<p>A numerical study of the downward mercury flow in a nonuniformly heated round tube under the influence of a transverse magnetic field was carried out using the LES method. The problem was solved in a wall-conjugate formulation with modeling a contamination layer (contact electrical resistance) on the inner surface of the tube wall. The calculations were carried out at the following values of the Reynolds, Prandtl, Grashof, and Hartmann numbers: Re = 10⁴, Pr = 0.024, Gr = 6·10⁷, 12·10⁷, Ha = 0–1000. It is shown that the electrical conductivity of the contamination layer has a significant effect on the stability of the flow and the occurrence of abnormally high low-frequency pulsations in the temperature of the liquid and tube wall.</p>