Investigation on the Injection of Exhaust Air Into Cavity Receivers

Concentrating solar thermal (CST) systems stands out as a promising renewable energy technology, leveraging radiative heat transfer to convert solar irradiance into thermal energy. Central receiver systems (CRS), a form of CST, demonstrate potential for diverse industrial applications due to their ability to operate at high temperatures. However, optimizing their efficiency remains a challenge, particularly regarding the utilization of air as a heat transfer fluid (HTF). This study investigates the impact of exhaust air reinjection on the performance of cavity receiver systems in CST. Previous research has explored similar concepts, but gaps remain in directly modeling exhaust air return, especially in the context of cavity receivers. Using a finite element method (FEM) model this research examines various parameters affecting exhaust air injection, including injection ring height and outlet air flow velocity. Results indicate a dependency between exhaust air reinjection velocity, total mass flow rate, and the air return ratio (ARR). Higher injection velocities, coupled with increased mass flow rates, lead to greater exhaust air loss and lower ARR values. Through parametric analysis, insights are gained into the geometry parameters crucial for optimizing ARR and enhancing receiver efficiency. The highest ARR of greater than 95% is achievable when the air is injected close to the aperture in the radial directions and the fluid velocity is minimized through lower flowrates or increased inlet boundary area. These findings contribute to advancing the understanding and design of cavity receiver systems for improved renewable energy utilization.