Characteristics of droplets from single and twin jet air induction nozzles: A preliminary investigation

Spray drift from pesticide application is of increasing social concern. Air induction nozzles produce large droplets some of which contain air bubbles, leading to spray drift mitigation and possibly to droplet deposit increase. The purpose of this study was to investigate droplet diameter and droplet axial velocity from sprays generated by three different air induction nozzles (namely two flat fan nozzles and a twin jet flat fan nozzle). The aim was to compare three sheets at the same injection pressure and two values of flow rate. These were a twin jet flat fan nozzle with a given flow rate and two single flat fan nozzles, one which delivered the same flow rate, the other which delivered half the flow rate. Phase Doppler Anemometry (PDA) measurements were carried out at several distances from the nozzle exit, and at various distances from the spray axis. The PDA simultaneously measured the droplet diameter and the droplet axial velocity. Measurements showed that the droplets generated by the twin jet nozzle were slightly larger, and had a narrower size spectrum than those produced by the single nozzle at the same flow rate. Droplets produced by the twin jet nozzle were faster and slowed very little downstream, compared to single nozzles. In addition, the comparison of sprays created by both single nozzles showed that the droplet size was similar whatever the flow rate. However, it has appeared that a higher flow rate led to a higher droplet frequency and a higher droplet velocity.

► Droplet diameter and axial velocity of three air induction nozzles were measured.
► Two flat fan nozzles and a twin jet flat fan nozzle were considered.
► Droplets from the twin jet nozzle were slightly larger, with a size spectrum narrower.
► Droplets produced by the twin jet nozzle were faster and slowed little downstream.
► Single nozzle droplet size was similar whatever the flow rate.