Fast modelling of plasma jet and particle behaviours in spray conditions (original) (raw)
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3D simulation of the plasma jet in thermal plasma spraying
Journal of Materials Processing Technology, 2005
In this paper, a continuous medium model and the k-ε turbulence formulations are employed to predict the plasma velocity, plasma temperature and argon molar concentration fields in three-dimensional (3D) space. Some important 3D information, such as the 3D continuous isothermal lines, isovelocity lines and the 3D appearance of the plasma jet, are described. This is hard to obtain directly using a 2D scheme. The calculated results will be theoretically helpful for further analysis of the temperature history and trajectories of the entrained particles, particle molten status in the plasma jet, and the deposition of the coatings.
Numerical modelling of plasma spray process
Journal of Physics: Conference Series, 2010
Reproduction of the coating quality in the plasma spraying is tough task. To overcome this problem, it is necessary to understand the behaviour of the arc inside the torch, plasma jet and particles in a plasma jet. Various experimental and modelling works have been carried out on these topics. In this article, a few of our new results of plasma arc inside the torch are presented and some of our simulated results of plasma jets and particle behaviour in a plasma jet are summarized. Electro-thermal efficiencies predicted using two different models are close to the measured one. The effect of atmosphere, where the plasma jet is issued, on temperature field is stronger than on velocity field. The influence of the carrier gas and particle loading on the plasma jet thermo-fluid fields is discussed. The effects of particle loading and turbulence modulation on the particle velocity and temperature are clarified. Turbulence modulation does not affect the particle dispersion significantly.
Modelling the Plasma Jet in Multi-Arc Plasma Spraying
Journal of Thermal Spray Technology, 2016
Particle in-flight characteristics in atmospheric plasma spraying process are determined by impulse and heat energy transferred between the plasma jet and injected powder particles. One of the important factors for the quality of the plasma-sprayed coatings is thus the distribution of plasma gas temperatures and velocities in plasma jet. Plasma jets generated by conventional single-arc plasma spraying systems and their interaction with powder particles were subject matter of intensive research. However, this does not apply to plasma jets generated by means of multi-arc plasma spraying systems yet. In this study, a numerical model has been developed which is designated to dealing with the flow characteristics of the plasma jet generated by means of a three-cathode spraying system. The upstream flow conditions, which were calculated using a priori conducted plasma generator simulations, have been coupled to the plasma jet simulations. The significances of the relevant numerical assumptions and aspects of the models are analyzed. The focus is placed on to the turbulence and diffusion/demixing modelling. A critical evaluation of the prediction power of the models is conducted by comparing the numerical results to the experimental results determined by means of emission spectroscopic computed tomography. It is evident that the numerical models exhibit a good accuracy for their intended use.
Journal of Thermal Spray Technology, 2003
A three-dimensional computational fluid dynamic (CFD) analysis using Fluent V5.4 was conducted on the in-flight particle behavior during the plasma spraying process with external injection. The spray process was modeled as a steady jet issuing from the torch nozzle via the heating of the arc gas by an electric arc within the nozzle. The stochastic discrete model was used for the particle distribution. The particle temperature, velocity, and size inside the plasma plume at a specified standoff distance have been investigated.The results show that carrier gas flow rate variation from 2 standard liters per minute (slm) to 4.0 slm can increase the centerline particle mean temperature and mean velocity by 10% and 16%, respectively, at the specified standoff distance. A further increase of the carrier gas flow rate to 6 slm did not change the particle temperature, but the particle velocity was decreased by 20%. It was also found that an increase in the total arc gas flow rate from 52 slm to 61 slm, with all other process parameters unchanged, resulted in a 17% higher particle velocity, but 6% lower particle temperature. Some of these computational findings were experimentally confirmed by Kucuk et al. For a given process parameter setting, the kinetic and thermal energy extracted by the particles reached a maximum for carrier gas flow rate of about 3.5-4.0 slm.
Plasma-particle interactions in plasma spraying systems
Metallurgical Transactions B, 1992
A mathematical formulation is presented to represent the interactions between the plasma jet exiting a nontransferred arc plasma torch and injected solid particles. This is a generic problem in plasma spraying operations. The calculations are based on the solution of the two-dimensional equation of motion and the thermal energy balance for the particles. Additionally, the plasma temperatures and velocities in the torch and plume are calculated using a mathematical model based on a simplified set of conservation equations. In the formulation, we allow for departure from continuum conditions, particle vaporization, and temperature gradients within the particles. The calculations are compared with previously published experimental measurements of alumina particles injected into a room-temperature, turbulent air jet and into the plume of a commercial plasma torch operating in a turbulent mode. The second set of experiments provides simultaneous measurement of particle temperature, size, and velocity and so form an excellent basis for testing our model. The comparison of the model and the measurements brings new insight into the behavior of particles in plasma jets.
