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In this study, a computer model based on discrete element method is employed to simulate the unsteady state heat transfer from the fuser roll to the toner and coating layer during the Xerography printing of coated papers. The model coating layers consisted of randomly arranged spherical pigment and latex particles with commercially relevant size distributions. Effects of coating characteristics, toner size, multiple toner layers, toner melting energy, toner thermal conductivity, coating layer thermal conductivity, and fuser roll temperature and pressure were investigated. Iso-thermal contours of fusing time were generated to demonstrate the relative importance of different fusing conditions and toner properties. Simulation results showed that temperature variation highly depended on the toner size, toner melting energy and the fuser roll temperature. Moreover, simultaneous coupling of the compressive stress and heat transfer indicated that the pressure exerted by the fuser roll did not significantly affect the rate of heat transfer. [Copyright &y& Elsevier]

Abstract: Effects of suction pressure and permeability on the steam heating characteristics of the wet paper are studied. Experimental results show that suction pressure enhances the energy absorption in the wet paper and effects of suction pressure strongly appear in the high-permeability paper, and also absorbed energy rate is decreased with increasing in heating time. From the numerical simulation results it is found that increase in moisture content and decrease of pressure gradient reduce the absorbed energy rate. Dimensionless numbers are derived from the basic equations to summarize the experimental and numerical simulation results. [Copyright &y& Elsevier]

Abstract: In the present work a number of configurations and difficulties of MEE system such as condensate flashing, vapor bleeding, steam splitting, preheating of liquor using condensate, variable physical properties and boiling point rise are taken into consideration to analyze the evaporation system. For this purpose seven effect evaporator system of a typical Indian pulp and paper industry is considered. The model developed is a set of nonlinear algebraic equations that include total and solute mass balances, energy balances, heat transfer rate equations, and the composition and temperature dependence of thermodynamic properties such as vapor pressures and enthalpies. The model is solved using nonlinear equation solver. Economic evaluation to optimize the number of flash tanks is carried out for seven effect evaporator system. The two different types of configurations of vapor bleeding are considered and compared. Considering optimum number of flash tanks and best configuration of vapor bleeding, a system is designed. Further, a modified system is found considering optimum number of flash tanks and preheating of liquor using condensate. This modified design enhances the steam economy by 23.77% and reduces the steam consumption by 36.76% in comparison to base case and thus, it is selected as optimum design. Finally, Pinch analysis of the MEE network has also been carried out and it is found that predicted results are compared well with base case. [Copyright &y& Elsevier]

• A comprehensive review on numerical simulations of boiling heat transfer from atomistic to mesoscopic and macroscopic scales is presented. • Critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling are highlighted. • Potential solutions and future research in the field of boiling heat transfer using the MDS, LB and CFD methods are proposed. Boiling is an efficient heat transfer mode with significant potential for thermal management in high-power electronic equipment. However, a comprehensive understanding of the boiling process, which encompasses bubble nucleation, growth, coalescence, slipping, and detachment across various scales, remains challenging. Molecular dynamics simulation, lattice Boltzmann, and computational fluid dynamics methods are popular and powerful tools for investigating boiling heat transfer phenomena at microscopic, mesoscopic, and macroscopic scales. These methods enable researchers to uncover the underlying boiling mechanisms and propose heat transfer enhancement techniques. Therefore, this paper provides a comprehensive review of boiling heat transfer, spanning from atomistic to mesoscopic and macroscopic scales, utilizing these three numerical methods. It addresses critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling, and proposes potential solutions and future researches, supplementing our previous review [Some advances in numerical simulations of multiscale heat transfer problems and particularly for boiling heat transfer, Annu. Rev. Heat Transf., 6 (2022) 217–269]. Besides, by shedding light on the characteristics of these numerical methods in studying boiling heat transfer, this paper aims to foster their development and advance enhanced heat transfer technologies. [ABSTRACT FROM AUTHOR]

• A 3D thermal lattice Boltzmann model for simulating melt flow and heat transfer in CZ single crystal growth has been constructed. • The coordinate system transformation is adopted to extend the application of LBM on 3D cylindrical cavities. • The critical Reynolds numbers are increased by introducing a transverse magnetic field. A three-dimensional (3D) thermal lattice Boltzmann model of crystal growth is presented to study the magneto-hydrodynamics (MHD) mixed convection in the melt of Czochralski silicon single crystal growth in this paper. In order to solve the problem of lattice Boltzmann method's difficulty in solving the flow of 3D cylindrical cavity, the 3D physical model of crystal growth is transformed from the Cartesian coordinate system to the Curvilinear coordinate system. And the irregular grids in the Cartesian coordinate system are transformed into regular grids in the Curvilinear coordinate system to facilitate the establishment of the Lattice Boltzmann model. Under the above operations, two coupled distribution functions are established to solve the governing equations. Two D3Q19 models are adopted to solve the melt velocity and temperature. And the 3D lattice Boltzmann modeling of crystal growth with cylinder boundary is realized by interpolation in Curvilinear coordinate system. The comparison with the experiment and other references proves that the proposed model and boundary treatment scheme is correct and it proposes a new way for studying the 3D crystal growth or other similar 3D cylindrical cavity simulations. Furthermore, the unstable melt flow for two cases are also simulated in this paper and the critical Reynolds number are also obtained. Results show that the introduction of the transverse magnetic field enhances the stability of the crystal growth system and increases the adjustable range of crystal rotation parameter. The obtained conclusion has an important reference for adjusting the process parameters during the CZ crystal growth. [ABSTRACT FROM AUTHOR]

The packing is the core heat transfer unit in the cooling tower. To improve the heat and mass transfer performance of the counterflow wet cooling tower, a new double S-wave structure packing is proposed in this paper, and its performance in heat-mass exchange is investigated using a combination of numerical simulation and experiment. The flow heat transfer performance of the double S-wave packing with different sheet spacing, tilt angle and inlet area is studied by numerical simulation, and the law of different structural parameters affecting the packing is derived to determine its optimal structure. The thermal and resistance performance of double S-wave packing and conventional double-folded packing under different working conditions were studied in comparison with each other by building an experimental bench. The results show that the cooling efficiency of double S-wave packing is 13.74% higher and the pressure drop is 3.58% lower than that of double-folded packing. The research results can provide important guidance and reference for engineering practice. [ABSTRACT FROM AUTHOR]

