Abstract:
This study presents a comprehensive experimental investigation into the convective heat losses of a semi-cylindrical cavity receiver, a geometry that holds considerable promise but has been inadequately explored in the context of parabolic trough concentrated solar power systems. The research systematically examines the impact of key operational and geometric parameters, including inclination angle, input heat flux, and—most critically—four distinct aperture configurations, namely Fully Open, Top, Bottom, and Center. The findings reveal a profound interdependence between aperture design and thermal performance. Specifically, increasing the inclination angle was found to expand the internal stagnant zone, thereby reducing convective loss and elevating surface temperatures; a shift from 0° to 90° resulted in dramatic convective loss reduction of up to 76 % for the Center configuration, under a constant surface heat flux of 440 W/m². The Center aperture configuration, characterized by sharp corners, was identified as the most effective for convective suppression due to a pronounced clogging effect that disrupts airflow stability. A novel dimensionless parameter, , was also introduced to quantify the ratio of the stagnant zone to the convective zone, based on the underlying stagnant and convective zone hypotheses, providing unprecedented insight into the internal aerothermal dynamics. Furthermore, an empirical correlation was developed for the Nusselt number, correlating with more than 85 % of the data points while maintaining a deviation of less than ± 20 %. This was accomplished by incorporating a new characteristic length and a Grashof number within the range of 10⁴ to 3.4 × 10⁸.
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