Flow Characteristics Of Gas Liquid Two Phase Flow In Inclined Pipe Under Vibration Condition

In recent years,nuclear-powered ships and floating nuclear energy desalination equipment have developed rapidly.These devices will betilting,swing,and fluctuant in the ocean due to the influence of natural conditions.All these additional movements will affect the flow characteristics of two-phase flow in nuclear power devices.For example,the influence of the additional inertial force caused by the swing will cause the gas-liquid two-phase flow patterns and the frictional resistance to change.The vibration will change the frequency of bubble detachment on the fuel rod wall in the nuclear reactor and promote the bubbles to get together.As a result,the effective gas-liquid heat transfer area is reduced,thereby changing the flow and heat transfer characteristics in the core.In addition,the vibration caused by the earthquake poses a great threat to the nuclear reactor.In the actual operation of the power plant,there is also a phenomenon of pipe vibration.This vibration will increase the fatigue load on the pipelines,thus an accident such as a leak or equipment damage chould occurred.Therefore,the research on the vibration of gas-liquid two-phase flow is very important.Domestic and foreign researchers have conducted a large number of experimental and theoretical studies on the flow characteristics of two-phase flow in a pipe under steady state conditions,while there are few studies on the gas-liquid two-phase flow under vibration condition.Therefore,the current theory of the two-phase flow developed under the steady state condition has certain limitations.In this paper,the two-phase flow experiment apparatus and the vibration device are combined to carry out experimental research on the gas-liquid two phase flow under the vibration condition.Flow pattern images and pressure fluctuation signals under vibration condition were collected.First,according to visual observation and high-speed camera,the flow patterns of the two-phase flow in the inclined pipe under vibration condition are defined.It has been found that flow patterns are different from those under steady state conditions.There are mainly bead flow,bubble flow,fluctuant slug flow,proto slug flow and annular flow.Among them,bead flow and fluctuant slug flow are the new flow patterns discovered under this experimental condition.Secondly,change the pipe inclination,vibration frequency and amplitude then analyze its effect on flow pattern transition.The flow pattern transition diagrams show that the fluctuant slug flow area expands with the increase of inclination while the other flow pattern area are relatively reduced.The influence of vibration frequency and amplitude on flow pattern transition boundary is basically the same.The bead flow and the proto slug flow areas expand with the increase of vibration frequency or vibration amplitude.In this paper,we use the average change rate of the media superficial velocity at the time of flow pattern transition as an indicator tomeasure the degree of influence of the three change factors on the experiment results.The calculation results show that the vibration frequency has the greatest influence on the flow pattern change among the three kinds of change factors.Finally,based on the differential pressure method and multi-scale entropy theory,the collected differential pressure fluctuation signals are analyzed.The multi-scale entropy of differential pressure signal under various operating conditions was calculated by MATLAB software,and the multi-scale entropy ratio of the smaller scale was fitted.The analysis results of the differential pressure fluctuation signals of the five typical flow patterns under 95 kinds of flow conditions show that the rate of change of entropy values of different flow patterns is obviously different at the lower scale(first nine)and the high-scale entropy can reflect the dynamic characteristics of different flow patterns.