Publications Details
First on-sun test of a NaK-78 pool-boiler solar receiver
During 1989-90, a refluxing liquid-metal pool-boiler solar receiver designed for dish/Stirling application at 75 kWt throughput was successfully demonstrated at Sandia National Laboratories. Significant features of this receiver included (1) boiling sodium as the heat transfer medium and (2) electric-discharge-machined (EDM) cavities as artificial nucleation sites to stabilize boiling. Following this first demonstration, a second-generation pool-boiler receiver that brings the concept closer to commercialization has been designed, constructed, and successfully tested. For long life, the new receiver is built from Haynes Alloy 230. For increased safety factors against film boiling and flooding, the absorber area and vapor-flow passages have been enlarged. To eliminate the need for trace heating, sodium has been replaced by the sodium-potassium alloy NaK-78. To reduce manufacturing costs, the receiver has a powdered-metal coating instead of EDM cavities for stabilization of boiling. To control incipient-boiling superheats, especially during hot restarts, it contains a small amount of xenon. In this paper, we present the receiver design and report the results of on-sun tests using a nominal 75 kWt test-bed concentrator to characterize boiling stability, hot-restart behavior, and thermal efficiency at temperatures up to 750°C. We also report briefly on late results from an advanced-concepts pool-boiler receiver.