Heat transfer augmentation in a solar air heater with conical roughness elements on the absorber

Abstract

Adding flow-disturbing components to the absorber plate's effective heat transfer zone is the most efficient Thermo-hydraulic performance enhancement approach for a solar air heater (SAH). Researchers are attempting to decide the best geometrical parameters for a SAH when the turbulent flow has fully established with fabricated roughness protrusions on the absorber surface plate in a cone-shaped contour. The Thermo-hydraulic performance of the proposed SAH design is taken into account throughout the optimization process. Air flow rate and geometrical variables such as the Reynolds number Re=3000 to 8000, relative rib pitch p/e=10 to 20, and relative rib gap w/e=4 to 8 are varied in a series of experiments to assess the SAH's performance. Flow angle of attack (α = 90°), relative roughness height (e/Dh = 0.08), and rectangular flow passage aspect ratio (W/H = 5) are maintained constant in all the trials for inline and staggered configurations. Series of tests are carried out to establish statistical correlations between the average Nusselt number and the average friction factor. Thermo-hydraulic performance is affected by the Reynolds number (Re) as well as relative roughness gaps (w/e) and relative roughness pitch (p/e) of the conical protrusions. There was a 64.5% increase in Nusselt number and a 153.3% increase in friction factor at Re = 8000, p/e = 10 and w/e = 4. Cone-shaped roughness, as suggested, has a Thermo-hydraulic efficiency index of 0.8233, which ocuurs at p/e = 20 and w/e = 8 at Re = 3000.

Keywords

• Efficiency index
• SAH
• Cone-shaped rib roughness