This study aims to investigate and compare the thermal performance of a solar air heater using a passive technique to enhance heat transfer between the absorber plate and the flowing fluid. The technique involves generating turbulence near the heat transferring surface through the use of artificial rib roughness. The study focuses on two different novel roughness geome-tries: full symmetrical arc rib roughness and half symmetrical arc rib roughness. By introducing additional gaps and varying the number of gaps in the roughness geometries, the study examines their effects on the solar air heaters thermal performance. The artificially roughened surface creates different turbulent zones, which are essential to the development of different types of turbulence in the vicinity of the heat transferring surface. The study finds that an optimal escalation in Nusselt number and friction factor by 2.36 and 3.45 times, respectively, occurs at certain gap numbers as 6 and ng as 5 for full symmetrical arc rib roughness. The maximum thermal-hydraulic performance parameter of 1.66 is attained at a Reynolds number of 6 000. The study also conducts correlation, mathematical modeling, and performance prediction under different operating circumstances.

As the cost of fuel rises, designing efficient solar air heaters (SAH) becomes increasingly important. By artificially roughening the absorber plate, solar air heaters’ performance can be augmented. Turbulators in different forms like ribs, delta winglets, vortex generators, etc. have been introduced to create local wall turbulence or for vortex generation. In the present work, a numerical investigation on a solar air heater has been conducted to examine the effect of three distinct turbulators (namely D-shaped, reverse D- and U-shaped) on the SAH thermo-hydraulic performance. The simulation has been carried out using the computational fluid dynamics, an advanced and modern simulation technique for Reynolds numbers ranging from 4000 to 18000 (turbulent airflow). For the purpose of comparison, constant ratios of turbulator height/hydraulic diameter and pitch/turbulator height, of 0.021 and 14.28, respectively, were adopted for all SAH configurations. Furthermore, the fluid flow has also been analyzed using turbulence kinetic energy and velocity contours. It was observed that the U-shaped turbulator has the highest value of Nusselt number followed by D-shaped and reverse D-shaped turbulators. However, in terms of friction factor, the D-shaped configuration has the highest value followed by reverse D-shaped and U-shaped geometries. It can be concluded that among all SAH configurations considered, the U-shaped has outperformed in terms of thermohydraulic performance factor.