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In order to make full use of the advantages of superheated steam (SHS), SHS injection in multi-point injection wells (MPIW) is proposed in this paper. Firstly, a mathematical model comprised of SHS flow model in inner tubing (IT) or long tubing (LT) and annulus, transient heat transfer model in oil layer is established. Secondly, type curves of SHS flow in MPIW is obtained by finite difference method on space and the iteration technique. Then, the effect of injection temperature on distributions of thermophysical properties of SHS in MPIW is discussed in detail. Results show that: (a) When the heat exchange between IT and annulus is taken into consideration. SHS temperature in IT has a decrease while SHS temperature in annulus has an increase. (b) With the help of MPIW, heating effect at both heel and toe points of the horizontal wellbores can be enhanced. (c) While the increase of SHS temperature certainly benefits the formation heating effect through the increase of both SHS temperature and superheat degree, the following decrease of SHS pressure in annulus will lead to the decrease of SHS absorption rate. This paper unravels some intrinsic flow characteristics of SHS in MPIW, which has a significant impact on the optimization of SHS injection parameters and analysis of heat transfer law in MPIW. [ABSTRACT FROM AUTHOR]

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

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

Highlights • The optimal pitch ratio of the ribs mounted in a channel is provided based on inverse analysis. • The entransy dissipation was taken as the objective function in the inverse method. • Taking entransy dissipation as objective function leads to a fast and stable convergence process. Abstract The ribbed surface is a widely used convection heat transfer enhancement technology. The geometric parameters of the ribbed surface have great influences on its heat transfer performance. It is crucial to determine the optimum geometric parameters. In the present work, the optimal arrangement of ribs mounted in a rectangular channel is provided by solving the inverse optimization problem with the entransy dissipation as the objective function. The parameter analysis based on the direct solution is firstly carried out to get an approximate range near the optimal pitch ratio which can provide the initial value for the inverse optimization problem; afterwards, the inverse optimization problem is solved by a modified simplified conjugate gradient method, and the accurate optimal pitch ratio is obtained; finally the optimization results are discussed in detail. The results indicate that, (1) the inverse optimization analysis presented in this paper can provide an accurate optimal value of the pitch ratio; (2) taking the entransy dissipation as the objective function could lead to a faster converge process and give a more stable result than taking the temperature data as the objective function; (3) the optimal value under the fixed heat flux boundary condition is slightly larger than that under the fixed temperature boundary condition. [ABSTRACT FROM AUTHOR]

• A mathematical model based on non-equilibrium formulation was established. • The simulation results show better accordance with the experimental results compared with the model based on equilibrium formulation. • The heat and mass transfer during the drying stage were analyzed. • The effects of different operating parameters on the drying time were investigated. Spray freeze drying has been expanding its influence in many fields. However, the long duration dramatically hinders its further development. A model established based on non-equilibrium formulation was established in this paper. The accuracy of the model proposed with that established based on equilibrium formulation was compared. And the history of temperature, vapor concentration and ice saturation were then investigated. Lastly, the effects of product thickness, particle diameter on the drying time were investigated. The simulation results reproduce well with the experimental data, and show a better agreement with the increase rate of experimentally measured temperature curve than that based on equilibrium formulation. In addition, the temperature increases from the bottom to the top region while the vapor concentration distribution presents the opposite trend. The ice saturation first obtains a slight increase and then decreases. Lastly, the drying time decreases as: (i) the product thickness decreases, (ii) the packing porosity increases and (iii) the chamber temperature increases. The mathematical model proposed in this paper could offer better understanding of the process and guide the design and optimization for the process. [ABSTRACT FROM AUTHOR]

In consideration of droplet flash evaporation and film flash evaporation, a comprehensive mathematical model of vacuum flash evaporation cooling (VFEC) was presented in this paper. Pure water was considered to be the working fluid. The droplet flash evaporation was modeled based on the diffusion-controlled evaporation model, while the film flash evaporation was modeled based on the film penetration theory. The droplet flash model coincided well with the experimental results reported in the literature and the comprehensive mathematical model was validated by experiment results in this paper. The droplet temperature and diameter after droplet flash evaporation were obtained numerically, and then analyzed. The effect of droplet flash evaporation on the surface temperature distribution, heat flux density, and heat transfer ratio of different mechanisms was studied based on the model. It can be concluded that the droplet flash evaporation, which can be expressed by the ratio of droplet-wall impaction heat transfer, had a great effect on vacuum flash evaporation cooling heat transfer. The droplet-wall impaction and film flash heat transfer were dominant in the vacuum flash evaporation cooling. The spray characteristics such as droplet diameter and temperature decreased a lot after droplet flash evaporation, compared to the initial parameters (measured by the PDA). After taking droplet flash into account, the surface temperature decreased and the heat flux increased. [ABSTRACT FROM AUTHOR]

