Dr. Mengnan Li (advised by Dr. Bolotnov)
Department of Nuclear Engineering
North Carolina State University

Abstract

The high-resolution two-phase flow data under the reactor conditions is sparse due to the extreme reactor operation conditions and measurement difficulties. Most of the current nuclear reactor two-phase simulations are adiabatic. Coupling boiling model with the current large scale two phase simulations will boost the development of system thermal hydraulics closures and provide assessment base for the validation of 3D multiphase computational fluid dynamics (M-CFD) model.

In this talk the speaker will introduce the boiling models developed for high resolution simulation and present the latest progress on model verification and validation. The boiling models associated with different mechanisms are developed and implemented in the high resolution multiphase flow solver – PHASTA, for example, the evaporation and condensation model and the contact angle model. The evaporation and condensation model considers the phase-change process including the moving of interface, mass increase inside the bubble and the heat transfer due to evaporation/condensation. This model is designed to resolve 3D interface in complex geometries represented with the unstructured grid, which allows us to investigate the boiling phenomenon in various conditions with lower cost (by utilizing localized mesh refinement for bubble growth region). The contact angle force model is coupled with evaporation and condensation model to accurately represent the evolution of contact angle in the boiling simulations. The bubble tracking algorithm which collects the detailed information regarding the individual bubble behavior is also brought into the evaporation and condensation model to support multi-bubble growth simulations and collect heat transfer information of interest (e.g. evaporation heat flux, bubble departure diameter, etc.) under various boiling conditions.

The latest progress on model verification and validation will be presented in the second part of this talk. The verification of the evaporation and condensation model is performed on the single and multi-bubble bubble growth in stagnant water. The bubble growth rate is compared with analytical solution for model error estimation. The contact angle force model is verified against the force balance analysis of the single bubble on the wall. The simulated bubble nucleation frequency in pool boiling simulation is validated against experimentally-based correlations. The bubble evolution and growth rate is compared with experimental data to validate the model performance under flow boiling condition. The multi-bubble flow boiling simulation is presented to demonstrate the potential of current model in solving boiling problems with complex geometries. In the end of talk, the future applications of high resolution boiling simulation will be briefly discussed.

Biography

Mengnan Li is a recent graduate Ph.D. of Nuclear Engineering Department at North Carolina State University. She got her bachelor degree of nuclear engineering in 2014 from Sichuan University, China and master degree of nuclear engineering in 2016 from NC State. She is a senior group member of the Multiphase Research Group led by Dr.Bolotnov. Her research mainly forces on the high resolution simulation of boiling phenomena in the nuclear reactor and the fundamental study of heat transfer mechanism in two-phase flow. During four year study in NC State, she actively involved in the IRP project “Development and Application of a Data-Driven Methodology for Validation of Risk-Informed Safety Margin Characterization Models” and CASL project. The latest research results are published in several conferences and peer reviewed scientific journals.

***This seminar will be streamed live on our NCStateNuclear YouTube channel***