Abstract
CFD analysis of 2-dimensional artificially roughened solar air heater duct with additional circular vortex generator, inserted in inlet section is carried out. Circular transverse ribs on the absorber plate are placed as usual. The analysis is done to investigate the effect of inserting additional vortex generator on the heat transfer and flow friction characteristics inside the solar air heater duct. This investigation covers relative roughness pitch in the range of 10 ≤ P/e ≤ 25 and relevant Reynolds numbers in the range of 3800 ≤ Re ≤ 18000. Relative roughness height (e/D) is kept constant as 0.03 for analysis. The turbulence created due to additional circular vortex generator increases the heat transfer rate and at the same time there is also increase in friction factor values. For combined arrangement of ribs and vortex generator, maximum Nusselt number is found to be 2.05 times that of the smooth duct. The enhancement in Nusselt number with ribs and additional vortex generator is found to be 1.06 times that of duct using ribs alone. The maximum increase in friction factor with ribs and circular vortex generator is found to be 2.91 times that of the smooth duct. Friction factor in a combined arrangement is 1.114 times that in a duct with ribs alone on the absorber plate. The augmentation in Thermal Enhancement Factor (TEF) with vortex generator in inlet section is found to be 1.06 times more than with circular ribs alone on the absorber plate.
Highlights
A solar air heater uses clean and sustainable solar energy and converts it into usable thermal energy
The additional turbulence created by the circular transverse vortex turbulator in inlet section is found to be very effective in the vicinity of the absorber plate
The effect of relative roughness pitch (P/e) using circular transverse ribs alone on the absorber plate is studied in terms of average Nusselt number, average friction factor, and thermal enhancement factor
Summary
A solar air heater uses clean and sustainable solar energy and converts it into usable thermal energy. Solar air heaters are widely used for drying of agricultural, textile, and marine products They are used for heating of buildings to maintain a comfortable environment in the winter season. The method used to increase the heat transfer coefficient between the working fluid (air) and absorber surface is to create the turbulence inside the solar air heater duct. Saini [1] reported that the height of the roughness element should be kept small in comparison with the duct dimension This is due to the fact that the application of artificial roughness results in higher heat transfer enhancement, this arrangement causes increase in friction losses leading to excessive power requirements for the air flow through the duct
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