Latent energy storage: Melting process around heating cylinders

AbstractA physical model to investigate the melting process around a multiple of heating cylinders in the presence of the natural convection has been carried out. A numerical code is developed using an unstructured finite-volume method and an enthalpy porosity technique to solve for natural convection coupled to solid-liquid phase change. It is found that during the melting process around the cylinders, natural convection circulation around each cylinder interacts with the other cylinders to influence the melt shape. In addition to natural convection, the heat source arrangement is an important factor in determining the melt shape

PCM Addition inside Solar Water Heaters: Numerical Comparative Approach

International audienceThe aim of this paper is to highlight the design of solar storage tank integrating PCM modules for solar hot water production. The objective is to simulate working cycle of solar thermal energy storage systems with encapsulated PCM operating under realistic environmental conditions (Marrakech, Morocco) and typical consumption load profile. Thus, two numerical codes were built to predict the temperature evolution in a storage tank simulation filled by PCM. This research aims to compare two numerical procedures: the technique of apparent specific heat capacity () and the Enthalpy method, basically used to simulate the phase change phenomena for latent storage inside a solar tank integrating spherical PCM capsules. Effects, advantages and limits of these numerical methods were examined via various numerical observations as well as a set of system thermal performance indicators. The assumptions, equations used in numerical modeling, the temperature profiles and the PCM liquid fraction evolution are presented and discussed as well. It was found that the time required for a complete melting inside the storage tank for the considered PCMs is 2.5 h and the increase in PCM amount decreases the melting velocity and enhance the heat losses to surrounding in dynamic mode. Results also show that the choice of a numerical method plays an important role in describing efficiently the phase change phenomena and system thermal performance. Based on the design and parameter studies performed, other suggestions and several numerical model improvements for further studies are as well addressed

Artificial neural-network based model to forecast the electrical and thermal efficiencies of PVT air collector systems

In the recent decade, Machine Learning techniques have been widely deployed in solar systems due their high accuracy in predicting the performances without going through the physical modelling. In this work, the Artificial Neural Network (ANN) method is adopted to forecast the electrical and thermal efficiencies of a photovoltaic/thermal (PVT) air collector system. Indeed, two accurate modelling techniques have been used to generate the output results for training and validation. Both deployed electrical and thermal models have been validated experimentally and demonstrated high accuracy. Then, real climatic samples of one year with a 10 minute step of the Jordan valley location have been adopted to generate the electrical and thermal efficiencies. These latter are used in the training and validation of the developed ANN model under various combinations of the weather variables. The solar irradiance and the module temperature are the most important variables to consider as input in a NN-based model respectively. The developed ANN model shows MAE of 0.0078% and 3.3607% in predicting the electrical and thermal efficiency respectively. The electrical efficiency can be predicted with higher accuracy than the thermal efficiency. Further, the results demonstrate that the ANN outperforms the LS-SVM in forecasting the PVT air collector performances

CFD Investigation of PCM Addition inside Solar Hot Water Storage Tanks

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Numerical simulation of the fluidized bed: application to ice slurry systems

International audienc

Performance Optimization of a Two-Phase Closed Thermosyphon through CFD Numerical Simulations

International audienceIn this paper, a comprehensive computational fluid dynamics (CFD) modeling was built to reproduce the pool boiling in the evaporator section and the liquid film condensation in a closed thermosyphon. The two phase Volume Of Fluids (VOF) model was used to simulate the heat transfer during evaporation and condensation inside a closed thermosyphon. This CFD model was validated using experimental results, and a good agreement was observed. Moreover, the results were analyzed in terms of the vapor volume fraction variation, temperature and vertical velocity at different locations along the thermosyphon. A parametric study was also conducted to enhance the performance of the thermosyphon designed for solar thermal energy applications like domestic hot water systems. It is found that the performance of the two-phase closed thermosyphon can be improved by tilted fins integration on the lateral surface of the condenser section

Modélisation et simulation numérique des transferts thermiques dans les conduites des capteurs solaires sous vide

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PCM storage for solar DHW: from an unfulfilled promise to a real benefit

ACLInternational audienceThe present numerical study is concerned with the use of phase change materials (PCMs) in solar-based domestic hot water (DHW) systems. During the last decade, the majority of the studies related to that issue concluded that the recourse to PCMs-based storage units was quite promising in order to enhance the overall performances of solar-based DHW systems. One recently interesting published numerical study (Talmatsky and Kribus, 2008), suggested though that this beneficial impact is not guaranteed since the gains observed over the day period brought by the presence of PCMs to store the solar energy were compensated by the losses undergone by the storage tank during the night. The origin of this absence of any beneficial impact of the use of PCMs in a DHW system has to be clearly understood in order to reconcile studies which indicated apparently contradictory findings. In that framework, the goal of the present contribution is to analyze the conditions under which such an absence of advantage of the use of PCMs in a DHW system were obtained in order to propose some possibilities of improvement for demonstrating the interest in using PCMs in solar-based DHW systems. Thus, the mathematical model based on the one reported in Talmatsky and Kribus (2008) is considered. This model describes the heat storage tank with PCM, collector, pump, controller and auxiliary heater. Realistic environmental conditions and typical end-user requirements are imposed

Crystallization of supercooled PCMs inside Emulsions: DSC applications

ACLInternational audienceHeat transfer characteristic during crystallization of the phase change material (PCM) dispersed inside an emulsion is investigated theoretically and experimentally by using Differential Scanning Calorimeter (DSC) technique. The dispersed PCMs are hexadecane, octadecane and water. Nucleation laws are used to simulate the supercooling phenomenon. The results indicate that the crystallization of the droplets stabilizes the emulsion temperature at a value corresponding to that at which probability of crystallization J(T) increases rapidly. To describe with accuracy the thermal properties of the PCM using DSC technique it is more appropriate to represent these properties versus the sample temperature and not as function of the plate temperature of DSC

Energy storage: Applications and challenges

International audienceIn this paper, an updated review of the state of technology and installations of several energy storage technologies were presented, and their various characteristics were analyzed. The analyses included their storage properties, current state in the industry and feasibility for future installation. The paper includes also the main characteristics of energy storage technologies suitable for renewable energy systems