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

Abstract

This work presents the nanostructured coating formation using suspension thermal spraying through the HVOF torch. The nanostructured coating formation requires nanosize powder particles to be injected inside a thermal spray torch using liquid feedstock. The liquid feedstock needs to be atomized when injected into the high-velocity oxygen fuel (HVOF) torch. This paper presents the effects of angular injection and effervescent atomization of the liquid feedstock on gas and droplet dynamics, vaporization rate, and secondary breakup in the high-velocity suspension flame spray (HVSFS) process. Different angular injections are tested to obtain the optimum value of the angle of injection. Moreover, effervescent atomization technique based on twin-fluid injection has been studied to increase the efficiency of the HVSFS process. Different solid nanoparticle concentrations in suspension droplets are considered. In angular injection the droplets are injected into the core of the combustion zone; this immediately evaporates the droplets, and evaporation is completed within the torch. The value of 10°-15°i s selected as the optimal angle of injection to improve the gas and droplet dynamics inside the torch, and to avoid the collision with the torch's wall. The efficiency of the effervescent atomization can be enhanced by using high gas-to-liquid mass flow rate ratio, to increase the spray cone angle for injecting the suspension liquid directly into the combustion flame. It is also found that the increment in the nanoparticle concentration has no considerable effects on the droplet disintegration process. However, the location of evaporation is significantly different for homogeneous and non-homogeneous droplets.

Grey modeling for thermal spray processing parameter analysis

“…To solve this problem, numerical modeling method was proposed with the increase of computation capability. Various models had been constructed to study the complex flow physics, combustion chemistry, flames formation and propagation involved in the thermal spraying processes (Mahrukh et al, 2016;Sobolev et al, 1995). The integral HVOF procedure, including the combustion processes, the heat, mass and momentum interactions between the flame, the suspension droplets (including vaporization) and the solid spray particles were modeled and analyzed by Dongmo et al (2009).…”

Numerical Analysis of the Effects of Using Effervescent Atomization on Solution Precursor Thermal Spraying Process

“…show good agreement with the experimental data. Hence, this model can be used in the numerical simulations of the effervescent spray atomization in the CH-2000 HVOF torch 37,42 . The coefficients of determination (R 2 ) is shown in Fig.…”

“…Moreover, in the flame jet, P-E droplets are evaporated and the droplets completely converted into the ethanol vapors which then burn inside the torch and improve its thermal and kinetic energies 42 .…”

“…= Atomization gas density (kg/m 3 ) ! = Initial wave amplitude = Infinitesimal wavy disturbance = Droplets' surface-tension (N/m) Representation of the SPTS process for nanoparticles formation from Representation of precursor injection into the CH-2000 HVOF torch (a) plain-orifice nozzle (N1), (b) angular injection nozzle (N2), (c) effervescent atomization nozzle (N3), (d) crosssection view of effervescent-type nozzle (N3)31,37,42…”

Experimental Investigation of the Performance and Spray Characteristics of a Supersonic Two-Phase Flow Ejector with Different Structures

“…Due to the pressure difference between the suction chamber and the secondary flow, the secondary fluid can be entrained in the primary flow in the form of small droplets or bubbles [17]. The phenomenon of spray pulsating exists in all nozzles [18,19]. For two-phase flow atomization, there are obvious fluctuations in the gas-liquid flow coefficient in the vicinity of the nozzle due to the gas phase.…”