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This paper addresses the multi-scale modeling of human thermal regulation and the evaluation of human thermal comfort when the human body is dressed. A multi-scale model incorporating models of three-dimensional bioheat transfer, systemic arterial thermo-fluid dynamics, a thermoregulatory system and clothing is developed to predict body temperature and quantitatively evaluate human thermoregulatory responses. The results show good consistency with the available data, indicating that the present model is capable of accurately predicting human thermal regulation. The inverse problem of predicting comfortable clothing thermal resistance is solved by a bisection searching algorithm. Values for the thermal resistance of comfortable clothing in the human resting state are obtained under different environmental temperatures from −5 °C to 20 °C. This study is beneficial for the design and selection of clothing (especially functional clothing) and shows potential application in the evaluation of the thermal comfort of building and driving environments. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents experimental and numerical studies on periodic convection flow and heat transfer in a lid-driven arc-shape cavity with temperature differential. Three cases were considered: Gr=2×105, 5×105 and 1.2×106 at Re=100 (Gr = Grashof number; Re = Reynolds number). The mathematical model was proposed in our previous study. The current study performs an experiment to validate this model, to corroborate the existence of the periodic flow, and to more deeply probe the internal flow and temperature characteristics. The experimental setup primarily comprised an arc-shape cavity, a moving lid, a thermo-system, a smoke generator and an image acquisition system. The periodic convection flow in the cavity was visualized using kerosene smoke. The numerical and experimental results consistently reveal that the periodic flow pattern was observed in the case with Gr=5×105, whereas the steady-state flow pattern took place in the other two cases (Gr=2×105 and Gr=1.2×106). The numerical simulation produced reasonable and satisfactory agreement with the experiment for the periodic flow pattern and period. The difference between the predicted and measured periods is less than 5%. The transport properties, such as average kinetic energy, overall Nusselt number, stream function, phase space trajectory, local kinetic energy, velocity history and temperature distribution, were further analyzed and discussed in this paper. The proposed numerical simulation not only confirms the experimental observation, but also enhances the understanding of periodic convection in an arc-shape cavity subjected to a moving lid and temperature differential. [Copyright &y& Elsevier]

Abstract: A model for predicting the flux and evaporation ratio in direct contact membrane distillation (DCMD) using a compressible membrane is presented. Polytetrafluoroethylene (PTFE) membranes, one of the most common types of membranes employed in MD, are characterised with high porosity (∼90%) and high hydrophobicity, and therefore have high water vapour permeability and high wetting resistance. However, the PTFE membrane is compressible due to its structure. Compression of the membrane will cause a change of its physical structure, such as porosity, thickness, and pore size. As a result, the thermal conductivity and vapour permeability of the membrane will be altered, causing a change in flux and energy efficiency. Such effects need to be accounted for when scaling up from laboratory data to full scale design, because there may be significant differences in the applied pressure. Therefore, in this paper, the influence of pressure on the flux of the compressible PTFE membrane was modelled. This paper also provides a mathematical method to correlate the applied pressures with physical structure changes based on the assumption of constant tortuosity. The modelling results were compared with experimental results over a range of variable process parameters, i.e., temperatures, velocities, membrane lengths, and pressure applied to the membrane. The errors between the model predictions and experimental results were less than 10% within the operating range used in this investigation. [Copyright &y& Elsevier]

Abstract: Combustion in fired heaters, boilers and furnaces often accounts for the major energy consumption on industrial processes. Small improvements in efficiency can result in large reductions in energy consumption, CO2 emissions, and operating costs. This paper will describe some useful low cost modelling techniques based on the zone method to help identify energy saving opportunities on high temperature fuel-fired process plant. The zone method has for many decades, been successfully applied to small batch furnaces through to large steel-reheating furnaces, glass tanks, boilers and fired heaters on petrochemical plant. Zone models can simulate both steady-state furnace operation and more complex transient operation typical of a production environment. These models can be used to predict thermal efficiency and performance, and more importantly, to assist in identifying and predicting energy saving opportunities from such measures as: [•] Improving air/fuel ratio and temperature controls. [•] Improved insulation. [•] Use of oxygen or oxygen enrichment. [•] Air preheating via flue gas heat recovery. [•] Modification to furnace geometry and hearth loading. There is also increasing interest in the application of refractory coatings for increasing surface radiation in fired plant. All of the techniques can yield savings ranging from a few percent upwards and can deliver rapid financial payback, but their evaluation often requires robust and reliable models in order to increase confidence in making financial investment decisions. This paper gives examples of how low cost modelling techniques can be applied to improve confidence in implementing energy efficiency improvements whilst safeguarding manufacturing output and quality. [Copyright &y& Elsevier]

Abstract: This paper explores the through-/in-plane characteristics of water transport in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). Theoretical analysis is performed on the non-isothermal two-phase flow under flow channels. A dimensionless group Da (Damkohler number for PEFC operation), defined as the ratio of water generation rate to water vapor-phase removal rate, is formulated to characterize the flow regimes in a PEFC. This group, lumping geometrical parameters and physical properties, compares the water vapor-phase removal capability (via water diffusion and holding capacity) with the rate of water production by the oxygen reduction reaction. We find that this dimensionless group can be used to characterize the non-isothermal, two-phase phenomena: when Da→0, the fuel cell is subjected to single-phase operation; while as Da→∞ we have full two-phase operation. A more precise expression is explored for the dimensionless group at the channel central line, i.e. Da 0: when Da 0>1 the entire cathode GDL–CL (catalyst layer) interface is in two-phase region, whereas part of the interface is free of liquid water for Da 0<1. The latter scenario is the concept that this paper proposes for improving fuel cell water management: the consequent co-occurrence of single- and two-phase flows in the in-plane direction at Da 0<1 is beneficial to avoid severe dryout and flooding. A two-phase transport model, describing the water and heat transport on the PEFC cathode side, is employed to perform a two-dimensional numerical study. Detailed liquid and temperature distributions are displayed. Simulation predictions are in reasonably good agreement with the dimensionless-group analysis. [Copyright &y& Elsevier]

