PIV measurements for flow pattern and void fraction in cavitating flows of He II and He I

Cavitation phenomena in both He I and He II flows were investigated through pressure measurements, the optical visualization method, and particle image velocimetry analysis. Quasi two-dimensional cavitation flows of liquid helium under nearly saturated vapor pressure condition were generated downstream of the throat of a Venturi channel and of a converging jet nozzle. At a sufficiently high flow velocity, the throat pressure falls below the saturated vapor pressure, generating vapor bubbles downstream of the throat. The pressure loss of the He II flows was almost independent of temperature and was larger than that for He I. Large differences in the void fraction between He I and He II was concluded from the result of PIV measurements. The void fraction for He II was larger than that for He I, which was found to be in good agreement with the visualization results.