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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: In the previous paper (Part I) of this series, mathematical models of airflow and heat transfer inside ventilated packaging systems were developed and presented based on the porous media approach. In the present paper (Part II), we describe the CFD methods used to solve the mathematical models for both layered and bulk packaging systems, and the structure of a user-friendly software package (called ‘CoolSimu’) that integrates the modeling system. We also present the results of several simulation tests for both layered cartons and bulk bins of fruit undergoing forced-air cooling. Overall, the CFD modeling system gave satisfactory predictions of temperature profiles of fruit. When model predictions and experimental product center temperature data were compared, good agreements were obtained. The lack of fit at certain locations inside the packaging was attributed to inaccurate temperature measurement and uncertainties in model input data. [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: The mathematical models of evaporative fluid coolers and evaporative condensers are studied in detail to perform a comprehensive design and rating analysis. The mathematical models are validated using experimental as well as numerical data reported in the literature. These models are integrated with the fouling model presented in an earlier paper, using the experimental data on tube fouling. In this paper, we use the fouling model to investigate the risk based thermal performance of these evaporative heat exchangers. It is demonstrated that thermal effectiveness of the evaporative heat exchangers degrades significantly with time indicating that, for a low risk level (p=0.01), there is about 66.7% decrease in effectiveness for the given fouling model. Furthermore, it is noted that there is about 4.7% increase in outlet process fluid temperature of the evaporative fluid cooler. Also, a parametric study is performed to evaluate the effect of elevation and mass flow rate ratio on typical performance parameters such as effectiveness for rating calculations while surface area for design calculations. [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]

Vacuum pre-cooling is a multi-physics process coupling heat transfer, water transport, and shrinkage, the stresses caused by water evaporation and temperature variation in food interact with its deformation. However, the developed models usually assume that the shrinkage of food is insignificant so that it is ignored, which is inconsistent with the actual vacuum pre-cooling process and makes the simulation results inaccurate. Taking strawberry as an example, a multiphase porous media model with heat-water and mechanics (HWM) bi-directional coupling was developed for food vacuum pre-cooling. The accuracy of the HWM model was verified by comparing the heat-water (HW) model without considering shrinkage and the experiments. The results show that the development of the evaporation front predicted by the HWM model is more sensitive to the vacuum chamber pressure change compared with the HW model. The maximum average relative errors corresponding to the temperature and shrinkage of the HWM model are 0.27% and 6.95%, respectively, which are better than the HW model. In addition, the edge gradient effect that occurs in the middle stage of vacuum pre-cooling was observed. When the vacuum chamber pressure approached the lowest point, the evaporation region rapidly developed toward the core. The increase of evaporation driving force and the decrease of boundary moisture caused drastic temperature and shrinkage changes on the product surface. The model developed in this paper considering shrinkage provides technical support to optimize the vacuum pre-cooling process and improve product quality. • Shrinkage of strawberry during vacuum pre-cooling was modeled. • Heat and mass transfer model coupled with shrinkage was developed. • An improved method of predicting vacuum chamber pressure was proposed. • The edge gradient effect due to pressure drop was predicted. [ABSTRACT FROM AUTHOR]

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]

A paper has been published in International Journal of Refrigeration, second law analysis of vapour absorption refrigeration (VAR) system using different mathematical expressions which obey thermodynamics principles. The present paper attempts to discuss and comment on the paper. Addition or subtraction of exergy of the heat flux (or exergy of heat transfer) in mathematical expression of internal irreversibility, are not meeting to direction principles of exergy flow. Therefore, internal irreversibility expressions must be corrected for future research based on second law in the field of VAR system. [ABSTRACT FROM AUTHOR]

A numerical model for heat and mass transfer in vacuum membrane distillation (VMD) under laminar flow was developed using Computational Fluid Dynamics (CFD). Three-dimensional (3D) simulations of temperature and concentration polarization in single and multiple fibre VMD modules were used to estimate permeate flux (kg m −2 h −1 ) over a range of temperatures (30–70 °C), vacuum pressures (10–100 mmHg), crossflow velocities (0.0072–0.72 m/s), and feed concentrations (0–0.4 kg/L NaCl). Simulated flux differed by less than 7% from experimental data for a module with comparable dimensions. Simulations indicate that a 56% increase in fibre packing density resulted in a 24% flux decline at high operating temperature (70 °C), and more than 50% flux decline at low crossflow velocity (0.0072 m/s). The effect of vacuum pressure on flux was found to be independent to the module packing density, while the effect of salt concentration was found to be 28% lower than estimates based on Raoult's law, due to lower spatial variations in membrane surface temperatures at higher salt concentrations. The approach developed in this paper may be used to evaluate performance of alternative configurations for VMD models to aid module design, scale-up and process optimization. [ABSTRACT FROM AUTHOR]

