Behavior of the Density Interface of Helium Stratification by an Impinging Jet

This study observed the breakup of helium stratification, which was 30 vol % helium in air and formed in the upper part of a cylindrical test vessel with a height of 9.5 m and a diameter of 3.4 m. An air jet collided with the density interface on which the restoring buoyancy of the helium and the disturbing inertial force of the impinging jet were balanced. The Reynolds number of the jet was about 20 000 at the exit of a vertical pipe located 3.0 m below the initial stratification. The helium concentration was measured by sampling the gas mixture with thermal conductivity analyzers. Particle image velocimetry (PIV) visualized the flow field of the jet impinging on the density interface. The density interface was clearly shown by the binary images generated from the number of tracer particles for the PIV. From the continuous impinging jet, the density interface gradually moved upward. The interaction Froude number, which was defined by the ratio of the inertial force of the impinging jet to the buoyancy of a light gas on the density interface, was about unity calculated by the helium concentration and the flow visualization. The density interface went up to 0.0002 m/s.