Falling Water Drop Velocities at 1570 m Elevation

ABSTRACT The velocities of freely falling water drops released from various heights in still air were measured using two different techniques at an elevation of 1570 m (5150 ft) above sea level. An electrostatic technique was used to measure the time for an electrically charged water drop to pass through two metal rings of known spacing. A photographic technique, using two electronic flash units, was used to photograph a falling drop against a grid background, at the beginning and ending of a known time interval. The measured results were compared to velocity data measured at sea level and to results from a computer model which predicts freely falling water drop velocities as a function of drop size, air pressure, and air temperature. The high elevation (low air presure and density) environment resulted in measured velocities significantly greater than those measured at sea level. The computer model predicted velocities close to the measured velocities. The computer model was also used to predict velocity differences at various elevations. Finally, the computer model was used with a fmite difference computer program of the ballistics of water drops from sprinklers to show the effect of elevation on the impact velocity and radius of throw of water drops from irrigation sprinklers.