Abstract: Modeling subcooled flow boiling in vertical channels at low pressures requires not only the consideration of the dynamic behaviors of two-phase flow and bubbles undergoing coalescence, breakup and condensation in the bulk subcooled liquid but also the characterization of the single-phase and local boiling heat transfer phenomena in the near-wall region. The focus of this paper is the assessment of the heat flux partitioning model in handling the latter physics of subcooled flow boiling. In order to achieve closure to the model, the current prevailing approach has always been the utilization of empirical correlations particularly for the active nucleation site density, bubble departure diameter and bubble departure frequency. A comprehensive survey of existing empirical correlations is presented in the first part of this paper to assess the performance of these empirical models. Selected combinations of empirical correlations are compared and validated against axial and local radial experiments encompassing a wide range of different mass and wall heat fluxes and inlet subcooling temperatures for subcooled flow boiling at low pressures. Based on the comparisons made against the axial and local distributions of void fraction and bubble Sauter diameter, not one single combination of empirical correlations has shown the propensity of providing satisfactory predictions covering the entire axial and local conditions. For the modeling of subcooled flow boiling at low pressures to become an effective predictive tool, it must therefore be complemented with further consideration of first principal models of the underlying physical phenomena. [Copyright &y& Elsevier]

Despite the fact that the conventional one-dimensional model for counter-flow spray separation tower is advanced in reasonable accuracy as well as time and computational resources saving, it fails to describe the physical processes in details. In this paper, the concept of supersaturated state of the moist air was introduced, then a new sectional one-dimensional model was developed with a detailed derivation. A prototypic apparatus was set up and the reliability of the model was validated by the experimental study. When predicting the outlet solution temperature and outlet moist air wet bulb temperature, the relative errors would be more pronounced with a bigger heat and mass transfer driving potential, but they would not exceed 3.59% and 9.54% respectively under the experimental conditions. The simplifying assumptions, the ignored heat and mass transfer at cyclone region and the measuring errors are mainly blamed for the predicted errors. An in-depth heat and mass transfer investigation was conducted with the help of the validated model by studying the profiles of humidity ratio and moist air dry bulb temperature. The proposed model succeeded in capturing the state transformation of the air flow along the axis of the tower and the effects of the operating parameters on the process profiles are discussed. [ABSTRACT FROM AUTHOR]

Flow resistance and enhanced heat transfer characteristics of TiO 2 -water nanofluids in a stainless-steel corrugated tube and a circular tube are investigated by experimental and numerical methods respectively. The flow and heat transfer characteristics of TiO 2 -water nanofluids and deionized water in test tubes are compared in this paper. In addition, effects of Reynolds number ( Re ) and nanoparticle mass fraction ( ω ) on flow and heat transfer performances are discussed respectively, and Nusselt number ( Nu ) and resistance coefficient ( f ) are studied respectively. Finally, comprehensive performance of flow resistance and heat transfer enhancement is evaluated. It can be obtained that adding nanoparticle into deionized water doesn’t cause a large additional resistance loss in some degree, while the combination of corrugated tube and TiO 2 -water nanofluids shows an excellent heat transfer enhancement, which can enhance the heat transfer by 53.95% at maximum extent. In addition, the corrugated tube has a strong sustainability in enhancing heat transfer. The enhanced heat transfer rising part (6000 ≤ Re ≤ 10,000) has a large rising slope (about 7.90E−5), and the descending slope (about 7.16E−6) of enhanced heat transfer part (10,000 ≤ Re ≤ 12,000) is small. [ABSTRACT FROM AUTHOR]

