A MATHEMATICAL-MODEL TO PREDICT THE WEAR RATE OF NOZZLES WITH ELLIPTIC ORIFICES

A mathematical model was developed to predict orifice wear rate for fa n-pattern, spray nozzles. Variables affecting nozzle wear rate in the model are usage time, spray pressure, initial orifice size, effective coefficient of friction between orifice wall and fluid, orifice materi al, and the fluid. Spray-pattern measurements for new and worn orifice s verified that wear mainly increased minor-axis length of the ellipti cal orifice with very little wear at the ends of the major axis. There was good agreement between predicted and measured flow rate increases for worn orifices with various materials and nominal capacities for u p to about 38% increase in flow rate relative to new orifices. Both th e model and experiments indicated nozzle wear rate increased with usag e time, spray pressure, effective coefficient of friction between nozz le orifice wall and fluid and ratio of major to minor axis of the elli ptical orifice.