CFD modeling for subcooled flow boiling: Actual state and parametric variations

For CFD modeling of subcooled flow boiling the Euler/Euler two-phase flow description with heat flux partitioning has been proven to be very successful to analyse experimental data. Robust predictive capabilities of the modeling however require that it is validated for a wide range of parameters. Suitable experiments should yield sufficient information for the verification of the microscopic details of the models. In the presented investigations experiments at the CEA facility DEBORA were investigated in which a vertical pipe was heated from the side wall. Measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size were performed. A comprehensive sensitive study of the wall boiling model showed that quantities with a strong influence on the amount of produced steam are the bubble size at detachment and the nucleation site density. In the paper the potential of the application of a population balance model is demonstrated. The measured gas bubble size profiles show an increase of the bubble size with increased distance from the heated wall caused by bubble coalescence. Furthermore the model framework is shown to be able to describe a shift from wall peak to core peak in the radial gas volume fraction profiles with increasing inlet temperature respective decreasing subcooling temperature.