Thermo-hydraulic performance investigation of solar air heater duct having staggered D-shaped ribs: Numerical approach

The thermohydraulic performance (THP) of a solar air heater (SAH) duct with staggered D-shaped ribs as roughness geometry is examined in this work using three-dimensional numerical investigation. The investigation is carried out at roughness parameters of radius of rib to transverse pitch (r/Ptv) ratios of 0.1-0.35 and longitudinal pitch to radius of rib (Plg/r) ratios of 4-10 under varied operating circumstances of Reynolds number (Re) from 10,200 to 20,200. The maximum Nusselt number (Nu) is obtained to be 81.3 at Re of 20,200, r/Ptv as 0.1, and Plg/r as 4. In contrast, the maximum friction factor (f) is obtained to be 0.0169 at Re of 10,200, r/Ptv as 0.35, and Plg/r as 4. In the range of parameters examined, the maximum enhancement in Nusselt number (Nu/Nus) is observed to be 1.35 at an optimal parameter of r/Ptv as 0.1, Plg/r as 4, and Re as 10,200. Correspondingly, the enhancement in the friction factor (f/fs) at this optimum parameter is 1.87. The maximum value of the THP parameter is found to be 1.1 at the same optimum range of parameters. In further analysis, correlations were developed for Nusselt number (Nu) and friction factor (f) in terms of r/Ptv, Plg/r, and Re with a deviation of +/- 2% and +/- 1.5%, respectively.