Microgravity Bubbly-to-Slug Flow Regime Transition Theory and Modeling

Abstract

In the published microgravity bubbly-slug data sets, the average critical void fraction for the bubbly-to-slug transition is observed to cluster around $\sim$0.20 and $\sim$0.45. The origin of what causes there to be two data subsets remains an open question. The $\sim$0.20 and $\sim$0.45 critical void fractions were reported by one researcher to occur during 1-g and $\mu$-g intervals on a reduced gravity aircraft, respectively. This suggests that the experiments belonging to the $\sim$0.20 data subset may have encountered undue buoyancy effects or perturbations which may have caused the bubbly-to-slug flow regime transitions to occur at prematurely low void fractions. Should this assertion hold, the ∼0.20 data subset can be treated separately from the ∼0.45 data subset, which provides a much clearer picture of the bubbly-to-slug flow regime transition. A new theory has been developed which explains the mechanics of the $\sim$0.45 data subset, for which corresponding physical and dimensionless models have been derived. The new theory and models are validated by their clear fit to the entirety of the published ∼0.45 data subset, however, they do not offer a firm explanation of the mechanics of the $\sim$0.20 data subset. This provides further indication that these two data subsets are indeed different. Further investigation into the differences between experiments and the manner in which they were conducted may explain the existence of these two data subsets.