Charge injection in horizontal eccentric annuli filled with a dielectric liquid

International audiencen this paper, we carry out a numerical study of the Coulomb-driven electro-convection flow in adielectricliquidusingthefinitevolumemethod(FVM).Thesystemunderstudyconsistsofaneccentricannulus layer subjected to strong unipolar injection from an inner cylinder. All equations are writtenin bi-cylindrical coordinate system and are expressed using the vorticity–stream function method. Thebehavior of the fluid for different system parameters is well studied. The taken parameters are in therange of eccentricity 0≤e≤80%, injection strength in the range of 0.5≤C≤10 and electric Rayleighnumberintherangeof30≤T≤1600.The distributions of the electric charge density and stream function are carefully examined. Thecomputations highlight a significant effect of the eccentricity value on the flow topography. Indeed,increasingtheeccentricityvalueleadstoasignificantreductioninelectro-plumesaswellascirculationcells number. Furthermore, an intensification in cells rotation, of about 116%, was recorded wheneccentricity reaches 80%. Depending on torque values e-T, we observe the existence of multicellularregimemadeofcounter-rotatingvortexes

Numerical Investigation of the Electro-Thermo Convection in an Inclined Cavity Filled with a Dielectric Fluid

The present work is a numerical analysis of electro-thermo convection, occurring in a square differentially heated cavity filled with a dielectric fluid. The cavity experiences the combined effects of viscous, electrical, and thermal forces. The equations modelling the physical problem are solved via the finite volume approach. The study focuses on the effect of cavity tilt on the fluid flow structure and thermal performance inside the enclosure under the action of an electric field. A parametric study was performed, where the tilt angle is getting varied between 0° and 90°, as well as the Rayleigh number (5000 ≤ Ra ≤ 250,000) and the electric field (0 ≤ T ≤ 800). Furthermore, the electric charge injection level C, the mobility M and the Prandtl Pr numbers were all adjusted to a value of 10. The obtained results demonstrate that the hydrodynamic and thermal fields are significantly impacted by the cavity inclination. In addition, regardless of the thermal Rayleigh’s number, high electric field values could govern fluid movement through electric forces. Electro-convection typically demonstrates an oscillating flow due to the tilting of the cavity which gives rise to a bicellular regime occupying the entire cavity. A correlation has been established to estimate heat transfer by considering various system parameters such as cavity inclination, electrical Rayleigh number, and thermal Rayleigh number

Numerical investigation of heat transfer enhancement in dielectric fluids through electro-thermo-capillary convection

In this study, a 2D numerical analysis was conducted to investigate electro-thermo-capillary convection in a 2D enclosure filled with a dielectric fluid. The enclosure had a free top surface and was subjected to buoyancy and electrical forces. The study considered a strong unipolar injection of electric charge (C = 10), a mobility number (M = 10), and a Prandtl number (Pr = 10). Calculations were performed for various thermal Rayleigh numbers (Ra) ranging from 5000 to 50,000, Marangoni numbers (Ma) varying from −5000 to 5000 and electric Rayleigh numbers (T) ranging from 100 to 800. The coupled equations governing the electro-thermo-convection problem (Navier-Stokes, energy, charge density transport, and the Maxwell-Gauss equations) were established and solved numerically using the FVM. This study involved mathematical modelling of complex and coupled phenomena, considering viscous, thermal, thermocapillary, and electrical instabilities. The findings showed a significant improvement in heat transfer with higher electrical and thermal Rayleigh numbers. Furthermore, the control of different forces led to an increase in the Nusselt number. Specifically, the application of thermal forces resulted in a 70% increase, while the use of thermocapillary forces led to a remarkable 169% increase. Additionally, electrical forces resulted in an impressive 224% increase. Multi-parameter correlations were established to estimate the Nusselt number as a function of the Marangoni, thermal and electrical Rayleigh numbers