PIV and shadowgraph measurements of thermo-electrohydrodynamic convection in a horizontal aligned differentially heated annulus at different gravity conditions
“…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.…”
Section: Resultsmentioning
confidence: 99%
“…Many theoretical and numerical analyses have been performed considering μg conditions in the case of stationary cylinders [10,11], as well as for the circular Couette flow [12–15]. Experiments under microgravity involved sounding rockets and drop tower experiments [16], as well as parabolic flights [17,18]. The last existing way to perform long duration μg conditions was to experiment onboard the International Space Station, e.g.…”
The stability of a non-isothermal circular Couette flow is analyzed when subjected to a dielectrophoretic force field. Outward and inward heating configurations are considered when the inner cylinder is rotating and the outer cylinder is at rest. In addition, an alternating voltage is applied between the two cylinders to induce a radial electric buoyancy that acts on the dielectric fluid. The linear stability analysis provides the threshold for the first transition to instability, as well as the corresponding wavenumber and frequency of the modes.
This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal
Philosophical Transactions
paper (part 1)’.
“…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.…”
Section: Resultsmentioning
confidence: 99%
“…Many theoretical and numerical analyses have been performed considering μg conditions in the case of stationary cylinders [10,11], as well as for the circular Couette flow [12–15]. Experiments under microgravity involved sounding rockets and drop tower experiments [16], as well as parabolic flights [17,18]. The last existing way to perform long duration μg conditions was to experiment onboard the International Space Station, e.g.…”
The stability of a non-isothermal circular Couette flow is analyzed when subjected to a dielectrophoretic force field. Outward and inward heating configurations are considered when the inner cylinder is rotating and the outer cylinder is at rest. In addition, an alternating voltage is applied between the two cylinders to induce a radial electric buoyancy that acts on the dielectric fluid. The linear stability analysis provides the threshold for the first transition to instability, as well as the corresponding wavenumber and frequency of the modes.
This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal
Philosophical Transactions
paper (part 1)’.
“…Seelig et al (2019) have estimated that for temperature difference 7 K and peak voltage 7 kV, the electric sedimentation velocity measured at the inner cylinder is 6.3 × 10 −6 mm s −1 . Considering the relatively short duration of the μg condition (6 min) and the thermo-electric convective fluid velocity being of the order of 0.1-1 mm s −1 (see Meier et al 2018;Meyer et al 2019;Szabo et al 2021), it is assumed that the sedimentation of the particles can be neglected. Two independent fluid loops are used to maintain the temperature difference T (see figure 2).…”
Section: Experimental Set-upmentioning
confidence: 99%
“…2019; Szabo et al. 2021), it is assumed that the sedimentation of the particles can be neglected. Figure 2.Schematic drawing of the fluid loops for the temperature control and gap mixing.…”
Section: Experimental Set-upmentioning
confidence: 99%
“…Recently, experiments have been carried out under the microgravity (μg) condition provided during parabolic flight campaigns (see Meyer et al 2017;Meier et al 2018). Visualisations of the flow and of the temperature variation led to the determination of the flow stability after the 22 s of a weightless environment (Szabo et al 2021). Although the growth of perturbations could be observed, a stationary flow could not be reached, and it was found that the experimental threshold for the destabilisation of the flow was at higher values than the value calculated from a linear stability theory (Yoshikawa et al 2013).…”
An experiment on convective flows induced by the dielectrophoretic force was performed under the microgravity condition provided during a sounding rocket flight. The dielectrophoretic force possesses a non-conservative term that can be seen as resulting from an electric gravity. That gravity can be responsible for an electric Rayleigh–Bénard convection between a hot inner cylinder and a cold outer cylinder when an electric field is applied in the radial direction. Four cells with independent temperature and electric field controls allowed the investigation of eight different values of the electric Rayleigh number relatively close to the onset of the thermo-electric instability. A linear stability analysis is performed to predict the stability threshold and the evolution of the growth rate of the instability. The three-dimensional structure of the flow is captured by simultaneous particle image velocimetry and by shadowgraphy. The amplitude of the instability modes and the time evolution of the flow is analysed, and various methods are proposed to extrapolate the experimental critical value of the electric Rayleigh number for the onset of convection. The measured critical electric Rayleigh number is in agreement with the prediction of the linear stability theory. The comparison of the new experimental results with previous ones from parabolic flight campaigns highlights the importance of long-term microgravity for the achievement of thermal convection at low values of the control parameters.
Thermo‐electrohydrodynamic convection is investigated in a shell with central force field to investigate convective pattern formation for potential heat transfer application and small scaled laboratory experiments e.g. the modelling of convection in planetary interiors or atmospheres. To induce TEHD convection the outer and inner shells are heated at different temperatures whereas an alternating electric potential is applied between both shells. The observation of the convective pattern formation suggest that dielectric fluids have a significant response to thermal and electrical forcing. The observed patterns ranged from quasi‐stationary convective modes in azimuthal direction to shape and mode amplitude vacillations with mode merging and separation that are classified into three regimes. The heat transfer was evaluated by the Nusselt number and showed an increase in heat transfer with electric forcing. However, the results indicate a much smaller heat transfer when compared to natural convection.
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