Numerical Study on Plasma Jet and Particle Behavior in Multi-arc Plasma Spraying (original) (raw)
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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.
Modelling and Experimental Investigation of A Plasma Spraying System
Ph.D. Dissertation, 2009
In this study, the relationship between the parameters of the atmospheric plasma spraying process and the in-flight properties of the particles was determined experimentally using an optical measurement system, DPV2000. The coating microstructure was investigated using analysis of SEM (Scanning Electron Microscope) images. The morphology of individual splats was studied to shed light on the relationship between the in-flight particle properties and the coating characteristics. The results demonstrate that changing the vertical position of the torch relative to the sensing head of DPV2000 has a strong effect on the particles velocities and temperature distributions. Also changing the distance between the torch and the sensing head increases the velocity gradient. Coating microstructure was studied by changing the spraying parameters, e.g. the stand-off distance, arc current, powder feed rate, and the Ar/ He mixture as a plasma gas. A Matlab code was constructed for porosity analysis of the SEM images of the coating. The coating cross-section analysis showed that the total porosity of the coating increased by decreasing the arc current, increasing the stand-off distance, decreasing powder feed rate and increasing helium flow rate. Two different material were used for the APS coating; the regular (r-YSZ) feed stoke and the nano size (n-YSZ) agglomerated powder, the results illustrate that the r- YSZ coating has higher total porosity at higher arc currents than n-YSZ coating. The splat flattening behavior was examined at different substrate temperatures, and different surface roughness for both powders. The results indicate that the flattening degree increases for high polished substrate with high temperature for the two material but the values for n- YSZ were higher than r-YSZ. Circularity of the splats increased as the arc current increased and stand-off distance decreased. A numerical 2-D model was prepared to study the effect of changing the plasma parameters on the particle behavior inside the plasma plume. It was found that an increase in the plasma gas flow rate, with all other process parameters unchanged, results in a higher particle velocity but lower particle temperature. The particle was modeled as discrete lagrangian entities while the injection process performed the diameter and particle injection velocity was changed. The results indicate that the particle temperature reaches its beak value at approximately 20 to 30 mm from the point of injection after that start to decrease slowly. The temperature of the smaller particles is larger than the larger particle. The velocity of the smaller particles increases faster than larger particles.
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.
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.
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.
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.
Numerical Simulation of Plasma Spraying Performance Index
E3S Web of Conferences, 2020
In recent years, there has been an increasing interest in plasma jet numerical simulation. Speed and temperature propagation in axial and radial direction in plasma jet significantly influences on speed and temperature of sprayed material and therefore on coating quality. However, there are few studies concerning plasma jet numerical simulation in modern software systems and they describe a specific problem. It is a wellknown fact that using simple structural components such as plasmatron heads for plasma thermal spraying allows us to increase the quality of zirconium oxide coatings by increasing the speed of spraying particles and decreasing their spread value and allows to increase economic efficiency of the process by increasing the operation factor of spraying material. However, scientists have not studied well the influence of the plasmatron head, which looks like a cone element, and the simulation of a high temperature flow along the channel is not mentioned in publications. T...
Fast modelling of plasma jet and particle behaviours in spray conditions
High Temperature Material Processes (An International Quarterly of High-Technology Plasma Processes), 2005
This paper presents a simplified code allowing to find in a few minutes the trends of the d.c. plasma spray process, at least for a single particles or a particles in flight. It is based on a parabolic 2D flow for the plasma jet and a 3D calculation for the heat and momentum transfer to particles. It neglects the carrier gas flow rate-plasma flow interaction but the obtained trends are in good agreement with those obtained with 3D sophisticated codes. However results depend strongly on the turbulence model, the plasma effect corrections chosen for the heat and momentum transfer. Thus, as with 3D codes, the model has top be backed by experiments. It can be used to train operators and let them "see" almost immediately the effects of the different macroscopic spray parameters. The code and the plasma properties used can be freely downloaded.
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.
Controlling particle injection in plasma spraying
Journal of Thermal Spray Technology, 2001
This paper reviews experimental and analytical techniques that examine the efficiency of systems for the injection of powders in plasma jets used in spray coating. The types of injectors, the experimental techniques for observing particle trajectories and distributions, and the mathematical models used to investigate the momentum and heat-transfer phenomena between particles, carrier gas, and plasma jet are described. Experimental data are presented from numerous examples from the plasma spraying of ceramic powders.