Electrothermoconvective instability of an ohmic liquid layer in an unsteady electric field

The electrothermoconvective instability of a plane horizontal layer of a po orly conducting, ohmic liquid subjected to a varying electric field is inve stigated in the EHD approximation, when the charge formation is produced by electroconduction. First, the spatio-temporal distributions of the electri c field, charge and temperature are found for the quasiequilibrium base sta te. Then Floquet theory is applied for finding various instability threshol ds in the linear approximation with and without the effect of buoyancy. The influence of a time-dependent electric field modulation on the behavior of the liquid layer is studied with and without an additional steady componen t. The limit of low-frequency electric field modulation is also studied. We show that, depending on the amplitude and frequency of modulation, the ele ctric field can stabilize an unstable base state or destabilize the equilib rium of the liquid. Besides synchronous and subharmonic responses to variat ions of the external electric field, the instability can be associated with two-frequency quasiperiodic disturbances. The stability maps of (thermal) Rayleigh number versus electrical Rayleigh number found, illustrate the int erplay between thermoconvection and electroconvection. (C) 2000 Elsevier Sc ience B.V. All rights reserved.