  Selective withdrawal is a desired phenomenon in transferring oil from large
caverns in US Strategic petroleum reserve, because entrainment of oil at the
time during withdrawal poses a risk of contaminating the environment. In order
to predict a critical submergence depth at a critical flow rate, a selective
withdrawal experiment at a high Reynolds Number was conducted. A tube was
positioned through a liquid-liquid interface that draws the lower liquid
upwards. Analysis of the normal stress balance across the interface produced a
Weber number, utilizing dynamic pressure scaling, that predicted the transition
to entrainment. An inviscid flow analysis, using Bernoulli's principle,
assuming an ellipsoidal control volume surface for the iso-velocity profile
produced a linear relationship between the Weber number and the scaled critical
submergence depth. The analytical model was validated using the experimental
data resulting in a robust model for predicting transition from selective
withdrawal to entrainment.
