For a long period, there was a resolution gap between numerical modeling and experimental measurements, making it hard to conduct a direct comparison between them, but they are now developing in parallel. In this work, we numerically study diffusive ionization wave and fast ionization wave discharge experiments using recently published electric-field-induced second-harmonic (E-FISH) data together with a classical fluid model. We propose a pressure-E/N range for the drift diffusion approximation and a pressure-grid range for the local field/mean energy approximation of the fluid model. The three-term Helmholtz photoionization model is generalized using parameters given for N 2 , O 2 , CO 2 , and air. The capabilities of the classical fluid method for modeling the inception, propagation, and channel breakdown stages are studied. The calculated electric field evolution of the ionization is compared with E-FISH measurements in the discharge development and gap-closing stages. The influence of electrode shape and predefined electron density on the streamer morphology and the long-standing inception problem of the ionization waves are discussed in detail. Within the application range of the classical fluid model, good agreement can be achieved between calculation and measurement.

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Water-based lubricants with different fractions of TiO2 nanoparticles ranging from 1.0 to 9.0 wt% were utilized to study the lubrication mechanisms during micro rolling tests and the tribological behaviour of nanolubricants during the micro rolling of copper foils. The results indicate that the application of TiO2 nanolubricants remarkably improves the surface quality of rolled copper foils during rolling processes. For lubricants with inadequate TiO2 nanoparticles, it is found that few TiO2 nanoparticles enter the contact regions between the rolls and foils, causing insufficient lubrication during rolling processes. Instead, for lubricants with excessive TiO2 nanoparticles, obvious agglomeration occurs at the contact regions and promotes the generation of voids on the surface of the rolled foils, thereby deteriorating the surface quality of the rolled copper foils. In addition, it is found that the surface quality of rolled foils is improved by utilizing a large reduction ratio. Overall, the fraction of 3.0 wt% TiO2 nanolubricants is optimal to improve the lubrication conditions at the contact regions, thereby improving the surface quality of the rolled copper foils.

Single-pulse nanosecond surface dielectric barrier discharges operated in synthetic air and pure nitrogen at elevated pressure (6 bar) have been numerically studied by the classical fluid method. The aim of this work is to provide the necessary basis for analyzing the surface streamer-to-filament transition phenomenon. The electrical parameters, discharge morphology and propagation dynamics, as well as the possible influence of photoionization, kinetics and gas heating on the surface streamer stage at elevated pressure are discussed in a combined numerical-analytical way. A good agreement between measurement, numerical simulation and analytical estimation is achieved. The streamer thickness is derived to be inversely proportional to the pressure, the average reduced electric field in the streamer channel ranges from 75-150 Td, and the average electron density in the channel is ∼ 10 22 m −3 for both polarities. The characteristic time of electron decay in the positive streamer channel is only on the order of ∼ 1 ns due to high charge exchange and electron-ion recombination rates. Photoionization provides an ionization source of 10 27 -10 28 m −3 s −1 in front of the streamer head for both gases. Stepwise ionization/dissociation significantly affects the discharge dynamics of negative polarity SDBD, while for positive polarity this influence is negligible. The fast gas heating could lead to ±0.15 cm change of the positive streamer length. The secondary surface ionization wave is numerically observed, providing a time duration 0.25-0.5 ns of high electric field (230 Td), making it possible for streamer-to-filament transition kinetics to take place.

The fast ionization wave (FIW) discharges in pure nitrogen in a capillary tube at 27 mbar, initiated by positive polarity, high-voltage nanosecond pulses, are numerically studied by coupled two-dimensional plasma fluid modeling. The 2D fluid code based on local mean energy approximation is validated and used, an extended three-exponential Helmholtz photoionization model is proposed for pure nitrogen. The development and structure of the nitrogen FIW is analyzed, the electric field and current are calculated compared with experimental measurements. The evolution of radial distribution of electrons and N2(C 3Π u ) during the FIW development stage and in the afterglow are analyzed, the radial profiles of electron density show a ‘hollow’ structure in the FIW development stage, the temporal-spatial evolution of N2(C 3Π u ) is dominated by the competition between the pooling reaction of N 2 ( A 3 Σ u + ) and the quenching by electrons. The role of photoionization on the nitrogen FIW radial morphology is discussed, the equivalent background electron density of photoionization in nitrogen discharge is suggested to be (4–6) × 1013 m−3. Spatial distribution of specific energy deposition (SED), fast gas heating (FGH) energy and temperature rise are obtained, heating efficiency varies with electric field E/N and SED and tends to be 10% at high SED. The dominating reactions responsible for FGH and their fractional contribution in space and time are analyzed, in the near axis region, pooling reactions of N 2 ( A 3 Σ u + ) and N2(B 3Π g ) contribute up to 80% FGH energy, electron impact dissociation of molecular nitrogen contributes about 10%, while e- N 2 + recombination and quenching of N(2 D) atoms by N2 molecules contribute rest.