*4.1. Hydrodynamic Study*

Steady-state CFD analysis was performed with the commercially available STAR-CD code. A half 3-dimensional (3D) model was meshed as shown schematically in Figure 6. To obtain a fully developed flow profile for the test tube, the length of each side of the specimen was extended to 250 mm in the simulations. All other dimensions are as in the specimen. The meshes were composed of tetrahedral cells, which were 0.75 mm in the straight part and 0.1875 mm in the two orifice sections. To study the hydrodynamic effects, it is necessary to understand the flow behavior deep in the viscous sublayer. This can generally be achieved by placing the first node at around *y*+ = 1. In this study, 45 layers of prism cells were meshed in the near-wall region. The distance of the first node of the prism layer from the wall is about 1.6 μm, corresponding to, approximately, *y*+ = 0.5. The expansion ratio of the prism layer is 1.1. There are approximately 7.6 million cells in the fluid field in total. The uniform flow speed at the inlet is 0.25 m/s, making the flow speed in the straight part approximately 0.7 m/s, which corresponds to that in the experiment. Good wettability is assumed for contact between LBE and the wall during the 3000 h operation, so the wall boundary is considered to be no-slip for the simulation. The *k* − *ε* LRN turbulence model was adopted to obtain detailed flow characteristics in the near-wall region using the equations detailed in Section 2.1. In addition, hydrodynamic simulation was performed to study the effects of the corroded morphology and angle of the orifices.

**Figure 6.** Example of a half 3D model used in the numerical simulation.
