CFD Analysis on Rectangular Shaped Variable Height Turbulators Fitted in a Solar Air Heater for Improved Thermal Performance

There have been various studies on the effect of turbulators of different shapes integrated with the absorber plate's underside for improved performance. However, a study on rectangular profiled variable height turbulators along the flow direction is not available. In this paper, an attempt has been made to explore in detail this aspect. The roughness of different kinds on the heat transfer surface mainly creates turbulence and breaks the laminar sub-layer, enhancing the heat transfer rate. In the present work, a solar air heater's performance incorporated rectangular profiled variable height turbulators of different configurations, i.e. increasing height turbulators, decreasing height turbulators and constant height turbulators, are being numerically investigated. For the base model, i.e. without any turbulators, a numerical and experimental analysis has been carried to establish the present analysis's overall validity. All tested turbulators show better performance compared to the base model. Configuration, which has to decrease in height towards the flow direction, shows relatively higher performance in terms of heat transfer coefficient, outlet temperature, and thermohydraulic enhancement factor than that of the other configurations. It is found from the analysis that for decreasing height turbulators, there is an enhancement of 21% to 0.2% for the Reynolds number from 3000 to 15000, respectively. For the higher Reynolds number above 15000, the THEF will be lesser than the base model.