Numerical Study of Bubble Rising and Coalescence Characteristics under Flow Pulsation Based on Particle Method

Ronghua Chen,Guanghui Su,Kailun Guo,Wenxi Tian,Dawei Zhao,Suizheng Qiu,Minghao Zhang

doi:10.1155/2019/2045751

Abstract

Two-phase flow instability may occur in nuclear reactor systems, which is often accompanied by periodic fluctuation in fluid flow rate. In this study, bubble rising and coalescence characteristics under inlet flow pulsation condition are analyzed based on the MPS-MAFL method. To begin with, the single bubble rising behavior under flow pulsation condition was simulated. The simulation results show that the bubble shape and rising velocity fluctuate periodically as same as the inlet flow rate. Additionally, the bubble pairs’ coalescence behavior under flow pulsation condition was simulated and compared with static condition results. It is found that the coalescence time of bubble pairs slightly increased under the pulsation condition, and then the bubbles will continue to pulsate with almost the same period as the inlet flow rate after coalescence. In view of these facts, this study could offer theory support and method basis to a better understanding of the two-phase flow configuration under flow pulsation condition.

Highlights

IntroductionTwo-phase flow phenomena could occur in nuclear reactor systems (steam generators, boiling water reactor cores, condensers, etc.), conventional power plants, refrigeration, and chemical and aerospace
Two-phase flow phenomena could occur in nuclear reactor systems, conventional power plants, refrigeration, and chemical and aerospace
Two-phase flow instability can degrade the performance of the equipment, which will cause many safety problems; for example, the mechanical forces caused by the flow oscillations will make the components undergo harmful forced mechanical vibrations, and continuous mechanical vibration could lead to fatigue failure of components

Summary

Introduction

Two-phase flow phenomena could occur in nuclear reactor systems (steam generators, boiling water reactor cores, condensers, etc.), conventional power plants, refrigeration, and chemical and aerospace. In a two-phase system, when mass flow density, void fraction, and pressure drop are coupled, the static flow instability (the flow is drifted by a slight disturbance) and the kinetic instability (constant/variable amplitude flow oscillations at a particular frequency) are collectively referred to as flow instability [1]. These flow instability phenomena are usually accompanied by periodic fluctuation in flow rate. Bubble dynamics is an indispensable part of the two-phase flow research and the intrinsic driving force of gas-liquid two-phase flow evolution.

Objectives

Methods

Results

Conclusion