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Abstract: This paper presents a thermal fluid analysis on the air cooling of a permanent magnet electric motor with a centrifugal impeller. A numerical model is developed for the heat transfer and fluid flow process. The flow rates of the cooling air are also experimentally measured. The agreement between the numerical model prediction and experimental data is reasonably good. Detailed structures of the cooling flow are presented. Convection heat transfer on the surface of the armature is quantified. Comments on the application of the motor architecture are given. Design modifications are proposed for performance improvements. [Copyright &y& Elsevier]

Abstract: The paper presents detailed numerical study of heat transfer enhancement by a spherical dimple placed on a wall in a narrow channel. RANS approach with MSST model is applied to investigate the influence of the depth to diameter ratio Δ and the Reynolds number on the flow and heat transfer. Numerical model was successfully validated using LDV measurements, pressure loss data and LES results. Special attention is paid to identification of the flow topology at different Δ and Reynolds numbers. Contribution of different heat exchanger surface parts to the heat transfer enhancement is analyzed. Application of entropy production as a criterion of heat exchanger efficiency is discussed. Detailed information gained from the present computations can be used to get a deep insight into flow physics over dimpled surfaces and as a benchmark for validation of numerical and experimental methods. [Copyright &y& Elsevier]

Abstract: Effective thermal conductivity (ETC) is an important parameter describing the thermal behaviour of packed beds with a stagnant or dynamic fluid, and has been extensively examined in the past decades. Recently, an approach of coupled discrete particle simulation (DPS) and computational fluid dynamics (CFD) has been extended to predict the ETC, allowing the elucidation of the underlying heat transfer mechanisms at a particle scale. However, because of the sensitivity of heat transfer to particle–particle contact, a large Young''s modulus and small time step have to be employed in the DPS to generate accurate results, resulting in a high computational cost. This paper proposed a method to overcome this problem. It is done by introducing a correction coefficient in the calculation of the particle–particle contact radius between colliding particles. The treatment is first implemented in our recent DPS-CFD modeling of the heat transfer in gas fluidization, and is validated by comparing the predicted ETC with literature data. The effects of model parameters, particle size, and bed average temperature on ETC are also analyzed. [Copyright &y& Elsevier]

Abstract: The mathematical modeling and computer simulation have been widely used in the analysis of system''s dynamic characteristics, and often useful for system control. One of the popular methods for this purpose is the lumped parameter method. For flow boiling heat transfer system, the traditional lumped parameter modeling method has a problem that the heat transfer coefficients change suddenly at the boundary of coolant phase change. It can cause error. In this paper, an idea of flexibility model is developed to deal with the boundary problem and to improve the model of flow boiling heat transfer. The segments of coolant phase change''s boundary are identified, and the membership functions which are derived from Fuzzy Mathematics are used to derive approximate expressions of heat transfer coefficient in those regions. The continuity of heat transfer coefficient can be described by those expressions. The membership functions are derived from mathematical analysis and transformation. The result shows that this idea is feasible and the conclusion is practicable. [Copyright &y& Elsevier]

Abstract: Due to its large apparent specific heat during the phase change period, microencapsulated phase change material slurry (MPCMS) has been suggested as a medium for heat transfer. In this paper, the convective heat transfer characteristics of MPCMS flowing in a circular tube were experimentally and numerically investigated. The enhanced convective heat transfer mechanism of MPCMS, especially in the thermal fully developed range, was analyzed by using the enthalpy model. Three kinds of fluid–pure water, micro-particle slurry and MPCMS were numerically investigated. The results show that in the phase change heat transfer region the Ste number and the Mr number are the most important parameters influencing the Nusselt number fluctuation profile and the dimensionless wall temperature. Reb , dp and c also influence the Nusselt number profile and the dimensionless wall temperature, but they are independent of phase change process. [Copyright &y& Elsevier]

Abstract: In Part І, a numerical model for coupled heat and moisture transfer in a run-around heat and moisture exchanger with a liquid desiccant coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The results from the numerical model for the case of only heat transfer for a single heat exchanger are compared to an available analytical solution and good agreement is obtained. For the simultaneous heat and moisture transfer in the run-around membrane energy exchanger (RAMEE), a comparison between numerical model results and experimental measurements obtained from laboratory testing for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. Part II of this paper applies the model for a range of initial conditions . [Copyright &y& Elsevier]

Abstract: This paper presents a two-dimensional mathematical model to evaluate transient heat and mass transfer in a metal hydride tank (hereinafter MHT) with metal foam heat exchanger. The model is validated by comparison with experimental data. A good agreement is obtained. A study of the geometric and the operating parameters of the metal foam (such as base material, pore size and relative density) has been carried out to identify their influence on the performance of the charging process of the MHT. After that, the model was used as a tool to predict the performance of the hydrogen-charging process of two configurations of MHTs with metal foam heat exchangers. The obtained results showed that the reduction of the storage time due to the metal foam heat exchanger can be more important when the MHT is equipped with a concentric heat exchanger tube. [Copyright &y& Elsevier]

