Three-dimensional analysis of a novel solar air heater conception, for an improved heat transfer and energy conversion

Abstract

Solar air heating systems remain expensive, so we conducted a parametric analyzis to enhance their performance. The study focuses on a solar air heating system with a new proposed configuration including ribs with and without perforations. In the first step, we used a technique to vary the spacing (d) at 0.5, 0.3, 0.25, 0.2, 0.15, and 0.1 m for cases (1) to (6) by adjusting the number of simple inserts (type A) fixed on the absorber. In the second step, we selected the values of (d) from cases (5) and (6) that corresponded to the best thermal performance factor. We then experimented with seven types of perforated inserts: (A), (B), (C), (D), (E), (F), and (G). Our calculations focused on the Nusselt number, the friction factor, the thermal performance factor, the kinetic dissipation rate, the kinetic energy, and the turbulent viscosity. The results indicate that the presence of the inserts generates disturbances that amplify the heat exchange, thereby increasing the heat transfer rate. A rib distribution (type G) with a 0.1 m pitch (case 6) proved to be the most efficient configuration for heat transfer. At a Reynolds number of 4000, the proposed design has a Nusselt ratio of Nu/Nus = 8.5 and a friction ratio of f/fs = 4.76 compared to a smooth absorber surface. Additionally, the proposed solar air heater configuration has a thermal performance factor (η) of η = 5.32. These findings demonstrate that the proposed configuration is highly efficient and can significantly increase the heat transfer inside the absorber, thus improving the energy conversion of solar air heaters.