0000000000139388
AUTHOR
O. Vohl
A Wind Tunnel Study of Turbulence Effects on the Scavenging of Aerosol Particles by Water Drops
Abstract Laboratory experiments are described where the effects of turbulence on the impaction scavenging of aerosol particles by water drops were investigated. During the experiments the drops were freely suspended at their terminal velocities in the Mainz vertical wind tunnel. Turbulence in the tunnel airstream was produced by placing a needle obstruction upstream of the floating drop. The energy dissipation rates e were between 0.03 and 0.5 m2 s−3. The power spectrum covered a range of k values between 102 and 3 × 103 m−1, agreeing with atmospheric observations within this range. Collector drops of 346-μm, 1.68-mm, and 2.88-mm radius were exposed to indium acetylacetonate aerosol particl…
A laboratory and theoretical study on the uptake of sulfur dioxide gas by small water drops containing hydrogen peroxide under laminar and turbulent conditions
Abstract Laboratory experiments are described where the uptake of SO2 gas by water drops containing H2O2 is investigated where the taken up S(IV) is quickly converted to S(VI). During the gas uptake the drops were freely suspended at their terminal velocity by means of the Mainz vertical wind tunnel. Two series of experiments were carried out, one with a laminar air flow in the wind tunnel, one with a turbulent air flow in the wind tunnel. Afterwards, the experimental results were compared against model computations using the so-called fully mixed convective diffusion model. The experimental results for laminar flow conditions showed that the fully mixed convective diffusion model for the u…
A Wind Tunnel and Theoretical Study of the Melting Behavior of Atmospheric Ice Particles. IV: Experiment and Theory for Snow Flakes
Abstract An experiment in the Mainz vertical Cloud Tunnel is described in which natural and laboratory-made aggregates of snow crystals (snow flakes) were melted under free fall conditions in the vertical air stream of the tunnel, which was allowed to warm up at the rates experienced by falling snow flakes in the atmosphere. The variation of the fall mode, the fall velocity, and the percentage of ice melted, as a function of percentage of distance travelled for 99% melting was recorded by cinematography. The laboratory results were confirmed by the results of a theoretical heat transfer model which we developed for the melting of a snow flake. In this model a snow flake was idealized by an …
A Wind Tunnel Study of the Effects of Turbulence on the Growth of Cloud Drops by Collision and Coalescence
A set of wind tunnel experiments was carried out to investigate the growth of single drops by collision coalescence with small droplets in laminar and turbulent flow. Analysis of the experiments shows that under otherwise similar conditions, there exists a tendency toward a faster drop growth under turbulence. The observed growth under laminar conditions agrees well with computed continuous growth of a collector drop using collision efficiencies reported in the literature.
Collision efficiencies empirically determined from laboratory investigations of collisional growth of small raindrops in a laminar flow field
In laboratory experiments at the vertical wind tunnel of the University of Mainz the collisional growth of drops with radii between 70 and 170 μm in radius were observed while the collector drop freely floated in a cloud of droplets with radii ranging from 1 to 7 μm. Previously existing tables with collision efficiency values were interpolated and completed in such a way that drop growth rates calculated with these collision efficiencies match with observed growth rates. These new tables provide collision efficiency values for a wide range of drop sizes and radius ratios p including those ranges where efficiency values missed so far. This is of high importance for small p-ratios where the c…