HeII co-current two phase flow at high vapor velocities

In the framework of LHC studies, we have performed several experiments on HeII co-current two-phase flow. It was found that for high vapor velocities, the heat exchange capacity between the HeII 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 semiangular flow pattern whereas light diffraction and scattering were used to detect liquid droplets. Finally, in addition to a circum...