CFD Investigation of Solar Air Heater Roughened with Transverse Discontinuous Trapezoidal Ribs

A three-dimensional Computational Fluid Dynamics (CFD) analysis was conducted to examine the thermal and hydraulic characteristics of a solar air heater featuring transverse ribs for surface roughness. These transverse ribs possess a trapezoidal cross-section and are positioned in a non-continuous manner. The study also includes an investigation into transverse continuous ribs with similar cross-sections. A comparative analysis was carried out, comparing discontinuous ribs to continuous ribs to gain insights into fluid flow characteristics. The research explores gap width (g) and discontinuous width (w) sizes across a range of Reynolds numbers spanning from 5000 to 24,000, with variations in gap and discontinuous width sizes between 7.5–12.5 mm and 20–50 mm, respectively. To ensure the accuracy of the numerical investigation, validation was conducted on both smooth and roughened ducts to select the appropriate turbulence model. The RNG k-ε turbulence model with enhanced wall treatment was selected. The study further delves into the reasons why the solar air heater exhibits superior performance when equipped with discontinuous ribs as opposed to continuous ribs. Consequently, the preference for discontinuous ribs arises from their ability to significantly reduce pressure drop penalties, making them a favorable choice over continuous ribs.