Abstract: To classify the flow features of gas-liquid flow induced by the helical tape, swirling flow of gas and liquid induced by a helical tape in a circular pipe is numerically simulated, air is the primary phase and water is the secondary phase, the flow pattern is mist flow. The effects of swirl on transition of flow pattern, distribution of gas and liquid phases, velocity field and swirl decay are investigated. The results show that mist flow is transformed to annular flow under the effect of helical tape. Secondary vortices appear in the helical tape region, these vortices develop and their structures change, the liquid film is not continuous along circumferential direction of the pipe due to non-uniform centrifugal force. Away from the helical tape, fluid flows helically without secondary vortices, droplets and liquid film distribution become uniform. Gas tangential velocity value is high away from the swirling center and low near the pipe center, there is an offset between swirling center and pipe center. Compared with twisted tape and smooth pipe, the extent of gas axial velocity enhancement near the pipe center induced by a helical tape is significantly larger than twisted tape which is larger than smooth pipe. Swirl number of the swirling flow induced by helical tape increases and decays slowly compared with twisted tape.

Key words: Gas-liquid swirling flow, Helical tape, Transition of flow pattern