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This paper describes an accurate model of the Electrical Power Subsystem (EPS) of the Thermal Analysis Support and Environment Characterization Laboratory (TASEC-Lab), a university experiment developed for using in high-altitude balloon missions to measure and analyze the convection heat transfer. A Li-ion battery and two high efficient DC–DC converters have been characterized through laboratory tests and fitting to the experimental results. The developed mathematical models described in this paper are used to carry out accurate EPS simulations and are validated by comparison with the experimental data. • Design and modeling of the electrical power subsystem of a stratospheric balloon experiment. • New Li-lion battery discharging model that describes the three main parts: initial decay, linear, and exponential decay. • Formulation of a new DC/DC converter efficiency model. • Simulation and model validation of the electrical power subsystem. [ABSTRACT FROM AUTHOR]

Absorption machines are frequently used for cooling and heating. However, they must be improved to achieve high performance at a lower cost. Being a key component of these machines, this paper focuses on the absorber and specifically on falling film absorber configuration due to its compactness and simple geometry. This paper reviews the different analytical and numerical approaches used to analyze the thermal, mass and hydrodynamic phenomena occurring in falling films for both smooth and wavy-laminar regimes. It shows the significant progress made since 2000 in terms of mathematical models developed and coupling effect resolution. Research using thermodynamics to identify, locate and quantify the entropy generation sources in falling film absorbers is also presented. [ABSTRACT FROM AUTHOR]

Grate boilers are widely applied in biomass combustion for heat and energy generation. However, grate-firing systems often suffer from low efficiency and high emission. Computational fluid dynamic (CFD) becomes increasingly popular as a flexible method to obtain the detailed combustion behaviors in the furnace, and to optimize the performance of existing grate boilers. This paper presents efforts toward a reliable baseline CFD model for an industrial biomass-fired grate boiler, where the structure of the fuel-bed was sufficiently considered. The combustion performances in the furnace were investigated experimentally and numerically by coupling the fuel bed and freeboard, to clarify the impact of bed structure on the simulation accuracy. Results show that when the bed structure has been taken into account, the predictions are in better agreement with the various measurements, as the deviations between them are all within 10 %. Moreover, the flame center drops, the total heat transferred to the water-cooled walls increases, and the residence time of flue gas is greatly prolonged from 2.76 s to 3.90 s, resulting in a distinct difference of the temperature and species patterns in the freeboard. The simulations will provide valuable theoretical guidance for the accurate modeling of grate-fired boiler. [Display omitted] • A baseline model is proposed for accurate modeling of biomass-fired grate boiler. • Effect of fuel-bed structure on the simulation of grate boiler is clarified in detail. • Bed structure greatly affects the predicted temperature and species patterns. • Flue gas residence time and heat transfer are also highly impacted by bed structure. [ABSTRACT FROM AUTHOR]

The paper presents the mathematical model of the heat transfer processes for a single screw ash cooler (SSAC) working with a circulating fluidized bed (CFB) boiler. The validation of the model is based on experimental measurements made on a 230 MWe power unit. The analysis of measurement data from two bottom ash coolers showed that the correct prediction of the outlet temperatures of ash and cooling water requires the determination of their individual ash filling characteristics (i.e. coolers). The numerical results confirm that the mixing model proposed by Schlünder correctly predicts the heat transfer coefficient for ash. The described mathematical model can monitor the operating conditions of the single screw ash cooler. It enables the determination of the optimal volumetric flow rates of the cooling water in order to get its highest possible outlet temperature, and then for this water to be used, e.g. for sanitary purposes. [Display omitted] • Mathematical model of ash cooler is successfully verified with experimental data. • Schlünder model of particle mixing is used to calculate heat transfer coefficient. • Characteristic of filling ash cooler with ash is a key part of mathematical model. [ABSTRACT FROM AUTHOR]

