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Melting metal powder particles in an inductively coupled r.f. plasma torch

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Abstract

A numerical model is developed for the prediction of melting metal powder particles in an inductively coupled r.f. plasma torch. The model is developed for dilute spray conditions where the gas phase flow is not affected by the loading condition. The governing equation for the gas phase flow contains the source terms from the electromagnetic field. The theoretical calculations have shown that particle thermal history and its velocity are greatly affected by the plasma operating conditions (i.e., carrier gas flow rate, injector location, and power level,etc.). Without the proper control of particle trajectories, particles may bounce around the fireball and exit the torch as unmelted or resolidified solid particles. With the insertion of an injector or injecting particles with a high carrier gas flow rate, the predictions show that even relatively small size particles can be directed into the fireball and maintained in the molten state before they impact on the substrate. Consequently, more uniform and dense deposits can be achieved.

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Abbreviations

C D :

drag coefficient

C p :

specific heat

d p :

diameter of the particle

E :

electric field

Fr :

electromagnetic force

f L :

liquid fraction in particle

g :

gravity

h t :

heat transfer coefficient

h :

enthalpy

H :

magnetic field

I :

coil current

k :

thermal conductivity

L 1L2,Lt :

r.f. torch dimensions (see Figure 2)

N :

number of turns in the induction coil

r :

radial direction

Re:

Reynolds number

T :

temperature

t :

time

u :

axial velocity

v :

radial velocity

w :

swirl velocity

z :

axial direction

p :

pressure

P :

power into the discharge zone

Pr:

Prandtl number

Q p :

volumetric ohmic heating

Q r :

volumetric radiation

Q 1 :

carrier gas flow rate

Q 2 :

plasma gas flow rate

Q 3 :

sheath gas flow rate

Q o :

total gas flow rate

r 3,Rc :

r.f. torch dimensions (see Figure 2)

U o :

inlet mean velocity

μ:

dynamic viscosity

v:

kinematic viscosity

ρ:

density

ξ:

magnetic permeability

θ:

tangential direction

σe :

electrical conductivity

λf :

latent heat of fusion

λe :

latent heat of evaporation

χ:

phase angle between magnetic and electric fields

ω:

oscillator frequency

ω-1 :

conductivity

f :

evaluated at film temperature

g :

plasma gas

p :

particle surface

R :

relative velocity

∞:

evaluated at free stream state

+:

dimensional quantity

0:

reference condition

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Authors and Affiliations

  1. Department of Materials Engineering, Drexel University, 19104, Philadelphia, PA

    Daniel Y. C. Wei & Diran Apelian

  2. Department of Mechanical and Mechanics Engineering, Drexel University, 19104, Philadelphia, PA

    Bakhtier Farouk

Authors
  1. Daniel Y. C. Wei
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  2. Bakhtier Farouk
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  3. Diran Apelian
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Wei, D.Y.C., Farouk, B. & Apelian, D. Melting metal powder particles in an inductively coupled r.f. plasma torch. Metall Trans B 19, 213–226 (1988). https://doi.org/10.1007/BF02654205

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