Leslie E. Sparks

A mathematical model for calculating electrical conditions in wire‐duct electrostatic precipitation devices

A new method is developed which can be used to calculate electrical conditions in wire‐duct electrostatic precipitation devices. The method, based upon a numerical solution to the governing differential equations under a suitable choice of boundary conditions, accounts for the effect of space charge and is applicable over the entire range of current and voltage before sparkover. The procedure yields voltage‐current characteristics and determines the electric potential and electric field strength as functions of position for each current and applied voltage. Predictions of the theory are compared with existing experimental data and the agreement is excellent.

Penetration of Ambient Fine Particles into the Indoor Environment

Several recent studies have indicated significant health risks associated with exposure to fine particles as measured outdoors. However, much of the exposure is believed to have occurred indoors. Consequently, there is considerable interest in the relationship between indoor and outdoor fine particles. This paper describes some results from a study in which the processes of particle removal from infiltrating air by building envelopes are simulated in a chamber. The chamber consists of two compartments, each having a volume of 19 m3. Particles with aerodynamic diameters in the range of 0.05 to 5

VOC Removal at Low Contaminant Concentrations Using Granular Activated Carbon

Small-scale beds of granular activated carbon (GAC) have been tested in this research using challenges of volatile organic compounds (VOCs) in air at concentrations ranging from approximately 0.5 to 100 ppm. The research linked the performance of GAC from high-concentration quickly completed tests to performance at low concentrations near those encountered indoors. For all tests, the carbon bed was approximately 2.54 cm thick and operated with a residence time of 0.11 s. The tests were conducted at 25 degrees C and 50% relative humidity. The measured 10% breakthrough times ranged from about 0.5 hour to several hundred hours. For the individual compounds, the relationship between the logarithms of breakthrough time and concentration was approximately linear over the experimental range, with different compounds producing lines having different slopes. The measured breakthrough times compared favorably to published data and models. The results suggest that higher-concentration single-component breakthrough tests, which are short and easily obtained, may be cautiously extrapolated to indoor concentrations for these compounds.

Negative corona in wire-plate electrostatic precipitators. Part I: Characteristics of individual tuft-corona discharges

Abstract The characteristics of individual fuft discharge in negative corona are invvestigated by modelling them with a micropoint projecting from the corona wire. The characteristics of these micropoints are shown to be similar to naturally produced tufts. Their V-I relationships and current density distributions are based on the better understood needleplane geometry characteristics but modified by the presence of the equipotential surface of the wire electrode. The maximum current density is calculated from the saturated current density equation. The onset voltage for the tuft corona on a wire is a function of the efficiency of production of electrons by positive ions. A fractional efficiecy of 1.0 corresponds to an onset voltage about 0.6 times the Peek onset voltage for a clean wire.

Charge measurements on individual particles exiting laboratory precipitators with positive and negative corona at various temperatures

The values of charge on individual particles exiting three different laboratory precipitators have been measured in an experimental apparatus containing a Millikan cell. Measurements were obtained for dioctylphthalate (DOP) droplets and fly ash particles at temperatures from 23 to 343u2009°C. At comparable voltages and currents for positive and negative coronas, the data show that the ratio of the values of negative‐to‐positive charge for radii in the range 0.6–1.3 μm increases from about 1 to 2 as the temperature increases from 37 to 343u2009°C. The predictions of a mathematical model of electrostatic precipitation which employs an ionic charging theory show good agreement with all the positive charging data, but show good agreement with the negative charging data only at temperatures below 37u2009°C. The differences in the measurements and the model predictions are consistent with the postulation of free electron charging at elevated temperatures in negative corona.

