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• HFE-7100 boiling curves from the onset of boiling to dry-out, in a vertical and rectangular mini-channel. • Local heat transfer coefficient (HTC) calculated with an inverse heat conduction method. • Influence of subcooling and pressure on heat transfer, pressure drop and flow patterns. • Increasing pressure improves the critical heat flux (CHF) and HTC, delays the dry-out, and reduces pressure drops. • Increasing subcooling improves CHF and HTC, delays the dry-out, and modifies the flow pattern. The background of this study is the problem of thermal runaway in the battery cells of electric vehicles. Increasingly powerful and compact battery packs require highly efficient thermal management. One potential solution is the direct liquid cooling of lithium-ion battery cells using a dielectric liquid which boils over a safety limit temperature. This approach intends to prevent in a first step the cell thermal runaway and if it fails in a second step its propagation to its neighbors: the liquid boiling helps to mitigate the cell temperature rise and to transport and spread the heat. The arrangement of the cells in the pack and their close spacing induce a scientific problem of convective boiling in a mini-channel. To enhance designs using this solution, a comprehensive understanding of flow boiling and a precise local heat transfer quantification is essential. The HFE-7100 has been selected as a working fluid for its attractive thermophysical properties and a suitable saturation temperature. The present paper introduces new experimental results of flow boiling dielectric fluid, the HFE-7100, in a vertical rectangular mini-channel. Measurements are carried out from start of boiling to dry-out. Boiling curves are obtained for a mass flux of 391 kg/(m².s), at different pressures (0.7, 1, 1.5 bar) and at different subcoolings (Δ T s u b = 0 ; 15 ; 30 ; 45 ∘ C). The test section is an aluminum block instrumented with three lines of five K-type thermocouples located all along the flow. The visualization of the flow is achieved through a glass pane with a high-speed camera to identify different flow patterns. The local heat transfer coefficient is calculated by a resolution of a 2D inverse heat conduction method. The experiment mainly aims at determining the heat transfer coefficient, the critical heat flux (CHF) and the pressure drop and at characterizing both the flow regimes and the dry-out phenomenon. The influence of subcooling and pressure on flow boiling is analyzed. An increase in subcooling enhances the CHF and the heat transfer coefficient, and delays the dry-out. Subcooling has an impact on the flow pattern and modifies the type of CHF. In the operating conditions tested, a decrease in pressure enhances CHF and delays dry-out. On the other hand, the heat transfer coefficient increases with rising pressure. Similarly, pressure drops are lower with higher pressure. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of the anomalous diffusive effects caused by micro-scale heterogeneity and kinetic and inertial thermal relaxations on the optically induced thermoelastic bending component of the photoacoustic response. We calculated the temperature distribution for a one-dimensional heat transfer problem with planar and periodic excitation, neglecting the influence of thermoelastic strains on the temperature profile. Thermoelastic bending was evaluated using a theoretical approximation of a thin plate, while pressure fluctuations in the photoacoustic cell were obtained by assuming adiabatic changes in the closed air. The model analysis shows that the relaxation processes could significantly affect the mechanical piston component of the photoacoustic response at frequencies higher than the minima of the inverse of two thermal relaxation times, while the influence of micro-scale heterogeneity is observable in the whole frequency range. • The hyperbolic DPL model enhances accuracy of thermoelastic effect at higher frequencies. • Sensitivity to fractional order of DPL model emphasizes precision in TE control. • Anomalous DPL heat diffusion shifts and attenuates the peak of the hyperbolic result. • Maximum damping occurs to identical kinetic and thermal relaxation times. [ABSTRACT FROM AUTHOR]

Highlights • Advection-diffusion problems with multi-term time-fractional derivatives and of variable coefficients are considered in higher dimensions. • These problems have applications mainly in heat conduction or heat transfer, mass and chemical transports into porous or nonporous media. • A meshless spectral radial point interpolation method (MSRPIM) using radial basis functions (RBFs) and point interpolation, is proposed and implemented for obtaining accurate solutions of these problems. • Stability analysis of the proposed method is carried out which is justified computationally. • Computed solutions obtained via different RBFs are matched with each other as well matched with the exact and earlier works for various fractional order derivatives. Comparisons reveal accuracy and efficiency of the proposed method in obtaining accurate solutions for such problems. Abstract In this paper, a weighted meshless spectral radial point interpolation method (MSRPIM) is implemented for the numerical solutions of a class of multi-term time fractional advection-diffusion problems with spatial and temporal dispersion. In the proposed methodology, meshless shape functions are used for discretization in space. These functions are generated via radial basis functions (RBFs) and point interpolation method. Weighted θ -scheme and first order finite differences together with a simple quadrature rule are employed for the discretization of time fractional derivatives. Efficiency and accuracy of the formulated method is validated in terms of number of nodal points N , time-step size τ and weight parameter θ ∈ [ 0 , 1 ]. Quality of the computed solutions are checked using E ∞ , E 2 and E rms error norms. Stability of the proposed method is analyzed theocratically and validated computationally, which is an important task of the current paper. Simulations reveal very good accuracy for both 1D and 2D test problems having constants and variable coefficients. [ABSTRACT FROM AUTHOR]

Highlights • A quantitative study of the frost distribution and growth on FTHX was reported. • Frost pattern between windward and leeward sides of FTHX was compared. • Frost thickness, density and mass on different parts of FTHX were analyzed. • The effects of frosting conditions on frost distribution and growth were studied. Abstract Recently, the authors have published a paper which provided the frost distribution and growth along the airflow direction of finned tube heat exchangers (FTHXs), and demonstrated that some frost was accumulated on the edge of windward fins at a given frosting condition. As a follow-up to the work reported in the previous paper, in the current paper, the effects of frosting conditions on frost distribution and growth characteristics of FTHXs with different fin pitches were experimentally investigated. The results showed that the protruded thickness of frost on the edge of windward fins and the ratio of the frost mass on the edge of windward fins to that on the entire FTHX were both increased with the increases in air temperature (T a) and relative humidity (RH a), but decreased with an increase in initial air face velocity (v a). In addition, the effects of RH a on the mass ratio were more significant than those of T a and v a. Furthermore, the averaged frost density on the edge of windward fins was increased with an increase in RH a ; and that on the surfaces of fins and tubes was increased with an increase in v a , but decreased with an increase in RH a. [ABSTRACT FROM AUTHOR]

• Application of MCrAlY coating to increase heat transfer during water spray cooling. • The use of the coating intensifies heat transfer compared to the uncoated surface. • The thickness of the coating affects the intensity of the heat removal. The main purpose of the paper was to determine the influence of NiCoCrAlY coating application and its thickness on the heat transfer during water spray cooling under surface boiling conditions. The scope of the research included: sensor preparation, measurements of the sensor temperature during cooling, and numerical calculations to determine the intensity of sensor cooling. The intensity of heat removal was determined by the average values of the heat flux on the cooled surfaces. The inverse method for the heat conduction equation was used to determine the heat transfer boundary conditions. Temperature measurements during cooling were carried out for an initial sensor temperature of 500°C, 700°C and 900°C and a liquid pressure 0.1 MPa, 0.2 MPa. Due to this, it was possible to select a coating thickness that contributed to the greatest extent to the increase in the intensity of heat dissipation from the hot surface. The highest values of the heat flux were obtained during the cooling of the sensor with a 134.5 μm coating. [ABSTRACT FROM AUTHOR]

