Effect of a new synthetic bubble model on forces in simulations of two-phase flows in tube bundles

Abstract

In this paper, the influence of the phase distribution imposed as an inlet boundary condition in a two-phase flow simulation is investigated. Firstly, a new inlet model is proposed which defines a transient inlet boundary condition to be applied in a subsequent Eulerian simulation, more specifically using the Volume-Of-Fluid method. This inlet model is aimed at generating large gas bubbles, making a Lagrangian approach less applicable. The new model, which is coined the “Synthetic Bubble Model” (SBM), generates a transient inlet condition with large gas bubbles such that there is no need for bubble creation through break-up of a continuous gas jet in a long inlet region upstream of the region of interest, which results in a smaller computational mesh. This model is applied on a 5-by-3 tube bundle subjected to an axially flowing air/water mixture and compared to a simulation with a precursor-domain in which bubbles are created by break-up of air jets imposed at the inlet. Compared to the precursor domain simulations, the SBM is both faster and more or equally accurate. Secondly, a tube bundle subjected to two-phase cross-flow is modelled. It is shown that the SBM yields better correspondence with the experimental force data than a steady inlet condition, in this case without addition of a precursor-domain (yielding a similar computational time for both simulations).