Effect of Inlet Conditions on Taylor Bubble Length in Microchannels

The effect of inlet conditions on the frequency and size of the bubbles that form during gas-liquid Taylor flow in microchannels is investigated in this paper. Three different inlet configurations, T-, Y-, and M-junction, and three test channels with hydraulic diameters 0.345 mm, 0.577 mm, and 0.816 mm were used. The test fluids were nitrogen and water or octane, which have different surface tensions. It was found that bubble length increased with increasing gas flow rate, gas inlet size, and liquid surface tension and with decreasing liquid flow rate. From the different inlet configurations, the M-junction resulted in the largest bubbles and the Y-junction in the smallest ones, particularly at low liquid flow rates. Bubble lengths calculated from experimental bubble formation frequencies were tested against a number of literature correlations but the agreement was not very good. Two new correlations were developed for the T- and the Y-junctions to calculate the unit cell (one bubble and one slug) frequency, from which the bubble length can be found. Bubble lengths predicted from these correlations were in good agreement with experimental ones obtained from video recordings.