Enhancing the thermal performance of a solar air heater by using single-pass semi-flexible foil ducts

Abstract

This study focused on improving the thermal performance of a solar air heater (SAH) using a single-pass semi-flexible foil duct that can be applied directly as an absorber without requiring any surface modification. In this regard, a series of tests were performed at the air mass flow rate of 0.013 kg/s, 0.03 kg/s, and natural convection to determine the effect of the new material on the performance of the heater, and results were compared to a heater with a flat plate absorber. The maximum and average thermal efficiency of the heater with single-pass semi-flexible ducts were found as 65.48% and 53.08% for 0.03 kg/s, respectively. The SAH with single-pass semi-flexible foil ducts provides an enhancement in the thermal efficiency of 18.82% compared to the heater with a flat absorber plate. The exergy efficiency ranged from 10% to 15% for the new design heater. The increase in the number of Nu in the new design heater was found 3.02 times higher than that of the flat plate heater for the studied parameter range. The heat transfer coefficient was augmented of 2.03 times in the single-pass semi-flexible duct. Accordingly, the results showed that the single-pass semi-flexible foil duct is more successful than the flat plate because it significantly increases thermal efficiency due to its unique curved inner surface structure and high surface area. However, it is recommended that the absorber be applied as multiple cycles to achieve higher efficiency and outlet air temperature.