EXPERIMENTAL-STUDY OF AEROSOL DEPOSITION IN STIRRED FLOW-FIELDS RANGING FROM LAMINAR TO TURBULENT FLOWS

The deposition of aerosol particles of 0.01-2-mu-m in diameter is investigated in laminar and turbulent flow fields, and deposition by air flow, particle diffusion and gravitational sedimentation is evaluated. In experiments, wall loss rates of monodisperse particles are measured in four stirred tanks (similar in form but different in size) with stirring Reynolds number Re ranging from 10 to 10(4). The result has shown that deposition velocities upsilon-d obtained for particles smaller than 0.1-mu-m, which range over several orders of magnitude, are almost proportional to Re0.56 when Re is larger than about 1500. At Re less-than-or-similar-to 200, a dimensionaless mass transfer rate (Sherwood number) Sh, which expresses a dimensionless deposition rate, is found to be equal to 1.1Re1/2Sc1/3, where Sc is the Schmidt number. The deposition velocities for 200 less-than-or-similar-to Re less-than-or-similar-to 1500 show that the increasing rate of upsilon-d with Re depends on Re, indicating the existence of a transitional regime concerning deposition. The influence of gravity is observed when the particle diameter exceeds 0.2-mu-m, and the deposition rate can be predicted well by summing the contributions of diffusive deposition and gravitational sedimentation of a particle.