Investigation of V-down staggered rib roughness for improved solar air heater efficiency: An experimental analysis

An investigational examination was conducted to examine the effect of V-down aligned gap with staggered rib roughness on the heat dissipation rate and frictional behaviour of airflow in a rectangular solar air heater (SAH) duct. The roughness geometry comprised both variable and fixed geometrical parameters: the variable parameters included the relative rib pitch (p/e) from 6 to 14, staggering ratio (p’/p) from 0.2 to 0.8, and relative size of staggered rib (r/g) from 0.25 to 2. Meanwhile, the fixed parameter included a relative gap breadth (g/e) of 4, number of gaps (Ng) of 3, and relative height of rib (e/D h ) of 0.0433. Span of Reynolds number (Re) varies from 4000 to 15,000 throughout this study. The geometrical parameters were analysed and optimized to evaluate the overall impact of roughness configuration on SAH performance. Results indicates that the maximum Nusselt number and friction factor were increased by up to 2.16 and 2.74 times, respectively compared to a smooth surface particularly at optimal configuration of p/e of 10, p’/p of 0.4, r/g of 1, e/D h of 0.043, g/e of 4, and Ng of 3. The thermal-hydraulic performance (THP) parameter of the proposed V-rib geometry was compared with existing V-rib geometries to validate the overall behaviour of the present rib roughness. Furthermore, correlations in terms of the heat transfer function R (e + ), and the roughness function G (e + ) were developed to predict the performance of the present V-rib roughness.