Abstract: Snow cover is a common and relatively stable land cover condition in winter for cold north regions in China. Snow cover has significant effects on water and heat transfers in frozen soil; it needs to be considered in the study of frozen soil water–heat coupled movements. On the basis of previous research results and physical process analysis of water and heat movements in snow cover and soil, a snow cover–soil union water–heat coupled movements model is established in this paper. The numerical simulation was conducted by using a finite difference method. The results indicate that the simulated values have a similar trend to the measured values and the numerical simulation had big relative errors. However, the average absolute errors of the total and liquid moisture content in frozen soil were all less than 4%, and that of the frozen soil temperature was 1.37 °C. The errors of the numerical simulation were still within the acceptable range. Thus, the snow cover–soil union water–heat coupled movement model constructed in this paper is rational. [Copyright &y& Elsevier]

Abstract: An experimental investigation has begun concerning the hygrothermal behaviour of wooden frame houses. The experimental set-up, consisting in a full-scale wooden frame house exposed to natural exterior climate is presented in the paper. It is located in Grenoble (South-East of France), and is equipped with over 150 sensors in order to collect a large amount of data (temperatures, relative humidity). The experimental data presented in the paper enable to get better understanding of coupled hygrothermal phenomena, and can be used to allow the validation of numerical models for heat, air and moisture transfers in wooden frame buildings. The analysed results demonstrate the importance of temperature-driven moisture diffusion from hygroscopic panelling. [Copyright &y& Elsevier]

Abstract: This paper describes the application of exergy analysis to human heat and mass exchange with the indoor environment. The basis for this paper is the existence of a formal similarity between the parameters defining human heat and mass transfer governed by physiological processes and the parameters defining exergy destruction. Basic heat and mass transfer is calculated using a standard two-node human physiological model. To enable an exergy analysis the model was divided according to heat and mass transfer over appropriate boundaries. The exergy analysis was performed for each process with regard to the type of exergy that participates in heat and mass exchange with respect to the indoor environment. The results provide insight into the complex interactions between the human body and environment as characterized by exergy destruction. Furthermore, the analysis indicates that at given physiological parameters only a certain combination of environmental conditions ensures minimal exergy destruction. These environmental and human conditions coincide with expected level of thermal comfort. [ABSTRACT FROM AUTHOR]

Abstract: In the last years, there has been a rapid growth of research and development activities on high temperature molten salts for nuclear and non-nuclear applications. The study of their heat transfer characteristics is a key issue in the current development of the molten salt reactor (MSR) that is one of the innovative nuclear reactors proposed by the Generation IV International Forum. The MSR is a sort of circulating fuel reactor (CFR), which adopts a molten halide salt mixture containing the fissile material and playing the distinctive role of both fuel and coolant. In a thermal-neutron-spectrum MSR, the reactor core is composed by a graphite matrix (neutron moderator), through which the liquid nuclear fuel flows and leads to a strong and intrinsic coupling between thermo-hydrodynamics and neutronics. This peculiar feature requires a suitable and qualified multi-physics simulation environment for a proper description of the system (fuel/coolant+graphite) behaviour. With reference to such complex and non-linear system, the present work is intended to give two different but linked contributions, in the perspective of a multi-physics modelling able to accurately describe the synergy of the involved different physical phenomena (e.g., by means of software). [(I)] On one hand, this work is aimed at establishing a useful validation framework for the assessment of computational fluid-dynamics (CFD) analyses of liquids with internal heat generation. For this purpose, an analytic approach for both fluid velocity and temperature fields in a circular pipe surrounded by a solid region has been developed. It is an extension of the approach elaborated for pipe flow in (Di Marcello, V., Cammi, A., Luzzi, L., 2010. A generalized approach to heat transfer in pipe flow with internal heat generation. Chemical Engineering Science 65, 1301−1310), in order to take into account the heat conduction in the solid domain (represented by the graphite matrix in the specific case of interest). [(II)] On the other hand, the paper presents a preliminary investigation of the thermal-hydraulic behaviour occurring in a typical graphite-moderated MSR core channel. The developed analytic approach has been conveniently applied to this case study: (i) by testing the capabilities of to evaluate the heat transfer characteristics and the hydrodynamic behaviour of such system; and (ii) by investigating the applicability of correlations for the Nusselt number to fluids with internal heat generation. For a deeper insight into the numerical solutions provided by COMSOL, a code-to-code comparison has been also carried out, adopting a dedicated CFD finite volume software (i.e., FLUENT®). As a result, a satisfactory agreement has been found between the analytic solution and the numerical computations provided by COMSOL and FLUENT for a wide range of Reynolds numbers. As concerns the Nusselt number evaluation, the correlations usually adopted for molten salts have been proved as unsuitable for the analysed system, whereas the correlation advanced in the above mentioned paper (that explicitly takes account of the internal heat source) appears more appropriate. The results of the present work are thought to be useful because they provide: (i) a “generalized” analytic approach to the heat transfer that is applicable in a more general context; (ii) an insight into the heat transfer characteristics of the considered graphite-moderated MSR core channel; and (iii) a preliminary assessment of computations that is essential in view of the adoption of multi-physics tools (like COMSOL) for more complex and representative simulations of the dynamic behaviour of the molten salt reactor, and more in general of other kinds of CFRs. [Copyright &y& Elsevier]

Abstract: Mathematical modeling of the convective processes caused by impact of various forces on the fluid and gas media is rather important nowadays. The increased interest to these problems is caused also by the preparation of experiments on the International Space Station in the frame of the scientific project “Convection and Interfacial Mass Exchange” (CIMEX) of the European Space Agency. They are the experiments to investigate the convective flows of the fluids with a thermocapillary interface between liquid and gas phases. In the case, when a gas flow generates the tangential stresses on a free boundary of liquid, the additional characteristics of the convective flows should be identified. In this paper a stationary coupled problem of gravitational, thermocapillary convection in a horizontal layer with free boundary under conditions of a co-current gas flow is studied. The kinematic and dynamic conditions are fulfilled exactly on the gas–liquid interface. The exact solutions for different types of thermal boundary conditions have been obtained. An evaporation effect through the gas–liquid interface is modeled qualitatively with the help of a heat transfer condition. It has been found that the direction of the velocity at the gas–liquid interface is determined by the governing parameters. The equal-zero condition for the interface velocity has been found, as well. The paper presents the velocity and temperature profiles in the conditions, which correspond qualitatively to the CIMEX experiments. [Copyright &y& Elsevier]

