SESSION 12
INVERSE RADIATION PROBLEMS III
INFRARED THERMOGRAPHY FOR MEASURING THE SURFACE
TEMPERATURE OF AN OXIDIC MELT
Christophe Journeau, Claude Jégou and
Gérard Cognet
C.E.A. (Commissariat à l'Énergie Atomique)
DER/SERA Projet VULCANO
Centre d'Etudes de Cadarache
13108 St. Paul lès Durance Cedex, France
The French Atomic Energy Commission (CEA) is conducting the VULCANO program to
analyze the behavior of the melted core of a Pressurized Water Reactor in the
unlikely event of a severe accident. The melted core and the melted reactor vessel structure form a mixture, named corium, of uranium dioxide, zirconia,
zirconium and steel which can reach temperatures as high as 3000oC.
We heat a corium representative mixture above its melting point and study it
while it cools down. In order to measure the surface temperature, a system
combining a bichromatic pyrometer and a short-wavelength infrared thermography
system is used. Since the camera is designed to measure blackbody surface
temperature below 1360oC we use window glass as a filter and
recalibrate the table of correspondences between the system isothermal units
and temperatures. High temperature experiments have been conducted to
demonstrate the feasibility of this technique. Firstly, the use of window glass as a filter is established with measurements of high temperature zirconia.
Then the technique to crosscalibrate a posteriori the thermography camera
images, using data from a bichromatic pyrometer measuring the gray body
temperature of a small area of the melt, is described. A practical procedure is finally proposed to measure surface temperatures in the
2000-3000o C range.
A BRIGHTNESS PYROMETER TECHNIQUE FOR TEMPERATURE
MEASUREMENTS IN THE FLAMES OF HYDROCARBON FUELS
V.I. Vladimirov, Yu. A. Gorshkov, V.S. Dozhdikov,
V.N. Senchenko
Institute for high temperature, Russ. Acad. Sci., Moscow, Russia
Optical methods has been for a long time used for a hot gas and flame
temperature measurement in bench scale experiments. However, in contrast to
solid - body pyrometry, they have not found yet industrial application. The
subject of the present work is development of gas -pyrometer technique, that
can be used to measure temperature in industrial burners with “hot” (e.g.
refractory lined) walls and in other types of high temperature facilities,
where the temperature is more or less uniform across the flame. The layout of
the instrument is shown in the Figure. The radiant flux emitted by the hot gas
(flame) Ff takes a focus by the lens S on the entrance aperture of
the brightness pyrometer detector.
The radiant flux of a calibrated light source FD takes a focus on
the same aperture stop by the lenses D and S while the diameters of the optical ports of the nozzle are sufficiently large not to restrict the measured optical fluxes. To determine the flame temperature, Ff ,FD, and
“source plus flame” flux FfD are measured. Two groups of methods to
determine a hot gas temperature Tf based on the three above signals
are available- the modified line-reversal technique and the brightness
pyrometer technique1. In the first method we obtain:
 (1)
where  is the
wavelength, C2 =1.4388 10-2 m K, TD is the
brightness temperature of the calibrated source. If the brightness pyrometer is
preliminary calibrated Tf can be determined by the method of
brightness pyrometer from the equation:
 (2)
where TL is a brightness temperature of the gas,  is the effective emissivity
of the gas defined in terms of the measured fluxes as
 (3)
The main sources of inaccuracy encountered in both methods include the error of the pyrometer calibration in eq.(2) and that of the source in eq.(1), error of
determination of effective wavelength , which is identical in both methods, error of the measurement
of the ratio (Ff+FD-FfD)/Ff
appearing in eq.(1) and error of in eq. (2). The above suggests that the methods are equivalent
from the point of view of accuracy of the measurements. Note, however, that
the use of the use of the brightness pyrometer requires no adjustment of the
geometrical factors to fulfil the condition Gs=GD,
because the calibrated source in this case is used only for “independent”
determination of the emissivity . This may substantially simplify the requirement imposed on
optical arrangement design and the alignment procedure in the field conditions.
