THEORETICAL STUDY OF POST EXIT BEHAVIOUR OF DROPLETS FROM A HIGH PRESSURE AGRO-FORESTRY SWIRL NOZZLE

Abstract

A better understanding of the fundamental principles underlying the movement of droplets which escaped from the exit orifice of a high pressure agro-forestry swirl nozzle in still air was developed. Equations of dynamic systems of droplets distribution at high pressure were used in conjunction with particle dynamics equations to develop mathematical models of motion phenomenon of liquid droplets in still air. The models were implemented with algorithm coded in C++ language to investigate the effects of droplet diameter, nozzle supply pressure, and time variation on selected motion parameters of drag force, Reynolds number, final velocity and distance.

The simulation results established that while viscous forces are predominant on droplets whose diameters ranged between 100 and 200 microns when they move in still air, inertia forces are predominant on droplets whose diameters are larger. The drag force increased with increase in droplets diameters and nozzle supply pressure. For a 5 fold increase in droplet diameter under the same nozzle supply pressure, drag force increases by 20 times. The pattern of variation of final velocities of liquid droplets in terms of droplet diameter and nozzle supply pressure is similar to that of the distance traveled by the droplets. The practical implication of these results is that whenever it is necessary to produce droplets whose diameters fall within the range of 100 and 200 microns with an agro-forestry swirl nozzle, auxiliary air blast must be provided before they could hit the intended target(s).