Transfert de chaleur par rayonnement dans un four d'incinération industriel: application de la méthode des zones

In the context of resource conservation, incineration of domestic wastes is a technique allowing an interesting potential in energy valorization. However, because of the variability (annual, monthly) in quality and quantity of raw material, one of the characteristics of waste incineration cogeneration power plants is their frequent partial or excess loading. In order to describe their behaviour at these non-nominal loads, there is a need for simulation tools which predict with accuracy the behaviour of the principal components of the plant at these loads. This paper presents an original approach for predicting the heat transfer in a waste incinerator. In particular, the model developed is applied to and validated with measurements from a waste incinerator located at the Cottendart waste incineration cogeneration power plant in Switzerland. The part of the incinerator studied is characterized by high gas temperatures (1 000-500 °C) for which radiative heat transfer represents the most important part of the global heat exchange. A three-dimensional model using nodal analysis is proposed. The radiative heat exchange is treated using the zone method. With a fine enough mesh, the behaviour of the system in regions far from the nominal point can be predicted with very high accuracy. This paper describes the model and the simulation results.     

Conductivité thermique de mousses cellulaires de carbone: Mesures par méthode flash et interprétation

This paper deals with the thermal diffusivity measurement of cellular carbon foams by the flash method. The thermal conductivity is obtained from the thermal diffusivity by using specific heat and density of carbon foam. These materials constitute non-homogeneous porous semitransparent media, hence the classic experimental set-up of the flash method must be adapted. A study is carried out in order to show the influence of the sample thickness, of the temperature, of the enclosed gas pressure and of the gas composition on the effective thermal conductivity. Identification functions are established in the monodimensional and bidimensional cases. Results indicate the dependence of the equivalent thermal conductivity upon the sample thickness. This result, attributed to radiative transfer, is confirmed by modelling. Radiative thermal conductivities are obtained with a Monte-Carlo code. Experimental and theoretical results are compared. It is demonstrated that the concept of effective conductivity is not relevant to these materials.     

Etude théorique de la durée de vie radiative du triplet métastable de quelques composés carbonylés

Les paramètres de phosphorescence (force d'oscillateur et durée de vie), sont déterminés théoriquement pour quelques composés carbonylés (formaldéhyde, benzaldéhyde, acétophénone, propiophénone, 2,4,5-triméthylbenzaldéhyde, et 3,4-diméthylacétophénone). La fonction d'onde de l'état singulet fondamental est obtenue à l'aide d'un calcul SCF utilisant la méthode CNDO/S de Del Bene et Jaffé. Les fonctions d'onde, les énergies et les moments de transition dipolaire électrique S_I ←S ₀ et T_J ←T ₁ sont déterminés à l'aide d'une interaction portant sur des configurations mono et diexcitées par rapport à l'état singulet fondamental.

Les paramètres de phosphorescence sont calculés en utilisant une approximation monocentrique et monoélectronique de l'opérateur hamiltonien de couplage spin-orbite. Cette approximation est justifiée par la comparaison des résultats obtenus avec les valeurs expérimentales, compte tenu de la concordance entre les conditions d'expérience et les hypothèses de calcul.     

Contrôle de matériaux d'origine biologique par méthode photothermique: intérêt de la détection pyroélectrique

Photothermal methods are well adapted to thin multilayer material analysis. In the particular case of biological materials, which are thermally fragile, low excitation power is required. We have studied whole human blood sedimentation by using photothermal radiometry and a photopyroelectric technique. Results obtained with random- and sine-modulated excitation are discussed. Evolution laws of plasma thicknesses and optical absorption coefficients during the process have been determined by identifying the parameters using different estimation methods. It appears that results are consistent with theoretical predictions of our 2D-thermophysical model and also with the values measured by the well-known Westergreen reference method, usually used in clinical analysis. Finally, in order to extend the investigation field of the pyroelectric method, particularly in the domain of biological materials, we have analysed the possibility of using the sensitive pyroelectric sensors without direct thermal contact with the sample and detecting the temperature changes at the sample surface through a thin air monolayer.     

