An Abstract of the Thesis Of
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AN ABSTRACT OF THE THESIS OF Tsung-Wen Chen for the degree of Master of Science in Nuclear Engineering presented on May 29, 2019. Title: A New Approach of Computational Fluid Dynamics Studying Power Transient Critical Heat Flux Abstract approved: _______________________________________________________________________ Wade R. Marcum Power transient boiling has been studied for decades, however, the mechanistic understanding of phenomena which occur during such an event remains incomplete. Due to a dearth of systematic researches, the information of studied phenomenon, detailed physics and applicable hypothesis are very limited. Transient critical heat flux (CHF) is paramount in determining the safe operations of a nuclear reactor. The Transient Reactor Test Loop (TRTL), serves as an out-of-pile facility which supports the testing of conditions experienced in the Transient REActor Test (TREAT) facility at the Idaho National Laboratory (INL). Specifically, the TRTL was designed and operates with the focus on the power transient boiling phenomenon under the Pressurized Water Reactor (PWR) condition. Since the direct application of power transient experiments may lead to a potential safety concern, it is crucial to develop a Computational Fluid Dynamics (CFD) model and simulation method that provides a feasible way to recognize the irregular type of boiling processes that takes place in the TRTL facility and would therefore take place within the TREAT facility as well. With the expensive computational cost and heavy instability from the fast-changing boundary conditions and complicated two-phase physics, the available literature associated with studying transient boiling via CFD is limited. In this study, a new approach is developed with the consideration of heating and temporal behavior. An integral view of the CFD study includes model selection, grid independent study and stability maintenance. To develop a qualitatively confident result from the new approach, a brief data benchmark via available past experimental studies is provided. In addition, a new hypothesis which is able to solve the current debating of the transient boiling phenomenon based on the simulation is discussed as well. © Copyright by Tsung-Wen Chen May 29, 2019 All Rights Reserved A New Approach of Computational Fluid Dynamics Studying Power Transient Critical Heat Flux by Tsung-Wen Chen A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented May 29, 2019 Commencement June 2020 Master of Science thesis of Tsung-Wen Chen presented on May 29, 2019. APPROVED: Major Professor, representing Nuclear Engineering Head of the School of Nuclear Science & Engineering Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Tsung-Wen Chen, Author ACKNOWLEDGEMENTS This work is done with many people’s effort. First, I would like to appreciate the assistance from my advisor Dr. W. Marcum. Thank for the guidance of my research, thesis and defense during his busy schedule. The instruction and feedback from him allowed me to overcome all the academic challenges and obstacles during the development of this study. I also want to thank all my committee members including Dr. G. Mignot, Dr. L. Minc and Dr. Q. Wu. for the guidance of my thesis and defense. Secondly, I would like to express the acknowledgement to my research group. Thank for the instructions from Yikuan Yan. Without the discussion of similar research area, this work cannot be completed. Thank for the company from Silvino Balderrama and Jonathan Gjmeso. Without the time that we spend in radiation center, this work cannot be finished. Thanks for the advice from Tristan Winkle. Without his advices on grammar and writing, this work cannot be finished. For other people in the research group, thank for their time that spend with me to practice my presentation and defense. Finally, I would like to contribute all my outcomes to my family. Thanks for the patience, support and all the encouragements from my parents, Jin-Hung Chen and Li-Ching Lin. In addition, I would like to express my deepest gratitude to my girlfriend, Ya-Chin Chen, for staying with me and work through those time with depression and sadness. Thank for their companionship along the entire path of my master degree. TABLE OF CONTENTS Page 1 INTRODUCTION .........................................................................................................1 1.1 Motivation ............................................................................................................... 3 1.2 Objectives ............................................................................................................... 4 2 SURVEY OF LITERATURE ........................................................................................6 2.1 Critical Heat Flux Phenomenon .............................................................................. 7 2.1.1 Boiling Curve .................................................................................................7 2.1.2 Hydrodynamic Instability Models .................................................................8 2.1.3 Macrolayer Dryout Models ..........................................................................11 2.1.4 Wettability....................................................................................................12 2.2 Transient Boiling .................................................................................................. 13 2.2.1 Power Transient CHF Experiments .............................................................13 2.2.2 Power Transient CHF Models .....................................................................18 2.2.3 Heterogeneous Spontaneous Nucleation......................................................20 2.2.4 Other Types of Transient CHF: Flow and Pressure .....................................23 2.3 Two-Phase Computational Fluid Dynamics in Star-CCM+ ................................. 24 2.3.1 Mesh Generating ..........................................................................................24 2.3.2 Turbulent Models .........................................................................................26 2.3.3 Two-Phase Heat Transfer Models in Star-CCM+ .......................................29 2.3.4 Simulation of CHF Using Star-CCM+ ........................................................32 3 METHOD AND METHODOLOGY ...........................................................................35 3.1 New Simulating Method ....................................................................................... 37 3.2 Improved Process of Transient Simulation ........................................................... 38 3.3 Geometry and Boundary Conditions .................................................................... 39 TABLE OF CONTENTS Page 3.3.1 Cladding Heater Boundary Conditions ........................................................40 3.3.2 Pipe Boundary Conditions ...........................................................................41 3.3.3 Conjugate Heat Transfer and Interface Types .............................................42 3.4 Grid Refinement Method ...................................................................................... 44 3.4.1 Mesh Types and Generating Modes ............................................................44 3.4.2 Mesh Refined Method..................................................................................46 3.4.3 Mesh Diagnosis ............................................................................................48 3.5 Setting of General Models and Eulerian Phases Material .................................... 50 3.5.1 General Models ............................................................................................50 3.5.2 Eulerian Multiphase Material ......................................................................53 3.5.3 Modeling Turbulent Flow ............................................................................56 3.6 Setting of Heat Transfer and Multiphase Interaction Models ............................... 61 3.6.1 Thermal Diffusion in EMP ..........................................................................61 3.6.2 Phase Momentum Transfer in EMP .............................................................63 3.6.3 Wall Boiling Model in EMP ........................................................................66 3.6.4 Rohsenow Boiling Model in VOF ...............................................................70 3.7 Convergence and Stability .................................................................................... 73 3.7.1 Double Precision Version ............................................................................73 3.7.2 Prism Layer Thickness and Wall Treatment ................................................73 3.7.3 Time Step .....................................................................................................74 3.7.4 Boundary Conditions ...................................................................................76 3.7.5 Wall Boiling Model Selection .....................................................................77 3.7.6 Turbulent Model Properties .........................................................................77 TABLE OF CONTENTS Page 3.7.7 Under Relaxation