• The chemical source term is the main control factor of thermal runaway. • The higher the temperature intensity, the shorter the explosion delay time. • The critical temperature of thermal runaway for AP/HTPB propellant is 458 K. • If the propellant is thick enough, the temperature distribution remains constant. For the safe use of solid rocket motors, it is crucial to investigate the thermal effect of AP/HTPB propellants. Transient high temperature may cause AP/HTPB propellants to burn or explode, resulting in serious damage. The fundamental equations that describe the thermal effect of AP/HTPB propellants are the heat conduction differential equation and Arrhenius law. In this paper, the thermal safety of AP/HTPB at transient high temperature is obtained by solving the heat conduction differential equation. The results show that the chemical source term S (T) is the main control factor of thermal runaway. When the action duration of the external high-temperature is short (ms-s magnitude), the first explosion occurs closest to the high-temperature source. When the action duration of the external high-temperature action is long (min-h magnitude), the first explosion occurs inside the propellant. The higher the high-temperature intensity of external action, the shorter the explosion delay time, but the explosion temperature does not change accordingly. The critical temperature of thermal runaway is 458 K under the condition of no shell and a high-temperature action duration of 2 h. At high-temperature intensities of 458 K, 459 K, and 500 K, the propellant explosion temperatures are 533 K, 539 K, and 540 K, and the explosion delay time is 1592s, 1102s, and 160 s, respectively. The critical duration of thermal runaway is 430 ms, 650 ms, 1350 ms, and 9820 ms, and the stable explosion delay time is 450 ms, 680 ms, 1400 ms, and 9920 ms, respectively, under the conditions of 2000 K, 1500 K, 1000 K, and 600 K without the shell. The propellant explosion temperature remains constant as the shell thickness grows while the explosion delay time gradually increases. When the propellant is thick enough, the temperature distribution of the system remains constant. The results of this study may be useful as a guide for assessing the thermal safety of AP/HTPB propellant. [ABSTRACT FROM AUTHOR]

In this paper, an innovative constitutive model of modified Fourier’s heat conduction law (Fick’s diffusion law), which takes the effects of relaxation time, Philip n-diffusion flux on heat transfer (diffusion) and thermal diffusivity parameters into account, the n-diffusion Cattaneo telegraph equation is firstly proposed. The approximate analytical solutions are obtained by employing the Adomian decomposition method which coincide with exact solution in good agreement. Moreover, the involved parameters have strong effects on the temperature distribution which are presented graphically and discussed. The mathematical method and techniques employed in this paper also have the significance for some other problems in science and engineering. The results showed that the temperature oscillates and decreases with increasing and decreasing of thermal diffusivity and relaxation time parameters, without and with reaction term respectively, but the oscillations of temperature decay rapidly until reaching zero with decreasing of Philip n-diffusion parameter for spatial evolution with and without reaction term. The temperature decreases with increasing parameter of relaxation time, Philip n-diffusion or thermal diffusivity for temporal evolution. [ABSTRACT FROM AUTHOR]

Highlights • Effect of wellbore stock liquid should be re-studied. • The wellbore stock liquid can be divided into two regions. • Effect of temperature distribution in heated oil region should be considered. Abstract This paper presents some comments on "Heat and mass transfer characteristics of steam in a horizontal wellbore with multi-point injection technique considering wellbore stock liquid" that was recently published on [International Journal of Heat and Mass Transfer 127 (2018) 949–958]. Overall, the paper deserves to be published on International Journal of Heat and Mass Transfer. However, some points should be noted to improve the paper. The model presented in their model neglected the heat conduction process, which can lead to a mis-understanding of behaviors of wellbore stock liquid during the steam injection process. In fact, the wellbore stock liquid can be divided into two regions: the heated oil region (region ①) and the cold region (region ②). The oil in region ① will be injected into reservoir, while the oil in region ② cannot flow. However, they assumed that oil in both regions can flow in the horizontal direction. Their purpose of making such an assumption is to build a model. However, this assumption is unreasonable and should be questioned. Their model can be improved by taking the temperature distribution in region ① into consideration. [ABSTRACT FROM AUTHOR]

• Semi-analytic methods are used to solve 3D DPL problems. • Compared with FEM, the semi-analytic method has higher computational efficiency. • The phase lag of heat flow and the phase lag of temperature gradient have influence on the temperature response speed and the formation of temperature field. With the development of picosecond laser technology, the dual-phase-lagging (DPL) model is more suitable to describe the heat transfer problem with micro-scale effect and micro-time effect. In this paper, a three-dimensional dual-phase-lagging heat transfer model for picosecond laser processing is established. Then Fourier transform (FT) and Laplace transform (LT) are used to derive the frequency response functions (FRFs) of the problem in the frequency domain, and the inverse Laplace transform (ILT) and discrete-convolution fast Fourier transform (DC-FFT) algorithm are used to solve the temperature field. The calculation accuracy of this method is verified and the effect of phase lag constants on temperature field is studied. The results show that the semi-analytical method has a high accuracy for solving the dual-phase-lagging heat conduction model, and the phase lag of heat flux will affect the heating rate in the heating stage, and the phase lag of temperature gradient will delay the formation of temperature field. The effect of phase lag constants on temperature-time history is investigated and the related phenomena are explained by using the two-step heat transfer theory. This semi-analytical method provides a new approach to solve the problem of three-dimensional dual-phase-lagging heat transfer. [ABSTRACT FROM AUTHOR]

• Developed a nonlocal continuum model of coupled microphase separation and heat transfer in block copolymer thin films. • Established constitutive relations of the phase-field model based on the self-consistent field theory of polymers. • Presented a finite element solution with unconditionally stable time-stepping schemes for accurate numerical simulations. • Conducted two- and three-dimensional numerical experiments to demonstrate thermally induced phase responses in copolymers. Directed self-assembly of block copolymer (BCP) has shown promise as a nano-patterning technology for various applications such as microelectronics, semiconductor manufacturing and biotechnology. In this paper, we present a thermodynamically consistent nonlocal model of phase transformation and heat transfer for BCP via the continuum theory of mixtures. Our model is developed based on the mass and energy balances of each phase and a set of microforce balances to describe the dynamics of microphase separation during self-assembly and the size and memory effects of heat conduction in BCP thin films. We derive constitutive relations for coupling the phase field and temperature through upscaling the self-consistent field theory of polymers, and present the connections between the derived nonlocal heat conduction model and the phonon Boltzmann transport equation. We provide a finite element solution of the proposed model that includes unconditionally stable time-stepping schemes, and we perform various numerical experiments that showcase different features of the model. Furthermore, we conduct three-dimensional numerical experiments of laser zone annealing process to qualitatively investigate the effect of laser velocity on the self-assembly behavior of BCP thin films. Our results show that the proposed model can simulate essential features of thermally induced phase responses of BCPs, consistent with experimental observations and high-fidelity simulations. [ABSTRACT FROM AUTHOR]