Abstract: This paper targets the efficient computational solution of the heat transfer processes that take place in the soil and at the soil–air interface and its use in non-destructive evaluation (NDE) techniques. In particular, the problem of the detection of plastic antipersonnel mines is considered. To this aim we projected a 3D finite-difference (FD) thermal model of the soil on a FPGA platform using Handel-C and VHDL. A speedup factor of 34 over a purely software solution is achieved, obtaining processing times that permit the use of the system on the field. [Copyright &y& Elsevier]

Abstract: Acrylamide formation in a food model during frying can be analyzed in space and time with a traditional heat and mass transfer approach. In this paper a joint simulation/experiment approach has been exploited: the computational fluid dynamics has been coupled to chemical kinetics, to describe concentration and temperature fields in a food substrate, subject to interdependent and non-uniform heat and mass transfer, while validating measurements have been performed by high performance liquid chromatography. A multi-objective SIMPLEX optimization has been finally employed for the overall model tuning, incorporating all phenomenological variations. The numerical results confirmed that the acrylamide formation is non-linearly dependent on the operating thermal regime, in general more than doubling its average levels when the process temperature is increased by 10% only. Based on the proposed acrylamide maps, a maximum concentration locus is found on the product’s upper corner, depending on the specific transport ensemble and therefore on the local process conditions. For potato frying at an initial temperature of 190°C, the maximum local acrylamide level after 4min (almost 4×10−2 mg/g) is almost four times the one obtained when frying at 170°C, while scaling only linearly with process duration. [Copyright &y& Elsevier]

Abstract: In the present study, a 3D numerical simulation of a whole heat exchanger with middle-overlapped helical baffles is carried out by using commercial codes of GAMBIT 2.3 and FLEUNT 6.3. At first, the computational model and numerical method of the whole heat exchanger with middle-overlapped helical baffles is presented in detail, and parallel computation mode is adopted for the simulation of a whole heat exchanger with six cycles of the middle-overlapped helical baffles of 40° helical angle on a grid system of 13.5-million cells; second, the validation of the computational model is performed by comparing the total pressure drop and average Nusselt number of the whole heat exchanger with experimental data. Reasonably good agreement is obtained, and the reasons causing to the discrepancy are analyzed. The shell-side fluid pressure and temperature fields of the whole area are then presented. Finally the cycle average Nusselt number of different cycle in the heat exchanger are compared and it is found that within the accuracy allowed in engineering computation, periodic model for one cycle can be used to investigate the heat transfer and pressure drop characteristics for different heat exchanger to save computational source. The companion paper will provide details of simulation results using the periodic model for different helical angles and different structures of helical baffles. [Copyright &y& Elsevier]

Abstract: One of the major challenges in the study of thermal transport and its analysis, based on the hyperbolic model associated with Cattaneo equation, is the fact that it is necessary to determine the thermal relaxation time for the analyzed materials. This parameter has been an elusive physical quantity to be determined experimentally even though it is of crucial importance in heat transport. In this paper a system formed by a semi-infinite layer in contact with a finite one, that is excited by a modulated heat source is studied. It is shown that a frequency range can be found in which the amplitude and phase of the spatial component of the oscillatory surface temperature show strong oscillations when the thermal relaxation time of the finite layer is close to its thermalization time. When the thermal effusivities of the layers are quite different or their thermal relaxation times are similar, it is shown that simple analytical expressions for the values of the maxima and minima of the oscillations as well as for the frequencies, at which they occur, are obtained. These results were used to establish a methodology to determine the thermal relaxation time as well as additional thermal properties of the finite layer. [Copyright &y& Elsevier]

Abstract: The paper deals with the experimental validation of a numerical model for the transport and combustion of cylindrical and disk-shaped firebrands. The model solves the conservation equations of brand mass, kinetic and angular momentum, and volume. Validation consists in predicting the mass and spatial distributions of glowing firebrands that were produced from the experimental generator developed by Manzello and coworkers [S.L. Manzello, J.R. Shields, T.G. Cleary, A. Maranghides, W.E. Mell, J.C. Yang, Y. Hayashi, D. Nii, T. Kurita, On the development and characterization of a firebrand generator, Fire Saf. J. 43 (2008) 258–268]. Ten thousand firebrands per run are released with initial conditions that are randomly generated according to probability distribution functions deduced from experimental mass and spatial distributions under no-wind conditions. Whatever the wind conditions considered, numerical results are found to be in good agreement with experimental data. [Copyright &y& Elsevier]

Abstract: The synthesis of a catalyst for a two-phase catalytic reaction, a millimeter-scale reactor experiment, and an analysis model for the prediction of reactor performance are presented in this paper. The catalyst nano-particulate perovskite La0.8Sr0.2CoO3 was prepared by a modified sol–gel method, in which PAA (poly acrylic acid) was added to catalyst precursors. A millimeter-scale reactor experiment with the prepared catalyst was carried. Concentrated hydrogen peroxide was decomposed in the reactor and the characteristics of the reactor were measured in terms of temperature distributions and liquid production rates. The results indicated a flow regime transition, which caused the change of reactor performance. An analysis model for two-phase catalytic reaction based on the lumped flow reactor model and the diagnostic data obtained on the temperature distributions and liquid production rates is proposed. Temperature distributions and heat transfer characteristics of the reactor were predicted by a semi-empirical analysis. In this analysis, the model of the Nusselt number (Nu) was proposed as . This expression of the model reflects the effects of temperature and coordinate location on the heat transfer characteristics of the reactor. From the modeled reactor, characteristics such as the increase of heat transfer in the mid and rear parts of the reactor with the increase of reactant flow rate were obtained. With the obtained results, a tool for the design and analysis of a down-scaled catalytic reaction device was obtained. [Copyright &y& Elsevier]