Abstract In this paper, numerical simulations are carried out to analyse the influence of geometrical parameters on the heat transfer and flow patterns for six spirally corrugated tubes at turbulent flow (R e = 25 × 10 3 ). Some previous studies are restricted to 2-D analyse or 3-D numerical simulations considering a reduced section length of the tubes as the computational domain in order to reduce the computation cost. The novelty of this paper is to perform a high cost numerical simulation using a computational domain with a length of the tube (L = 2 m) and dimensions similar to those used in commercial applications. In addition, a new non-dimensional parameter, the corrugation shape factor (C S F) is proposed, which takes into account the width of the corrugation, a geometrical dimension obviated in other studies. A 3-D unstructured tetrahedral mesh was created, and a grid independence analysis of the numerical solution was performed. The Realizable k − ε turbulence model with enhanced wall treatment was proposed to model the turbulence. Simulations were validated with experimental data available in the open literature. Regarding the ratio between height and diameter (H / D), the Nusselt number augmentation seems to augment as the H / D increases for low values of H / D (H / D < 0.05), whereas it decreases for values of H / D > 0.05. Considering the cases with the same diameter, in all the analysed cases, the pressure drop and Nusselt number augmentation decrease linearly as the P / D increases as well as both parameters increase linearly as the H / D , S I and C S F increase. The numerical results indicate that the augmentation of the Nusselt number and the friction factor (compared with the smooth tube) increases approximately linearly with the C S F in the range tested in this work (4 < C S F < 18), regardless of the tube diameter. [ABSTRACT FROM AUTHOR]

Highlights • Gas injection increases a maximal velocity within the boundary layer. • Gas suction decreases an overshoot phenomenon till his absolute vanishing. • Separation of thermal boundary layer at gas injection. • Conventional point of thermal boundary layer separation is proposed. Abstract The paper reports on numerical simulation of an accelerated laminar boundary layer over the heated permeable wall. Xenon was used as a working gas. The finite difference method was applied to solve the system of laminar boundary layer equations with variable gas properties. It has been shown that the gas injection in the mentioned conditions increases maximal velocity within the boundary layer and decreases skin-friction coefficient and thermal Stanton number. On the contrary, gas suction decreases an overshoot phenomenon down to its vanishing and increases skin-friction coefficient and thermal Stanton number up to the value at asymptotic suction. The paper considers a separation of thermal boundary layer at gas injection. The proposed conventional point of this separation is situated farther from the leading edge than the separation point of the dynamic boundary layer. [ABSTRACT FROM AUTHOR]

Highlights • We establish a more reasonable vortex cooling model for gas turbine blade leading edge. • Experiments and numerical simulations are conducted. • Influential mechanisms of temperature ratios are revealed more deeply. • This paper provides a guideline for the gas turbine blade leading edge cooling. Abstract Based on combined Infrared Thermography and numerical simulations, the heat transfer and flow performance in a vortex cooling configuration with 5 nozzles were investigated at various Reynolds numbers and temperature ratios. Validation was conducted between experiment and numerical simulation and results showed that the k - ω turbulence model has the best accuracy to predict the vortex cooling behavior. High Nusselt number regions appear under each nozzle in all cases, but air from downstream nozzles is easily impacted because of the “anti-cross flow” ability. Along the axial direction, targeting surface has a fluctuant heat transfer coefficient distribution, while along the circumferential direction, the heat transfer coefficient decreases linearly. Overall heat transfer coefficient increases with increasing Reynolds number and decreasing temperature ratio. Especially, the influence of temperature ratio under 3 setting methods is compared and discussed in detail, revealing the fundamental impact of temperature ratios. A globally-averaged Nusselt number correlation is presented over 22,000 < Re D < 39,000, 0.88 < TR < 0.94, and results in this paper are compared with other vortex cooling systems. [ABSTRACT FROM AUTHOR]

• An enhanced heat transfer structure is proposed, which can improve efficiency by 29 %. • The performance of the new structure was investigated by numerical simulation. • Experimental tests were conducted to prove the effectiveness of the new structure. To enhance the heat transfer efficiency of the helically coiled tubes heat exchangers, this paper proposes a double shell-passes structure designed for a multi-layer helically coiled tubes heat exchanger. Numerical simulation is employed to investigate the performance of the Double Shell-passes Multi-layer Helically Coiled Tubes Heat Exchanger (DSMHCTHE). Furthermore, an experimental test system is constructed to validate the simulation results, exploring the performance under different operating conditions. A comparative analysis is conducted with the traditional Multi-Layer Helical Tube Heat Exchanger (MHCTHE). The results indicate that, under identical experimental conditions, the heat transfer rate and thermal effectiveness of DSMHCTHE increased by 5.1 % to 12.9 %. The overall heat transfer coefficient showed an improvement ranging from 21.5 % to 29.0 %, while the shell-side heat transfer coefficient increased by 36.2 % to 47.5 %. However, the shell-side pressure drop increased by 60.7 % to 83.4 %. Utilizing the heat exchanger's comprehensive performance as the evaluation criterion, it was observed that DSMHCTHE exhibited superior comprehensive performance. In comparison to MHCTHE, the comprehensive performance of DSMHCTHE improved by 12 %. The design of the double shell-passes configuration has shown significant enhancements in both convective heat transfer and overall performance, highlighting the superior application potential of DSMHCTHE. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the spray cooling heat transfer characteristics using CFD method. The two phase mathematical model is established based on Euler-Lagrange approach. In this model, unsteady-state flow conditions are simulated. Heat and mass transfer between the vapor and the water droplet are computed. The averaged error of numerical results is 10% compared to experimental results in our previous papers. It is concluded that the heat flux and its distribution on heated surface are influenced by the heated surface temperature, mass flux, nozzle to surface distance and the number of nozzles. Furthermore, the heat flux distribution do not change obviously with the increasing of heated surface temperature, and the heat flux increases with the increasing of mass flux. Moreover, there is an optimal nozzle to surface distance while the spray impingement zone circumscribes in heated surface, and more nozzles lead to higher heat flux and better heat flux distribution on heated surface. Considering the disadvantage of manufacture difficulty and cost increase for more nozzles, there is an optimal nozzle number in certain space and heat dissipation requirement. The optimal number of nozzles is 8 in this article. [ABSTRACT FROM AUTHOR]

The particle sedimentation and phase change in the mushy zone are accompanied by a variety of complex transfer processes involving momentum, heat, and mass. It is very important to investigate the coupling process of particle settling and melting in the mushy zone for revealing the mechanism of the solid-liquid phase change. In this paper, the motion process and heat transfer characteristics of an elliptic particle as well as two particle interactions in the vertical channel were solved by the finite element method with the consideration of coupling of the phase change and motion. The Arbitrary Lagrangian-Euler Method (ALE) was employed to track the interface of the moving particle and fluid. Results show that the elliptical particle settles along the channel's center line vertically under gravity and undergoes phase change simultaneously. Uneven velocity and temperature fields surrounding the particle are generated by sedimentation, resulting in the particle with an irregular shape. When the initial position of the particle deviates from the center line, the particle deflects during the sedimentation and shifts both left and right in the X -direction. The different initial angles of settling also affect the sedimentation velocity and melting rate. When two particles settle simultaneously, they will lead to complex movement and heat transfer due to the interaction between each other. If the arrangement is eccentric, both particles undergo complex deflections during sedimentation, leading to different melting rates for the two particles. [ABSTRACT FROM AUTHOR]

