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The article presents a review of works on mathematical modelling of biomass pyrolysis process. Models types, number of dimensions, captured phenomena, type and dimensions of the reactors and biomass particles as well as models validation methods were analysed. Particular attention was paid to descriptions of chemical reactions, which are the essence of biomass thermal decomposition simulation. The article briefly describes the most important issues related to biomass pyrolysis and provides a review of commonly used methods of modelling this process with emphasis on solutions "ready to employ" in CFD modelling. A summary of other review papers on this topic is also provided. The problem of mathematical modelling in the context of "model - an engineering tool" was also discussed. Mathematical model for an engineering applications must be prepared with consideration of necessary consensus between the calculations accuracy, calculation time, preparation efforts and analysis requirements. Therefore, in pyrolysis modelling context, the inclusion of chemical reactions and changes of heat transport conditions were considered as priority, while taking into account moisture evaporation and bed shrinkage should be conditioned by their actual contribution in the calculations accuracy and by their influence on the calculations time. • A review of research on mathematical modelling of biomass pyrolysis is presented. • Captured phenomena, kinetic models, properties change, reactor types are summarized. • Compromise between model precision and calculations costs is discussed. [ABSTRACT FROM AUTHOR]

The photovoltaic thermal collector can provide thermal and heat power at the same time. In this paper, a photovoltaic/thermal sheet and tube collector has been numerically investigated. The paper focuses on the development of a hybrid solar collector PV/T. This model will be applied to optimize the operation of the PVT collector in the semi-arid climate. A mathematical model has been developed to determine the dynamic behavior of the collector, based on the energy balance of six main components namely a transparent cover, a PV module, a plate absorber, a tube, water in the tube and insulation. It has been validated by comparing the obtained simulation results with experimental results available in literature, where good agreement has been noted. Using our developed model, the heat and electrical power of sheet and tube collector has been analyzed for four typical days of year with the meteorological parameters of Monastir, Tunisia. Furthermore, the effect of solar radiation, the inlet water temperature, the number of glazing covers and the conductive heat transfer coefficient between plate absorber and PV module have been involved to identify their influence on the thermal and electrical efficiencies. The monthly thermal and electrical energies is also evaluated. [ABSTRACT FROM AUTHOR]

Abstract: This paper examined the features of three typical thermal storage systems including: 1) direct storage of heat transfer fluid in containers, 2) storage of thermal energy in a packed bed of solid filler material, with energy being carried in/out by a flowing heat transfer fluid which directly contacts the packed bed, and 3) a system in which heat transfer fluid flows through tubes that are imbedded into a thermal storage material which may be solid, liquid, or a mixture of the two. The similarity of the three types of thermal storage systems was discussed, and generalized energy storage governing equations were introduced in both dimensional and dimensionless forms. The temperatures of the heat transfer fluid during energy charge and discharge processes and the overall energy storage efficiencies were studied through solution of the energy storage governing equations. Finally, provided in the paper are a series of generalized charts bearing curves for energy storage effectiveness against four dimensionless parameters grouped up from many of the thermal storage system properties including dimensions, fluid and thermal storage material properties, as well as the operational conditions including mass flow rate of the fluid, and the ratio of energy charge and discharge time periods. Engineers can conveniently look up the charts to design and calibrate the size of thermal storage tanks and operational conditions without doing complicated individual modeling and computations. It is expected that the charts will serve as standard tools for thermal storage system design and calibration. [Copyright &y& Elsevier]

Abstract: This paper presents the analytical and experimental investigations of the phase change heat transfer characteristics and thermodynamic behavior of spherically enclosed phase change material (PCM) with dispersion of nanoparticles for latent thermal energy storage (LTES) system in buildings. In this study, the heat transfer characteristics in terms of the transient temperature variations, moving interface positions, complete rate of solidification and melting were analyzed for the six different PCMs considered in pure form and with dispersed nanoparticles as well. The heat transfer characteristics of the PCMs considered were analytically modeled and experimentally evaluated for the steady state and transient conditions for various heat generation parameters during freezing and melting cycles of the LTES system. The experimental results infer that for the same thermal load conditions the rate of solidification for the PCMs decreased with the increased mass fractions of nanoparticles while compared to the pure PCMs. For the same operating conditions of the LTES system, similar heat transfer characteristics were observed for the six PCMs considered. In this paper, the analytical model solutions and experimental results for the 60% n-tetradecane: 40% n-hexadecane PCM are presented. The solidification time for the 60% n-tetradecane: 40% n-hexadecane PCM embedded with the aluminium and alumina nanoparticles were expected to reduce by 12.97% and 4.97% than at its pure form respectively. Besides, the test results indicate that by increasing the mass fraction of the nanoparticles beyond the limiting value of 0.07 the rate of solidification was not significant further. Furthermore, the rate of melting was improved significantly for the PCMs embedded with the dispersed nanoparticles than the pure PCMs. The analytical solutions obtained for the pure and dispersed nanoparticles based PCMs were validated using the experimental results. The deviations observed between the analytical solutions and the experimental results were in the range of 10%–13%. Based on the analytical and experimental results the present nanoencapsulated LTES system can be regarded as a potential substitute for the conventional LTES system in buildings for achieving enhanced heat transfer characteristics and energy efficiency. [Copyright &y& Elsevier]