Abstract: An integrated model for the composting process was developed. The structure of the model is such that it can be implemented in any mixture of different substrates, even in the case of co-composting of a solid waste with industrial wastewater. This paper presents a mathematical formulation of the physicochemical and biological principles that govern the composting process. The model of the co-composting ecosystem included mass transfer, heat transfer and biological processes. The biological processes included in the model were hydrolysis of particulate substrates, microbial growth and death. Two microbial populations (bacteria and fungi) were selected using Monod kinetics. Growth limiting functions of inhibitory factors, moisture and dissolved oxygen were added in the Monod kinetics. The bacteria were considered to utilise the easy biodegradable carbon hydrolysis product, fungi the difficult one, while both could degrade the carbon of wastewater. The mass balances of the most important nutrients, nitrogen and phosphorous, were also included in this approach. Model computer simulations provided results that fitted satisfactory the experimental data. Conclusively, the model could be a useful tool for the prediction of the co-composting process performance in the future and could be used to assist in the operation of co-composting plants. [Copyright &y& Elsevier]

Abstract: This paper describes an electrochemical model, which studies the performance of multi-bundles integrated-planar solid oxide fuel cell (IP-SOFC strip) fuelled by pure hydrogen. Following a description of the basic geometries and general premises the approaches and simplifications for the calculation of ohmic resistance, gas flow, heat and mass transfers are given. The effect of fuel pressure ratio and the temperature variation are investigated in a parameter study. The model results have been validates well with experimental data obtained from a full-size prototype of IP-SOFC technology for the second generation hybrid application; it is found that the ohmic and cathode activation overpotentials represent a major loss in fuel cell voltage. The results obtained from both strips also demonstrated acceptable performance and good reproducibility bundles to bundles at 900°C. These results indicated weak effect of parameter variation on the bundles to bundles performances. [Copyright &y& Elsevier]

Abstract: For purposes of an accurate mathematical modeling, it is essential to establish trustworthy boundary conditions. The heat transfer that occurs at the casting/mold interface is one of these important conditions, which is a fundamental task during unsteady solidification in permanent mold casting processes. This paper presents an overview of the inverse analysis technique (IHCP) applied to the determination of interfacial heat transfer coefficients, hi , for a number of alloy solidification situations. A search algorithm is used to find the transient metal/mold interface coefficient during solidification which is reported either as a function of the casting surface temperature or time. Factors affecting hi such as the direction of gravity in relation to the growth interface, the initial melt temperature profile, the wettability of the liquid layer in contact with the mold inner surface, were individually analyzed and experimental laws for hi have been established. [Copyright &y& Elsevier]

Abstract: A family of composite sorbents has been acknowledged as promising thermal storage materials for low grade thermal energy storage owing to its high specific storage capacity and low regenerating temperature. This paper reports a simplified numerical model aiming to determine the dynamic characteristics of the composite sorbents and evaluate the specific capacity and COP of the open-type thermal energy storage system. The computational results were validated with the experimental measurements carried out on an open-type thermal energy storage set-up filled with composite sorbents. By using the simplified numerical model, the dynamic characteristics of the composite sorbents in the thermal energy storage process were determined. The effects of the composite sorbents and the operating parameters on thermal energy storage system performance were also evaluated. [Copyright &y& Elsevier]

Summary: Groundwater temperatures, especially in shallow (quaternary) aquifers respond to ground surface temperatures which in turn depend on climate and land use. Groundwater temperatures, therefore, are modified by climate change and urban development. In northern temperate climate regions seasonal temperature cycles penetrate the ground to depths on the order of 10–15m. In this paper, we develop and apply analytic heat transfer relationships for 1-D unsteady effective diffusion of heat through an unsaturated zone into a flowing aquifer a short distance below the ground surface. We estimate how changes in land use (urban development) and climate change may affect shallow groundwater temperatures. We consider both long-term trends and seasonal cycles in surface temperature changes. Our analysis indicates that a fully urbanized downtown area at the latitude of Minneapolis/St. Paul is likely to have a groundwater temperature that is nearly 3°C warmer than an undeveloped agricultural area at the same geographic location. Pavements are the main cause of this change. Data collected by the Minnesota Pollution Control Agency (MPCA) in the St. Cloud, MN area confirm that land use influences groundwater temperatures. Ground surface temperatures are also projected to rise in response to global warming. In the extreme case of a doubling of atmospheric carbon dioxide (2×CO2 climate scenario), groundwater temperatures in the Minneapolis/St. Paul metropolitan area could therefore rise by up to 4°C. Compounding a land use change from “undeveloped” to “fully urbanized” and a 2×CO2 climate scenario, groundwater temperatures are projected to rise by about 5°C at the latitude of Minneapolis/St. Paul. [Copyright &y& Elsevier]

