Thermal performance of a dual-channel, helium-cooled, tungsten heat exchanger

Helium-cooled, refractory heat exchangers are now under consideration for f irst wall and divertor applications. These refractory devices take advantag e of high temperature operation with large delta-Ts to effectively handle h igh heat fluxes. The high temperature helium can then be used in a gas turb ine for high-efficiency power conversion. Over the last five years, heat removal with helium was shown to increase dr amatically by using porous metal to provide a very large effective surface area for heat transfer in a small volume. Last year, the thermal performanc e of a bare-copper, dual-channel, helium-cooled, porous metal divertor mock -up was evaluated on the 30 kW Electron Beam Test System at Sandia National Laboratories. The module survived a maximum absorbed heat flux of 34.6 MW/ m(2) and reached a maximum surface temperature of 593 degreesC for uniform power loading of 3 kW absorbed on a 2-cm(2) area. An impressive 10 kW of po wer was absorbed on an area of 24 cm(2) Recently, a similar dual-module, helium-cooled heat exchanger made almost e ntirely of tungsten was designed and fabricated by Thermacore, Inc. and tes ted at Sandia. A complete flow test of each channel was performed to determ ine the actual pressure drop characteristics. Each channel was equipped wit h delta-P transducers and platinum resistance temperature devices (RTDs) fo r independent calorimetry. One mass flow meter monitored the total flow to the heat exchanger, while a second monitored flow in only one of the channe ls. The thermal response of each tungsten module was obtained for heat fluxes i n excess of 5 MW/m2 using 50 degreesC helium at 4 MPa. Fatigue cycles were also performed to assess the fracture toughness of the tungsten modules. A description of the module design and new results on flow instabilities are also presented.