Dan Rafiroiu

Corona and electrostatic electrodes for high-tension separators

Abstract A systematic reseach has been performed, aiming at the optimization of the corona and electrostatic electrodes of roll-type high-tension separators for mixed granular solids. The theoretical analysis of corona-charging and charge-neutralization processes has led to a crude evaluation of the electrical parameters (corona current per unit of length, power of the corona discharge) which should characterize the electrodes for a certain application. Computer modelling of the electric field has enabled the formulation of several design principles, which have been fully-verified by the experiments. Laboratory tests have been carried out in order to compare the various technical solutions and to state some criteria for electrode evaluation. The preliminary reports on the industrial application of the suggested electrode designs are extremely encouraging.

Charging of insulating spheres on the surface of an electrode affected by monopolar ions

The charge acquired by an insulating sphere in a uniform monoionized electric field has been accurately evaluated by Pauthenier. In certain electrostatic applications, such as the electroseparation of mixed granular solids, the particles to be charged are on the surface of an electrode. Under these circumstances, Pautheniers formula is no longer valid, because the field is nonuniform. This paper addresses this problem from both a computational and an experimental point of view. A numerical method of field analysis was employed for the evaluation of the charge acquired by spheres of various dielectric constants, on the surface of a plate electrode. The numerically computed values of the saturation charge in this situation were always greater than those given by Pautheniers formula. The experiments were carried out on laboratory equipment provided with various types of corona electrodes. An electrometer was used to measure the charge acquired by calibrated spheres of polyamide (3 mm diameter) when subjected to the positive or negative corona discharge generated between these electrodes and a metallic rotating roll electrode (150 mm diameter) connected to the ground. The experimental data were in good agreement with the theoretical predictions; the saturation charge increases linearly with the applied voltage, up to a threshold at which the self discharge of the particle occurs. The efficiency of ionic charging was shown to depend on the type of corona electrode that is employed.

3D Modeling of the Induced Electric Field of Transcranial Magnetic Stimulation

The objective of our study was to make use of the MQS solver available under SEMCAD-X simulation environment and the high-resolution 3D head-and-brain model available through the IT’IS Foundation, to make a full 3D analysis of the TMS procedure. The electromagnetic field induced by two typical stimulating coils has been modeled, and their efficiencies compared. The comparison was made based on the distributions of the induced electric field, the activation function and the induced current density distribution.

Fast Virtual Fractional Flow Reserve Based Upon Steady-State Computational Fluid Dynamics Analysis: Results From the VIRTU-Fast Study

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Premises for the mathematical modeling of the combined corona-electrostatic field of roll-type separators

Corona and induction charging mechanisms are frequently associated in modern roll-type electrostatic separators. Various electrode configurations have been proposed and numerous attempts have been made in order to fully-characterize them. This paper approaches this problem from a computational point of view. The boundary element method is employed for analyzing the electrostatic field distribution generated by a typical arrangement, consisting of a wire-type corona electrode and an ellipse profile nonionizing electrode. The computed results pointed out the effect of various parameters on the uniformity of the electric field near the ionizing element and at the surface of the grounded rotating rod electrode. These data can be used by the designer in order to improve the electrode configuration, produce a uniform field in the active zone of the separator and reduce the corona inception voltage. At the same time, they paved the way for an original algorithm for the computation of the electric field distribution in the presence of the space charge generated by the corona electrodes.

Corona inception in typical electrode configurations for electrostatic processes applications

The corona inception electric field at the surface of a wire electrode is usually evaluated by an empirical formula established by Peek. That formula was found to be valid in several simple electrode configurations (wire cylinder, wire plate), which are typical to electrostatic precipitators. The aim of this paper is to extend the study to other situations encountered in electrostatic applications. The experimental setup specifically modeled the several electrode arrangements which are commonly used with roll-type electrostatic separators. It consisted of wire-type corona electrodes, connected to a regulated DC high-voltage supply, and a rotating roll electrode, connected to the ground. The effect of associating the corona wire to one or several tubular electrodes of various shapes and sizes was investigated. The experimentally determined corona inception voltage was used as input data of a boundary-element-method program for the electric field computation. The computed values of the electric field were compared with those given by Peeks formula for wire electrodes of the same radius. The derived conclusions can be of help in the custom design of the corona electrode arrangements for various electrostatic applications.

Adaptation and development of software simulation methodologies for cardiovascular engineering: present and future challenges from an end-user perspective.

This paper describes the use of diverse software tools in cardiovascular applications. These tools were primarily developed in the field of engineering and the applications presented push the boundaries of the software to address events related to venous and arterial valve closure, exploration of dynamic boundary conditions or the inclusion of multi-scale boundary conditions from protein to organ levels. The future of cardiovascular research and the challenges that modellers and clinicians face from validation to clinical uptake are discussed from an end-user perspective.

Inception of corona discharges in typical electrode configurations for electrostatic processes applications

The corona inception electric field at the surface of a wire electrode is usually evaluated by an empirical formula established by Peek. That formula was found to be valid in several simple electrode configurations (wire-cylinder, wire-plate), which are typical to electrostatic precipitators. The aim of this paper is to extend the study to other situations encountered in electrostatic applications. The experimental setup specifically modeled the several electrode arrangements which are commonly used with roll-type electrostatic separators. It consisted of several types of corona electrodes, connected to a regulated DC high-voltage supply, and a rotating roll electrode, with an embedded current probe, connected to the ground. The effect of associating the corona wire to one or several tubular electrodes of various shapes and sizes was investigated. The experimentally-determined corona inception voltage was used as input data of a boundary element method program for the electric field computation. The computed values of the electric field were compared with those given by Peeks formula for wire electrodes of same radius. The derived conclusions can be of help in the custom design of the corona electrode arrangements for various electrostatic applications.

Multiple-needle corona electrodes for electrostatic processes application

Corona from high-voltage electrodes is employed in various electrostatic installations, such as: ozonizers, air filters, powder sprayers, separators. Multiple-needle electrode designs are preferred whenever low corona onset voltage and good resistance to mechanical shocks are required. The present work aims at identifying a simple solution to overcome the main drawback of this type of electrode: the nonuniformity of the generated space-charge. The experiments were carried out with various models of electrodes, having one or several rows of stainless steel needles. A current probe, consisting of an enameled copper wire (diameter: 0.4 mm), was embedded in the center of a plane collecting electrode. For a given inter-electrode distance (5 to 50 mm) and a fixed position of the multiple-needle electrode, the collecting plate was translated along two orthogonal directions, so that the current probe could scan a 75 mm/spl times/75 mm square. The results depended on the inter-electrode distance and on the high-voltage level. An explanation is given to some observations made on a roll-type electrostatic separator provided with two models of multiple-needle corona electrodes. An improved electrode design was proposed for the industrial installations.

Evaluating the efficiency of stimulators used in magnetic stimulation of the spinal cord

This paper aims in evaluating the efficiency of magnetic stimulators capable of stimulating neural tracts of the spinal cord in healthy subjects. Our previous preliminary tests had shown that the commercial clinical magnetic stimulator Magstim Rapid2 was unable to activate nerve structures located in the spinal cord, with its maximum deliverable energy. In this study we evaluate the characteristics of magnetic stimulators designed and tested (by modelling) for this specific application and we show that the circular commercial coil is the most efficient applicable shape, and no improvements could be gained by changing the distribution of the windings of the magnetic coils. The main conclusion of the study was that a much higher initial voltage should be loaded by the stimulators capacitor in order to achieve activation of neural tracts within the spinal cord.