A Numerical Simulation of Warm Fog Dissipation by Electrically Enhanced Coalescence: Part II. Charged Drop Seeding

Abstract

A numerical study of the use of highly charged water drops to clear warm fog has been conducted. The mechanism studied is the polarization of neutral fog droplets and their capture by the charged drops. A multi-level microphysical model is used to investigate the degree of visibility improvement resulting from variations in seeding drop size and charge, the concentration of seeding material and the fog being seeded. It is determined that visibility improvement decreases with decreasing fog droplet size and increases with increasing seeding rate and seeding drop charge. For the same amount of seeding water, a treatment spectrum with an average radius between 10 and 15 ?m is ideal. In contrast to the findings of Part I (an applied electric field), visibility improvement here results both from a removal of fog water (to the ground) and from a transfer of water from the fog spectrum to the larger treatment drops. Field tests of this technique have proven inconclusive. A further evaluation is made by comparing model results to comparable numerical experiments of hygroscopic seeding, a technique that has been field tested on several occasions. It is concluded that the charges and treatment concentrations simulated in this study would not be adequate for clearing fog; unless charges and seeding concentrations can be greatly increased, charged drop seeding is probably not a viable fog dissipation technique.