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Supercritical cryogenic hydrogen is being considered as a coolant for certain high heat flux thermal management applications, including hypersonic vehicles such as the National Aero-Space Plane and high power spacecraft systems for the Strategic Defense Initiative. The safety issues associated with hydrogen make testing with this coolant difficult and costly. Supercritical cryogenic helium is an attractive alternate coolant for prototype component testing. This paper presents a comparative analytical study of the behavior of supercritical cryogenic hydrogen and helium coolants. A detailed three-dimensional finite element analysis of a coolant channel in a test panel was used to compare the calculated heat transfer coefficient and panel temperatures for four different, commonly used turbulent flow heat transfer coefficient correlations for supercritical hydrogen and helium.

A thermal management concept providing high heat flux capability for High Power Microwave (HPM) source devices used in Directed Energy Weapon (DEW) Systems is presented. Obstacles to the practical application of DEW to aircraft require effective solutions to high heat flux thermal management. Our approach utilizes enhanced cooling mechanisms (subcooled nucleate flow-boiling) coupled with an optimized cooling channel geometry fully integrated within the HPM source device structure. The concept developed has demonstrated effective cooling for heat fluxes up to 900 W/cm2. The design and integration of our thermal management system with HPM source hardware is presented. In addition, experimental testing validating the thermal capability and demonstrating the overall operation of the HPM pulsed-power system is discussed.