KINETICS OF WETTING IN WASHOUT OF DUST
T. G. OWE BERG, T. A. GAUKLER, and LAVON A. SQUIER
Aerojet-General Corporation, Downey, California
ABSTRACT
The rates of wetting of solids by water were measured under conditions
simulating those in washout of dust by a water spray and of radioactive
debris by
rain. The solid was pressed against a water drop, and the
event was followed by high-speed photography at 26,000 frames/sec. A
voltage was applied between the solid and the water drop so as to sim-
ulate an electrostatic charge. The delay between contact and wetting
depends upon the wettability of the solidandthe voltage applied. Wetting
is the formation of hydrogen bonds between H,O molecules in the water
drop and OH on the surface of the solid. This process requires the re-
orientation of bonds in the drop by an electric field operating on the
dipole moment of the bond. Wetting in collision requires that wetting
occur rapidly enough, i.e., before rebounce. In the case of mild steel,
wetting is promoted by hydrogen in the steel and does not occur if hydrogen is not present.
INTRODUCTION
An important problem in industrial hygiene is how to get rid of
harmful dust in the air. One approach to this problem that has been
tried extensively in mines is to wash out the dust by a water spray.
Recently, such washout has attracted attention as a natural process for
deposition of radioactive debris, notably washout by rain.
A conceivable mechanism for such washout is the collision and
coalescence between dust particles and spray drops or between debris
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