Abstract: This paper presents the numerical simulation of heat transfer and solidification process in an industrial silicon directional solidification system. The energy efficiency in the production system is analyzed. The effects of the heating power and the position of the side insulation layer on the solidification interface position/shape are investigated. The numerical results indicate that the directional solidification of the silicon can be controlled by adjusting the heating power and moving the side insulation layer. The knowledge gained from the thermal analysis can be used to improve the energy efficiency in the current silicon production system. An easy method to detect the solidification interface shape was proposed and has been conceptually proven. [Copyright &y& Elsevier]

Abstract: Tailrace tunnel ventilating can be used as a highly efficient and energy saving air conditioning for factory buildings in hydropower station. This paper describes an improved model of heat and moisture transfer for tailrace tunnel ventilating system with the assumption of thermal insulated for the tunnel wall and with the same temperature at any cross section as the wet bulb temperature of that air, and the improved model has been validated against the field test from Yingxiuwan hydropower station and compared with the reference simplified model, the results show that the improved model has a good agreement with the field test data and a better precision than the reference simplified model for the performance prediction of heat and moisture transfer of tailrace tunnel ventilating, especially for the short tunnel system. Moreover, the thermodynamic calculation method of heat and moisture transfer is presented, and the method is intended for use in annual performances prediction or design tools for tailrace tunnel ventilating system in hydropower station. [Copyright &y& Elsevier]

Abstract: This paper deals with the mathematical modelling of a furnace devoted to the limestone processing. The novelty of this reactor is that the energy required by the endothermic reaction of calcination is provided by the combustion of biomass, making it compatible with sustainable development. The model is based on balance equations completed with phenomenological relations for the estimation of heat and mass transfer inside the reactor and for the estimation of the kinetics of the reaction. In a first section, the equations describing the behaviour of a single reacting particle of limestone are derived. The model relies on the assumption that the reacting particle obeys the shrinking core model. Then this model of a single particle is introduced in a more general one-dimensional model describing the whole furnace, where the different relevant properties depend upon the location within the reactor. Some industrial information is compared to numerical predictions, thus validating the model. Also the results provided by the numerical model allow for a better comprehension of the different phenomena occurring within the reactor. [Copyright &y& Elsevier]

Abstract: The drawing process for the fabrication of a hollow optical fiber involves the flow of glass, which is largely heated by thermal radiation, in an inert gas environment. It is critical to maintain the central core, which can collapse if the thermal conditions are not properly imposed and controlled. This paper presents the analysis and simulation of this complicated process. A numerical model is developed, validated, and applied to simulate the hollow optical fiber drawing process under a wide range of boundary conditions, particularly draw speed, tension, and temperature. A feasible domain of the drawing process is identified to give the range of the drawing parameters for which the geometry of the fiber is maintained and collapse of the core and viscous rupture of the fiber are avoided. The effects of drawing temperature and feeding speed, which are crucial factors in determining the geometry and quality of the fiber, are investigated in detail. A multi-variable unconstrained optimal design problem is posed and considered in terms of the feasible domain. An appropriate objective function, comprised of the maximum velocity lag, thermally induced defect concentration and draw tension, is proposed to quantify the quality of the hollow fiber. The univariate search method is then applied to obtain the optimal drawing temperature and feeding speed. This study provides a basis for the optimization of hollow fiber drawing process and indicates that a substantial improvement in fiber quality can be achieved. [Copyright &y& Elsevier]

Abstract: Various properties of turbulence are discussed with a perspective of their influence on turbulence modelling (TM). The paper considers the relation between spectral properties and TM, the inherent errors associated with TM, the distinction between modelling and numerical errors, local and global processes in turbulence development, the influence of dimensionality on applicability of various models, the potential of LES, and wall proximity corrections. The emphasis is on understanding when and why TM works, not on demonstrative results. [Copyright &y& Elsevier]

Abstract: The power densities present within a fusion device and its heating systems require the use of high heat flux (HHF) devices to sustain power densities >10MW/m2 in steady state. One such device, known as the Hypervapotron, uses internal water cooling along with a series of fins and cavities perpendicular to the flow to maximise the heat transfer capability. UKAEA, in collaboration with Cranfield University, have initiated a study whereby computational fluid dynamics (CFD) software will be used to predict the variation of heat transfer coefficients (HTC) throughout the Hypervapotron, allowing accurate calculations of both thermal and thermo-mechanical performance. In this paper, the first steps in this process are presented. In particular, different turbulence models are assessed and best practices identified for predicting single phase flow and heat transfer within Hypervapotron-sized cavities. [Copyright &y& Elsevier]

Abstract: Numerous Probabilistic Risk Assessments (PRAs) have shown that fire is a major contributor to Nuclear Power Plant (NPP) risks. However, prediction and estimation of the likelihood of fire-induced damage to electrical cables and circuits and their potential effects on the safety of the NPPs are still a practical challenge, particularly because of the lack of physics-based models with which to perform consistent and objective assessments. This paper contains a discussion of two models – the heat transfer and the IR “K-factor” models – to estimate the likelihood of fire-induced cable damage given a specified fire profile. The results of this research will help to (1) develop a consistent framework to estimate the likelihood of fire-induced cable failure modes, and (2) develop some guidance to evaluate and/or reduce the risks associated with these failure modes in existing and new NPPs. The models are developed (i.e., their parameters are estimated) based on the test data from various fire damage tests sponsored by the nuclear industry and the U.S. Nuclear Regulatory Commission (NRC). Among the models evaluated, the physics-based heat transfer model is promising because it takes into account the properties and characteristics of the cables and cable materials and the characteristics of the thermal insult. This model can be used to estimate the probability of cable damage (P CD ) under different thermal conditions. [Copyright &y& Elsevier]

