Post on 21-Aug-2015
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• Particle diagnostics are useful and widely used in the thermal spray process
for various purposes. However, temperature measurement of in-flight
particles was found to be challenging because of the potential contribution
of the non-thermal signals affecting the measurement process and
perturbing the obtained signals. In that context, temperature measurement
for in-flight particles in suspension plasma spraying becomes even more
difficult because of the small diameter of the particles, the metallic vapors
and the radiation of the plasma surrounding the particles. In order to
evaluate the temperature of inflight particles, two color pyrometer and
spectroscopic analysis are useful tools that have been applied before on
different thermal spraying processes. In this work, the emission spectra in
the visible/near infrared optical range (600nm to 1000nm) were investigated
from two different positions. Firstly, emission spectrum was recorded from
the front direction in order to assess the influence of the plasma radiation
emitted from the core of the plasma torch that is reflected by the in-flight
particles in all spatial directions, on the temperature measurement.
Secondly, emission spectra were collected radially relative to the torch axis
at different axial locations. To conduct those measurements, 20wt% YSZ
particles in pure ethanol were sprayed and characterized.
Method
Conclusions
Influence of the Plasma Radiation Scattered by Inflight Particles on
Temperature Measurement in Suspension Plasma Spraying
B. Aziz and C. MoreauMechanical Engineering Department, Concordia University
Thermal Spray Laboratory
• The radiation of the in-flight particles was assumed to be a black body
radiation according to Planck’s law of radiation
Introduction Results
• Mie Solution at scattering angle of θ
= 90° and λ = 995nm. The refractive
index of 𝑌𝑆𝑍 particles was taken to
be 𝑛 = 2.18 − 0.02𝑖. On the other
side, the mean particle size
distribution was taken to be 1.5μ𝑚with 20% standard deviation.
According to Mie solution, the
scattered radiation at 995nm
calculated at 1m from the torch axis
is illustrated in (Fig.1).Fig. 1: Radiation intensity in (nW/Sr) as
a function of the scattering angle
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
600 700 800 900 1000
Ca
lib
rati
on
Fa
cto
r (C
ou
nts
/uS
)/[u
W/c
m^
2.n
m]
Wavelegnth in nm
• The spectrometer was
radiometrically calibrated using a pre-
calibrated light source with known
emission at each wavelength
associated with the responsivity of the
CCD camera(350nm to 1050nm) as
it’s illustrated in (Fig.2).
Fig.2 Calibration Factor [Counts/ uS]
/ [uW/cm^2.nm]
• To calculate the power incident
on the particles, the emitted
spectra for the plasma only, then
(Plasma + Ethanol), and finally
(Plasma + Ethanol + Powder) at
80cm axial distance from the
torch plane were conducted
(Fig.3).
Fig. 4 Spectrum Collected from the front direction
Fig. 5 Spectrum collected radially
relative to the spray direction, at 10 cm
from the torch exit
Zr
Fig. 6 Apparent particle’s surface
temperature as a function of true particle’s
surface temperature
1200
1700
2200
2700
3200
3700
4200
1200 2200 3200 4200Ap
pa
ren
t S
urf
ace
Te
mp
era
ture
(°
C)
True Surface Temperature (°C)
995/785
995/877
• At 10 cm from the torch exit, the calculated error in temperature
measurement due to the scattered radiation by the in-flight particles at their
melting temperature (2700ºC) was found to be 1º; however, at 2500°C the
amount of error was quantified to be 16°. On the other hand, the calculated
error is negligible at the 2700ºC while taking the intensity ratio at λ1 =995±25nm; λ2 = 877±25nm nm (995/877) as illustrated in Fig.6
• In this work, a methodology was explained to investigate the influence of
the plasma radiation scattered by YSZ particles in suspension plasma
spraying on the particle temperature measurement. It was demonstrated that
the error resulted from this source varies strongly with the detection
wavelengths. The error between the true and apparent surface temperature of
the zirconia particles was estimated 1°C at its melting point depending on
the selected wavelength bandwidths, and 16° at true particle’s surface
temperature of 2500°C
Fig. 3 Schematic for experimental setup
Acknowledgement1. Dr. Fadhel Ben Ettouil who provided an extensive support and sincere efforts
during the experimental work with the plasma spray system.
2. Dr. Patrick Gougeon for enriching discussions and advices on the content of
this paper