Effect of quartz aperture covers on the fluid dynamics and thermal efficiency of falling particle receivers

Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this work, quartz half-shells are investigated for use as full or partial aperture covers to reduce receiver thermal losses. A receiver subdomain and surrounding air are modeled using ANSYS® Fluent®. The model is used to simulate fluid dynamics and heat transfer for the following cases: (1) open aperture, (2), aperture fully covered by quartz half-shells, and (3) aperture partially covered by quartz half-shells. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting the aperture. Contrary to expected outcomes, results show that quartz aperture covers can increase radiative losses and result in modest to nonexistent reductions in advective losses. The increased radiative losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection. Quartz half-shell total transmissivity was measured experimentally using a radiometer and the National Solar Thermal Test Facility heliostat field. Average measured total transmissivities are 0.97±0.01 and 0.94±0.02 for concave and convex side toward the heliostat field, respectively. Quartz half-shell aperture covers did not yield expected efficiency gains in numerical results due to increased radiative losses, but efficiency improvement in some numerical results and the performance of quartz half-shells subject to concentrated solar radiation suggest quartz half-shell aperture covers should be investigated further.