A Computational and Experimental Investigation into Radial Injection for Suspension High Velocity Oxy-Fuel (SHVOF) Thermal Spray

Chadha, S. L.; Jefferson-Loveday, Richard; Venturi, Federico; Hussain, Tanvir

doi:10.1007/s11666-019-00888-8

Cited by 10 publications

(8 citation statements)

References 28 publications

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“…Therefore, it should be taken into account that even if higher values are reached at 75 kW, these could refer to a smaller fraction of particles compared to the 50 kW and 25 kW case. Additional considerations on these measured values can be made upon comparison with flame temperature and velocity values simulated using the eddy dissipation concept model from a recently published work on this same HVOF setup [20]. According to these simulations, the 75 kW flame at 100 mm stand-off distance is characterized by a gas temperature and velocity around 1800…”

Section: In-flight Temperature and Velocity Measurementsmentioning

confidence: 99%

“…The stand-off distances used in S-HVOF thermal spray are normally much shorter than those used in this work, at around 85 mm. Such a short stand-off distance proves unsuitable for GNP spray since the hot jet (1850 °C at 85 mm for a 75 kW flame [20]), as it sweeps the substrate surface, transfers an amount of heat that accumulates on the sample and which GNPs are not able to withstand and may degrade. Moreover, the combustion jet from the S-HVOF thermal spray gun is capable of mechanically removing the loosely bonded GNPs from the substrate surface, hence lowering the deposition efficiency.…”

Section: Gnp Thin Film Depositionmentioning

confidence: 99%

See 1 more Smart Citation

Radial Injection in Suspension High Velocity Oxy-Fuel (S-HVOF) Thermal Spray of Graphene Nanoplatelets for Tribology

Venturi

Hussain

2019

J Therm Spray Tech

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Friction is a major issue in energy efficiency of any apparatus composed of moving mechanical parts, affecting durability and reliability. Graphene nanoplatelets (GNPs) are good candidates for reducing friction and wear, and suspension high velocity oxy-fuel (SHVOF) thermal spray is a promising technique for their scalable and fast deposition, but it can expose them to excessive heat. In this work, we explore radial injection of GNPs in SHVOF thermal spray as a means of reducing their interaction with the hot flame, while still allowing a high momentum transfer and effective deposition. Feedstock injection parameters, such as flowrate, injection angle and position, were studied using high-speed imaging and particles temperature and velocity monitoring at different flame powers using Accuraspray 4.0.Unlubricated ball-on-flat sliding wear tests against an alumina counterbody ball showed a friction coefficient reduction up to a factor 10 compared to the bare substrate, down to 0.07. The deposited layer of GNPs protects the underlying substrate by allowing low-friction dry sliding. A Transmission Electron Microscopy study showed GNPs preserved crystallinity after spray, and became amorphised and wrinkled upon wear. This study focused on GNPs but is relevant to other heat-and oxidation-sensitive materials such as polymers, nitrides and 2D materials. The unprecedented mechanical [1] and tribological [2] properties of graphene have attracted a wide range of interests in using it as a solid lubricant [3]. The lubricating effect favors a lowering of the coefficient of friction and a delay in damaging the lubricated surfaces. This can effectively improve the durability of moving mechanical parts, by reducing localized heating and subsequent wear. Some small-scale deposition techniques [4, 5] can be hardly employed for covering large areas with a considerable amount of graphene. Simple techniques like drop casting and airbrush spray [6] would allow the deposition;however, they do not provide a good bonding with the substrate. Conversely, spray techniques such as supersonic cold spray [7] proved suitable for large scale graphene coverage and enhanced the bonding with the substrate due to the high velocity at impact. An even better graphene-substrate adhesion could be reached with thermal spray, as it gives not only high kinetic energy but also a higher amount of heat to the particles. In particular, Suspension High Velocity Oxy Fuel (S-HVOF) thermal spray [8] is a good candidate for this task. This relatively new technique allows the injection and spray of suspension in HVOF instead of powders, thus allowing to handle finer particles, down to the micro-to-nano scale. Overall, this technique provides high acceleration and has a relatively low flame temperature compared to plasma spray. Graphene is known to be stable at high temperatures in an inert environment, however in air it starts degrading at around 250 °C, and a consistent mass loss can occur at around 500 °C, according to thermogravimetric analyses (TGA) [9]. The use ...

