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Helium cooling is an attractive alternative to water cooling for high heat flux components. Helium offers advantages from safety considerations, such as excellent radiation stability and chemical inertness. General Atomics (GA) has considerable expertise in use of helium cooling due to its high temperature gas cooled reactor experience. In order to prove the feasibility of helium cooling at high heat flux levels of above 5 MW/m2, GA designed, fabricated, and tested a helium cooled module. The module was sized to have a heat flux surface of 25 mm wide and 80 mm long due to test setup limitations on maximum deposited power. WIth a smooth flow channel, a flow rate of 0.23 kg/s, and a pumping power of 2300 W was required to keep the copper module surface temperature below 500 degrees C at a heat flux level of 10 MW/m2. Hence, different techniques were examined to enhance the heat transfer, which in turn reduced the flow and pumping power required. It was concluded that an extended surface was the most practical solution. An optimization study was performed to find the best parameters. The module with an optimized extended surface geometry was estimated to require a flow of about 0.032 kg/s and a pumping power of 50 W to remove 20 kW of power. This is more than an order of magnitude reduction in pumping power required compared to the smooth channel. The module was made from dispersion strengthened copper. The fabricated geometry was slightly different than the optimized design due to constraints of machining. The fabrication was done by electro discharge matching. The testing was carried out at the electron beam test facility of Sandia National Laboratory, Albuquerque. The specifications of the loop and the electron beam testing facility were: 4 MPa pressure, 32 g/s of helium flow, and 30 kW beam power. The testing was carried out during August 1993 and again in December 1994. The testing confirmed the design calculations.
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