A Study of a Powder Coating Gun Near Field: Particle Flow in an Isothermal Staggered Concentric Air Jet

Abstract

An experimental study of inert particle dispersion in an isothermal concentric air jet near field was conducted for cases of standard non-staggered and alternative staggered jet nozzles, each taken from a polymer powder flame deposition gun. The experimental work consisted of analysis of high speed digital images of the inert two phase isothermal jet flow, illuminated by a laser light sheet along and across the jet axis. The analysis of particle spread in the jet, represented by families of particle density distributions, clearly showed that the staggered nozzles resulted in a better-focused flow, with narrower distributions in the near field, and in the elimination of the recirculation zone that disrupted the particle flow in a non-staggered nozzle arrangement. In all cases, histograms of the cross-sectional particle area density were found to be approximately Gaussian. It was also found that there was a wide variation in the size and shape of the ground polymer particles used and these two characteristics caused a wide variation in the radial and axial velocities of the particles. Despite the differences between single-phase numerical simulations and experimental results, reported in Payne et al. [1], the introduction of particles into a numerical model produced satisfactory agreement with the particle velocities found experimentally.

Experimental study of an inert isothermal air carbon dioxide jet with and without a second phase

“…The flow visualization used a sheet of laser light, created by the apparatus shown in Payne et al, placed either through the centreline of the gun head to illuminate each jet from its origin, or at a right angle to the axis of the coaxial air jet just downstream of the origin of the central jet. When the sheet of laser light was placed longitudinally, it was positioned so that it illuminated four nozzles emitting air or CO 2 (in place of propane), two on one side of the coaxial air jet, one each from the inner and outer rings, and the two diametrically opposite them.…”

“…Two earlier papers by Payne et al reported on experimental and numerical studies of the flow field created by an innovative gun head design for a polymer flame deposition process. Payne et al studied the isothermal air‐only coaxial jet.…”

“…Payne et al studied the isothermal air‐only coaxial jet. Another paper by Payne et al reported on studies of the inert isothermal coaxial air jet with ground polymer particles injected into the central air jet upstream of the gun head. The current paper reports on experimental studies of the mixing of the coaxial air jet and air or CO 2 , which replaces propane to form additional air or CO 2 jets.…”

“…The innovative gun head used for most of the work reported on by Payne et al and in this paper is shown schematically in Figure . The downstream staggering of the central jet allows the annular air jet to decelerate as it mixes with the stationary ambient air before the annular air mixes with the air from the central jet.…”

“…An older gun head design was also used for some of the work reported in Payne et al and for some of the work reported here. In this older gun head, the central and annular air jet nozzles are in the same plane.…”