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Numerical simulations of mixing conditions and aerosol dynamics in the CERN CLOUD chamber

by J. Voigtländer, J. Duplissy, L. Rondo, A. Kürten, F. Stratmann
Atmospheric Chemistry and Physics ()
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To study the effect of galactic cosmic rays on aerosols and clouds, the\nCosmics Leaving OUtdoor Droplets (CLOUD) project was established.\nExperiments are carried out at a 26.1 m(3) tank at CERN (Switzerland).\nIn the experiments, the effect of ionizing radiation on H2SO4 particle\nformation and growth is investigated. To evaluate the experimental\nconfiguration, the experiment was simulated using a coupled\nmultidimensional computational fluid dynamics (CFD) - particle model. In\nthe model the coupled fields of gas/vapor species, temperature, flow\nvelocity and particle properties were computed to investigate mixing\nstate and mixing times of the CLOUD tank's contents. Simulation results\nshow that a 1-fan configuration, as used in first experiments, may not\nbe sufficient to ensure a homogeneously mixed chamber. To mix the tank\nproperly, two fans and sufficiently high fan speeds are necessary. The\n1/e response times for instantaneous changes of wall temperature and\nsaturation ratio were found to be in the order of few minutes. Particle\nnucleation and growth was also simulated and particle number size\ndistribution properties of the freshly nucleated particles (particle\nnumber, mean size, standard deviation of the assumed log-normal\ndistribution) were found to be distributed over the tank's volume\nsimilar to the gas species.

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