Study on Instabilities of Two-Phase He II/vapor flow in a pipe

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The aim of this research is to analyze the flow instability of multi-phase flow of liquid helium which consists of superfluid, normalfluid and vapor phase.The experimental apparatus for the generation of multiphase flow of superfluid helium is improved. It is important to shield the superfliud helium from the heat for high accuracy measurement. To protect the liquid helium from the outside heat the copper shield is added to the upstream and downstream tank and around the test section. Using this improved apparatus, the two-phase flow of superfluid helium is generated at the test section and the data of the relation between Reynolds number and cavitation number are obtained. For this reason, it is confirmed that the cavitation number is decreased as the Reynolds number is increased.Moreover, the phenomena are analyzed by the numerical method. The two-phase flow is assumed as bubble cavitation and the governing equations are constructed so that continuum equation, momentum equation and energy conservation is satisfied. These equations are solved by SMAC method and the flow structure at the nozzle is analyzed. Consequently, at the blowdown, the pressure decreases immediately and vortex is generated downstream of the throat.