Flow regime identification and classification based on void fraction and differential pressure of vertical two-phase flow in rectangular channel

Abstract

Better understanding of two-phase flow in narrow rectangular channels is important because it is considerably different from that in round tubes. Two-phase flow in narrow rectangular channels is invariably employed in most of the research reactors that use plate-type nuclear fuels around the world, high-heat-flux compact heat exchangers, and high-performance micro-electronics. In this study, an objective attempt was made to identify and classify various flow regimes in co-current air–water two-phase flow for vertical upward and downward direction flow inside a narrow rectangular channel. The void fraction and differential pressure data of the flow were measured. Flow regimes were identified based on visual observation, mean void fraction, and differential pressure data. A high-speed camera was used to capture images, and the void fraction was measured and analyzed by the electrical impedance method. In addition, digital image analysis was conducted, and differential pressures were measured using differential pressure transducers. Four flow patterns were identified for the vertical upward flow, and seven flow patterns were identified for the vertical downward flow in a narrow rectangular channel.