A Liquid Helium Film Heat Pipe/Heat Switch
We report on the development of a compact, high conductance heat pipe/heat switch using liquid helium and a wick material. As a heat pipe its operation is similar to that of capillary pumped loop heat pipes except that it is very small. The device is also used as a heat switch by attaching a getter which can be heated. The helium is desorbed from the getter heating to ~35K by using a small (< 3mW) power and the switch is then on. The on state conductance of the first device tested was over 400 mW per Kelvin at 1.8K. Unheated, the getter quickly cools and adsorbs enough helium so that the heat switch turns off. For the first device tested the switch turned off at a getter temperature of 24K. The off conductance was 3.5 microwatts per Kelvin at 1.5K. This first version had a maximum heat flow capability of 4 mW. Future switches will be designed for a larger temperature and heat flow operating range and decreased off state conductance. This device was designed to replace gas-gap heat switches currently used in adiabatic demagnetization refrigerators.
KeywordsHeat Pipe Liquid Helium State Conductance Mass Transport Rate Helium Film
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- 2.A.T. Serlemitsos, M. SanSebastian, and E. Kunes, Final design of the Astro-E XRS ADR, submitted for publication in Adv. Cryo. Eng. 43.Google Scholar
- 5.I. Rudnick, On the thickness, Doppler shift, superfluid density and critical velocity of a flowing unsaturated helium film, in: “Liquid and Solid Helium,” C. G. Kuper, S. G. Lipson, and M. Revzen, eds. Wiley and Sons, New York (1975), p. 311.Google Scholar
- 7.P. J. Shirron and M. J. DiPirro, Suppression of superfluid film flow in the XRS helium dewar, submitted for publication in Adv. Cryo. Eng. 43.Google Scholar
- 8.D. Finotello, Y.Y. Yu, and F.M. Gasparini, Universal behavior of 4He films as a function of thickness near the Kosterlitz-Thouless transition, Phys. Rev. B 41:10994 (1990). The fact that the superfluid transition is suppressed for thin films is, of course, well established. In this reference a film of 5.06 nm thickness had a superfluid transition temperature of 2.011K. Even though 1.92K is lower than this temperature and a 5.06 nm film still only represents less that 1% of the total helium in the system, a much thicker film may be required to carry the relatively large heat load used in our tests.Google Scholar