Reflux pool-boiler as a heat-transport device for Stirling engines: On-sun test program results.

摘要

The efficient operation of a Stirling engine requires the application of a high heat flux to the relatively small area occupied by the heater head tubes. Previous attempts to couple solar energy to Stirling engines generally involved directly illuminating the heater head tubes with concentrated sunlight. In this study, operation of 75-kW, sodium reflux pool-boiler solar receiver has been demonstrated and its performance characterized on Sandia's nominal 75-kW parabolic-dish concentrator, using a cold-water gas-gap calorimeter to simulate Stirling engine operation. The pool boiler (and more generally liquid-metal reflux receivers) supplies heat to the engine in the form of latent heat released from condensation of the metal vapor on the heater head tubes. The advantages of the pool boiler include uniform tube temperature, leading to longer life and higher temperature available to the engine, and decoupling of the design of the solar absorber from the engine heater head. The two-phase system allows high input thermal flux, reducing the receiver size and losses, therefore improving system efficiency. The receiver design is reported here along with test results including transient operations, steady-state performance evaluation, operation at various temperatures, and x-ray studies of the boiling behavior. Also reported are a fist-order cost analysis, plans for future studies, and the integration of the receiver with a Stirling Thermal Motors STM4-120 Stirling engine. 19 refs., 11 figs.