中文摘要：

气泡发生器是钍基熔盐堆脱气系统的关键部件，其功用为将载气碎化成尺寸均匀的小气泡。本文在脱气系统水实验回路实验研究基础上，采用数值模拟方法，应用SIMPLEC算法对标准的k-ε湍流模型和多相流混合模型进行耦合求解，分析了沿气泡发生器流动方向的气液两相流场速度变化、压力变化、湍动能分布规律。沿流向的速度分布表明，气相从喉部开始沿壁面流动，包围位于中心区域的水相，气相速度在扩张段入口处明显降低，速度梯度的变化形成剪切，使得气相破碎、分裂；压力分布表明，在气泡发生器的扩张段入口附近出现了压力梯度的峰值，与实验中测得的气泡集中碎化的位置相近，说明压力的迅速回升可能加速了气泡的碎化；湍动能分布表明，扩张段出口湍动能相对较大，说明此处气液两相能量交换强烈，产生强烈的剪切应力，使气液两相彼此剪切、破碎。以上结果说明，扩张端入口处由于较大的速度梯度及湍动能峰值，导致产生巨大的剪切应力，使气泡出现集中破裂现象。

英文摘要：

Background： Bubble generator is a key device in the off-gas removal system of the molten salt reactor （MSR） for breaking up the carrier gas into tiny bubbles. Purpose： The distribution rules of velocity, pressure and turbulent kinetic energy along the flow direction of the Venturi bubble generator were analyzed with the software FLUENT. Methods： Based on the experimental water loop with the target bubble generator, numerical simulation using FLUENT was performed. Both the multiphase model （Mixture）, standard k-e turbulent model were adopted and the SIMPLEC method was employed to get the coupled solutions. Results： The distribution of velocity along the flow direction shows that the air is entrained by the water flew in the throat section and the air flew close to the wall of the generator. The speed of air is reduced significantly in the diverging portion of the bubble generator. The velocity gradient creates great shear stress, making the bubbles break up. The distribution of pressure shows that the peak of the pressure gradient appears at the entrance of the diverging portion of the bubble generator. The numerical results are very close to the data in the experiment, which indicates that the quick recovery of pressure may accelerate the breakup of bubble. The turbulent kinetic energy peaks at the entrance of the diverging portion of the bubble generator, which suggests that strong energy exchange there, resulting in strong shear stress to break up the bubbles. Conclusion： The large velocity gradient and the peak of turbulent kinetic energy at the entrance of the diverging portion of the bubble generator cause great shear stress, which is the reason for the bubble breakup taking place intensively there.