Experimental Study On Gas-liquid Two-phase Flow Patterns In Long-distance Water Pipe

Long-distance water pipes inevitably exist a large number of gas. It may resultin six kinds of gas-liquid two phase flow patterns in the process of system runningthat include stratified flow, wave flow, slug flow, plug flow, bubble flow andannular flow. Gas-water two phase flow may produce large pressure fluctuation andpipeline vibration, and even causes pipe broken. Study on gas-liquid two phase flowpatterns in long-distance water pipe, will help us to deepen understanding on theinteraction and the influence between gas and water in the water supply pipe. At thesame time, it has a positive significance to reduce pipe burst and water leakage, etc.This paper designs and builds a long-distance water pipe test platform, andtaking air and water as two phase medium, using means such as pressure, flowmeasurement and photography, does experimental study on the gas-liquid two phaseflow, and obtains flow pattern imagines of the inner diameter90mm pipe system,and extracts the gray-level histogram features. According to a lot of experimentalresults, this paper draws the flow pattern maps, gives the appearing scopes ofdifferent flow patterns. The flow pattern maps when adjusting the head and endmotorized valve are different, and flow pattern transition boundary is a variationrange.For different flow patterns at different positions of the pipeline system, thispaper obtains the curves of pressure fluctuation, and analyzes their relationship. Theresults show that compared with single water phase flow, average pressurefluctuations have little difference when the volume flow of gas and water changes;when trace gases (0.3~0.5m~3/h) exist in the pipes, the standard deviation of pressurefluctuations is less than single water phase flow. In addition, when the volume flowof gas and water reaches some value, the pressure standard deviation is largest, andpipeline vibration is severe.Finally, pump boundary condition of the pump-stopping process is establishedcombined with the water pump characteristic curve. Through the experiments, thispaper analyses the impacts on pump-stopping pressure fluctuation of the water flowand air flow, the results show that when the water flow is small, by adding gases, thedramatic change of pipe pressure can be eased, while not very obvious when thewater flow is large.