Heat transfer enhancement in solar air heater

This paper presents results of an experimental investigation of heat transfer in rectangular duct with repeated ribs in W-continuous pattern. The ribs in W-pattern have been tested for both pointing upstream (W-up) and downstream (W-down) to the flow. The duct has width to height ratio of 8, relative roughness pitch of 10, relative roughness height of 0.03375, angle of attack of ribs in W-pattern is 45o and Reynolds number ranges from 2300-14000. Roughened wall of the duct is uniformly heated while the remaining three walls are insulated. These conditions correspond closely to those found in solar air heaters. The heat transfer results have been compared with those for smooth ducts under similar flow and thermal boundary condition. Enhancement of heat transfer by providing W–shape roughness is 2.39 times to that of smooth plate for W-down ribs and 2.21 times to that of smooth plate for W-up ribs respectively