Magnetohydrodynamics test of a one-sixth scale model of a CTR recirculating lithium blanket

A one-sixth scale model of an element of a recirculating lithium blanket for a fusion reactor was tested experimentally. The scale model was instrumented to measure flow, pressure drop and pumping power as functions of the applied magnetic field (0 to 4 T) and the pump current (0 to 300 amp dc). Reynolds numbers as high as 22,000, magnetic Reynolds numbers up to 0.047 and a maximum Hartmann number of 12,000 were obtained with a wall-to-fluid conductivity ratio of 0.0158. The ratio of loop pressure drop to fluid (NaK 44) velocity increased as a quadratic function of the magnetic field. The square term was dominant for the higher values of magnetic field and is predictable by simple laminar magnetohydrodynamic theory. For any given velocity and magnetic field the pressure drop in the field-flow-aligned legs of the loop is much greater than it would be in ordinary hydrodynamic flow, but nevertheless is more than an order of magnitude less than the pressure drop encountered when the fluid flows across the magnetic field. The pumping power was measured as a function of magnetic field and fluid velocity. For fields greater than 1 T and velocities exceeding 1 cm/sec the pumping power varied as the square of the product of the fluid velocity and the magnetic field. The measured value of the proportionality factor agrees with predictions based on certain simplifying assumptions. The extrapolation of these experimental results to a full scale recirculating lithium blanket indicates that no excessive pressure or pumping power is likely to result unless a drastic change in flow regime occurs as the MHD parameters are increased. There appears to be no reason to expect any such drastic change. (U.S.)