Convection heat loss analysis of a wind-skirted open-cavity tubular receiver for a solar-dish Brayton cycle

• A coiled large-pipe solar dish-Brayton receiver with a wind-skirt is considered. • Naturalistic (outdoor) testing is conducted, capturing in-field ambient conditions. • Heated air is passed through at various temperatures and elevation angles. • Experimental convection heat loss is compared with correlations in literature. • Closest correlation fits the experimental convection heat loss within 3% difference. Solar-dish Brayton cycle receivers connected to radial turbomachinery usually require large pipe diameters to minimize pressure losses and improve overall cycle performance. However, most convection heat loss correlations in literature are developed for cavity receivers with isothermal assumptions, relatively small pipe diameters, and a unique receiver geometry. The current study therefore compared the similarity of prominent convection heat loss correlations in literature to experimental 5-minute steady-state results from in-field, naturalistic, heat loss testing for a solar-dish Brayton cycle receiver. A large pipe, helically-coiled, open-cavity tubular solar receiver with a wind-skirt was tested. Parametric control was exercised over elevation angles between 22.5° and 90°, average air mass flow rates between 33 g/s and 68 g/s and average inner-cavity temperatures up to 550 °C. Average ambient temperatures ranged from 13 °C to 22 °C and average wind speeds ranged from 0.5 m/s to 3.3 m/s. Results showed that the correlation providing the best fit to the experimental convection heat loss results (with an average difference of 3 %) had the unique ability to account for having a heated coil surface deeper into the cavity.