Primary breakup of liquid sheets in crossflow and liquid jets in gaseous coflow

Abstract

This thesis discusses the breakup of liquid sheets under the influence of crossflow and the breakup of micro-liquid jets in coflow air. The breakup of liquid jets and sheets is important for many applications, e.g., agricultural sprays, fuel atomization, and spray coatings, nasal spray delivery, among others. The aerodynamic effects on the liquid breakup process are studied experimentally to identify the breakup regime transitions and droplet sizes. Two different setups were used to investigate experimentally the breakup process in both the crossflow and coflow configurations. A subsonic wind tunnel was used to simulate the crosswind effects on flat fan nozzle spray. Two flat fan nozzles were mounted at the ceiling of the test section of the wind tunnel. Rotameters, pitot tube, and inclined manometer were used to measure the flowrates and velocities, respectively. A micro coflow injector was constructed at the new product development center from two beveled needles (16G and 30G) one inside the other and were used to study breakup of micro liquid jet in with and without the presence of coflowing air.

A high-speed digital imaging technique was used in both setups to capture different breakup regimes and to measure the breakup regime transitions, the location of the end of the liquid core, the breakup time, the location, and the size of droplets at the onset of breakup and the spray trajectory. The effects of spray angle for flat fan nozzle spray and the aerodynamic effects on the spray outcomes are presented in this thesis. The results were correlated using phenomenological analyses. For liquid sheets in crossflow, the aerodynamic effects were responsible for initiating bag breakup and reducing the droplet sizes. which are susceptible to drift. This would be problematic for spraying herbicides in windy conditions. For the breakup of micro liquid jets in gaseous coflow the aerodynamic effects resulted in accelerating the breakup process and reducing the droplet sizes. The results show that the presence of air resulted in a large reduction of the droplet sizes compared with pressure atomization only. The effects of reducing the injector size on different measurements were obvious when compared with previous studies of larger coflowing injectors.