Influence of surface oxidation on electric potential measurements in MHD liquid metal flows

Experimental investigations for magnetohydrodynamic flows in rectangular ducts are performed using GaInSn as model fluid. Measurements of electric potential on channel walls and inside the flow show reproducible discrepancies compared to analytical results. These discrepancies can be ascribed to the formation of oxide layers causing a contact resistance between the electrically conducting duct walls and the liquid metal. An exact analytical solution for pressure drop, velocity and potential distributions has been derived taking into account the presence of a contact resistance. Analytical results for velocity and potential profiles and for pressure drop are discussed for different values of contact resistance and strength of the applied magnetic field. A comparison of measured potential with data from the analytical solution allows estimating the order of magnitude of the contact resistance in the present experiments.