Abstract: Thermodynamic optimization models of gas-hydrate cool storage and cool release processes are established in this paper. The optimal temperature configuration at the sensible heat transfer stage and the optimal gas hydrate phase change rate configuration at the phase change stage in the processes of gas hydrate charging and discharging are obtained by taking entropy generation minimization as optimization objective. The optimal control strategies of the cool storage system are determined. The research results indicate that the optimal operating characteristic of the gas-hydrate cool storage system can be achieved by keeping the phase change rates uniform, which are regulated and controlled according to constant heat transfer rates in the charging and discharging processes of gas hydrate. The analysis method and the results presented in this paper can provide important guidelines for optimal design and operation of gas-hydrate cool storage system. [Copyright &y& Elsevier]

Abstract: We present a two-phase multiscale solidification model, which accounts for coupled heat, mass, solute and momentum transfer and notably describes the motion of globular equiaxed grains. On the microscopic scale the model takes into account nucleation, finite diffusion in both solid and liquid phases, and resolves the diffusion-controlled phase change by a solute balance at the solid–liquid interface coupled with a thermodynamic equilibrium condition for the interface. The main idea of the paper is the solution algorithm of the multiscale model. We propose and present in detail an operator splitting method that resolves the global conservation equations in two stages. In the first solution stage we resolve and integrate globally only the convection terms. In the second solution stage we resolve and integrate locally the contributions of the grain growth kinetics, i.e. the phase change and the microscopic diffusion. We analyze this splitting method based on a scaling analysis that shows that the justification of the method stems from the separation of time scales of convection, diffusion and phase change. We discuss this scale separation in detail and define a test case that is presented and analyzed in a companion paper. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical study on laminar forced convection of water in offset strip-fin microchannels network heat sinks for microelectronic cooling. A 3-dimensional mathematical model, consisting of N–S equations and energy conservation equation, with the conjugate heat transfer between the heat sink base and liquid coolant taken into consideration is solved numerically. The heat transfer and fluid flow characteristics in offset strip-fin microchannels heat sinks are analyzed and the heat transfer enhancement mechanism is discussed. Effects of geometric size of strip-fin on the heat sink performance are investigated. It is found that there is an optimal strip-fin size to minimize the pressure drop or pumping power on the constraint condition of maximum wall temperature, and this optimal size depends on the input heat flux and the maximum wall temperature. The results of this paper are helpful to the design and optimization of offset strip-fin microchannel heat sinks for microelectronic cooling. [Copyright &y& Elsevier]

Abstract: Enthalpy exchangers have been used as an efficient means to recover both sensible heat and moisture from exhaust ventilation air. A cross-flow plate-fin structure is the most popular arrangement for the exchanger core due to its compactness and high mechanical strength even with very small channel wall thickness. Traditionally, hygroscopic paper is selected as the plate and fin materials. Though the sensible effectiveness with this material is satisfactorily high, the latent effectiveness is disappointingly low due to the low moisture diffusivity in paper. To solve this problem, in this study, a novel concept is proposed to augment moisture transfer in the exchanger. Plates and fins are made with different materials. A novel membrane – the composite supported liquid membrane (CSLM) is used as the plate material. Paper is still used as the fin material for its cheapness and high support strength. To make comparisons, two cores, one is paper-fin and paper-plate, and another one is paper-fin and membrane-plate, are constructed and tested for heat and moisture recovery. Simultaneous heat and moisture transfer in the plate-fin core is studied. Mathematical model governing the heat and moisture transfer in the cores is set up and numerically solved. Both the experimental data and numerical results indicate that the latent effectiveness of the paper-fin and membrane-plate core is 60% higher than the traditional paper-fin and paper-plate core, due to the high moisture diffusivity in the CSLM. [Copyright &y& Elsevier]

• The desirable operating conditions to achieve high operational efficiency are obtained. • The performance of the IEC under different operating conditions is investigated. • The mathematical model is validated against published data. • The optimal dimensions that give good efficiency in climates with moderate humidity are highlighted. [Display omitted] This paper presents a study investigating and analyzing the effect of heat and mass exchanger (HMX) dimensions and the flow parameters on the indirect evaporative cooler (IEC) system's performance. For this purpose, a mathematical model based on heat and mass transfer concepts was developed, and the model was verified using experimental and simulation results from published papers. Simulations were performed based on different operating and structural conditions affecting the outlet air temperature, cooling capacity, coefficient of performance, and wet-bulb efficiency. Results showed that the optimal dimensions that give good efficiency in climates with moderate humidity, the length of the duct should be between 0.6 to 1.0 m , the width of the channel between 0.3 to 0.5 m , and the channel gap between 0.004 to 0.008 m. It has also been observed that the increasing working air velocity has a positive effect on cooling performance, and its velocity should not be less than 1 m / s. As for increasing the product air velocity, it reduces the heat exchange period, which is undesirable, so it should not exceed 1 m / s. The prescribed flow rate ratio between product and working air should be 0.3 to 0.5. This analysis provides desirable operating conditions to achieve high operational efficiency as well as optimal dimensions for designing such a cooler. [ABSTRACT FROM AUTHOR]

Abstract: Agricultural residues (agro-biomass) can produce energy by thermochemical conversion. Gasification is becoming one of the best clean technologies for power production. Thermochemical process of gasification sets free the solid fuel inherent energy and converts the solid phase into a mixture of gases (producer gas or syngas) that carries a percentage of this energy. Fluidized bed reactors may be used for biomass gasification offering many advantages such as: (1) the superior mixing properties and (2) the enhanced heat transfer rates between the gas and the particles as well as between the particles and the heat exchanger surfaces. In this paper gasification process applied to agricultural residues is reviewed by means of modelling. Description of various stages of the biomass gasification in a fluidized bed is made and the whole spectrum of problems from the processes in an individual biomass particle (drying, pyrolysis, fragmentation and charl burning) to the global mass transfer and chemical processes in a fluidized bed reactor and freeboard is presented. The paper discusses also the specific problems arising from using agricultural residues as raw material and recommends further experimental studies necessary for process optimisation and for scale up. Extensive investigation of gasification plant behaviour depending on various operating parameters is always required in order to support the optimisation procedure and mathematical models are helpful to reduce the temporal and financial efforts. [Copyright &y& Elsevier]

