A Study of Horizontal Multiphase Flow - Annular Two Phase Gas/Liquid Systems Using Eulerian Model of Fluent

Abstract

A common problem for working with two-phase flows is that of phase flow mal- distribution. This mal-distribution results in less than optimal performance and in lower product quality. To overcome this problem, engineers have performed experiments, using water and air as test fluids, with improved distribution as a result. However, the experiments are uncomfortably costly in terms of both money and time and hence, alternatives to these are welcomed. In this Master Thesis of 06 credit hours, the task undertaken was to simulate and create two-phase annular flows of water and air with the help of the CFD code FLUENT. The model used for the simulations was the Volume Of Fluid (VOF) model that adopts a homogeneous multiphase theory in which it is assumed that the phases are so well mixed that they flow with the same velocity, i.e., no slip is allowed between the phases. The reason for this was most likely due to the fact that the geometry of the pipe was in 2-D in order for the VOF model to account for surface tension effects in a proper fashion. Due to the time constraints, only horizontal flow was simulated. The parameters of interest concerned the ratio between the mass flow rate of the water phase to the mass flow rate of the water phase at the inlet as well as the establishment of the flow pattern of the two-phase flow involving annular flows. Another conclusion was that the VOF model seemed to encounter problems with flows that concerned relatively low volume fractions for one of the phases. The Lagrangian discrete phase model available in FLUENT would probably come through with better results for such conditions but no time was available to implement it in the present thesis. In conclusion, it can be stated that it is possible, given the right conditions, to perform comparatively accurate simulations concerning two-phase flows in pipe applications with the VOF model available in FLUENT.