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In this paper, we report a qualitative model of operation and energy release in pulsed dielectric barrier discharges (DBDs). We demonstrate that pulsed DBDs operate according to the “maximum power principle” and explain the relevant physical processes. Compared to experimental data, the proposed model allows an accurate estimation of the discharge pulse energy as a function of dielectric properties, electrode size, and pulse parameters (shape and voltage amplitude). [ABSTRACT FROM AUTHOR]

The structure, fluid-dynamic behavior, temperature, and radiation emission of a cold atmospheric pressure plasma jet driven by high-voltage pulses with rise time and duration of a few nanoseconds have been investigated. Intensified charge-coupled device (iCCD) imaging revealed that the discharge starts when voltage values of 5–10 kV are reached on the rising front of the applied voltage pulse; the discharge then propagates downstream the source outlet with a velocity around 10^7 – 10^8 cm/s. Light emission was observed to increase and decrease periodically and repetitively during discharge propagation. The structure of the plasma plume presents a single front or either several branched subfronts, depending on the operating conditions; merging results of investigations by means of Schlieren and iCCD imaging suggests that branching of the discharge front occurs in spatial regions where the flow is turbulent. By means of optical emission spectroscopy, discharge emission was observed in the ultraviolet-visible (UV-VIS) spectral range (N2, N2+, OH, and NO emission bands); total UV irradiance was lower than 1 $\mu $ W/ \mathrm{cm}^{2} even at short distances from the device outlet (<15 mm). Plasma plume temperature does not exceed 45 °C for all the tested operating conditions and values close to ambient temperature were measured around 10 mm downstream the source outlet. [ABSTRACT FROM PUBLISHER]

In this paper, a plasma arc welding (PAW) process operating in pure Ar with constant current at 40 A has been characterized by means of a thermofluid-dynamic modeling and optical emission spectroscopy (OES). Excitation temperature of Ar atoms in the fringes of the arc measured using the OES has been found higher than temperature calculated from local thermodynamic equilibrium modeling, even if radiation reabsorption is taken into account using a discrete ordinate model; on the contrary, excitation temperature of Ar atoms is in a good agreement with electron temperature calculated using a two-temperature model for thermal nonequilibrium neglecting radiation reabsorption. Results reported suggest that for the investigated PAW process, thermal nonequilibrium due to steep radial temperature gradients induces a Boltzmann distribution of excited states at the electron temperature. [ABSTRACT FROM PUBLISHER]

Dielectric barrier discharges (DBDs) are being studied for a wide range of biomedical and industrial applications. In this paper, qualitative results coming from synchronized high-speed and Schlieren multi-imaging of a unipolar nanosecond-pulsed DBD are presented, with the final aim of showing plasma structure, filament movement, and refractive index gradients in different interelectrode gaps and counter electrode materials. [ABSTRACT FROM PUBLISHER]

Intense and energetic atmospheric plasma was achieved by jet-to-jet coupling using an array of plasma jets arranged in an axisymmetric structure. To highlight the effects of pulse repetition frequency, peak voltage and mass flow rate on the transition from a coupled mode to an uncoupled one, qualitative results coming from iCCD imaging of a nanopulsed Gatling machine gun-like plasma source will be shown. Moreover, results on surface modifications and bacterial inactivation will be presented. [ABSTRACT FROM PUBLISHER]

High-speed and Schlieren imaging have been used to visualize ignition transients, discharge behavior and flow fields of a plasma device integrating a low-power inductively coupled plasma torch, generating a high temperature thermal plasma, with a quenching device, able to cool the gaseous effluent down to biocompatible temperatures for effective use in biomedical applications. [ABSTRACT FROM PUBLISHER]

A 3-D time-dependent simulation of a laboratory-scale inductively coupled thermal plasma torch system has been carried out to investigate unsteady turbulent flow patterns, which may arise in the reaction chamber as a consequence of a sharp expansion of the gas at the torch outlet. A large eddy simulation model has been used to predict the instantaneous flow field without any time filtering, as done in the Reynolds averaged Navier–Stokes models (for example, \kappa-\varepsilon or Reynolds stress model). [ABSTRACT FROM AUTHOR]

High-speed imaging of the pilot arc transient phase in plasma arc cutting has been carried out synchronizing the use of two high-speed cameras in conjunction with an optical system suitably designed for producing multiple synchronized views of the same phenomenon. Such imaging techniques have allowed a deeper understanding of the pilot arcing process, owing to the simultaneous visualization of anode and cathode attachments and through the development of tomographic reconstruction of the pilot arc. [ABSTRACT FROM AUTHOR]