Investigation for the Optimal Thermo Hydraulic Performance in Three Sides Artificially Roughened Solar Air Heaters

Provision of artificial roughness on the absorber plate enhances heat transfer rate in solar air heaters, which also results in higher value of friction factor and more pumping power required. Based on the analysis (Prasad et al., 2015) for optimization of thermo hydraulic performance in three sides artificially roughened solar air heater, the present investigation deals with the results on optimal thermo hydraulic performance of such solar air heaters. The results have been represented in terms of the roughness Reynolds number, e+ , an efficiency parameter L-1 ,which combines the effect of efficiency roughness parameter, C-1 and Stanton number roughness parameter, B-1 , given byL -1=C-1 –B -1 and is equivalent to the thermo hydraulic performance parameter thermo . Results validate that the value of 23.12 23 opt e    , always corresponds to the optimal thermo hydraulic performance for such solar air heaters. It has been found that three sides roughened solar air heaters are thermally and thermo hydraulically superior than those of one side roughened solar air heaters of Prasad and Saini, (1988) and Verma and Prasad, (2000) under the same operating conditions. Optimal thermo hydraulic performance curves have been prepared to select the values of the roughness and flow parameters (p/e, e/D and Re), to design such solar air heaters to obtain optimal thermo hydraulic performance.