• Experimental study was performed for the internally heated corium pool with high Rayleigh numbers. • Transient model was developed for the high-Rayleigh-number corium pool with heat and mass transfer. • The component diffusion at interface will influence the corresponding liquidus temperature and transient heat transfer. The natural convection heat transfer driven by internal decay heat and the diffusive mass transfer at the crust interface are the critical problems in study of thermal behaviors in volumetrically heated reactor corium pools. In this paper, experiment and transient code were developed to analyze the heat and mass transfer characteristics in the high-Rayleigh-number corium pool. The COPRA experiment was carried out in seven tests with different heights and heating powers. The near-wall modified low-Reynolds-number k - ε turbulence model was used for the natural convection simulation in the whole flow region. Both the heat transfer with phase change and the diffusive mass transfer at crust interface boundary were taken into consideration. In addition, the heat conduction in the crust and wall, as well as the heat radiation in top space were included. The validation was performed for the developed code with transient simulation of COPRA experimental tests. The calculation results agreed well with experimental data for the pool temperature, heat flux and crust distributions, proving the reliability of the transient analysis code for the corium pool simulation with heat and mass transfer. [ABSTRACT FROM AUTHOR]

• Liquid film flow boiling heat transfer for successive droplets impacting on cylinder. • Reducing droplet impact frequency can increase vaporization rate up to 2.3 times. • Increasing droplet impact velocity can increase vaporization rate up to 6 times. • CHF triggering mechanism on cylinder differs from that on the flat surface. • A correlation to predict boiling heat transfer within mean absolute error 11.9%. The situation on boiling heat transfer when droplets impact on heated cylinder is popular in the industrial applications, but the research in this field is very lacking. In this paper, an experiment that generates continuous high heat flux in one-dimensional heat conduction was designed to study the liquid film flow boiling heat transfer on cylinder for successive droplets impact, and the effects of droplet impact frequency and droplet impact velocity were analyzed. The results show that, at the single-phase heat transfer stage, increasing the droplet impact frequency or impact velocity can promote heat transfer performance. At the initial stage of nucleate boiling, increasing the two influencing factors makes more heat be taken away by sensible heat and latent heat of liquid vaporization. However, at the later stage of nucleate boiling, the droplet impact frequency has little effect on the heat transfer performance. The heat converted into the sensible heat of liquid is small due to low impact frequency, but the elevation of latent heat of liquid vaporization makes up for the shortage, resulting in the heat transfer performance being unexpectedly similar with the high impact frequency. At this stage, increasing droplet impact velocity does not affect the heat taken away by the sensible heat of liquid, but boosts the liquid vaporization rate and utilizes the latent heat of vaporization. Furthermore, the triggering mechanism of critical heat flux on the cylinder was revealed, which obviously differs from the case of droplets impacting on the flat surface. Finally, an empirical correlation to predict the boiling heat transfer characteristics was established. [ABSTRACT FROM AUTHOR]

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]

Abstract: The paper presents a new approximate method of solving nonlinear direct and inverse heat conduction problems. A nonlinear differential operator is resolved into a linear and nonlinear part. The nonlinearity is treated as an inhomogeneity for the linear operator. Next, the method of successive approximations is used. To solve the problem in each iteration the Trefftz functions (harmonic polynomials) are utilized. The approach presented in the paper has been applied to solve a direct and boundary inverse problem (identification of boundary condition). The sensitiveness of the method according to data disturbance has been checked. [Copyright &y& Elsevier]

Abstract: This paper deals with an inverse problem of determining a heat source function in heat conduction equations when the solution is known in a discrete point set. Being different from other ordinary inverse source problems which are often dependent on only one variable, the unknown coefficient in this paper not only depends on the space variable x, but also depends on the time t. On the basis of the optimal control framework, the inverse problem is transformed into an optimization problem. The existence and necessary condition of the minimizer for the cost functional are established. The convergence of the minimizer as the mesh parameters tend to zero is also proved. The conjugate gradient method is applied to the inverse problem and some typical numerical experiments are performed in the paper. The numerical results show that the proposed method is stable and the unknown heat source is recovered very well. [Copyright &y& Elsevier]

Abstract: In this paper power limits and other performance indicators are investigated in various power generation systems with downgrading or upgrading of resources. Energy flux (power) is created in a power generator located between a resource fluid (‘upper’ fluid 1) and the environmental fluid (‘lower’ fluid, 2). Transfer phenomena, fluid properties and conductance values of dissipative layers or conductors influence the rate of power yield. While temperatures T i of participating media are only necessary variables to describe purely thermal systems, in the present work both temperatures and chemical potentials μ k are essential. This case is associated with engines propelled by fluxes of both energy and substance (chemical and electrochemical engines). Optimization methods are applied to determine power generation limits which are important performance indicators for various energy converters, such as thermal, solar, chemical, and electrochemical engines. Methodological similarity is shown when analysing power limits in thermal machines and fuel cells. Numerical approaches are based on the methods of dynamic programing (DP) or Pontryagin’s maximum principle. In view of the limitation of DP to systems with low dimensionality of state vector, we focus here on the Pontryagin’s method, which involves discrete canonical algorithms derived from the process Hamiltonian. Some new or relatively unknown properties of these algorithms are described in the context of their application to power systems. In fuel cells and other electrochemical systems downgrading or upgrading of resources may also occur. However, we restrict here to the steady-state fuel cells. An approximate (topology-ignoring) analysis shows that, in linear systems, only at most 1/4 of power dissipated in the natural transfer process can be transformed into mechanical or electric power. This indicator may be viewed as a new form of the second law efficiency. The relevant experimental data obtained at the institute of Power Engineering are also presented in this paper. [Copyright &y& Elsevier]

Abstract: The presented paper displays a method of solving the inverse problems of heat transfer in multi-connected regions, consisting in iterative solving of convergent series of the direct problems. For known temperature and flux values at the outer boundary of the region the temperature and flux values at the inner boundaries are sought (the cauchy problem for the Laplace equation). In case of such a formulation of the problem, the solution does not always exist, one of the conditions is met in the mean-square sense, providing the optimization criterion. The idea of the process consists in solving the direct problem in which the boundary condition is subject to iterative changes so as to attain minimum of the optimization criterion (the square functional). Two algorithms have been formulated. In the first of them the heat flux at the inner boundaries of the region, while in the other the temperature were subject to changes. Convergence of both the algorithms have been compared. The numerical calculation has been made for selected examples, for which an analytical solution is known. The effect of random disturbance of the boundary conditions on the solution obtained with iterative algorithms has been checked. Moreover, a function was defined, serving as convergence measure of the solution of the inverse problem solved with the algorithms proposed in the paper. The properties of the function give evidence that it tends to the value exceeding unity. [Copyright &y& Elsevier]