Experimental studies used for evaluation of quality of the fire-fighters protective clothing are based on irradiation of the clothing sample by an external pulse of a given duration. The other side of the clothing sample is in contact with a material imitating the human skin, which has properties different than these of the skin. Therefore the problem considered in this paper was: what conditions should be satisfied to convert the experimental results, carried out on the stand with a skin-imitating material, to the case of the real human skin with different properties for which the experiments are not made? This will allow for better evaluation of the clothing protecting properties and estimation of the possible burns. Due to multilayer structure of the protective clothing and skin as well as complex phenomena involved in energy transfer through them the problem is very complicated. Therefore at the first attempt to solve the problem a simplified two-layer, clothing-skin system irradiated from external heat source was considered in the present paper. Temperature variation in the system was initially determined using the in-house 1D numerical code accounting for heat conduction in the skin and clothing, non-grey thermal radiation absorption, scattering and emission together with the water vapour diffusion and phase transformations of bound water to the gaseous phase in the protective clothing. Then the analytical model for temperature variation in the considered system was proposed and solved using the Laplace transform approach. In the latter model water vapour diffusion with its phase transformations were excluded and radiation emission was neglected. The analytical model allowed for deriving a formula which can be applied for converting the skin surface temperature obtained from the experiments carried out using the skin-imitating material to the material having skin properties. In order to verify the range of validity of the formula the analytical predictions were compared to the results of numerical simulations of temperature in the protective clothing-skin system considering cases in which different phenomena were included. For the majority of the cases studied good matching between analytical and numerical results was obtained for time corresponding to the heating and cooling processes of the protective clothing-skin system. [ABSTRACT FROM AUTHOR]

Efficient cooling system is an essential part of heavy duty extrusion pelleting line which plays an important role in 300 kt/a production engineering of polyolefin. In this paper, a wickless gravity-assisted two-phase cooling system (WGATPCS) used in heavy duty extrusion pelleting line was presented. The volume of the fluid (VOF) model in FLUENT was used to simulate the two-phase flow and heat transfer characteristic during the operation of WGATPCS by solving the equations of continuity, momentum and energy. The vapor velocity and temperature distribution of cooling system were obtained. The operating conditions applied in this paper are the followings: the filling ratio is 0.3, cooling water flow rate is 180 L/h, and heating power is 11 kW. The predicted temperature profile showed a good agreement with experimental data and the maximum relative error was below 0.99%. Therefore, it was concluded that the CFD model successfully reproduced the heat and mass transfer processes in proposed cooling system. The variation of liquid film thickness, the characteristics of liquid film and vapor-liquid interface were also analyzed. The maximum liquid film thickness was 0.017 mm at the bottom of condenser pipe, the velocity of vapor and liquid at vapor-liquid interface were 0.00785 m/s and 0.09 m/s respectively. The average condensation and evaporation heat transfer coefficients were 68083 W/(m 2 K) and 3929 W/(m 2 K), respectively. [ABSTRACT FROM AUTHOR]

This paper presents a computational heat transfer model of a rotary kiln used for the production of rutile titanium dioxide by the calcination of paste-like hydrous titanium dioxide. The work details the modelling of several chemical reactions occurring in the solid bed region along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. Finite-difference techniques are used and the steady state thermal conditions are assumed. The kiln is divided into axial segments of equal length. The solution is of marching type and proceeds from the solid inlet to the solid outlet. The direction of gas flow is opposite to that of the solids. Mass balance of each species in the solid charge, and mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperatures, and species concentration at the exit of that segment. The kiln length predicted by the present model is 45.75 m as compared to 45 m of an actual kiln reported by Ginsberg and Modigell (2011). The steady-state axial gas and solid temperature profiles have been also satisfactorily validated with the numerical results of the aforementioned paper. The output data consist of refractory wall temperature distribution, the axial solids and gas temperature profiles, axial solids composition profile, the length required for drying of the solid charge and the total kiln length required to achieve 98% conversion of anatase TiO 2 to rutile TiO 2 . A detailed parametric study with respect to the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and kiln rotational speed lent a good physical insight into the rutile-TiO 2 production process in a rotary kiln. [ABSTRACT FROM AUTHOR]

Actual thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, do not provide any estimate on the velocity of the groundwater flow and its orientation. These parameters are important for sizing geothermal borefield, since they influence the heat transfer around a geothermal borehole and the surrounding ground. To correct this shortcoming, a conceptual test has been developed in which heating cable sections inject heat in a borehole. Three temperature probes are strategically located at the borehole edge. This paper applies inverse heat transfer strategies to this thermal response test concept in order to identify the ground thermal conductivity, as well as the groundwater flow velocity and its direction. The suggested thermal response test and parameters estimation methodology are detailed. The influence of initial guessed values for the three unknown parameters was also studied. The work presented in this paper was carried out by numerical simulations. [ABSTRACT FROM AUTHOR]

• Normal mode stability analysis performed on counjugate heat transfer (CHT) 1D problem. • Stability analysis reveals existence of lower stability bound for coupling coefficient in Robin-Dirichlet interface boundary conditions. • Validity of stability analysis results is verified empirically. • Stability analysis is extended to more general CHT problems. This paper aims to evaluate and validate a mathematical coupling model, based on a normal mode stability analysis, for steady conjugate heat transfer problems. In order to achieve this goal, an aerothermal computational code was designed specifically ex novo to meet the needs of the current study. A large number of numerical simulations were carried out within the framework of the Dirichlet-Robin fluid-solid interface procedure and with conditions strictly identical to those adopted in the mathematical model. These coupled computations have been synthesized in five representative cases. The computed results show that the stability limit and the numerical Biot number derived from the coupling model are very reliable parameters. Many other physical and numerical aspects, such as the splitting of the coupling period are also considered in this work from which some interesting and promising results are obtained. At the end of this paper, we assess the general potential, limits and constraints of the mathematical model and its extension to multidimensional cases is discussed. [ABSTRACT FROM AUTHOR]

In this paper an attempt has been made with experimental as well as theoretical analysis to find the variation in heat transfer coefficient with Reynolds number and numerical simulation attempt has also been done with different turbulence models in forced convection turbulent flows. Experimental analysis was carried out by using forced convection experimental setup at constant power supply to the heater and by varying the different flow rates of air with the help of a blower. The tube heat exchanger is fully insulated. In turbulent flows, the heat transfer coefficient is greatly affected by the turbulence, hence in this paper numerical analysis was carried out with different turbulence models and analysis has been done with both experimental and theoretical values to find the best turbulence model. [ABSTRACT FROM AUTHOR]

In this paper an attempt has been made to find the enhancement of heat transfer with different types of twisted tape inserts (TTWTT), that is inserts of twisted tape over the twisted tape at an angles of 90 and 180 degrees twist. In plain twisted tape at the location of swirl flow the mixing of fluid particle are not satisfactory so that the heat transfer is somewhat less than the turbulent regime so in this paper numerical analysis of thermal and hydraulic characteristics of water flow has been studied by inserting twisted tapes over the main twisted tape at the location of uniform stream lines forming zone. The numerical simulation was performed in order to gain an understanding of physical behaviour of the fluid flow (decaying swirling flow field), fluid temperature and local Nusselt number characteristics of a tube fitted with TTWTT. [ABSTRACT FROM AUTHOR]