Abstract: Hourly energy simulations are an important part of the design and analysis of ground-source heat pump systems. In order to evaluate the fluid temperature in the borehole of a geothermal heat pump system, most of the current models express the heat transfer rate as a sum of step changes in heat transfer rate. The borehole temperature is then computed as a superposition of the different contributions of each time step. The main difference between the different models lies in the way the step response is computed. Since all these methods are based on a convolution scheme, long time simulations are very time consuming. Many load aggregation algorithms have been proposed in order to reduce this computational time. In a previous paper we proposed a new algorithm to evaluate the overall response which was much faster than the classical aggregation schemes. However this new algorithm was based on the cylindrical source step response for a single borehole. In this paper, we present a generalization of this scheme for any kind of step response making it a very powerful tool for hourly simulations. [Copyright &y& Elsevier]

The hybrid ground-coupled heat pump (HGCHP) systems with supplemental heat rejecter/supplier can effectively solve heat imbalance problems in the subsurface, and consequently improve the operation performance of the geothermal systems. For example, solar energy and/or industrial waste heat may be used as stable heat sources for underground heat storage in northern China with higher heating load, and cooling towers are installed to release heat into the air in southern China, where more cooling demand is needed. This paper reviews and discusses different HGCHP systems, which have been applied in China. And based on the heat transfer model of vertical borehole heat exchangers (BHE) for HGCHP systems, physical and mathematical models of multistage series circuits are developed to illustrate the heat transfer process of the underground thermal storage. A set of parameters, such as borehole spacing, heat recharging rate fractions and thermal properties of soils, which affect the thermal performance of the ground heat exchangers are analyzed, and the optimal solutions are discussed for engineering application. [ABSTRACT FROM AUTHOR]

Abstract: Jet impingement has been verified as an effective method to enhance convective heat transfer. To make better use of this effect, vacuum glazed transpired solar collector with slit-like perforations is developed. In this paper, a mathematical model based on energy balance equations for the solar collector has been developed to predict its thermal performance. Then experiments have been carried out to verify the model. The results of experiment and simulation have achieved good agreement with the same trend and average deviation of 2.25%. It shows that the model is correct and accurate enough to predict the thermal performance of the collector. Based on simulation results of the model, the effects of key parameters on the thermal performance are analyzed. The key parameters include equivalent diameter of perforation, pitch of perforations, collector height, emissivity of the absorber plate and vacuum glass cover, transmittance of vacuum glass cover. The results of the model are useful in designing and optimizing the vacuum glazed transpired solar collector for different applications. [Copyright &y& Elsevier]

Abstract: 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: 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: 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: This paper describes the modelling and simulation of a wind-hydrogen system aimed at supplying electrical and thermal residential loads, where the thermal load is in part supplied by a catalytic hydrogen combustion device with hydrogen stored in a metal hydride system composed of a cluster of five metal hydride tanks equipped with a metal foam heat exchanger. The complete mathematical model has been developed from models available in literature and describing the different sub-systems that constitute the overall wind-hydrogen system. It has been later implemented in a multi-domain software environment to simulate system operations. Results over a year-long simulation show complete stand-alone capabilities, with an electrical efficiency and a combined heat and power efficiency of 8.2% and 12.5% respectively. At the end of the simulation period, a hydrogen annual surplus of 110.5 kg is left over which can, for instance, be used to feed a hydrogen powered car for about 9500 km. [Copyright &y& Elsevier]

