Heat Transfer and Pressure Drop in a Double-Pass Solar Air Heater With Arc-Shaped Artificial Roughness

Abstract

An experimental and theoretical study has been performed to analyze the heat transfer and pressure drop performance of a double-pass solar air heater having arc-shaped roughness. The investigations are performed for the Reynolds number ranging from 3000 to 12,000, relative roughness pitch (p/e) ranging from 8 to 12, relative roughness height (e/d) of 0.0433, and the angle of attack (α/90) of 0.3333. The investigation has covered different performance parameters such as Nusselt number, friction factor, and thermal performance factor of rough and smooth double-pass solar air heater. A significant enhancement is observed in the heat transfer coefficient by the authors and the theoretical and experimental data are found in good agreement. The correlations for Nusselt number and friction factor are obtained for the range of parameters investigated. The maximum improvement in the Nusselt number for the rough double-pass solar air heater is obtained as 1.7 times that of the smooth double-pass solar air heater for Reynolds number of 11,283 with a relative roughness pitch of 8 and relative roughness height of 0.0433. The corresponding thermal performance factor of 1.4 is obtained for this case.