Investigation on performance enhancement due to staggered piece in a broken arc rib roughened solar air heater duct

This paper presents an experimental investigation on heat transfer and friction factor characteristics of solar air heater duct whose absorber is roughened with “broken arc rib combined with staggered rib piece”. The duct has aspect ratio of 12 and the absorber is heated with uniform heat flux while others three walls are insulated. The rib roughness has fixed relative staggered rib position, relative roughness height, relative gap size, relative gap position, arc angle and relative roughness pitch of 0.4, 0.043, 1.0, 0.65, 30° and 10 respectively. The relative staggered rib size and Reynolds number were varied from 1 to 6 and 2000 to 16,000 respectively. The effect of staggered rib on the flow pattern has also been observed using ANSYS Academic Research CFD 15.0. The maximum enhancement in Nusselt number and friction factor over that of broken arc rib roughened duct under similar flow and boundary conditions has been found to be 2.60 and 2.27 times respectively. The corresponding enhancements over that of smooth duct are 3.06 and 2.50 times respectively. The thermo-hydraulic performance of duct roughened with present rib roughness has been considerably enhanced and was found to be highest for relative staggered rib size of 4.