Experimental investigation on convection heat transfer in solar air heater with perforated-winglet vortex generators

Abstract

An experimental investigation on thermal and flow friction characteristics of turbulent flow in a solar air heater duct with perforated rectangular winglet (PRW) vortex generators placed repeatedly on the absorber plate has been carried out. The experimental work is performed by varying the airflow rate in the form of Reynolds number from 5300 to 23,000. The PRW elements are mounted repeatedly with four perforated-winglets having punched hole diameters, (d=1.5, 3, 5 and 8 mm) at a single attack angle (α=45^o), pitch ratio (PR=2) and blockage ratio (BR=0.4). Influences of the PRW parameters on heat transfer characteristics in terms of Nusselt number (Nu) and friction factor (f) are investigated. The obtained result reveals that the employ of PRW elements provides much higher heat transfer and friction loss than using the duct alone. Although the non-perforated rectangular winglet, RW (without holes) gives the maximum heat transfer and friction loss but the highest thermal performance is found for the PRW with punched hole diameter of 5 mm.