Numerical Study on Liquid-Vapor Phase Change with Applications in Vapor Bubble Dynamics

Bardia, R. Numerical Study on Liquid-Vapor Phase Change With Applications in Vapor Bubble Dynamics. University of Wisconsin-Madison, 2020.

This thesis presents a detailed analysis of vapor bubble dynamics and the interfacial process of liquid-vapor phase change. A spherically symmetric model for a single vapor bubble is employed to present a numerical and theoretical analysis of the intermediate bubble collapse, where, in contrast to the thermally induced or inertia dominated collapse, both the effects of liquid-vapor interfacial heat transfer and the advection of the surrounding liquid play an important role. The contrast in thermal, intermediate, and inertial behavior of collapse is represented in the form of a regime map defined by two non-dimensional quantities, Bsat and ξ, which can be directly evaluated from the initial system conditions of collapse.

The same model is also used to simulate a spherically symmetric bubble growth configuration to assess the physical validity of a constant interface temperature assumption made by Highly-Resolved Simulation (HRS) studies aimed at solving flows undergoing phase change. Results show that HRS predictions are inaccurate during the initial period of bubble growth, which coincides with the inertial growth stage. A closed-form expression for a threshold time is derived, beyond which the commonly employed HRS assumptions hold.

Forgoing the limitation of spherical symmetry, the second theme of this thesis is on the development of a general two-phase flow solver that can handle the phase change process. Under a finite volume framework using a geometric Volume of Fluid (gVoF) approach, two key challenges with phase change flows have been addressed in this work, namely, (i) added deformation of the interface, and (ii) capture of velocity and pressure gradient discontinuity at the interface, both caused due to phase change. To track the interface in the gVoF scheme, an effective flux is defined that captures the effect of phase change on interface motion. This method improves upon the source term approach used in other studies. For the solution of velocity and pressure, a ghost fluid approach has been implemented, which is the first of its kind in a VoF-based phase change solver.