In the framework of LHC studies, we have performed several experiments on He II co-current two-phase flow. It was found that for high vapor velocities, the heat exchange capacity between the He II flow and the pipe wall is significantly better than what can be accounted for by the liquid to wall interface of a stratified two-phase flow pattern. This seems to indicate a transition from a pure stratified two-phase flow into either a partially annular two-phase flow or a stratified two-phase flow including liquid droplets in the vapor flow or a combination of the two. In the last two cases, it is assumed that liquid droplets which get dispersed on the tube wall increase the wetted surface. A new facility has been designed to analyze this flow behavior. High sensitivity capacitive liquid level sensors glued onto the inner wall of the pipe were used in order to detect a possible semi-annular flow pattern whereas light diffraction and scattering were used to detect liquid droplets. Finally, in addition to a circumferential heat exchange box, local heat exchange boxes located at different azimuth positions are added. Description of this new facility, calibration of the local heat exchange boxes and first results are presented. ABSTRACTIn the framework of LHC studies, we have performed several experiments on He II co-current two-phase flow. It was found that for high vapor velocities, the heat exchange capacity between the He II flow and the pipe wall is significantly better than what can be accounted for by the liquid to wall interface of a stratified two-phase flow pattern. This seems to indicate a transition from a pure stratified two-phase flow into either a partially annular two-phase flow or a stratified two-phase flow including liquid droplets in the vapor flow or a combination of the two. In the last two cases, it is assumed that liquid droplets which get dispersed on the tube wall increase the wetted surface. A new facility has been designed to analyze this flow behavior. High sensitivity capacitive liquid level sensors [1] glued onto the inner wall of the pipe were used in order to detect a possible semi-annular flow pattern whereas light diffraction and scattering[2] were used to detect liquid droplets. Finally, in addition to a circumferential heat exchange box, local heat exchange boxes located at different azimuth positions are added. Description of this new facility, calibration of the local heat exchange boxes and first results are presented.
The LHC development program relies on cryogenic tests of prototype and model magnets. This vigorous program is pursued in a dedicated test facility based on several vertical cryostats working at superfluid helium temperatures. The performance of the facility is detailed. Goals and test equipment for currently performed studies are reviewed: quench analysis and magnet protection studies, measurement of the field quality, test of ancillary electrical equipment like diodes and busbars. The paper covers the equipment available for tests of prototypes and some special series of LHC magnets to come. ABSTRACTWe describe the optical techniques we used to detect droplets in the HeII two phase flow of the Cryoloop experiment. These include quantitative light scattering, imaging, and laser phase sensitive anemometry and granulometry (PDPA). We demonstrate that droplets appear for vapor velocities larger than 5 m/s, and that they progressively invade the entire pipe cross section as the vapor velocity is increased. Estimates are given for the droplet size and density.
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