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Abstract
Very slow air flows (.01cm/s), induced by a column of 5–15 μ m diameter droplets settling in a 9 mm diameter chamber were measured with a laser light velocimeter apparatus. We measured the air flow velocity as the difference between the Doppler-measured Stokes settling velocity of individual droplets and the settling velocity calculated from simultaneous optical measurements of droplet diameter. Experimental conditions included a wide range of droplet sizes, relatively slow air motion, and many droplets being in the laser beam at the same time.
We describe the interaction of the particles with the air in terms of a simple two-fluid model with an exact solution of the Navier-Stokes equation.