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 ε 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-?m, 1.68-mm, and 2.88-mm radius were exposed to indium acetylacetonate aerosol particles (having mean radii in the range of 0.16?0.24 ?m) in the turbulent core for exposure times between 70 and 100 s. The collection efficiency for each drop size was determined by analyzing the accrued aerosol mass and compared with efficiencies for laminar conditions found in the literature. The results showed no enhancement of the collection efficiency owing to turbulence effects within the bounds of experimental error.