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Section: In-flight Temperature and Velocity Measurementsmentioning

confidence: 99%

Section: Gnp Thin Film Depositionmentioning

confidence: 99%

Radial Injection in Suspension High Velocity Oxy-Fuel (S-HVOF) Thermal Spray of Graphene Nanoplatelets for Tribology

Venturi

Hussain

2019

J Therm Spray Tech

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“…It was found that the suspension penetration becomes more efficient and higher particle velocity and temperature can be obtained if the injector is near the torch exit and its angle is toward the torch [12]. The stated suspension model has been used by several researchers so far to simulate different suspension thermal spray processes, and its accuracy and reliability have been verified under various operating conditions [12][13][14][15][16][17][18][19][20][21][22]. For instance, Pourang et al [13] used the mentioned approach and analyzed the temporal evolution of a 40 µm suspension droplet containing zirconia (10 wt.%) and After the suspension breakup, the liquid evaporation becomes dominant.…”

Section: Introductionmentioning

confidence: 99%

“…It was shown that suspension penetration depth, as well as droplet/particle trajectory, temperature, and velocity, are a strong function of plasma jet fluctuations and injection properties such as injection velocity. In addition to the SPS simulations, the stated model was successfully used by Jadidi et al [19,20] and Chadha et al [21,22] to model suspension high-velocity oxygen-fuel (HVOF) process as well. It should be pointed out that for simulating suspension HVOF, the Taylor Analogy Breakup (TAB) model was used to model the droplet breakup since the Weber number is relatively low in this process.…”

Section: Introductionmentioning

confidence: 99%

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

Jadidi

Moghtadernejad

Hanson

2020

Fluids

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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.

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“…This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) ( Esther Dongmo et al, 2009 ;Jadidi et al, 2016 ). Traditionally, the blob method is employed to model the injection of suspension into the combustion chamber ( Chadha et al, 2019b ;Chadha et al, 2019a ). For the blob method the jet is simplified to an injection of discrete droplets that can undergo secondary breakup.…”

Section: Introductionmentioning

confidence: 99%

A high-fidelity simulation of the primary breakup within suspension high velocity oxy fuel thermal spray using a coupled volume of fluid and discrete phase model

Chadha

Jefferson-Loveday

Hussain

2020

International Journal of Multiphase Flow

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In the suspension high velocity oxy fuel (SHVOF) thermal spray, a suspension is injected into the combustion chamber where the jet undergoes primary and secondary breakup. Current knowledge of the primary breakup within the combustion chamber is very limited as experimental investigations are impeded due to direct observational inaccessibility. Numerical methods are also limited due to the computational costs associated with resolving the entire range of multiphase structures within SHVOF thermal spray. This paper employs a coupled volume of fluid and discrete phase model, combined with a combustion model, to simulate primary breakup at a fraction of the cost of a fully resolved simulation. A high-fidelity model is employed within this study to model the combustion chamber; the model shows a backflow region that will contribute to clogging within the nozzle. This study modifies the injector type for SHVOF thermal spray by introducing a co-flow around the liquid injection to reduce clogging within the combustion chamber. This study shows that introducing a co-flow of gas at a velocity of 200 m/s around the liquid injection reduces the backflow region by 40% within the combustion chamber. The addition of a gas co-flow results in a smaller region of backflow. Small suspension droplets with insufficient momentum are unable to overcome the backflow and will likely deposit themselves onto the wall of the combustion chamber. The deposition of the particles on the walls causes clogging of nozzles often seen in SHVOF thermal spray. The addition of a gas co-flow results in an increase in the velocity of droplets formed during primary breakup. The greater droplet velocity allows for small droplets to overcome the small backflow region near the liquid injection. The Sauter mean diameters predicted from the numerical model are compared to experimental measurements available within the literature and shows good agreement.

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A Computational and Experimental Investigation into Radial Injection for Suspension High Velocity Oxy-Fuel (SHVOF) Thermal Spray

Cited by 10 publications

References 28 publications

Radial Injection in Suspension High Velocity Oxy-Fuel (S-HVOF) Thermal Spray of Graphene Nanoplatelets for Tribology

Radial Injection in Suspension High Velocity Oxy-Fuel (S-HVOF) Thermal Spray of Graphene Nanoplatelets for Tribology

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

A high-fidelity simulation of the primary breakup within suspension high velocity oxy fuel thermal spray using a coupled volume of fluid and discrete phase model

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