MHD mixed convection flow in the WCLL: Heat transfer analysis and cooling system optimization

In the Water-Cooled Lithium Lead (WCLL) blanket, a critical problem faced by the design is to ensure that the breeding zone (BZ) is properly cooled to avoid the loss of mechanical properties in the structural materials. CFD simulations are performed using ANSYS CFX to assess the cooling system performances accounting for the magnetic field effect in the sub-channel closest to the first wall (FW). Here, intense buoyancy forces (Gr approximate to 10(10)) interact with the pressure-driven flow (Re approximate to 10(3)) in a MHD mixed convection regime. A constant magnetic field, parallel to the toroidal direction, is assumed with Ha = 8550. The walls bounding the channel and the water pipes are modeled as perfectly conducting. The magnetic field is found to dampen the velocity fluctuations triggered by the buoyancy forces and the flow is similar to a forced convection regime. The PbLi heat transfer coefficient is reduced to one-third of its ordinary hydrodynamic value and, consequently, hot-spots close to the FW are observed, where T-Max approximate to 1000 K. Optimization strategies for the BZ cooling system layout are proposed and implemented in the CFD model, thus fulfilling the design criterion.