Analysis and Correlations of Geometrical Aspects of Solar Air Heaters With Different Turbulator Angles

Abstract

Abstract. In this article, turbulent forced convection heat transfer in different geometries of solar air heaters (SAHs) where turbulators are set at different angles is investigated for best thermal performance. Six turbulator arrangements are examined (labeled G1–G6), and a comprehensive analysis is presented. Each configuration is equipped with 32 discrete, rotatable turbulators, along with various surface modifications designed to enhance heat transfer. The model developed is validated using experimental, numerical, and correlation data from the published literature. The performance is measured in terms of the Reynolds number (3000≤ReDh≤13,000), solar irradiance (200≤I˙≤1000), and the turbulator angle (0 deg ≤α≤ 45 deg). The model developed can predict several key thermal and flow parameters, including the average absorber temperature (T¯a), absorber temperature contours, local air temperature (Tl), magnitude of the resultant air velocity (U), pressure drop (ΔP), average Nusselt number (Nu¯Dh), and the performance enhancement coefficient (PEC). The model outcomes reveal that the turbulator angle exerts a noticeable influence on the heat transfer rate. Both the Reynolds number and turbulator angles are found to positively correlate with the average Nusselt number (Nu¯Dh), indicating enhanced heat transfer by convection at higher flowrates and larger turbulator angles. This is especially true for the G1 and G3 configurations due to enhanced flow disturbance and the more effective mixing associated with these two configurations. Additionally, increasing solar irradiance is observed to slightly reduce the Nusselt number. This is the case primarily due to the elevated initial surface temperature, which reduces the temperature difference between the heated surface and the airflow. Analysis of the PEC further confirms that G1 consistently outperforms the other configurations, achieving PEC values up to 2 at α=45 deg and high Reynolds numbers. Despite a general decrease in the PEC at moderate Reynolds numbers, the PEC increases again at higher flowrates due to the fact that the increase in thermal gains outpaces the increase in the frictional pressure drop. Overall, the findings highlight the critical role of turbulator geometry and angles. The developed correlations are derived to calculate the average Nusselt number, the average pressure drop, and the performance enhancement coefficient for various configurations, turbulator angles, and their effects on air flow within a SAH in various turbulator settings.