Numerical Study On Gas-liquid Two-phase Flow Regimes In Capillary

In this thesis,the characteristics of gas-liquid two phase flow pattern,Taylor flow and flow boiling heat transfer in capillary were simulated and studied.Adopting appropriate VOF models and research methods,we will investigate the influence of the external structure and fluid property on the gas-liquid two-phase flow pattern,and also analyze the characteristics of the flow boiling heat transfer in the capillary.In this paper,a standard quadrilateral mesh method was adopted,we can accurately capture the interface of the gas-liquid two-phase flow by strictly encrypting the mesh on the wall.By using the VOF model in the FLUENT solver,the two-dimensional numerical simulation of gas-liquid two-phase flow in the T type capillary was carried out.We have simulated the flow pattern and the Taylor flow under different gas and liquid phases,and we draw the flow diagram that the velocity of gas-liquid two phase is horizontal coordinate and vertical coordinate.The simulation results are compared with the experimental data of the gas-liquid two-phase flow in circular micro channel,and the results are very consistent with the experimental data when the gas-liquid two phase at a low rate.In addition,by changing the equivalent diameter of the capillary at a certain rate of gas-liquid two-phase flow,We observed the variation of the length of the gas-liquid column in the Taylor flow,and found that the simulation values we obtained,predictive values of correlation,and the previous experimental values were very consistent in a certain range,which further illustrates the rationality of the calculation model of this paper.By establishing a suitable calculation model of gas-liquid two phases and twodimensional mathematical model,parameters such as viscous force,surface tension,contact angle,inlet geometry and wall roughness are changed to analysis their effects on the flow characteristics of Taylor flow in the capillary.The simulation studies show that the effect of surface tension on Taylor flow is very small,while the differences of geometrical structure of inlet of the capillary will make the two phases in the Taylor flow different.The change of the contact angle of the wall will make the Length of gas-liquid column in Taylor flow presents linear variation of the concavefunction.With the increase of viscosity,the Length of gas-liquid column in capillary will decreased,the change of wall roughness will directly affect the flow pattern of Taylor flow in the capillary.We conduct simulation studies of flow boiling heat transfer in capillary tubes,the flow pattern of gas-liquid two-phase flow in tube of flow boiling was analyzed.and the temperature changes in capillary under the condition of flow boiling and the movement of bubbles in the tube were investigated,then we found that the majority of the mainstream temperature in the capillary is close to the saturation temperature of working fluid during the process of flow boiling,The flow pattern in the pipe is changed from single phase flow to bubble flow and slug flow.Finally,due to the phase change of the working medium,the changing back to single-phase flow pattern.The bubbles in capillary the can also be merged,separated,re-merged and re-separated repeatedly.