Abstract: In this paper, the porous NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) has been investigated experimentally and numerically. The mathematical models about the ignition and the sintering were constructed to investigate the effect of the preheating temperature and the coil temperature on the combustion. The results showed that the temperature difference between the ignition face and the bottom face was large due to low heat transfer conductivity. The ignition time would increase with the decrease of the coil temperature and the preheating temperature. The temperatures for different locations showed a strong dependence on the combustion time for lower preheating temperature, for the preheating temperature 1173K, this mode of the combustion has transferred from SHS to thermal explosion. The transient partial molten phenomenon occurred during the process of combustion, which was more homogenous for preheating temperature 873K. The mean velocity of the combustion wave was investigated systematically. An experiment was also carried out to investigate the ignition and SHS reaction for porous NiTi alloy in this paper. It was found that the results of experiment and numerical simulation were shown in good consistence. [Copyright &y& Elsevier]

Abstract: The thermal problem defined for the validation challenge workshop involves a simple one-dimensional slab geometry with a defined heat flux at the front face, adiabatic conditions at the rear face, and a provided baseline predictive simulation model to be used to simulate the time-dependent heatup of the slab. This paper will discuss a clustering methodology using a surrogate heat transfer algorithm that allows propagation of the uncertainties in the model parameters using a very limited series of full simulations. This clustering methodology can be used when the predictive model to be run is very expensive, and only a few simulation runs are possible. A series of time-dependent statistical comparisons designed to validate the model against experimental data provided in the problem formulation will also be presented, and limitations of the approach discussed. The purpose of this paper is to represent methods of propagation of uncertainty with limited computer runs, validation with uncertain data, and decision-making under uncertainty. The final results of the analysis indicate that the there is approximately 95% confidence that the regulatory criteria under consideration would be failed given the high level of physical data provided. [Copyright &y& Elsevier]

Abstract: A sequence of mathematical models describing the electrothermal ribbon printing process is developed. The models describe the electrical processes, heat generation and heat transfer within the ribbon and the transfer of ink from the ribbon to paper. Account has been taken of the nonlinear electrical properties of the ribbon. A model of the paper surface has been developed in order to model the transfer of the ink from the ribbon to the paper. The partial differential equations describing the electric field, the heat flow and the stresses in the ink have been solved using standard techniques. [Copyright &y& Elsevier]

Abstract: This paper deals with the modeling of the thermal field during machining processes by laser beam local heating. The analysis refers to the identification of mathematical models suitable to describe the large variety of complex phenomena which occur during the machining process. Specifically, this paper provides the modelling assessment to deal with the solution of mathematical problems toward simulation and with specific engineering applications related to the above technological system. [Copyright &y& Elsevier]

In this paper, integral mathematic model of fluid flow and heat transfer of GTAW arc and weld pool was established. This model built in this paper may avoid the assumption which surface temperature of weld pool is constant and at the same time provide reliable boundary conditions for analyzing of weld pool. Using finite element analysis software ANSYS, behavior of welding arc and weld pool was systematically analyzed including welding arc temperature field, current density distribution, fluid flow in weld pool and effects of a few forces on weld pool shape. The calculated results were proved by experiments. [Copyright &y& Elsevier]

This paper presents a theoretical study on the optimization of key material parameters of multilayer clothing assemblies for thermal comfort in cold climate. A mathematical model of heat and moisture transfer through a multilayer clothing assembly is established. The existence and uniqueness of the solution of the model are verified by using the fixed point theorem. The model predicts the optimum thicknesses and porosities of the two internal layers of the clothing assembly, with which the thermal comfort index will fall within the required intervals with the greatest probability. This study is significant for the optimum design of multilayer clothing assembly for thermal comfort. [ABSTRACT FROM AUTHOR]

Nanofluids have gained significant attention in recent years due their great potential for heat transfer enhancement . The heat transfer of nanofluids can be numerically studied using a single-phase or two-phase approaches. The first assumes that the fluid phase and nanoparticles are in thermal equilibrium and move with the same velocity, while the second requires more computational effort but provides the possibility of understanding the behavior of both fluid phase and solid particles in the heat transfer mechanism. This paper reviews various computational approaches to predict fluid flow and heat transfer characteristics of nanofluids. The characteristics of single-phase and two-phase (volume of fluid, mixture, Eulerian–Lagrangian and Eulerian–Eulerian) approaches have been analyzed and discussed systematically. Latest development and recent researches related to the computational nanofluids are also given. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model for simulating Tempcore process, the model consisting of three successive parts. Thermal model is used to predict the temperature distribution across the bar over its whole quenching and self-tempering rout. The output of this model is used to calculate the area of martensite formed in outer layer and ferrite–pearlite heart. The composite rule of mixtures (ROM) is used to correlate the tensile yield strength of the bar with the martensite and ferrite–pearlite volume fraction. The model is capable of predicting the effect of various process parameters namely; bar diameter, rolling temperature, number and setting of cooling nozzles, cooling water flow rate and quenching time on the thermal conditions across the bar during different stages of the process, structure formed and tensile behavior of the rebar. A good agreement is found between the predicted results and the experimental data for B500B steel with diameters from 10 to 16 mm and yield strength varied from 400 MPa to 700 MPa. [ABSTRACT FROM AUTHOR]

The thermal gas mass flow meter is an important meter used in industrial measurement. When the environmental temperature changes, the measured gas physical parameters change correspondingly and the thermal gas mass flow meter output signal is affected, causing large measurement error. The influence of gas temperature on the sheathed probe measurements is analyzed in this paper based on experiments and heat transfer theory using a three dimensional probe and gas heat transfer mathematical model based on the heat conduction equation. The probe heat transfer process is analyzed under convection heat transfer coupling conditions. The experimental data were analyzed and compared against the theoretical results, with a maximum average relative error of only 4.56%. The rationality of the theoretical method is thus verified. [ABSTRACT FROM AUTHOR]

