Energy and exergy analyses of a parabolic trough collector operated with nanofluids for medium and high temperature applications

Thermal performance of parabolic trough collectors (PTCs) can be improved by suspending nanoparticles into the traditionally used heat transfer fluids. In this work, a one-dimensional mathematical model is proposed to investigate the effect of various nanoprticles suspended in the working fluid for medium and high temperature PTCs. The major finding of this work is that the nanofluid enhances the thermal efficiency of the PTC slightly. High operating temperatures are more suitable for using nanofluids and generate higher relative gains of energy delivered. It is also found that the exergetic efficiency improvement is more important than energetic efficiency. The peak exergy efficiency is achieved by the CuO based nanofluid and is about 9.05%. The maximum daily relative gain of thermal energy delivered is found to be 1.46% by using 5% of Al2O3 in the base fluid. Optimal control of the operating conditions can lead to maximum energetic and exergetic performances of the PTC

Exergy based performance evaluation of latent heat thermal storage system: A review

Phase change material (PCM) based latent heat thermal storage (LHTS) systems provide an attractive solution to bridge the gap between energy source and demand, if source is intermittent and time dependent. The optimization of LHTS systems is not necessarily on the basis of performance study through energy analysis, but on the basis of exergy based performance study. The exergy based performance evaluation and subsequent optimization of LHTS units have been a growing interest among the researchers in recent years. This can be seen through the various works reported in the literature. This paper reviews the various procedures adopted for the exergy based performance evaluation of LHTS units. The influence of operating and design parameters on the exergy stored/retrieved and thus, on the optimization is addressed as a main aspect. The need of exergy analysis for the comparative evaluation of LHTS systems with performance enhancement techniques is emphasized. Thermoeconomics methods applicable to LHTS systems are also presented in this paper.Latent heat thermal energy storage Exergy analysis Entropy generation Thermoeconomics

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

CFD Investigation of PCM Addition inside Solar Hot Water Storage Tanks

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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

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

Power, efficiency and irreversibility analysis of latent energy system

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

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