Flow patterns of an air-water mixture at the exit of a micro T-junction

An experimental investigation of typical flow patterns in adiabatic gas-liquid mixture (air-water) generated in a micro T-junction varying the superficial velocity of the fluids is presented. The micro T-junction is made as intersection of two glass microchannels with a rectangular cross-section having a width of 300 mu m and a height of 256 mu m. The air-water mixture is obtained by means of an injection of air in perpendicular direction with respect to a straight stream of water. The air flow is broken in slugs having geometrical characteristics depending on the superficial velocity ratio imposed. Changing the air and water superficial velocity from 0.005 m/s up to a maximum value of 0.15 m/s, different kinds of intermittent slugs have been observed. In this way, a flow pattern map has been generated in order to reword the main characteristics of the intermittent slug flow generated after the T-junction as a function of the superficial air-water velocity ratio. In order to build the flow pattern map, 256 experimental runs characterized by different values of superficial velocity have been made. Different kinds of Taylor bubble flows have been observed during this experimental campaign: for a fixed low value of the air flow rate, by increasing the water flow rate it has been evidenced how the formation of the bubbles becomes faster and the length of the single bubble becomes shorter. A detailed discussion of the impact of the superficial air to water velocity ratio on the observed flow patterns is given.