Etude numérique des effets de densité dans un jet de mélange turbulent en microgravité

Numerical study of density effects on a turbulent mixing jet in microgravity. The aim of this paper is to present density effects on a turbulent heterogeneous mixing free jet in microgravity. The influence of the inlet density ratio S between the jet and the surrounding gas is pointed out from numerical simulations based on second order single point closure schemes. The mean quantities, entrainment, expansion and second order moments are presented. The density ratio varies from 0,14 to 5,11. Results are discussed in comparison with both experimental data and asymptotical considerations. It is shown that the density ratio effects on the jet development vanish far from the exit leading to self-similar profiles (full self-preservation according to George [1]).     

Une nouvelle méthode calorimétrique périodique de mesure de l'émissivité des matériaux opaques à température ambiante

This paper presents a new calorimetric periodic technique for measuring emissivity of opaque materials at room temperature, without surface temperature measurement. The sample is in a vacuum chamber, so the thermal losses are only radiative. The presented technique requires thermal modulation of one side of the sample (the front side). The measured signals are the sample's front side temperature and the infrared flux of the other side (back side). Experimental data and a heat conduction model are compared, yielding the Biot number which characterizes the thermal losses. Using the identified value of the Biot number, it is possible to access the total hemispherical emissivity. Measurements have been carried out on a PVC sample (5 mm thick) coated with black paint and on a PVC sample coated with aluminium paint. The results are concordant with the expected ones ; the repeatability error is about 3 %.     

Développement de lasers visibles pompés par diode à base de cristaux de Nd:GdCOB autodoubleurs de fréquence

We present the performances of a diode-pumped solid-state laser operating in the visible by self-frequency-doubling. A cw output power of 115 mW at 545 nm has been obtained in a stable concave–concave cavity by using a crystal of Nd:GdCa₄O(BO₃)₃ pumped by a 2 W high-brightness laser diode. In a plano–plano cavity, similar to a microchip laser, we have obtained, for the first time to our knowledge, an output power of 22 mW in the green.     

Résistivité électrique et effet Hall de métaux et semiconducteurs fondus

An apparatus is described for measuring the Hall effect and the electrical resistivity of molten metals and semiconductors, based on a cross-modulation method with alternating magnetic and electric fields. A quarz sample holder with five graphite electrodes may be used at temperatures up to 1000°C. The results of experiments for Na, Zn, Cd, Hg, Ga, Ge and Sb are consistent with the values given by the free-electron model. The calculated electronic mobilities are in agreement with measured values. The addition of small quantities of impurities (<1% Sb) into molten Te does not affect its electrical properties.     

Sur les possibiliti es de l'analyse par activation appliquée en médecine

An fur et à mesure que l'analyse par activation se développe dans toutes les branches de l,industric et de la science, en tant que méthode analytique actuelle, son application devient det plus en plus importante dans les domaines de la médecine, de la biologie et de la biochimie, ainsi que dans les domaines des recherches et des contrôles des radioéléments destinés à usage médical.     

Effet de second ordre pour des protons de méthylène en ENDOR

An indirect second-order effect occurs between the methylene-group protons of a radical created by gamma irradiation in a 1, 2, 4-triazol single crystal; this gives a non-crossing phenomenon which is observed on the ENDOR transitions. It is necessary to take this into account in the expression for the transitions, which then allows us to determine the hyperfine tensors of the two protons. Moreover, the presence of this effect helps in the identification of the transitions and the signs of the couplings.     

Pyrométrie multispectrale infrarouge: application aux métaux

Infrared multiwavelength pyrometry: application to metals. The aim of this work is the temperature measurement of welded metallic materials in order to study the cooling kinetic in solid phase during the welding. To take the constraints of the process into account, a fast noncontract method is indispensable. Moreover, the emissive properties of the metal evolve during the process and cannot be known a priori. The multiwavelength pyrometry can solve this problem : first the thermal emission is simultaneously measured at N wavelengths, then a parameter identification technique using a physical or an empirical model for the emissivity leads to the identification of the temperature and the spectral emissivity. We adapted this method to a temperature range between 500 K and the melting/solidification temperature of the metallic material. Various metallic samples have been studied (steels, titanium, aluminium). For each sample, the results present a relative deviation between the identified and experimental (thermocouple) temperatures of less than 2 %, for the more adapted theoretical models. This study does not lead to objective rules for the choice of the emissivity model. On the other hand, for some groups of materials (austenitic stainless steels, and carbon steels), it has been possible to select one or several models giving suitable results for similar samples.     

