Abstract
The solar air heater has a low convective heat transfer coefficient because the absorber plate and moving air form a laminar sub-layer. Adding artificial roughness to the absorber surface is one of the most efficient heat transfer and thermal efficiency augmentation techniques utilised in SAH duct construction. The absorber plate is given new double arc discrete shaped roughness geometry. The Nu, f, and ηth characteristics of a rectangular duct were evaluated employing a new double arc discrete roughness element on one side of the SAH wall and insulation on the other three sides.The outdoor investigation has been carried out with roughness parameters are relative roughness pitch (p/e) of 6.67, 8.33,10,11.67, relative roughness height (e/Dh) of 0.027, angle of arc or attack angle (α) of 60°, Reynolds number (Re) in the range of 3000–14000, and as aspect ratio (W/ H) of 8 were selected. Solar radiation intensity ranged from 860 W/m2 to 895 W/m2 on a bright sunny day was used. Between 11:00 A.M. and 2:00P.M., from morning to afternoon, the outside test was also done. Optimum results were found at a p/e of 8.33 and α of 60° for Nu, h and f & THP. Optimum results were found at a p/e of 11.67 and α of 60° for ηth. The maximum enhancement of Nu & f by 2.87 & 2.47 of the roughened plate respectively was found when compared to the smooth absorber plate under similar flow conditions. Maximum value of Nu and f were found 121.66 and 0.0342 respectively. Maximum value of h and ηth were noticed 75.23 W/m2k and 87.95% respectively. The maximum enhancement of thermo-hydraulic performance (THP) was noticed under-investigated parameters of 2.82 at p/e of 8.33, and Re of 13935. Heat transfer and friction factor correlations have been developed deviation were found with experimental values within ± 18%.The mathematical model, which is utilised for SAH duct design and performance prediction under various operating conditions, has been validated using experimental data.
NSTL
Elsevier