Existence of magnetic field causes heat transfer to reduce in free convection but in several engineering uses for example: electronic application; enhancing heat transfer is a purpose. Thus, nanofluid should be selected as working fluid. Nanofluid is dispersion of very small metal particles in the base fluid. Two phase and single phase are two ways for estimating the behavior of nanofluid. At first model, nanofluid suppose as homogenous fluid without any slip mechanism. But in second method, slip velocities are included. Brownian motion and Thermophoresis impacts are taken into consideration in second approach. In this paper, previous publications about nanofluid hydrothermal treatment in existence of magnetic field are reviewed. Rely of variable and constant magnetic fields, Ferrohydrodynamic (FHD) and Magnetohydrodynamic (MHD) can take role in simulations. Numerical and analytical methods are considered by authors. Results proved that temperature gradient augments with augment of solid particle concentration and buoyancy forces, while it decreases with augment of magnetic field. [ABSTRACT FROM AUTHOR]

In this paper, a numerical study of heat and mass transfer in counter-flow indirect evaporative air coolers is presented using an approach proposed by previous work. The mathematical model equations of continuity, momentum, energy and concentration are solved by the finite volume method to obtain the value of primary outlet dimensionless temperature. This mathematical model developed is validated against published data acquired from literature. The key target of presented analysis is to develop a performance correlation based on five dimensionless factors: ratio of channel length to half width of secondary air channel, ratio of water to secondary air mass flow rate, primary air inlet Reynolds number, secondary air inlet dimensionless temperature and water film inlet dimensionless temperature. Numerical simulations are performed by changing the value of each dimensionless factor under a constant value for other parameters. The simulation results are regressed to obtain the empirical constants of the correlation. The value of outlet dimensionless temperature is varied from 0.47 to 0.92. The developed correlation can predict the performance of the counter-flow indirect evaporative air coolers within a discrepancy of 12.6%. The correlation would be helpful to provide a simpler equation to improve the calculation speed within the engineering allowable accuracy range. [ABSTRACT FROM AUTHOR]

The paper deals with the development of convective flows in a complex system of thin liquid layers occurring under the effect of thermal load. To study this process a mathematical model which is based on the decomposition of complex problem into unitary elements (modules) with some set of rules allowing their linkage with each other was constructed. Each module represents a monotypic local model. The fluid flow and heat transfer in each of these modules are described by the Navier-Stokes and thermal conductivity equations. The boundary conditions required to solve these systems of equations are represented explicitly and written in the form of conservation laws. The numerical analysis of effect of thermal load on the characteristics of the liquid layers movement depending on the Marangoni number is carried out. It is shown that physical and thermophysical properties of liquid layers play the decisive role. It is exactly they control the convective flows in layers and determine the position and shape of interfaces. The results of model problem solutions are presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new frequency domain method to model the heat transfer between the injected/extracted heat and the temperature of the fluid exiting a borehole heat exchanger. The method is based on in situ measurements and focuses particularly on the short-term borehole heat transfer. It uses a rational function of the Warburg variable in the Laplace domain to model the borehole heat transfer. The rational model is transformed to a time domain model using inverse Laplace transformation. This time domain model makes it possible to calculate the temperature response on a random heat variation signal. The paper also demonstrates a new way to perform the classical thermal response test. Instead of injecting a constant amount of heat, the experiments have been performed using multiple short-duration heat injections. In this way, the obtained rational heat transfer model contains information about both the short- and the long-term heat transfer. The results obtained using the proposed modeling method are compared with those obtained from a state-of-the-art analytical method. The time domain model can be used to design a controller to optimize the performance of a Ground Source Heat Pump system, the efficiency of which depends strongly on the temperature of the fluid exiting the borehole. [Copyright &y& Elsevier]

Abstract: In this paper, a transient numerical model for a liquid-to-air membrane energy exchanger (LAMEE) is developed and the results are compared to the experimental data. The data for the sensible, latent and total effectiveness are compared with transient and steady-state simulations for various values of NTU and operating parameters (Cr∗, inlet temperature and humidity) while the exchanger undergoes a step change in inlet conditions and reaches a new steady-state. The transient and steady-state performances are shown to be a function of the design and operating parameters. The paper also shows that buoyancy forces become important and affect the LAMEE performance under certain operating conditions. The verified numerical model is used to investigate the impact of outdoor air conditions on the LAMEE performance. [Copyright &y& Elsevier]

