INTERMITTENT CONTROL OF LIQUID FLOW FROM FAN NOZZLES IN CONCURRENT AIR STREAMS - WIND-TUNNEL STUDIES OF DROPLET SIZE EFFECTS

High-frequency, intermittent operation of hydraulic atomization nozzle s can modulate flow rate without distorting droplet size spectra or sp ray distribution patterns. A direct-acting, coaxial solenoid valve was used for rapid (10 Hz) intermittent actuation of spray; modulation of the valve duty cycle was used to control temporally-averaged, volumet ric flow rate. This study investigated the effects of intermittent flo w control on droplet size spectra from fan nozzles operating in air st reams similar to air-carrier and aircraft sprayers. Droplet size spect ra were slightly affected by flow control over a 4:1 range. The predom inant effect was increased production of larger droplets as flow was r educed; however, the effect was so slight that the volume median diame ter of the droplet size distributions was not altered significantly. I n equivalent comof low flow rate nozzles operating conand higher flow rate nozzles operating intermittently, the intermittently controlled n ozzles produced significantly larger droplets. The effects of intermit tent flow control were similar for all air stream velocities. The flow control valve and technique appeared suitable for use on air-carrier and aircraft spraying systems. (C) 1995 Silsoe Research Institute