Experimental investigation of heat transfer and flow analysis of artificially roughened solar air heater by using double arc reverse shaped roughness with gap on the absorber plate

Abstract

Artificial roughness in the form of ribs is a convenient method for the enhancement of heat transfer coefficient in a solar air heater. In the present paper, an indoor experimental examination of Nusselt number (Nu) and friction factor (f) characteristics of a Solar air heater using novel discrete double arc reverse form roughness bottom side of the absorber plate was carried out. The range for criterion, relative roughness pitch (p/e) of 6.67, relative roughness height (e/Dh) of 0.027, angle of arc (α) of 30°,45°, 60°, 75°, Reynolds number (Re) of 3000 to 14000, aspect ratio (W/H) of 8 were applied in between the laboratory test. It has been found that the performance of roughened solar air heater duct is better than the performance of a smooth duct for the range of roughness parameters investigated. Enhancement of heat transfer coefficient (h) was noticed 266% more than a smooth channel. Increments of Nusselt number (Nu) and friction factor (f) were found at 268% and 221% more than smooth channel respectively. Maximum thermal efficiency was found 137% more than a smooth channel. Thermo-hydraulic concepts have been used to identify the ideal design and operating conditions. Depending on the insolation, it has been discovered that systems running within a certain Reynolds number range operate better thermo-hydraulically. The range of Thermo-hydraulic performance (THP) improved along with the increment of the Reynolds number. At a relative roughness pitch (p/e) of 6.67, a relative roughness height of 0.027, along the angle of arc (α) of 60°, the highest improvement of Thermo-hydraulic performance (THP) was noticed 2.22.