Computer Simulation of Variables that Influence Spray Drift

A computer program was used to determine the effects of several variables on drift distances of spray droplets. Variables were initial droplet size, velocity and height of discharge, wind velocity, turbulence intensity and relative humidity, and volatility of the liquid. For relative humidity and wind velocity ranges of 20-80% and 0.5-4.0 m/s, all water droplets 50 µm diameter and smaller that were directed downward with initial velocity of 20 m/s either completely evaporated or drifted farther than 6 m before depositing 0.5 m below point of discharge. With 20 m/s initial droplet velocity, 2.0 m/s wind velocity (20% turbulence intensity) and 60% relative humidity, 100 and 200 µm diameter droplets deposited at mean distances from point of discharge of 2.6 and 0.13 m respectively. Drift distances of water droplets as large as 200 µm diameter were influenced by initial droplet velocity and height of discharge. Experimental data verified the accuracy of the computer program in predicting drift distances of water droplets.