Electron swarm parameters and dielectric strength of C5F10O and its mixtures with CO2 and dry air

Perfluoroketone C5F10O is considered as a potential SF6 alternative. The GWP (Global warming potential) of C5F10O is extremely low and even close to that of air. We investigated the electrical insulation properties of the C5F10O by pulsed Townsend (PT) experiment. The rate coefficients of ionization, attachment, and effective ionization, as well as the electron drift velocity and the longitudinal electron diffusion coefficient in pure C5F10O were obtained. We conclude that the density-reduced critical electric field of pure C5F10O is (768±5)Td and ion kinetics are not exist or negligible in C5F10O. Furthermore, the swarm parameters of C5F10O /CO2 and C5F10O /Air mixtures with C5F10O percentage up to 30% were measured in a wide E/N-range. C5F10O has good synergism with both CO2 and dry air and air behaves better. The synergistic effect coefficients were also calculated. To have the same (E/N)crit as pure SF6, the mixing ratio of C5F10O should be 30% in the mixture with CO2 and 26% in the mixture with dry air. The obtained electron swarm parameters in this paper provide a supplement for the fundamental data set of these novel gases, and also lay the foundation for fluid model simulations of gas discharge.

Electron Swarm Parameters and Dielectric Properties of the Superconducting Binary Mixtures of He-H2

In this study, the electron energy distribution function EEDF, the electron swarm parameters, the effective ionization coefficients, and the critical field strength (dielectric strength) in binary He-H2 gas mixture which used as cryogenic for high-temperature superconducting power application, are evaluated by using two-term approximation of the Boltzmann equation over the range of E/N ( the electric field to gas density) from 1 to 100 Td ( 1 Td=10-17 Vcm2) at temperature 77 K and pressure 2MPa, taking into account elastic and inelastic cross-section. Using the calculated EEDF, the electron swarm parameters (electron drift velocity, mean electron energy, diffusion coefficient, electron mobility, ionization and attachment coefficient) are calculated. At low reduced electric field E/N, the EEDF close Maxwellian distribution, at high E/N, due to vibrational excitation of H2 the calculated distribution function is non-Maxwellian. Besides, in the He-H2 mixture, it is found that increasing small amount of H2 enhances to shift the tail of EEDF to the lower energy region, the reduced ionization coefficient α/N. reduced effective ionization coefficient (α-η)/N) decreases, while, reduced attachment coefficient η/N, reduced critical electric field strength (E/N)crt. and critical electric field Ecrt. Increases, because of hydrogen’s large ionization cross-sections. The dielectric strength of 5% H2 in mixture is in good agreement with experimental values, it is found that dielectric strength depend on pressure and temperature. The electron swarm parameters in pure gaseous helium (He) and hydrogen (H2), in satisfying agreement with previous available theoretical and experimental values. The validity of the calculated values has been confirmed by two-term approximation of the Boltzmann equation analysis.

Effective ionization coefficients for low current dc discharges in alcohol vapours at low pressure

This paper presents results for effective ionisation coefficients ($$\alpha _{\mathrm {eff}}/N$$ α eff / N , N—gas density) obtained from the breakdown voltage and emission profile measurements in low-pressure dc discharges in vapours of alcohols: methanol, ethanol, isopropanol, and n-butanol. Our results for $$\alpha _{\mathrm {eff}}/N$$ α eff / N are determined from the axial emission profiles in low-current Townsend discharge and lay in the interval of reduced electric field E/N (E—electric field, N—gas density), from 1 kTd to 8.8 kTd. We also give a comparison of our experimental results with those from the available literature. Our data cover the high E/N range of the standard operating conditions and in the region where other data are available we have a good agreement. Graphic abstract

On Refining the Criterion for a Single Avalanche-tо-Streamer Transition in Air in Strong Uniform Electric Fields

The article presents the results from mathematical modeling of avalanche-to-streamer transitions in an air discharge gap. The electric field is uniform with the strength E0=50--70 kV/cm, and the atmospheric conditions are standard. The consideration is limited to single avalanche-to-streamer (SATS) transitions. The moment of time corresponding to the plasma streamer channel incipience is taken as the transition moment. As a result of the SATS transition, a two-headed streamer is generated. First, its negative anode-directed head is formed from the avalanche. After that, its positive cathode-directed head emerges from the avalanche track. Behind it, the field strength decreases to a critical value at which effective impact ionization is impossible. The streamer plasma channel occurs earlier, in the negative head incipience process. When it appears, effective ionization still continues between the avalanche and its track. The critical number of electrons in the avalanche, which is determined by the time the channel appears, depends weakly on the E0 value if the avalanche-streamer transition occurs far from the electrodes. In this case, it is about 30 million. If the transition occurs near the electrodes, this number lies in the range from 40 to 50 million particles.

Ionization and Attachment Coefficients in C4F7N Gas Measured by the Steady-State Townsend Method

The normalized Townsend first ionization coefficient α/N and normalized attachment coefficient η/N in pure C4F7N were measured by using the steady-state Townsend (SST) method for a range of reduced electric fields E/N from 750 to 1150 Td at room temperature (20 °C). Meanwhile, the effective ionization coefficients are obtained. All SST experimental results show good agreement with pulsed Townsend (PT) experiment results. Comparisons of the critical electric fields of C4F7N with SF6 and other alternative gases such as c-C4F8 and CF3I indicate that C4F7N has a better insulation performance with a much higher normalized critical electric field at 959.19 Td.

Collection efficiency of <i>α</i>-pinene secondary organic aerosol particles explored via light-scattering single-particle aerosol mass spectrometry

We investigated the collection efficiency and effective ionization efficiency for secondary organic aerosol (SOA) particles made from α-pinene + O3 using the single-particle capabilities of the aerosol mass spectrometer (AMS). The mean count-based collection efficiency (CEp) for SOA across these experiments is 0.30 (±0.04 SD), ranging from 0.25 to 0.40. The mean mass-based collection efficiency (CEm) is 0.49 (±0.07 SD). This sub-unit collection efficiency and delayed vaporization is attributable to particle bounce in the vaporization region. Using the coupled optical and chemical detection of the light-scattering single-particle (LSSP) module of the AMS, we provide clear evidence that delayed vaporization is somewhat of a misnomer for these particles: SOA particles measured as a part of the AMS mass distribution do not vaporize at a slow rate; rather, they flash-vaporize, albeit often not on the initial impact with the vaporizer but instead upon a subsequent impact with a hot surface in the vaporization region. We also find that the effective ionization efficiency (defined as ions per particle, IPP) decreases with delayed arrival time. CEp is not a function of particle size (for the mobility diameter range investigated, 170–460 nm), but we did see a decrease in CEp with thermodenuder temperature, implying that oxidation state and/or volatility can affect CEp for SOA. By measuring the mean ions per particle produced for monodisperse particles as a function of signal delay time, we can separately determine CEp and CEm and thus more accurately measure the relative ionization efficiency (compared to ammonium nitrate) of different particle types.