One of the most feasible solutions for reducing the global energy consumption and associated CO 2 emissions, is through usage of more efficient insulation systems in buildings and refrigeration units. Commercialization of high-performance thermal insulation will significantly contribute to environmentally sustainable future development. Aerogel composites provide superior thermal resistance and enable new design approaches for high performance insulation systems. This paper presents a theoretical and experimental study on the effective thermal conductivity of aerogel composites. The analytical model represents aerogel composites with a unit cell consisting of a cylindrical fiber surrounded by a packed bed of aerogel particles. The model accounts for various heat transfer mechanisms, namely conduction in the solid, gas conduction, and radiation. The properties and microstructure of two types of aerogel composites (Cryogel® Z and ThermalWrap™) were studied with scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and Fourier transform infrared spectroscopy (FTIR). The apparent thermal conductivity of the samples of aerogel blanket were measured using heat flow meter (HFM) at mean temperature ranging from −20 °C to 80 °C and the results polished thorough two-thickness method to de-convolute the effect of thermal contact resistance (TCR), between the sample and HFM hot and cold plates, from the apparent thermal conductivity values. The effective thermal conductivity results were found to increase from 0.0135 to 0.0175 W m −1 K −1 for Cryogel® Z and 0.0188 to 0.0271 W m −1 K −1 for ThermalWrap™ at mentioned temperature range. The analytically predicted variation in the effective thermal conductivity as a function of temperature agreed well with the experimental data. Using the proposed model, parametric studies were performed to investigate the effect of blanket porosity and fiber thermal conductivity on the effective thermal conductivity of aerogel composites. [ABSTRACT FROM AUTHOR]

This paper presents a novel hybrid between a tubular solar receiver and a combustor, called the Hybrid Solar Receiver Combustor (HSRC), and reports on the development and application of an analytical model to describe its performance. The analytical model accounts for the variability of the solar resource with a pseudo steady state balance of the mass and energy flow, which calculates the heat transfer throughout the device. A systematic investigation of the influence of variation in all controlling parameters on performance and weight is undertaken. The results provide new understanding of the performance of the device relative to the solar-only and combustion-only counterparts, and further justification for its ongoing development. [ABSTRACT FROM AUTHOR]

The subject of this paper was to develop a mathematical model of a non-contacting face seal describing the phenomenon of the heat transfer in the system: sealing rings – fluid film. The function of non-contacting face seals used in rotor machines is to separate the working agent from the external environment. The nature of operation of non-contacting face seals allows the fluid to leak through the clearance not bigger than a few micrometres. During the operation of the rotor machine between the co-operating rings, an intense conversion of mechanical energy into heat occurs. At first, the heat flux generated in the fluid film is channelled to the sealing rings and then to the surrounding fluid. The solution of the presented model was conducted with the use of analytical methods for the direct and the inverse heat transfer problem. The distribution of the temperature fields in the sealing rings for the direct heat transfer problem was determined with the use of Fourier–Bessel series as the surface function of two variables ( r , θ ) for the cross-section of a ring. The inverse heat transfer problem was solved with the use of Trefftz functions. The presented computational methods allow a more detailed identification of the phenomenon of the heat transfer in non-contacting face seals and indicate a direction of further research and preparation of new computational methods. [ABSTRACT FROM AUTHOR]

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0 °C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters. [ABSTRACT FROM AUTHOR]

Loosening local equilibrium assumptions in two-phase flow in porous media gives rise to new, unknown variables. More specifically, when loosening the local thermal equilibrium assumption, one has to describe the heat transfer between multiple phases, present at the same mathematical point. In this paper, we calibrate a macro-scale mathematical model which is free of local equilibrium assumptions to experimental observations. We emphasize the correct determination and upscaling of necessary input parameters from the experimental data achieved by image analysis. By choosing an appropriate scaling parameter, we are able to reproduce experimental measurements satisfactorily. This is a first step towards quantifying heat transfer in two-phase flow in porous media. Ultimately, our aim is to find the limits of the applicability of local equilibrium assumptions in two-phase flow in porous media. [ABSTRACT FROM AUTHOR]

The thermodynamic efficiencies of regenerative cooling cycles are directly linked to the heat transfer effectiveness and thermal losses in the regenerator. This paper proposes a performance analysis for regenerators based on the Entropy Generation Minimization (EGM) theory. The mathematical model consists of the one-dimensional Brinkman–Forchheimer equation to describe the fluid flow in the porous matrix and coupled energy equations to determine the temperatures in the fluid and solid phases. The cycle-average entropy generation contributions due to axial heat conduction, fluid friction and interstitial heat transfer are calculated. The influences of parameters such as the mass flow rate, operating frequency, regenerator cross sectional area, housing aspect ratio, utilization factor and particle diameter are evaluated according to the variable geometry ( VG ) and fixed face (cross-section) area ( FA ) performance evaluation criteria (PEC). Optimal regenerator configurations are found for each PEC for flow rates between 40 and 300 kg/h (0.01 and 0.083 kg/s) and frequencies between 1 and 4 Hz with constraints of regenerator effectiveness equal to 95% and temperature span of 40 K. [ABSTRACT FROM AUTHOR]

The steady natural convection in a two-dimensional porous square cavity filled with a nanofluid and including internal heat generation is presented in this paper. The mathematical model considered consists of the Darcy equation for the momentum, while a new model is proposed for the energy and nanoparticles’ concentration equations. The system of partial differential equations is written in terms of a dimensionless stream function, temperature and concentration of the nanoparticles and is solved numerically using the finite difference method. The effects of the governing parameters, such as: Rayleigh number Ra , the Lewis number Le and the dimensionless ratio between the thermophoretic and Brownian coefficients N BT on the velocity, temperature and nanoparticles’ concentration, Nusselt and Sherwood numbers are studied. It is found that the addition of the nanoparticles into the fluid saturated porous medium reduces the temperature and enhances the heat transfer when the value of the thermal conductivity of the nanoparticles is much higher than the thermal conductivity of the solid structure of the porous medium. This addition has almost no effect on the flow and heat transfer characteristics when the values of the thermal conductivity of the nanoparticles and the thermal conductivity of the solid structure of the porous medium have close values. [ABSTRACT FROM AUTHOR]

