Identification optimale des propriétés thermophysiques d’un revêtement

The inverse problem of simultaneous estimation of diffusivity and effusivity of a coating is solved. It deals with: the experiment definition (pulsed photothermal method), the developpement of the corresponding parametrized direct model, the minimisation of the ordinary least squares objective function and the analysis of confidence of the estimated parameters. The optimal design of experiment, based on the analysis of the sensitivity coefficients of the direct model, enables to limit the noise amplification during inversion. Such a methodology has made a coating caracterisation possible, even if its thermophysical properties were close to those of Us substrate (chromium/steel).     

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₊.     

Gestion de la thermique dans les procédés d'adsorption de gaz

Thermal aspects of gas adsorption processes. The adsorption of gases is an exothermal phenomenon, and fixed bed adsorption operations produce high thermal effects. Similarly, applying temperature changes to a process can modify adsorption.The purpose of this paper is to illustrate the basic features of non-isothermal adsorption, the most salient of which is the effect of relative velocities of heat and concentration waves. It is shown that there may exist a temperature at which a reversal occurs in the order of those velocities. A simple purification process is suggested, based on the temperature modulation of the gas mixture fed to the column. Examples are calculated with data corresponding to carbon dioxide adsorption on 13X molecular sieves.     

Modélisation de séchoirs à tapis. Utilisation des réseaux de neurones

Modelling of convective layer dryers. Using neural networks. Dryer modelling is considered in this paper. A dryer scale approach is implemented in order to write the classical differential equations through parameters such as the heat transfer coefficient or drying kinetics. The behaviour of the dryers is described by a non-linear system which integrates these equations in a transfer network using the finite difference method. The finite difference method is easy to implement, but appears to be too slow for dryer designing. So, in the second part of the study, neural networks are used to model drying process in steady state. When applying neural networks method to the design of dryers, one of the main problems is to find necessary and sufficient inputs so that the neural networks can learn transfers laws. To reduce the problem, each output is defined by a single neural network and non-dimensional numbers are used. The following step deals with the determination of the number of neurones and the minimization of output error for each efficiency (change of training points). Then, neural networks are used to simulate different configurations of dryers. Results are compared with the finite difference method and an industrial application is studied in the last chapter.     

Influence des phénomènes d'hystérésis sur les propriétés hydriques de matériaux poreux: Comparaison de deux modèles de simulation du comportement thermohydrique de parois de bâtiment

Porous materials hysteretic moisture characteristics : influence on water content distributions in buildings walls. Comparison of two simulation models. Two models for determining the temperature and moisture distributions within a wall are presented. The first one is a direct application of the classical Philip and de Vries model. The second one, using the suction potential, is derived from Milly's researches and is more efficient because it allows the hysteresis phenomena to be taken into account. First, the different equilibrium and transfer parameters used in the models are reviewed. Indications are given on how they can be experimentally determined and results for two cement pastes and a cellular concrete are illustrated. Then, calculation results of water content distributions for the two models are presented for an homogeneous cellular concrete wall in steady environmental conditions. In that particular case, the two models estimations are in good agreement despite different numerical treatments and experimental procedures. Using Milly's model with cyclic boundaries conditions, a significant influence of hysteresis phenomena is clearly shown.     

Modélisation d'un échangeur de chaleur compact à courants croisés séparés par des couches de matériau à changement de phase

A mathematical model was developed to predict the thermal behaviour of a crossflow compact heat exchanger with layers of phase change material (PCM) operating under winter conditions. The model is validated and a parametric study is conducted to determine the design and operating conditions that promote condensation and may lead eventually to the frosting of the exchanger. The transient and steady-state thermal efficiency of the exchanger are also predicted as a function of the number of thermal units NTU_f, of the ratio of the products of the mass flow rate by the heat capacity on the cold and hot sides C and of the Biot number Bi. Results indicate that for Bi = 0.6 (which corresponds to a 3 mm thick PCM layer), condensation occurs when NTU_f ≥ 2.0 for C = 1.0 and when NTU_f ≥ 5.0 for C = 0.5. If the thickness of the PCM layer increases, condensation is avoided and the duration of the heat recovery period is prolonged. At the same time however, the steady state thermal efficiency diminishes. A heat exchanger for which Bi = 0.6, C = 0.5 and NTU_f = 4.0 appears to be a good compromise for acceptable heat recovery and efficiency. In this case, the heat recovery period lasts 1.6 h and the steady state thermal efficiency levels off at 64 %.     

