Design and thermal performance evaluation of a new solar air collector with comprehensive consideration of five factors of phase-change materials and copper foam combination

Abstract

The low thermal conductivity of phase-change materials (PCMs) reduces the heat storage capacity, heat release efficiency, heat peak migration capacity, and heat collection efficiency of PCM-based solar air collectors (SACs) in building heating systems, thereby affecting the comprehensive heating requirements of building users. To solve this problem, in this study, a new SAC was designed with PCMs and copper foam (Type 2: PCMACFC-SAC model) by comprehensively considering five factors, namely thermal conductivity, heat storage capacity, heat release efficiency, heat peak migration capacity, and heat collection efficiency, based on a pure PCM-based SAC (Type 1: PCM-SAC model). Thereafter, the two models were compared. Comparative results of the thermal-performance evaluation index revealed that the thermal conductivity of the Type 2 test block was 2.2–2.3 times that of the Type 1 test block, indicating significantly improved thermal conductivity of the copper foam and PCM composite test block. Although the PCMACFC-SAC displayed better heat storage speed rate, time, and quantity, its nighttime heat release time was approximately 19.64% less than that of the PCMs-SAC; PCMACFC-SAC had a lower output temperature and smaller temperature fluctuation range over the solar day, which can increase indoor thermal comfort. The daily average heat collection efficiency of the PCMACFC-SAC decreased by 12.77%, indicating a stronger heat peak migration ability, which can transfer a greater amount of heat energy to be released at night.