Gas-Liquid Two-Phase Flow through an Orifice in Millimeter-Scale Rectangular Channel

An experimental investigation is carried out on air-water two-phase flow through a plate orifice in a millimeter-scale rectangular channel. The width of the channel is kept constant at 50 mm and the height is varied from 0.19 mm to 2.00 mm. The contraction ratio of the orifice is varied from 0.04 to 0.4, and the thickness of the orifice also is allowed to vary over a wide range. The flow patterns upstream and downstream of the orifice are observed with a high-speed camera and by visual inspection. The conditions for occurrence of the observed flow patterns are presented on a flow pattern map. The velocity of the leading edge of a bubble, representing the bubble velocity, is deduced from the camera images. In the upstream part of the test section the bubble velocity is approximated by the sum of the superficial velocities of air and water. A correlation is proposed for the maximum bubble velocity in the whole test section as a function of the two superficial velocities and the contraction ratio.