裂变气体分离器气泡分离轨迹的数值模拟

钍基熔盐堆是我国重点开发的第四代核反应堆之一,其裂变反应产生的中子俘获截面大的Kr、Xe等裂变气体以微气泡的形式存在于熔盐冷却剂中,对裂变气体的分离是提高熔盐堆中子经济性、实现燃料深燃耗的重要环节。为定量地获得分离器内气泡的分离行为,采用数值模拟和理论建模相结合的方法,得到旋流场的流场分布特征;通过建立旋流场中气泡运动控制方程,分析并计算不同旋流度和气泡直径下的分离长度。与实验数据对比发现,数值模拟结果和实验数据吻合良好,表明数值模拟方法可以用于气液分离器的优化设计。

Numerical simulation of bubble separation trajectory in fission gas removal system

Background: One advantage of the liquid fueled Thorium Molten Salt Reactor (TMSR) is that the fuel can be burned up deeply with the neutron poisonous gas removal system that can be achieved by bubbling degassing approach. In order to quantify the separation efficiency for the separator and provide useful guidelines to determine the dimensions for the separator, the separation trajectories of bubbles with different sizes in the swirl flow inside the separator are needed.Purpose: This study aims to develop an alternative method to predict the bubble's motion which can avoid the troubleshooting induced by the two-phase simulation.Methods: The Lagrangian approach is modified to obtain the continuous phase velocity by a single phase simulation, and curve fitting is applied to further approximation of this velocity. Combing the known velocity distribution with explicit mathematical expression and the interaction model for the gas-liquid interface, a mathematical model to calculate the bubble motion is well posed. Results: A comparison between the numerical results and the experimental data indicates that the result agrees well with each other. As for the separation length concerned, the maximal error is less than 20%.Conclusion: It has theoretical guidance meaning for research on the movement of bubbles in cyclone separator. And it can be used to guide the determination of swirl chamber space.