Fully developed periodic and thermal performance evaluation of a solar air heater channel with wavy-triangular ribs placed on an absorber plate

Abstract

The heat transfer rate, flow topology, friction loss and thermal performance factor (TEF) of newly design wavy-triangular ribs mounted on an absorber plate in a solar air heater channel were numerically investigated. The effects of the blockage ratio, BR = 0.02–0.1 and the pitch ratio, PR = 0.4–1.5 were studied in the turbulent flow region, Re = 3000–20,000. The numerical results showed that the RNG k-ε turbulent model is recommended for the present case since the model gives the most accurate predictions compared to other turbulent models. The wavy-triangular ribs induced vortex flows that effectively disrupted the thermal boundary layers leading to enhanced heat transfer rate from the absorber plate to the air. Increasing the Reynolds number (Re) and blockage ratio (BR), while decreasing the pitch ratio (PR) led to increased vortex strength that helps in reducing the thermal boundary layer thickness, thus promoting heat transfer. Over the range investigated, the channel with wavy-triangular ribs provided higher friction factors (f) and Nusselt numbers (Nu) than a smooth channel by 5.8–304% and 13.8–171%, respectively. In addition, the ribs with a blockage ratio of BR = 0.07 and a pitch ratio of PR = 0.5 gave the highest TEF of 2.62 at Re = 3000.