Numerical investigation of heat transfer augmentation of a curved solar air heater with inverted T-shaped ribs

Abstract

Laminar sub-layer formation in a smooth solar air heater (SAH) is one of the reasons for the low heat transfer coefficient. One of the most effective ways to overcome the problem and improve the heat transfer rate inside the SAH is to use artificial roughness in the form of ribs. The present investigation studies the consequence of inverted T-shaped ribs on the absorber plate of a CSAH. The absorber plate is exposed to a constant heat flux of 1000 W/m2 and is made up of aluminium. The investigation is done on the effect of Reynolds number (Re), relative roughness pitch (P/e), and relative roughness height (e/Dh) on entropy generation, fluid flow, and heat transfer characteristics of the system. A 2D fluid domain has been considered for the numerical analysis, and FVM is used to solve the equations of continuity, momentum, and energy. The governing equations are solved using the SST k-omega model. Thermo-hydraulic performance parameter (THPP) is also calculated using Nu(avg_r) and f(avg_r), which further helped to determine the optimal arrangement of inverted T-shaped ribs on the absorber plate of the SAH. The maximum THPP of 4.7744 is found for P/e = 7.143 at Re = 18000. Correlation for Nu(avg_r) and f(avg_r) as a function of Re and P/e is developed. Entropy generation per unit length due to fluid friction and heat transfer has been graphically represented.