In order to understand thermal characteristics of high altitude airships, the numerical simulation of convective-radiative coupled heat transfer performance at a certain time in a day is carried out using Ansys Fluent software. The governing equations of flow are using the compressible Reynolds averaged N-S equations and standard κ-ɛ turbulence model. A non-uniform temperature distribution boundary condition in the complex thermal environment and heat transfer mechanism is applied on the surface of high altitude airships based on user definition function (UDF) programming. The paper then simulates the external convection heat transfer characteristics at various flow conditions at 40 degrees north latitude at the altitude about 20 km at noon in the summer solstice. Finally, the corresponding calculation results of the surface temperature distribution, the flow field distribution and the convective heat flux distribution of airship envelope are presented, which are also analyzed in this paper. [ABSTRACT FROM AUTHOR]

In the numerical simulation of heat transfer and fluid flow problems, residual is often adopted as a convergence criterion. Since residual is susceptible to several factors, such as the property of physical problems, the expression form of discretized equations, the scale of grid and the nondimensionalization of governing equations, the converged value differs greatly in different cases. Thus, it is hard to set a specific residual value in a specific numerical calculation. To give a universal convergence criterion in this paper, a residual based on normalization idea is proposed. Range of specified values of this improved convergence criterion for general heat transfer and fluid flow problems is also given in this paper. Numerical simulation results indicate that the improved convergence criterion based on normalized residual is much more reasonable than the one based on traditional residual. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is to define the guidelines for the design of new boiling test sections with a large number of artificial nucleation sites during nucleate boiling for thin substrates horizontally immersed in a saturated liquid with artificial cavities located on the upper surface. The findings of numerical simulations of pool boiling heat transfer for a single bubble and for a large number of nucleation sites based on the analysis of experimental cases were analysed. Dedicated test sections were used in experiments for the study of boiling mechanisms and interactions between active sites so that the numerical models representing the physics of the problem could be improved. The hybrid nature of the code used in this study, combining the complete solution of the three-dimensional time-dependent energy equation in the solid substrate with semi-empirical models representing the physical phenomena occurring in the liquid side, in a simplified way, allows a large number of simulations in a reasonable computational time. The present paper focuses in the first part on the capability of the model to reproduce the experimental results for various conditions, while in the second part, the results for a large number of nucleation sites are analysed. Regarding the single bubble growth, two series of simulations will be presented in this paper: the first one analyses the mechanisms of nucleate boiling on a silicon substrate immersed in the dielectric fluid FC-72. The second series studies the behaviour of bubbles on metallic substrates, platinum and titanium, in saturated water. In the last section, the effect of the position of a site during simulations of a large population of sites (of the order of 100) on the waiting time, growth time, type and occurrence of coalescence and the thermal characteristics is presented. [Copyright &y& Elsevier]

• Fully resolved simulations of fluid-particle systems. • Surface reaction with significant heat effects. • Temperature-dependent reaction rates determined by the Arrhenius equation. • Simulation parameters adopted from realistic POX reaction. In this paper, an efficient ghost-cell based immersed boundary method (IBM) is used to perform direct numerical simulation (DNS) of reactive fluid-particle systems. With an exothermic first order reaction proceeding at the exterior particle surface, the solid temperature rises and consequently increases the reaction rate via an Arrhenius temperature dependence. In other words, the heat and mass transport is dependently coupled through the particle thermal energy equation and the Arrhenius equation, and they offer dynamic boundary conditions for the fluid phase thermal energy equation and species equation respectively. The fluid-solid coupling is enforced at the exact position of the particle surface by implicit incorporation of the boundary conditions into the discretized momentum, species and thermal energy conservation equations of the fluid phase. Different fluid-particle systems are studied with increasing complexity: a single sphere, three spheres and a dense array consisting of hundreds of randomly generated particles. In these systems the mutual impacts between heat and mass transport processes are investigated. [ABSTRACT FROM AUTHOR]

• Applying strongly-coupled fluid-solid model in thermal field. • Coupling coolant channel, hot channel, film hole together. • Analyzing the temperature distribution near the interface. • Analyzing the global flow structure. This paper applied the state-of-the-art flow simulation method, i.e. Direct Numerical Simulation (DNS), and strongly coupled the DNS with the heat-transfer governing equations to solve the flow and thermal problems in 3-dimensional (3D) film-cooling structures in the aero-engine. The strongly-coupled fluid-solid simulation was conducted to study the heat exchange on the wall surfaces and was compared to the case with the adiabatic heat-transfer boundary condition on the wall surface. The inlet condition was given as the uniform flow. The width of the delivery channel was used as the characteristic length. The Prandtl number was set at Pr = 0.71. The DNS was performed at lower Reynolds number of Re = 500 with the far-field condition being applied in the y and z directions. The dimensionless velocity, turbulence intensity, pressure, and temperature were analysed. The results suggested that the coolant flow was driven by the pressure in the delivery channel with strong vortical interactions and high turbulence shears. In the simulation with the strongly-coupled fluid-solid model, the solutions presented the interactions in the heat transfer near interfaces, the temperature wall boundary layer was observed and presented approximate linear profiles near the wall surfaces. The effects of the delivery channel were concentrated beyond the linear layers. The study discovered two important fluid-solid coupling parameters and pointed out the necessity of applying the strongly-coupled fluid-solid heat-transfer model in the thermal simulation. [ABSTRACT FROM AUTHOR]

Workers exposed to hot environment experiences physiological changes, implicating human health and occupational safety. Phase change material (PCM) cooling vest is effective for personal cooling and thermal comfort. In this paper, the human-PCM-clothing model was constructed by combining the bioheat model and the PCM-clothing model to predict the cooling effect of PCM on thermal response in hot environments. The multi-segmented human bioheat model considered the effects of high temperature on metabolic rate, blood flow rate, and dehydration on the sweating rate. The PCM-clothing model analyzed heat and mass transfer between the PCM and its thermal environment. The model was tested with published data and the relative errors between the simulated and measured results were below 2.2% for mean skin and 0.33% for core temperature. The numerical parametric study was investigated to study the effects of the melting temperature and latent heat of the PCM packages on heat transfer. PCM with high latent heat and appropriate melting temperatures benefits body cooling performance. The equation for the optimum solution corresponding to the latent heat of PCM at different melting temperatures was derived. This study can guide the choice of PCM packages and the human thermal response analysis in a hot environment. • The human-PCM-clothing model was established to predict the cooling effect of PCM. • Multi-segmented bioheat model was improved for workers working in a hot environment. • PCM clothing model for heat and mass transfer between different layers was proposed. • The optimum latent heat for different melting temperatures of PCM was obtained. [ABSTRACT FROM AUTHOR]

