Discharge coefficients of flat-fan nozzles

Abstract

The discharge coefficient (Cd) is a measure of how much of the pressure energy of a nozzle is converted into kinetic energy. With the discharge coefficient known, the exit velocity of the liquid sheet from the nozzle can be calculated from the pressure. It is important to be able to accurately calculate this nozzle exit velocity for use in initializing computational simulations such as AGDISP or CFD. The objective of this work was to measure the discharge coefficients for different types of flat-fan nozzles. In this work, a phase-Doppler interferometer was used to measure the exit velocity for standard, pre-orifice, and air-induction flat-fan nozzles, for rated sizes from 01 to 06, at pressures from 1 to 6 bar. From these velocities, discharge coefficients were calculated. The standard flat-fan nozzles had the highest discharge coefficients, while the air-induction nozzles had the lowest discharge coefficients. For a fixed type of nozzle design, the discharge coefficient increased slightly with the rated flow rate. The discharge coefficient decreased slightly with increasing pressure for a given nozzle. Much of the differences in droplet size for different types of nozzles can be explained by atomization theory as a result of the differences in discharge coefficients for the different nozzle designs.