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Abstract: In this paper, we investigate the time-dependent heat and mass transfer in a molten carbonate fuel cell at start-up. Thus, a three-dimensional, transient mathematical model is presented through a comprehensive inclusion of various physical, chemical and electrochemical processes that occur within the different components of molten carbonate fuel cells. The model is proposed as a predictive tool to provide a three-dimensional demonstration of variable variations at system start-up. The local distribution of field variables and quantities are showcased. It reveals that the electrochemical reaction rate is dominated by the over-potential, not by the reactants' molar fraction. Reversible heat generation and consumption mechanisms of the cathode and anode are dominant in the first 10 s while the heat conduction from the solid materials to the gas phase is negligible. Meanwhile, activation and ohmic heating have nearly the same impact within the anode and cathode. Based on these findings, the importance of heat conduction and its main features are finally assessed. [Copyright &y& Elsevier]

Abstract: This paper presents a finite element model for the solution of thermal elastohydrodynamic lubrication in coated circular contacts. The model is based on a full-system finite element resolution of the elastohydrodynamic and heat transfer equations. The effects of the coating's thermal and mechanical properties on lubrication performance are investigated. Two categories of surface coatings are considered based on thermal properties: high and low thermal inertia. It is found that low thermal inertia surface coatings act as insulators leading to a localized increase in the lubricant's temperature at the center of the contact. Therefore, friction can be significantly reduced while film thickness is barely affected. The opposite effect is observed for high thermal inertia coatings. These effects increase with coating's thickness. [Copyright &y& Elsevier]

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

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

Abstract: The paper aims to overview various mathematical models for modeling the simultaneous heat and mass transfer process in the liquid desiccant dehumidifier. Firstly, the dehumidification principle is introduced briefly. Then the models are interpreted in terms of two classes of dehumidifiers. For the adiabatic dehumidifier, the models are mainly classified into three types: finite difference model, effectiveness NTU (ε–NTU) model, and simplified models. For the internally cooled dehumidifier, there are also three kinds of models: models without considering liquid film thickness, models considering uniform liquid film thickness, and models considering variable liquid film thickness. This review is meaningful for comprehending the development process and research status of the models and choosing suitable models for prediction. In addition, some suggestions are proposed for the model improvement. [Copyright &y& Elsevier]

Abstract: In this paper, a physical model is built to study the eutectic and progressive melting of salt solution in DSC (Differential Scanning Calorimetry) cells. The finite volume method is utilized to solve the heat transfer problem, and the general implicit source-based enthalpy method is employed to handle the absorbed latent heat during the phase change process. The resulting numerical solution is implicit in nature and although iteration on the time step is needed at each time level, the tridiagonal matrix algorithm can be utilized within the iterations leading to efficient and accurate solutions. The effects of the heating rate and the initial salt concentration on the kinetics of the melting process are examined. [Copyright &y& Elsevier]

Abstract: Combustion of pulverized coal in oxy-combustion technology is one of the effective ways to reduce the emission of greenhouse gases into the atmosphere. The process of transition from conventional combustion in air to the oxy-combustion technology, however, requires a thorough investigations of the phenomena occurring during the combustion process, that can be greatly supported by numerical modeling. The paper presents the results of numerical simulations of pulverized coal combustion process in swirl burner using RANS (Reynolds-averaged Navier–Stokes equations) and LES (large Eddy simulation) methods for turbulent flow. Numerical simulations have been performed for the oxyfuel test facility located at the Institute of Heat and Mass Transfer at RWTH Aachen University. Detailed analysis of the flow field inside the combustion chamber for cold flow and for the flow with combustion using different numerical methods for turbulent flows have been done. Comparison of the air and oxy-coal combustion process for pulverized coal shows significant differences in temperature, especially close to the burner exit. Additionally the influence of the combustion model on the results has been shown for oxy-combustion test case. [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 presents numerical calculations of the temperature field obtained for the case of a neonate placed under a radiant warmer. The results of the simulations show a very non-uniform temperature distribution on the skin of the neonate, which may cause increased evaporation leading to severe dehydration. For this reason, we propose some modifications on the geometry and operation of the radiant warmer, in order to make the temperature distribution more uniform and prevent the high temperature gradients observed on the surface of the neonate. It is concluded that placing a high conductivity blanket over the neonate and introducing additional screens along the side of the mattress, thus recovering the radiation heat escaping through the side boundaries, helped providing more uniform temperature fields. [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: The paper presents a new proposal of a discrete event simulation (DEVS) model for heat transfer in an enclosure. To our knowledge this is the first proposal in this direction, therefore the model is not comprehensive (has no windows, no ground coupling, etcetera). It is a first step of DEVS into the heat transfer in buildings. The model presented is just one possible implementation for a single thermal zone, although it has been designed to be used in multi-zone models. Common methods like CTF (conduction transfer functions) or RTF (response transfer functions) cannot be used. Instead it employs the successive transition state formulation for the 1D conduction heat transfer through multi-layered walls. An example test room has been calculated and the results compared with software that uses well known methods (CTF, RTF). Finally the DEVS model has been tested with a random convective internal-load signal. [Copyright &y& Elsevier]

