| Accurately predicting the minimum gas velocity of continuous liquid-carrying and the flow-field parameters of gas-liquid two-phase flow in wet gas pipelines is essential for preventing the liquid loading and ensuring the safe and stable operation of the pipeline system.Current research in gas-liquid two-phase flow have concentrated on horizontal or vertical pipe flow,and the relevant mathematical models can reliably predict flow parameters such as the pressure gradient and liquid holdup.But these models are used for gas-liquid two-phase flow in inclined pipes,which will lead to significant bias and even errors.Under light,this paper combines theoretical and experimental research methods to analyze the flow properties,such as gas-liquid configuration,shear stress distribution and the interface fluctuations,etc.,and its mechanism of action on liquid holdup and pressure gradient at critical and supercritical conditions in inclined pipes are systematically investigated.It provides theoretical support for clarifying the two-phase flow and liquid-carrying characteristics in the pipe,solving the problem of liquid loading in the pipes,and ensuring the stable and safe operation of the wet gas system.The main contents in this psper are summarized as follows:(1)Based on the principle of minimum energy of phase equilibrium,and a new mechanistic model to predict the gas-liquid configuration is developed.The effects of wettability,surface tension,and interphase shear stress on the gas liquid distribution are comprehensively considered,and the new model can accurately predict the evolution law of gas liquid distribution in gas-liquid two-phase flow.Theoretical study found that the interface shape of gas-liquid flow with low liquid holdup is more easily affected by the wettability and the surface tension and tend to be curved interface.Liquid holdup,inclination angle,Bond number,and Weber number all have an impact on the gas-liquid distribution.The research on gas-liquid distribution lays the foundation for further in-depth research on the gas-liquid two-phase flow and liquid-carrying characteristics in inclined pipes.(2)A general mechanism model of gas-liquid two-phase flow at critical conditions in inclined pipes is innovatively established,which can accurately predict the gas-liquid configuration and critical flow parameters at the same time,and from the perspective of energy transformation in the flow process,a correction method is proposed when the new model is used in a high-pressure two-phase flow system.The experimental data and the actual data of 42 gas wells are used to verify the new model proposed in this paper.The results show that the new model can accurately predict the critical liquid-carrying velocity in pipes and wellbore,and effectively judge the liquid loading in gas wells.Theoretical model demonstrated for the first time that the critical carry-liquid velocity will reach the maximum value when the deviation angle is between 45° and 60°,and the gas well is most prone to liquid loading at this time.(3)Based on the principle of work or energy of Kelvin-Helmholtz instability theory,the mathematical model of interface fluctuation and instability of liquid film are established,and analysis provide the first insights into the mechanism underlying the mechanical properties governing interface fluctuation with inclinations.In addition to considering Bernoulli force,capillary force,and surface tension,the model also quantifies the work done by gravity on the wave interface.The results from the present theoretical investigation show that the interface wave in inclined pipes is more likely to increase the amplitude under the action of Bernoulli force,while the gravity and capillary are conducive to the stabilization of the liquid film.(4)A general mechanism model of gas-liquid two-phase flow at supercritical conditions in inclined pipes is innovatively established,which can accurately predict the gas-liquid configuration and flow parameters at the same time,and analysis revealed the mechanism of flow pattern transition from stratified flow to annular flow from the energy perspective,a correction method is proposed when the new model is used in a high-pressure two-phase flow system.The comparison with the experimental data shows that the new model can effectively predict the flow field characteristics such as gas-liquid distribution,liquid holdup and pressure gradient of gas-liquid two-phase flow with low liquid holdup in inclined pipes.(5)a detailed visualization experiment of gas-liquid two-phase flow at critical and supercritical conditions in inclined pipes was designed and carried out,and the characteristics of flow pattern,gas-liquid phase distribution,liquid-wall and interfacial shear stress distribution during gas-liquid two-phase flowwere explored:(1)The gas-liquid two-phase flow and the liquid-carrying process in inclined pipes belong to the stratified flow with low liquid holdup(ε<0.1),but at the supercritical conditions,when the liquid flow rate decreases,the stratified flow is transformed into stream flow due to the influence of wettability.(2)The experimental study found for the first time that the convex gas-liquid configuration at the critical conditions,which are valuable for the supplementation and perfection of the gas-liquid configuration in the gas-liquid two-phase flow.(3)The experiment found the linear correlation between the interfacial friction factor and the inclination angle at critical conditions,and innovatively established the calculation model of interfacial friction factor at critical conditions.(4)The experiment found for the first time the nonlinear correlation between the liquid-wall shear stress,the interfacial shear stress and the gas-liquid configuration at supercritical conditions,and established a semi-empirical relationship between the three,which provides a new idea for exploring the shear stress between the liquid and wall and interfacial shear stress in gas-liquid two-phase flow.In summary,this paper innovatively established the mechanism model of gas liquid configuration,shear stress distribution of liquid-wall and interfacial,interface wave and the instability of film interface fluctuation and liquid film instability in the process of gas-liquid two-phase flow in inclined pipelines.On this basis,a general mechanism model of gas-liquid two-phase flow is established,which can realizes the simultaneous prediction of gas-liquid phase distribution and flow parameters.The research results provide new methods and solutions for solving wellbore and pipeline fluid accumulation and ensuring the smooth and safe operation of wet gas pipelines,and promotes the study of complex nonlinear gas-liquid two-phase motion systems in inclined pipelines under the interaction of turbulent flow fields and waves.this paper innovatively establishes a general mechanism model of gas-liquid phase distribution,shear stress distribution,and gas-liquid two-phase flow in inclined pipes,which can be used for the accurate prediction of flow-field parameters and liquid-carrying characteristics at critical and supercritical conditions.The findings in this work will provide new methods and solutions for solving the engineering problems of liquid loading in wellbore and pipeline,ensure the smooth and safe operation of wet gas pipelines,and promote the study on complex nonlinear motion systems of gas-liquid two-phase in inclined pipes under the interactions between the turbulent flow field of the gas phase and waves on a laminar or turbulent liquid phase. |
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