Performance Enhancement of Solar Air Heater Using Artificial Roughness

Abstract

Solar air heater is the most economical and basic device through which solar energy is converted into thermal energy. It is widely used for drying of agriculture product, space heating, seasoning of timber, curing industrial products, drying concrete/clay building components, etc. The thermal efficiency of the solar air heater is usually poor due to low convective heat transfer coefficient. The formation of laminar viscous sub-layer on the absorber plate is the main reason for the low heat transfer coefficient. In this study, 3D Numerical analysis of solar air heater duct was carried out with and without grooves in the reverse NACA profile ribs (i.e. fluid flows from trailing edge to leading edge). To optimize the groove dimensions, parametric studies was done with various groove sizes, groove numbers and groove angles in the wide range of Reynolds number from 6000 to 18000. From the numerical experimentations, three numbers of grooves with 3 mm width at 75° angle were found to be the most favourable among the all variations. In this case, the Nusselt number and friction factor were improved by 1.74 to 2.7% and 4.61 to 13.81 % in comparison without groove plate at different Reynolds numbers. The maximum value of thermo-hydraulic performance parameter (THPP) was found as 2.25 at Reynolds number of 6000. In the second phase, experimental investigations were carried out on solar air heater with reverse NACA profile ribs before and after creating three grooves of 3 mm size at angle of 75°. It led to 10.60% improvement in Nusselt number and 7.22% improvement in friction factor in comparison with the without groove profile at Reynolds number of 8000. The maximum Nusselt number was found as 118.48 at Reynolds number of 18000. The THPP for this case was found as 2.23 at Reynolds number 8000.