Experimental and numerical study on thermal storage efficiency of solar flat plate collector based on photothermal conversion composite phase change material PA/EG/CuS-CNTs

This study proposes the combination of copper sulfide‑carbon nanotubes (CuS-CNTs) photothermal material with paraffin/expanded graphite. A flat-plate collector based on this material is also designed. Unlike traditional collectors that integrate phase change materials, the composite phase change material in this design can directly absorb sunlight and store heat. The goal is to reduce heat loss from the collector and improve system stability and efficiency. The novelty of this study lies in the preparation of a composite phase change material with high photothermal conversion efficiency, high thermal conductivity, and good shape stability. This material can realize the integration of photothermal conversion and thermal energy storage inside the collector. Key results show that when the CuS-CNTs content is 10%, the photothermal conversion efficiency of the composite phase change material increases from 61.07% to 94.03%. The total efficiency of the solar water heating system reaches as high as 56%. These results indicate that the addition of CuS-CNTs can significantly improve the photothermal conversion efficiency of the material. The prepared composite phase change material has great application prospects in the field of solar energy. In addition, this work uses numerical simulation for analysis. The optimal parameter combination for the collector is determined as an upper layer material density of 0.8 g/cm 3 , a lower layer material density of 0.8 g/cm 3 , and a thickness ratio of 1:1. These findings provide reference and guidance for the structural design of high-performance flat-plate collectors.