SBIR-STTR Award

Separating liquid droplets from the boiler output to provide a high-quality vapor stream for the turbine of a Rankine cycle power system is difficult in space because of gravity, size, and weight considerations. Entrained liquid droplets cause rapid erosion of the turbine blades and reduce the system's reliability. A porous metal barrier is used as a vapor-liquid separator. The basic concept is that the liquid impinging on a porous metal surface can flow through it to a lower pressure regime whereas vapor flow is restricted because of capillary forces. When the lower pressure side of the porous surface is coupled to a jet pump, so designed that it can recirculate the liquid flow, then a compact and reliable vapor-liquid separator having no moving parts is available to the Rankine cycle space power source. Phase I of this research is devoted to examining specific design concepts using a variety of porous materials, geometries, and working fluids. Both the direct-cycle potassium-cooled reactor system and the lithium-potassium reactor system will be examined. The porous barrier location may be at various locations or combinations thereof, including the boiler outlet, piping sections, or specific locations in the turbine. Experimental data from gaseous diffusion barrier technology and from low-gravity (aircraft flight) tests of the medium power reactor experiment (MPRE) will be used. Viable materials and geometries will be assembled and tested during Phase II using water-steam mixtures. Arrangements will be made with the Oak Ridge National Laboratory to test some liquid metal systems in existing facilities. These Phase II tests shall include those systems deemed viable for space applications and those considered commercially attractive.Anticipated Results/Potential Commercial Applications as described by the awardee:Theoretical and empirical proof that a porous metal barrier can be used to separate liquid from the vapor-liquid output of a Rankine cycle space power system will be provided. Feasibility of this concept can lead to longer lived, more reliable, and less expensive space power systems. It may also have applications in ground based large steam turbines and in detection devices such as quality meters for liquid metal systems.

The Phase I analysis of the potential usefulness of a porous membrane to control free liquid surfaces in micro-gravity produced promising results. Three primary objectives set forth in the Phase I proposal were met, and four additional objectives were established and met. Based on this work we concluded the following: (I) high quality porous materials are now available commercially to facilitate development of the Membrane Liquid Trap (MLT); (2) permeability and vapor-breakthrough limits are adequate to permit compact, effective designs; (3) removal of liquid droplets larger than 30,*m will avoid turbine erosion, and this can be done effectively with the MLT; (4) promising geometries of an MLT were conceived and were selected for testing in Phase II, each of them having its own desirable performance characteristics (moreover, a concept for moisture removal from turbine stator blades using an MLT arrangement was developed that reduces sensitivity to droplet ingestion); (5) computer analyses of droplet trajectories in candidate geometries predicted as high as 99% efficiency in droplet mass removal; (6) air-water testing of candidate geometries in Phase 11 will give adequate measurement of performance in water-steam and potassium liquid-vapor applications. Based on these results, viable materials and geometries will be assembled and tested during Phase II using water-steam mixtures. Arrangements will be attempted with the Oak Ridge National Laboratory to test some liquid metal systems in existing facilities. The Phase 11 tests will include systems deemed viable for space applications and those considered commercially attractive.Anticipated Results/Potential Commercial Applications as described by the awardee: It is anticipated that demonstration of adequate performance of the MLT will yield confidence in its potential for application in a direct Rankine cycle space power system and that the possibility of its use in a terrestrial power system will be quantified. MLT application in a space power reactor would permit a system with higher power, lighter weight, and higher reliability than previously thought possible. MLT application in a terrestrial power system would result in smaller BWR vessels, PWR steam generators, smaller moisture separator/reheaters, and extended life for turbine blades. Either application will result in expanded markets for commercial suppliers of membrane materials which are currently focused on ultrafiltration applications.Topic 13: Space Nuclear Power Technology and Systems Concepts