Study On Flow Mechanism And Measurement Method Of Pseudo-Slug Flow

With the development of the gas-liquid two-phase flow dynamics theory and the continuous improvement of two-phase flowrate measurement requirements,the importance of pseudo-slug flow research has become increasingly prominent.It is very difficult to accurately measure the characteristic parameters of pseudo-slug flow because of the high complexity and randomness of the gas-liquid two-phase space-time distribution.This paper focuses on the theoretical analysis and experimental research on the flow mechanism of horizontal pseudo-slug flow and gas-liquid two-phase flowrate measurement.The main research contents are as follows:First,a set of controllable pseudo-slug flow generation device and visual measurement system are developed.The device can form pseudo-slug flow with different liquid-slug body lengths and occurrence frequencies in the experimental pipeline.Meanwhile,the software and hardware systems ensure the safe,controllable and intelligent operation of the experiment.Combined with a high-speed camera shooting system,a 16*16 wire-mesh imaging sensor and conductance ring velocity measurement system are used to conduct experimental research on the horizontal pseudo-slug flow from different aspects.Secondly,the flow mechanism of horizontal pseudo-slug flow is studied.By means of the controllable pseudo-slug flow generation device,two typical pseudo-slug flow patterns,long-aerated and instant-aerated pseudo-slug flow are observed using high-speed camera capture,wire-mesh radial and axial imaging.Both of them have the intermittent flow characteristics.The gas-liquid two-phase spatial and temporal distribution evolution characteristics are that the gas penetrates the pseudo-slug body,and exists continuously in the pipeline.With the increase of the superficial gas velocity and liquid volume fraction,the volatility of void fraction increases,and the frequency of liquid-slug body occurance increases.The experimental data of the conductance ring velocity measurement sensor confirm that there is a significant slip between the gas and liquid in the pseudo-slug body region,which is the most fundamental feature to distinguish the traditional slug flow from the pseudo-slug flow.Thirdly,when predicting the pressure drop,the Venturi sensor is split into four parts according to its geometric structure,which includes straight tube section,convergent section,throat section,and divergent section.The pressure drop of the straight tube section before and after is mainly affected by the friction between the gas and the pipe wall and the friction between the gas and liquid.A drift flux model based on the ? correction coefficient is established when predicting the void fracion in the convergent section.The fluid flow inertia on the change of static pressure at the junction of convergent section and throat section is considered for the pressure drop in the throat section.In the divergent section,a boundary layer prediction model based on the weight coefficient ? is established for the existence of inverse pressure gradient.Based on the above analysis,a set of Venturi pressure drop prediction model is established.Compared with the experimental data of Venturi with three deifferent diameters of 50 mm,80 mm,and 100 mm,the pressure drop prediction error is within ±15%.Finally,based on the pressure drop theory and experimental research,the flowrate measurement model of gas-liquid two-phase in pseudo-slug flow is established by using a single Venturi.The time domain signal analysis shows that the differential pressure signal contains much information of the pseudo-slug flow.The Fourier transform and multi-scale wavelet transform are used to analyze the convergent differential pressure.According to the characteristic law of time-frequency domain,a "film-slug region wavelet threshold model" is proposed.Based on the time-average information and pulsation information of the convergent differential pressure,a volume gas fraction prediction model in the liquid-slug body is established.Based on this,a set of two-phase flowrate measurement model is established to realize the effective measurement for the gas-liquid two-phase flowrate in the pseudo-slug flow.Compared to the experiment,the confidence probability of ±10% relative deviation band is 97.78% for the gas,and the confidence probability of ±20% relative deviation band is 95% for the liquid.