Reduction of MHD Pressure Drop of Liquid Metal Flow by Insulation, Part I: Insulated Circular Ducts

For reducing the liquid metal MHD pressure drop in the inlet and outlet pipings of a fusion power reactor, the authors proposed a circular duct of electrically insulating function which consists of an outer pipe of metal structure and an inner pipe of insulating ceramics. A basic experiment was made with NaK. The test section which was made of a 25.4 mm O.D. 2.1 mm thick 304-SS pipe and a concentrically inserted 20 mm O.D., 1.0 mm thick FRP pipe with 0.6 mm clearance filled with NaK. The results are quite encouraging as summarized below. (1) The MHD drop gradient is proportional to the flow velocity U and the magnetic flux density B (c.f. B² for a conducting duct). (2) It is 1.6 times larger than the Shercliff's theory for perfect insulation. (3) It is reduced down to 4.6% at B= 1.0 T and to 3.2% at B= 1.5 T in comparison with the case of uninsulated duct, and to less than 1% if merely extended to B= 5 T or higher.