Thermohydraulic performance and correlation development for solar air heater having rough absorber surface using chamfered-square elements

Abstract

A very simple and economical device used for harnessing freely available energy from sun is solar air heater. But these solar air heaters are inefficient due to the low co-efficient of heat of air. Making artificially rough absorber plate is very common amongst the various techniques applied on solar air heater to enhance the performance. Square elements cut diagonally and glued on the absorber surface to generate the roughness. The impact of roughness parameters such Relative roughness height (RRH) of 0.44 to 0.077, Relative roughness pitch(RRP) of 3 to 9 and square element arm length (ALSE) of 4 mm to 10 mm on the performance of an artificially roughened solar air heater has been numerically explored. The Reynolds number of the absorber plate was adjusted from 4250 to 20000, but the heat flux remained constant at 1000 W/m2. The flow turbulence was handled using the “ANSYS FLUENT software's renormalized group (RNG) k-ε with enhanced wall treatment” turbulence model. In terms of Nusselt number and friction factor, the effects of roughness parameters such as RRP, RRH, and ALSE on the performance of artificially roughened solar air heaters have been explored. To test their increased efficiency, Nusselt number and friction factor of roughened solar air heaters (SAH) has been compared at similar flow conditions with plain one.