Effect of the irradiation intensity on the photo-thermal conversion performance of composite phase change materials: An experimental approach

Composite phase change materials (CPCM) containing photo absorbers are regarded as promising conversion and thermal energy storage materials for solar energy. Understanding the impact of irradiation intensity on the photo-thermal conversion process is of crucial significance for improving the photo-thermal conversion efficiency (PTCE) of CPCM. However, previous studies have overlooked the evolution of temperature patterns and the solid-liquid phase interface in CPCM, posing challenges in revealing photo-thermal conversion characteristics. In response to these challenges, the present study introduces an improved test method that integrates monitoring plane and infrared thermography. Paraffin/graphite nanoparticles CPCM are used as conversion and thermal storage material. The results show that the dominated heat transfer mode in different stages is different, and the natural convection within the liquid CPCM has enhanced the melting process. When the irradiation intensity is increased from 450 W/m² to 1250 W/m², the average temperature and average charging rate increase by 33.75% and 197.27%, respectively. At an irradiation intensity of 1050 W/m², the CPCM achieves the highest overall PTCE of 42.40%, which is an 8.85% increase in contrast to the irradiation intensity of 450 W/m². The results provide guidance for improving the PTCE of CPCM in the application of direct absorption solar collectors.