Thermal performance of solar air heater having discrete symmetrical arc rib with staggered rib roughness

Abstract

This paper investigates physics of forced flow underneath the absorber plate in solar air heater (SAH) integrated with new arc geometry namely discrete symmetrical arc rib with staggered rib roughness. This article signifies the impact of roughness pitch relative to rib height (p/e) on the thermal performance of rectangular roughened SAH duct having discrete symmetrical arc rib with staggered rib (present study). Novel arc rib geometry (present study) is achieved by providing an additional gap in a significantly long continuous arc segment of existing best arc rib geometry to break the boundary layer reformation along it. Range of parameters considered for experimental run for new geometry were Reynolds number (Re) as 3000–15,000, roughness pitch relative to rib height (p/e) of 6–14, flow attack angle (α) of 30°, staggered rib pitch relative to roughness pitch (p′/p) of 0.4, number of symmetrical gap over full arc (N_g) as 6, number of additional gap in symmetrical arc elements (n_g) as 5, gap width relative to rib height (g/e) as 3, rib height relative to hydraulic diameter (e/D_h) as 0.043, relative gap position (d/w) and additional gap width relative to rib height (g′/e) as 0.65 and 1 respectively. Five different roughened test plate with the variation of p/e as 6, 8, 10, 12, and 14 were tested. Optimum augmentation is perceived in Nu at p/e as 10 and for f at p/e as 8. Maximum thermo-hydraulic performance parameter (THPP) is achieved at p/e as 10 that corresponds to Re as 6000. Correlation, mathematical model, performance prediction and economic evaluation have also been done under different operation conditions.