The strong coupling heat transfer between subassemblies and inter-wrapper gaps is closely related to the safety of the sodium-cooled fast reactor (SFR). Therefore, it is very important to carry out a detailed thermal hydraulic analysis of the core. In this paper, the inter-wrapper channel is modeled using the subchannel analysis method. A core thermal-hydraulic analysis code SACOS-Na (Subchannel Analysis Code Of Safety for SFR) is developed by using SIMPLE algorithm. For the subassembly module, a total of three experiments, including ORNL 19-pin experiment, TOSHIBA 37-pin experiment and KNS 37-pin experiment, are adopted to demonstrate the feasibility of the mathematical and physical models and numerical algorithms of the SACOS-Na as well as the rationality of the selected auxiliary models. For the inter-wrapper gap module, WEISS 2-subassembly experiment and CCTL-CFR 3-subassembly experiment are used to verify not only the simulation capability for backflow and strong inter-subassembly heat transfer, but also the heat structure model and the subchannel modeling approach on inter-wrapper gaps. In addition, the prediction accuracy of SACOS-Na has reached the advanced international level by comparing with the worldwide well-known core thermal hydraulic analysis codes. • The subchannel modeling method is adopted to build the mesh for inter-wrapper channels. • The SIMPLE algorithm is used to solve the problems of the reverse flow and inter-subassembly heat transfer occurred in SFRs. • The universal core thermal-hydraulic analysis code SACOS-Na for SFRs is developed. • The accuracy and reliability of the SACOS-Na are discussed from all aspects. [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]

• 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]

• Molecular distillation processes and equipment have been revised. • Molecular distillation models and the corresponding equations governing the mass, energy and momentum phenomena have been reviewed. • Thermodynamic and transport properties estimation methods of natural-based mixtures were reviewed. • Several molecular distillation applications on different mixtures have been presented and summarized including operation conditions. Molecular distillation is a separation technique used to separate thermosensible compounds. This process is often used to obtain concentrates of value-added products. For this reason, the research in this field has grown steadily during the past years. However, many efforts to simulate the transport phenomena occurring in this process and the thermodynamic properties of the molecules to be separated have fallen flat. Achieving a simulation that resembles what occurs in this process requires a thorough understanding of the molecular behavior of various substances under different conditions. This paper reviews several recently proposed methodologies to predict this behavior during the molecular distillation process. Thus, group contribution models and empirical correlations are used to estimate the value of some properties and coefficients which, in turn, determine the specific ways in which heat, mass, and momentum vary in a Molecular Distillation separation system. The transfer equations are discussed in mathematical models. Thin film, vapor phase, molecule collision, and mean free path are also important topics in molecular distillation, so they are also discussed in this review. Finally, some applications are summarized and a new case for the cannabis industry is supported. [Display omitted] [ABSTRACT FROM AUTHOR]

• 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]

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

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

The paper presents the development of a complete analytical model of a thermoelectric generator (TEG). Based on data coming from a small number of easily obtainable measurements, the model makes it possible to determine basic parameters of the TEG. Owing to measurements performed in the steady state and immediately after a rapid change of the TEG electrical state, the following quantities can be established analytically: the Seebeck coefficient, thermal conductivity and thermal resistance between heat exchangers and the TEG. The applied rapid method is based on the large difference in inertia between the electric and the thermal field. A rapid change from the short-circuit to the open-circuit electrical state makes it possible to record the voltage for the system thermal state corresponding to the short circuit. Experimental tests were carried out on a commercially available thermoelectric generator and the results proved the developed model usefulness. The simulation results show that the thermal resistance of the contact layers between the heat exchangers and the thermoelectric generators caused a loss of the temperature difference of the junctions from 30% at the recommended mechanical load to even over 50% if the clamping force was too low. Due to that, the determined power ratio, being an indicator of the utilization of the theoretical power capacity of a system burdened with thermal resistance, reaches values lower than 40% for the required clamping force and is below 20% for improper contact conditions The impact of the accuracy of the measurements on the values of the system parameters obtained from the model is evaluated by means of sensitivity analysis. [ABSTRACT FROM AUTHOR]