• A new Lattice Boltzmann formulation for conduction heat transfer in heterogeneous media is presented. • Innovative double distribution functions of the LB method are elaborated to solve conduction heat transfer in heterogeneous media. • Solution of benchmark conduction heat transfer problems is performed. • All validations are made with the control volumes method (CVM) solutions. In this paper, we propose an innovative formulation of the "well-known" thermal lattice Boltzmann method for solving transient conduction heat transfer problems in heterogeneous media: the DD-CHT LB method for Double Distribution – Conjugate Heat Transfer. The main idea of this new formulation is to bring out a second distribution function that represent the effect of thermal inertia and its variation in a heterogeneous media. By adopting this original formulation we achieved several goals, mainly conservation of local properties of the studied media and ensuring the stability of the proposed formulation by avoiding any alteration of the "well-known" TLBM collision step. Validation of the formulation is fulfilled through three different benchmark conduction heat transfer problems in heterogeneous media. All results are compared with those obtained by the Control Volume Method (CVM) and excellent agreements were found. [ABSTRACT FROM AUTHOR]

Highlights • Heat and mass transfer in finned inclined heat sink filled with nano-PCM is studied. • Effect of inclination angle on natural convection melting in a finned cavity. • Study on melting intensity for Nano-PCM properties increase at different Ra. • For low Ra melting time is reduced with nanoparticles addition at any inclination. • NanoPCM melts faster for inclination greater than 90° at high Ra. Abstract The use of materials such as paraffin is widespread in modern energy industries. The ability to absorb a large amount of energy during a phase transition at a constant temperature conditions allows to store and transport the heat. The intensity of melting is related to the thermophysical characteristics of the material and the geometric parameters of the system. Heat transfer inside the system is carried out due to the heat conduction, while in the melt the convective heat transfer intensifies the process. In this paper, a numerical study of heat transfer inside a domain filled with paraffin with nanoparticles and heated from a source of constant volumetric heat generation is performed. A two-dimensional model of the melting process has been formulated in the dimensionless variables "stream function–vorticity–temperature", taking into account the natural convective heat transfer occurring in the melt. The system of partial differential equations has been solved using the finite difference method. The simulation has been carried out at different inclination angles of the considered system. Local and integral characteristics of the melting process at different heating levels of the system have been obtained. [ABSTRACT FROM AUTHOR]

Highlights • The heat equation is solved in frequency domain for anisotropic three-dimensional multi-layered media. • Space and time dependent solution is obtained via efficient numerical inverse transforms. • Convective boundaries and moving sources are considered. • The semi-analytical solution is verified against a finite element solution. Abstract In this paper, a semi-analytical solution of the time-dependent heat conduction equation is presented for laterally infinite, multi-layered media with anisotropic thermal conductivities, convective outer boundaries and perfect thermal contact between the layers. Space and time-dependent moving heat sources on the boundary as well as inside the medium are considered. In addition, the outer fluid temperature may also depend on space and time. The derived solutions are successfully compared to numerical solutions. A Python implementation of the solution is made freely available. [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 • Solution of heat conduction problems with internal sources. • Introduction of a partition coefficient. • Solution of electrothermal problems. • Non-uniform heat sources. Abstract In the heat transfer literature, resistance and quadrupole concepts are used to solve heat conduction problems with or without internal heat generation, see for example Maillet et al. (2000). However, in most cases, the heat transfer is unidirectional. In this paper, we present a general approach to solve conduction problems with internal sources. This is done by simply introducing a partition coefficient β. The pertinence of this approach is mathematically demonstrated for both steady state and transient problems. Under steady state conditions, β represents a resistance partition coefficient while under transient conditions β is a quadrupole partition coefficient. In each case, the resulting equivalent thermal circuits are presented. Finally, the proposed approach is applied to electrothermal problems with heat generation due to the joule effect, the result is remarkable, that is, the partition coefficient β is a constant equal to 1/2. [ABSTRACT FROM AUTHOR]

Highlights • Experimental results at high condensation temperatures. • R245fa and its HFO replacements R1233zd are tested. • Different working fluids show diverse heat transfer mechanisms. • New heat transfer and pressure drop correlations are developed. Abstract The fundamental understanding of the thermal–hydraulic performance of working fluids during condensation is important for the optimal design of the condenser in various thermodynamic cycles. This paper is aimed at obtaining flow condensation heat transfer and pressure drop characteristics in a plate heat exchanger during the working conditions of the condenser of either organic Rankine cycle power systems or heat pump units. The selected working fluids are two hydrofluorocarbons, R134a and R245fa, as well as their hydrofluoroolefin replacements, R1234ze(E) and R1233zd(E). Measurements of heat transfer coefficients and pressure drops were carried out with varying saturation temperature, mass flux, and liquid Reynolds number, ranging from 30 °C to 70 °C, 16 kg/m2s to 90 kg/m2s and 65 to 877, respectively. Based on commonly used existing correlations, new heat transfer and pressure drop correlations were developed, including the effect of the surface tension. The experimental data indicate that different heat transfer mechanisms occur at low liquid Reynolds number with the different working fluids. The results suggest higher heat transfer coefficients and pressure drops for R1234ze(E) and R1233zd(E) than for R134a and R245fa at the same working conditions. The new correlations enable significantly better prediction accuracies for the experimental results in this study than existing correlations, indicating that the surface tension is a suitable parameter to consider in mini and micro-scale condensation heat transfer. [ABSTRACT FROM AUTHOR]

Highlights • Heat transfer of supercritical fluid upward in vertical tube is investigated. • Heatflux fluctuation is found at the trans-critical section. • Traditional correlation can't predict heatflux fluctuation. • Heatflux fluctuation mechanism is analyzed in detail. • Influence of operating conditions on heat transfer characteristics is investigated. Abstract The supercritical fluid has been extensively applied in many industry applications and heat transfer characteristics of the supercritical fluid play an important role in system safety and economic design. In this paper, heat transfer characteristics and mechanism of the supercritical fluid upward in vertical tube with constant wall temperature are numerically investigated. Heat transfer fluctuation phenomenon is found at the trans-critical section where fluid experiences the pseudo-critical point. Heat transfer fluctuation takes place only when the wall temperature is higher than the pseudo-critical temperature and the bulk temperature is lower than the pseudo-critical temperature. The traditional prediction correlation can't predict heat transfer fluctuation at the trans-critical section correctly. Heatflux fluctuation is caused by the buoyancy effect. The buoyancy effect induces the periodic flow variation and the periodic convective heat transfer variation on the radial direction, which determine heatflux fluctuation on the wall. The fluctuation amplitude of heatflux on the wall decreases along the axial direction due to the weakened buoyancy effect. Influence of operating conditions on heat transfer of the supercritical fluid is investigated. R134a is chosen as the working fluid. Operating condition includes mass flow ranging from 500 to 800 kg/(m2 s), inlet temperature ranging from 313.15 to 343.15 K, wall temperature ranging from 403.15 to 433.15 K and operating pressure ranging from 4.35 to 5.04 MPa. It is observed that heat transfer coefficient rises with mass flow, wall temperature and operating pressure increasing, but it doesn't vary obviously with inlet temperature. Fluctuation amplitude of heat transfer coefficient decreases with mass flow, wall temperature, inlet temperature and operating pressure increasing. [ABSTRACT FROM AUTHOR]

