Split of two-phase plug flow with elongated bubbles at a microscale branching T-junction

Abstract

In the present work, the behavior of the elongated bubbles in two-phase plug flow at a microscale branching T-junction was studied both experimentally and numerically, and the effect of the bubble length on the split ratio of the gas flow to the branch was tested. The T-junction consists of a main, branch and a run with their cross section of 0.6 mm x 0.6 mm. Air and water were taken as the test fluids and the instantaneous motion of the nose, body and the tail parts of the bubbles at the T-junction region was examined in detail. Only the body part appeared longer with the longer bubbles while the shapes (and volumes) of the nose and the tail parts remained unchanged. When the body part occupied the T-junction region, the volumetric flow rates of the gas to the branch maintained constant and became almost equivalent to the total volumetric flow rate to the branch. (Similarly, when a liquid slug occupied the T-junction region, the volumetric flow rate of the liquid to the branch appeared the same with the total volumetric flow rate to the branch.) On the other hand, the volumetric flow rates of the nose and the tail parts to the branch varied drastically with time due to the complicated flow patterns around them. Thus, for given flow rates of the gas and the liquid phases at the main, the flow mal-distribution was more likely to occur with the shorter bubbles because the relative portions of the nose and the tail are larger in a unit cell, which consists of a bubble and a liquid slug. Hence, for accurate prediction of the splitting behavior of the two-phase plug flow at branching T-junctions, the length information of the unit cell is essential in addition to the flow rate of each phase at the main.