Performance studies on a solar air heater having combined V and I shaped ribs
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Date
2019-08
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
The use of artificial roughness on the underside of the absorber plate enhances the performance of the conventional solar air heater with little penalty of pressure drop. An experimental and CFD study on new roughness geometry in the form of combined V and I shaped ribs on the underside of the absorber plate has been carried out to increase the heat transfer and reduce friction factor in the present work. Experimental setup is designed and fabricated for the performance study novel roughness geometry for indoor conditions with a constant heat flux applied to the absorber plate. The experiments are conducted on three different relative roughness pitches of 20, 30, 40 and smooth plate for Reynolds number varying from 3500 to 10,500. Variation of Nusselt numbers (Nu) has been studied with Reynolds numbers and comparison has been made between roughened and smooth plate absorber. As a result of study, performance study, it has been found that the absorber plate having relative roughness pitch of 20 shows highest thermo-hydraulic performance. The highest thermo-hydraulic performance parameter is found to be 1.72 at Reynolds number (Re) of 10151 for roughness pitch of 20. Experimental results have also been correlated in terms of Reynolds number (Re) and relative roughness pitch (P/e) to develop new correlations of heat transfer and friction factor. The results of CFD
analysis are found to be in good agreement with the experimental results for relative roughness pitch of 20. For rectangular duct having combined V and I shaped ribs on absorber plate, the highest enhancement in friction factor is found to be 3.77 times at Reynolds number 3569 as compared to smooth plate solar air heater. The highest increase in friction factor is found to be at relative roughness pitch of 20. The values
of Nusselt numbers obtained from correlation lies within 0 to ± 5% of experimental values and the values of friction factor obtained from correlation lies within 0 to ± 12% of experimental values for the range of parameters studied in this work.
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