Abstract: Nowadays, consumers look for minimally processed, additive-free food products that maintain their organoleptic properties. This has led to the development of new technologies for food processing. One emerging technology is high hydrostatic pressure, as it proves to be very effective in prolonging the shelf life of foods without losing its properties. Recent research has involved modelling and simulating the effect of combining thermal and high pressure processes (see Denys et al. (2000) [3], Infante et al. (2009) [5], Knoerzer et al. (2007) [6], Otero et al. (2007) [9]). The focus is mainly on the inactivation of certain enzymes and microorganisms that are harmful to food. Various mathematical models that study the behaviour of these enzymes and microorganisms during a high pressure process have been proposed (see Infante et al. (2009) [5], Knoerzer et al. (2007) [6]). Such models need the temperature and pressure profiles of the whole process as an input. In this paper we present two dimensional models, with different types of boundary conditions, to calculate the temperature profile for solid type foods. We give an exact solution and propose several simplifications, in both two and one dimensions. The temperature profile of these simplified two and one dimensional models is calculated both numerically and analytically, and the solutions are compared. Our results show a very good agreement for all the approximations proposed, and so we can conclude that the simplifications and dimensional reduction are reasonable for certain parameter values, which are specified in this work. [Copyright &y& Elsevier]

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

Abstract: This paper describes the analysis of a real case of multiple Aquifer Thermal Energy Storage systems. The Hague, the capital city of the province of South Holland in the Netherlands, is densely populated with many ATES systems. A total of 19 ATES systems are installed in an area of 3.8 km2 with a total of 76 functioning wells. The analysis focuses on the development of a coupled groundwater flow and heat transfer model over a period of 10 years. Results are then post-processed to evaluate efficiency of each individual well and system. Efficiency of the ATES systems has ranged between 68% and 87%. The analysis showed that efficiency tends, in general, to increase over time and stabilize at an asymptotic value after few years. Analysis of interference among individual wells of an ATES system and wells of other systems showed that interference could, in fact, have a positive impact on the efficiency of a well/system. Interference can increase efficiency of an ATES system since it can help in trapping energy (cold or warm) within the capture zone of all operating ATES systems. In the study area, the interference phenomenon affects efficiency, in general, positively where it increases the efficiency of individually operating wells by a maximum of 20%. However, the phenomenon also affects efficiency of some wells negatively where it reduces the efficiency of individually operating wells by a maximum of 25%. In average, systems in the study area are positively affected by interferences among each other with an overall average of 3.2% for all wells (over the 10 years operation period). [Copyright &y& Elsevier]

Abstract: Continuous frying systems are very energy intensive. They also involve the interaction of many variables and complex heat and mass transfer processes. Better control of these processes can lead not only to improved product quality but also energy reduction. This paper presents a model that can simulate the dynamic behaviour of a continuous frying system in sufficient detail that enables the influence of controls on the important product attributes of moisture and oil content to be investigated. A conjugate 2-D transient model of the fryer was used to develop correlations for the oil and moisture content based on the important fryer control variables, namely supply oil temperature, potato mass throughput, fryer paddle velocity and crisp takeout velocity. The correlations were validated against data for an industrial continuous fryer system and used within the overall frying system model which was implemented in MATLAB. Proportional Integral (PI) controls implemented within the MATLAB/Simulink environment have shown that closer control of the important parameters can lead to 10% energy savings compared to the actual industrial frying system. The modelling approaches developed can also be used to investigate further improvements in the design and control of continuous frying systems. [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: Heat transfer by natural convection occurs in many physical problems and engineering applications such as geothermal systems, heat exchangers, petroleum reservoirs and nuclear waste repositories. These problems and phenomena are modeled by ordinary or partial differential equations. In most cases, experimental solutions cannot be applied to these problems, so these equations should be solved using special techniques. Recently, much attention has been devoted to these methods to construct analytic solutions; such as the perturbation method. Perturbation techniques are dependent upon small parameter. Thus, it is worthwhile developing a new technique independent of small parameter. The Reconstruction of Variational Iteration Method technique is a powerful and convenient algorithm in finding the solutions for the equations. While this method is capable of reducing the size of calculation, it overcomes the difficulty of the perturbation technique or Adomian polynomials by applying Laplace Transform. In this paper an analysis has been performed to study the natural convection of a non-Newtonian fluid between two infinite parallel vertical flat plates and the effects of the non-Newtonian nature of fluid on the heat transfer are studied. In order to compare with exact solution, velocity and temperature profiles are shown graphically. The obtained results are valid with significant accuracy. [Copyright &y& Elsevier]

