Effect of roughness shape on heat transfer and flow friction characteristics of solar air heater with roughened absorber plate

A 2-D computational analysis is carried out to assess the comparative performance of the absorber plate of a solar air heater with different roughness elements using commercial software package Fluent 6.1. The assessment is based on heat transfer enhancement with minimum pressure penalty. Ten different rib shapes (viz. Rectangular, Square, Chamfered, Triangular, Semicircle etc) are investigated at the Reynolds number range from about 3000-20000, in which solar air heaters normally operate. The SST k omega turbulence model is selected by comparing the predictions of different turbulence models with experimental results available in the literature. Using the selected turbulence model a computational analysis is carried out to predict the heat transfer performance and flow friction characteristics of absorber plates with 10 different rib roughness elements. The analysis is carried out for both the flow regimes i.e. transitional flow regime (5 <= e(+) <= 70) and fully rough regime (e(+) >= 70).