Doctoral Dissertations

Date of Award

12-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Agricultural Engineering

Major Professor

Alvin R. Womac

Abstract

Research focused on (1) the development of a new model on fan atomization, (2) the design and development of a variable-flow fan nozzle (VFFN) for on-the-go control of precision chemical application, and (3) the development of a phase-partition air sampler (PPAS) to evaluate spray drift from the VFFN. Relationships of spray angle, spray thickness, droplet size, and the spray velocity to the nozzle geometry were analytically explained by the new model. Three VFFN prototypes with spray angles of 50, 70 and 90 degrees and one PPAS prototype were designed and successfully tested. A new model on fan atomization was based on geometric wave theory for compressible liquid impact (Lesser, 1981). The new model was different from the current models which were based on incompressible liquid impact theory. The current models explained that fan atomization was the disintegration of spray sheets into drops by wave formation. The new model explained fan atomization from impact of two oblique jets due to continuous jetting from the compressing of liquid. Jetting was created when spray droplets were spalled from the compressed liquid. The new model predicted that as the angle between the two oblique jets increased, spray angle increased, spray thickness decreased, spray velocity decreased, and droplet size decreased. The key component of the VFFN was a special variable orifice that performed two main functions: (1) metering the fluid and (2) forming a fan spray. The flow rate of the VFFN was controlled through regulation of the liquid line pressure at a fixed liquid control pressure. The flow increased linearly with liquid line pressure at a fixed liquid control pressure. The droplet size spectrum emitted from the VFFN was primarily varied through regulation of the liquid control pressure. Experimental results for current nozzle dimensions indicated that a 13.3:1 flow turndown ratio was achieved at a fixed liquid control pressure. By adjusting liquid control pressure from 414 to 138 kPa, the D0.1, Dv0.s, and Dv0.e was controlled from 58 to 190 μm, 141 to 522 μm, and 300 to 850 μm, respectively. Independent control of liquid flow rate and drop size spectrum was achieved by separately varying liquid line pressure and liquid control pressure.

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