MEASUREMENTS OF THE MEAN FORCE ON A PARTICLE NEAR A BOUNDARY IN TURBULENT FLOW.

The transport of particles through gaseous systems is controlled by three factors: their arrival to the surface; whether or not they bounce upon impact; and when (if ever) they are resuspended from the surface. One of the parameters required in determining whether or not a particle is suspended is the lift force acting on the particle. We demonstrate that the fluid lift forces acting on particles as small as 1 mu m in diameter can be modeled by particles of several mm in diameter. However, the forces involved in modeling such small particles are around 10** minus **8 N, which is several orders of magnitude smaller than reported in published measurement of fluid lift forces. A system to determine such lift forces has been developed and is described. Measurements of the mean force acting on particles on both rough and smooth surfaces are presented.