In this paper, mixed convection of non-Newtonian nanofluid, using the Buongiorno’s mathematical model in a cavity has been analyzed by Finite Difference Lattice Boltzmann method (FDLBM). The cavity is filled with nanofluid which the mixture shows shear-thinning behavior. The Prandtl number is fixed at Pr = 1. This study has been performed for the certain pertinent parameters of Richardson number ( Ri = 0.001, 0.01, and 1), buoyancy ratio number ( Nr = 0.1, 1, and 20), power-law index ( n = 0.2–1), Lewis number ( Le = 1, 5, and 10), Thermophoresis parameter ( Nt = 0.1, 0.5, 1), and Brownian motion parameter ( Nb = 0.1, 1, 5). Results indicate that the augmentation of the power-law index causes heat and mass transfer to drop at Ri = 0.001 and 0.01. The drop of Richardson number from Ri = 1 to 0.001 enhances heat and mass transfer for various power-law indexes. The increase in the Lewis number augments mass transfer while it causes heat transfer to drop. The rise of the Thermophoresis and Brownian motion parameters ameliorates mass transfer and declines heat transfer significantly. The augmentation of buoyancy ratio number enhances heat and mass transfer. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses results of simulations conducted for non-contacting face seals showing the influence of the operational parameters on the distributions of temperature in the structural elements and the fluid film separating the sealing rings. The mathematical model developed for noncontacting face seals consists of cross-coupled differential equations with partial derivatives. We solved it analytically, taking into account various boundary conditions. The heat equations were solved using the method of separation of variables. The derived relationships were based on Bessel functions of the first and second kinds. By defining the relationships describing the distributions of temperature in the sealing rings and the fluid film separating them, we could determine the effect of the operational parameters on the variability of temperature fields. Confirmation of the simulation results with experimental data is essential to better recognize the phenomena taking place in the sealing assembly and improve the design of non-contacting seals so that they can be used in various industrial applications. In this paper, we also describe a specially designed test stand for compensation of the misalignment of the flexibly mounted ring and automatic control of the radial clearance height. The test stand can also be used to verify the results of analytical studies. [Copyright &y& Elsevier]

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

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

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

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

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

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]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Abstract: Thermal modeling of some nano-scale devices requires attention to multiple length scales and physical phenomena, ranging from continuum level heat diffusion to atomic-scale interactions and phonon confinement. At the nanometer-scale, thermal phenomena such as ballistic phonon transport may be important. The present paper uses a multiscale thermal modeling approach including diffusion in the Boltzmann Transport Equation (BTE) to study heat transport in several applications like Silicon on Insulator transistors, Si thin films with heat pulse, a Si thin film sandwiched between two bulk layers of Silicon dioxide as in solar cells. Analytical solutions of both a multilayered Fourier model and a simple gray BTE with and without a diffusion term in the steady state are computed. Thermal modeling and analysis of some of these applications is performed using the COMSOL Multiphysics finite element software package. The BTE model with and without diffusion for multilayers is discussed for interface conditions involving reflectance and transmittance of phonons. The results obtained from the models are compared to existing published results for Si/Si, Si/Diamond layers and are found to be in good agreement. [Copyright &y& Elsevier]

Abstract: Metal foams are a class of cellular structured materials with open cells randomly oriented and mostly homogeneous in size and shape. In the last decade, several authors have discussed the interesting heat transfer capabilities of these materials as enhanced surfaces for air conditioning, refrigeration, and electronic cooling applications. This paper experimentally characterizes twenty-one aluminum and copper foam samples with different number of pores per linear inch (PPI), which vary between 5 and 40 and with porosity ranging between 0.896 and 0.956; samples of different heights (20 and 40mm) have been studied. The most important parameters both geometrical (porosity, pore density, and foam core height) and operative (air mass flow rate, imposed heat flux) affecting the heat transfer and fluid flow behavior of these enhanced surfaces are analyzed and discussed. The results are presented with reference to different performance parameters: overall and interstitial heat transfer coefficients, foam finned surface efficiency, normalized mean wall temperature, pumping power per area density, and pressure gradient. From the experimental measurements two correlations for the heat transfer coefficient and pressure drop calculations have been developed, validated and here proposed. These models can be successfully used to optimize different foam heat exchangers for any given application. [Copyright &y& Elsevier]

