Active phase separation of He II using porous media

Abstract

Vapor-Liquid phase separation (VLPS) using a porous plug has been demonstrated in space by the Infrared Astronomical Satellite. Porous media phase separators are usually considered passive devices in contrast to the active phase separators using slits. A number of future space missions, however, require variable heat rejection capability, e.g. Gravity Probe-B and ASTROMAG. Therefore, it is the purpose of this paper to investigate the feasibility of rejecting heat loads in a wide range by controlling a valve downstream of a porous medium VLPS. A high throughput 5-15 μm bronze plug was used for the study. By the manipulation of the downstream valve(s), heat loads in the range from 0.5 W to 35 mW were expelled from the experimental cryostat. A major concern in using this technique is the fear of liquid breakthrough. As the pressure difference across the phase separator (ΔP) is reduced by throttling the valve, the thermomechanical force required to prevent breakthrough is also reduced. A separate experiment was conducted to explore this limit. Breakthrough was not detected for ΔP>1 torr in both a 2-5 μm and a 3-10 μm stainless steel plug. This method proves to be very promising for rejecting variable heat rates by using porous media as VLPS.