Superfluid transport and its applications in space

Various transport modes in superfluid helium are discussed in this paper. They include zero net mass flow (ZNMF) and finite mass flow (FMF) for pure superfluid and normal fluid flow. An attempt is made to characterize these transport modes in a common frame of reference. Two dimensionless numbers are used, namely the dimensionless heat flux number and the dimensionless driving force number. The equations are generalized by the use of a characteristic length so that they can be applied to the transport of He II in any geometry. The theories are then extended to applications in space. In particular, fountain effect pumps (FEPs) and superfluid management at zero g by vapour—liquid phase separators (VLPSs) will be discussed in detail. While transport in a phase separator is close to that of ZNMF, the flow in a FEP belongs to the FMF mode. The transport modes of the above systems using porous media are found to be strongly size dependent. For VLPSs, the heat rejection rate is proportional to the square root of plug permeability, K P. As in the case of FEPs, the volumetric flow rate is inversely proportional to K P. These findings are supported by ZNMF data in capillaries and FMF (gravitational flow) data in millipores, respectively.