabilities. Special attention was paid to the possible occurrence of characteristic instabilities during condensation in mini-channels, so-called capillary blocking.The experimental investigation was based on the condensation of R134a and R404A refrigerants in horizontal tubular mini-channels with internal diameters of D = 0.64; 0.90; 1.40; 1.44; 1.92; 2.30 and 3.30 mm. Propagation of impulsive instabilities was a result of a sudden change in the refrigerant flow-rate inside mini-channels.

    更新日期:2018-09-18
  • Air-side heat transfer enhancement in plate-fin channel with an airfoil-based self-agitator
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Kuojiang Li, Xianchen Xu, Zheng Li, Hsiu-Hung Chen, YangYang Chen, Sheng Wang, Zhaoqing Ke, Guoliang Huang, Chung-lung Chen, Chien-Hua Chen

    Airfoil-based self-agitators (AFAs) were installed in multiple plate-fin channels integrated with cantilever beams. The heat transfer enhancement and pressure drop characteristics of this AFA design were experimentally investigated and compared with the clean channel case. We found that the AFA vibrates periodically and generates vortices, which enhance flow mixing and thus heat transfer performance. A rectangular shaped airfoil-based self-agitator (RAFA) and a delta shaped airfoil-based self-agitator (DAFA) with variable chord lengths were designed to investigate shape and size effects on thermal performance. Measurements were also carried out for DAFAs with different layouts, such as multiple rows of DAFAs installed inside a single channel. For the chosen heat sink and assigned working conditions, the best heat transfer performance was obtained with four rows of DAFAs, which caused an 80% increase in overall Nusselt number over the clean channel at the same Reynolds number and a 50% rejected heat increase at the same pumping power due to the strong longitudinal vortices generated by the presence of the AFAs.

    更新日期:2018-09-18
  • Effects of temperature-dependent properties on natural convection of power-law nanofluids in rectangular cavities with sinusoidal temperature distribution
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Lei Wang, Changsheng Huang, Xuguang Yang, Zhenhua Chai, Baochang Shi

    In this paper, the effects of temperature-dependent properties on natural convection of nanofluids in rectangular cavities with sinusoidal temperature distribution are investigated in detail with lattice Boltzmann method. To improve the computational efficiency, all simulations are performed on the Graphics Processing Unit (GPU) using NVIDIA’s CUDA. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. The effects of power-law index (0.5⩽n⩽1.5), thermal Rayleigh number (104⩽Raf⩽106), diameter of nanoparticle (25nm⩽ds⩽100nm), nanoparticle volume fraction (0.0⩽ϕ⩽0.04), temperature of the cooled sidewall (315K⩽Tc⩽335K), temperature difference between the sidewalls (10K⩽ΔT⩽50K), amplitude ratio (0.0⩽A⩽1.0), wave number (0.0⩽ω⩽6.0), phase deviation (0.0⩽θ⩽π) and aspect ratio (0.250⩽AR⩽4.00) on heat and fluid flows are investigated. The results reveal that there is an optimal volume fraction ϕopt at which the maximum heat transfer enhancement is obtained, and the value of ϕopt is found to increase slightly with decreasing the nanoparticle diameter, and to increase remarkably with increasing the temperature of Tc or ΔT. In addition, the average Nusselt number is generally decreased with increasing power-law index, while increased with increasing A and ω. Further, we found that the average Nusselt number behaves nonlinearly with the phase deviation parameter. Moreover, the present results also indicate that there is an optimal value of aspect ratio at which the impact of AR on heat transfer is the most pronounced.

    更新日期:2018-09-18
  • Investigation on optimization of the thermal performance for compressible laminar natural convection flow in open-ended vertical channel
    Int. J. Heat Mass Transf. (IF 3.891) Pub Date : 2018-09-17
    Deboprasad Talukdar, Chung-Gang Li, Makoto Tsubokura

    The present paper focuses on the optimization of the thermal performance for compressible laminar natural convection flow induced under high-temperature difference in an open-ended vertical channel by optimizing the channel inter-plate spacing using numerical simulation. The present investigation is conducted for a wide range of Rayleigh number (Ra) 104 to 107 in channel heated asymmetrically by uniform surface temperature with air (Pr0.72) as working fluid. Several values of channel gap between plates, new modified preconditioned all-speed Roe scheme along with dual time stepping technique and modified Local One-dimensional Inviscid (LODI) relations as channel inlet and outlet boundary conditions suitable for compressible laminar natural convection is employed for the current simulation. Heat transfer rate in terms of average Nusselt number is obtained for all Rayleigh number and channel aspect ratio is obtained. Variation of thermal and velocity profiles, the variation of average Nusselt number and mass flow rate into the channel for the combination of each Rayleigh number and channel aspect ratio is reported. From the results obtained, a correlation for optimum aspect ratio with Rayleigh number which maximizes the heat transfer within the channel is presented.

    更新日期:2018-09-18
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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