Heat transfer in MHD-flow at high Hartmann numbers and improvement by turbulence promotion

L. Barleon - K. J. Mack - R. Kirchner - R. Stieglitz

Association KfK-EURATOM, Kernforschungszentrum Karlsruhe GmbH, IATF, Postfach 36 40, 76021 Karlsruhe, Germany

Abstract
A heal transfer-experiment was carried out in the MEKKA-facility in which the side wall of a rectangular (80 mm X 40 mm) test section is heated over a length of 0.5 m using a direct contact heater, which allows a homogeneous heat flux up to 20 W/cm. The liquid metal contacting surfaces of the test section made of stainless steel are electrically insulated by a temperature resisting painting. Hartmann numbers to 5000 (2 Tesia), interaction parameters 320-22,000, Peclet numbers 44-2200 based on the half-width in the field direction (a = 40 mm), and velocities of 0.04-2.5 mis were achieved. Tlie working fluid was NaK (sodium potassium eutectic). The experiments showed that even in the case of the smooth channel without any turbulence promoter the heat transfer is improved with respect to laminar slug flow for Peclet-numbers above 140 due to the stan of a two dimensional vortex structure. Supplementary experiments conducted in the horse truck Indium-Gallium-Tin (eutectic) loop GALINKA showed the existence and the high stability of two-dimensional vortices with the vorticity axis parallel to the field in rectangular ducts with electrically insulating walls.