New results have been obtained on the characteristics of the superfluid plug as a nonmechanical control device for supplying cold helium vapour on demand from a container of superfluid helium. The superfluid plug is a device which has been proposed for space applications to serve as a phase separator for liquid helium in the superfluid state. Typical plugs are made of a porous material having pores of one to ten pm in diameter. The experimental arrangement is such that one side of the plug is in contact with the superfluid liquid helium while vapour at a low pressure (of order 1 to 10 torr) is maintained on the other side.
The data reported here are for a plug with approximately 5/am diameter pores. Temperatures, pressures, and flow rate were monitored during the experiment. A theoretical background and steady state data are presented on mass flow rates and pressures as a function of liquid temperature.
The typical response of the flow rate to a change in heat input from a heater is an exponential rise or fall to an equilibrium flow rate which is proportional to the amount of heat input. The time constants of the exponential changes were measured for two heater control modes under study. The study has included an investigation of the important parameters effecting the dynamic response of the plug including the superfluid properties, plug material properties, plug pore size and plug permeability. Operating temperatures from 1.5 K to the lambda point were investigated and heating rates up to two watts were applied. These tests serve to demonstrate that the superfluid plug can be employed as a flow control device in a control system designed to provide coolant on demand.
Superfluid plug as a control device for helium coolant