Experimental investigations of fine particle charging by unipolar ions — A review

Abstract Many theories have been offered in attempts to describe accurately the rate of charge accumulation of fine particles in a unipolar ion field. There has been little experimental data, however, for comparison with these new theories. In this study, the existing experimental data are reviewed and compiled, and additional particle charging experiments done to extend the quantity of data. Before this study was performed the majority of the experimental data which was available for comparison with particle charging theories was contained in a paper by G. Hewitt, published in 1957. Hewitts experiments were carefully done, but the range of experimental variables was limited and his work was never independently verified. The experiments reported here followed Hewitts procedures closely and were designed to extend the quantity of experimental data. There is some overlap between this and Hewitts data, and in these instances, the agreement is good. Experimental results are presented in this paper for the charging rate of particles of 0.109–7 μm dia. at various values of electric field strength, ion density and charging time. A limited amount of data is also given which shows the important effects on the charging rate of variations in the particle dielectric constant and the polarity of the corona ion source.

Evaluation of sink effects on VOCs from a latex paint.

The sink strength of two common indoor materials, a carpet and a gypsum board, was evaluated by environmental chamber tests with four volatile organic compounds (VOCs): propylene glycol, ethylene glycol, 2-(2-butoxyethoxy)ethanol (BEE), and Texanol. These oxygenated compounds represent the major VOCs emitted from a latex paint. Each chamber test included two phases. Phase 1 was the dosing/sorption period during which sink materials (pieces of carpet and gypsum board samples) were exposed to the four VOCs. The sink strength of each material tested was characterized by the amount of the VOCs adsorbed or absorbed. Phase 2 was the purging/de-sorption period during which the chambers with the dosed sink materials were flushed with purified air. The reemission rates of the adsorbed VOCs from the sinks were reflected by the amount of the VOCs being flushed. Phase 1 results indicated that the sink strength for the four target compounds is more than 1 order of magnitude higher than that for other VOCs previously tested by the U.S. Environmental Protection Agency (EPA). The high sink strength reflected the unusually high sorption capacity of common indoor materials for the four VOCs. Phase 2 results showed that reemission was an extremely slow process. If all the VOCs adsorbed were reemittable, it would take more than a year to completely flush out the VOCs from the sink materials tested. The long reemission process can result in chronic and low-level exposure to the VOCs after painting interior walls and surfaces.

Narrow-gap point-to-plane corona with high velocity flows

Corona discharge has been used in the detoxification of chemical agents or their simulants, for which the degree of destruction depends on the strength of the electric field or electron energy. To help clarify this process, a mathematical model describing the narrow-gap point-to-plane corona system has been developed. Narrow-gap electrodes are characterized by extremely high electron activity and the presence of positive and negative ions. The three-dimensional spatial distributions in the electron density and the electric field are of primary interest. The results indicate the potential problems of the corona device and may prove useful for obtaining an optimum design. >

Measurement of ion mobilities in air and sulfur dioxide-air mixtures as a function of temperature

Abstract Ion mobilities have been measured for air with varying concentrations of water vapor and for dilute sulfur dioxide-air mixtures. The conditions used were fairly comparable to those experienced in electrostatic precipitators, both laboratory and full-scale units. The mobilities of the negative ions exhibited a fairly strong temperature dependence. The reduced mobilities for sulfur dioxide-air mixtures were comparable to the reduced mobility for air. The results should be useful in precipitator modeling applications.

VOC Sink Behaviour on Building Materials – Model Evaluation

The event of 11 September 2001 underscored the need to study the vulnerability of buildings to weapons of mass destruction, including chemical, biological, physical and radiological agents. Should these agents be released inside a building, they would interact with interior surfaces, building materials and furnishings, and could remain for a long period in an indoor environment. This study provides insights into the sink effect and absorption mechanisms of volatile organic compounds (VOCs) in indoor environments. In this study, the sink effect was investigated with building materials (e.g. painted gypsum wallboard, vinyl flooring, carpet and mortar) and VOCs, ethylbenzene, 1-butanol, decane and dodecane, which were used as surrogates of toxic chemicals. Vinyl flooring has the strongest sink for ethylbenzene and dodecane. The sink experimental data were employed to evaluate the Langmuir-isotherm and diffusion sink models. Test data were also compared to a no-sink model. The sorption and desorption rate constants for the Langmuir-isotherm model were obtained. Mass balance was analysed. There were strong correlations between equilibrium partition coefficients from the Langmuir-isotherm model and equilibrium partition coefficients and the effective diffusion coefficients from the sink diffusion model.