Thermo-fluid dynamic experiment of He II cavitating flow

Abstract

We have conducted a series of experiments of superfluid helium, He II, cavitating flows. For the purpose of comparison, normal fluid, He I, flows were also examined. In the experiments liquid helium flows driven by a bellows pump were investigated by flow visualization method and PIV, and through the measurements of the temperature depression and the pressure loss. The most noticeable features characterizing superfluid cavitating flows arise from superthermal conduction, the specific heat anomaly and quantized vortices. Due to the superthermal conduction phenomena, latent heat can be supplied to cavitation bubbles from bulk liquid almost without limit, and consequently the development of cavitation is considerably rapid and in large-scale in He II. The specific heat becomes extremely large across the lambda phase transition line from He I to He II, which is known as the specific heat anomaly. In the present study, the experimental results obtained so far were examined with respect to the thermodynamic effect in He II cavitating flows referring to the Brennen thermodynamic parameter ?. It is seen that in most aspects the thermodynamic effect is negligible in cavitating flows of He II owing to the superthermal conduction. This means He II hardly behaves as a cryogenic fluid in cavitation phenomena. It is, on the other hand, found that the temperature depression is not negligible and there is apparent temperature dependence in its variation. Consequently, He II may, in some aspects, be expected to behave as a cryogenic fluid in cavitation because of extremely large void fraction.