The two phase flow characteristics of helium I are of interest since under most operational scenarios this cryogenic fluid exists in both liquid and vapor form because of its extremely low boiling point and latent heat of vaporization. There is a significant knowledge gap in the flow boiling parameters of helium (heat transfer coefficient, pressure drop and dryout heat flux) for high Reynolds number vertical up-flows (Re =10^5-10^6). This dissertation fills this gap and helps to expand the use of helium as an inert simulant for hydrogen.

Since no prior correlations for the flow boiling parameters existed for vertical up-flows of helium at these Reynolds numbers, any predictions of these parameters were dependent on correlations that were tested at lower Reynolds numbers, or correlations based on other fluids. The thermophysical properties of helium I are significantly different from most other fluids; therefore the capability of prior correlations in predicting experimental observations was limited. As part of this research new correlations are proposed for the flow boiling parameters. This research begins the investigation of a new regime for two-phase helium I flows at Reynolds numbers above 3e5. The techniques described will enable future work to address other gaps in knowledge for helium I flows that still remain.

The prior heat transfer coefficient correlation over-predicted the data that was collected for this research. The new correlation improves the agreement with data by a factor of 98. Two prior models for pressure drop, the separated flow model and the homogeneous flow model, under-predict the observed pressure drop. The newer versions of the separated flow and the homogeneous flow correlations improve agreement with the data by about a factor of 3 and by more than a factor of 2 respectively. The previous dryout heat flux correlation considerably over predicts the observed dryout heat flux. The new correlation improves agreement with the data by a factor of 21.

Significant cryogenic challenges were overcome to collect the research data. The strategies described for surmounting the diverse challenges such as thermal acoustic oscillations and low dryout heat flux could be used by future two-phase cryogenic flow researchers.