Abstract: 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-ε 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.

Key words: Molten salt reactor (MSR), Bubble generator, Bubble breakup, Numerical study