Performance investigation on a new solar air heater using phase change material/expanded metal mesh composite as heat storage unit: An experimental study

Abstract

Solar air heaters (SAHs) integrated with heat storage units commonly utilize phase change materials (PCMs) such as paraffin and salt hydrates. Since PCMs have low thermal conductivities that cause the heat to penetrate PCM with delays, a lag occurs in the charge/discharge and reduces heat storage units’ performance. Recently several expensive technologies, such as encapsulation and tubular containers, have been suggested to improve the performance. The current study represents an innovative and simple technique to address this problem by increasing the charge/discharge rate. This technique suggests using PCM embedded in expanded metal meshes (EMMs). EMMs are Rabitz wire meshes used extensively in construction works and have high thermal conductivities. In this study, a novel double-pass SAH design using integrated PCM and a perforated absorber plate was constructed. Three scenarios were developed, including SAH without PCM, SAH with PCM, and SAH with PCM/EMM. The experimental runs were carried out for two mass flow rates of 0.012 kg/s and 0.025 kg/s for 24 h. The obtained results prove that PCM and PCM/EMM increase the total heat gain and energy efficiency by nearly 45.88% and 48.19%, respectively, compared to commercial SAHs in the air mass flow rate of 0.025 kg/s. The exhaust temperature in the SAH with PCM/EMM is higher than the SAH using PCM in the evening, proving the EMM accelerates the discharge rate. The daily efficiency of the novel SAH using PCM/EMM reaches 76%. However, the exergy efficiency decreases by using PCM and PCM/EMM due to reducing the exhaust air temperature.