Abstract: In the paper, being the first part out of two (the second one is focused on processes of heat transfer), results of the computer simulations of the flow in a circular pipe with a ball inserts turbulising the flow are presented. An influence of the diameter of balls and their longitudinal distance on a pressure drop in the turbulent flow as a function of the Reynolds number (for Re =10,000÷300,000) was analyzed. The investigations were carried out for different diameters of the balls (Db =7, 10, 13, 16 and 19mm) and different distances between them (L =20, 24, 28, 32, 36, 40, 48, 60 and 85mm) at a constant inner diameter of the tube (Dp =26mm). The results indicate that for the whole tested range of ball diameters and their longitudinal arrangements, there is an analytical dependency which allows for expressing a friction factor by the relationship: f =A⋅Re B. The constants A and B were functions of two variables: a dimensionless diameter of the ball (X = Db/Dp) and a dimensionless longitudinal distance between balls (Y = L/Dp). These two constants are closely related. They can be calculated analytically for the entire range of X and Y using a formula of the fourth order surface polynomial (15 coefficients of that polynomial are presented in the paper). The paper presents also experimental investigations carried out using a PIV (Particle Image Velocimetry) apparatus. A comparative analysis of selected inserts and numerical calculations was the goal. The obtained results show a good correlation between the experiment and computer modelling. [Copyright &y& Elsevier]

Abstract: This paper investigates heat transfer between particles during particle–particle and particle–wall collisions in fluid–solid flows. A model is described, which is based on the work by Sun and Chen (1988) [27], who described heat conduction between elastic, non-cohesive particles. The model of Sun and Chen is, in this work, extended to investigate how cohesion and viscoelasticity, elements that are always present in real systems, of the colliding particles influence the process of heat transfer. This was done by adopting three different soft-sphere models. At the end of the paper dimensional analysis is applied and, by fitting relations between the resulting dimensionless groups to numerical simulations using the models developed, “empirical” relations for the heat transfer during particle–particle and particle–wall collisions are derived. These empirical relations are suitable for use with hard-sphere collision models. [Copyright &y& Elsevier]

Highlights • First BeLi 2 F 4 loop to operate in 40 years. • Salt can withstand large temperature gradients. • Flow is stable but contains odd temperature jumps and spikes. • Heat transfer follows normal correlation behavior but is offset. Abstract A new large natural circulation FLiBe loop has operated for the first time in 40 years. Reaching temperatures above 700 °C with stable flow rates around 5 cm/s, the loop exhibits a range of flow phenomena pertinent to high temperature natural circulation safety systems for nuclear reactors. This paper discusses the system and several operating conditions spanning a wide range of behavior to aid the development of other systems, simulation benchmarks, or system-codes. Analysis of heat transport phenomena indicates that standard Nusselt number correlations apply to a first approximation. More accurate salt-freezing models may be necessary for air-cooled salt-systems due to the insulating affect of the low thermal-conductivity frozen salt layer on the cold pipe walls. [ABSTRACT FROM AUTHOR]

Abstract To overcome the deficiencies of parallel-flow shell and tube heat exchanger with round rod baffles (RRB-STHX), STHX with a new type of anti-vibration baffle (hexagon clamping baffle) and equilateral triangle cross sectioned wire coils (HCBetsw-STHX) is proposed in this paper. Response surface methodology (RSM) is adopted to investigate its thermal-hydraulic performance. Baffle distance, coil pitch, coil diameter and Reynolds number are considered as four design parameters. Analysis is conducted based on CFD to acquire the objective functions (Nu H , Nu H / Nu R , f H , f H / f R and PEC) for different combination of design parameters. The RSM with Central Composite design is used to identify the relationships between the objective functions and the design parameters. Variances of the linear term, quadratic term and interactive term for design parameters in the response variables are analyzed. The mechanism of heat transfer enhancement of HCBetsw-STHX is illustrated from the view of field synergy theory. The results indicate that the heat transfer enhancement of HCBetsw-STHX is quite better than that of RRB-STHX. In the given design space, the Nu H / Nu R is in the range of 1.335–1.720; the f H / f R is in the range of 5.462–12.936. The most significant factor on Nu H is Reynolds number, while the most significant effect factor on Nu H / Nu R , f H , f H / f R and PEC is coil pitch. The sensitivity of three objective functions (Nu H , f H and PEC) to design parameters is explored. In addition, the design parameters optimization for the maximum value of Nu H and PEC and that for the minimum value of f H are also carried out and corresponding flow structures are shown and illustrated. Highlights • A new parallel-flow heat exchanger with hexagon clamping baffles and wire coils is proposed. • Parameter sensitivity of factors on thermal-hydraulic performance is explored. • Design parameters optimization is explored to maximize the Nu and PEC and to minimize the f based on the generated response surface. [ABSTRACT FROM AUTHOR]

Highlights • Six heat transfer regimes identified. • Existence of a turbulent flow but laminar-like heat transfer regime for low Prandtl numbers. • Prediction of Nusselt number in turbulent flow and turbulent heat transfer regime. Abstract This paper investigates heat transfer regimes in fully developed plane channel flows without considering the buoyancy effect. Analyzing the governing thermal energy equation, aided by direct numerical simulation (DNS) data, six heat transfer regimes are identified including (i) laminar flow and laminar heat transfer (LamF-LamH), (ii) transitional flow and laminar-like heat transfer (TraF-LamH), (iii) transitional flow and transitional heat transfer (TraF-TraH), (iv) turbulent flow but laminar-like heat transfer (TurF-LamH), (v) turbulent flow and transitional heat transfer (TurF-TraH), and (vi) turbulent flow and turbulent heat transfer (TurF-TurH). One key result is the clarification of a TurF-LamH regime which exists only for low Prandtl number fluid (Pr ≪ 1). A critical non-dimensional number is determined as Re τ Pr 1 / 2 ≲ 50 where Re τ is the Reynolds number defined by the channel half-height δ and the frictional velocity u τ . In the TurF-LamH regime, the simplified thermal energy equation yields a prediction of Nusselt number as Nu ≈ 6.0. The clarification of the TurF-LamH regime provides valuable insight into the understanding of the Nusselt number data for liquid metals, which have very low Prandtl number. Another major finding is that, in the TurF-TurH regime, the Kader-Yaglom-style equation is shown to be better than the traditional power law correlations at predicting Nusselt number, for either low or high Prandtl numbers. No separate correlations are needed for the prediction of Nusselt number at low Prandtl numbers and high Prandtl numbers. Another advantage of the Kader-Yaglom-style equation is that the equation can be theoretically connected to the log-law for the mean velocity and the mean temperature. More importantly, in the TurF-TurH regime the prediction of Kader-Yaglom-style equation can be reliably extended to ultra high Reynolds numbers, for either low or high Prandtl numbers. [ABSTRACT FROM AUTHOR]

