High-temperature phase change materials for short-term thermal energy storage in the solar receiver: Selection and analysis

The Dish-micro gas turbine (D-MGT) system could be an alternative way for small-scale power production (<100 kW) in rural areas. For such solar plants, the natural intermittence of solar flux is a major concern. The integration of a short-term thermal storage system into the solar receiver could lead to the reduction of the solar radiation fluctuation effects on the overall system. For these receivers, a concept of thermal storage using Phase Change Materials (PCMs) has been presented by authors in previous studies. The MGT can work with a minimum temperature of 800 degrees C at least and not convenient for a temperature below this limit. Therefore, the selection of PCMs for such high-temperature applications is a challenging task due to the demanding properties of the storage system and the limited information available in the literature. This study is based on the selection of the suitable PCM for the high-temperature solar receiver of the D-MGT system, preliminary analysis of the receiver with the selected PCMs and the detailed thermal analysis using a numerical approach. After the detailed survey, metallic PCMs are found suitable for this particular application. Based on the requirements of the MGT, the initial collection of the PCMs has melting temperatures higher than 800 degrees C and the latent heat of fusion greater than 500 kJ/kg. Four PCMs have been shortlisted based on their suitable properties for this application and selected for further analysis. The melting behaviour of the PCMs has modelled analytically by considering one dimensional Stefan problem. The effect of the properties of the PCM on its melting has been investigated by analytical models. The detailed charging and discharging behavior of the PCMs has been carried out with the help of 3D CFD simulations using Ansys Fluent 19.1. The results showed the good behavior of PCMs in stabilizing the outlet air temperature above 800 degrees C for 20-30 min of discharge phase. The MgSi showed better results than other candidates as it could maintain the outlet air temperature above 850 degrees C for 30 min during the discharging phase and completely melt after the 90 min of charging phase.