Experimental and numerical study on the effect of tubular solar absorber on the performance of counterflow double pass solar air heater

The problem of solar radiation intermittency can significantly affect the thermal performance of solar air heaters (SAHs). The efficient solution for this problem is utilizing thermal storage to store the thermal energy and using it again in off sunshine hours. The present study analyzed the thermal performance of two configurations of counterflow double pass solar air heater. The first configuration included a conventional flat plate solar absorber, while the second configuration involved tubular capsules that are filled with water as a sensible thermal storage material. The tubular capsules have been installed longitudinally in parallel to the direction of airflow. The study involved numerical and experimental parts. The results showed a remarkable enhancement in useful energy production when using the tubular capsules. Moreover, the SAH with tubular capsules can produce useful energy for a longer time due to the presence of the thermal storage material within capsules. It is found that the total useful energy in the case of tubular capsules is about 4082, 4295.3, 4426, 4584, and 4693 (W) at a mass flow rate of 0.03, 0.025, 0.02, 0.015, and 0.01 (kg/s) respectively, with an increment of 39.1, 51.2, 59.4, 74.8, and 89.6% respectively as compared with the flat-plate absorber. In addition, the average thermo-hydraulic efficiency in the case of tubular capsules are higher than those values which are achieved in flat plate case by about 9.3, 15, 19.6, 28.2, and 40% at a mass flow rate of 0.03, 0.025, 0.02, 0.015, and 0.01 kg/s respectively.