Procédure rapide de choix de réseaux d'échangeurs de chaleur

A fast calculation of a reasonable solution for the choice of a heat exchanger network able to make some imposed cooling and warming up tasks, with the use of auxiliary utilities, is developed in this article.This problem boils down to the internal heat exchanger network choice with respect to a constraint limiting the exchange area, maximizing the heat recovery and minimizing the number of stream matching.These internal matches are made one by one with respect to the tasks to be effected at each step. Amongst the possible matches, we have retained the privilegied ones, ie matches saturating a maximum number of constraints. Some procedures are implemented so as to choose among this set of privilegied matches.The illustration with some literature problems shows that an algorithm made up with these procedures carries out a good compromise between the quality of the obtained solution and the computer time.     

Quelques nouvelles propriétés de régularité de l'opérateur de Gribov

In this work, we establish new regularity properties for Gribov's operator:H=A ^* A ₊ iA ^*(A+A ^*)A;(,)², whereA ^* andA are the creation and annihilation operators. Particularly, we prove that for all >0,H ^–1 is in the class of Carleman's operatorl ₁₊.     

Identification des propriétés thermiques de composites fibres de verre/résines thermodurcissables: Application à l'optimisation des procédés de moulage

Identification of glass fiber/thermosetting resins composites thermal properties. Application to the optimization of molding processes. A procedure has been developed to optimize molding processes of thermosetting composite materials. Three stages have been distinguished. In the first one, some thermal and kinetic properties have been measured by differential scanning calorimetry. Thermal conductivities have been identified afterwards in thick instrumented pieces, placed in a thermally regulated press. High dependences of thermal conductivities on temperature and transformation degree have been shown. Secondly, coupled heat transfers have been numerically simulated and results have been satisfactorily compared with experimental thermograms. Finally, optimization technics based on effective inverse methods have been used.These points have been illustrated with two examples : glass fiber/epoxy resin and glass fiber/polyester. Sufficient mechanical characteristics of the first one, which is cured in oven, and good surface aspect of the second, that is made by injection in heated and closed molds, had to be obtained. The results let foresee real improvement of the corresponding molding processes.     

Partie 2: Les colloïdes de l'or radioactif 198Au à usage médical

On a étudié le comportement biochimique de l'or colloídal radioactif ¹⁹⁸Au à usage thérapeutique, diagnostique et lymphographique dans les tissus des souris et rats blancs. La r?partition des colloides de l,or radioactif a été étudiée dans les tissus des souris blanches (Cæur, foie, poumons, reins, rate) ainsi que l,élimination de l,or colloidal par voie urinaire soit de différentes charges de production, soit en fonction du temps de vieillissement. La pureté radiochimique et la valeur du pH ont été suivies simultanément. La taille des particules colloidales de l,or radioactif à usage thérapeutique et diagnostique a été déterminée (d=200…3 Å). La pureté radioactive de l,or colloidal ¹⁹⁸Au a été aussi étudiée.     

Transfert thermique pour la condensation du R123, du R134a et de leurs mélanges,en écoulement forcé entre deux plaques planes horizontales. Etude numérique.

Heat transfer for forced convection condensation of R123, R134a and their mixtures flowing between two horizontal parallel plates. Numerical study. Film condensation of pure and binary mixtures flowing between parallel plates is treated numerically. The coupled equations of mass, momentum, species and energy conservations for the two phases are solved with an implicite scheme. In this study, we retained the pressure forces, the liquid and vapor interfacial shear stress, the Dufour effect, the inertia and enthalpy convection terms, the turbulence in the two phases and the variation of the physical properties with the temperature and concentration. The results obtained for the condensation of refrigerants R123 and R134a, show strong influence of the composition of mixture on the mean heat transfer coefficient and the total pressure loss. The calculated mean Nusselt number is in good agreement with the experimental correlations of Mochizuki and Inoué [6] and Akers and Rosson [24]. A new correlation for the mean heat transfer for forced convection condensation of pure refrigerants R123 and R134a and their mixtures between horizontal flate plates is proposed.     

Application, à un cristal de béryl,d'une nouvelle méthode d'étude par réflexion

The vibrational frequencies of beryl are determined from a measurement of the optical constants with a method utilizing reflexion from samples with and without an evaporated layer of an optically known substance.