Abstract
Abstract A roughened solar air heater is developed numerically and experimentally with a novel roughness in the absorber. The roughness incorporated is a combination of rectangular and semi-circular ribs. The analysis is done to improve the thermal characteristics considering two cases. Type A with ribs placed above the absorber and Type B with ribs placed below it. Several operating parameters are investigated including heat flux, Reynolds number (Re), relative obstacle relative height (h/H) ranging from 400 W/m2 to 1000 W/m2, 4000 to 10,000, and 0.4 to 1.0, respectively. The relative pitch is kept constant at 15 mm. The governing equations are simulated employing the renormalization group k–ε turbulence flow model. The results indicated that both Type A and Type B achieved significant improvements over the smooth duct. Type A exhibited a maximum Nusselt number of 4.24, while Type B achieved 3.93 in comparison with smooth duct at Re of 10,000, respectively. The thermal enhancement factor (TEF) ranges from 1.32 to 1.79 for Type A and 1.26 to 1.69 for Type B at a heat flux intensity of 1000 W/m2. Also at a relative height of 1.0, Type A demonstrated the highest TEF of 1.79 at Re = 10,000 and provided a maximum exergy efficiency of 11.2%.
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