Highlights • Natural convection of power-law nanofluids is studied with GPU based LB model. • Effects of temperature-dependent properties are considered. • There exist an optimal value of θ opt at which the maximum N u av is obtained. Abstract 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 Al 2 O 3 nanoparticles. The effects of power-law index (0.5 ⩽ n ⩽ 1.5), thermal Rayleigh number ( 10 4 ⩽ Ra f ⩽ 10 6 ), diameter of nanoparticle (25 nm ⩽ d s ⩽ 100 nm), nanoparticle volume fraction (0.0 ⩽ ϕ ⩽ 0.04), temperature of the cooled sidewall (315 K ⩽ T c ⩽ 335 K), temperature difference between the sidewalls (10 K ⩽ Δ T ⩽ 50 K), 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 ϕ opt at which the maximum heat transfer enhancement is obtained, and the value of ϕ opt is found to increase slightly with decreasing the nanoparticle diameter, and to increase remarkably with increasing the temperature of T c or Δ T. 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. [ABSTRACT FROM AUTHOR]

Highlights • We propose a spatio-temporal dependent heat flux identification on a braking system. • This approach combines modal reduction and conjugate gradient method. • First, Branch Eigenmodes Reduction Method is used to build a thermal reduced model. • In a second step, the heat flux density received by the braking pad is parametrized. • The goal is to identify the excitation states of each mode of this parametrization. Abstract 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. [ABSTRACT FROM AUTHOR]

Highlights • Heat transfer and pressure loss in swirl cooling tubes with dimples were numerically obtained. • Total heat transfer performance of the swirl tubes with dimples can be increased. • Pressure loss of the swirl tubes with dimples can be decreased. • Dimple depths have appreciable influences on the heat transfer and pressure loss. • Detailed interactions of the swirling flow with dimples at the wall were provided. Abstract This paper presents a numerical study of heat transfer and pressure loss characteristics in a swirl cooling tube with five tangential inlet jets and with dimples on the tube inner surface. The swirl tube has a length of 20 times the tube diameter, and the Reynolds number based on the tube diameter ranges from 10,000 to 40,000. Polyhedral meshes as well as the SST k - ω turbulence model were chosen for the numerical calculations. A swirl cooling system with a smooth tube was investigated as baseline, and comparatively with dimples on the tube inner surface. The results showed different swirling flow and heat transfer patterns in the swirl tubes. Dimples on the tube inner surface can reduce the wetted-area averaged heat transfer coefficient on the tube inner surface. However, the total heat transferred in the dimpled swirl cooling tubes can be increased by up to 7.2% due to the increased heat transfer area and the interactions between the swirling flow and the dimpled wall. On the other hand, the pressure loss in the dimpled tube can be appreciably reduced by up to 17.6% compared with that of the smooth swirl tube. Detailed flow interactions between the jets, the tube wall and the dimples are illustrated to explain the heat transfer change and pressure loss reduction mechanisms. [ABSTRACT FROM AUTHOR]

Highlights • Imposing high-temperature difference strongly influences velocity and thermal field. • Chimney effect and thermal startification influences heat transfer inside channel. • Maximum heat transfer occurs at optimum aspect ratio of channel. • Value of optimum aspect ratio decreases with increase of Rayleigh number. Abstract 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) 10 4 to 10 7 in channel heated asymmetrically by uniform surface temperature with air (P r 0.72) 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. [ABSTRACT FROM AUTHOR]

Highlights • Development and implementing multifidelity POD in stochastic heat transfer problems. • Combination of POD method with sparse PCE to reduce the computational cost of UQ. • Quantifying the effect of geometrical uncertainties in conjugate heat transfer of C3X. • Quantifying the effect of stochastic heat flux in heat transfer of ribbed passages. Abstract To increase the contribution and reliability of computational fluid dynamics efforts in design process of industrial equipments, it is necessary to quantify the effects of uncertainties on the system performance. Due to exponentially increment of the computational cost with number of uncertain variables for uncertainty quantification using classical polynomial chaos expansion methodology, reducing the required number of samples for uncertainty quantification is a real engineering challenge. In this paper, the proper orthogonal decomposition method based on the multifidelity approach is combined with the full and sparse polynomial chaos expansions for efficient uncertainty quantification of complex heat transfer problems with large number of random variables. The conjugate conduction heat transfer in NASA C3X cooled gas turbine blade with geometrical uncertainties and the convective heat transfer in ribbed passage with the stochastic wall heat flux boundary condition are considered as the test cases. Results of uncertainty quantification analysis in both test cases showed that proposed multi-fidelity approaches are able to produce the statistical quantities with much lower computational cost compare to the classical regression-based polynomial chaos method. It is shown that the combination of the proper orthogonal decomposition with the sparse polynomial chaos gives a computational gain at least 2 times greater than combination of the proper orthogonal decomposition with the full polynomial chaos expansion. [ABSTRACT FROM AUTHOR]

Highlights • We made simultaneous observations of the dynamics and thermal behavior of dry patches. • The critical heat flux phenomenon occurred during the rewetting of a large dry patch. • The bubbles nucleating at the advancing liquid front played a key role in the failure of the rewetting. • We determined an empirical value for the critical line density of the bubbles at the triple contact line. Abstract We observed the dynamics of dry patches underneath massive bubbles during the pool boiling of saturated water under atmospheric pressure, and measured the associated temperature distribution. We synchronized the observations both spatially and temporally using high-speed total reflection and infrared thermometry techniques. The observations presented in this paper provide evidence that the critical heat flux phenomenon is triggered during the rewetting of large dry patches with periphery temperatures that are much lower than minimum film boiling temperature, so-called Leidenfrost point. As the liquid meniscus advanced toward the dry patch, numerous secondary bubbles nucleated and impeded the flow of liquid toward the dry patch. This prevented the liquid from rewetting the dry patch. The key physical mechanism for triggering CHF is initiated when the line density of the secondary bubbles nucleating at the periphery of a shrinking dry patch underneath a departing mushroom bubble exceeds a critical value. These bubbles completely block the liquid inflow into the dry patch and prevent rewetting, eventually causing the dry patch to expand irreversibly. We used our experimental data to determine an empirical value of the critical line nucleation site density. [ABSTRACT FROM AUTHOR]

