Özet:

A comparative study based on exergetic performance of two different types of artificial roughness geometries on the absorber plate of solar air heater has been presented. The performance evaluation in terms of thermal efficiency (ɳth), effective efficiency (ɳeff), exergetic efficiency (ɳII) and different exergy loss parameters has been carried out analytically, for various values of temperature rise parameter (∆T/I) and relative roughness height (e/D). The second law based exergy analysis is suitable for design of rib roughened solar air heaters as it incorporates quality of useful energy output and pumping power. The two roughness geometries are discrete W-shape rib roughness and W-shape rib roughness have been selected. The correlations for heat transfer and coefficient of friction developed by respective investigators have been used to calculate efficiencies. It was investigated that discrete W-shape rib roughness has better thermal efficiency (ɳth), effective efficiency (ɳeff) and exergetic efficiency (ɳII) as compared to the W-shape rib roughness. The optimum parameters are relative roughness height (e/D) of 0.3375 at an angle of attack of 60º and isolation value of 1000 w/m2. It was investigated that discrete W-shaped rib roughness has 33% more exergetic efficiency then W-shaped rib roughness under similar performance parameters such as aspect ratio (8), relative roughness height (e/D) of 0.03375, angle of attack (α) of 60º, relative roughness pitch (P/e) of 10 and isolation value of 1000 w/m2 with Reynolds number ranges from 4000 to 14000. Curves of thermal efficiency (ɳth), effective efficiency (ɳeff), exergetic efficiency (ɳII) and different exergy loss parameters with respect to temperature rise parameter (∆T/I) and relative roughness height (e/D) are also plotted.

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