Abstract: A Flibe blanket has been proposed to be used in FFHR. Since Flibe has poor heat transfer performance, heat transfer promoter is required, and a sphere-packed pipe (SPP) has been proposed to enhance the heat transfer performance in the Flibe blanket. In this paper, the fluid flow and heat transfer characteristics in the SPP is evaluated numerically using a k–ɛ turbulent model for the flow field and an algebraic model for the thermal field. As a result, it was shown that bypass flows in the SPP play a significant role in heat transfer. Also it is thought that the turbulent energy can strongly affect heat transfer performance. [Copyright &y& Elsevier]

Abstract: The Parabolic Trough Collector (PTC) is the most common type of high-temperature solar thermal technology, in which the heat transfer fluid is usually synthetic oil, molten salt or water/steam. Experiences in existing plants have shown some operating problems with all these types of fluid, which limit solar to thermal efficiency and increase power plant costs. To solve such constraints an innovative solar Transparent Parabolic Through Collector (TPTC) working with gas-based nanofluid has been proposed and investigated in the present paper. Transparent receivers combined with gas-based nanofluids were found to be able to directly adsorb solar radiation due to the very high total surface of nanoparticles. The use of directly radiated nanoparticles allows compensating the relatively low heat transfer coefficient typical of gaseous heat transfer fluids with an increase of the exchange surface. Yet to allow a complete absorption of the solar energy within the transparent receiver tube a proper mixture of CuO and Ni nanoparticles has been designed. The proposed solar collector has been modelled by means of a discretized in space model to simplify the description of the behaviour of the physical system under the assumptions of quasi steady state conditions. The above-mentioned model has then been used to run an optimization procedure to define the main geometrical and operational parameters of the TPTC. Simulations have shown that the maximum TPTC solar to thermal efficiency is 62.5%, for a nanofluid outlet temperature of 650 °C and a nanoparticles volume concentration of 0.3%. [Copyright &y& Elsevier]

Abstract: This paper presents a parametric study on instantaneous heat transfer of a direct-injection hydrogen-fueled engine using a multidimensional model. A simplified single-step mechanism was considered for estimating the reaction rate of hydrogen oxidation. The modified wall-function was used for resolving the near-wall transport. An arbitrary Lagrangian–Eulerian algorithm was adopted for solving the governing equations. Experimental measurements were implemented to verify the developed model. They show that the instantaneous heat-transfer model is sufficiently accurate. The influence of engine speed, equivalence ratio, and the start of injection timing were investigated. The flow fields appeared to have greater size vectors and coarser distribution with an increase of engine speed. A heterogeneous distribution was obtained for an ultra-lean mixture condition (φ ≤ 0.5), which decreased with an increase of equivalence ratio. There was no pronounced influence of the start of injection on the flow field pattern and mixture homogeneity. Thermal field analysis was used to demonstrate trends in the instantaneous heat transfer. It was observed that there was a crucial distinction between the lean and ultra-lean mixtures as well as the engine speed. Furthermore, a non-uniform behavior was found for the impact of the equivalence ratio on temperature distribution. It is clear that the developed models are powerful tools for estimating the heat transfer of the hydrogen-fueled engine. The developed predictive correlation is highly accurate in predicting the heat transfer of the hydrogen-fueled engine, focusing on the equivalence ratio as a governing variable. [Copyright &y& Elsevier]

Highlights: [•] Wet method is a promising method to fabricate VIP core materials. [•] A multiphase medium model was established in this paper. [•] We analyzed the moisture and heat transfer characteristics during convection drying. [•] We compared the distinctions among different drying conditions. [ABSTRACT FROM AUTHOR]

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: The present study investigates the dynamic functioning of a new solar desalination process based on the humidification/dehumidification (HD) principle. The design and the principle of working of the desalination system are described. The paper deals with the modeling, simulation aspects, and experimental validation of the main components of the system. Mathematical models were established including the mechanism of heat and mass transfer in the various components. These models use real meteorological data to predict the performance of a thermal solar driven system. Series of experiments were conducted and experimental results were then compared with the simulation results. Our findings showed that the developed models could be used to design and help in predicting the behavior of the installation in various meteorological conditions. [Copyright &y& Elsevier]

