Experimental investigation and theoretical analysis on a mid-temperature solar collector/storage system with composite PCM

This paper presents a solar collector/storage system designed for mid-temperature application. In this system, the phase change material (PCM) composited by erythritol and expanded graphite with melting temperature of 119 °C was filled in the aluminum pipes, and those pipes were placed inside the evacuated tubes. The heat pipes were immersed in PCM to transfer heat from PCM to fluid. According to the tests of thermophysical properties, the composite PCM with 3 wt% expanded graphite was chosen as a suitable material for heat storage. Then, both the experimental setup and numerical model were established to investigate the thermal performance of this system. The exposure experiments were carried out in August, the results showed that the storage efficiency reached 40.17% for mid-temperature utilization. In addition, the numerical model was validated by the experimental data. Based on the numerical model, the effects of solar irradiance and storage tube diameter on thermal performance of this system were also analyzed.