An experimental investigation of new roughness patterns (dimples with alternative protrusions) for the performance enhancement of solar air heater

Abstract

Conventional solar air heater (SAH) has poor performance and in this work, an initiative has been taken to improve their overall performance with the help of a combined roughness pattern over the absorber plate. The experimental setup has been designed and fabricated having a rectangular duct with one heat-absorbing side (with roughness). The combination of dimple and protrusion roughness elements are arranged alternatively over the absorber plate for performance improvement of SAH. The precise placement of these roughness elements over the heat-absorbing side has been ensured with relative roughness pitch (RRP; P/e), print diameter to hydraulic diameter (d/D), and relative roughness height (RRH, e/D) which ranged from 10 to 20, 0.025–0.045, and 0.25 to 0.5, respectively. It is discovered with the experimental results that the thermal performance increases along with the pressure loss in the roughened SAH (rSAH). The heat flow increment is comparatively higher at the trailing and the leading edge of the dimple and the protrusion because of flow separation, reattachment, and flow impingement. The thermal performance is the highest while RRP, RRH, d/D are 10, 0.036, and d/D = 0.35, respectively. The proposed roughness pattern has resulted in a 2.1 and 1.95 times higher thermal augmentation and overall performance of SAH over the conventional.