Performance Analysis of solar air heater having absorber plate artificially roughened by chamfered-square elements

A very common technique to improve the thermo hydraulic performance of solar air heater is providing artificial roughness on absorber plate. Diagonally chamfered cuboids has been used to generate roughness and applied on the absorber surface. A numerical study is performed to study the enhancement of the thermo hydraulic performance of the heater for thoroughness parameters of relative roughness pitch (transverse and longitudinal) of 6 to 14, cross section of cuboids from 8 mm to 14 mm and relative roughness height of 0.44 to 0.088. The Reynolds number is kept in the range of 5000 to 22500 with a constant heat flux of 1000 W/m2 on the absorber plate. The numerical computation is conducted by using the ANSYS FLUENT CFD software. The standard k-ε turbulence model with enhanced wall treatment has been used to handle the flow turbulence. The Nusselt number and the average friction factor are determined for different values of relative roughness pitch (transverse and longitudinal), cross section of cuboids and relative roughness height. The values of Nusselt number and friction factor of roughened solar air heater is compared with smooth duct at similar flow condition to find out the enhanced performance.