G.S.P. Castle

Contact charging between insulators

Abstract Contact charging between insulators was one of the earliest manifestations of electrical science. Yet reproducible experiments remain a challenge and a generally agreed upon theory of insulator-insulator charging remains elusive. The experimental difficulties in this field and current progress towards a satisfactory theory are discussed. Some recent experimental results are shown and unanswered questions identified.

ELECTROSTATIC SEPARATION OF PLASTICS FOR RECYCLING

Abstract The authors describe some successful experiments for electrostatic separation of various two-component mixtures of plastic waste. Two methods of triboelectric charging of plastics are described. One consists of a fluidized bed system with a central feeding tube. The second is a novel form of a rotating tube charger. Separation takes place in an electrostatic separation tower equipped with a set of nine sampling bins at the bottom for collection of the components. Numerous experiments have shown the feasibility of obtaining extract contents in excess of 99%. The rotating tube charger is preferred over the fluidized bed because of its simplicity and energy savings. The process has recently been adapted to an industrial scale capable of processing 1000 kg/hour and is currently being used to separate post-industrial plastic waste.

The measurement of bipolar charge in polydisperse powders using a vertical array of Faraday pail sensors

A vertical array of Faraday pail sensors was developed to partially separate bipolar charged polydisperse powder and measure the charge-to-mass ratio of the powder deposited in each Faraday pail. In our experiments, the system consisted of seven Faraday pails, six special Faraday pails, which were mounted vertically in cascade, and a normal Faraday pail located at the bottom. The inner and outer pails of the special Faraday pails had open holes on the upper and lower covers. The bipolar charged polydisperse powder was sampled from an earthed metallic fluidized bed with an earthed metallic vertical tube at the axis of the bed. As the powder falls, individual particles experience separation forces due to the gravity segregation and space charge repulsion. The particles thus deposit into different inner Faraday pails according to their charge, size and mass. Each powder sample was collected and the charge-to-mass ratio was measured. The size distribution of the particles sampled from each Faraday pail was analyzed to clarify the effect of this factor on contact charging between particles.

General model of sphere-sphere insulator contact electrification

Abstract A general surface state model for sphere-sphere contact charging is suggested from which the familiar low and high density limits are derived. Such a model is applicable to electrophotographic toner-carrier charging experiments. The model is tested against an extended set of toner-carrier charging data gathered from the literature covering a wide range of material properties. In addition, data are reported for the special case of a conductive carrier and an insulating negative charging toner. These results show that the majority of the data agree with the high density limit of the model.

The effects of high field DC pulse and liquid medium conductivity on survivability of Lactobacillus brevis

Survivability of Lactobacillus brevis cells in suspensions of phosphate buffer solutions of different conductivities (170 μS/cm to 2230 μS/cm) using electric pulse application has been investigated under varied test conditions. Survivability decreased rapidly with the application of the first few pulses (approx. 25 to 50 depending on the test conditions). However, the destruction performance decreased with increased number of pulse applications. Hence to obtain a maximum reduction in survivability, the electrical conditions should be so selected that effective killing is achieved with the fewest number of pulses applied. The maximum reduction in survivability (N/N0, approx. 10−7) was obtained in liquid possessing the lowest conductivity (170 μS/cm) with an application of 150 pulses of 160-μs pulse width. Despite the increase in liquid medium temperature during pulse treatment, the killing was significantly due to pulse as the maximum temperature rise (22° C) during treatment was insufficient to cause any synergistic effect of temperature and pulse treatment. In this work we have shown for the first time that if the pulse width is kept constant, the higher reduction in survivabilities observed in liquids with lower conductivities was primarily due to conductivity influencing the membrane permeability. The small change in test liquid pH (<0.5) indicated that the killing of cells was affected primarily by high field pulses rather than by-products of electrolysis in the medium of different conductivities.

Effects of high electric field pulses on Lactobacillus brevis at elevated temperatures

The technique of electroporation has been successfully applied to caused a nonthermal lethal effect on the bacterial cells Lactobacillus brevis in a buffered phosphate solution. Tests were carried out at different temperatures (24 degrees C, 30 degrees C, 45 degrees C, and 60 degrees C) to determine if there is a synergistic effect of temperature and electric pulse treatment on the destruction of L. brevis cells. Experimental results indicate that the viability of L. brevis declines exponentially with treatment time and is electric field and temperature dependent.<<ETX>>

Trichel pulse characteristics—negative corona discharge in air

In this paper a three-species two-dimensional model is used for the simulation of the Trichel pulse regime of corona discharge in air for a point-plane configuration. Effects of different parameters of the model on Trichel pulse characteristics (Trichel pulse period and the average corona current) are studied. The parameters of interest are external resistance of the circuit, secondary electron emission coefficient and negative and positive ion mobilities. Moreover, the numerical simulation was performed for the configuration used in the experimental analysis reported in the literature and the results proved to be very compatible.

Industrial applications of electrostatics: the past, present and future

Abstract Although the scientific principles governing electrostatic forces have been known for many centuries the first successful industrial application did not occur until 1907. The development of two major present technologies, electrostatic precipitation and electrostatic coating is described and important features characteristic of each are identified. It is suggested that in the future a number of new industrial applications will come from developments in micro-electrical mechanical systems (MEMS), biotechnology, ultra fine particles and space.

Numerical Simulation of Trichel Pulses in a Negative Corona Discharge in Air

In this paper, a new 2-D model is presented for numerical simulation of Trichel pulses in a point-plane configuration. Both radial and axial components of the electric field are considered and it is assumed that three ionic species exist in the air gap: electrons, and positive and negative oxygen ions. The Poisson equation is solved for electric field calculations and three continuity equations for modeling the transport of charge densities in the air gap. The finite element method (FEM) is used for solving the Poisson equation and a combined Flux Corrected Transport-FEM is used for the charge transport equations. Trichel pulses for different applied voltages are shown and the characteristics of these pulses at different voltages are compared with experimental results reported in the literature. The time variation of the electric field on the corona electrode at different stages of one Trichel pulse is also presented. Moreover, the distributions of electron, positive ion and negative ion densities at different stages of the Trichel pulse are discussed.

Ozone Generation in an Electrostatic Precipitator With a Heated Corona Wire

The body of information in this paper is directed to individuals involved in the design of electrostatic precipitators or of any devices utilizing the corona discharge where the ozone generation is considered to be a problem. A method that gives as much as 85 % reduction in the ozone generation per unit corona current for a given corona wire is described. The electrical parameters governing the formation of O3 in an electrical discharge are summarized. It is shown that a reduction in the average gas density in the ionized sheath of a corona discharge should lead to lower O3 generation. Experiments were carried out with an a.c. heating current being used to heat a corona wire in a cylindrical geometry corona section. It was found that as the heating power applied to the wire increased, the O3 generation per unit corona current decreased for both positive and negative corona. An experimental formula was obtained that relates the heating power to the O3 generation with and without heating for positive corona...