Liquid metal, an electrically conducting fluid, buoyancy driven convection heat transfer processes are fundamental problems in the design of the fusion reactor due to the influence of the large temperature difference and the strong magnetic field. An investigation of liquid metal buoyancy driven convection heat transfer is conducted in a rectangular enclosure with a square cross-section under the influence of a uniform horizontal magnetic field. Two opposite vertical walls are maintained at different temperatures and the other four walls are thermally insulating. The applied magnetic field is perpendicular to the temperature gradient. Ultrasound Doppler velocimetry measurement method is used to get natural convection velocity in different temperature difference and different magnetic field intensities. The flow is characterized by the external Grash of number, Gr, determined from the temperature difference of the side walls, and the Hartmann number, Ha, determined from the intensities of the imposed magnetic field. Two multiple linear regression models of the Nusselt number based on the Hartmann layers theory are summarized which indicate that the induced current's restraining influence determines the natural convection heat transfer process of viscous electric liquids in a strong magnetic field. (C) 2017 Elsevier Ltd. All rights reserved.