| Gas-liquid two-phase flow system is widely used in nuclear power generation,long-distance petroleum transportation,chemical pressure vessel equipment operation,etc.As the most important part of gas-liquid two-phase flow system,flow pattern affects the accuracy of flow parameter measurement and the operating characteristics of the mobile system.Therefore,studying the gas-liquid two-phase flow pattern in tubes plays a crucial role in improving energy efficiency.Experts and scholars at home and abroad have accomplished a lot of visualization experiments of gas-liquid two-phase flow patterns in horizontal tubes.However,due to the limitation of experimental conditions,research on gas-liquid two-phase flow patterns in different media,different tube diameters and different inclination angles are less studied,hence,technical support for practical applications such as natural gas transmission,nuclear reactors,steam generators,micro-reactors and boiler inclined cross-pipes can't be provided.In summary,studying the influence of different media,tube diameter and inclination angles on gas-liquid two-phase flow pattern in tubes with numerical simulation method has certain theoretical significance and practical application value.Firstly,the VOSET method with high interface capture capability is used to numerically simulate the gas-liquid two-phase flow pattern of different media in the vertical tubes.The flow pattern is drawn to analyze the influence of changing media on the flow transition boundary and the corresponding flow pattern transformation relations are modified.The results show that the change of the flow boundary between slug flow and bubble flow is the most obvious in the process of changing medium,and it has a positive correlation with the change of viscosity.The flow boundary between annular flow and tow annular flow is the least affected by the change of medium.Then,through the numerical simulation of the change of tube diameter,it is found that with the increasing of tube diameter,the area of Taylor flow in the flow pattern gradually decreases,and area of bubble flow gradually increases.The flow boundary between Taylor flow and bubble flow is the most sensitive to tube diameter variation.In small diameter tubes,there is almost no bubble flow,and the transition of flow pattern boundary between churn flow and annular flow is different from the ones in conventional tubes.The length of the Taylor bubble in Taylor flow is positively correlated with the tube diameter,and increases with the increasing of gas phase velocity.In large diameter tubes,annular flow does not exist when turbulent flow exists in tubes with diameter over 150 mm.Finally,the numerical simulation of the gas-liquid two-phase flow pattern in different inclination angles shows that,stratified flow only exists in horizontal tubes.Wavy flow and intermittent flow transform into the churn flow in vertical tubes.Changing of the inclination angles has the greatest influence on the transition from slug flow to churn flow.The variation of inclination angle from 0° to 30° influences the flow pattern boundaries most in the flow pattern map.As the incliantion angle increases,the area of the annular flow and the bubble flow in the flow pattern gradually increases,and the area of the slug flow gradually decreases.The research conclusions above make furthermore improvement on the trend of gas-liquid two-phase flow pattern transformation under different conditions and establish the theoretical basis of gas-liquid two-phase flow pattern.Certain reference value for practical engineering applications is brought as well. |
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