Highlights • Can modification of surfaces enhance heat transfer in a vertical falling film unit? • Experimental and numerical studies (VOF) of hydrodynamics and heat transfer. • Significant bulk mixing is induced by the modified surfaces. • Modified surfaces affect flow structures similarly as backflow in waves. • Modification of surfaces improved heat transfer by a factor of 2.5. Abstract In this paper we investigate experimentally and numerically the potential improvement of heat transfer in falling film units by introducing modifications of the heat transfer surfaces. Two different modified surfaces are investigated and the obtained results are compared to the ones acquired on a smooth surface. In our experiments we work with a broad range of operating conditions with Kapitza and Reynolds numbers in the range of Ka = 167–574 and Re 18–423, respectively. We compare local heat transfer measurements conducted at multiple positions and relate them to the film thickness measurements conducted by a laser triangulation scanner. Our experiments identify both cases where the introduction of modified surfaces significantly enhances the heat transfer and conditions where such a measure does not have a significant impact. The observed differences are compared to numerical simulations providing details of the flow structures in the liquid film in different cases. For that purpose, we directly solve the full Navier-Stokes equations in two dimensions, using the volume of fluid (VOF) numerical framework. Our results reveal that the heat transfer can be enhanced by a factor of up to 2.5 due to appearance of significantly enlarged time-dependent recirculation zones occurring behind the surface modifications, as opposed to such zones present in falling film units with smooth heat-transfer surfaces. [ABSTRACT FROM AUTHOR]

Highlights • A hyperbolic lattice Boltzmann method (HLBM) is proposed based on CV model and classical LBM. • A non-Fourier heat conduction process was simulated by HLBM and classical LBM. • The results of HLBM are closer to the experimental values than that of classical LBM. Abstract Classical lattice Boltzmann method (LBM) can recover Fourier's law. Since Fourier's law results in a parabolic heat conduction equation, the classical LBM is called the parabolic Boltzmann method (PLBM). But the Fourier's law is based on the absurd assumption that the heat transfer rate is infinite, so whether the classical LBM can be used to observe the non-Fourier heat transfer problem remains controversial. In this paper, a hyperbolic lattice Boltzmann method (HLBM), which can be used to analyze the non-Fourier effect, was derived based on the Cattaneo-Vernotte (CV) model. To verify the accuracy of the HLBM, the process of a gold film irradiated by the laser was simulated using the HLBM and the PLBM and the results were compared with the experimental data. Because of the non-equilibrium heat transfer between electron and lattice during the laser irradiation, the two-step HLBM/PLBM models were proposed according to the two-temperature model. The results show that the electron temperatures simulated by the two models are not much different from each other, and both of them coincide with the experimental values. However, the thresholds obtained by the two models are different, and the results of HLBM are closer to the experimental values. [ABSTRACT FROM AUTHOR]

Highlights • Heat transfer, pressure loss and turbulent flow structure of miniature structured ribs are presented. • Experiments and numerical simulations have been done. • W-shaped miniature ribs have the best thermal performance by vortex flow. • Miniature structured ribs can achieve high heat transfer performance while having relatively low pressure losses. Abstract This paper presents an experimental and numerical study of turbulent flow heat transfer and pressure loss in channels with structured miniature ribs on one wall with the aim to improve the internal cooling performance of gas turbine blades and combustor liners. Miniature transverse, angled, V-shaped and W-shaped ribs are investigated respectively in the study, and the aspect ratio of the channels is kept to be 6:1, and the rib pitch to height ratio is 10 and the rib height to mean hydraulic diameter ratio is 0.029. The experiments were carried out at the Reynolds numbers ranging from 10,000 to 60,000, and a low-Reynolds number k -ε turbulence model was also adopted to simulate the turbulent flow and heat transfer in the channels. Both experimental and numerical results have shown that the shapes of miniature ribs have appreciable influences on the heat transfer and pressure loss performance in the channels. The experiments showed that the W ribs have the highest heat transfer and pressure loss performance in the channel, and the angled ribs have the lowest heat transfer and pressure loss performance in the channel. The W-ribbed channel shows respectively the globally averaged Nusselt numbers and overall Nusselt numbers of 2.2–2.6 and 2.9–3.3 times those of a smooth channel, and the friction factors of 2.5–3.7 times those of the smooth channel, which are higher than those of the V-ribbed channel and the transverse-ribbed channel. The miniature structured ribs show appreciable higher thermal performance than the conventional sized ribs. Furthermore, the numerical simulations show different vortex flow structures near the wall induced by the structured miniature ribs on the wall, which are responsible for the high-performance heat transfer enhancement. [ABSTRACT FROM AUTHOR]

Highlights • Measuring heat flux distribution by infrared camera with a multi-color-reference. • Multi-color-reference with multiple emissivity supplies reference info for measurement. • This method can measure the emissivity and heat transfer coefficient concurrently. • Combining the advantage of contact and non-contact measurement. • The novel model has been analyzed and verified by simulation and experiment. Abstract Accurate measurement of heat flux (HF) is significant in both industrial engineering and scientific research. It is acknowledged that the radiative HF can be easily determined by radiometers. In order to measure the conductive or convective HF distribution flowing across a surface, this paper presents a novel non-contact measuring method based on the infrared (IR) technique and inverse heat transfer method (IHTM). In addition, a specially designed multi-color-reference (MCR) which is composed of four sectors with four different known emissivity will be attached to the focused surface in the practical measurement. Therefore, different radiation signals among the four different sectors of MCR as well as the focused surface will be detected by an IR camera, through which a whole radiation temperature map can be obtained. Based on the differences in the radiation temperatures of the surface and MCR, the IHTM can be adopted to yield useful boundary conditions such as emissivity of the surface, convective heat transfer coefficient, and the critical HF distribution. The measuring method presented in this study combines the advantages of contact and non-contact measurement, which can accurately obtain the HF distribution under the difficult-contacted conditions such as the HF monitoring of a boiling furnace, HF estimating of the aerodynamic heating surface, etc. Numerical simulation and experimental verification were organized to justify the newly-developed measuring method. Relative error in the simulation is estimated to be less than 2%, and that in the experiment is calculated to be around 4.23%. The result displays a relatively high precision of the measuring method, demonstrating that such a method can be applied in practical application. [ABSTRACT FROM AUTHOR]