Abstract: Determining laminar burning velocities from the pressure trace in constant volume combustion requires knowledge of the burnt fraction as a function of pressure, . In recent literature is either determined via numerical modeling or via the oversimplified assumption that is equal to the fractional pressure rise. Recently, we have shown that the latter violates energy conservation, and derived alternative analytical relations based on zone modeling which are more simple to apply than numerical models. However we had to assume perfect gas behavior, neglecting dissociation. In this paper we systematically compare our analytical models with a numerical two-zone model and with a 1D unsteady simulation (1DUS) of a spherical stoichiometric methane–air flame in a constant volume. Results indicate that our analytical models reasonably describe the burnt fraction as a function of fractional pressure rise. However the relation also involves the (theoretical) end pressure . Its value significantly affects , with a relative sensitivity close to minus one, and is influenced by dissociation. Evaluating from an equilibrium code, in combination with the analytical model, provides results within 3% accuracy. This approach removes the need for numerical modeling of intermediate stages of combustion. Still, highest accuracy for is achieved using numerical models that account for dissociation also for intermediate stages. Comparing results of the 1DUS with the two-zone equilibrium model shows that the combined effect of detailed chemistry, flame stretch, heat transfer between zones, and the temperature gradient in the burnt mixture is limited to about 1% for the example case. [Copyright &y& Elsevier]

Abstract: The main focus of this paper is the modeling, simulation, and analysis of the calcium bromide hydrolysis reactor stage in the calcium–bromine thermochemical water-splitting cycle for nuclear hydrogen production. One reactor concept is to use a spray of calcium bromide into steam, in which the heat of fusion supplies the heat of reaction. Droplet models were built up in a series of steps incorporating various physical phenomena, including droplet flow, heat transfer, phase change, and reaction, separately. Given the large heat reservoir contained in a pool of molten calcium bromide that allows bubbles to rise easily, using a bubble column reactor for the hydrolysis appears to be a feasible and promising alternative to the spray reactor concept. The two limiting cases of bubble geometry, spherical and spherical-cap, are considered in the modeling. Results for both droplet and bubble modeling with COMSOL MULTIPHYSICS™ are presented, with recommendations for the path forward. [Copyright &y& Elsevier]

Abstract: In this paper, nitrogen was used as an alternative gas for its fine protection to weld pool and relatively low cost, in contrast to widely used argon and helium shielding gases in gas tungsten arc welding (GTAW). A two-dimensional axisymmetric numerical model from McKelliget et al. was adopted to describe the heat transfer and fluid flow in the gas tungsten arc (GTA) to predict the basic energy source properties of nitrogen GTA. Simulation results showed that the arc temperature contours, the distribution of heat flux and current density at the anode agree well with experimental results in literature for both argon-shielded arc and nitrogen-shielded arc. To solve the model, the nitrogen arc plasma properties, i.e. temperature, voltage drop and flow fields have been derived. And the distribution of the heat flux, current density and gas shear stress at the anode with the different arc lengths and welding currents has been studied. Moreover, by comparing with the properties between the argon and nitrogen arc, the results indicate that the nitrogen arc is more contraction than that of argon arc under the same arc length and welding current. Especially, the increasing of the maximum of heat flux and current density at the anode shows that the nitrogen GTA possessed excellent energy source properties for GTAW in contrast to the argon arc. [Copyright &y& Elsevier]

Abstract: Understanding the heat and mass transfer phenomena in a coal gasifier is very useful for the assessment of gasifier performance and optimization of the design and operating parameters. In this paper, performance of an entrained flow air blown laboratory scale gasifier is numerically simulated with Fluent software. In the model, the continuous phase conservation equations are solved in an Eulerian frame, while those of particle phase are solved in a Lagrangian frame, with coupling between the two phases carried out through interactive source terms. The dispersion of the particles due to turbulence is predicted using a stochastic tracking model, in conjunction with the k–ε equations for the gas phase. The coal gasification model adopted includes devolatilization, combustion of volatiles, char combustion and gasification. The gasification performance inside the gasifier has been predicted for different air ratios as well as for different air and steam inlet temperatures. The overall temperature inside the gasifier is found to increase when the degree of air/steam pre-heating is increased, resulting in acceleration of the different reaction steps in the gasifier. The overall gasification performance indices such as carbon conversion, heating value of the exit gas and cold gas efficiency have been predicted. The predicted results show good agreement with available experimental data in literature. [Copyright &y& Elsevier]

Abstract: In present paper, a numerical model combined radiation and conduction heat transfer was developed to predict the effective thermal conductivity of fibrous insulation at various temperatures and pressures. Effective thermal conductivities of the fibrous insulation were measured over a wide range of temperature (300–973 K) and pressure () using a developed apparatus. The transmittance spectra in the wavelength range of 2.5–25 μm were also measured at temperatures up to 973 K using a Fourier Transform Infrared Spectrometer. From transmittance data, the spectral extinction coefficients and Rosseland mean extinction coefficients were obtained at various temperatures to investigate the radiative heat transfer in fibrous insulation. The numerical and experimental data were compared. It was found that the calculated values corresponded with the experimental values within an average of 14.7 percent. Numerical results were consistent with experimental results throughout the investigated environmental conditions. [Copyright &y& Elsevier]