Abstract: The present paper describes a mathematical study on peristaltic flow of viscoelastic fluids (with the robust Jeffrey model) through a finite length channel under the influence of heat transfer. The study is motivated by the need to further elucidate the mechanisms inherent in swallowing of diverse food bolus types (bread, fruit jam and almost all edible semi-solids) through the oesophagus, by taking account of the viscous and elastic effects. The expressions for temperature field, axial velocity, transverse velocity, volume flow rate, pressure gradient, local wall shear stress, mechanical efficiency, stream function, and reflux limit are obtained, when the Reynolds number is small and the wavelength is large, by using appropriate analytical and numerical methods. The computational results are presented in graphical form. The influence of thermophysical (heat transfer), relaxation time and retardation time parameters on pressure distribution, local wall shear stress profiles, temperature profiles and velocity profiles are studied in detail. Furthermore we investigate the effects of these parameters on two inherent phenomena (reflux and trapping) characterizing peristaltic flow using streamline plots. The present study emphasizes an important observation, namely that pressure along the entire length of the channel reduces when the magnitude of relaxation time (retardation time is fixed) or Grashof number or indeed thermal conductivity increase, whereas pressure is enhanced by increasing the magnitude of retardation time (relaxation time is fixed). [Copyright &y& Elsevier]

Abstract: This paper deals with the development of a phenomenological combustion single zone model of Diesel engine. The aim of this work is to build a model suitable for HiL (Hardware in the Loop), and thus to be able to run in Real-Time applications. The combustion sub-model estimates the heat release rate by the sum of two algebraic expressions related to premixed and diffusive burning process. The Wiebe correlation has been used to model each algebraic expression of the combustion sub-model. The ignition delay time required by the combustion sub-model has been modeled through an Arrhenius correlation and an algebraic simple correlation. An extensive identification analysis has been performed to express their dependence with respect to engine operating conditions. The global model has been built with the constraints of computational CPU load that characterize the real time simulations. The accuracy of the model in predicting the in cylinder pressure has been tested over a large set of measurements at different engine operating conditions. The comparison of in-cylinder pressure profiles with experimental traces has shown that the Arrhenius expression is less accurate than the simple correlation. However, these two approaches may be used in real time modeling. [Copyright &y& Elsevier]

Abstract: This paper presents a novel superstructure and optimization model for the simultaneous synthesis of process water and heat exchanger networks. This superstructure combines the water network and heat exchanger network using interconnecting hot and cold streams. The water network has been extended for both direct and indirect heat exchanges. In addition, opportunities for heat integration between hot and cold streams, splitting and mixing of the freshwater and wastewater streams are incorporated within the superstructure. The proposed model is formulated as a non-convex MINLP (mixed-integer non-linear program), where the objective is to minimize the total annual costs of the network. A new convex hull formulation is presented for identifying the streams' roles within the network. Three examples involving single and multiple contaminant problems are presented in order to illustrate the applicability and capabilities of the proposed superstructure and model. In all cases the resultant networks exhibit lower total annual costs, whilst the freshwater and utilities consumption are the same as reported in the literature. In addition, novel designs for heat-integrated process water networks with smaller or same number of heat exchangers are presented. [Copyright &y& Elsevier]

Abstract: This paper deals with the determination of dried cake resistance in a freeze-drying process using the Smart Soft Sensor, a process analytical technology recently proposed by the authors to monitor the primary drying stage of a freeze-drying process. This sensor uses the measurement of product temperature, a mathematical model of the process, and the Kalman filter algorithm to estimate the residual amount of ice in the vial as a function of time, as well as the coefficient of heat transfer between the shelf and the product and the resistance of the dried cake to vapor flow. It does not require expensive (additional) hardware in a freeze-dryer, provided that thermocouples are available. At first, the effect of the insertion of the thermocouple in a vial on the structure of the product is investigated by means of experimental tests, comparing both sublimation rate and cake structure in vials with and without thermocouple. This is required to assess that the temperature measured by the thermocouple is the same of the product in the non-monitored vials, at least in a non-GMP environment, or when controlled nucleation methods are used. Then, results about cake resistance obtained in an extended experimental campaign with aqueous solutions containing different excipients (sucrose, mannitol and polyvinylpyrrolidone), processed in various operating conditions, are presented, with the goal to point out the accuracy of the proposed methodology. [Copyright &y& Elsevier]

