Pressure drop and velocity changes in MHD pipe flows due to a local interruption of the insulation

In liquid metal blanket concepts, such as the dual coolant lead lithium (DCLL) blanket, in which the PbLi serves to cool the breeding zone, the liquid metal has to flow with sufficiently large velocity to guarantee a suitable removal of the volumetric heat generated in the fluid. Large velocities lead to a high pressure drop caused by magnetohydrodynamic (MHD) interactions of the liquid metal with the plasma confining magnetic field. In order to reduce MHD pressure losses in DCLL blankets, it is foreseen to decouple electrically the PbLi from the conducting wall of the ducts. This can be achieved by inserting insulating layers inside pipes and channels. In this paper we investigate MHD flows in well-conducting pipes with flow channel inserts (FCI). The influence on the pressure drop of the finite electric conductance of the layer and of the presence of an interruption in the insulation is analyzed. Numerical results show that under realistic operating conditions, i.e. for sufficiently small electric conductance of the insert and large magnetic fields, the ensuing additional MHD pressure losses are still acceptable. However, the discontinuity of the insulation causes significant modifications of the velocity distribution in the pipe, which have to be taken into account, since they can affect heat and mass transfer phenomena.