Flow Patterns of Gas-Liquid Two-phase Flow through an Abrupt Expansion in Millimeter-Scale Rectangular Channel

The effect of an abrupt expansion on the flow pattern of air-water two-phase flow in a millimeter-scale rectangular channel was investigated. The channel height was fixed as 0.19 mm, 0.50 mm, 1.00 mm and 2.00 mm. The expansion ratio was 5, 2.5, 1.67 and 1.25 for every channel height. The superficial velocity of air was varied from 5.0 cm/s to 80.0 cm/s and that of water was varied from 10.0 cm/s to 80.0 cm/s. As a result, a flow pattern with recirculation zone was observed in the channel height of 2.00 mm and 1.00 mm. This is the same pattern as that in the conventional scale pipes and ducts with an abrupt expansion. Furthermore, there was no effect of an abrupt expansion on the flow pattern when the expansion ratio was close to unity. On the other hand, in the channel height of 0.19 mm, each bubble spread in the lateral direction after it passed through the abrupt expansion. This is an interesting phenomenon in the small channel height