Atmospheric Chemistry and Physics, vol. 12, issue 4 (2012) pp. 2205-2214
To study the effect of galactic cosmic rays on aerosols and clouds, the
Cosmics Leaving OUtdoor Droplets (CLOUD) project was established.
Experiments are carried out at a 26.1 m(3) tank at CERN (Switzerland).
In the experiments, the effect of ionizing radiation on H2SO4 particle
formation and growth is investigated. To evaluate the experimental
configuration, the experiment was simulated using a coupled
multidimensional computational fluid dynamics (CFD) - particle model. In
the model the coupled fields of gas/vapor species, temperature, flow
velocity and particle properties were computed to investigate mixing
state and mixing times of the CLOUD tank's contents. Simulation results
show that a 1-fan configuration, as used in first experiments, may not
be sufficient to ensure a homogeneously mixed chamber. To mix the tank
properly, two fans and sufficiently high fan speeds are necessary. The
1/e response times for instantaneous changes of wall temperature and
saturation ratio were found to be in the order of few minutes. Particle
nucleation and growth was also simulated and particle number size
distribution properties of the freshly nucleated particles (particle
number, mean size, standard deviation of the assumed log-normal
distribution) were found to be distributed over the tank's volume
similar to the gas species.
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