Experimental Investigation of Reynolds Number, Nusselt Number & Friction Factor of Artificially Roughened Solar Air Heater

Solar air heaters are cheap and extensively used solar energy collection devices for space heating, seasoning of timber, curing of industrial products and can also be effectively used for curing/drying of concrete/clay building components and in air-conditioning systems. In this article, the effect of relative roughness height on Nusselt number and friction factor in an artificially roughened solar air heater having circular-sectioned symmetrical right angle roughness (duct aspect ratio, AR = 1) is studied. Circular-sectioned symmetrical right angle geometry are applied at the underside of the top of the duct, that is, on the absorber plate. The pitch (P) and height (e) are varied by keeping pitch-to-height ratio constant (P/e = 35mm). The height-to-hydraulic-diameter ratio (e/D) studied is 0.013 mm. For each height-to-hydraulic diameter ratio (e/D), simulations are executed at six Reynolds numbers from 3500 to 13,000 (relevant in solar air heater). The thermal enhancement factor for e/D = 0.013 is found to be the best for the investigated range of parameters. Experimental investigation of effect of relative roughness height on Nusselt number and friction factor in an artificially roughened solar air heater.