Study On Interface Instability Of Gas-shear-thinning Fluid Two-phase Churn Flow

Gas-liquid churn flow is characterized by the liquid frequently oscillating up and down and the presence of droplet entrainment with the complex evolution of gas-liquid interface.The gas-shear-thinning fluid two-phase churn flow exits widely in industrial applications,which is of great significance for the safe and reliable operation of the system.However,there is little research about.Therefore,it is necessary to study on the interface instability mechanism in gas-shear-thinning fluid churn flow.Based on Kelvin-Helmholtz instability,this paper study the instability of interface in the shear-thinning non-Newtonian fluid churn flow by mechanism modeling method.And the criteria and models of slug-to-churn flow pattern transformation and droplet entrainment are established as the more application of the gas-liquid phase instability.The main work and conclusions are as follows.(1)Based on interface instability,the mechanism model of gas-non-Newtonian fluid interface instability in churn flow is built used the power law model.Orr-Sommerfeld equation(O-S equation)of non-Newtonian fluid compared with O-S equation of Newtonian fluid,which shows the influence of two-phase flow on film stability,is used to verify the gas-non-Newtonian liquid interfacial instability model.(2)It is proposed that the wake effect and flooding theory was considered in the slug-to-churn flow pattern transition effects mechanism,which takes into account the effect of the liquid which feed into falling film because of the shrinking liquid slug.The generation,growth and motion model of huge wave on falling film is established which bases on the interface instability analysis and the force analysis of the huge wave.And the criterion for slug flow to churn flow is characterized by the appearance of the most dangerous wave.According to experimental data in literature and my own experiment data,the parameter x of gas-water two phase flow is 0.4 and of gas-non-Newtonian two phase flow is 0.37,which is defined as the radio of the amplitude of the most dangerous wave and pipe diameter.It proves that rheological property of liquid also influences the criterion of flow pattern transition,but the degree of shear-thinning has little influence on the criterion.And the transition boundary moves down with the decrease of pipe diameter or the increase of pressure.(3)Also based on the interface instability analysis,the droplet entrainment model is built up for different pipe diameter by using the forces analysis on the wave crest region.And the influence mechanism of rheological property on the critical wavelength for interface instability and droplet entrainment rate in churn flow are analyzed: with the enhancement of shear thinning characteristics,the critical wavelength increases,the droplet entrainment rate decreases.