In this paper, an experimental study of laminar magnetohydrodynamic (MHD)
buoyancy-driven flow in a cylindrical cell with axis horizontal is described. A steady
uniform magnetic field is applied vertically to the mercury-filled cell, which is also
subjected to a horizontal temperature gradient. The main features of this internal
MHD thermogravitational flow are made experimentally evident from temperature
and electric potential measurements. Whatever the level of convection, raising the
Hartmann number Ha to a value of the order of 10 is sufficient to stabilize an
initially turbulent flow. At much higher values of the Hartmann number (Ha∼100)
the MHD effects cause a change of regime from boundary-layer driven to core
driven. In this latter regime an inviscid inertialess MHD core flow is bounded by a
Hartmann layer on the horizontal cylindrical wall and viscous layers on the endwalls.
Since the Hartmann layer is found to stay electrically inactive along the cell, the
relevant asymptotic (Ha[Gt ]1) laws for velocity and heat transfer are found from the
balance between the curl of buoyancy and Lorentz forces in the core, together with
the condition that the flow of electric current between core and Hartmann layer is
negligible. A modified Rayleigh number RaG/Ha2,
which is a measure of the ratio of thermal convection to diffusion when there is a balance
between buoyancy and Lorentz forces, is the determining parameter for the flow.