F. Pontiga

Plasma chemical and electrical modelling of a negative DC corona in pure oxygen

A complex plasma chemical and electrical model of a negative stationary wire-to-cylinder corona discharge in pure oxygen is presented. The corona discharge is assumed to have axial and azimuthal symmetry. The experimental current–voltage characteristic is required as input data, but there are no other adjustable or empirical parameters. The experimental validation of the results of the model comes from its prediction of the ozone concentration. The role played by different reactions and species is analysed in detail using the results of the simulation. The effect of the gas temperature and of the decomposition of ozone at the electrodes is also investigated. The agreement between the model and the experiments is excellent when the effect of ozone decomposition at the electrodes is taken into account.

Physical mechanisms of instability in a liquid layer subjected to an electric field and a thermal gradient

The linear stability of a plane layer of dielectric liquid subjected to an electric field and a thermal gradient is studied. The liquid is supposed to have a non‐negligible residual conductivity and to exhibit an injection of charge from one of the electrodes. Both effects are due to the dissolution of a given salt in the liquid. The ionic mobility and the dielectric constant are temperature dependent. The stability of this configuration is studied with the help of an heuristic model and a precise discussion of the physical mechanisms of instability is made. Complete sets of the stability maps corresponding to different cases are presented.

Electrical conduction of electrolyte solutions in nonpolar liquids

Certain nonpolar liquids, when doped with specific salts, are able to produce sustained and reproducible ion injections from one of the electrodes. Electronic transfer to the ionic pairs attached to the electrodes and the subsequent extraction of the free ions by the Schottky effect are the mechanisms responsible for this injection. The electrical conduction of these liquids is studied, using a recently proposed electric-field dependent law for the injection of ions and Onsager theory for the dissociation of ionic pairs in the bulk. Recombination is allowed between electrolytic ions and injected ions. The current-voltage characteristics predicted with this model have been presented in term of dimensionless parameters, so that an easy comparison with experiments can be done. Special attention has been paid to distinguish the contribution of the dissociation and the injection in the total current. The electric field distortion and the charge density at the injector has also been determined.

Experimental investigation and numerical modelling of positive corona discharge: ozone generation

The spatial distribution of the species generated in a wire-cylinder positive corona discharge in pure oxygen has been computed using a plasma chemistry model that includes the most significant reactions between electrons, ions, atoms and molecules. The plasma chemistry model is included in the continuity equations of each species, which are coupled with Poissons equation for the electric field and the energy conservation equation for the gas temperature. The current–voltage characteristic measured in the experiments has been used as an input data to the numerical simulation. The numerical model is able to reproduce the basic structure of the positive corona discharge and highlights the importance of Joule heating on ozone generation. The average ozone density has been computed as a function of current intensity and compared with the experimental measurements of ozone concentration determined by UV absorption spectroscopy.

Particle-in-cell simulation of Trichel pulses in pure oxygen

The development and propagation of Trichel pulses in oxygen have been numerically simulated using an improved fluid particle-in-cell (PIC) method. The numerical method has been optimized to accurately reproduce sequences of about 100 Trichel pulses (~1 ms). A classical one-dimensional model of negative corona in sphere-to-plane geometry has been used to formulate the continuity equations for electrons and ions. The effects of ionization, attachment and secondary-electron emission from the cathode have all been considered. The electric field has been obtained from the solution of Poissons equation in two dimensions. Using this model, the temporal and electrical characteristics of Trichel pulses have been investigated, in particular, the relation between applied voltage, pulse frequency and time-averaged current intensity and charge.

A Study of Ozone Generation by Negative Corona Discharge Through Different Plasma Chemistry Models

Abstract The Steady radial distribution of chemical species in a wire‐to‐cylinder ozone generator filled with pure oxygen has been computed by applying four different plasma chemistry models of increasing complexity. The most complete model considers ten species (e, O2 +, O2 −, O3 −, O−, O2, O2(1Δg), O2(1∑g +), O and O3) and 79 reactions, including ionization by electron impact, electron attachment and detachment, electron-ion recombination, charge transfer, etc. The chemical model is coupled with the electrical model through Poissons equation. The spatially averaged ozone density has been computed as a function of the current intensity and compared with the experimental values obtained by UV spectroscopy.

Ozone generation by negative corona discharge: the effect of Joule heating

Ozone generation in pure oxygen using a wire-to-cylinder corona discharge reactor is experimentally and numerically investigated. Ozone concentration is determined by means of direct UV spectroscopy and the effects of Joule heating and ozone decomposition on the electrodes are analysed for different discharge gaps. The numerical model combines the physical processes in the corona discharge with the chemistry of ozone formation and destruction. The chemical kinetics model and the electrical model are coupled through Poissons equation, and the current?voltage (CV) characteristic measured in experiments is used as input data to the numerical simulation. The numerical model is able to predict the radial distributions of electrons, ions, atoms and molecules for each applied voltage of the CV characteristic. In particular, the evolution of ozone density inside the discharge cell has been investigated as a function of current intensity and applied voltage.

Electrical and chemical model of negative corona in oxygen at atmospheric pressure

Abstract Negative corona discharge in oxygen at room temperature and atmospheric pressure is numerically investigated with four physico-chemical models of increasing complexity. The current intensity measured in wire-cylinder corona discharge is used as an input to the numerical modeling and the densities of positive, negative and neutral species are computed.

STABILITY ANALYSIS OF A TAYLOR-COUETTE FLOW OF INSULATING FLUID SUBJECTED TO RADIAL UNIPOLAR INJECTION OF CHARGE

The linear stability of a dielectric fluid filling a cylindrical capacitor is analyzed. The outer or the inner cylinders forming the capacitor may rotate with fixed angular velocities, thus generating a Taylor-Couette flow inside the fluid. A weak, moderate or strong injection of charge is assumed to occur at the anode when a high voltage is applied to the electrodes. The physical mechanisms associated to the instability of the steady flow are discussed. Special attention is paid to the case when the mobility of ions is similar to or smaller than the hydrodynamic mobility of the fluid.

The onset of electrothermal convection in nonpolar liquids on the basis of a dissociation-injection conductivity model

The onset of convection for a layer of nonpolar liquid subjected to an adverse thermal gradient and an intense electric field is examined. The electrical conductivity is determined by a physicochemical model that is based on dissociation and injection charge generation. Static instabilities and overstabilities are predicted as a function of strength of injection, C, and residual conduction, C/sub 0/. Physical and mathematical arguments show that for values of C larger (smaller) than approximately 2.8 C/sub 0/, the regime is injection dominated (conduction dominated). It is also shown that dissociation always plays a stabilizing role, unlike injection, which can have either a stabilizing or a destabilizing effect due to its indirect coupling with thermal perturbations.<<ETX>>