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| Titel |
An unheated permeation device for calibrating atmospheric VOC measurements |
| VerfasserIn |
J. Brito, A. Zahn |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 10 ; Nr. 4, no. 10 (2011-10-13), S.2143-2152 |
| Datensatznummer |
250002114
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| Publikation (Nr.) |
 copernicus.org/amt-4-2143-2011.pdf |
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| Zusammenfassung |
| The development of an unpowered permeation device for continuous calibration
of in-situ instruments measuring atmospheric volatile organic compounds
(VOCs) is described. Being lightweight and compact, and containing only
negligible amounts of chemicals, the device is especially suited for field
use such as on board aircraft. Its speciality is to maintain the permeation
process in thermal equilibrium, so that the instantaneous permeation rate can
be ascribed to a simple temperature measurement. This equilibrium state is
maintained by a combination of three features: (i) a thin PTFE membrane as
permeation medium which guarantees short stabilization times, (ii) a water
bath as heat buffer, and (iii) a vacuum-panel based insulation, in which
features (ii) and (iii) minimize temperature drifts to ~30 mK h−1 per
Kelvin temperature difference to the environment. The respective uncertainty
of the permeation rate due to thermal non-equilibrium is kept below 1%. An
extensive theory part details the major permeation processes of gases through
porous polymers, being Fick's diffusion, Knudsen flow, and viscous flow. Both
the measured stabilization time and the measured temperature dependence of
the permeation rate independently indicate that the permeation can be
described by a viscous flow model, where diffusion of the gas molecules in
large pores (having a diameter of >0.05 μm) dominates. |
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