Abstract: An improved understanding of the heat transfer in materials consisting of two layers (splat and substrate) is essential for many industrial applications. We are interested in the deposition, rapid cooling and solidification of metal droplets (known as splats) brought into contact with a cold substrate. We therefore need to understand the temperature history in both the splat and the substrate, including phase change phenomena. A new model of the thermal contact resistance based on a random distribution of contact points, rather than the uniform distribution commonly used, is presented in this paper. Phase change has been also considered, using the enthalpy-porosity formulation. Simulations have been conducted with the commercial package CFX-4. The computational results for the cooling rate of the splat obtained using the random contact distribution model are in good agreement with available experimental results. In addition, results obtained from the random model provide information on the inhomogeneity affecting the temperature at the interface between the splat and the substrate. [Copyright &y& Elsevier]

Abstract: In this paper, we present a new development of loop heat pipe (LHP) technology in its applications to cooling systems for high-power IGBT elements. An advanced method of LHP evaporator wick manufacturing has been proposed. Following this approach, a 16mm outer diameter and 280mm-length LHP evaporator was designed and manufactured. Nickel and titanium particles were used as raw material in LHP evaporator wick fabrication. LHP with a nominal capacity as high as 900W for steady-state condition and more than 900W for a periodic mode of operation at a temperature level below 100°C and a heat transfer distance of 1.5m was designed through the cooling of a high-power electronic module. An experimental program was developed to execute LHP performance tests and monitor its operability over a span of time. An investigation of the effects of LHP performance of parameters such as evaporator and condenser temperatures and LHP orientation in a gravity field was brought about. As regards the results of this initial series of tests, it was found that LHP spatial orientation within the nominal range of heat loads has no drastic effect on overall LHP functioning, whereas condenser temperature does play an important role, especially in the range of heat load close to critical. A 2D nodal model of the evaporator was developed and provides us with confirmation of the suggestion that when high-power dissipation levels are available, low wick conductivity is well adapted for LHP applications. [Copyright &y& Elsevier]

Abstract: Unsteady natural convection in a reservoir model subject to constant cooling at the water surface is considered in this paper. In such a case, the unequal heat loss resulting from a varying water depth creates a horizontal temperature gradient which in turn drives a horizontal exchange flow between the coastal region and the main water body of the reservoir. Understanding of the flow mechanisms pertinent to this flow is important for predicting the transport of nutrients and pollutants across the reservoir. The present numerical simulations impose random perturbations at the water surface in order to trigger flow instabilities. First, numerical tests are carried out to investigate the flow response to different perturbation amplitudes. These tests reveal a linear range of the flow response to the perturbations. Subsequently, the transient flow development at different stages is described in details based on numerical data, and the effects of the Grashof number on the unsteady flow are examined. [Copyright &y& Elsevier]

Abstract: In the paper, numerical and experimental analyses of heat and mass transfer during frost formation on a fin-and-tube heat exchanger have been presented. Modelling of the frost formation on cold surfaces placed in a humid air stream, requires a complex mathematical approach. A transient two-dimensional mathematical model of frost formation has been developed. The applied mathematical model has been defined using governing equations for the boundary layer that include air and frost sub-domains as well as a boundary condition on the air–frost interface. The mathematical model with initial and boundary conditions has been discretised according to the finite volume method and solved numerically using the SIMPLER algorithm for the velocity–pressure coupling. Results have shown that the frost layer formation significantly influences the heat transfer between air and fins. As a result of numerical calculations, time-wise frost thickness variations for different air humidities, temperatures and velocities have been presented. Using the developed mathematical model, the algorithm and the computer code, which have been experimentally validated, it is possible to predict a decrease of exchanged heat flux in the heat exchanger under frost growth conditions. [Copyright &y& Elsevier]

Abstract: The paper discusses heat transfer enhancement and deterioration phenomena observed in experimental data for fluids at supercritical pressure. The results obtained by the application of various CFD turbulence models in the prediction of experimental data for water and carbon dioxide flowing in circular tubes are firstly described. On this basis, the capabilities of the addressed models in predicting the observed phenomena are shortly discussed. Then, the analysis focuses on further results obtained by a low-Reynolds number k – ε model addressing one of the considered experimental apparatuses by changing the operating conditions. In particular, the usual imposed heat flux boundary condition is changed to assigned wall temperature, in order to highlight effects otherwise impossible to point out. The obtained results, supported by considerations drawn from experimental information, allow comparing the trends observed for heat transfer deterioration at supercritical pressure with those typical of the thermal crisis in boiling systems, clarifying old concepts of similarity among them. [Copyright &y& Elsevier]

