CFD analysis of solar air heater duct having square wave profiled transverse ribs as roughness elements

In this investigation, the thermal and hydraulic performance of solar air heater duct roughened with non-uniform cross-sectioned square wave profiled transverse rib is carried out in ANSYS Fluent 15.0. The 3-D investigation considered parameters as relative roughness pitch 4-30 and Reynolds number 3000-15,000, while relative roughness height has been fixed as 0.043. The turbulence model RNG k-epsilon with enhanced wall treatment and one periodic length was selected for analysis. The CFD methodology has been validated with the experimental results available in literature. The maximum augmentation in Nusselt number and friction factor over smooth duct was found to be 2.14 times and 3.55 times respectively at relative roughness pitch of 10 and Reynolds number of 15,000. The heat transfer and fluid flow process are discussed and visualized using streamlines and contours. The maximum thermohydraulic performance parameter was observed to be 1.43 at relative roughness pitch of 10 and Reynolds number of 12,000. The thermohydraulic performance for the non-uniform rib was also observed to be more than uniform cross-sectioned rib.