Highlights • Conjugate heat transfer method was adopted to modelling resistance furnace. • PID method was proposed to define heat generation rate of the energy source. • The prediction of equilibration time for GH4169 superalloy was validated. Abstract The simulation of heating process of superalloys is of great significance to predict the temperature distribution and equilibration time of workpiece. In this paper, a new method was proposed to simulate the heating process of superalloy billet in resistance furnace for all strategies of thermal schemes using commercial CFD software FLUENT. In the model, numerical analysis of natural convection and surface thermal radiation in a chamber electric furnace having heat-conducting solid walls of finite thickness with a heat source located in the side and top walls of the furnace in conditions of convective heat exchange with environment has been carried out, and such conjugate heat transfer process was solved by FLUENT solver. Furthermore, a PID methods was proposed to control the energy source of the resistance wires based on FLUENT UDF, in order to regulate the furnace temperature according thermal scheme. This model was validated through temperature measurement experiment in a small chamber resistance furnace. Compared with the measured data, the model was adequate for predicting the temperature profile and equilibration time of superalloy. [ABSTRACT FROM AUTHOR]

Abstract: A hot moving (rotating) cylinder was heated up to 500–600°C and then was cooled by a planar water jet impinging on a line parallel to the symmetry axis. The time dependent wall temperature was measured using embedded thermocouples and the corresponding wall heat fluxes were estimated through an inverse conduction method. In a recent paper, we showed that cooling rates depend on the subcooled temperature of the jet, the velocity of the jet and the surface-to-jet velocity ratio. Since the initial temperature of the cylinder was higher than the Leidenfrost temperature, we observed all the boiling regimes from film boiling to nucleate boiling. The objectives of this paper are firstly to describe the current conditions which exist in the Run Out Table in hot rolling mills, secondly to review the main experimental studies dedicated to jet cooling which have led to modelling heat transfer in boiling conditions and finally to propose new correlations taking into account the velocity of the wall. [Copyright &y& Elsevier]

Abstract: Heat transfer enhancement of phase change materials (PCMs) is essential in order to achieve high charge and discharge powers of latent heat storage systems. The utilisation of highly conductive fins is an effective method to improve heat transfer. In the presented paper, solidification times of two fundamental geometries are examined by analytical modelling and numerical computation. These geometries are the finned plane wall and a single tube which is radial-finned on the outside. The paper describes approximate analytical solutions based on the effective medium approach which include the boundary conditions, as well as material and geometric parameters. [Copyright &y& Elsevier]

Abstract: Effects of thermal radiation on solidification heat transfer must be considered inside semitransparent media. This paper investigates coupled heat transfer of solidification and radiation within a two-dimensional rectangular semitransparent medium having gradient index. Solidification process is supposed to happen at some temperature range, and accordingly three zones including liquid-, solid- and mushy-zones exist in phase-change media. In different phase field, parameters of thermophysical property are assumed different and those of radiative property are assumed same. Governing equation includes conduction, radiation and phase-change terms, and radiation and phase-change are treated as source terms in the equation, respectively. A Galerkin finite element method is used to solve energy equation of coupled radiation and phase-change heat transfer. This paper analyzes effect of thermal radiation on phase-change heat transfer and those of refractive index distributions on temperature fields and liquid fraction distributions during radiation–solidification coupled heat transfer. From the results, we can find that refractive index gradient has a major influence on phase-change process and compared with the case of smaller index gradient, bigger gradient can speed up phase-change heat transfer in semitransparent media. [Copyright &y& Elsevier]

Performance of shallow geothermal systems such as borehole thermal energy storage (BTES) and ground source heat pump (GSHP) mainly depends on the thermal properties of the subsurface and proper design of borehole heat exchangers (BHE). This paper introduces a novel hybrid approach for measuring the effectiveness of BHEs and surrounding subsurface thermal properties, which combines traditional thermal response test (TRT) with the borehole temperature relaxation method (BTR), based on two dimensional radial conductive heat transfer. The new method allows for: (1) evaluation of how convective heat loss at groundwater layers influence estimation of subsurface thermal properties; (2) examination of non-uniform heat transfer through a BHE to stratified subsurface layers; and, (3) calculation of depth-dependency of thermal properties of unsaturated subsurface layers. The hybrid approach was tested using a 50 m U-type BHE, the results of which indicated that convective heat transfer at the groundwater level altered the real value of effective thermal conductivity from 0.45 to 1.56 W/m K. The non-uniformity of heat transfer along the BHE was confirmed by calculations that showed subsurface thermal conductivities were depth dependent, varying between 0.34 and 0.61 W/m K. [ABSTRACT FROM AUTHOR]

A new approach, radial integration polygonal boundary element method (RIPBEM), for solving heat conduction problems is presented in this paper. The proposed RIPBEM is a new concept in boundary element method (BEM), which would be of great flexibility in mesh generation of complex 3D geometries. Due to the characteristic of arbitrary shapes of polygonal elements, conventional shape functions are insufficient. Moreover, the resulted surface boundary integrals cannot be directly evaluated by the standard Gauss quadrature. To solve these problems, general shape functions for polygonal elements with arbitrary number of nodes are given. To generally and numerically calculate the resulted surface integrals, the radial integration method (RIM) is employed to convert the surface boundary integrals into equivalent contour line integrals of the polygonal elements. As for 3D domain integrals, they are transformed to equivalent line integrals using RIM twice. This methodology can explicitly eliminate strong singularities. Several numerical examples are given to show the effectiveness and the accuracy of the proposed polygonal boundary element method for solving heat conduction problems. [ABSTRACT FROM AUTHOR]

Abstract: The present review is intended to encompass the heat transfer literature published in 2005. While of a wide-range in scope, some selection is inevitable. We restrict ourselves to papers published in English through a peer-review process, with selected translations from journals published in other languages. Papers from conference proceedings generally are not included, though the Proceeding itself may be cited in the introduction. A significant fraction of the papers reviewed herein relates to the science of heat transfer, including experimental, analytical and numerical studies. Other papers cover applications where heat transfer plays a major role, not only in man-made devices but in natural systems as well. The papers are grouped into major subject areas and then into subfields within these areas. In addition to reviewing the literature, we mention major conferences held in 2005, major awards related to heat transfer presented in 2005, and books on heat transfer published during the year. [ABSTRACT FROM AUTHOR]

Abstract: The present review covers the heat transfer literature published in 2004 in English language, including some translations of foreign language papers. Though extensive, some selection is necessary. Only articles published by a process of peer review in archival journals are reviewed. Papers are grouped into subject-oriented sections and further divided into sub-fields. Many papers deal with the fundamental science of heat transfer, including experimental, numerical and analytical work; others relate to applications or natural systems. In addition to reviewing journal articles, this Review also takes note of important conferences and meetings on heat transfer and related areas, major awards presented in 2004, and relevant books published in 2004. [ABSTRACT FROM AUTHOR]

