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Context: A radial temperature difference together with an inhomogeneous radial electric field gradient is applied to a dielectric fluid confined in a vertical cylindrical annulus inducing thermal electro-hydrodynamic convection. Aims: Identification of the stability of the flow and hence of the line of marginal stability separating stable laminar free (natural) convection from thermal electro-hydrodynamic convection, its flow structures, pattern formation and critical parameters. Methods: Combination of different measurement techniques, namely the shadowgraph method and particle image velocimetry, as well as numerical simulation are used to qualify/quantify the flow. Results: We identify the transition from stable laminar free convection to thermal electro-hydrodynamic convective flow in a wide range of Rayleigh number and electric potential. The line of marginal stability found confirms results from linear stability analysis. The flow after first transition forms a structure of axially aligned stationary columnar modes. We experimentally confirm critical parameters resulting from linear stability analysis and we show numerically an enhancement of heat transfer.

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A dielectric fluid is confined in a stationary vertical cylindrical annulus. A temperature difference is applied between the two cylinders, as well as an alternating electric potential. This configuration creates an active force called dielectrophoretic force, which acts as a thermal buoyancy force. Different axial gravity intensities are considered, so that two thermal buoyancies will affect the flow: the thermoelectric buoyancy intervenes in the radial direction and the Archimedean buoyancy acts in the axial direction. Linear stability analysis and direct numerical simulation are performed following experimental research that has been performed during parabolic flight campaigns.

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