Abstract: In this paper, a magnesium (Mg) reduction model considering both heat transfer and chemical reaction kinetics was firstly developed. The reduction model was carried out on a single retort to investigate the impact of different constant heating temperature on the magnesium reduction process in the retort. And then, the reduction model was incorporated into the conventional coal combustion model to describe the process of magnesium production in a coal-fired furnace. The comprehensive model was solved according to the actual industrial operation. The characteristics of magnesium production in the coal-fired furnace, such as thermal-flow field around the retorts in the furnace, the distribution of magnesium reduction extent in the retorts and the total extent of magnesium reduction with time were in detail studied. Especially, the impact of external thermal-flow around the retorts on the extent of magnesium reduction was investigated and discussed. [Copyright &y& Elsevier]

Abstract: In this paper a fictitious domain method is used to study the local heat transfer from an isothermal circular cylinder at low to moderate Reynolds numbers in order to provide a high quality correlation for the calculation of the local Nusselt numbers. A trigonometric series with 13 coefficients is found to best describe the local Nusselt number curves. A 5th order 2D polynomial in terms of Reynolds and Prandtl numbers is then used to provide a correlation for each of the 13 coefficients. A very high resolution database consisting of 25 Reynolds numbers from 10 to 250 in increments of 10, and 24 Prandtl numbers from 0.1 to 40 comprising a total of 600 simulations is used for the modeling. In addition to the 5th order polynomials cubic interpolants are also used to provide highly accurate fits. The maximum error in calculating the average Nusselt number is always less that 2.5% for the cubic interpolants and is 10% maximum for the 5th order polynomials. [Copyright &y& Elsevier]

Abstract: The paper addresses results for the case of convective drying of particulate solids in a packed and in a fluid bed, analyzing agreement between the numerical results and the results of corresponding experimental investigation, as well as the differences between packed and fluid bed operation. In the fluid bed simulation model of unsteady simultaneous one-dimensional heat and mass transfer between solids, gas phase and bubble phase during drying process, based on two-phase bubbling model, it is assumed that the gas–solid interface is at thermodynamic equilibrium. The basic idea is to calculate heat and mass transfer between gas and particles (i.e., the drying process) in suspension phase as for a packed bed of particles, where the drying rate (evaporated moisture flux) of the specific product is calculated by applying the concept of a “drying coefficient”. Mixing of the particles (i.e., the impact onto the heat and mass transfer coefficients) in the case of fluid bed is taken into account by means of the diffusion term in the differential equations, using an effective particle diffusion coefficient. Model validation was done on the basis of the experimental data obtained with narrow fraction of poppy seeds characterized by mean equivalent particle diameter (dS , d =0.75mm), re-wetted with required (calculated) amount of water up to the initial moisture content (X 0 =0.54) for all experiments. Comparison of the drying kinetics, both experimental and numerical, has shown that higher gas (drying agent) temperatures, as well as velocities (flow-rates), induce faster drying. This effect is more pronounced for deeper beds, because of the larger amount of wet material to be dried using the same drying agent capacity. Bed temperature differences along the bed height are significant inside the packed bed, while in the fluid bed, for the same drying conditions, are almost negligible due to mixing of particles. Residence time is shorter in the case of a fluid bed drying compared to a packed bed drying. [Copyright &y& Elsevier]

