A numerical framework for bubble transport in a subcooled fluid flow
Journal article, 2017
In this paper we present a framework for the simulation of dispersed bubbly two-phase
flows, with the specific aim of describing vapor–liquid systems with condensation. We
formulate and implement a framework that consists of a population balance equation
(PBE) for the bubble size distribution and an Eulerian–Eulerian two-fluid solver. The
PBE is discretized using the Direct Quadrature Method of Moments (DQMOM) in which
we include the condensation of the bubbles as an internal phase space convection. We
investigate the robustness of the DQMOM formulation and the numerical issues arising
from the rapid shrinkage of the vapor bubbles. In contrast to a PBE method based on
the multiple-size-group (MUSIG) method, the DQMOM formulation allows us to compute
a distribution with dynamic bubble sizes. Such a property is advantageous to capture
the wide range of bubble sizes associated with the condensation process. Furthermore,
we compare the computational performance of the DQMOM-based framework with the
MUSIG method. The results demonstrate that DQMOM is able to retrieve the bubble size
distribution with a good numerical precision in only a small fraction of the computational
time required by MUSIG. For the two-fluid solver, we examine the implementation of
the mass, momentum and enthalpy conservation equations in relation to the coupling
to the PBE. In particular, we propose a formulation of the pressure and liquid continuity
equations, that was shown to correctly preserve mass when computing the vapor fraction
with DQMOM. In addition, the conservation of enthalpy was also proven. Therefore a
consistent overall framework that couples the PBE and two-fluid solvers is achieved.
Two-fluid
Direct quadrature method of moments
PBE
Condensation
CFD