下載次數：487次 瀏覽次數：732次發布時間：2015-11-16 17:04Introduction
When operated standalone or within an Electrostatic Classifier Model 3082with date code
May 2014 or earlier, at certain flow rates, Radioactive Neutralizers Model 3077 and 3077A may not
sufficiently charge the sample aerosol to an equilibrium distribution.
This issue has occasionally been observed in the past (Liu and Deshler [2003] Aero. Sci. Technol.
27:916-923) but the root cause was unclear. We are happy to report a thorough investigation and
solutions to the issue. The following document explains it in detail and can be used to determine
whether a specific experimental setup may or may not be affected. The use of a 3077(A) neutralizer
in a 3080 classifier is not affected by this issue.
The 3077(A) aerosol neutralizer may have reduced neutralization efficiency at certain flow rates
when operated outside a classifier or within a 3082 classifier with date code May 2014 or earlier. In
these configurations, the flow through the neutralizer may be laminar causing fluid near the
centerline of the flow to pass through the neutralizer body rapidly while fluid near the outer edges
of the flow recirculates within the neutralizer. The discrepancy in residence time within the
neutralizer causes insufficient neutralization of the aerosol along the neutralizer centerline.
Depending on the state of charge of the aerosol being measured, insufficient neutralization can lead
to inaccurate size distributions and number concentrations. As shown in Figure 1, for a highly precharged
aerosol, between sample flow rates of 0.7 L/min and 2.5 L/min, the insufficient charging of
the 3077(A) neutralizer installed in a 3082 classifier results in incorrect total concentration
measurements. Figure 2 shows the overestimation dependence on particle size for a highly precharged
example aerosol.
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