Abstract: Many energy conversion and other thermal-fluid systems exhibit unsteady convective heat exchange. In such systems, generic spatiotemporal variations in the flow give rise to variations in the heat flux for a given fluid–solid temperature difference, which can be interpreted as spatiotemporal fluctuations of the instantaneous heat transfer coefficient. These variations can lead to unsteady conjugate heat transfer, in which the exchanged heat flux arises from an interaction between the bulk fluid temperature and the temperature in the solid. Further, the nonlinear coupling between the fluctuating temperature differences and the heat transfer coefficient can lead to an effect we refer to as augmentation, which quantitatively describes the ability of a particular arrangement to have a different time-mean heat flux from the product between the mean heat transfer coefficient and the mean temperature difference across the fluid. It is important to be able to understand and to model in a simple framework the effects of the material properties, the geometry and the character of the heat transfer coefficient on the thermal response of the fluid–solid system, and consequently to predict the overall heat transfer performance of these systems. This paper, which follows on from its predecessor [1], is concerned with the phenomenon of augmentation in simple, one-dimensional, unsteady and conjugate fluid–solid systems. A simple semi-analytical one-dimensional model of heat transfer with a time-varying heat transfer coefficient, which was presented in Mathie and Markides [1], is applied herein to two different paradigm problems. Such a model can be an important tool in the design of improved heat exchangers and thermal insulation, through for example, the novel selection of materials to exploit these augmentation effects. The first flow considered is a thin, wavy fluid film flowing over a heated plate. This film flow exhibits a periodic fluctuation in the heat transfer coefficient, that is linked to the wavy interfacial deformations of free surface of the liquid film. The second flow considered concerns the heat transfer behind a backwards-facing step, which exhibits broadband fluctuations in the heat transfer coefficient due to the flow separation and turbulence behind the step. The model predictions of the augmentation ratio for these problems are also compared to direct measurements from each case. Good agreement is observed with the experimental results for the global heat transfer trends. In both cases the augmentation ratio was negative, reflecting a reduction in time-averaged heat transfer. For the backwards-facing step flow a low magnitude of augmentation ratio was observed, however, the thin film flows exhibited augmentation ratios of as high as 10%. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional model describing thermal and hydrodynamic characteristics of a Microtube heat sink with tangential impingement with nanoencapsulated phase change materials (NEPCM) slurry as coolant. In this study, octadecane for NEPCM and polyalphaolefin (PAO) is used as a base fluid. The continuity, momentum, and energy equations are solved using a finite volume method. The model is validated by comparing results with available data in the literature. The effects of dominant parameters including mass concentration and melting range of NEPCM as well as Reynolds number on temperature uniformity, thermal resistance, Nusselt number, pressure drop and generated entropies in the system are investigated. Results indicated that adding NEPCM to base fluid leads to considerable heat transfer enhancement. However, using NEPCM slurry as coolant has also induced drastic effects on the pressure drop that increases with mass concentration and Reynolds number. It was found that that an increase in nanoparticles mass concentration, inlet Reynolds number and melting range of NEPCM, results in a higher Nusselt number, better temperature uniformity and lower thermal resistance. Furthermore, the effects of different parameters on slurry entropy production are demonstrated. It is found that generated total entropy decreases with increasing mass concentration and Reynolds number. [Copyright &y& Elsevier]

Abstract: Phase change material (PCM) suspensions have received wide spread attention for increased thermal storage in various thermal systems such as heat sinks for electronics and solar thermal applications. To achieve further heat transfer enhancement, this paper investigates the effect of focusing micron-sized phase-change particles (PCMs) to a layer near the heated wall of a parallel plate channel. A numerical model for fully-developed laminar flow with a constant heat flux applied to one wall is developed. Melting of the focused PCMs is incorporated using a temperature-dependent effective heat capacity. The effect of channel height, height of the focused PCM stream, heat flux, and fluid properties on the peak local Nusselt number (Nu∗ ) and the averaged Nusselt number over the melting length (Numelt ) are investigated. Compared to the thermally-developed Nusselt number for this geometry (Nuo =5.385), Numelt and Nu∗ enhancements of 8% and 19% were determined, respectively. The local heat transfer performance is optimized when the PCMs are confined to within 30% of the channel height. The present work provides an extended understanding of local heat transfer characteristics during melting of flowing PCM suspensions, and offers a new method for enhancing heat transfer performance in various thermal-fluidic systems. [Copyright &y& Elsevier]

Abstract: Oxy-fuel combustion is one of the promising options for carbon dioxide capture in future coal power plants. Radiative properties of combustion gases and heat transfer characteristics inside oxy-fuel furnaces are different from those found in air-fired furnace. Nowadays, few publications provide appropriate radiation property correlations for oxy-fuel conditions. The available correlations are based on previous versions of HITRAN database, which is not accurate for prediction of spectral intensities at high temperature in combustion applications or above 1000K. This paper considers the determination and evaluation of new correlations for the weighted-sum-of-gray-gases model to predict the radiative transfer in gases under oxy-fuel conditions. The new correlations are fitted from emittance charts calculated from the up-to-date HITEMP 2010 database for molar ratios of water vapor to carbon dioxide between 0.125 and 4, temperature range of 400–2500K, and pressure path-length varying from 0.001 to 60barm. The new correlations are validated by comparing the radiative source term with line-by-line calculations from HITEMP 2010 database for a one-dimensional slab system. The radiative transfer equation is solved with the discrete ordinate method. [Copyright &y& Elsevier]

