Philip Lawless

Control of volatile organic compounds by an AC energized ferroelectric pellet reactor and a pulsed corona reactor

Two laboratory-scale plasma reactors, an alternating-current-energized ferroelectric (high-dielectric ceramic) packed-bed reactor and a nanosecond pulsed corona reactor, were constructured. The aim was to develop baseline engineering data to demonstrate the feasibility of applying plasma reactors to the destruction of various volatile organic compounds (VOCs). Gas retention time, concentration, and corona power were varied to determine the effect on destruction efficiency, using gas chromatography for each VOC. Complete destruction was obtained for toluene. Conversions of methylene chloride at 95% and trichlorotrifluoroethane (known as CFC-113) at 67% were achieved. The conversion was dependent on the electron energy of the reactor and was also related to how strongly the halogen species were bonded with carbon.<<ETX>>

Characterization of indoor-outdoor aerosol concentration relationships during the Fresno PM exposure studies

Particle size distributions were measured indoors and outdoors of a single, detached residence during the Fresno particulate matter exposure studies in winter (February 1-28, 1999) and spring (April 18-May 16, 1999). Data was collected for particle sizes ranging from about 0.01 to 2.5

Modeling particulate charging in ESPs

In electrostatic precipitators there is a strong interaction between the particulate space charge and the operating voltage and current of an electrical section. Calculating either the space charge or the operating point when the other is fixed is not difficult, but calculating both self-consistently is much more difficult. A method is proposed that makes the problem straightforward. An iterative solution is required, but the closure rate should be acceptable. >

Comparison of germanium and silicon needles as emitter electrodes for air ionizers

Germanium (Ge) and silicon (Si) needles were tested as emitter electrodes for use in low particle generating static eliminators. The materials were found to oxidize with minimal incorporation of nitrogen, and the negative polarity enlitters oxidzed at a greater rate than the positive polarity emitters. The negative polarity silicon emitters generated severall orders of magnitude greater particle emissions than any of the other emitters tested. The mean particle size was about 0.015μm. Although the germanium emitters oxidized, no evidence was found to indicate particles were shed from h s material. Preliminary data indcates the emitters perform equally well in Class 100 cleanroom air, and lowest particle generation is achieved when germanium electrodes are purged with dry air.

Characteristics of a fast rise time power supply for a pulsed plasma reactor for chemical vapor destruction

Rotating spark gap devices for switching high voltage direct current (DC) into a corona plasma reactor can achieve pulse rise times in the range of tens of nanoseconds. The fast rise times lead to vigorous plasma generation without sparking at instantaneous applied voltages higher than can be obtained with DC. The resulting energetic plasma is effective for destroying a variety of molecules. The spark gap circuit configuration plays an important role in the effectiveness of the plasma generation. A single-gap circuit is effective for generating moderate peak voltages, but is limited by a multiple sparking phenomenon. A double-gap circuit can achieve equal peak voltages with every spark, but with a reduced number of pulses, compared to the single gap. Both configurations have an upper voltage imposed by the changing impedance of the reactor as voltage and frequency are varied. The pulse characteristics are reported for both types of circuits. The general performance of the reactors for destruction of some compounds with both circuits is also reported.

Characteristics of a fast rise time power supply for a pulsed plasma reactor

Rotating spark gap devices for switching high-voltage direct current into a corona plasma reactor can achieve pulse rise times in the range of tens of nanoseconds. A single-gap circuit is effective for generating moderate peak voltages, but is limited by a multiple sparking phenomenon. A double-gap circuit can achieve equal peak voltages with every spark, but with a reduced number of pulses, compared to the single gap. Both configurations have an upper voltage imposed by the changing impedance of the reactor as voltage and frequency are varied. The pulse characteristics are reported for both types of circuits, along with some spectroscopic analyses. The general performance of the reactors for destruction of some compounds with both circuits is also reported. The single-gap supply is shown to provide a wider range of operating parameters than the double-gap supply but it is much more difficult to characterize the pulses, particularly their frequency, than with the double-gap supply.<<ETX>>

Theoretical Response of Laser Aerosol Spectrometers and Data Inversion by Stochastic Reconstruction

Laser optical particle spectrometers have been used to obtain real-time particle counts and infer mass information over a substantial portion of the PM2.5 mass range by means of dynamic aerosol calibrations. The theoretical response of such instruments is quite calculable, as many authors have demonstrated, but the total response still has some problem areas. This article addresses the theoretical response, comparing the calculations to the instrument calibration and other experimental data. Other instrument characteristics, particularly the particle path through the instrument, affect the total response. When the whole instrument is considered, theoretical predictions of response with changes of index of refraction can be made with some confidence. The calculated response of such spectrometers is nonmonotonic with particle size for most indices of refraction, making inversion of the acquired data difficult. A data inversion algorithm has been devised to incorporate all the response effects and overcome the multivalued nature of the response curve. The inversion algorithm simulates particles passing through the instrument, subject to constraints imposed by the instrument (and user) according to the information desired. The inversion technique is robust and should be useful in other aerosol applications as well. The software algorithm source files mentioned in this article are available online at http://taylorandfrancis.metapress.com/openurl.asp?genre=article&id=doi:10.1080/02786820490439710 To access this file, click on the issue link for 38(5), then select this article. In order to access the full article online, you must either have an institutional subscription or a member subscription accessed through www.aaar.org.

Bounded logarithm scale for particle count data

ABSTRACT When graphing or plotting count data from particle sensors, there is always the problem of handling zero values if a logarithmic scale is desired. The one plotting (or programming) may skip the offending values, leaving all values equal to 1 across the bottom of the graph. Or, a constant may be added to all the counts to provide an offset from zero. We offer an approach with the advantage of changing only one label on the graph, yet allowing all values between 0 and 1 to be plotted automatically. The change is simple to program and can be equally easily used in manual plotting.

Problems Using Carbon-vane Pumps in Nitrogen Gas

ABSTRACT We experienced repeated failures of carbon vane pumps in an aerosol counter when sampling from nitrogen gas. The nature of the problem and a cure are presented.