Abstract: This paper is the first of a two-part study concerning the dynamics of heat transfer during nucleation process of saturated FC-72 liquid. Experimental results discussed in this paper provide new physical insight on the nature of heat transfer events at the nucleation site during the nucleate boiling process. The thermal field underneath a bubble during the boiling of FC-72 was measured with a spatial resolution of 22--40μm. The time period of activation, area of influence, and magnitude of three different mechanisms of heat transfer active at the nucleation site were determined. These mechanisms consisted of: (1) microlayer evaporation following the rapid bubble expansion, (2) transient conduction due to rewetting of the surface during bubble departure, and (3) microconvection in the region external to the bubble/surface contact area. The area of influence of the transient conduction mechanism was found to be limited to the bubble/surface contact area, with most of the heat transfer occurring prior to the bubble detachment from the surface. The microconvection heat transfer mechanism was localized primarily outside the contact area and was found to be steady in nature. All three mechanisms of heat transfer were found to make significant contributions to the total surface heat transfer. The second part of this study provides the theoretical analysis of the results. [Copyright &y& Elsevier]

Abstract: This paper is the second part of a two-part study concerning the dynamics of heat transfer during the nucleation process of FC-72 liquid. The experimental findings on the nature of different heat transfer mechanisms involved in the nucleation process were discussed in part I. In this paper, the experimental results are compared with the existing boiling models. The boiling models based on dominance of a single mechanism of heat transfer did not match the experimental results. However, the Rohsenow model was found to closely predict the heat transfer through the microconvection mechanism that is primarily active outside the bubble/surface contact area. An existing transient conduction model was modified to predict the surface heat transfer during the rewetting process (i.e. transient conduction mechanism). This model takes into account the gradual rewetting of the surface during the transient conduction process rather than a simple sudden surface coverage assumption commonly used in the boiling literature. The initial superheat energy of the microlayer (i.e. microlayer sensible energy) was accurately calculated and found to significantly contribute in microlayer evaporation. This even exceeded the direct wall heat transfer to microlayer at high surface superheat temperatures. A composite model was introduced that closely matches our experimental results. It incorporates models for three mechanisms of heat transfer including microlayer evaporation, transient conduction, microconvection, as well as their influence area and activation time. The significance of this development is that, for the first time, all submodels of the composite correlation were independently verified using experimental results. [Copyright &y& Elsevier]

The sequential function specification method (SFSM) for solution of the inverse heat conduction problem was introduced by Beck (1968) [1] , and described in more detail [2] in 1985. This method assumes a functional form for the unknown heat flux in order to add more (future) data to regularize the problem and facilitate estimation of the next heat flux component. Two basic forms for the unknown heat flux have been well-explored: a constant function (zeroth order polynomial), and a linear function of time (a first order polynomial). Until now, only these two “traditional” forms have been used and higher order polynomial function approximations have not been considered. A generalized polynomial sequential function specification method (SFSM) is developed and evaluated in this paper. For higher order polynomials, the proper balance of past and future time step information is not obvious; the optimal balance is investigated herein. A generalized algorithm is used to define polynomials of any degree and estimate heat fluxes using SFSM with any number of past and future data. Seven heat flux test cases, including three non-polynomial heat flux variations, are used to evaluate the traditional and new methods, and the “optimal” number of future time steps is chosen for each case. The filter coefficient concept [3] provides additional insights into the new SFSM approaches. Filter coefficients are calculated with the optimal number of future time steps and the results are discussed. [ABSTRACT FROM AUTHOR]

This paper is concerned with the thermal and laminar boundary layer flow over rotating axisymmetric bodies in an otherwise still fluid. The thermal boundary layer flow equations for two types of spheroids (prolate and oblate) are formulated. Similarly to the previous work of other researchers, the laminar flow equations for two types of spheroids are also reproduced. Furthermore, the series solutions are derived for the thermal and laminar flow equations for each body. The series solutions are numerically calculated and the laminar flow profiles for each spheroid along with its heat transfer profile are visualized in detail. It is shown that for increasing eccentricity, the convection effects are increasing at higher latitudes of prolate spheroids, while the conduction effects are dominated at these higher latitudes of oblate spheroids. The results for spheres are reproduced in the case of zero eccentricity. By using commercial routines from NAG, the solutions for rotating spheres in the case of laminar flow are also mentioned as in the previous existing works. In particular, the results from the transformation technique of solutions are in good agreement with those obtained from NAG in the case of spheres, particularly at lower latitudes for all eccentricities. [ABSTRACT FROM AUTHOR]

In this paper, the heat transfer within an eccentric annulus containing heat-generating fluid is investigated. The inner cylinder of the annulus is heated and kept at constant temperature, while the outer cylinder is cooled and maintained at a constant temperature lower than that of the inner cylinder. The full governing equations of mass, momentum, and energy have been solved to investigate the characteristics of flow and thermal fields within the annulus. Besides considering the numerical solution in the case of natural convection at moderate Rayleigh number of 10 4 , the study also considered the numerical and analytical solutions in case of pure heat conduction within the annulus. Moreover, the study discussed the effect of annulus radius ratio Rr, the eccentricity e, and the heat generation parameter S on the heat transfer process. The study considered the range of Rr from 1.4 to 3.2, the range of e from −0.6 to 0.6, and the range of S up to 5. The study manifests that the numerical results for the case of pure conduction are in excellent agreement with the corresponding analytical results. The results for both pure conduction and natural convection cases showed that the average dimensionless temperature of the heat generation fluid increases with the increase in S. Similarly, the heat rejected from the outer cylinder increases with the increase in S for a given Rr. On the contrary, the heat added to the annulus through the inner cylinder decreases as S increases and changes to heat rejection if S exceeds a certain critical value S ∗ . The value of S ∗ is found to decrease with the increase in Rr for both pure conduction and natural convection cases. Moreover, the heat transfer rates at inner and outer walls of the annulus decrease for a given Rr as the inner cylinder moves upward from negative eccentricity to positive eccentricity until both start increasing again at a certain positive eccentricity. [ABSTRACT FROM AUTHOR]

This paper provides an insight into the heat transfer in the solid backbone of aerogel and an effective approach to model the apparent solid thermal conductivity of aerogels. First, a model for the thermal conductivity of aerogel solid backbone is developed based on thermal constriction resistance between interconnected nano-particles by taking into account the size effect of a single particle, and validated by the numerical solutions of the gray Boltzmann transport equation (BTE). Then, combined with the analytical expression derived based on the Laplace heat conduction equation, the proposed model is used to predict the apparent solid thermal conductivity of aerogels, and the predictions are in good agreement with the available experimental data of different kinds of aerogels. [ABSTRACT FROM AUTHOR]

