Thermal performance analysis of a double-pass solar air heater with lava rock as porous and sensible heat storage material

Abstract

This study investigates the utilization of lava rock as a sensitive heat storage material in a double-pass solar air heater. Three configurations were examined: (i) Double-pass solar air heater without the lava rock, (ii) Double-pass solar air heater with a 50 % lava rock packed bed, and (iii) Double-pass solar air heater with a 100 % lava rock packed bed. The experiments were performed indoors under the solar simulator with solar irradiances ranging from 590 to 1000 W/m2 with varying mass flow rates of 0.02, 0.06, and 0.12 kg/s. Results indicate a significant improvement in thermal efficiency with the addition of lava rock. At 1000 W/m2 solar irradiance, the configurations (i), (ii), and (iii) exhibited thermal efficiencies ranging from 18.2 % to 65.02 %, 25.27 % to 72.17 %, and 26.28 % to 76.41 %, respectively. Lava rock's integration into the double-pass solar air heater significantly lowered the temperature of the absorber plate as compared to the conventional double-pass solar air heater, showcasing the thermal storage properties of the lava rock. Under solar irradiance of 1000 W/m2 and a mass flow rate of 0.06 kg/s, the temperature of the absorber plate dropped from 91.3 °C in configuration (i) to 80.0 °C in configuration (ii), a decrease of 12.56 %, and to 71.4 °C in configuration (iii), a decrease of 21.74 %, respectively. The configuration (iii), utilizing a 100 % lava rock packed bed, exhibited the most enhanced thermal performance, representing the potential of lava rock as a sensible heating storage material in double-pass solar air heaters for improved heat retention and utilization under varying solar conditions. Moreover, the use of a double-pass solar air heater with lava rock results in a consistent and even distribution of temperature throughout the heater.