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.     

Effets comparés des impuretés de terres rares sur la résonance ferrimagnétique et la relaxation nucléaire dans le grenat de fer et d’yttrium

The anomalous properties of impure yttrium iron garnet are related to the susceptibilities of the rare earth ions which it contains. The susceptibilities are calculated assuming a slow relaxation. It is shown that the success of the theory of “slow relaxation” requires the existence of a coupling between the transverse magnetization of the iron lattice on the one hand, and components of the magnetic moments of the rare earth ions, with non zero diagonal matrix elements, on the other hand. The temperature variations of the ferrimagnetic linewidth and the nuclear relaxation time are compared.     

L'origine des régularités constatées dans les observations interférométriques de Dayton C. Miller 1925–1926 : variations de température ou anisotropie de l'espace

It is utterly impossible to consider that the regularities displayed in Miller's interferometric observations can be explained by temperature effects. As a result the light velocity is not invariant whatever its direction and consequently the principle of invariance of light velocity on which fundamentally does rest the special theory of relativity is invalidated by the observation data.     

Theorie statistique des alliages metalliques binaires liquides a l'aide d'une methode de groupes de sites—Analyse de l'ordre local: II. Application a des alliages présentant une courbe d'enthalpie libre de mélange dissymétrique par rapport à la concentration

The model proposed in the preceding article is modified as to explain the non-symmetry of the enthalpy of mixing. Studied alloys are supposed to be compound-forming alloys so that the local order is modified. The structure of the compound is assumed to be A₃B.     

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.     

Modélisation du comportement thermique d'un espace urbain: Calcul de la réponse en température des structures et de l'air ambiant

This paper presents theoretical modelling works on the thermal behaviour of an urban space (street). A calculation code, named Codyflow, has been developed in order to simulate the thermal response of an urban system to climatic solicitations. The model allows us to take into consideration, on the one hand, the radiative flux soliciting the urban canyon, on the other hand, heat transfers inside the system. The airflow solicitation, which plays a part in the convective exchanges and in the ambient air temperature, is calculated by the CFD code Fluent. Some simulation results, obtained by the code Codyflow, are presented. They bring to the fore the influence of many factors on the thermal response of the urban canyon: the geometrical configuration, the used materials (through their thermophysical characteristics) and the airflow solicitation. These results allow us to predict the thermal behaviour of urban spaces for the benefit of architects and urban designers in the conception phase of an urban plan.     

Etude théorique du spectre infra-rouge des complexes liés par liaison hydrogène à l'état gazeux: complexe ClH … O(CH3)2, son homologue deutérié et complexes voisins

Un modèle théorique est proposé en vue de reconstituer des spectres d'absorption IR des complexes du type ClH … O(CH₃)₂ en phase gazeuse. Ces complexes sont assimilés à des supermolécules triatomiques linéaires AH … B pour lesquelles la vibration v _AH et la vibration v _AH … B sont couplées par un potentiel anharmonique. Le terme couplant ces deux vibrations peut être atteint de manière précise par la connaissance de l'évolution du spectre en fonction de la température. Le modèle permet de reproduire de façon satisfaisante les spectres I.R. de ClH … O(CH₃)₂ et de ClD … O(CH₃)₂. On reproduit également mais de façon moins précise les spectres de quelques complexes voisins pour lesquels on ne possède pas de résultats en fonction de la température.