A study of liquid droplet disintegration for the development of nanostructured coatings

Abstract

Thermal spray coatings produced from a liquid feedstock are receiving an increasing level of interest due to the advanced, nanostructured coatings which are obtainable by these processes. In this article, a high‐velocity oxy‐fuel (HVOF) thermal spray system is computationally investigated to make a scientific assessment of the liquid droplet behavior on injection. An existing liquid‐fuelled HVOF thermal spray gun is simulated using the computational fluid dynamic approach. The steady‐state gas‐phase dynamics are initialized by the introduction of liquid kerosene and oxygen which react within the combustion chamber producing a realistic compressible, turbulent jet. Discrete‐phase water droplets are injected at the powder injection port. On injection, the water droplets breakup and vaporize, while being entrained through the acceleration barrel of the HVOF system. The results obtained give an insight to the mechanism which control the water droplet sizes and disintegration process, and serve as a fundamental reference for future development of liquid feedstock devices. © 2012 American Institute of Chemical Engineers AIChE J, 2012

Effects of angular injection, and effervescent atomization on high-velocity suspension flame spray process

“…The Discrete Phase Model (DPM) treated the liquid droplets in Lagrangian manner and tracked the droplets throughout their flight. The TAB and DPM models are well adapted to the conditions of spraying and validated in the earlier studies; details can be found in [20,50,51,64].…”

“…The hydrodynamic force required for the deformation of droplets is related to the surface tension force acting to retain the droplet form by We. Since the Ohnesorge number (Oh) remains below 0.1 (Oh ≪ 0.1) in the computational domain, the main parameter related to breakup physics is the We [20,64,65]. The Discrete Phase Model (DPM) treated the liquid droplets in Lagrangian manner and tracked the droplets throughout their flight.…”

“…Detailed descriptions of the gas phase, discrete phase, breakup and combustion models are reported elsewhere [25,27,30,51,54,59,[61][62][63]. The employed mathematical models have been strongly tested against experimental and numerical data [50,[52][53][54]60,64,65], the test results are not repeated here for brevity. Only the detailed modelling equations for the ETI are presented here for a clear understanding in Section 2.1 [33,49].…”

“…The secondary breakup of droplets to smaller ones was modelled by the Taylor Analogy Breakup (TAB) model as the Weber number is less than 100 (We b 100) [20,50,64,65]. Different regimes of droplet fragmentation are determined by using the critical value of We.…”

A Comprehensive Review on Fluid Dynamics and Transport of Suspension/Liquid Droplets and Particles in High-Velocity Oxygen-Fuel (HVOF) Thermal Spray

“…They also concluded that the aqueous solution has a larger influence on the gas dynamics, in contrast to the organic solvent that has less impact on the gas velocity and temperature. Tabbara and Gu [282] modeled the water droplet injection into a liquid-fueled HVOF torch (JP5000). Liquid kerosene and oxygen were axially injected into the combustion chamber while water droplets were injected into the barrel radially.…”