Heat Transfer and Friction Characteristics of Broken arc ribs roughened solar air heater ducts

Abstract

A study was conducted to enhance heat transfer of a solar air heater having rectangular duct provided with artificial roughness in the form of broken arc ribs. The duct has an aspect ratio of 12. Five broken arc rib roughened plates having relative roughness pitch of 4, 6, 8, 10 and 12 have been tested for flow Reynolds number between 2, 000 to 16, 000. The arc angle, relative roughness height, relative gap width and relative gap position were fixed as 30°, 0.043, 1.0 units and 0.5 units, respectively. The maximum value of Nusselt number and friction factor was found corresponding to relative roughness pitch of 10. The maximum enhancement in Nusselt number of roughened solar air heater as compared to conventional smooth solar air heater was found to be 159 per cent with a corresponding increase in friction factor enhancement of 132 per cent at relative roughness pitch of 10 and Reynolds number of 12, 000.