Highlights • The mechanistic formation and physically self-consistent depletion of microlayers beneath growing bubbles with heat conduction into the solid is demonstrated. • Validation of the microlayer formation and ∼depletion model with recent measurements. • Predictions are used to identify the circumstances and phenomena that cause microlayers to be generated. • Predictions demonstrate that the importance of microlayers to bubble growth increases with the superheat. • Investigation of the significance of evaporative thermal resistance for microlayer formation and evaporation. Abstract Microlayers, the few-microns-thick layers of liquid that sometimes remain beneath bubbles growing on a heated substrate, are widely observed in experiments, but theoretical understanding of their formation, behaviour and role in bubble growth is limited. In this paper we present detailed interface-tracking simulations of the formation and depletion of such microlayers. Validation of our results is presented to the degree that available measurements of such a rapid and microscopic phenomenon allow. The work extends previous mechanistic hydrodynamic-only CFD simulations of early microlayer formation up to typical bubble departure times. These calculations confirm the understanding that the bubble growth rate and the resulting bubble shape determine the presence and overall extent of microlayers underneath steam bubbles. Their thickness is strongly influenced by viscous effects and surface tension. We then present coupled, physically self-consistent CFD simulations of the formation and evaporative depletion of such microlayers. This modelling suggests strongly that the evaporation process itself constitutes a significant fraction of the small resistance to heat and mass transfer presented by the very thin liquid layer. Inclusion of representations of evaporative thermal resistance, consistent with those suggested in the literature, is seen to promote the prediction of microlayer formation. Identification of the classes of conditions under which microlayers seem likely to be formed is presented, along with an assessment of their relative contributions to bubble growth. Comparisons of the predictions with recent detailed microlayer measurements indicate good agreement. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an effective quasi one-dimensional (1-D) computational simulation methodology for steady annular/stratified internal condensing flows of pure vapor. In-channel and in-tube flows are considered for a range of gravity component values in the direction of the flow. For these flows, three sets of results are presented and they are obtained from: (i) a full 2-D CFD based approach, (ii) the quasi-1D approach introduced here, and (iii) relevant experimental results for gravity driven condensing flows of FC-72. Besides demonstrating differences between shear and gravity driven annular flows, the paper also presents a map that distinguishes shear driven, gravity driven, and “mixed” driven flows within the non-dimensional parameter space that govern these duct flows. The paper also demonstrates that μm-scale hydraulic diameter ducts typically experience shear/pressure driven flows. [Copyright &y& Elsevier]

Highlights • Relative humidity has little effect on the temperature distribution of the fin. • No condensation occurs near the inlet area. • The maximum condensation mass flux is detected in the second row of pipe. • Relative humidity has little influence on the sensible heat transfer rate. • But manifests profound effects on the latent and total heat transfer rate. Abstract The heat and mass transfer of a five-row fin-and-tube heat exchanger under dehumidifying conditions is numerically studied in this paper, and the distributions of vapor condensation mass rate for both fin and tube surfaces are obtained. The influences of vapor mass percent of humid air and inlet velocity on heat and mass transfer are investigated. Numerical results reveal that relative humidity has little effect on the temperature distribution of the fin under humid conditions. It is also noticed that no condensation occurs near the inlet area, and the maximum condensation mass flux is detected in the second row of pipe; this phenomenon is more obvious at higher inlet velocities. Relative humidity has little influence on the sensible heat transfer rate; however, it manifests profound effects on the latent heat transfer rate and total heat transfer rate. The dimensionless heat and mass transfer factors are also obtained from the numerical study and compared with the correlations in literature. [ABSTRACT FROM AUTHOR]

Highlights • Diffuse-interface simulation of bubble dynamics in a binary mixture is performed. • Local accumulation of gas with the bubble is critical to continuous bubble growth. • Strong thermocapillary flow peaks before bubble pinch-off from the biphilic surface. Abstract In this paper, we numerically study pool boiling of a binary (water and nitrogen) mixture on a surface endowed with a combination of hydrophobicity and hydrophilicity (i.e., the so called biphilic surface). Here we adopt a numerical approach based on the phase field theory, where the vapor-liquid interface is assumed to be of a finite thickness (hence diffusive in nature) and requires no explicit tracking schemes. The theoretical modeling of two-phase heat and mass transfer in water diluted with nitrogen demonstrates the significant impact of impurities on bubble dynamics. The simulations show that locally high concentrations of nitrogen gas within the vapor bubble is essential to weakening the condensation effect, which results in sustained bubble growth and ultimately (partial) departure from the surface under the artificially enlarged gravity. Simply increasing the solubility of nitrogen in water, however, turns out to be counterproductive because possible re-dissolution of the aggregated nitrogen by the bulk water could deprive the bubble of vital gas contents, leading instead to continuous bubble shrinkage and collapse. Additionally, it is found that with the significant accumulation of nitrogen, the bubble interface is increasingly dominated by a strong interfacial thermocapillary flow due to the Marangoni effect. [ABSTRACT FROM AUTHOR]

Highlights • Effects of slip velocity and wall temperature on temperature jump condition are investigated. • Modified Patterson temperature jump condition is proposed by involving viscous heat generation. • This modified jump condition can predict the surface gas temperature for the airfoil case Kn = 0.26. Abstract Recently, new type of the Smoluchowski temperature jump condition has been proposed by considering viscous heat generation in rarefied gas flow simulations, and improved prediction of the surface gas temperature in comparing with DSMC data. Two forms of the Patterson jump condition have been revisited for rarefied gas flow simulations in the literature. In this paper, the modified Patterson temperature jump condition is proposed by considering viscous heat generation. We numerically investigate the effect of the slip velocity, the wall temperature and viscous heat generation on the surface gas temperature for external high-speed rarefied gas flow simulations by using various forms of the Patterson jump condition. Three configurations such as the sharp leading-edge flat plate, the sharp 25–55-deg biconic, and micro-airfoil NACA0012 are selected for simulations with Mach number from 2 to 15.6, and Knudsen number ranging from 0.04 to 0.26. The simulation results obtained show that the modified Patterson jump condition gives good agreement with the DSMC data, and predict temperatures better than those of new type of the Smoluchowski jump condition for all cases considered. [ABSTRACT FROM AUTHOR]

This paper presents a direct numerical simulation (DNS) technique, the Finite Element Fictitious Boundary Method (FEM-FBM) for the simulation of fluid-solid two-phase flows with heat transfer. The heat transfer equation is introduced to study thermal convection in fluid-solid two-phase flows. The Boussinesq approximation is considered for the coupling of momentum and temperature flow fields. Multi-grid finite element solver is used to compute flow equations of mass, momentum, and energy on a fixed Eulerian mesh which is independent of time and the solid particles are allowed to move freely in the whole computational domain. Fictitious boundary method (FBM) is used to treat the particles inside the fluid, FBM takes account of the thermal and momentum interaction between the fluid and the particles. The accuracy and stability of presented method are validated by comparing our test cases results with the results reported in the available literature. Numerical tests are performed to show that this method is potentially powerful and provides an efficient approach to simulate complex thermal convective particulate flows with a large number of particles. [ABSTRACT FROM AUTHOR]

Wedge-shaped hot-films are a promising alternative to hot-wires for supersonic free flow disturbance measurements if hot-wires cannot be used due to harsh flow conditions. Up to the present, wedge hot-films could not serve as quantitative tools because of an insufficient modelling of the substrate’s influence on the thermal balance. The present paper shows a static calibration of a wedge-shaped hot-film sensor that is based on a combination of an analytical, a numerical and an experimental approach. The substrate’s impact was analysed by the help of CFD simulations and modelled by a newly introduced substrate factor. The obtained sensitivities were discussed and qualitatively explained compared with standard hot-wires. A quantitative comparison of experimentally detected mass flux fluctuations proved the wedge hot-film data to match similar hot-wire results very well. The presented approach has the potential to upgrade hot-films of various shapes to tools for quantitative fluctuation measurements. [ABSTRACT FROM AUTHOR]