Abstract: The development of two analytical models that describe the thermal behaviour of solar air heaters of double-parallel flow and double-pass counter flow is presented. Based on the local energy balances, algebraic expressions for the efficiency factor F′ and the overall heat loss coefficient, U L , as well as air temperature distributions along the collectors were obtained. In addition, the expressions of the mean temperatures of the two air streams and of the absorber plate were determined. The model corresponding to the solar collector with double-parallel flow predicts that the mass flow of air flowing between the absorber plate and the transparent cover is greater than the mass flow circulating through the other channel. The model corresponding to the solar collector of double-pass counter flow indicates that increasing the airflow proportionally increases the percentage temperature rise in the inlet channel. The analytical expressions developed are valuable tools that can be included in computational codes for the design and thermal analysis of solar air heating facilities or to improve current facilities. The paper include a graphic to estimate the heat transfer coefficients involved in energy balances. [Copyright &y& Elsevier]

Abstract: Based on finite-time thermodynamics, a comparative performance analysis of air standard Dual and Dual-Atkinson cycles with heat-transfer loss, friction like term losses and variable specific-heats of the working fluid have been performed. Also the effects of heat loss, as characterized by a percentage of the fuel’s energy, friction and variable specific-heats of the working fluid, on performance of the mentioned irreversible cycles are analyzed. Moreover, detailed numerical examples show the relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the thermal efficiency of cycles. Results show the importance of consideration of heat loss effects on the both cycles’ performance. Also performance comparison of two cycles show that heat efficiency and power output of a Dual-Atkinson cycle are higher than a Dual cycle’s ones. The results obtained from this paper will provide guidance for the design of Dual-Atkinson engines. [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: One of the main drawbacks in modeling absorption chillers is the lack of justified hypotheses of heat and mass diffusion in an annular flow on the outer surface of horizontal tubes. Heat and mass transfer in diffusion is a three-dimensional problem with vector characteristics. This paper introduces the characterization of vapor–absorbent heat and mass transfer phenomena in three dimensional space to obtain steady state simulation results for single effect LiBr–H2O absorption chillers. It is thus possible for the first time to ascertain in the simulation that the heat and mass transfer characteristics are not uniform throughout the solution film. The diffusion boundary layer gradually becomes thicker towards the downstream tubes, which has previously been assumed but never confirmed in simulations. The radial component of the concentration field exhibits a potential for determining an optimum film thickness which enhances the system performance. The ability to use the proposed model with various absorbents and different cooling capacities increases its applicability. The model also offers the possibility to analyze different firing techniques at different temperatures. All the simulation results are consistent with the experimental data found in the literature. [Copyright &y& Elsevier]

Abstract: In the present paper, a computational fluid dynamics (CFD) modeling study was performed for the combustion of the brown coal in a large-scale tangentially-fired furnace (550MW) under different operating conditions. The AVL Fire CFD code has been used to model the combustion processes. The mathematical models of coal combustion with the appropriate kinetic parameters were written and incorporated to the code as user defined functions. These models consist of pulverised coal (PC) devolatilization, char burnout, and heat and mass transfer. The simulation of the PC combustion was carried out using multi-step reaction chemistry mechanisms. The level of confidence of this numerical model was based on the previous validations of the lignite combustion in a lab-scale furnace, as well as the validation parameters of the present furnace at the standard existing conditions in terms of temperature values and species concentrations. Performance of the boiler under ten different operating conditions was investigated. The strategy of operation schemes for the first six combustion scenarios were based on the change of the out-of-service (turned off) burners under full load operation, while the rest cases were carried out at 20% lower and 20% higher loads than the standard operating conditions. The validated model was used to perform the following investigation parameters: furnace gas temperatures, species concentrations (O2, CO and CO2), velocity distributions, and char consumption. The predictions demonstrated that there are good temperature distributions in the furnace when the turned off burners are set in the opposite direction under full load operation. For higher aerodynamic effect, the numerical results showed improvements on the combustion characteristics in terms of species concentrations and char burnout rates in comparison with the standard operating case. The findings of this study provide good information to optimize the operations of the utility tangentially coal-fired boiler with less emission. [Copyright &y& Elsevier]

Abstract: In order to study the influence of moisture transfer on the wall internal surface temperature, a coupled heat and moisture transfer transient model was proposed in this paper. Relative humidity and temperature were chosen as the driving potentials. The accuracy of the proposed model was verified by comparing the simulated results with the experimental data. By employing the developed model, the internal surface temperature of walls made of different materials was evaluated under the constant and variable boundary conditions. The results show that the effect of moisture transfer on the wall internal surface temperature is significant. When the moisture transfer is taken into account, the internal surface temperature has cooling effect on the indoor air and is beneficial to improve the indoor thermal environment during the working hours in summer, which lays a scientific basis for low energy building design. [Copyright &y& Elsevier]

