Adrian Samuila

Tribocharging of Mixed Granular Plastics in a Fluidized-Bed Device

The output of any electrostatic separation process is strongly dependent on the effectiveness of particle charging. The aim of the present paper is to evaluate the effects of several factors that might influence the efficiency of a fluidized bed tribocharger, in the presence of an electric field orthogonally oriented to the direction of the fluidization air. The experiments were carried out on several synthetic mixtures of binary granular mixtures. The velocity of the fluidization air, the duration of the tribocharging process, and the composition of the mixture were the three process variables investigated. Whenever possible, the effects of these variables on the output of the process (i.e., the mass and the charge of the granules collected at the electrodes), were evaluated using the experimental design methodology. The results of full- and composite-factorial experimental designs were analyzed with a commercial software (MODDE 5.0, Umetrics). The effectiveness of the charging process was found to depend significantly on each of these factors. The propitious aerodynamic design of the device is a prerequisite for the successful industry application of the technique.

Behavior of Conducting Particles in a New Electrostatic Separator with Two High-Voltage Electrodes

The objective of this work was to analyze the behavior of good conducting granules in a newly designed plate-type electrostatic separator. Commercial software was employed for the numerical analysis of the electric field generated by an original electrode configuration. This enabled the evaluation of the electric charge and forces on conducting particles. The trajectory of a single particle was calculated over a set of 1300 points. The simulated results show that the trajectories depend on the applied voltage, the radius, and the mass density of the granules. They were found in good agreement with the experiments carried out on a laboratory electrostatic separator.

Numerical Modeling of Insulating Particles Trajectories in Roll-type Corona-Electrostatic Separators

The trajectories of the insulating particles in roll-type corona-electrostatic separators depend on the configuration of the electrode system, the applied high voltage, the roll speed, the size of the particles and the relative humidity of the ambient air. The aim of this work was to point out how numerical modeling can be of use in the study of the effects of these factors. Particle charging is modeled using the Pautheniers equation for spheres in uniform electric field. The equation of particle discharging was obtained after an experimental study of the surface potential decay of a granular layer of insulating material in contact with an electrode. The trajectories are computed based on the balance equation of the electrical and mechanical forces that act on such charged particles. The numerical results are in good agreement with the experimental findings.

Experimental modeling of the tribo-aero-electrostatic separation of mixed granular plastics

A tribo-aero-electrostatic separator can be successfully employed for the selective sorting of granular mixtures of polymers. The tribocharging of the material to be separated occurs in a parallelepiped fluidized bed. Two opposite walls of this device consist of metallic plates connected to two DC high-voltage supplies of opposite polarities, so that the charged granules are attracted to these electrodes and separated while still in fluidized state. The granules are then collected in two recipients each placed in a Faraday pail, to allow the instantaneous measurement of the mass and charge of the separated products. The experiments were carried out on binary mixtures of virgin polyamide and polycarbonate granules both in intermittent and continuous regime Real-time data-acquisition enable the monitoring of the separation outcome, i.e. mass, purity and charge, at various values of the applied voltage, of the mass of material and of the proportions in the granular mixture.

Comparative Experimental Study of Triboelectric Charging of Two Size Classes of Granular Plastics

The free fall triboelectrostatic separation is widely used for the selective sorting of plastics from granular industrial waste. The electric charge per mass ratio of the granules is a critical parameter influencing the purity of recycled plastics and the efficiency of the electrostatic separation process. The aim of the present study is to validate an experimental procedure for the optimization of the vibratory-type tribocharging device for granular plastics. This tribocharger is composed of a metal plate covered with a thin PET (polyethylene terephthalate) layer. The amplitude of the vibratory motion of the plate can be adjusted using a potentiometer. The length of the vibratory feeder, the flow rate, and the velocity, at which the granules move on its surface, are the variables that can be controlled in order to optimize the tribocharging process. As particle size is an important physical factor influencing the charging process, the study was focused on two size classes (1 to 2 mm and 2 to 5 mm) of ABS (acrylonitrile butadiene styrene) granules originating from the recycling process of waste electrical and electronic equipment. The optimum operating conditions, obtained by using the response surface modeling methodology, differ between the two size classes of granules. Both the length of the vibratory tray and the velocity of the granules on its surface have a significant effect on the outcome of the tribocharging process.

Numerical and Experimental Modeling of Star-Connected Three-Phase Capacitors

This paper is aimed at characterizing two possible designs of star-connected three-phase capacitors developed for utilization with the protection schemes of industrial installations. A superficial charge simulation program was employed for estimating the capacitances of one design. The results pointed out the influence of various geometrical parameters on the magnitude of the mutual capacitance between the armatures of any two of the three elementary capacitors of the three-phase unit. The experimental results confirmed the theoretical predictions and validated the advantageous features of a second design, which ensured balanced mutual capacitances between the three phases.

Robust Design and Capability Evaluation of a Tribo-Aerodynamic Charging Process for Fine Particles

Robustness and capability are critical issues for the industrial application of any novel electrostatic process. The aim of the present work is double: - show how experimental design methodology can contribute to assessing the robustness of a given tribo-aerodynamic charging process; - validate a procedure for evaluating the capability of two tribo-aerodynamic chargers, with respect to the specific requirements of electrostatic separation applications. The results of three fractional factorial experimental designs performed on starch and flour powders, in two devices similar to the tribo-guns employed for electrostatic powder coating, demonstrate that the tribo-aerodynamic charging is robust with respect to the three main control variables of the process: the injection and vortex pressures of the air in the pneumatic circuit, and the material feed-rate. The capability indexes computed for both the straight-type and spiral-type tribo charges were satisfactory.

Molecular Dynamics of Poly 3-Hexyl Thiophene by Broadband Dielectric Spectroscopy

Some of the most exciting novel approaches for renewable solar energy conversion are the organic photovoltaic devices that take advantage of the unique properties of polymers such as poly(3-hexylthiphene) (P3HT). Although this type of devices present significant advantages (stability, price) their long-term performance has to be continuously improved. This study describes the dielectric behaviour of pristine poly(3- hexylthiophene) (P3HT) and its nanocomposites versus temperature and frequency by using broadband dielectric spectroscopy. Dielectric spectra reveal the existence of two relaxation phenomena (alpha, beta), below and above the glass transition. The a relaxation is related to the crystallization phenomena and the beta relaxation is due to dipolar polarization processes. These results can be incorporated into a continuous understanding of the electrical behaviours of such polymers, which play extremely important roles in the overall quality of photovoltaic devices that use such polymeric materials.