Atomization characteristics in pneumatic counterfiowing internal mixing nozzle

Abstract

In an effort to illustrate the global variation of SMD(Sauter mean diameter, or D32) and AMD (Arithmetic mean diameter, or D lO ) at five axial downstream locations (i. e., at Z=30, 50, 80, 120, and 170 mm) under the different experimental conditions, the radial coordinate is normalized by the spray half-width. Experimental data to analyze the atomization characteristics concerning with an internal mixing type have been obtained using a PDPA (Phase Doppler Particle Analyzer). The air injection pressure was varied from 40 kPa to 120 kPa. In this study, counterflowing internal mixing nozzles manufactured at an angle of 15·with axi-symmetric tangential-drilled four holes have been considered. By comparing the results, it is clearly possible to discern the effects of increasing air pressure, suggesting that the disintegration process is enhanced and finer spray droplets can be obtained under higher air assist. The variations in D 32 are attributed to the characteristic feature of internal mixing nozzle in which the droplets are preferentially ejected downward with strong axial momentum, and dispersed with the larger droplets which are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup by higher shear stresses at farther axial locations. The poor atomization around the centre close to the nozzle exit is attributed to the fact that the relatively lower rates of spherical particles are detected and these drops are not subject to instantaneous breakup in spite of the strong axial momentum. However, substantial increases in SMD from the central part toward the edge of the spray as they go farther downstream are mainly due to the fact that the relative velocity of droplet is too low to cause any subsequent disintegration.

Effect of Low ALR on the Spray Characteristics of a Pressure-swirl Duplex Nozzle

“…The relative velocity increases with the air pressure due to the increase of the air density. This decreases the mean drop size in the central downstream region implies to a decrease in volume flux which is substantially in good agreement with the distribution of number density (Lee and Rho 2000).…”

Investigation of turbulent spray disintegration characteristics depending on the nozzle configuration

“…Kennedy (1986) found that the SMD was varied linearly with the liquid surface tension while the influence of the viscosity was minimized. Lee (2000Lee ( -2001 showed that the smaller droplets were inwardly entrained from the spray boundary. Mullinger and Chigier (1974) showed the advantage for the internal mixing atomizers that the atomizing fluid could generally be supplied to the mixing region at a higher pressure than the external mixing type.…”

Geometrical effects on spray characteristics of air-pressurized swirl flows

“…Their experimental observations were mainly focused on the3-D mean velocities, 3-D RMS velocity fluctuations, liquid flux, and SMD, concluding that the turbulence close to the nozzle exit may influence the droplet dispersion and, thus, the rate of spread of the spray, which is determined by the initial droplet trajectories after the breakup of the liquid jet and the droplet centrifugal effect due to air swirl. In an attempt to understand the disintegration mechanism, which is affected by swirl flows, researchers (Lee et al and Elkotp et al,) [11,12,13,14] measured mean and fluctuating velocities. They found that the droplet diameter is progressively reduced as the ALR is increased.…”