Abstrakt
In this work we investigate the present capabilities of computational
fluid dynamics for wall boiling. The computational model used combines the
Euler/Euler two-phase flow description with heat flux partitioning. This
kind of modeling was previously applied to boiling water under high
pressure conditions relevant to nuclear power systems. Similar conditions
in terms of the relevant non-dimensional numbers have been realized in the
DEBORA tests using dichlorodifluoromethane (R12) as the working fluid.
This facilitated measurements of radial profiles for gas volume fraction,
gas velocity, bubble size and liquid temperature as well as axial profiles
of wall temperature. After reviewing the theoretical and experimental
basis of correlations used in the ANSYS CFX model used for the
calculations, we give a careful assessment of the necessary recalibrations
to describe the DEBORA tests. The basic CFX model is validated by a
detailed comparison to the experimental data for two selected test cases.
Simulations with a single set of calibrated parameters are found to give
reasonable quantitative agreement with the data for several tests within a
certain range of conditions and reproduce the observed tendencies
correctly. Several model refinements are then presented each of which is
designed to improve one of the remaining deviations between simulation and
measurements. Specifically we consider a homogeneous MUSIG model for the
bubble size, modified bubble forces, a wall function for turbulent boiling
flow and a partial slip boundary condition for the liquid phase. Finally,
needs for further model developments are identified and promising
directions discussed.
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