DESIGN AND TESTS OF A VARIABLE–FLOW FAN NOZZLE

Abstract

A new–concept variable–flow fan nozzle (VFFN) was developed with an aim to variable–rate chemical application. A split–end meter plunger in a tapered sleeve served as a variable orifice that varied flow rate and droplet size and created a fan spray by impinging streams of liquid together. The fan spray exited at a right angle to the plane of the slit as previously hypothesized due to jetting of spalled droplets. Longitudinal position of the plunger in the sleeve determined instantaneous nozzle capacity. A diaphragm was selected to position the plunger for simplicity in this study. Vector force analyses indicated that longitudinal plunger position depended on line pressure, control pressure, diaphragm area, plunger end area, spring constant of split plunger end, maximum slit opening, and taper angle. As expected, the prototype flow rate was sensitive (~0.02 L min –1 kPa –1 line pressure) to the pressure balance across a 248–mm 2 diaphragm and to a 15,500 N m –1 plunger spring constant. Three VFFN prototypes with spray angles of 50
, 70
, and 90
were constructed and tested. A single prototype was tested rather than a boom full of prototypes. Results indicated that the VFFN spray angle equaled the taper angle of the nozzle sleeve at a line pressure of 276 kPa. Observed turndown ratio (maximum to minimum flow rate) for the 90
prototype was 13 to 1 based on spray angles, flow rates, and pattern widths (at 45 cm nozzle height) ranging from 65
to 100
, 0.227 to 3.028 L min –1 , and 70 to 110 cm, respectively. Multiple prototype effects on spray distribution across a boom were not investigated. By adjusting the control pressure from 414 to 138 kPa, the droplet spectrum DV0.1, Dv0.5, and Dv0.9 values were varied from 58 to 190
m, 141 to 522
m, and 300 to 850
m, respectively. Independent control of liquid flow rate and droplet size spectrum was achieved by separately varying line pressure and control pressure.