Laboratory Measurements of Particle Capture by Evaporating Cloud Drops

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Abstract
The capture efficiencies of evaporating cloud drops (56–93 μm radius) for particles of manganese hypophosphite (0.58–3.2 μm radius) were obtained experimentally. In each experimental run, a large number of widely spaced uniform size drops fell through a monodisperse cloud of particles at ∼30% relative humidity. The major attachment mechanisms were thermodiffusiophoresis for the smaller particles and inertial impaction for the larger particles. The experimental values were compared to efficiencies computed using convective diffusion and trajectory models. Good agreement between our experiments and theory was found for the larger particles scavenged by inertial impaction but not for the smaller ones scavenged by phoretic forces. Various potential reasons for this disagreement are discussed. Abstract The capture efficiencies of evaporating cloud drops (56–93 μm radius) for particles of manganese hypophosphite (0.58–3.2 μm radius) were obtained experimentally. In each experimental run, a large number of widely spaced uniform size drops fell through a monodisperse cloud of particles at ∼30% relative humidity. The major attachment mechanisms were thermodiffusiophoresis for the smaller particles and inertial impaction for the larger particles. The experimental values were compared to efficiencies computed using convective diffusion and trajectory models. Good agreement between our experiments and theory was found for the larger particles scavenged by inertial impaction but not for the smaller ones scavenged by phoretic forces. Various potential reasons for this disagreement are discussed.

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