A bulk nucleation model for flashing applications

Abstract

Modeling flash evaporation cases is challenging due to their occurrence in high temperatures and mass flow rates, along with mass transfer taking place in a narrow region of space. As an improvement to the previous Limited Evaporation model, which was based on the normalized critical work of nucleation, a new Bulk Nucleation model based on Classical Nucleation theory is developed and tested in comparison with liquid–vapor evaporation experiments conducted at the Brookhaven National Laboratories. The original theory is modified to take into account the cluster size formed during nucleation and a minimum threshold of vapor volume fraction required to trigger large-scale mass transfer. The Bulk Nucleation model shows better predictions for radial volume fractions, representing an improvement over well-correlated predictions for area-averaged pressure and volume fractions. The discrepancy in the radial volume fractions is attributed to the presence of pressure taps used in experiments, which protrude into the fluid domain. The role of model parameters such as cluster size and vapor volume fractions in the mass transfer model is also discussed in detail in this study. Similar to previous work, the new model is implemented in the open-source Computational Fluid Dynamics solver OpenFOAM in an Euler–Euler framework, which provides for the use of inter-momentum forces such as lift, drag, and turbulent dispersion, which are essential for accurate predictions for transport and generation of new vapor bubbles.