Parametric Study and Heat Transfer and Performance Enhancement Coefficient Correlations of Solar Air Heaters With Different Turbulator Angles

Abstract

Abstract. Turbulent forced convection heat transfer from a flat-plate solar air heater (SAH) with multiple parameters is investigated. The SAH is equipped with 32 discrete rotatable turbulators and different surface modifications to enhance heat transfer. Independent parameters to be varied include the Reynolds number (3000≤ReDh≤13,000), solar irradiance (200≤I˙≤1000), the angle of the turbulators (0 deg ≤α≤45 deg), the non-dimensional pin height of the turbulators (HT*=0.01 and 0.02), and the non-dimensional length of the turbulators on each side (LT*=0.02 and 0.03). The developed model is capable of computing the average absorber temperature (T¯a), local absorber temperature contours, local air temperatures (Tl), magnitude of the resultant air velocity (U), pressure drop (ΔP), the average Nusselt number (Nu¯Dh), and the performance enhancement coefficient (PEC) of the SAH. The results indicate that the angle of the turbulators has a moderate effect on the heat transfer rate. Increasing the Reynolds number and the angle of the turbulators increases the average Nusselt number (Nu¯Dh). An increase in the Reynolds number initially causes a decrease in the PEC, but with further increases in the Reynolds number, the PEC switches to an upward trend. The results also indicate that longer and larger turbulator pin height contribute to an improved heat transfer rate. New correlations to calculate the average Nusselt number, the average pressure drop, and the performance enhancement coefficient for air flow within the solar air heater at different turbulator angles have also been developed. This study should provide insight and practical design guidelines of the performance of SAHs.