Christophe Journeau, Claude Jégou and Gérard Cognet
C.E.A. (Commissariat à l'Énergie Atomique)
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.


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:
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:
where TL is a brightness temperature of the gas, is the effective emissivity of the gas defined in terms of the measured fluxes as
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
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.
  1. Penner, S.S., Quantitative molecular spectroscopy and gas emissivities. Addison-Wesley publishing company, inc. Reading, Massachusetts, U.S.A., 1959.
  2. 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.


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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