CFD based performance analysis of a solar air heater duct provided with artificial roughness

In the present work the performance of a solar air heater duct provided with artificial roughness in the form of thin circular wire in arc shaped geometry has been analysed using Computational Fluid Dynamics (CFD). The effect of arc shaped geometry on heat transfer coefficient, friction factor and performance enhancement was investigated covering the range of roughness parameter (relative roughness height (e/D) from 0.0299 to 0.0426 and relative roughness angle (α/90) from 0.333 to 0.666) and working parameter (Reynolds number, Re from 6000 to 18,000 and solar radiation of 1000 W/m2). Different turbulent models have been used for the analysis and their results are compared. Renormalization-group (RNG) k-ɛ model based results have been found in good agreement and accordingly this model is used to predict heat transfer and friction factor in the duct. The overall enhancement ratio has been calculated in order to discuss the overall effect of the roughness and working parameters. A maximum value of overall enhancement ratio has been found to be as 1.7 for the range of parameters investigated.