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]

The paper presents an investigation of the thermal performance of an innovative insulation wrap for food freezing, transportation and storage. The wrap is made of two outer polypropylene films and an internal folded polypropylene film welded together to form rectangular internal air cells. A mathematical model of heat transfer is presented and experimentally validated, with discrepancies less than 10% when there is no internal convection effect and generally less than 12% when internal convection is present. A thermal effectiveness of film usage was proposed and analyzed in order to find the best fold geometry. A mathematical model of the effectiveness and its experimental validation showed good agreement (discrepancies less than 13%). By using a criteria map, we recommend the following geometry: wrap thickness more than 5 and less than 10 mm; fold spacing more than 6 and less than 10 mm. [ABSTRACT FROM AUTHOR]

In the last decades numerous coal mines have been closed. One way to overtake the costs associated to the mine closure is the geothermal use of the water stored in the closed and flooded mine workings. The temperature of the water flooding from the mine voids, in some cases reaching depths of several hundreds of meters, is suitable for space heating and cooling by means of the use of ground source (geothermal) heat pumps (low-enthalpy geothermal systems). Flooded mine voids constitute new-created pseudokarstic aquifers or reservoirs, which can store significant volumes of groundwater. However, the recharge and the heat capacity of these systems are finite, and this is the main concern when using mine water as a heat source or sink. These reservoirs can be regulated by means of flow extraction and injection depending on the use demands; notwithstanding, these flows have to be limited to a sustainable value, in order to avoid the exhaustion of the capacity of the aquifer to provide or store heat. Several numerical and analytical models have been created with this aim, with the shortage of hydrogeological and thermal data as main drawback. A literature review of the existent flow and heat transfer models applied to geothermal use of mine water has been undertaken, both analytical and numerical models are considered. The main parameters that have influence in the flow and heat exchange processes, have been analysed. The present paper can be used as basic guidelines to aid when selecting a modelling method for a specific scenario. [ABSTRACT FROM AUTHOR]

This paper addresses the optimal arrangement and design of a dual pressure heat recovery steam generator coupled to two steam turbines. A superstructure that embeds various alternative configurations is optimized considering the following two single objective functions: (a) the maximization of the total net power generation for a given total heat transfer area and (b) the minimization of the total heat transfer area for a given total net power. The optimal number of heat exchangers and pumps and how they should be connected are the discrete decisions. The dimensions and operating conditions are the continuous decisions. A discrete and continuous mathematical model is developed and logical propositions are used for discrete decisions. The results are compared with a reference case reported by other authors. The results indicated that the optimization of the proposed superstructure allowed to find a more efficient HRSG configuration. The obtained configurations differ from the configuration of the reference case in how the heat exchangers and pumps are connected. A considerable increase in about 8% of the total net power generation in (a) and a significant reduction in about 24% of the total heat transfer area in (b) are achieved when compared to the reference case. [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 hybrid ground-coupled heat pump (HGCHP) systems with supplemental heat rejecter/supplier can effectively solve heat imbalance problems in the subsurface, and consequently improve the operation performance of the geothermal systems. For example, solar energy and/or industrial waste heat may be used as stable heat sources for underground heat storage in northern China with higher heating load, and cooling towers are installed to release heat into the air in southern China, where more cooling demand is needed. This paper reviews and discusses different HGCHP systems, which have been applied in China. And based on the heat transfer model of vertical borehole heat exchangers (BHE) for HGCHP systems, physical and mathematical models of multistage series circuits are developed to illustrate the heat transfer process of the underground thermal storage. A set of parameters, such as borehole spacing, heat recharging rate fractions and thermal properties of soils, which affect the thermal performance of the ground heat exchangers are analyzed, and the optimal solutions are discussed for engineering application. [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]

