中法核工程与技术学院第94期学术午餐会

中法核工程与技术学院第94期学术午餐会

94^th Academic Lunch Seminar of Sino-French Institute of Nuclear Engineering and Technology

Topic: Numerical Simulation on Boiling Phenomena: A Review

Speaker: Prof. Tomoaki Kunugi

Time: 12:40 – 14:00, Tuesday November 13, 2018

Venue: F309 in the teaching building, Zhuhai Campus, SYSU

Organizer: Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-sen University

Language: English

Abstract:

Despite extensive research efforts regarding the boiling heat transfer, the mechanism of the nucleate boiling phenomena is still unclear, and therefore its mechanistic model without any empirical correlation has not been developed. Since the tempo-spatial scales of boiling phenomena widely vary with from molecular scale motion in heat conduction resume to convective motion being governed by macroscopic scale in bulk fluid, the scales of phenomena interested in will be clear if a mechanistic boiling model is developed. Especially, the nucleation process must be considered very fast molecules’ motions, thus the non-thermal equilibrium state will play a very important role in this time scale. A numerical simulation of the boiling phenomena is one of the promising approaches to clarify the heat transfer characteristics of boiling phenomena and discuss their mechanism. With the advances in recent years of high performance computational technology, several numerical procedures to simultaneously solve the conservation equations of mass, momentum, and energy for liquid and vapor phases when bubbles are continuously growing at and near the heater surface have been developed.

In this review, the fundamental feature of boiling, critical heat flux (CHF) problems in pool and flow boiling phenomena and their critical issues including their multi-scale modeling are firstly discussed. The numerical approaches in micro, meso and macroscale are overviewed and discussed their features and weak points. In concretely, molecular dynamics simulation as a microscopic scale approach are reviewed and pointed out the mathematical problem and the limitation of the spatial size is up to 1mm. Then, a phase-field and diffused interface methods as a mesoscopic scale approach are discussed from the free energy density distribution point of view and more advanced scheme such as Dynamic van der Waals Theory and the numerical treatment of wettability or contact angle as the boundary condition and the limitations of applicability to real two-phase flows are also discussed. Eulerian one-fluid model, such as VOF (Volume of fluid) method and FT (Front tracking method) as a macroscopic scale approach are explained and with the numerical treatment of wettability or contact angle as the boundary condition are discussed. As for the phase change model, a microlayer model, Lee's model combined with the evaporation and condensation model based on kinetic gas theory like Schrage's model and Tanasawa's model, and Kunugi-Ose's model combined both temperature recovery method and VOF limiter based on the relaxation time are discussed. Finally, as the example, subcooled pool and flow boiling simulation results obtained by using MARS (Multi-interface Advection and Reconstruction Solver) are shown.

About the speaker:

Dr. Kunugi, professor at Kyoto University, is an international authority in computational multiphase flow and heat transfer technology and is a specialist in nuclear reactor thermal-hydraulics, safety technology and fusion nuclear technology. He was the first to develop the automatic liquid-crystal thermometry and found the leakage heat flow inside the heat transfer plate by using the numerical simulation coupled with the measured surface temperature via this liquid-crystal thermometry. He has been developing several CFD codes including RANS, LES and DNS for single phase flows and DNS for multiphase flows including phase change phenomena. He found the turbulence structure of turbulent free-surface flows with deformed interfaces. He also invented a new heat transfer enhancement augmentation by a nano- and micro-scale porous layer formed on the surface without the pressure drop increase.

Professor Kunugi has published over 300 archival publications, including monographs and textbooks, journal papers and contributions at international conferences.