Abstract
To enhance the thermal performance of solar air heaters (SAHs), protrusion ribs on the absorber are considered to be an attractive solution due to their several advantages. These ribs do not cause a significant pressure drop in the SAH duct and help to enhance the heat transfer to flowing air. On the other hand, a degree of roughness of the protrusion rib on the absorber can be produced by pressing the indenting device without adding additional mass. In this paper, the thermo-hydraulic performances of different roughnesses of the conical protrusion rib on the absorber plate have been evaluated by the mutual consideration of thermal as well as hydraulic performance in term of net effective efficiency. Therefore, an analytical technique has been exploited to predict the characteristics of the net effective efficiency under various operating conditions, such as the flow Reynolds number, temperature increase parameter and insolation. The effects of the conical protrusion rib roughness—namely the relative rib pitch (p/e) and relative rib height e/D) in the ranges of 6–12 and 0.200–0.044, respectively—have been evaluated. The highest value of net effective efficiency of 70.92% was achieved at a p/e of 10 and e/D of 0.0289. The optimization of the rib parameters has been carried out in different ranges of temperature increase parameters for the highest values of net effective efficiency. A unique combination of rib parameters—a p/e of 10 and e/D of 0.044—are observed to lead to the best performance when operating a solar air heater with a temperature increase parameter of more than 0.00789 K·m2/W.
Highlights
Energy demand is growing rapidly due to industrialization and urbanization, with social and cultural development leading to a large amount of energy consumption per capita
An analytical study has been conducted to predict the characteristics of the net effective efficiency of a conical protrusion rib-roughened absorber surface in an Solar air heaters (SAHs)
In order to evaluate the enhancement factor, the net effective efficiency of a roughened absorber has been compared to the net effective efficiency of a smooth absorber operating under similar conditions
Summary
Energy demand is growing rapidly due to industrialization and urbanization, with social and cultural development leading to a large amount of energy consumption per capita. The literature shows that the performance of protrusion rib roughnesses has been studied based on the useful heat gain, Nusselt number and friction factor enhancement, all of which do not determine the roughness and operating parameters for best performance. In the view of the above, it is necessary to evaluate the overall performance or thermo-hydraulic performance with the mutual consideration of useful heat gain and pumping power to propel the air through the SAH simultaneously In this present study, the net effective efficiencies of conical protrusion rib roughnesses have been evaluated to meet the following objectives: firstly, to evaluate the net effective efficiency of conical protrusion rib roughnesses using correlations of the friction factor and Nusselt number at various kinds of insolation, as published in a previous study [28]; secondly, to optimize the Energies 2021, 14, x FOR PEER REVIEW.
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