Abstract: Air is a cheap and safe fluid, widely used in electronic, aerospace and air conditioning applications. Because of its poor heat transfer properties, it usually flows through extended surfaces, such as finned surfaces, to enhance the convective heat transfer. In this paper, experimental results are reviewed and numerical studies during turbulent air forced convection through extended surfaces are presented. The thermal and hydraulic behavior of a reference trapezoidal finned surface, experimentally evaluated by present authors in an open-circuit wind tunnel, has been compared with numerical simulations carried out by using the commercial CFD software COMSOL Multiphysics. Once the model has been validated, numerical simulations have been extended to other rectangular finned configurations, in order to study the effects of the fin thickness, fin pitch and fin height on the thermo-hydraulic behavior of the extended surfaces. Moreover, several pin fin surfaces have been simulated in the same range of operating conditions previously analyzed. Numerical results about heat transfer and pressure drop, both for plain finned surfaces and for pin fin surfaces, have been compared with empirical correlations from the open literature, and more accurate equations have been developed and proposed. As shown with an optimization example, these new equations can be used as an easy-to-implement calculation approach for heat sink design in electronic thermal management. [Copyright &y& Elsevier]

Abstract: There are two different ways to model reactive transport: ad hoc and innovative reaction-based approaches. The former, such as the Kd simplification of adsorption, has been widely employed by practitioners, while the latter has been mainly used in scientific communities for elucidating mechanisms of biogeochemical transport processes. It is believed that innovative mechanistic-based models could serve as protocols for environmental remediation as well. This paper reviews the development of a mechanistically coupled fluid flow, thermal transport, hydrologic transport, and reactive biogeochemical model and example-applications to environmental remediation problems. Theoretical bases are sufficiently described. Four example problems previously carried out are used to demonstrate how numerical experimentation can be used to evaluate the feasibility of different remediation approaches. The first one involved the application of a 56-species uranium tailing problem to the Melton Branch Subwatershed at Oak Ridge National Laboratory (ORNL) using the parallel version of the model. Simulations were made to demonstrate the potential mobilization of uranium and other chelating agents in the proposed waste disposal site. The second problem simulated laboratory-scale system to investigate the role of natural attenuation in potential off-site migration of uranium from uranium mill tailings after restoration. It showed inadequacy of using a single Kd even for a homogeneous medium. The third example simulated laboratory experiments involving extremely high concentrations of uranium, technetium, aluminum, nitrate, and toxic metals (e.g., Ni, Cr, Co). The fourth example modeled microbially-mediated immobilization of uranium in an unconfined aquifer using acetate amendment in a field-scale experiment. The purposes of these modeling studies were to simulate various mechanisms of mobilization and immobilization of radioactive wastes and to illustrate how to apply reactive transport models for environmental remediation. [Copyright &y& Elsevier]

Abstract: In this paper, we developed a mathematical model to numerically analyze the coal pyrolysis and heat transfer inside a heated coal particle. The distributed activation energy model (DAEM) was used to depict the coal pyrolysis. The heat transfer and temperature variation of a coal particle were modeled with a transient energy conservation equation. The endothermic effect of decomposition and the transpirational convective heat transfer were taken into account in the model. We firstly validated the coupled comprehensive model with published experimental data of both pulverized coal and large particles. Then, the temperature history and coal pyrolysis of coal particle heated were numerically analyzed. To physically understand the transient temperature and volatile evolution of coal particle, we clarified the effects of endothermic of pyrolysis, transpirational convection and particle size. [Copyright &y& Elsevier]

