Abstract
Abstract. 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 m3 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.
Highlights
Atmospheric aerosols are complicated multiphase systems, influencing Earth’ climate directly via absorption and scattering of solar radiation and indirectly via cloud processes
This paper presents numerical simulation results for a cloud tank with the geometry of the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber concerning the mixing state with respect to both, gaseous species and particles
Due to molecular and turbulent vapor mass diffusion, H2SO4 is continuously lost to the wall
Summary
Atmospheric aerosols are complicated multiphase systems, influencing Earth’ climate directly via absorption and scattering of solar radiation and indirectly via cloud processes. Largest uncertainties in understanding the current climate change are attributed to aerosols and clouds (IPCC2007) These uncertainties partly result from solarrelated contributions and require further research. Particle nucleation and the effects of ionisation on particle nucleation, the Cosmics Leaving OUtdoor Droplets (CLOUD) project was established. Within this project, experiments are carried out at a large volume cloud chamber (26.1 m2) located at CERN (Switzerland). The chamber is equipped with a large number of different instruments to study aerosol cloud cosmic rays micro physics under well defined conditions. This paper presents numerical simulation results for a cloud tank with the geometry of the CLOUD chamber concerning the mixing state with respect to both, gaseous species and particles. After a very brief description of the experimental set up, fundamental aspects of the simulations are given, followed by several model results in comparison to experimental data
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