CFD of spray-steam condensation, spray-wall interaction and heat transfer

Sammanfattning

This thesis investigates the possibilities for simulating spray cooling in pressurizer systems in pressurized water reactors (PWRs) using OpenFOAM. Spray cooling in pressurizers is part of the mechanism for regulating the pressure. The multiphase flow associated with the process is highly complex and difficult to study experimentally due to harsh operating conditions. An improved understanding of these processes is important for future investigations of thermal stress in the tank. The work focuses on evaluating Lagrangian particle tracking (LPT) submodels for atomization, breakup and droplet collision. Both simplified spray cases for investigating the submodels and validation cases based on experimental data provided by Vattenfall were evaluated. In addition, the hybrid VoF-LPT solver atomizationFOAM was tested. The result showed a significant difference between the investigated LPT submodels. Spray width was shown to be strongly dependent on operating pressure due to the pressure dependence of breakup models. Validation against experimental data showed significant limitations of pure LPT approaches for dense sprays. Most model combinations were unable to reproduce experimentally observed droplet coalescence behavior. The Reitz KHRT breakup model showed the best potential in reproducing coalescence behavior seen in experiments. Limitations remained in accurately reproducing liquid structures near the nozzle. The hybrid VoF-LPT solver atomizationFOAM showed promising result by producing spray shapes that agreed well with experimental observations, particularly regarding spray width and the representation of large scale fluid structures. However, the investigated setup was highly simplified and further validation under more representative conditions is required.