In this paper we present a computational fluid dynamics model for predicting the heat release rates of liquid pool fires. The model makes use of the one-dimensional heat transfer solver to provide the liquid surface boundary condition for the gas phase solver. The in-depth radiation transport is solved by a one-dimensional radiation transport model together with effective absorption coefficients determined from experimental data. The model accounts for the convective heat transfer in the liquid phase by modifying the thermal conductivity. The model is implemented as a boundary condition in the fire dynamics simulator (FDS). The model is validated by comparing experimental and predicted evaporation rates for water and a range of hydrocarbon fuels. The sensitivity of the results to the modelling assumptions and model input parameters is studied. The in-depth heat transfer appears to have a significant effect on the fire dynamics, except for the peak burning rates, which depend most importantly on the gas phase combustion. [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 mathematical model has been developed to describe the hydrodynamics of supercritical fluid flow in the reactor, heat, and mass transfer during drying processes for aerogels production. The model is based on the provisions of continuum mechanics, and Ansys Fluent is used for its calculation. In this research, the medium inside the reactor is considered as homogeneous two-component compressible viscous fluid, which is described by Peng–Robinson equation of state. In this paper we consider the model of supercritical drying process. A considerable part of the mathematical model is description of the fluid flow inside the porous body (aerogel), where only diffusive transport of substance occurs. The model is used to scale-up the supercritical drying process; the reactor geometry and process parameters optimization in order to intensify the production process, achieve desired properties of aerogels. The geometry of 5 l reactor is proposed and studied using the developed model. [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]

Most test methods use skin burn prediction to evaluate the thermal protective performance of clothing. In this paper, we reviewed different burn prediction methods used in clothing evaluation. The empirical criterion and the mathematical model were analyzed in detail as well as their relationship and limitations. Using an empirical criterion, the onset of skin burn is determined by the accumulated skin surface energy in certain periods. On the other hand, the mathematical model, which indicates denatured collagen, is more complex, which involves a heat transfer model and a burn model. Further studies should be conducted to examine the situations where the prediction methods are derived. New technologies may be used in the future to explore precise or suitable prediction methods for both flash fire tests and increasingly lower-intensity tests. [ABSTRACT FROM AUTHOR]

Classical Nusselt’s condensate falling film theory is extended in this paper to the case when the base fluid is added ingredients of some frequently used popular nanoparticles. The resulting mixture, i.e, nanofluids, is analytically investigated either when the nanoparticles are uniformly distributed across the condensate boundary layer which is the most used model (single phase) in the literature, or when the concentration of nanoparticles through the film is allowed to vary from the wall to the outer edge of the condensate film in the light of modified Buongiorno’s nanofluid model (multi-phase) incorporating mechanisms of the Brownian and thermophoretic diffusion. In both theoretical cases, momentum and energy equations are solved analytically to deduce the flow and heat transport phenomena. As a result, the influences of employed nanofluids on the flow and heat of the condensate film are determined exactly. When the concentration of nanoparticles is assumed constant both models are shown to coincide. Otherwise, effects of nanofluids as compared to the regular fluid on the velocity profiles, the mass flow rate, the thickness of the condensate film and the Nusselt number are easy to conceive from both single and multi-phase models. In particular, the theoretical treatment in both models enables us to understand the heat transfer enhancement feature of the nanofluids models. When the diffusion parameter is increased in the multi-phase model, more enhancement in the rate of heat transfer is observed. In agreement with the experimental evidences, the water-based nanofluid with nanoparticles A g is the best heat transferring mixture. [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]

In this paper (i) literature data on the thermal conductivity of (highly) porous ceramics and (ii) related analytical modelling schemes based on the effective media theory are reviewed. The latter do not seem to satisfactorily represent the experimentally observed quadratic power-law scaling of effective thermal conductivity with respect to the volume fraction of the solid material phase (or relative density). In the analytical/modelling part, two microstructural configurations of the conducting and the non-conducting material phase, respectively, are investigated: (i) thin, interconnected spherical shells of the conducting material in a simple cubic arrangement and (ii) regular and statistically random packing of solid, conducting spheres. These microstructural configurations differ from the arrangement used for derivation of classical homogenization schemes based on the effective media theory, i.e. non-conducting pores in a conducting solid matrix. [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]

Fire fighting is a hazardous occupation and the use of good quality thermal protective clothing is vital in the prevention of heat related injuries. Protective fire fighting clothing is generally chosen for its thermal and fire resistant properties, while also considering the weight, bulk and ease of movement of the suit. This research proposes incorporating a phase change material (PCM) into the fabric of the fire fighting suit in conjunction with air gaps to increase the thermal protection. A mathematical model of heat transport through a suit that contains PCMs and air gaps is presented. We investigate the distribution of temperature within the fabric during exposure to different fire situations. To assess the protective nature of the clothing, we model the skin as three layers with differing thermal properties (the epidermis, dermis and the subcutaneous layer) and examine the temperatures within the skin. The model can then be used to determine if the inclusion of a PCM layer would provide increased thermal protection to the fire fighter. Our earlier research has indicated that the most effective position for a PCM layer is near the outside of the suit. This paper will focus on the effect of the PCM layer in combination with air layers in the suit. Our results clearly show that an additional air layer increases the protection provided by the suit. This benefit comes without significantly increasing the overall weight of the suit. [ABSTRACT FROM AUTHOR]

