Numerical Study of the Effects of Twin-Fluid Atomization on the Suspension Plasma Spraying Process

Abstract

Suspension plasma spraying (SPS) is an effective technique to enhance the quality of the thermal barrier, wear-resistant, corrosion-resistant, and superhydrophobic coatings. To create the suspension in the SPS technique, nano and sub-micron solid particles are added to a base liquid (typically water or ethanol). Subsequently, by using either a mechanical injection system with a plain orifice or a twin-fluid atomizer (e.g., air-blast or effervescent), the suspension is injected into the high-velocity high-temperature plasma flow. In the present work, we simulate the interactions between the air-blast suspension spray and the plasma crossflow by using a three-dimensional two-way coupled Eulerian–Lagrangian model. Here, the suspension consists of ethanol (85 wt.%) and nickel (15 wt.%). Furthermore, at the standoff distance of 40 mm, a flat substrate is placed. To model the turbulence and the droplet breakup, Reynolds Stress Model (RSM) and Kelvin-Helmholtz Rayleigh-Taylor breakup model are used, respectively. Tracking of the fine particles is continued after suspension’s fragmentation and evaporation, until their deposition on the substrate. In addition, the effects of several parameters such as suspension mass flow rate, spray angle, and injector location on the in-flight behavior of droplets/particles as well as the particle velocity and temperature upon impact are investigated. It is shown that the injector location and the spray angle have a significant influence on the droplet/particle in-flight behavior. If the injector is far from the plasma or the spray angle is too wide, the particle temperature and velocity upon impact decrease considerably.

Relationships between arc plasma jet properties and plasma/liquid interaction mechanisms for the deposition of nanostructured ceramic coatings

“…When travelling the hot plasma core, ligaments and drops undergo catastrophic fragmentation at high Weber numbers (𝑊 𝑒 > 100) resulting into droplets ( tens of µm in diameter) due to Kelvin-Helmholtz and Rayleigh-Taylor fluid instabilities (46,49,50). Figure 5A displays that the liquid column, injected with a speed of about 30 m.s -1 , is actually fragmented at the neck of instabilities growing from its surface due to shearing stress.…”

“…Jaddidi et al [46,47] exhaustively reviewed heat transfer in the SPS process and also highlighted the classification of breakup phenomena of liquid columns for primary fragmentation and of drops for secondary fragmentation according to the plasma gas Weber number (W e = ρ G U 2 G D/σ), the momentum flux ratio q = ρ L U 2 L /ρ G U 2 G and the Ohnesorge number of drops Oh = µ L / √ ρ L d L σ L where (ρ, U) G and (ρ, U) L are respectively, the (density, relative velocity) of the plasma gas and the liquid phase, σ L is the surface tension, µ L the dynamic viscosity of the liquid phase, D is the diameter of liquid column and d L is the diameter of the drop. According to the considerations in the previous section relating to specific enthalpy and plasma speed, mechanical fragmentation is expected due to W e > 100 while the liquid column momentum flux, or its dynamic pressure, remains higher that of the plasma jet (q > 1).…”

“…As pointed out by Meillot et al [48], the Weber number may be high in the fringes of the plasma due to the high velocity gradient and high plasma density. When traveling through the hot plasma core, filaments and drops undergo catastrophic fragmentation at high Weber numbers (W e > 100) resulting in droplets (∼tens of µm in diameter) due to Kelvin-Helmholtz and Rayleigh-Taylor fluid instabilities [46,49,50]. Figure 5(A) shows that the liquid column, injected at a speed of about 30 m s −1 , is actually fragmented at the neck of the instabilities growing from its surface due to shearing stress.…”

Investigation on the Impact of Excitation Amplitude on AFM-TM Microcantilever Beam System’s Dynamic Characteristics and Implementation of an Equivalent Circuit

“…Nonetheless, the advancements in measurement technology within the micro and nano-domains have revealed that certain dynamic characteristics of these mechanical systems cannot be fully elucidated by classical mechanics. Consequently, the impact of quantum mechanics on microelectromechanical systems (MEMS) is becoming increasingly prominent, and its mode of action has garnered widespread attention in recent years [ 2 , 3 ].…”