Thermal convection in a cylindrical annulus under a combined effect of the radial and vertical gravity

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

“…We show experimentally a regime diagram spanned by the non-dimensional Rayleigh number and electric potential. We experimentally identify the line of marginal stability for the experiment cells of different aspect ratio and confirm linear stability analysis from Meyer et al (2017). The flow structure in the stable laminar free convective and in the thermal electro-hydrodynamic convective regime will be described in section 6.1.…”

“…Heating of the inner cylinder is realised by pumping silicone oil Elbesil B5 via in/outlets into the inner cylinder. For experiments with the shadowgraph method applied we heat and cool with a custom-built technique very detailed described in Meyer et al (2017) and Meier et al (2018). For experiments using particle image velocimetry, we heat and cool with two thermostats.…”

“…Thus the dielectrophoretic (DEP) force has been remained in focus up to now, e.g. very recently in Laohalertdecha et al (2007); Marucho and Campo (2013); Dahley (2014); Travnikov et al (2015Travnikov et al ( , 2016; Futterer et al (2016); Meyer et al (2017Meyer et al ( , 2018; Meier et al (2018); Zaussinger et al (2018). The dielectrophoretic force depends on E 2 instead of E and is therefore independent of the direction of E. If the frequency of the electric potential Φ is high enough it can be time-averaged over a period of the electric field.…”

“…The problem of onset of convective instability of a dielectric fluid confined in a concentric vertical annulus subjected to Archimedean buoyancy force due to a radial temperature difference and Earth's gravity, and to dielectrophoretic force due to a radial alternating electric field has been studied by many authors experimentally (Smylie, 1966;Chandra and Smylie, 1972;Dahley, 2014;Futterer et al, 2016;Meyer et al, 2017), theoretically (Takashima, 1980;Takashima and Hamabata, 1984;Stiles and Kagan, 1993;Meyer, 2017) and numerically (Takashima and Hamabata, 1984;Smieszek et al, 2008). Consider a vertical cylindrical annulus with an inner heated cylinder maintained at temperature T 1 and an outer cooled cylinder maintained at temperature T 2 .…”

“…This suggests the instability is driven by the same mechanism as in the gravity-driven ordinary thermal convection. Meyer et al (2017) reported the flow after the first transition is axially aligned and consists of stationary columnar modes. Meier et al (2018) demonstrated experimentally the existence of those columnar modes for a few tuple of (∆T, V 0 ).…”