Constructal design of different ribs for thermo-fluid performance enhancement of a solar air heater (SAH)

Abstract

In this paper, the constructal theory has been applied to evolve six new types of ribs (T-rib, left arm inclined T-rib, right arm inclined T-rib, Y-rib, concave and convex T-ribs) for a solar air heater (SAH). The fluid flow and heat transfer characteristics of the SAH with these ribs have been numerically investigated by solving the mass, momentum, energy, and turbulence equations employing the finite volume technique of ANSYS Fluent R16. The SST k−ωmodel has been used to solve the turbulence quantities, especially, the turbulent kinetic energy (k), and the specific dissipation rate (ω). The performance of the SAH has been obtained by varying different prominienet parameters of importance, such as the pitch (20 mm–90 mm), stem height (3 mm–11 mm), the inclination angle of the rib (0o-60°) and Reynolds number (5000–18,000). The optimal lengths for the pitch (i.e., 80 mm) and for the stem height (i.e., 8 mm) have been found out for T-ribs. It has been observed that the Nusselt number for T-rib increases by 191% in a range of Reynolds number, 5000–18,000, and at the optimum pitch and stem height. It is also observed that the Nusselt number marginally increases with the inclination angle of the rib. The concave T-rib and convex T-ribs have been evolved from the basic T-rib. Among all the considered ribs, the T-rib is found to be the best heat transfer enhancer keeping the friction factor at a low value. We found a higher Nusselt number and a lower friction factor for the present SAH with the T-ribs, as compared to that of the SAHs considered by previous researchers. The thermo-hydraulic performance (THPP) of a SAH with present rib (i.e., T-rib or the concave T-rib) has been observed to be more than SAH with other shapes of ribs used by previous researchers.