Thermal convection experiments in a liquid gallium layer subject to a uniform
rotation and a uniform vertical magnetic field are carried out as a function of
rotation rate and magnetic field strength. Our purpose is to measure heat transfer
in a low-Prandtl-number (Pr = 0.023), electrically conducting fluid as a function of
the applied temperature difference, rotation rate, applied magnetic field strength and
fluid-layer aspect ratio. For Rayleigh–Bénard (non-rotating, non-magnetic) convection
we obtain a Nusselt number–Rayleigh number law Nu = 0.129Ra0.272±0.006 over the
range 3.0 × 103 < Ra < 1.6 × 104.
For non-rotating magnetoconvection, we find that
the critical Rayleigh number RaC increases linearly with magnetic energy density,
and a heat transfer law of the form Nu ∼ Ra1/2. Coherent thermal oscillations are
detected in magnetoconvection at ∼ 1.4RaC. For rotating magnetoconvection, we find
that the convective heat transfer is inhibited by rotation, in general agreement with
theoretical predictions. At low rotation rates, the critical Rayleigh number increases
linearly with magnetic field intensity. At moderate rotation rates, coherent thermal
oscillations are detected near the onset of convection. The oscillation frequencies are
close to the frequency of rotation, indicating inertially driven, oscillatory convection.
In nearly all of our experiments, no well-defined, steady convective regime is found.
Instead, we detect unsteady or turbulent convection just after onset.