## 3 Results and Discussion
### Simulation Analysis of the Migration Tank
#### 3.1.2 Simulation Results and Their Analysis  
According to the obtained simulation data (Figure 2), the electric field in the measuring cell can be separated into three areas: a cathode area (tungsten rod, blue region), an anode area (carbon rod, red region), and a transition area. The potentials of the cathode tungsten rod and anode carbon rod remain unchanged, making the cell an equipotential body. Under the action of the flow field in the electrolytic cell, the latter can be divided into three complete areas owing to the isolation effect of the baffle in the middle zone.  
Assuming uniform electrolyte conductivity in the electrolytic cell, the electric potential in the cell is evenly distributed, and the equipotential line between the anode and the anode is perpendicular to the ground. However, owing to the effect of flow field, the conductivity of the molten pool in the tank varies slightly. Therefore, the electric field and current distribution change on both sides of the electrode. The potentials of the cathode and anode near the intermediate transition isolation zone are stable, and there is a linear gradient along the vertical direction of the electrode. The intermediate transition zone exhibits a high gradient, which satisfies the requirements for determining the electromigration number.  
During the electromigration process, a dynamic gas layer is formed on the anode surface, and the gas layer becomes thicker as the height of the anode increases. The conductivity of the electrolyte near the anode is affected by the gas layer and increases with increasing gas content [24,25]. After coupling the electric field with the flow field, the flow field gradient between the surface of the molten salt and the inside of the molten pool decreases due to the floating and stirring of gas molecules.  
In addition, the tiny area at the bottom of the anode, because of weak electric field intensity and low current density at the anode bottom before coupling, becomes a stagnant area with a low flow field gradient. Owing to the electric field coupling effect and gas generation, the electric field distribution at the bottom of the tank is uniform, and the field intensity gradient and current density increase; as a result, the flow field gradient at the anode bottom increases more than the electrostatic field. Because of the presence of the electric field between the anode and the cathode, the rate of the gas generation on the  
Figure 2: Potential distribution diagram of the three-electrode area.  
anode surface depends only on the current density; therefore, the electric field produces a negligible effect on the flow field. The main reason for the observed high flow field intensity on the anode surface is the strengthening of the adsorption-desorption effect in this region caused by gas generation. Owing to the low gas density, the rising process causes a strong convective movement, which accelerates the fluid movement. Due to the stable electric field at the bottom of the electrolytic cell, there is no large electrode polarization; therefore, the relative velocity of the melt in this area is small, and the convection effect is weak.