Investigation of the Dielectric Strength of Supercritical Carbon Dioxide–trifluoroiodomethane Fluid Mixtures

We investigate the dielectric strength of supercritical carbon dioxide–trifluoroiodomethane (CO2–CF3I) fluid mixtures. Supercritical fluids (SCFs), as a novel dielectric medium, combine advantageous properties of gaseous and liquid dielectrics: most notably, low viscosity, high heat transfer capability, and high dielectric strength. To our knowledge, this supercritical mixture of substances has never been investigated with respect to its dielectric properties. Our results suggest that supercritical CO2–CF3I binary mixtures have the electrical breakdown behavior similar to what we had observed in pure SCFs near the critical point. Specifically, we present the first evidence that the density fluctuation in SCF binary mixtures has a direct impact on the mean free path of electrons. By adjusting the mixing ratio, we show that the region where the discontinuity of breakdown voltage occurs shifts based on the ratio of the two substances. In addition, the experiment result shows a dielectric strength of the supercritical CF3I–CO2 mixture reaching up to 350 kV/mm, which is comparable to solid insulating materials. This paper indicates the suitability of using the supercritical CF3I–CO2 mixture as a dielectric medium for high power density applications.