Investigation of Thermo-Hydraulic Performance of a Solar Air Heater with Elliptical Ribs

Ribbed roughness generates turbulent flow, enhancing mixing within the air duct. This turbulence increases heat transfer (HT) rates by disrupting the thermal boundary layer, facilitating better thermal contact between the working fluid and the absorber plate. Rib-type roughness at the bottom of the receiver plate is a productive method to enhance the thermal and hydraulic behavior of a solar air heater (SAH). Various investigators have carried many kinds of research on circular or semi-circular, triangular, rectangular ribs attached to the heated wall of SAH. However, the current study investigates the two-dimensional CFD analysis of a novel quarter-elliptical rib inside a rectangular duct with a fully developed flow. The RNG k-ϵ turbulence model with the SIMPLE algorithm is assigned to solve the Navier Stoke equation and energy equation with the help of the version of ANSYS R19.2. Reynolds number (Re) is considered in the span of 3,500 ≤ Re ≤ 16,000 for the current investigation. The aluminum absorber plate is provided with a steady heat flux of 1 kW/m2 at a constant rate. The smooth duct set up is validated with both experimental results as well as with the empirical correlation. The heat transfer and thermo-hydraulic characteristics (THC) of the rib roughened SAH are analyzed by changing relative pitch ratio (p/e) from 5 to 15 and width ratio (e/w) from 1 to 2 with a constant height ratio (e/D) of 0.045. The temperature, pressure, turbulent kinetic energy (TKE), and velocity contours are provided to illustrate the flow characteristics of the fluid. Maximum thermo-hydraulic enhancement factor (THEF) of 1.63 is observed at p/e ratio of 5 and e/w ratio of 2 for Reynolds number 6,500.