Structure optimization of U-tube solar collector integrated with phase change materials

Abstract

Solar collectors are significantly influenced by weather conditions, leading to a mismatch between thermal energy production and demand. To mitigate this issue, U-tube solar collectors integrated with phase change material (PCM) were investigated to store excess solar energy and regulate the temperature of collectors. This study investigates the effects of fin spacing and fin length on the heat transfer performance of these collectors under various conditions. Additionally, the impact of different collector tube lengths was analyzed. The results show that adding fins in solar collectors enhances temperature distribution uniformity and accelerates the PCM melting process. And the addition of fins to the U-tube produces faster temperature increase and significant improvement of temperature uniformity. In configurations featuring with fin length 20 mm and fin spacing 30 mm, the average PCM temperature decreased by 9.4 % and the liquid fraction decreased by 10.2 %, compared with non-finned. Smaller fin spacing or longer fins can improve heat transfer efficiency, and reduce PCM temperatures and liquid fractions. The 2L configuration exhibited optimal performance with an average PCM temperature of 330 K and a liquid fraction of 0.60 and achieved a significant reduction in time to reach 318 K by 47.9 % when compared to the L configuration.