High-frequency, intermittent operation of hydraulic atomization nozzles can modulate flow rate without distorting droplet size spectra or spray 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, volumetric flow rate. This study investigated the effects of intermittent flow control on droplet size spectra from fan nozzles operating in air streams similar to air-carrier and aircraft sprayers. Droplet size spectra were slightly affected by flow control over a 4:1 range. The predominant effect was increased production of larger droplets as flow was reduced; however, the effect was so slight that the volume median diameter of the droplet size distributions was not altered significantly. In equivalent comof low flow rate nozzles operating conand higher flow rate nozzles operating intermittently, the intermittently controlled nozzles produced significantly larger droplets. The effects of intermittent 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.
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