Micro-laminated pin array solar receivers for high flux heating of supercritical carbon dioxide part 2: On-sun performance

The thermal characterization of a micro-pin solar thermal receiver (MSTR) for supercritical carbon dioxide (sCO₂) gaseous working fluid is presented. In a companion paper of this two-part study [1], the design and fabrication methodologies employed in the development of the MSTR were presented. As described in Fronk et al. [1], the MSTR is formed by a microlamination process with brazed headers to form multiple unit cell flow paths with fluid inlet/outlet ports. In this part of the study, on-sun tests to estimate the thermo-fluidic performance of the MSTRs using a parabolic dish concentrator are described for a 15 cm × 15 cm design with 6 unit cells. The MSTR is installed in a closed-loop sCO₂ test facility coupled to a seven-meter diameter parabolic dish. On-sun tests were performed at a receiver inlet pressure of up to 15.5 MPa and a receiver inlet temperature ranging between 31 to 398 °C. Receiver thermal efficiencies were calculated using an indirect estimation of the absorbed flux, by summing the convective and radiative losses and absorbed energy to the fluid. Thermal efficiency greater than 0.98 were obtained for estimated incident heat flux of 34–40 W/cm² at average surface temperatures ranging from 113 to 332 °C and peak surface temperatures of up to 550 °C. A sensitivity analysis, performed on the convective and radiative losses, indicates the lower limit of efficiency to be within 1.5 % of the estimated value. After a few hours of testing, the receiver failed due to an internal flow blockage that led to overheating. Optical and microstructure analysis is performed on the 15 cm × 15 cm and a failed 8 cm × 8 cm MSTR from prior work to identify possible reasons for failure.