This mini review paper summarizes the multi-disciplinary, multi-objective and multi-scale constructal optimizations for heat conduction and thermal insulation processes, fluid flow processes, convective heat transfer processes of fins, vascular networks and heat exchangers, mass transfer processes of porous mediums, heat and mass transfer processes of solid–gas reactors and solid oxide fuel cells as well as generalized transfer process performed in the Naval University of Engineering. The results show that the performances of transfer bodies are improved when model improvements are considered, therefore, the application values are considerable for designers. New optimal constructs of various transfer processes are obtained when different indexes are taken as the optimization objectives, and different optimal design schemes can be chosen according to practical design requirements. The flows of generalized transfer process include heat flow, mass flow, material flow, etc. Many optimal results of various transfer processes are special cases of the generalized transfer process. Performance improvements are made and different optimal design schemes are obtained in this review, which help to implement optimal designs of practical transfer processes and systems. [ABSTRACT FROM AUTHOR]

This paper investigates effects of buoyancy-driven motion on the “slowly reacting” mode of combustion, and its thermal-explosion limits, of an initially cold gaseous mixture enclosed in a spherical vessel with a constant wall temperature. As in Frank-Kamenetskii’s seminal analysis, the strong temperature dependence of the effective overall reaction is modeled with a single irreversible reaction with an Arrhenius rate having a large activation energy. Besides the classical Damköhler number Da , measuring the ratio of the heat-release rate by chemical reaction evaluated at the wall temperature to the rate of heat removal by heat conduction to the wall, the solution is seen to depend on the Rayleigh number Ra , measuring the effect of buoyancy-induced motion on the heat-transport rate. For values of Da below a critical value Da c the system evolves in a slowly reacting mode where the heat losses to the wall limit the temperature increase associated with the chemical reaction, whereas for Da > Da c the initial stage of slow reaction ends abruptly at a well-defined ignition time, at which a thermal runaway occurs. Transient numerical integrations of the initial stage of slow reaction, formulated in the distinguished limit Da ∼ 1 and Ra ∼ 1 with account taken of the effects of the temporal pressure variation, are used to investigate influences of natural convection on thermal-explosion development, including changes in ignition times for Da > Da c and modified explosion curves. Our analysis reveals that Frank-Kamenetskii’s criterion for the determination of critical explosion conditions, based on the investigation of existence of steady solutions, provides values of Da c ( Ra ) that are identical to those extracted from the transient computations. Specific consideration is given to the structure of the steady solution in the asymptotic limit Ra ≫ 1 in which the flow includes a thin chemically frozen near-wall boundary layer of downward moving cold gas bounding a central inviscid region of slowly rising reacting flow driven by the boundary-layer entrainment, with the critical explosion conditions predicted to occur for Da c ∼ Ra 1 / 4 . The mathematical structure of the resulting boundary-layer problem is fundamentally similar to that found in the unrelated problem of flow in curved pipes at large Dean numbers. As in that similar problem, the boundary layer exhibits a region of recirculating flow, so that the problem must be formulated as a boundary-value problem accounting for the self-similar local solutions that exist near the upper and lower stagnation points. The problem is solved with use made of an approximate integral method. The resulting asymptotic prediction for the critical Damköhler number Da c = 0.655 Ra 1 / 4 is found to be in excellent agreement with the results obtained by integration of the complete conservation equations for Ra ≫ 1 . [ABSTRACT FROM AUTHOR]

In this paper, the C-V wave model was adopted to study the thermal response of a square plate which is irradiated by a moving temporally non-Gaussian laser pulse. The governing equation was solved by using the method of mode superposition. The propagation and rebounding of thermal wave was confirmed. The dependence of the wave velocity on relaxation time was discussed. The influences of scanning velocity and wave velocity on the temperature distribution were also indicated. [ABSTRACT FROM AUTHOR]

This paper aims at enhancing the boiling and condensation co-existing phase change heat transfer process inside a small and closed space by heat-conduction bridges. The working fluid is deionized water and the copper heat-conduction bridges are machined directly on the boiling surface and connect the boiling and the condensation surface. Three different heat-conduction bridges that are all rectangular pillars of different sizes and layouts are tested. Experiments were carried out to study the influences of working fluid filling ratio, the cross sectional area size of the heat-conduction bridge and the gap between the heat-conduction bridges (the bridge gap) on boiling and condensation co-existing heat transfer inside the small and closed space. Experimental results show that the heat-conduction bridges can greatly enhance the boiling and condensation co-existing heat transfer process. The optimum filling ratio is 50% for 3 type heat-conduction bridges. The boiling, condensation and overall heat transfer coefficient of the heat-conduction bridges whose cross-sectional area is 2 mm × 2 mm and bridge gap is 1 mm (HCB-C) is the largest among the three heat-conduction bridges. [ABSTRACT FROM AUTHOR]

This paper presents an electrical heating model using alternating current (AC) for the silicon rods located in a 24-rod Siemens reactor. In this model, the combined effects of heat dissipation (radiation, convection, and reaction energy), skin effect, and heat conduction owing to Joule effect are examined. The presence of the skin effect, which yields an important radial temperature profile controlled by the heat conduction equation for the rods, has been considered. The present model is validated using industrial current data, and it is observed that the numerical results are in good agreement with them. The influence of the location of the silicon rods, AC frequency, radius of rod, and wall emissivity on the temperature profile and current density has been studied through the application of the developed model. Tailoring the temperature profile of silicon rods and extending the maximum deposition radius has also been performed. Voltage-current curves, which are applied to generate the required heat during the manufacturing period, have also been studied using different AC frequencies and wall emissivities. [ABSTRACT FROM AUTHOR]

• An improved thermodynamic analysis method is presented and validated. • Unsteady local conductive and radiative entropy generation rates are analyzed. • Exergy storage rate and exergetic efficiency is obtained. • An uniform and centralized heating strategy is proposed. This paper presents an improved thermodynamic analysis method used to evaluate the irreversibility and efficiency of a coupled conductive-radiative heat transfer process. The exergy analysis of the conductive-radiative process is developed based on the exergy balance equation. In the method, the local entropy generation rates due to the radiative heat transfer and heat conduction processes are calculated. Based on the entropy generation analysis, an exergy analysis is performed, the stored exergy of the system and the exergetic efficiency are determined, and the thermodynamic efficiency of the system is further evaluated. The results are verified by the principle of exergy balance and the exergy generation rate calculated by the method does not deviate from the theoretical value by more than 0.1%. Four heat source distributions are specified in the numerical analysis, which include completely uniform, partially uniform, and non-uniform heat source distributions in the numerical analysis. The effects of heat source distribution, conductive-radiative coefficient and total heat generation rate of medium on entropy generation and stored exergy of system are investigated. The numerical results show that the average temperatures and exergy storage rate of the systems with partially uniform heat source distribution are 5.1–79.7 K and 6.8–49.8% higher than the other distributions, and uniform and centralized heat generation in the internal region of the system is proposed. The total stored exergy of the systems has a tendency to first increase and then decrease, reaching its maximum at N = 1 as the conduction and radiation coefficients increase, and increasing as the total heat generation rate increases. [ABSTRACT FROM AUTHOR]