In this paper, a distributed parameter model for tubular reactor in the ethylene cracking furnace based on 3-D temperature reconstruction is developed. The mathematical model was formulated to predict the distributions of the heat flux and the tube temperature while considering a non-uniform distribution of the surface heat transfer and the ethylene pyrolysis process. The results show that the heat flux distribution on the tubular reactor has four high heat flux zones, and the tube temperature reaches a maximum of 1088 °C. The value of the maximum tube temperature decreases compared with the value of the maximum heat flux due to the heat exchange coefficient of pyrolysis gas increasing slowly in the bend region. The tube temperature distribution was validated by using a spectrometer system and the errors between three major product yields at the tube outlet obtained by the proposed model and in-situ measured values were within 5%. This distributed parameter model can be used as a guide for ethylene cracking furnace operators and as a tool for design. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of heat and mass transfer in indirect evaporative air coolers with four air flow patterns: parallel-flow, counter-flow, cross-flow and regenerative. The numerical simulation was performed on the basis of original two-dimensional heat and mass transfer models (in the case of cross-flow heat exchanger the model was 3D). The mathematical models developed were validated against published experimental data presented in Appendix A . It was established, that heat and mass transfer processes in the wet channels of counter-flow, cross-flow and regenerative indirect evaporative coolers are characterized by creation of two particular heat and mass transfer zones. Detail analysis of the temperature and humidity ratio distributions and boundary conditions, characterizing the coupled heat and mass transfer process in each of these determined zones, revels the violation of the Lewis relation unity under a certain inlet and operation conditions. A theoretical method for estimating the Lewis factor was proposed. Using the developed models the thermal performances of the conventional designs of indirect evaporative air coolers were analyzed numerically and preferable climatic zones for considered heat exchanger were established. Four novel heat exchangers utilizing the advantages of the basic cycles heat exchangers were presented. [ABSTRACT FROM AUTHOR]

This paper investigates a mathematical simulation of the heat and mass transfer in the two different Maisotsenko Cycle (M-Cycle) heat and mass exchangers used for the indirect evaporative cooling in different air-conditioning systems. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process, thus quantifying the overall heat exchangers’ performance. The mathematical model was validated against the experimental data. Numerical simulations reveal many unique features of the considered units, enabling an accurate prediction of their performance. Results of the model allow for comparison of the two types of heat exchangers in different applications for air conditioning systems in order to obtain optimal efficiency. [ABSTRACT FROM AUTHOR]

This paper presents a transient model of internal catalytic combustion suitable for isolated channels and monolith reactors. Due to time-scales in the problem, the model considers a quasi-steady gas phase with a transient solid. The gas is described by axially varying bulk temperature and species. The gas includes lateral diffusion via transfer coefficients and the specification of a gas-phase species concentration at the wall; axial diffusion is neglected. The solid phase is a thermally thin shell with axially varying temperature, surface species, and surface species concentrations. The solid includes axial heat conduction and external heat loss by convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations with respect to axial position; the upstream (inlet) boundary conditions are specified and the axially varying solid properties are parameters in integration. The solid phase discretizes into a system of stiff ordinary differential-algebraic equations with respect to time. The time evolution of the system comes from alternating integrations of the quasi-steady gas phase and transient solid. The model is compared to two experimental cases using CO fuel: (1) steady-state conversion in an isothermal platinum tube and (2) transient propagation of a catalytic reaction inside a small platinum tube and includes external tube temperature measurements. This work presents sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, external heat-loss, and others. Under mass-transfer limited conditions, global transfer coefficients are adequate to predict fuel conversion. Near light-off, the model predictions improve for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increases compared to O 2 . For the second case, predictions of transient propagation speeds are good for equivalence ratios near unity and greater but require adjustment of external heat loss or kinetics to match under lean conditions. [ABSTRACT FROM AUTHOR]

Laminar and turbulent forced convection heat transfer and flow characteristics of nanofluids in small smooth tubes are numerically simulated using two kinds of multiphase-flow models. The simulated results are compared with the experimental results from the published papers and the traditional predicting correlations to investigate the applicability of these models for nanofluids. The multiphase-flow models including mixture model and Eulerian model, and both of them belong to the well-known Euler–Euler model. The effects of various parameters such as Reynolds number and nanoparticles concentration on the heat transfer and flow characteristics are investigated and discussed in each model. The study results show that little deviation exists between the simulated results and the traditional predicting correlations for low concentration nanofluid, which indicates that low concentration nanofluid has no meaningful nano-effect on forced convection heat transfer. While, non-traditional fluid characteristics occur and increase with increasing the nanoparticles concentration, and the simulated results using special models of multiphase flow are closer to the experimental data than that of the traditional correlations, which means the multiphase flow models are more accurate than traditional correlations for high concentration nanofluid. Moreover, the numerical results also indicate that the drag coefficients of simulated results have only little difference less than 0.4% with that of experimental results for nanofluids in the laminar flow region. However, the drag coefficients of simulated results have a increase by about 60–22% compared with the experimental results in the turbulent flow region. As conclusion, the present study indicates that the two-phase models, including mixture model and Eulerian model, can predict the forced convection heat transfer and flow characteristics of nanofluid well, and have important implications for the application of nanofluid. [ABSTRACT FROM AUTHOR]

Liquid-to air membrane energy exchangers (LAMEEs) are novel membrane based energy exchangers that allow simultaneous heat and moisture transfer between salt solutions and air streams. The similarity between a small-scale (2.5 L/s) LAMEE and a full-scale (100 L/s) LAMEE is investigated, both experimentally and numerically, in this paper. Dimensional analysis of the coupled heat and mass transfer equations in the air-side, solution side and membrane of the LAMEE shows that five important dimensionless parameters affect the performance of LAMEEs: (1) number of heat transfer units, NTU, (2) thermal capacity ratio, Cr*, (3) number of mass transfer units, NTUm, (4) mass flow rate ratio, m*, and (5) operating factor, H*. The differences in the small-scale and full-scale LAMEEs effectivenesses are numerically investigated for these five important dimensionless parameters. The results show that in most cases the differences between the small-scale and full-scale LAMEE effectivenesses are less than 2%. The comparison between the experimental and numerical sensible, latent and total effectivenesses of the small-scale LAMEE and the full-scale LAMEE shows that there is a similarity between the small-scale and full-scale LAMEEs, and that the small-scale LAMEE effectiveness results can be used to predict the performance of the full-scale LAMEE. [ABSTRACT FROM AUTHOR]

