Modeling of fully-developed, liquid metal, thin film flows for fusion divertor applications

Interest in thin film flows of liquid metal (LM) in a strong magnetic field has increased due to the possible application of such flows to the protection of divertor surfaces in a tokamak fusion reactor. In order to investigate the behavior of such a thin film flow in the fully-developed limit, a two-dimensional numerical model of open-channel, magnetohydrodynamic (MHD) flow has been constructed. This flow is contained in a chute of arbitrary electrical conductance with a magnetic field perpendicular to the flow direction but with arbitrary azimuthal orientation. Results of this self-consistent model are used to examine issues of importance to the successful fusion divertor application of thin film flow, such as the uniform film height and heat transfer of the films. It is seen that the flow height can be dominated by even a small transverse component of the field, rather than the stronger coplanar component, due to the elongated nature of the film. The model is also used to determine the validity of the Hartmann-averaging technique, an approximation used extensively in previous developing film models to account for the effects of a dominant coplanar field. This Hartmann-averaging is shown to be accurate in predicting the behavior of the core flow in the strong coplanar MHD interaction regimes, but cannot predict the flow quantity in parallel layer jets that can make up an appreciable portion of the flow. The Hartmann-averaging method is seen to be unsuitable for elongated flows dominated by the transverse field component. (orig.)