The present paper describes the experimental analysis of heat transfer and friction factor for glass protected three-side artificially roughened rectangular duct solar air heaters (SAHs) having an arrangement of multiple-v and transverse wires (top wall multi-v and two side walls transverse) under the absorber plate, and compares their performance with that of one-side roughened solar air heaters under similar operating conditions. The investigated three-side solar air heaters are characterized by a larger rate of heat transfer and friction factor as compared to one-side artificially roughened SAHs by 24–76% and 4–36%, respectively, for the identical operating parameters. The air temperature below the three-side rugged duct is by 34.6% higher than that of the one-side roughened duct. Three-side solar air heaters are superior as compared to one-side artificially roughened solar air heaters qualitatively and quantitatively both.

Artificial roughness has been found to enhance the thermal performance from the collector to air in the solar air heater duct. This paper presents the results of experimental investigation on thermal performance of three sides solar air heater roughened with combination of multiple-v and transverse wire. The range of variation of system and operating parameters is investigated within the limits of relative roughness pitch of 10−25, relative roughness height of 0.018−0.042, angle of attack of 30°−75° at varying flow Reynolds number in the of range of 3000−12000 for fixed value of relative roughness width of 6. The augmentation in fluid temperature flowing under three side’s roughened duct is found to be 36.57% more than that of one side roughened duct. The maximum thermal efficiency is obtained at relative roughness pitch of 10 and relative roughness height of 0.042, and angle of attack of 60°. The augmentation in thermal efficiency of three sides over those of one side roughened duct is found to be 46−57% for varying values of relative roughness pitch, 38−50% for varying values of relative roughness height, and 40−46% for varying values of angle of attack.