Performance Evaluation of a Solar Air Heater Roughened with Conic-Curve Profile Ribs Based on Efficiencies and Entropy Generation

Abstract

First and second laws of thermodynamics are well-established benchmarks to assess a thermal system. The literature revealed that efficiencies of a solar air heater are still low because the transport properties and heat transfer coefficient of the air are not superior. In the previous study, the heat and fluid flow characteristics and thermohydraulic performance of the solar air heater roughened conic-curve profile ribs were numerically examined. In the present extended work, the thermal efficiency, effective efficiency, and exergy efficiency were analytically evaluated. The entropy generation in the vicinity of the rib and the Bejan number along the length of the absorber plate were numerically analysed. These considerations aimed to provide a comprehensive evaluation and subsequent minimization of entropy generation. The impacts of the conic constant and Reynolds number on the above parameters were considered. The results indicated that decreasing the conic constant induced an increase in all efficiencies and a decrease in the entropy generation number. The maximum effective efficiency of 0.6719 occurred at a Reynolds number of 20,122, whereas the exergy efficiency of 0.01527 was obtained at a Reynolds number of 2786. The highest entropy generation due to heat transfer was found at the upstream and downstream corners of a rib and at the position just behind the detachment point. The largest entropy generation due to viscous dissipation was identified at the position in front of the rib tip. The entropy generation due to heat transfer was much higher than the entropy generation due to viscous dissipation.