Droplet Size of Cooling Tower Fog

Abstract

Fog from cooling towers causes problems of visibility and icing along roadways adjacent to the towers; moreover, the visible plume from the towers offers difficulty in that it is equated by much of the public with air pollution. It is desirable to know the size of the fog droplets in order to plan abatement procedures and to determine the airborne lifetimes of such fogs.

The methodology involved capturing the droplets on slides coated with a vaseline-mineral oil mixture, making photomicrographs of the droplets, counting and sizing the droplets into eight droplet diameter increments; namely, <5 μm, 5–10 μm, 10–20 μm, 20–40 μm, 40–60 μm, 60–80 μm, 80–100 μm, and >100 μm. The resulting distribution was similar to that for natural fogs and clouds; i.e., it was bi-modal, the first mode at <5 μm containing the vast majority of the droplets, and the second at 20–40 μm. This study agrees with others that the size distribution of a fog in a saturated environment is continuously changing, with the smaller droplets tending to evaporate and the larger ones tending to grow, thus shifting the second mode toward larger sizes.