Numerical assessment of the effect of tube geometries on the performance of phase change material (PCM) integrated solar receiver for dish-micro gas turbine systems

Abstract

The temperature distribution and melting/solidification behavior of the Phase Change Material (PCM) depends largely on the arrangement of working fluid tubes in the PCM volume. A well-designed tube arrangement in the PCM results in more effective heat transfer and thermal storage. The authors previously presented a concept of Phase Change Material (PCM) integrated solar receiver for short-term thermal storage in the dish-micro gas turbine system. This solar receiver has a cylindrical shape structure filled with PCM, twelve tubes of working fluid (air) immersed in the PCM, and a conical cavity on its front surface. For such a compact thermal storage component, energy storage in the PCM and the charging/discharging rate largely depend on the arrangement of working fluid tubes in the PCM volume. The design of tubes should allow the proper distribution and release of heat in the PCM during the charging and discharging phases, respectively. In this study, the melting behavior and heat storage capacity of the PCM integrated solar receiver were analyzed by considering three different arrangements of the working fluid tubes with two cavity structures; a solar receiver with conical shaped cavity and 172° bend tubes, solar receiver with cylindrical shaped cavity and U-shaped tubes and solar receiver with conical shaped cavity with double helical tubes. The 3D numerical analysis were conducted by using Ansys Fluent 2022R1 to evaluate the effect of tube arrangements on the temperature distribution in PCM volume, melting behavior of PCM and the total storage capacity of the component. Temperature distribution on the cavity walls and heat losses were also considered. The transient simulations were performed using k−ε turbulent model with S2S radiation model and ray-tracing model. The results showed a significant effect of tube geometries on the PCM melting behavior inside the solar receiver. It was found that, in the solar receiver with conical shaped cavity and 172° bend tubes, the tubes arrangement is more suitable throughout the PCM volume and represents a more uniform temperature and melting behavior. Moreover, the pressure drop was much higher in the double helical tubes compared to other bend tubes.