The charging of small particles for electrostatic precipitation

Hewitt, G. W.

doi:10.1109/tce.1957.6372672

Cited by 87 publications

(94 citation statements)

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“…In experimental investigation of the charging of small particles in electrostatic gas cleaning, Hewitt (1957) made a number of innovations that were adopted in later mobility analyzers. A corona discharge ion source was used to introduce ions into a low electric field space in which aerosol particles could undergo unipolar charging in the presence FIGU RE 27.…”

Section: Electrical Aerosol Analyzermentioning

confidence: 99%

“…The extracted aerosol was passed through a chamber where it was exposed to a-radiation to neutralize it in order to minimize particle losses due to space-charge-induced electrostatic precipitation. (Reprinted from Hewitt, 1957O 1957 of a controlled concentration of gas ions and under a controlled electric fieldu. An alternating electric field was applied to the charging region to ensure efficient charging with minimal particle losses.…”

Section: Electrical Aerosol Analyzermentioning

confidence: 99%

“…As in Hewitt's (1957) DMA, unipolar diffusion charging was employed in this instrument. By exposing the particles to relatively low concentrations of gas ions in the absence of an applied electric field, charging levels resulted that led to a monotonic trend of particle mobility with particle size.…”

Section: Electrical Aerosol Analyzermentioning

confidence: 99%

“…Although the value of differential measurements of the mobility distribution was rec- ognized in the earliest days of ion mobility measurements (Zeleny, 1900), and reiterated in numerous developments over several decades (Erikson, 1921;Hewitt, 1957;Mikasi, 1950;Matisen et al, 1992), the focus on air ions and the need to measure extremely small currents hindered the development of practical differential instruments for many years. However, the need for a source of monodisperse particles with which to calibrate other aerosol instruments led to a development that ultimately enabled high-resolution electrical mobility measurements of aerosol-size distributions.…”

Section: The Differential Mobility Analyzermentioning

confidence: 99%

“…Like the earliest of the attempts at a differential instrument, this development came from the University of Minnesota. In 1974, Liu and Pui (1974b) calibrated a number of condensation nucleus counters using a version of Hewitt's instrument (Hewitt, 1957) for which they coined the name, diflerential mobility analyzer. With this device, which is illustrated in Fig.…”

Section: The Differential Mobility Analyzermentioning

confidence: 99%

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History of Electrical Aerosol Measurements

Flagan

1998

Aerosol Science and Technology

217

117

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ABSTRACT. Early studies of atmospheric electricity suggested that the electrical conductivity of the atmosphere should be sufficient to dissipate the charge on the surface of the earth in a matter of minutes. Efforts to understand how substantial electric fields could be maintained globally in spite of the high dissipation rates were propelled into the forefront of physics research at the turn of the century when it was observed that the newly discovered X-rays produced ions that behaved much like those in the atmosphere. Many of the approaches that are now employed in electrical measurements of aerosols were first conceived during the first three decades of this century. Initially the focus was on gas ions, but they were found to consist of charged clusters of water molecules that exhibited a number of distinct mobilities that were substantially lower than those that resulted after long efforts to dry the gas. The coaxial condenser mobility analyzer, introduced by McClelland in 1898 and enhanced by Zeleny in 1900, was used to measure atmospheric ions as early as 1901 by Ebert. Based upon atmospheric measurements with this device in 1905, Langevin reported on the existence of ions with mobilities 3000 times lower than those observed in the laboratory studies. These so-called large ions correspond to particles in what we now know as the accumulation mode of the atmospheric aerosol. The aspiration condenser dominated measurements of atmospheric ions for six decades even though Erikson developed a differential mobility analyzer by 1921, and Rohmann produced a differential mobility sampler in 1923. Only after electronics was improved in the 1950s and 1960s were these instruments reintroduced. It was based upon condenser measurements of atmospheric "ions" that Junge first described the structure of the ultrafine particle size distribution in 1955.The development of the Whitby Aerosol Analyzer in 1966 built upon earlier developments, including the Faraday cup electrometer that was used by both Zeleny and McClelland at the turn of the century, and a long history of mobility analyzers. This instrument represented a breakthrough nonetheless since it was the first mobility aerosol analyzer that was sufficiently refined and robust to be commercially produced. That instrument was refined into the electrical aerosol analyzer ( E M ) that became the primary tool for characterizing ultrafine aerosol particles in the atmosphere for a number of years. At the same time that the E M was developed, the differential mobility analyzer was reintroduced in a form that quickly became the standard for production of submicron calibration aerosols. Early efforts to transform that instrument from a calibration tool to a measurement device met with limited success due to the lack of a suitable detector. The introduction of a continuous flow condensation nucleus counter was followed quickly by the development of computerized differential mobility analysis of particle-size distributions and later accelerated through the introduction of scannin...

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Section: Electrical Aerosol Analyzermentioning

confidence: 99%

Section: Electrical Aerosol Analyzermentioning

confidence: 99%

Section: Electrical Aerosol Analyzermentioning

confidence: 99%