Publications Details
Test results from a full-scale sodium reflux pool-boiler receiver
A sodium reflux pool-boiler solar receiver has been tested on a nominal 75-kWt parabolic dish concentrator. The purpose was to demonstrate the feasibility of reflux receiver technology for application to Stirling engine dish electric systems. In this application, pool boilers (and more generally liquid metal reflux receivers) have advantages over directly illuminated tube receivers. The advantages include more uniform temperature, which results in longer lifetime and higher temperature available to the engine. The absorber was a 70° half-angle spherical segment with an 8.63 inches radius, positioned behind an 8.65 inches diameter aperture. The relatively small size of this receiver, which minimized thermal losses, fabrication costs, and sodium inventory, was possible because of its excellent internal heat transfer characteristics. Tests were run at sodium temperatures up to 800°C and receiver input power levels as high as 67 kWt. At maximum input power, the peak in the solar flux distribution on the absorber was calculated to be 73 Wt/cm2. Receiver efficiency was about 90% when the input power and sodium temperature were at their maximum values. To promote stable boiling, the receiver design included 35 equally spaced artificial cavities in the absorber wetted surface. In all tests, stable boiling was always observed. Under certain conditions during both real and simulated cloud transients, high incipient boiling superheats were observed. This behavior could be suppressed either actively by momentarily increasing the thermal load on the receiver or passively by the addition of a small amount of xenon into the boiler.