Abstract: Planted roofs are passive cooling techniques that reduce the thermal load of buildings. In this paper, the authors have developed a model for evaluating the cooling potential of green roofs. Transfer equations are solved using a finite difference scheme and Thomas algorithm. The study was conducted taking into account the Togolese climate conditions. The effect of Leaf Area Index (LAI) and Biot (Bi) number on diurnal variation of the Solar Heat gain Factor (SHF) is presented and analysed. A correlation for the estimation of the Solar Heat gain Factor as a function of LAI and Bi has been established. The results presented in terms of evapotranspiration (ET) and Solar Heat gains Factor (SHF) show notably that the foliage density and hence the vegetable canopy type selection influence the thermal efficiency of the bioclimatic insulation screen greatly. It was found that a larger LAI reduces the solar flux penetration, stabilizes the fluctuating values, and reduces the indoor air temperature. [Copyright &y& Elsevier]

Abstract: This paper describes the experimental studies carried out to test thermal cycling of a real-scale PCM–air heat exchanger at ambient temperatures. To achieve this goal an experimental setup previously designed and used for testing real-scale prototypes of PCM–air heat exchangers is modified. The PCM used is commercially available, organic, and paraffin based. The total energy exchanged during melting and solidification, as well as the time elapsed until total melting/solidification are determined from the power curves experimentally obtained. The influence of the inlet air temperature and air flow is studied, and results show that the continuous thermal cycling of the unit is a repetitive process: running experiments with similar conditions leads to the same thermal behavior, no degradation in the PCM properties is noticed. Pressure drop is measured for different air flows. Depending on the inlet air temperature, full solidification of the PCM could be achieved in less than 3h for an 8°C temperature difference between the inlet air and the average phase change of the PCM. Average thermal powers of up to 4.5kW and 3.5kW for 1h are obtained for melting and solidification stages, respectively. An empirical model is developed from the experimental results, which could be a useful designing tool for applications that use such technology: green housing, curing and drying processes, plant production, HVAC, and free-cooling. [Copyright &y& Elsevier]

Abstract: In this paper an improvement of the model CaRM (CApacity Resistance Model) is presented to consider the borehole thermal capacitance, both of the filling material of the borehole and of the heat carrier fluid inside the ground heat exchanger. Several models, numerical and analytical, are available in literature for short time step analyses of ground-coupled heat pump systems. According to the modelling for the surrounding ground, the new approach for the inside of the borehole is based on electrical analogy. In this study the double U-tube ground heat exchanger is analyzed. The new model has been validated by means of a commercial software based on the finite elements method as well as measurements of ground response test, using a suitable plant system. In this last comparison, the contribution of the thermal capacitance of the circulating fluid is investigated, since it is frequently neglected in short time step simulations. In both cases, there is agreement between the CaRM results and data from numerical simulations and measurements as well. [Copyright &y& Elsevier]

Abstract: Analysis of borehole thermal resistance is important for the standard sizing of ground heat exchanger (GHE). In this paper, a p-linear dimensionless average fluid temperature is proposed to estimate borehole thermal resistance. A p-linear dimensionless fluid temperature and p-linear dimensionless average fluid temperature are introduced, and the p-linear dimensionless fluid temperature is compared with theoretical dimensionless fluid temperature calculated by quasi-three-dimensional model for both single and double U-tubes. Results show that the p-linear dimensionless temperatures with parameters p →0 and p = −1/2 are respectively in good agreement with the theoretical dimensionless fluid temperatures of single and double U-tubes. Therefore, the dimensionless logarithmic mean temperature for p →0 and the dimensionless geometric mean temperature for p =−1/2 should respectively be adopted to reasonably estimate the thermal resistance of single and double U-tube boreholes. [ABSTRACT FROM AUTHOR]

The calorific losses through the sidewalls delay drying, particularly in the higher racks of the foodstuff dryers, which provide us information on total drying time. One notes a temperature gradient of the air during its circulation upwards, between the entry and the exit of the empty dryer. This gradient is more significant with the decrease of the air velocity.The heat transfer coefficient by forced convection between the air and the interior walls is often determined by using the average Nusselt number defined in flow of boundary layer on plane plate (laminar regime). In addition, the presence of the grills, on which slices of product are spread, causes turbulence which is not taken into account by this coefficient of Nusselt number. In this paper, we determine the heat transfer coefficient between the air and the sidewalls of a dryer experimentally. The latter contains grills on which thin layer slices of a dry material (wood) of the same geometry as the initial potato slices are spread. This leads us to determine an expression of the Nusselt number of the form Nu=aRebPr1/3, without mass transfer. Thereafter, this correlation of the Nusselt number is introduced into the mathematical model, already suggested in our former work, which predicts the performances, in forced convection, of the foodstuff dryers. In the end, the influence of these losses is presented by means of a comparative study between various models, those that take into account and those that ignore these losses between two beds of slices. The results thus obtained are compared with the experiment in an application on potato drying. [Copyright &y& Elsevier]