Experimental thermal performance investigation of a commercial recyclic thermal energy storage integrated solar air heater

This work presents the experimental thermal performance of a commercial thermal energy storage integrated solar air heater under recyclic air flow. Solar air heater is design for large absorber area of 2 m2, which is increased to about 12 % by using a wavy absorber plate of amplitude 0.01 m and 0.075 m as a wavelength. A thermal energy storage system of height 4 cm is developed by using two wavy plates, i.e., one as absorber plate and other as a lower plate. Paraffin wax of volume approximate to 80 kg and melting point of 38 degrees C as a phase change material (PCM) is used to achieve longer thermal energy backup. An excellent convective air heating, PCM melting and thermal energy backup is obtained using the wavy PCM unit as an integral part of the solar air heater. The advantages of employing recyclic air flow over and under the PCM unit are the high rate of heat transfer to air and heating of PCM unit from the bottom side before and after the mid of the day, i.e., about three hours including mid hours of the day. Designed solar air heater is constructed using commercial materials for high thermal outputs. The output of solar air heater presents a thermal backup of about 20-24 h at the maximum air temperature of 73 degrees C. The maximum outlet air temperature of about 73 degrees C, 64 degrees C, 67 degrees C and 65 degrees C is obtained during the month of June, July, August and September, respectively. The maximum Delta T of about 20-32 degrees C is obtained during the month of June-September. The mass flow rate of 0.01-0.02 kg/s is found suitable to provide almost 24 h' thermal backup during the month of June, while for others it is 0.01 kg/s. Marginal pressure drop penalty is obtained, which is found to be 48 Pa at a mass flow rate of 0.02 kg/s. The maximum thermal efficiency of the solar air heater is obtained during the month of June and found to be as 53 %. The results of the designed solar air heater are expected to support hot air requirements potentially for space heating applications.