In this paper we consider the fundamental problem of how to design the spacing between two plane and parallel tree structures buried in and transferring heat to a conducting medium. The Y and T tree-shaped structures are configured as two palms facing each other. The search for the optimal spacing is pursued in solid domains with three sizes. First, we studied a cube where the tree palms structure grow to the second level bifurcation. Second and third, we considered a small cube and a large cube where the tree structure consists of just the first level bifurcation. The results show that the best spacing between palms is half of the side of the cube, in order to avoid the interference between the two tree and adiabatic boundaries of the cube in which the trees structures are embedded. The spacing is possible to optimize, without being affected by the shape of the structure, the bifurcation level of the structure and the size of cube. The decision of optimal spacing is not affected by changes in the volume fraction occupied by tree structure in the conducting body. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the improved heat flux partitioning model based on first principal models of the underlying physics in determining the active nucleation site density, bubble size and bubble frequency is evaluated for subcooled flow boiling in vertical heated channels at low pressures. Salient features of this model include the fractal approach in determining the active nucleation site density, the force balance model in determining bubble diameters at sliding and lift-off as well as bubble frequency through the consideration of growth and waiting times and the additional heat flux at the heated wall due to surface quenching of sliding bubbles. Model predictions, covering a wide range of different mass and heat fluxes and inlet subcooling temperatures, are compared against local and axial measurements. In comparison to the measured data and selected combinations of empirical correlations such as described in Part 1, the current model predictions clearly demonstrate the effect of the subcooling effect on the activation of nucleation sites at the heated wall. The selected combinations of empirical correlations consistently under-estimate the wall superheat temperature while the current model yields predictions that agree very well with experimentally measured temperatures. Bubble sliding along the heat wall and its influence on heat partitioning and surface quenching heat flux has been ascertained to play an important role during the subcooled flow boiling process. [Copyright &y& Elsevier]

Abstract: This paper presents the advanced object-oriented design of finite element representations in a complex multi-physics finite element environment OOFEM [1–3]. The focus is on reuse of existing single-physics capabilities when implementing elements for coupled simulations. This has been achieved by decoupling the description of element geometry, element problem specific capabilities, element interpolation, and integration schemes. The individual problem specific capabilities, represented by a hierarchy of classes derived form ElementEvaluator, can be assembled together to define an evaluator for coupled analysis. The presented design leads to an extremely flexible implementation, with clean modular design. The application is demonstrated on an implicit gradient formulation of a damage-plastic model and on coupled heat and mass transfer. [Copyright &y& Elsevier]

Abstract: This paper presents a simple and rapid mathematical model to calculate the non-steady-state startup process and study the isothermal characteristics of a particular heat pipe. The model takes into consideration the special structure and usage conditions, where vapor temperature in the heat pipe changes only over time. This vapor temperature change correlation is calculated numerically and is set as the temperature boundary condition for the working well. The temperature, velocity and pressure distribution in the working well are then solved using FLUENT. The results manifest that the time required for approaching steady condition are 450s, 550s and 600s with water bath temperatures of 330K, 340K and 350K, respectively. The comparison of the calculations and experimental data shows good agreement, and the maximum deviation is 3.7K. [Copyright &y& Elsevier]

Abstract: The formation of particulate deposits on flue gas heat exchanger surfaces will reduce heat transfer efficiency, increase the instability of equipment operation and introduce a major uncertainty into the heat exchanger design. In this paper, a numerical model was developed to predict the flue-ash particle deposition rate by considering particles transport, sticking and rebound behaviors based on the software FLUENT, extended by user-defined functions (UDFs). The numerical model was applied to cross-flow tube bundle heat exchangers with a 6-row tube arrangement. The effects of six parameters (particle diameter, flow velocity, spanwise tube pitch, longitudinal tube pitch, tube geometry shape, and arrangement) on fouling rate, as well as on the heat transfer and hydrodynamics performance, were examined. It was found that particle deposits accumulated primarily in the flow stagnation region, recirculation region, the vortex separation and reattachment regions. Increasing particle diameter moved the deposition zones towards the windward side of tubes. Using both oval tubes and staggered arrangements can reduce the fouling rate. With the increase in longitudinal tube pitch, both the particulate deposit rate and the heat transfer performance increased. To account for fouling and heat transfer performance, a tube spacing value of 2 was recommended. [Copyright &y& Elsevier]

Abstract: Small scale particles/pores from micrometers and down to nanometers often occur in multi-functional porous electrodes in fuel cells, to enhance the catalytic reaction activities and accordingly the cell performance. Multi-component and -phase mass transport phenomena of reactants and products are strongly coupled with other transport processes as well as various reactions. All these processes form inter-linked circuits for the mass, heat and electricity, which determine electrode design, cell structure/configuration and operation, hence overall performance. Understanding of gas diffusion mechanisms and accurate estimating of the overall diffusion coefficient are essential for the operation and design of fuel cells, especially at high current density conditions. Several intensive research and investigations have appeared in recent years involving both experimental and modeling approaches for porous structure reconstruction and evaluation of effective diffusion coefficients. In this paper, the mass transfer equations commonly used for continuum models at porous-average level are outlined and highlighted, with the purpose to provide a general overview of the validity and the limitation of these approaches. The most often used models in the open literature are reviewed and discussed focusing on the effective gas diffusion coefficients and tortuosity factors. It is revealed that the effects of both small scale (Knudsen number) and tortuous pathways (tortuosity factor) on the effective diffusion coefficients are significant for the specific layers in the electrodes. Summary and suggestions are also provided for better understanding of gas diffusion phenomena and implementation of the effective gas diffusion coefficient models for fuel cell electrodes. [Copyright &y& Elsevier]

