Velocity measurements of the buoyancy-driven exchange flow between helium and air through a small opening

In this paper, experimental results of visualization and velocity measurements of the buoyancy-driven exchange flows through the small opening are described. This type flow might be caused by a pipe rupture accident in a high temperature gas cooled reactor. After helium gas had been filled in the test cylinder, the cap covered the top of the opening was abruptly removed. Then an ascending helium current issuing from the opening and an entering air current into the test cylinder were occurred. The ascending flows seeded with fine particles were illuminated by sweeping beam scanned by a polygon mirror in vertical and horizontal planes. And multi-exposure specklegrams of the flows were recorded on the films. The velocity vector diagrams of the helium current were obtained from the specklegrams by means of Young's fringe method. Experimental results show that maximum velocity of helium current depends on the shapes of the opening with/without throat. (author)