Thermal performance improvement of a solar air heater fitted with winglet vortex generators

Numerical simulations are carried out to investigate the thermal and flow characteristics of a solar air heater (SAH) embedded with winglet vortex generator (WVG) for the Reynolds number (Re) ranging from 3500 to 16,000. The geometrical parameters of WVG considered are the tip edge ratio (c/alpha) from 0 to 1 and the angle of attack (alpha) from 30 degrees to 90 degrees, respectively. Computations are based on the finite volume method coupled with the SIMPLE algorithm. The effects of WVG on the dimensionless parameters, Nusselt number (Nu), friction factor (f), Nusselt number ratio (Nu/Nu(s)), friction factor ratio (f/f(s)), and thermal enhancement factor (TEF) are discussed. Nu and f increase with the initial increase of alpha from 30 degrees to 60 degrees and then decrease with a further increase in alpha. The maximum values of Nu and f appears at alpha = 60 degrees and c/alpha = 1. The results show that the WVG with c/alpha = 0 and alpha = 30 degrees provides the best TEF in the range from 1.72 to 2.20. The internal flow behavior along with the distribution of the temperature field and streamlines is explored to explain the effect of WVG configurations on heat transfer and friction factor, respectively. The modified WVG affects the flow and temperature fields, which leads to a significant enhancement in the convective heat transfer rate.