Abstract: This paper proposes an effective general numerical procedure for the accurate evaluation of the geometric view factors between equally sized spheres in a randomly packed assembly. The procedure is a novel combination of three key techniques: the Tanaka integral expression for the view factor between two equal spheres, the product form of the Fibonacci integration scheme for integrals on spheres, and the non-uniform variable scaling. The Tanaka integral not only provides a simple integral to numerically compute the exact value of the view factor between two unit spheres without a blockage, but also plays a fundamental role in improving the computed shaded view factor between two spheres subject to any blockage. The product Fibonacci integration scheme, essentially a ray-tracing method, appears to be a low cost but sufficiently accurate cubature for evaluating the dual-integral defining the view factor. The use of a particular non-uniform scaling function very favourably modulates the properties of the view factor integrals, and thus substantially improves the solution accuracy of the Fibonacci integration scheme. Several practical issues associated with the accuracy and efficiency of the procedure are discussed, and test cases are provided to illustrate the applicability of the procedure. [Copyright &y& Elsevier]

Abstract: This paper investigates the numerical simulation of non-Fourier transient heat transfer in a two-dimensional sub-100nm metal-oxide-semiconductor field-effect transistor (MOSFET). The dual-phase-lag (DPL) model with a specific normalization procedure is introduced for the modeling of nanoscale heat transport. The boundary conditions are selected similar to what existed in a real MOSFET device, both uniform and non-uniform heat generations within the transistor are applied, and the end parts of the top boundary which are in contact with the metallic material are left open. A temperature-jump boundary condition is used on all boundaries in order to consider the boundary phonon scattering at micro and nanoscale. A three-level finite difference scheme has been employed to generate the numerical results which are illustrated for a silicon sub-100nm MOSFET corresponding to the Knudsen number of 10. The results are presented at real times less than 50ps to avoid the three-dimensional effects. It is concluded that the combination of the DPL model with mixed-type temperature boundary condition is able to predict the heat flux and temperature distribution obtained from the Boltzmann transport equation (BTE) more accurate than the ballistic-diffusive equations (BDE). After verification of our results, the thermal field and the hotspot temperature within the bulk silicon are presented and the effect of adding a layer of silicon-dioxide to the transistor on its thermal behavior has been investigated. [Copyright &y& Elsevier]

Abstract: The application of ground heat exchangers (GHEs) has attracted much attention for its advantages in terms of energy-saving and emission-reduction. Therefore, it is significant to introduce heat transfer into investigation, the paper illustrated the existing heat transfer models in order to analyze the GHEs with buried coils. Line heat source, cylindrical heat source and ring-coil heat source are introduced step by step. For the present, the borehole GHEs are the mainstream, and in recent years pile foundation GHEs have been followed with interest on account of heat transfer superiority as well as lowering initial cost and saving land area. Concerning that groundwater flow exist in geological stratum sometimes, so that the thermal analysis about heat transfer should be composed of two cases, i.e. models under the condition of both pure conduction and combination that include conduction and advection. It is obvious that ring-coil model is on the verge of actual situation for pile foundation GHEs with buried coils from the academic research perspectives, nevertheless for some engineering computation problems which the result error can be permitted in the certain range, other heat transfer models can be chosen in order to simplify the calculation process. [Copyright &y& Elsevier]

Abstract: An experimental validation for a computational fluid dynamics (CFD) and an effectiveness-number of transfer units (ε-NTU) model for tubes in a large phase change material (PCM) tank has been conducted. The inlet and outlet heat transfer fluid (HTF) temperatures as well as twelve temperature locations in the PCM tank were compared with the CFD results. The average effectiveness of the phase change process of each experimental point was also compared with results from the CFD as well as the ε-NTU models. From this study, it was concluded that the CFD model and the ε-NTU model developed can accurately predict the behaviour of the thermal storage system during the freezing process. There are however, discrepancies in the melting process due to the exclusion of the effect of natural convection in the models. Using the experimental results, an effective thermal conductivity has been determined to account for buoyancy for various distances of tubes. The paper gives details of the CFD model of the phase change thermal storage system, and presents results from the CFD model, experiments and ε-NTU model. [Copyright &y& Elsevier]