Abstract: The paper presents the geometry of infinite regular polyhedrons that can be used to construct the heat exchange units. The basic structural component of the infinite solid consists of six hexagons, which meet in the common vertex. The mathematical model of heat and mass transfer inside the labyrinth heat exchanger is shown. The first and the second Kirchhoff’s laws are used to simulate fluid flow distribution at hydraulic network created with connected basic solids. Heat balance equations are adopted to describe forced convection heat transfer inside developed heat exchanger. Good accordance among the experimental data and calculation results over whole simulation range is obtained. The efficiency and thermal characteristic of the labyrinth heat exchanger is presented in the form of graphs. [Copyright &y& Elsevier]

Greenhouses provide a controlled environment that is suitable for plants growth and cultivation. In this paper the maximum temperature change inside the greenhouse is to be reduced by the use of energy storage in a phase change material PCM. A mathematical model is developed for the storage material and for the greenhouse. The coupled models are solved using numerical methods and Java code program. The effect of different parameters on the inside greenhouse temperature is investigated. The temperature swing between maximum and minimum values during 24 h can be reduced by 3–5°C using the PCM storage. This can be improved further by enhancing the heat transfer between the PCM storage and the air inside the greenhouse. [Copyright &y& Elsevier]

Abstract: This paper presents a mathematical model for determining optimal configuration of plate finned tube condensers widely used in air conditioning system. The condenser investigated in this work is a cross-flow air-refrigerant type with aluminium plain fin geometry. Refrigerant HFC 134a flows inside while air flows outside the copper tubes. Minimum entropy change of air and refrigerant is used as the criterion for analysis. This entropy change resulting from losses due to heat transfer and pressure drop can be represented in a form of entropy generation number, . The proposed mathematical model is divided into three regions: superheated, two-phase and sub-cooled regions. Effects of heat transfer and pressure drop of air side and refrigerant side on entropy generation rate are simultaneously analyzed through the implicit method. Results from the mathematical model show that entropy generation number decreases with increasing fin pitch and decreasing number of rows and tube diameter. In addition, this work also presents an optimal configuration of condenser. The optimal tube diameter and the number of fin per inch are 6.35–12.7 mm ( inch) and 11–12, respectively. [Copyright &y& Elsevier]

Abstract: This paper presents the advantages of a Branch Eigenmodes Reduced Model used in a control process of a heating system. The experimental setup is a 3D heat conductive system in which a heat source is set. First, the reduced model is used to solve the non-linear Inverse Heat Conduction Problem: identification of the heat source strength variations from time-varying temperatures. Then, the reduced model is used to control hot points in the system. The objective of the method is to allow sequential temperature control by decreasing the computation time necessary for the simulation. [Copyright &y& Elsevier]

Abstract: In this paper, we apply two mathematical tools for the analysis of models describing heat and mass transfer in dispersed systems, namely scale analysis and integral approximation. The particular model investigated is a 1-D model describing the cooling of packed beds of fresh agricultural produce using the porous media approach. With scale analysis, one can determine relevant terms in the model and subsequently one can make justified approximations. Traditionally, in the porous media approach one assumes that temperature gradients in individual products are negligible, as expressed by the Biot number Bi <0.1. By means of the integral approximation method, we have shown that the porous medium approach can be extended to the range Bi <10 via the definition of an internal heat resistance. Via the integral approximation method, we have calculated the internal resistance for a variety of products having simple geometries. Scale analysis shows that for the problem investigated, there are two regimes, depending on whether solid and fluid phase are in so-called local thermal equilibrium. [Copyright &y& Elsevier]

Abstract: This work presents a numerical solution of Burgers’ equation using the Network Simulation Method, a method that has been used previously to solve problems of heat transfer through the electro-thermal analogy. In this paper, the analogy is extended to velocity, providing an electro-motion analogy. This method permits the direct visualisation of the local and/or integrated transport variables (velocities, temperatures, fluxes) at any point or section of the medium. It also permits both transient and steady-state problems to be solved simultaneously, while programming does not require the manipulation of sophisticated mathematical software that is inherent in other numerical methods. The accuracy and effectiveness of the method is demonstrated by comparing the results with the information existing in the literature. [Copyright &y& Elsevier]

Abstract: The dehumidifier and regenerator are key components in liquid desiccant air conditioning systems. Many researchers have developed mathematical models of the coupled heat and mass transfer processes in the dehumidifier or regenerator, and most of the models were solved numerically. Compared with numerical solutions, analytical solutions have more advantages in analyzing the parameters that affect the heat and mass transfer performance. This paper presents analytical solutions of the air and desiccant parameters inside the parallel flow, counter flow and cross flow dehumidifier/regenerator under some reasonable assumptions based on the available heat and mass transfer models. The analytical solutions of the air and desiccant parameters within the dehumidifier/regenerator show good agreement with the corresponding numerical results, and the analytical solutions of the enthalpy and moisture efficiencies agree well with experimental findings. The method developed here can be used in the optimal design of the dehumidifier or regenerator. [Copyright &y& Elsevier]

Abstract: In this paper, a method for monitoring the performance degradation in a heat exchanger is presented. This method is based on the use of an adaptive observer which estimates the overall heat transfer coefficient U. The monitoring of this parameter can be useful to decide when the heat exchanger needs preventive or corrective maintenance. A simplified mathematical model of the heat exchanger is used to synthesize the adaptive observer. The effectiveness of the proposed method is demonstrated via numerical simulations and through experimental results. [Copyright &y& Elsevier]

