Optimization of the mass ratio and melting temperature of PCMs integrated in Salt Gradient Solar Ponds

Phase Change Materials (PCMs) are promising materials to increase the storage capacity of solar energy-based systems, such as Salt Gradient Solar Ponds (SGSPs), as they are characterized by a large latent heat during the solid-liquid phase change. This paper introduces an optimization study for PCM integration in SGSP, in terms of PCM mass ratio (14 %, 19 %, 28 % and 47 %) in the lower convective zone and PCM melting temperature (35 °C, 44 °C and 50 °C). Numerically, a 2D model is developed, consisting in the continuity equation as well on momentum, thermal energy and diffusion equations. In order to validate this numerical model, an experimental campaign of a parallelepiped SGSP with PCM capsules in the bottom is constructed. The latter is tested for two PCMs (RT35HC and RT44HC) and under different climatic conditions of March and June. Numerical and experimental have been compared in which the maximum average relative error does not exceed 4.62 %, which ensures a positive validation. The optimization returns that the final liquid fraction of PCM decreases both increasing the mass ratio and melting temperature. Higher mass ratios reduce the final temperature of the PCM (49.5 °C with 14 % and 42 °C with 47 % for RT35HC), and also with higher melting temperatures reduce the thermal energy stored, since the pond tends to work only as a sensible energy storage system

Effects of Double-Diffusive Convection on Calculation Time and Accuracy Results of a Salt Gradient Solar Pond: Numerical Investigation and Experimental Validation

The main aim of this study is to investigate numerically and experimentally the effects of double-diffusive convection on calculation time and accuracy results of a Salt Gradient Solar Pond (SGSP). To this end, two-numerical models are developed based on the Fortran programming language. The first one is based on energy balance neglecting the development of double-diffusive convection, while the second is two-dimensional and is based on Navier-Stokes, heat, and mass transfer equations considering the development of double-diffusive convection. The heat losses via the upper part, bottom, and vertical walls, as well as the internal heating of saltwater, are considered. In order to validate and compare both numerical models, a laboratory-scale SGSP is designed, built, and tested indoors for 82 h. Results indicate that the two numerical models developed can predict the SGSP thermal behavior with good accuracy. Furthermore, the average relative error between experimental and numerical results is around 9.39% for Upper Convective Zone (UCZ) and 2.92% for Lower Convective Zone (LCZ) based on the first model. This error reduces to about 5.98% for UCZ and 3.74% for LCZ by using the second model. Consequently, the neglect of double-diffusive convection in the SGSP modeling tends to overestimate the thermal energy stored in the storage zone by about 4.3%. Based on the calculation time analysis, results show that the second model returns a calculation time hundreds of times larger than the first one and, accordingly, an increase in computational cost