Energy conversion devices undergo thermal loading during their operation as a result of inefficiencies in the energy conversion process. This will eventually lead to degradation and possible failure of the device if the heat generated is not properly managed. The ability to accurately predict the thermal behavior of such a device during the initial developmental stage is an important requirement. However, accurate predictions of critical temperature is challenging due to the variation of heat transfer parameters from one device to another. The ability to determine the model parameters is key to accurately representing the heat transfer in such a device. This paper presents the use of an inverse identification technique to estimate the model parameters of an energy conversion device designed for vehicular applications. To simulate the imperfect contact and the presence of insulating materials in the permanent magnet electric machine, thin material are introduced at the component interface of the numerical model. The proposed inverse identification method is used to estimate the equivalent thermal conductance of the thin material. In addition, the electromagnetic losses generated in the permanent magnet is also derived indirectly from the temperature measurement using the same method. With the thermal properties and input parameters of the numerical model obtained from the inverse identification method, the critical temperature of the device can be predicted more accurately. The deviation between the maximum measured and predicted winding temperature is less than 2.4%. [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]

Once-Through Steam Generator (OTSG) with smaller size and larger heat transfer capability, is typically used for Small and Medium sized Reactors (SMRs). Because the Integrated Pressurized Water Reactor (IPWR) uses OTSG, the feed water is heated to superheated steam by primary coolant, and the higher steam temperature could improve the thermal efficiency of the reactor power plant. However, the smaller size and heat capacity make stable operation more difficult. In this paper, a mathematical model of IPWR is established using RELAP5 code, and a coordination control scheme is used to study the rapid load following characteristics of OTSG. The effects of main operating parameters related to stable operation of OTSG are investigated. Average coolant temperature, steam pressure and OTSG grouping run operation boundary are confirmed. This operation boundary can be used to design and optimize the control system. [ABSTRACT FROM AUTHOR]

Development of appropriate heat transfer models to investigate the thermal behavior of living tissues has become increasingly important in simulations of cancer hyperthermia. In this paper, a review is initially presented of the more important general models developed for heat transfer description of perfused tissues. Comparisons are then made between Pennes' simplified Weinbaum and Jiji “WJ” and the more recent porous media “PM” bioheat models. For this purpose, a mathematical model is developed for the heat transfer in a cylindrical medium containing parallel counter-current pairs of small vessels with characteristics as much as possible similar to those of living tissues. The validity of the models is examined and confirmed using the Pennes in vivo experiments and one-dimensional analytical solutions. For consideration of interstitial hyperthermia treatment the smaller cylindrical zone with typical heat generation, is assumed in the center of the main cylinder. The numerical simulation results revealed that, despite difference in temperature distributions calculated by these three models at normal condition, the heat affected zone at hyperthermic condition predicted by all three models are similar. [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: Jet impingement has been verified as an effective method to enhance convective heat transfer. To make better use of this effect, vacuum glazed transpired solar collector with slit-like perforations is developed. In this paper, a mathematical model based on energy balance equations for the solar collector has been developed to predict its thermal performance. Then experiments have been carried out to verify the model. The results of experiment and simulation have achieved good agreement with the same trend and average deviation of 2.25%. It shows that the model is correct and accurate enough to predict the thermal performance of the collector. Based on simulation results of the model, the effects of key parameters on the thermal performance are analyzed. The key parameters include equivalent diameter of perforation, pitch of perforations, collector height, emissivity of the absorber plate and vacuum glass cover, transmittance of vacuum glass cover. The results of the model are useful in designing and optimizing the vacuum glazed transpired solar collector for different applications. [Copyright &y& Elsevier]

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 is concerned with the global solvability of three-dimensional models for smart materials undergoing phase transitions with heat transfer. The problem is formulated within the framework of generalized standard solids by the coupling of the momentum equilibrium equation and the flow rule with the heat transfer equation. Under appropriate regularity assumptions on the initial data, a global existence result for this thermodynamically consistent system is established by using a fixed-point argument combined with energy estimates. [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]