An extension of the foam-based heat sink, heat exchangers are used to transfer heat from a hot fluid (liquid or gas) to a cooler fluid. The two are separated by an impermeable wall, so each experiences an environment similar to that of the actively cooled heat sinks. Because foam-based heat exchangers are compact, a smaller and less expensive unit can perform as efficiently as a larger, conventional device.
Ultramet fabricated heat exchangers consisting of tungsten foam-filled tungsten tubes under a program for nuclear reactor component development funded by the Department of Energy. High heat flux testing with helium coolant was performed at the Sandia Plasma Materials Test Facility (Albuquerque, NM) using the electron beam test system.
In this test at Sandia, the part was subjected to 44 shots, which ranged from 60 to 100 seconds, with the electron beam focused at the 3.8-cm length of the foam section. The heat flux varied from 2.26 MW/m2 (226 W/cm2) to 22.36 MW/m2 (2236 W/cm2), at which point the part failed. The helium removed more than 7100 W steady state from the sample at the highest heat flux. Sandia described this result as “a world-record heat flux for a helium-cooled refractory device.” The heat flux performance of the tungsten foam/tungsten tube structure was approximately five times better than that of a tungsten tube with no foam.