Equilibrium - convection transition of an electroconductive fluid under simultaneous actions of gravitation, temperature, magnetic and electric fields

A. I. Raitchenko

Institute for Problems of Materials Science, Ukrainian National Academy of Sciences, 252142 Kiev, Ukraine

Abstract
The number of factors influencing the equilibrium-convection onset conditions de-pends radically on its electroconductivity and on temperature coefficient of electro-conductivity of fluid. These factors (along with the thermal expansion in the gravita-tional field) include the magnetic and electric fields also. If the spatial Lorentz-force originating from the intercrossed electric and magnetic fields action is directed downwards, its effect enhances the gravitational action, and the value of critical Rayleigh number must decrease; the reverse situation (increase of critical Rayleigh number) can be observed in case of Lorentz-force directed upwards. The extent of such an influence is determined by the dimensionless complex, namely relation of the spatial Lorentz-force to the hydrostatic head of the fluid column with the unit height in the gravitational field. It is ascertained that the competition between the electromagnetic force due to non-uniformity of electroconductivity on account of its temperature dependence and the buoyancy force may have an ambiguous effect, either increase or decrease of the critical Rayleigh numbers. The effect of such a bal-ance of actions is measured by the value of corresponding dimensionless complex which may be named as magnetic-electric-thermal-resistive-buoyant (METRB) crite-rion (number). Influences of the electromagnetic-gravitational-hydrostatic relation number and the METRB number can strengthen or weaken one another; in par-ticular case, they can "annihilate" mutually, and then the critical Rayleigh numbers must remain invariable. The proposed conception is useful to the analysis of situa-tions in liquid conductors, in conductive gases (plasma), in terrestrial, planetary, and stellar atmospheres. Figs 3, Refs 34.