In the line of previous work done at CEA Grenoble, large size experiments were performed with the support of CERN for the validation of the LHC two phase superfluid helium cooling scheme. In order to be as close as possible to the real configuration, a straight, inclinable 22 m long line of 40 mm I.D. was built. Very accurate measurements of temperatures and pressures obtained after in situ re-calibration and verified by independent sensors allowed us to validate our two-phase flow model. Although we focus on pressure losses and heat exchange results in relation to power injected, additional measurements such as quality, void fraction, and total mass flow rate enable a complete description of the two-phase flow. Experiments were carried out to cover the whole range of the future LHC He II two-phase flow heat exchanger pipe: slope between 0 and 2.8 %, temperature between 1.8 and 2 K, total mass flow rate up to 7.5 g/s. Results confirm the validity of choice for the LHC cooling scheme. ABSTRACTIn the line of previous work done at CEA Grenoble, large size experiments were performed with the support of CERN for the validation of the LHC two phase superfluid helium cooling scheme. In order to be as close as possible to the real configuration, a straight, inclinable 22 m long line of 40 mm I.D. was built. Very accurate measurements of temperatures and pressures obtained after in situ re-calibration and verified by independent sensors allowed us to validate our two-phase flow model. Although we focus on pressure losses and heat exchange results in relation to power injected, additional measurements such as quality, void fraction, and total mass flow rate enable a complete description of the two-phase flow. Experiments were carried out to cover the whole range of the future LHC He II two-phase flow heat exchanger pipe: slope between 0 and 2.8 %, temperature between 1.8 and 2 K, total mass flow rate up to 7.5 g/s. Results confirm the validity of choice for the LHC cooling scheme.
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.
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