Experimental investigation on thermal performance enhancement in multi V-Pattern convex protrusion roughened solar air heater

The heat transfer coefficient of solar air heaters (SAHs) is limited due to the active viscous laminar sub-layer on the absorber's surface. Artificial roughness is introduced to destroy the viscous sub-layer formed underside of the absorber surface of the SAH duct. An experimental investigation was performed upon a novel roughness geometry multi v-pattern convex protrusion planted on an absorber to analyze Nu and f augmentation of rough ducts compared to smooth ones. The investigation was conducted for Re range 2500 -18,500, relative protrusion width (Wd/Wv) 1, 2, 3, 4, and 5, relative protrusion height (e/Dh) = 0.03, relative protrusion pitch (p/e) = 10, relative print diameter (e/d) = 0.5, alpha = 60o, and W/H = 12. The investigation is conducted with the objective to achieve the optimum roughness geometrical parameter amongst investigated values. Results for thermal and thermohydraulic performance parameters have also been worked out and reported. The key findings in the present work were compared with single and multi v roughness in rib shapes. The findings were conclusive and worth evaluating. The maximum Nusselt number and friction is obtained corresponding to Wd/Wv = 4 and 5, respectively. The maximum thermal efficiency is 66% obtained at Wd/Wv = 4, p/e = 10, and e/Dh = 0.03. The maximum THPP is observed to be 3.29 at Re = 13000.