Abstract: This paper presents results obtained from a numerical simulation for the horizontal slinky-loop heat exchanger of a ground-source heat pump system. A three-dimensional numerical model was developed and the results of the thermal performance of various heat exchanger configurations are presented. The investigation was carried out on five types of loop pitch (loop spacing), three types of loop diameter, three values of soil thermal properties, and allowing continuous and intermittent operation. Comparison was made for the heat transfer rate, the amount of pipe material needed, as well as excavation work required for the horizontal slinky-loop heat exchanger. The results indicate that system parameters have a significant effect on the thermal performance of the system. [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: Common approaches to the simulation of borehole heat exchangers assume heat transfer within the circulating fluid and grout to be in a quasi-steady state and ignore axial conduction heat transfer. This paper presents a numerical model that is three-dimensional, includes explicit representations of the circulating fluid and other borehole components, and so allows calculation of dynamic behaviours over short and long timescales. The model is formulated using a finite volume approach using multi-block meshes to represent the ground, pipes, fluid and grout in a geometrically correct manner. Validation and verification exercises are presented that use both short timescale data to identify transport delay effects, and long timescale data to examine the modelling of seasonal heat transfer and show the model is capable of predicting outlet temperatures and heat transfer rates accurately. At long timescales borehole heat transfer seems well characterized by the mean fluid and borehole wall temperature if the fluid circulating velocity is reasonably high but at lower flow rates this is not the case. Study of the short timescale dynamics has shown that nonlinearities in the temperature and heat flux profiles are noticeable over the whole velocity range of practical interest. The importance of representing the thermal mass of the grout and the dynamic variations in temperature gradient as well as the fluid transport within the borehole has been highlighted. Implications for simplified modelling approaches are also discussed. [Copyright &y& Elsevier]

Abstract: Cold-formed thin-walled steel sections are usually used as the load-bearing elements of wall panels in building construction. Such panels consist of channel steel sections with gypsum plasterboard layers attached to the flanges on the outside and interior insulation. This paper proposes a simple method to calculate temperature distributions in the steel section when the panel is exposed to fire from one side. This method calculates the average temperatures in the flanges of the steel section and assumes that the temperature in the web is linear. The proposed method is based on simple heat balance analysis for a few nodes representing the key components of the panel. The thermal resistance of these nodes is obtained from the weighted average of thermal resistances in an effective width of the panel within which heat transfer in the panel width direction is assumed to occur. The effective width of the panel for calculating the weighted average of thermal resistances can be taken as the steel section flange width plus 15% of the difference between 300mm and the flange width of the steel section. Validity of the proposed method has been checked by comparison of the temperature results between the proposed 1-D modelling and 2-D ABAQUS Finite Element modelling for an extensive set of parametric and sensitivity studies covering different steel section dimensions (width, depth, thickness and lips), different spacing between steel section, number of gypsum layers (1 or 2) and different interior insulation properties. Further assessment of accuracy of the proposed temperature calculation method has been provided by comparing compressive resistance of the steel studs between using temperature profiles produced by 2-D ABAQUS Finite Element simulation and by using the proposed simplified method. Although the simplified method still requires a numerical procedure, it is extremely easy to implement to give designers of this structural system a much more efficient tool than using Finite Element simulations to calculate its fire resistance. [Copyright &y& Elsevier]

Abstract: The OpenSees framework has been extended to deal with frame structures under fire conditions. OpenSees is an object-oriented, open source software framework developed at UC Berkeley and has so far been focused on providing an advanced computational tool for analyzing the non-linear response of structural frames subjected to seismic excitations. New classes defining time-dependent temperature distributions in the cross-section of members have been created and OpenSees material classes have been modified to include temperature dependent properties based on the Eurocode. New functions and interfaces have been added into existing element and section classes to calculate the member actions due to arbitrary thermal loading taking into account material degradation with increasing temperature for non-linear analyses. This paper reports on a number of benchmark tests to ascertain the performance of the new codes implemented in OpenSees for beams, frames, and plate structures. The analysis procedures being developed for structures exposed to fire in OpenSees will make it easier for users to define temperature-dependent material properties and allow for arbitrary non-uniform temperature distributions across and along an element by interfacing a fire and heat transfer analysis module also being developed for OpenSees. This work will also enable the modeling of earthquake damaged structural frames subjected to a subsequent fire. [Copyright &y& Elsevier]

Abstract: This paper presents a methodology combining experimental measurements with computational modeling to find the heat flux extracted during spray cooling of a metal surface. Controlled experiments are performed to impinge air-mist spray onto a metal probe surface while applying induction heating to follow a desired temperature history. A transient axisymmetric computational model of induction heating which couples electromagnetics and heat conduction has been developed and validated with a test problem. The model is calibrated to match transient dry measurements and then used to simulate a steady-state air-mist spray cooling experiment in order to quantify the heat extracted from the probe surface by the boiling water droplets. A detailed example is presented to illustrate this approach. [Copyright &y& Elsevier]

