Heat-Pipe reflux receivers have been identified as a desirable interface to couple a Stirling engine with a parabolic dish solar concentrator. The reflux receiver provides power uniformly and nearly isothermally to the engine heater heads while de-coupling the heater head design from the solar absorber surface design. Therefore, the heat pipe reflux receiver allows the receiver and heater head to be independently thermally optimized, leading to high receiver thermal transport efficiency.
Dynatherm Corporation designed and fabricated a screen-wick heat-pipe receiver for possible application to the Cummins Power Generation, Inc. first-generation 4kWe free-piston dish-Stirling system, which required up to 30 kWt. The receiver features a composite absorber wick and a homogeneous sponge-wick on the aft dome to provide sodium to the absorber during hot restarts. The screen wick is attached to the absorber dome by spot welds. Refluxing troughs collect the condensate in a cylindrical condenser and return it directly to the absorber surface. The receiver was fabricated and lamp tested to 16 kWt throughput by Dynatherm.
The receiver has been tested on Sandia's 60 kWt solar furnace to a throughput power of 27.5 kWt and vapor space temperature up to 780°C. Infrared thermography was used to monitor the entire absorber dome for impending dryout while the receiver was tested. The receiver was started using solar input, without the assistance of electrical pre-heaters. The power was extracted with a gas-gap cold-water calorimeter to simulate the operation of a Stirling engine.
The receiver design, thermal performance analysis, flux distribution analysis, test results, and post-test analysis are presented.