Aspect ratio effects on heat transfer in MHD laminar flow through rectangular channels in the plasma facing components of fusion reactors

Convective heat transfer in MHD laminar flow through rectangular ducts in the plasma facing components (PFCs) of fusion reactors is analyzed numerically to estimate: the effects of channel aspect ratio, defined as the ratio of the lengths of the plasma facing side to the other side. The adverse effect of the nonuniformity of surface heat flux on Nusselt number (Nu) at the plasma facing side can be alleviated by increasing the aspect ratio of a rectangular duct. At the center and corner of the plasma facing side of a square duct, the Nu for non-MHD flow are 6.8 and 2.2, respectively, for uniform surface heat flux. In the presence of a strong transverse magnetic field, Nu at the center and corner increases to 23 and 3.4, respectively. However, when the heat flux is highly nonuniform, as in the PFCs, Nu decreases from 23 to 3.1 at the center and from 3.4 to 3.0 at the corner. When the aspect ratio is increased to 4, Nu at the center and corner increase to 5.0 and 4.75, or by 47% and 58%, respectively. The optimum aspect ratio for best thermal performance is a function of transverse magnetic field strength and increases with it