Abstract
Turbulent flow in multi-function micro-plasma spray, as well as the trajectories and state-changing course of alumina particles in the plasma jet were simulated. The distribution of temperature and velocity of the plasma jet and in-flight alumina particles is discussed. Calculations show that particles are heated and accelerated sufficiently by the plasma flame due to a longer travel time than that of external injection system, therefore, possess higher temperature and velocity. Alumina particles temperature and velocity increase rapidly along the jet axis at the initial stage, but then decrease gradually. The velocity and surface temperature of in-flight alumina particles are measured by Spray Watch-2i system. The velocity and surface temperature of alumina particles measured agree well with the simulation results, confirming that the simulation model is suitable for the prediction of the turbulent flow and the particle characteristics, which also reveals the superiority of the plasma spray gun in this multi-function micro-plasma spraying system.
Highlights
Plasma spray process consists in injecting powder particles into a plasma jet where they are heated and simultaneously accelerated and after a given dwell-time, impact on the substrate to form lamellae, the stacking of which forming the deposit
The present paper presents a 2D thermo-mechanical model based on the following assumptions: (1)The plasma is in local thermodynamic equilibrium, the temperature of the gas atoms, ions and electrons at a point are equal, and can be characterized by a single temperature; (2)The plasma gas is ideal gas, which is composed of only one species: Ar; (3)Thermal physical characteristics of gas components are independent of practical states; (4) No energy is lost by radiation; (5)During a certain period, the plasma jet flow is a steady-state system
Based on the determination of plasma jet velocity and temperature at nozzle exit and the gas components, boundary condition was decided, which is the key of the simulation result, a computational fluid dynamics (CFD) program FLUENT 6.0 was implemented investigate the distributions of plasma jet velocity and temperature
Summary
Plasma spray process consists in injecting powder particles into a plasma jet where they are heated and simultaneously accelerated and after a given dwell-time, impact on the substrate to form lamellae, the stacking of which forming the deposit. A plasma sprayed coating is the result of the impact of melted and partially melted particles, their flattening and the corresponding splats layering on the substrate surface. Multi-function micro-plasma spraying has been successfully developed [3] Turbulent flow in this multi-function micro-plasma spraying, as well as the trajectories and state-changing course of alumina particles are simulated by combining standard k-İ turbulent model, particle heating and accelerating model and energy conservation. The distribution of temperature and velocity of the plasma jet and in-flight alumina particles is discussed. The temperature and velocity of flying particles in the plasma flame are measured using on-line monitoring system the “Spray Watch-2i System”, the measured data are compared with simulation results verify the validity of the use of simulation
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