Chasseneuil-du-Poitou, France
Chasseneuil-du-Poitou, France

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Dantchi K.,Bulgarian Academy of Science | Philippe T.,Institute PPRIMME | Hubert R.,Institute PPRIMME | Christophe L.,Institute PPRIMME
Proceedings - IEEE International Conference on Dielectric Liquids | Year: 2011

We study the electro-thermo-convective phenomena in a dielectric liquid layer of depth H placed between two electrodes and subjected to the simultaneous action of an electric field and a thermal gradient. The full set of governing equations is directly solved using a finite volume method. In this paper we first heat from the lower electrode and apply the electric potential when the thermal steady state is obtained. Only the case of strong injection of electric charges is considered. The flow pattern and Nusselt number strongly depend on the following non dimensional characteristic parameters: electrical parameter T, Rayleigh number Ra, Prandtl number Pr and mobility parameter M. The electro-convective flow structure is analysed in a rectangular cavity of length 2H, where the pure thermo-convection gives rise to two rolls whereas the pure electro-convection (with injection) gives a four roll pattern. The combined effect of both electric and thermal field on the flow patterns and on Nusselt number is analyzed for different values of Pr and M. © 2011 IEEE.


Dantchi K.,Bulgarian Academy of Science | Philippe T.,Institute PPRIMME | Hubert R.,Institute PPRIMME
Journal of Electrostatics | Year: 2013

In this article we study the electro-thermal convection in a dielectric liquid layer placed between two electrodes and subjected to the simultaneous action of an electric field and a thermal gradient. The full set of equations describing the electro-thermo-convective phenomena is directly solved using a finite volume method. We first heat the liquid from below at time t=0, wait for the thermal steady state and then inject the electric charges by applying the electric potential. The development of the electro-convective motion is analysed in detail in two cases: 1) strong injection from the lower electrode, 2) strong injection from the upper one. We also study the heat transfer enhancement due to electro-convection. The evolution in time of the Nusselt number Nu for different combinations of the two usual non-dimensional parameters associated to the electro-thermo-convection phenomena (Rayleigh number Ra and the electrical parameter T) is also given and analysed. We study the electro-thermal convection in dielectric liquid layer under action of electric field and thermal gradient. The relevant equations are solved by finite-volume method. The convective motion and heat transfer is analysed for strong injection from the lower and upper electrode. We show that: electro-convection significantly increases heat transfer; Nusselt number is independent of the Rayleigh number; the difference between both cases of injection is negligible. © 2013 Elsevier B.V.


Dantchi K.,Bulgarian Academy of Science | Philippe T.,Institute Pprimme | Hubert R.,Institute Pprimme | Jian W.,Institute Pprimme | Christophe L.,Institute Pprimme
Journal of Electrostatics | Year: 2013

In this article the electro-thermo-convective phenomena in a dielectric liquid enclosed in a 2D cavity and subjected to the simultaneous action of an electric field and a thermal gradient is studied. We solved directly the full set of coupled equations of Electro-Hydro-Dynamic (EHD) and energy equation using a finite volume method. In order to characterize the influence of the electric field on heat transfer the liquid is first heated (from a lateral wall) till the thermal steady state is obtained and then the electric potential and injection of electric charge is applied. Two cases of injection are considered: from the lower electrode and from a lateral wall (left or right). The flow pattern and Nusselt number strongly depend on the non-dimensional characteristic parameters: electrical parameter, Rayleigh number, Prandtl number and mobility parameter M. The convective motion passing from a purely thermal convection to a purely electrical convection and the number of electro-thermo-convective rolls patterns are investigated.As a consequence of the analysis of the combined effect of electric and thermal fields on the flow structure and on Nusselt number, we have also evaluated the heat transfer enhancement due to electroconvection. It is shown that the injection of electric charge increases the heat transfer and Nusselt number is independent of Rayleigh number for high enough values of T. © 2013 Elsevier B.V.


Demenet J.-L.,Institute PPRIMME | Amer M.,Institute PPRIMME | Tromas C.,Institute PPRIMME | Rabier J.,Institute PPRIMME
Materials Science Forum | Year: 2012

4H-SiC intrinsic homoepitaxied single crystals have been nano indented at room temperature using a spherical indentor and the related deformation microstructures have been analyzed by TEM. Dislocations are lying on the basal plane but have been found to be perfect, in contrast with observations made at higher temperature. Although such a change in deformation mechanism has been observed in other semiconductors such as silicon and indium antimonide, it was unexpected in a very low stacking fault material such as SiC. © (2012) Trans Tech Publications.


Rabier J.,Institute PPRIMME | Pizzagalli L.,Institute PPRIMME
Journal of Physics: Conference Series | Year: 2011

The mechanism of dislocation dipole annihilation has been investigated in C and Si using atomistic calculations with the aim of studying their annihilation by-products. It is shown, in C as well as in Si, that dipole annihilation yields debris that can be depicted as a cluster of vacancies, or alternately by two internal free surfaces. These defects have no strain field and can hardly be seen using usual TEM techniques. This suggests that the brown colouration of diamond could be due to microstructures resulting from deformation mechanisms associated with dipole formation and their annihilation rather than to a climb mechanism and vacancy aggregation. In silicon where a number of dipoles have been evidenced by TEM when dislocation trails are found, such debris could be the missing link responsible for the observation of strong chemical reactivity and electrical activity in the wake of moving dislocations. © Published under licence by IOP Publishing Ltd 2011.


Demenet J.L.,Institute PPRIMME | Amer M.,Institute PPRIMME | Mussi A.,Institute PPRIMME | Mussi A.,CNRS Materials and Transformations Unit of UMET | Rabier J.,Institute PPRIMME
Journal of Physics: Conference Series | Year: 2011

Instrumented micro-indentations have been performed at room temperature on 4H-SiC homoepitaxial single crystals with different doping. For these experiments, it appears that the pop-in event occurs at the same level of load for intrinsic and n-type SiC and at a higher load level for p-type. Correlation of the pop-in event with dislocation nucleation indicates that doping acts on dislocation nucleation and that p-type doping plays a hardening role on the plastic behaviour of 4H-SiC. This result is confirmed by the conventional measurement of imprint size using scanning electron microscopy. © Published under licence by IOP Publishing Ltd 2011.

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