Heat transfer and friction factor correlations for a solar air heater duct roughened artificially with V-ribs with symmetrical gaps

An experimental study has been carried out for enhancement of heat transfer coefficient of a solar air heater having roughened air duct artificially roughened in the form of V-ribs with symmetrical gaps as turbulence promoter. In present work an experimental investigation of heat transfer and friction of artificial roughness in the form of V-ribs with symmetrical gaps were investigated. The investigation encompassed Reynolds number (Re) ranging from 4000 to 18,000, Number of gaps (Ng) values of 1-5, relative gap width (g/e) values of 1-5, relative roughness pitch (P/e) values of 6-12, angle of attack (α) range of 30-75° and relative roughness height (e/D) values of 0.043. For Nusselt number (Nu), the maximum enhancement of the order of 3.6 times that of smooth duct has been obtained, similarly friction factor (f) also increases by 3.67 folds of that of the smooth duct. The rib parameters corresponding to maximum increase in Nu and f were Ng = 3, g/e = 4, P/e = 10 and α = 60°. Based on the experimental data, correlations for Nu and f have been developed as function of roughness parameters of V-ribs with symmetrical gap and flow Reynolds number.