Performance improvement of solar air heater duct-employing rib roughness on absorber: an experimental study

Solar energy is a pure and plentiful source of power for daily activities. Out of many solar thermal system, Solar air heaters (SAHs) are frequently regarded as the most economical and practical method of heating and drying indoor spaces. Due to its poor performance and minimal heat transfer capacity, its applicability in certain circumstances is quite limited. In this paper, an effort has been made to improve the heat transfer efficiency of SAH by utilizing hybrid ribs. Hybrid rib roughnesses are designed to integrate V-shaped ribs downstream of arc-shaped ribs and were experimentally tested in the SAH duct at Reynolds numbers (RN) between 2000 and 16,000. The various roughness pattern i.e. arc angle (alpha), relative V ribs position (d/w), relative rib pitch (p/e) and relative rib height (e/Dh) have been exploited in the range of 30o-75o, 0.2-0.8, 8-14 and 0.036-0.056, respectively. As a result, maximum enhancement in NuNu has been found as 3.75 at alpha = 45o, d/w = 0.5, p/e = 12, e/D = 0.056. Thermohydraulic Performance (TP) parameters have also been evaluated for all set of parameters and it was found to be maximum 2.49 at alpha = 45o, d/w = 0.5, p/e = 12, and e/Dh = 0.036.