Abstract: The paper presents a new proposal of a discrete event simulation (DEVS) model for heat transfer in an enclosure. To our knowledge this is the first proposal in this direction, therefore the model is not comprehensive (has no windows, no ground coupling, etcetera). It is a first step of DEVS into the heat transfer in buildings. The model presented is just one possible implementation for a single thermal zone, although it has been designed to be used in multi-zone models. Common methods like CTF (conduction transfer functions) or RTF (response transfer functions) cannot be used. Instead it employs the successive transition state formulation for the 1D conduction heat transfer through multi-layered walls. An example test room has been calculated and the results compared with software that uses well known methods (CTF, RTF). Finally the DEVS model has been tested with a random convective internal-load signal. [Copyright &y& Elsevier]

Abstract: This paper examines numerically the heat transfer enhancement in a pipe partially filled with a porous medium under local thermal non-equilibrium (LTNE) condition. The flow inside the porous material is modelled using the Darcy–Brinkman–Forchheimer model. The effect of different parameters such as, inertia (F), Darcy number (Da), conductivity ratio, porosity and particle diameter on the validity of local thermal equilibrium (LTE) are studied. The optimum porous thickness for heat transfer enhancement under varying F and with reasonable pressure drop is determined. The pipe wall is under constant wall temperature boundary condition. Two models are considered at the interface between the porous medium and the fluid. The differences between these models in predicting the temperature of the fluid and solid phases as well as the Nusselt (Nu) number for different pertinent parameters are discussed. In general, the two interface models result in similar trends of Nu number variation versus porous thickness ratio. However, considerably different values of Nu number are obtained from the two interface models. The effects of inertia term on the Nu number and pressure drop are further studied. For a given model and for Da<10−3, the Nu number is found independent of F. However, for Da>10−3 as F increases the computed Nu number increases. [Copyright &y& Elsevier]

Abstract: Conventional network structure modifications for retrofitting heat exchanger networks (HENs) usually require a large network superstructure, which might lead to very large scale retrofit models, and thus increases the computational difficulties of optimization, especially for industrial applications. This paper presents a novel optimization approach of retrofitting HENs for both small scale and industrial scale problems. To overcome the drawback of the existing retrofit research, a simple but efficient method is proposed to determine the network retrofit superstructure based on the concept of pinching match. Then two optimization stages (network structure optimization and investment optimization) are solved with the MILP-based iteration method that has been developed. The proposed approach has many benefits for solving HEN retrofit problems. First, smaller size of retrofit superstructure is provided based on the pinching match analysis. Second, the MILP-based iteration method developed converts conventional a mixed integer non-linear programming (MINLP) to a mixed integer linear programming (MILP), and significantly reduce the computational difficulties of nonlinear programming associated with configurational changes or structural modifications for existing heat exchanging arrangements, which is upgraded based on the MILP-based iterative method proposed by Pan et al. (2012a) for retrofitting HENs with heat transfer intensifications, as the earlier work was only applicable to the cases without network topology modification. In case studies, the new proposed approach is compared with the existing methods in two literature examples and one industrial problem, demonstrating that the new proposed approach is able to obtain better and more realistic solutions for HEN retrofitting considering the economic trade-offs between energy savings and investments. [Copyright &y& Elsevier]

Abstract: Heat transfer by natural convection occurs in many physical problems and engineering applications such as geothermal systems, heat exchangers, petroleum reservoirs and nuclear waste repositories. These problems and phenomena are modeled by ordinary or partial differential equations. In most cases, experimental solutions cannot be applied to these problems, so these equations should be solved using special techniques. Recently, much attention has been devoted to these methods to construct analytic solutions; such as the perturbation method. Perturbation techniques are dependent upon small parameter. Thus, it is worthwhile developing a new technique independent of small parameter. The Reconstruction of Variational Iteration Method technique is a powerful and convenient algorithm in finding the solutions for the equations. While this method is capable of reducing the size of calculation, it overcomes the difficulty of the perturbation technique or Adomian polynomials by applying Laplace Transform. In this paper an analysis has been performed to study the natural convection of a non-Newtonian fluid between two infinite parallel vertical flat plates and the effects of the non-Newtonian nature of fluid on the heat transfer are studied. In order to compare with exact solution, velocity and temperature profiles are shown graphically. The obtained results are valid with significant accuracy. [Copyright &y& Elsevier]

Abstract: Adequate modeling of radiation heat transfer is important in CFD simulation of coal gasification process. In an entrained-flow gasifer, the non-participating effect of coal particles, soot, ashes, and reactive gases could significantly affect the temperature distribution in the gasifier and hence affects the local reaction rate and life expectancy of wall materials. For slagging type gasifiers, radiation further affects the forming process of corrosive slag on the wall which can expedite degradation of the refractory lining in the gasifier. For these reasons, this paper focuses on investigating applications of five different radiation models to coal gasification process, including Discrete Transfer Radiation Model (DTRM), P-1 Radiation Model, Rosseland Radiation Model, Surface-to-Surface (S2S) Radiation Model, and Discrete Ordinates (DO) Radiation Model. The objective is to identify the pros and cons of each model’s applicability to the gasification process and determine which radiation model is most appropriate for simulating the process in entrained-flow gasifiers. The Eulerian–Lagrangian approach is applied to solve the Navier–Stokes equations, nine species transport equations, and seven global reactions consisting of three heterogeneous reactions and four homogeneous reactions. The coal particles are tracked with the Lagrangian method. Six cases are studied—one without the radiation model and the other five with different radiation models. The result reveals that the various radiation models yield uncomfortably large uncertainties in predicting syngas composition, syngas temperature, and wall temperature. The Rosseland model does not yield reasonable and realistic results for gasification process. The DTRM model predicts very high syngas and wall temperatures in the dry coal feed case. In the one-stage coal slurry case, DTRM result is close to the S2S result. The P1 method seems to behave stably and is robust in predicting the syngas temperature and composition; it yields the result most close to the mean, but it seems to underpredict the gasifier’s inner wall temperature. [Copyright &y& Elsevier]