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Heat transfer and friction factor correlation development for double-pass solar air heater having V-shaped ribs as roughness elements

In this present study, an experimental investigation has been carried out for a roughened double-pass solar air heater. The respective variation in other parameters, such as relative roughness pitch (p/e), relative roughness height (e/Dh), and angle of attack (α), were 5–20, 0.022–0.044, and 30°–75°, respectively. The effect of roughness and operating parameters on Nusselt number (Nu) and friction factor (f) has been determined, and the results are compared with those of a smooth absorber plate; considerable enhancement in both heat transfer and friction factor is noticed. Utilizing these experimental data, correlations for Nusselt number and friction factor correlations were also developed.