Numerical simulation of vapor condensation in gas-water stratified wavy pipe flow with varying interface location

Abstract

When the natural gas with vapor is flowing in production pipeline, condensation occurs and leads to serious problems such as condensed liquid accumulation, pressure and flow rate fluctuations, and pipeline blockage or corrosion. The motivation is to study phase change of vapor and liquid level change during the condensing process of water-bearing natural gas characterized by coupled hydro-thermal transition and phase change process. A hydro-thermal-mass transfer coupling model is established to investigate the mechanisms and effects of the condensation on the gas-liquid two-phase wavy flow in production pipelines. The bipolar coordinate system is utilized to obtain a rectangular calculation domain. An adaptive meshing method is developed to automatically refine the grid near the wavy gas-liquid interface which is moving continuously. Large eddy simulation model is used to calculate turbulent viscosity. The pressure gradient, liquid holdup, velocity distribution, shear stress and temperature value are predicted and validated. A good agreement is achieved when compared with experimental data. During phase change process, the numerical model is well exploited to investigate mass transfer in pipeline flow. The temperature drop along the pipe leads to the reduction of gas mass flow rate and the rise of liquid level, which results in further pressure drop. Latent heat is released during the vapor condensing process which slows down the temperature drop. Larger temperature drop results in bigger liquid holdup while larger pressure drop causes smaller liquid holdup. The value of velocity with phase change is smaller than that without phase change while the temperature with phase change is higher. The highest temperature locates in gas phase. But near pipe wall the temperature of liquid region is higher than gas region. Thus, the numerical model can be widely applied to predict the pipeline operating parameters and global fluid properties which are essential to the design of downstream equipment and the guarantee of flow assurance.