Two-phase visualization at cryogenic temperature Original Research Article

This paper presents two different applications for two-phase visualization at low temperature. In the first application, a CCD video camera located inside vacuum is directly supported by the Pyrex pipe containing a two-phase superfluid flow. In the case of slightly positive slopes in which the flow is co-current but ascending, two different flow patterns have been seen, stratified and intermittent, depending on the vapor mass flow. Experimental investigations from stratified to intermittent flow have been made visually and compared to a code derived from the Taitler/Dukler model. The second application concerns phase transition of hydrogen near critical point (33 K) in zero gravity. The experiments have been performed in a cryostat equipped with a 10 T superconducting coil allowing the gravity compensation for hydrogen. Images of the condensation cell are shifted to the top of the cryostat with a specific cryogenic endoscope because CCD cameras do not work in high magnetic fields. The sample was enlightened with diffuse or parallel (coherent) light using a second endoscope. Images obtained in this apparatus are similar with those obtained in space.