Highlights • A grille-sphere composite packed bed is proposed for improving efficiency. • Heat transfer performance of composite packed bed is experimentally investigated. • Heat transfer of composite packed bed is analyzed with numerical simulation. • Evaluation methods of heat transfer performances of packed beds are introduced. • Grille can change velocity distribution and enhance heat transfer in packed beds. Abstract Packed beds are widely used in industries, in which the flow and heat transfer characteristics of the packed bed may have a significant effect on the energy efficiency of the whole system. The flow and heat transfer characteristics of packed beds are greatly dependent on their structures. Therefore, it is crucial to develop new packing structures to improve the overall heat transfer performance of packed beds. In the present paper, a grille-sphere composite structured packed bed (GSCSPB) was developed. The new structure aims at overcoming the shortcomings of both randomly packed beds and traditional structured packed beds. A naphthalene sublimation experiment is conducted to measure the pressure drop and heat transfer in GSCSPB and evaluations of the comprehensive heat transfer performance are made to compare the GSCSPB with the randomly packed bed and structured packed bed. A 3-D model is set up to analyze the mechanism of the heat transfer enhancement by using FLUENT 14.0. Results show that firstly, GSCSPB has an excellent design property to reduce the pressure drop of the randomly packed bed and enhance the heat transfer of the structured packed bed, obtaining the highest overall heat transfer performance among the compared packed beds. Secondly, it demonstrates that the existence of the grille wall can change the velocity and temperature distributions, thus the heat transfer is enhanced in GSCSPB compared with a similar configuration without the grille. Finally, it indicates that the grille will help to design a new packing configuration which could achieve a structured packed bed easily and improve the overall heat transfer efficiency. [ABSTRACT FROM AUTHOR]

The reflow soldering process of large size components was always problematic in microelectronics manufacturing due to the possibility of component displacement failures after soldering; like tombstone formation or skewing, which can be traced back to the different heating of the opposite component sides. During vapour phase soldering, the efficiency of heat transfer highly depends on the thickness of the condensate layer. In this paper, the inhomogeneity of condensate layer formation and its effects were investigated at large size components during vapour phase soldering by numerical simulations. For this purpose, a 3D computational fluid dynamic model was established. According to the condensate layer formation in different cases, the onset differences in the melting of the solder alloy at the opposite leads of the component were calculated. By the results, the risk of the component displacement during reflow soldering was analysed. It was found, that the congestion of the condensate layer around the large size components can cause considerable differences in the onset of the solder alloy melting, which can yield in component displacement failures after soldering. The extent of difference in the onset of melting depends on the location of the component on the board and on the applied soak temperature. Keep-out zones on the board were suggested to reduce the possibility of the component displacement failures during the vapour phase soldering process. [ABSTRACT FROM AUTHOR]

In order to study the heat transfer characteristics (HTCs) of molten salt outside the tube bundle in a shell-and-tube heat exchanger (STHE) without baffle plates, the HTCs of molten salt (204.06 °C~236.91 °C) are experimentally and numerically investigated in this paper. Firstly, the HTCs of molten salt (3514 <  Re  < 5482) is experimentally studied based on the test platform with HITEC salt and oil. Then the empirical heat transfer equations of molten salt applied in the shell side of STHE are fitted. Finally, the comparison between the experimental and numerical results is conducted. The results show that the fitted equations agree well with the experimental data and the fitted deviations are only 8%. The error is about 11% between the simulation and experiment results which indicates that the HTCs of molten salt STHE would be predicted well using the simulation method. The numerical results also show that there exist flow dead zones in the STHE which could weaken the molten salt HTCs. [ABSTRACT FROM AUTHOR]

The influence of mounting angle on heat dissipation performance of a heat sink under natural convection condition is investigated in this paper by numerical simulation and experimental test. It is found that the heat sink achieves the highest cooling power when its mounting angle is 90°, while it reaches the lowest when the mounting angle is 15°, which is 6.88% lower than that of 90°. A heat transfer stagnation zone is the main factor that affects the cooling power of the heat sink, and its location and area vary with the mounting angle. It is identified that cutting the heat transfer stagnation zone is an effective way to improve the heat sink performance. [ABSTRACT FROM AUTHOR]

Abstract: This paper is devoted to the presentation of a new model for fin-and-tube evaporators, focusing on the solid core simulation and its integration with a quasi-homogeneous two-phase flow model for the in-tube refrigerant flow. Special attention is given to separated in-tube flow patterns (stratified, stratified-wavy), because of their importance in liquid overfeed and domestic refrigerator evaporators and the impact on the solid core temperature distribution. The paper presents the solid core formulation and numerical method, the in-tube two-phase flow model, and describes the proposed integration algorithm between them. A selected single-tube baseline case is analysed in full detail, showing the impact of stratified flow on the fin-and-tube temperature distributions. Additional studies are finally presented analysing different flow transitions (single phase to stratified flow, stratified-wavy flow to annular flow, annular flow to partial dry-out) and several operating parameters (flow regime, tube material, tube thickness). Special attention is given to the influence of the flow pattern on the fin-and-tube core temperature profiles. [Copyright &y& Elsevier]

Abstract: Three-dimensional numerical analysis for fully developed incompressible fluid flow and heat transfer through triangular microchannels over the slip flow regime is simulated in this paper. In order to study the flow through the channel, the Navier–Stokes equations are solved in conjunction with slip/jump boundary conditions. The influences of Knudsen number (0.001< Kn <0.1), aspect ratio (0.2< A <4.5), and Reynolds number (1< Re <15) on the fluid flow and heat transfer characteristics are extensively investigated in the paper. The numerical results reveal that the rarefaction decreases the Poiseuille number, while its effect on the Nusselt number completely depends on the interaction between velocity slip and temperature jump. It is also found that the aspect ratio has an important role in the analysis, but the variation of Reynolds number is less remarkable. [Copyright &y& Elsevier]

This paper reports on a project to construct and test an instrument that, for the first time, enables the accurate measurement of convective heat transfer coefficients (chtcs) in real buildings. Computer simulation models for the prediction of heat and airflow in buildings commonly rely on such empirically derived values. However, there are large uncertainties associated with their evaluation and use.The instrument described in this paper has been tested by measuring the chtcs on a heated plate mounted in a test room. The experimental work reported here was made up of two parts:The results are encouraging. Comparisons of the chtcs determined by the new instrument and the chtcs determined by the ‘traditional’ heated plate method have shown close agreement. It seems that the new instrument has great potential for use in real buildings. [Copyright &y& Elsevier]