Abstract: This paper concerns mathematical and numerical modeling of thermal phenomena accompanying single laser and laser-arc hybrid butt welding of steel sheets. Coupled heat transfer and fluid flow in the fusion zone were described respectively by transient heat transfer equation and Navier–Stokes equation. Laser beam and electric arc heat sources were modeled using different heat source power distributions. Latent heat associated with the material’s state changes, buoyancy forces and liquid material flow through a porous medium were taken into account in considerations. Differential governing equations were numerically solved using projection method combined with finite volume method. Elaborated solution algorithm was implemented into computer solver used for simulation of heat transfer and fluid flow during welding. The geometry of the weld and heat affected zone as well as cooling rates were estimated on the basis of numerically obtained temperature field. [Copyright &y& Elsevier]

Abstract: This paper focuses on the mathematical modeling and optimization of Multi-Effect Evaporation plants (MEE). A simplified and detailed enough model to accurately predict the MEE system performance is presented. The model is highly nonlinear and it is based on mass and energy balances which are derived from a superstructure. The superstructure involves several process configurations which have to be simultaneously optimized to determine the best stream flow-patterns (synthesis), the size of each evaporation effect (sizing) and the operating conditions of the whole process. Beside the conventional configuration, the model also includes different alternative flow-patterns for the distillate and the vapor streams. An equation-oriented environment was selected to develop and implement the model, allowing different application instances, such as simulation, sensitivity analysis and optimization, to be easily performed. Simulation results have shown a good agreement with realistic design data and other authors'' results. A ranking of the model parameters is presented according to their impact on the heat transfer area. Moreover, optimization results showed that the modification of the flow patterns improve the process performance, reducing the process specific total heat transfer area in about 5% compared to the optimal value of the conventional case. [Copyright &y& Elsevier]

Abstract: This paper investigates the effect of implementing a varying effective thermal conductivity term on heat transfer simulations within a metal hydride (MH) reactor. The work presented utilises a 1D transient heat transfer analysis comparing simulations either with a fixed effective thermal conductivity or a varying effective thermal conductivity. This builds on previously published work in the literature that has investigated varying effective thermal conductivity for metal hydrides at a single point. The results of these simulations are compared to experimental work for validation. The 1D simulation results clearly show that the varying effective thermal conductivity term more closely matches experimental results compared to the fixed effective thermal conductivity term. The results show that whilst a 1D simplification within the model may be valid in a bed some distance from the heating source, there are issues close to the heating source. It is speculated that neglect of losses outside of the 1D assumption are the cause of these issues. [Copyright &y& Elsevier]

Abstract: The continuous development of electronic devices requires optimum solutions for heat dissipation. This prompts the needs to the development of novel polymer composites that possess high thermal conductivity and high electrical resistivity. This paper discusses the challenges in this research area and some potential strategies to solve the problems. In this work, a thermal conductivity analyzer was designed and implemented to measure the effective thermal conductivity of composites with heterogeneous structures. An analytical model was developed to simulate the effect of contents of spherical fillers on the effective thermal conductivity of the composites. Using the developed model, together with experimentally-measured effective thermal conductivity of various composites, a semi-empirical approach was developed to estimate the thermal interfacial resistance at the polymer–filler interface. [Copyright &y& Elsevier]

Abstract: In this paper a numerical model to analyze the thermal behaviour of vertical ground heat exchangers with a helical shaped pipe is presented. This type of configuration can be a suitable alternative to conventional ground heat exchangers, especially when the heating and cooling loads of the building are very low. The model describes the heat transfer problem by means of a network of interconnected thermal resistances and capacitances. Moreover, as the investigated ground heat exchanger is usually installed in shallow depth, the model takes into account the interaction between the ground and the ambient environment which affects the fluid heat carrier temperature into the heat exchanger and, as a consequence, the energy efficiency of the heat pump. After a sensitivity analysis on the mesh parameters, the presented model is compared with experimental data and the simulation results show good agreement with the measurements. Finally, analyses to investigate the influence of the weather conditions, of the axial heat transfer and of the pitch between the turns of the helical pipe for two types of ground are carried out. [Copyright &y& Elsevier]

Abstract: In this paper a two-dimensional model of an annular cylindrical reactor filled with metal hydride suitable for hydrogen storage is presented. Comparison of the computed bed temperatures with published experimental data shows a reasonably good agreement except for the initial period. Effects of hydrogen pressure and external fluid temperatures on heat transfer and entropy generation are obtained. Results show that the time required for hydrogen charging and discharging is higher when the thermal capacity of the reactor wall is considered. The time required for absorption and desorption can be reduced significantly by varying the hydrogen gas pressure and external fluid temperatures. However, along with reduction in time the entropy generated during hydrogen storage and discharge increases significantly. Results also show that for the given input conditions, heat transfer between the external fluid and hydride bed is the main source of entropy generation. [Copyright &y& Elsevier]