This paper presents a mathematical model based on a three-phase theory, which is used to describe the mass and heat transfer between the gas and solids phases in a batch fluidised bed dryer. In the model, it is assumed that the dilute phase (i.e., bubble) is plug flow while the interstitial gas and the solid particles are considered as being perfectly mixed. The thermal conductivity of wet particles is modelled using a serial and parallel circuit. The moisture diffusion in wet particles was simulated using a numerical finite volume method. Applying a simplified lumped model to a single solid particle, the heat and mass transfer between the interstitial gas and solid phase is taken into account during the whole drying process as three drying rate periods: warming-up, constant rate and falling-rate. The effects of the process parameters, such as particle size, gas velocity, inlet gas temperature and relative humidity, on the moisture content of solids in the bed have been studied by numerical computation using this model. The results are in good agreement with experimental data of heat and mass transfer in fluidised bed dryers. The model will be employed for online simulation of a fluidised bed dryer and for online control. [Copyright &y& Elsevier]

Abstract: This paper introduces a general computational model for beer pasteurization tunnels, which could be applied for any pasteurization tunnel in the food industry. A simplified physical model, which combines fundamental and empirical correlations, and principles of classical thermodynamics, and heat transfer, is developed and the resulting three-dimensional differential equations are discretized in space using a three-dimensional cell centered finite volume scheme. Therefore, the combination of the proposed simplified physical model with the adopted finite volume scheme for the numerical discretization of the differential equations is called a volume element model, VEM [Vargas, J. V. C., Stanescu, G., Florea, R., & Campos, M. C. (2001). A numerical model to predict the thermal and psychrometric response of electronic packages. ASME Journal of Electronic Packaging 123(3), 200–210]. The numerical results of the model were validated by direct comparison with actual temperature experimental data, measured with a mobile temperature recorder traveling within such a tunnel at a brewery company. Next, an optimization study was conducted with the experimentally validated and adjusted mathematical model, determining the optimal geometry for minimum energy consumption by the tunnel, identifying, as a physical constraint, the total tunnel volume (or mass of material). A parametric analysis investigated the optimized system response to the variation of total tunnel volume, inlet water temperature, production rate, pipe diameter and insulation layer thickness, from the energetic point of view. It was shown that the optimum tunnel length found is ‘robust’ with respect to the variation of total tunnel volume, combining quality of the final product with minimum energy consumption. The proposed methodology is shown to allow a coarse converged mesh through the experimental validation of numerical results, therefore combining numerical accuracy with low computational time. As a result, the model is expected to be a useful tool for simulation, design, and optimization of pasteurization tunnels. [Copyright &y& Elsevier]

Abstract: This paper presents the results of a predictive two-dimensional mathematical model of an adsorption cooling machine consisting of a double consolidated adsorbent bed with internal heat recovery. The results of a base-case, taken as a reference, demonstrated that the COP of the double bed adsorption refrigeration cycle increases with respect to the single bed configuration. However, it was verified that, in order to maximize also the specific power of the machine, the adsorbent beds must have proper thermo-physical properties. Consequently, a sensitivity analysis was carried out, studying the influence of the main heat and mass transfer parameters on the performance of the machine. The results obtained allowed us to define the adsorbent bed design that maximizes its heat and mass transfer properties, as well as the most profitable heat recovery conditions. [Copyright &y& Elsevier]

Abstract: This paper describes the numerical simulation of heat transfer in a system for growing corundum single-crystal plates (leucosapphire and ruby) of size 200×200mm. A mathematical model accounting for the radiative and conductive heat transfer has been developed. Three-dimensional computations have been made with minor simplifications of the furnace geometry. The thermal fields at various positions of the crystal container and the effect of various setup units and their design on the temperature distribution are analyzed. The computed crystallization front shape is compared with the available experimental data. Numerical analysis was used to optimize the hot zone design. [Copyright &y& Elsevier]

Abstract: This paper presents an analytical solution of the hyperbolic heat conduction equation for the case of a thin slab symmetrically heated on both sides. In the mathematical model adopted, the heating is treated as an internal heat source with capacity dependent on coordinate and time, while walls of the slab are assumed to be insulated. The solution is obtained by Laplace transforms method taking advantage of the method of superposition. The analytical solution is validated by comparison with the results from a numerical model. [Copyright &y& Elsevier]

Abstract: The paper presents a general mathematical model for disperse systems in which direct interactions between particles are taken into consideration. The model is formulated in terms of transition measures, introduced on the basis of conditional Markov processes. The population balance equation, describing the behaviour of interactive populations, is developed in a general form of continuous and discontinuous terms. Moment equations are presented and analysed for the axial dispersion model with interparticle exchange processes of heat and mass. The applicability of the model is illustrated by applying it for describing a process of heating particles by gas with interparticle heat transfer, and a mass exchange process between fluid particles. [Copyright &y& Elsevier]

Abstract: This paper presents a mathematical model for heat and moisture transfer through cloth. A two-dimensional mathematical model, which considers complicated heat and mass transfer is developed. The coupled partial differential equations are created based on integrations of porous medium equations and heat, diffusion equations. A non-linearized implicit finite-difference method is presented to find numerical solutions of the two-dimensional simulation model. Results obtained by the present method are found to agree satisfactorily with the experimental data available in the literature. [Copyright &y& Elsevier]