On the other hand, at Tf~TD, i.e. close in line reversal
conditions, q. (1) reduces to
 (4)
In this case the accuracy may increase owing to the fact that the properties
appear only in the small correction term. The instrument developed in this work comprises both the calibrated reference source and the calibrated brightness
pyrometer and can realize both methods. If Tf is close to the
steady-state brightness temperature of the source, the former can be estimated
from eq. (4). If this condition does not hold Tf is calculated from
eq. (2) with simultaneous indication of both the brightness temperature and
of the gas. For
measurements in the nozzle of the combustion chamber, the instrument can be
mounted in situ as shown in the figure. The reference source is the is the
model of absolute black body. The image of the source is formed in the plane of
the window D, with a magnification by factor of 5. The optical ports have been
specially designed to keep the windows clean. The dimensions of the optical
arrangement have been selected according to ref.2. The measurements
were made in the near infrared spectrum of combustion products in the vicinity
of =2.80  m. The signals generated by the
detector have been processed using the digital controller in accordance with
the algorithm outlined above. The instrument has been tested both on the
propane-fired burner and in the industrial high temperature blast furnace
stove.
References
- Penner, S.S., Quantitative molecular spectroscopy and gas emissivities.
Addison-Wesley publishing company, inc. Reading, Massachusetts, U.S.A., 1959.
- Gorshkov, Yu. A., and Vladimirov, V.I. Lýne reversal gas flow temperature
measurements. Evaluations of the optical arrangements for the instrument.
Endhoven University of Technology, Netherlands. Report 93-E-278, 47p, December
1993.
SPECTRORADIOMETRIC STUDY OF THE SURFACE POLLUTION
INFLUENCE ON THE RADIATIVE PROPERTIES
OF ROLLING STEEL SHEETS.
APPLICATION TO CONTINUOUS ANNEALING FURNACES
P-J. Krauth* and C. Bissieux**
*IRSID, Centre Commun de Recherche du Groupe Usinor-Sacilor
Département Mesures, Contrôle Automatisme
Voie Romaine BP 320, 57214 Maizières-lès-Metz.
**Universitè de Reims
Laboratoire d'Energètique et d'Optique
Moulin de la Housse BP 347, 51062 Reims cedex.
The complexity of the manufacture process, the quality and the nature of the
steel industry products, require an accurate thermal treatment which are
controlled through non-contact optical measurements. The radiative properties
of metal sheet are important physical parameters. In fact, the emissivity
governs the heating of the product. Therefore it is very important to know with
precision the radiative parameters when conducting temperature measurements
using optical pyrometers or for the thermal treatment optimization.
This study therefore concerns two processes of the steel sheets elaboration:
the rolling and the continuous annealing. The first process defined the
dimensional characteristics of the product (thickness). Whereas the second
restores its mechanical characteristics to the steel.The rolling process
generate a roughness and a surface pollution constituted of oils and thin
particles of iron. The radiative properties of the iron sheet can be modified
by this residual film.
The purpose of this research is to study the influence of the surface pollution
on the radiative properties and on the heating kinetics during the thermal
treatment within the continuous annealing furnace. For completeness, both
theoretical and experimental studies were carried out.
The surface pollution film resulting from rolling operations is similar to a
semitransparent medium. We built a model to calculate the radiative transfers
in an isothermal semitransparent medium, for an unidimensional geometry. In the case of non-scattering semitransparent medium with a specular reflection at the interface, there is an analytical solution to the radiative transfer equations. This model uses the discrete ordinates method which offers the advantage to
take into account the high anisotropies of the radiative properties at the
interface.
We developed an experimental set-up to measure the directional spectral
emissivity of the sheets under industrial thermal treatment conditions. This
device is composed of a spectroradiometer and an annealing process simulator.
It allows to hat the samples up to a temperature of one thousand Celcius
degrees and to determine the spectral radiative properties within the range
2-14 micrometers.
We experimentally determined the principal thermophysical properties of the
bare steel sheet and of the residual film (semitransparent medium). We also
studied the influence of the surface morphology of the sheet on its radiative
properties and we determined its optical index. The absorption coefficient of
the semitransparent medium was obtained by transmittivity measurements. We
compared the measured emissivity with the calculated one for different
samples.
The results permit us to better understand the physical phenomena due to the
surface pollution on the sheet metal. The polluted sheet emissivity strongly
increases compared to that of clean sheet, even for thin films. The
modification of these radiative properties causes an important over-heating of
the strips within the annealing furnace.
In fact, the optimization of the industrial thermal treatment requires a
on-line control of the radiative properties of the product (for example the
reflectivity). To be efficient, this control must be done before the thermal
treatment at the entry to the annealing furnace. It could be used, in a
feedback loop, to react in real time the annealing furnace heating power.
Key words: emissivity, radiative properties, steel sheet, rolling oil,
semitransparent medium, spectroradiometry, thermal treatment, continuous
annealing.
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