A 3D simulation of two-phase flow in an effervescent atomizer for suspension plasma spray

In the suspension spray of nanoparticles, where the attempt is to reach nano-scaled uniform coatings, there is a vital demand to produce a controllable and non-pulsating spray. Effervescent atomizers, in which a gas is bubbled into the bulk of liquid through an aerator, have shown to be a technological alternative to the conventional atomizers when liquid atomization with various concentrations of nano-particles is required. Thus, understanding the behavior of gas and liquid flow through the nozzle is crucial to predict the condition of resultant spray. The two-phase flow inside an effervescent atomizer is numerically investigated. Using an incompressible Eulerian/Eulerian approach, the three-dimensional structure of two-phase flow inside an aerated-liquid injector is modeled. The behaviour of liquid film carrying nano-particles in the discharge passage is studied using different Gas to Liquid mass flow Ratios (GLR), ranging from 0.08% to 1.25%. These numerical results are compared with the experimental data available in literature. The effect of nano-sized solid particles concentration on the liquid film thickness at the exit of the atomizer is studied through the change in liquid bulk density and viscosity. The results show that the atomizing gas-to-liquid mass flow ratio (GLR) does play a key role on the flow behaviour inside the atomizer. At low GLRs of 0.15%, the thickness of the liquid film decreases rapidly and as GLR increases to 1.25% the liquid film thickness dependency on GLR reduces. The results also show that there is no significant effect of particle concentrations, varying within the range of Newtonian fluid, on the liquid film thickness. This feature makes effervescent atomizers a technology choice for controllable suspension thermal spray processes. (C) 2008 Elsevier B.V. All rights reserved.