Numerical Study on Plasma Jet and Particle Behavior in Multi-arc Plasma Spraying
Journal of Thermal Spray Technology, 2017
Plasma jet and particle behavior in conventional single-arc plasma spraying has been subject to intensive numerical research. However, multi-arc plasma spraying is a different case which has yet to be investigated more closely. Numerical models developed to investigate the characteristics of multi-arc plasma spraying (plasma generator, plasma jet, and plasma-particle interaction models) were introduced in previous publications by the authors. The plasma generator and plasma jet models were already validated by comparing calculated plasma temperatures with results of emission spectroscopic computed tomography. In this study, the above-mentioned models were subjected to further validation effort. Calculated particle in-flight characteristics were compared with those determined by means of particle diagnostics and high-speed videography. The results show very good agreement. The main aim of the current publication is to derive conclusions regarding the general characteristics of plasma jet and particle in-flight behavior in multi-arc plasma spraying. For this purpose, a numerical parameter study is conducted in which the validated models are used to allow variations in the process parameters. Results regarding plasma jet/particle in-flight temperatures and velocities are presented. Furthermore, the general characteristics of plasma jet and particle behavior in multi-arc plasma spraying are discussed and explained. This contributes to better understanding of the multi-arc plasma spraying process, in particular regarding the injection behavior of particles into hot regions of the plasma jet. Finally, an example test case showing a possible practical application area of the models is introduced.
CFD simulation of particle movement during atmospheric plasma spraying
2018
Atmospheric Plasma Spraying (APS) is a powder based coating process with versatile applications in terms of functional layers like corrosion, wear resistant or thermal barrier coatings. However, the fundamental process interactions cannot fully be described and understood experimentally. Therefore, a supportive CFD model was carried out by use of ANSYS 19.0. In detail, the CFD model consists of direct coupled electromagnetic and hydrodynamic formalisms. The particle behaviour was described by a simple multiphase reaction routine. Based on the CFD model, the resulting temperature field and the particle behaviour can be investigated. Especially, the particle trajectory, which represents the particle dwell time in the plasma stream, is of special interest for the final APS coating. Therefore, the description of a stable heat source is of major priority. This work shows a promising approach to evaluate the above mentioned particle and plasma properties, supported by a systematic parameter investigation. The obtained and experimental validated data can be used for a better process understanding as well as for further process optimisation.
3-D time-dependent modelling of the plasma spray process. Part 1: flow modelling
International Journal of Thermal Sciences, 2005
The plasma spray process is widely used to produce thick coatings by the successive pilling of particles deposited in a molten or semi-molten state on a prepared substrate. However, this process includes time-dependent phenomena that affect the reliability of the process and reproducibility of coating. These phenomena are principally linked to the continuous movement of the electric arc root on the anode wall in the plasma gun. Such a movement leads to arc length variations resulting in fluctuations in arc voltage, enthalpy input to the flow and instabilities in the plasma jet. This paper presents an attempt to develop a time-dependent and 3-D model of the plasma spray process that can provide a useful insight in the time-evolution of the performance of the process. The effect of the transient behaviour of the arc on the gas flow is modelled with a time dependant heat source located inside the nozzle and evolving with the arc voltage. The first stage of the study consisted in the validation of the flow model thanks to the comparison of steady-state computed results with experimental data. The second dealt the time-dependant simulation of the flow.
Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions
Coatings, 2021
Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decr...
Spray parameters and particle behavior relationships during plasma spraying
Journal of Thermal Spray Technology, 1993
Using laser anemometry, laser fluxmetry, and statistical two-color pyrometry, the velocity, number flux, and surface temperature distributions of alumina and zirconia particles in dc plasma jets have been determined inflight for various spraying parameters. The flux measurements emphasized the importance of the carrier gas flow rate, which must be adjusted to the plasma jet momentum depending on the arc current, nozzle diameter, gas flow rate, and gas nature. It has also been shown that the particle trajectories depend both on the particle size and injection velocity distributions and that the position and tilting of the injector plays a great role. The particle size drastically influences its surface temperature and velocity, and for the refractory materials studied, only the particles below 45 μm in diameter are fully molten in Ar-H2 (30 vol%) plasma jets at 40 kW. The morphology of the particles is also a critical parameter. The agglomerated particles partially explode upon penetration into the jet, and the heat propagation phenomenon is seriously enhanced, particularly for particles larger than 40 μm. The effects of the arc current and gas flow rate have been studied, and the results obtained in an air atmosphere cannot be understood without considering the enhanced pumping of air when the plasma velocity is increased. The Ar-He (60 vol%) and Ar-H2 (30 vol%) plasma jets, when conditions are found where both plasma jets have about the same dimensions, do not result in the same treatment for the particles. The particles are not as well heated in the Ar-He jet compared to the Ar-H2 jet. Where the surrounding atmosphere is pure argon instead of air (in a controlled atmosphere chamber), he radial velocity and temperature distributions are broadened, and if the velocities are about the same, the temperatures are higher. The use of nozzle shields delays the air pumping and increases both the velocity and surface temperature of the particles. However, the velocity increase in this case does not seem to be an advantage for coating properties.