13 December 2021

Thesis defense of Miss Michelle NASSAR

Thesis defense of Miss Michelle NASSAR - Salle de Communication au Bâtiment H1 -SP2MI - 13/12/2021 10h00

Electrical devices, especially embedded ones, are becoming more and more compact and require higher power consumption. In fact, all these electrical components produce heat that must be evacuated to maintain an efficient operation. In this context, the electrofluidodynamics team at the Pprime Institute works on developing electrohydrodynamic (EHD) systems that have shown numerous advantages for both spatial and terrestrial applications. In order to achieve an optimized performance, EHD systems use ecofriendly dielectric liquids, such as Hydrofluoroethers (HFE), whose electrical behavior is not well defined yet. The objective of the current work is to characterize the variations of the electrical properties of HFE 7000 and 7100 in function of temperature. Several methods are used to analyze the electrical behavior of these liquids at low voltage. The first method is in accordance with the guidelines of the IEC 61620 standard and the second one is based on dielectric spectroscopy.

The study is then extended to the thermal behavior under high voltage. The analysis of the currentvoltage characteristics makes it possible to highlight the three typical zones of the electrical behavior: ohmic, quasiohmic and injection, and thus to define the limits of the conduction and injection (or iondrag) regimes. The study at high voltage also addresses, in compliance with the IEC 60156 standard, the problem of the dielectric strength of the two HFEs at different temperatures in both gas and liquid phases. Finally, an innovative preliminary study on the Kerr effect in HFE7100 is conducted. It shows

that this electrooptical effect can be used to study the development of charged layers at the HFE/electrode interfaces. In conclusion, the results obtained in this work contribute to the understanding of the electrical behavior of HFEs. This is necessary to improve and optimize the performance of EHD systems working with these liquids.