Numerical Study On Interfacial Characteristics Of Gas-liquid Churn Flow In Vertical Tube

Churn flow is an instable flow pattern appeared when the bubbles explode in slug flow. As an important flow pattern happens in the transition between slug flow and annular flow, churn flow mainly appeared in vertical and inclined tubes. Liquid phase moves up and down alternately in large diameter tubes, but the oscillation will not happen in small diameter tubes. So the churn flow is also named foam flow as it like foam in boiling condition. In addition, cause the flow pattern to include continue gas bubble like the annular flow, the flow pattern is also called after quasi annular flow. Different names show the complication of churn flow, scientists give many different models due to different cases on theory of forming and transition of churn flow. However the field of churn flow also has a lot of difficult problems. The given conclusion contains big disputes too. Aim for promoting the development of study on the gas-liquid churn flow theory, and provide scientific foundation for security analysis and the design of industrial equipments. The project focuses on the gas-liquid churn flow in vertical tubes under different conditions by means of numerical simulation.By pre processing software Gambit, a model of gas-liquid churn flow in vertical tube was created in this thesis. The simulation domain and boundary conditions were specified according to the characteristics of gas-liquid churn flow, and then the proper computational grid was exported. By software Fluent, based on the VOF model and standard k-ε model for turbulent flow, second order upwind format for difference scheme, RESTO! format for pressure discrimination, and PISO format for pressure-velocity coupling, simulate the gas-liquid churn flow in vertical tubes. The influence of gravity and pressure on gas-liquid churn flow was investigated in the simulation. The study includes air-water and refrigerant R134a vapour-liquid, and the comparison between these two was provided. Analyze the influence of physical properties on churn flow interface characteristics. The conclusion shows that the influence of gravity and pressure on the height, period and stability of gas-liquid churn flow interface wave is obvious. There is a big difference between refrigerant R134a vapour-liquid churn flow and air-water churn flow even in the same condition. The difference mainly comes from the difference of face tension.