Temperature uniformity in the CERN CLOUD chamber
The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (European Council for Nuclear Research) investigates the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the...
Main Authors: | , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-12-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | https://www.atmos-meas-tech.net/10/5075/2017/amt-10-5075-2017.pdf |
Summary: | The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (European Council for Nuclear Research) investigates the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. A key feature of the CLOUD
experiment is precise control of the experimental parameters. Temperature
uniformity and stability in the chamber are important since many of the
processes under study are sensitive to temperature and also to contaminants
that can be released from the stainless steel walls by upward temperature
fluctuations. The air enclosed within the 26 m<sup>3</sup> CLOUD chamber is
equipped with several arrays (<q>strings</q>) of high precision, fast-response
thermometers to measure its temperature. Here we present a study of the air
temperature uniformity inside the CLOUD chamber under various experimental
conditions. Measurements were performed under calibration conditions and run
conditions, which are distinguished by the flow rate of fresh air and trace
gases entering the chamber at 20 and up to 210 L min<sup>−1</sup>,
respectively. During steady-state calibration runs between −70 and
+20 °C, the air temperature uniformity is better than
±0.06 °C in the radial direction and ±0.1 °C in the
vertical direction. Larger non-uniformities are present during experimental
runs, depending on the temperature control of the make-up air and trace gases
(since some trace gases require elevated temperatures until injection into
the chamber). The temperature stability is ±0.04 °C over periods
of several hours during either calibration or steady-state run conditions.
During rapid adiabatic expansions to activate cloud droplets and ice
particles, the chamber walls are up to 10 °C warmer than the
enclosed air. This results in temperature differences of ±1.5 °C
in the vertical direction and ±1 °C in the horizontal direction,
while the air returns to its equilibrium temperature with a time constant of
about 200 s. |
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ISSN: | 1867-1381 1867-8548 |