Thermal performance analysis of a solar air collection-cascade storage system integrated with micro-heat pipe arrays

This study aims to establish a novel solar air collection-cascade storage system. Flat-plate micro-heat pipe arrays are applied in collector and heat storage units for heat transfer enhancement. To increase energy utilization ratio and improve system stability, a cascade storage configuration using paraffin and lauric acid is adopted. In the charging process, the cascade heat storage units store the solar irradiance collected by the collector in the phase change materials through the heat exchange fluid (air). During the discharging process, air takes away the heat stored in the phase change material. The heat transfer process and thermal performance of the system was analyzed experimentally in different volume flow rates from the perspectives of energy and exergy. The experimental results show that the air flow rate affects the thermal performance of the system significantly: as the volume flow rate increases, the heat collection power and efficiency show an upward trend, and the heat storage power and heat storage efficiency also show an increasing trend. Contrary to the increasing trend of exergy storage efficiency, exergy extraction efficiency decreases with increasing volume flow rate. An airflow rate of 220 m(3)/h obtains the highest average heat collection power and average heat collection efficiency, which are 542.0 W and 35.8%, respectively. In this condition, the average heat storage power and average heat storage efficiency of latent heat storage unit I are 175.1 W and 67.5%, respectively, and those of unit II are 136.0 W and 87.5%, respectively.