Dielectrophoretic force-driven convection in annular geometry under Earth’s gravity

Abstract

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.

Thermoelectric instabilities in a circular Couette flow

“…The associated axial wavenumber undergoes a discontinuous change each time when |nc| changes and it globally decreases with L until it vanishes at normalTac=0. The columnar structure of the thermoelectric instability was predicted by Meyer et al [20] theoretically, and it was numerically and experimentally confirmed by Seelig et al [24]. As long as Ta≠0, the centrifugal force favours the occurrence of inclined vortices.…”

“…They also have well-known properties and have a wide range of available viscosities. In particular, silicone oil B5 has often been used during numerous parabolic flight campaigns and laboratory experiments [17,18,20,24], where its compatibility with hollow borosilicate glass micro-sized particles for the use of particle image velocimetry, especially regarding the effect of the radial sedimentation velocity due to the electric gravity was proven [24]. Hence, this study used the following parameters Pr=65, δ=1 and Ga=535 for the present analysis.…”

“…Turnbull and Melcher [34] have shown the validity of the time-averaged description by successfully predicting the onset of thermoelectric convection. The characteristic time of viscous dissipation for the silicone oil used by Seelig et al [24] is τν=5 s, so a frequency of the electric tension of 200 Hz was used to avoid charges relaxation inside the fluid and to ensure the validity of the time-averaged description.…”

“…It is only recently that the theoretical and numerical works have investigated the case of a stationary cylindrical annulus [20–22] with applied electric field under Earth’s gravity conditions. In contrast, laboratory experiments had already been performed in the 1970s by Chandra and Smylie [23], but the most recent investigations of Seelig et al have shown good agreement among theoretical, numerical and experimental investigations [24].…”

Theoretical and experimental analysis of negative dielectrophoresis‐induced particle trajectories

“…In order to optimize the trapping of cells on the chip, it is nessesary to further understandthe effects of DEP and other chip-generated forces on cell collection. It has been reported that Joule heating of the electrodes can introduce confounding effects during DEP experiments [22,[40][41][42][43]. The production of a temperature gradient, due to heating of the electrodes at the bottom of the fluidic chamber, can create localized buoyancy-driven convection of the media [44][45][46][47].…”