Hot strip method: application to thermal characterisation of orthotropic media

International audienceThis study deals with determination of the thermal conductivity tensor for orthotropic media and more specifically for multilayers with isotropic thermal characteristics in the planes parallel to the layers. The work described has been conducted using two ordinary experimental devices: a device based on the hot-wire method and a device based on the hot-strip method. Hot-wire measurements give the thermal conductivity in the planes parallel to layers. Introducing this value in a model adequate to describe orthotropic behaviour and using an appropriate identification method, hot-strip measurements then give the transverse thermal conductivity. The validity of this approach is demonstrated by the results obtained on a stratified medium with known thermal characteristics. Then, transverse thermal measurements were made on a non-woven wood fibre insulator

A new simple device to estimate thermophysical properties of insulating materials

International audienceThe method described here is to measure thermal conductivity of super insulating materials. The principle is based on a simple transient experiment and a single temperature measurement, The main idea is to control the heat flux diffusion in the sample by the adjunction of a semi infinite highly conductive medium

Energy valorization of industrial biomass: Using a batch frying process for sewage sludge

Issu de : WasteEng 08 - 2nd International conference on engineering for waste valorisation, Patras, GREECE, June 3-5, 2008International audienceThis paper studies the energy valorization of sewage sludge using a batch fry–drying process. Drying processes was carried out by emerging the cylindrical samples of the sewage sludge in the preheated recycled cooking oil. Experimental frying curves for different conditions were determined. Calorific values for the fried sewage sludge were hence determined to be around 24 MJ kg−1, showing the auto-combustion potential of the fried sludge. A one-dimensional model allowing for the prediction of the water removal during frying was developed. Another water replacement model for oil intake in the fried sewage sludge was also developed. Typical frying curves were obtained and validated against the experimental data

A Kriging constrained efficient global optimization approach applied to low-energy building design problems

3rd Symposium on Inverse Problems, Design and Optimization (IPDO) / School on Physical Properties, Joao Pessoa, BRAZIL, AUG 25-27, 2010International audienceLow-energy building design is constrained not only by the total cost but also by both the energy demand and the comfort requirements. However, the evaluation of these criteria may require the implementation of time-consuming tasks, such as the direct building thermal simulation, which leads to difficulties in the design process. Moreover, it is of interest in this field to provide the designer with a large range of acceptable solutions rather than some unique optimal design. In this article, the application of an efficient global optimization approach is proposed as a tool to analyse the response functions of a building design problem. The method is based on a Kriging metamodel, which provides the global prediction of the objective and constraint functions, and an evaluation of uncertainty of the prediction at each point. The criterion for the infill sample selection is a generalized expected improvement function with desirable properties for stochastic responses. This criterion is maximized according to different constraints. First, inexpensive constraints are used as boundary constraints. Then, the expected violation criterion is used as a penalty. We use a particle swarm optimization algorithm to maximize the infill sample criterion according to the constraints. This approach is shown to be efficient for the building design problem, since the optimization is performed with an important reduction of the number of objective and constraint function calls. The Kriging metamodel is used to evaluate the sensitivity and the possible range of variations of the design parameters near their optimal values

Measurements of comparative apparent thermal conductivity of large monolithic silica aerogels for transparent superinsulation applications

International audienceLarge monolithic crack-free transparent silica aerogels were prepared by a patented sol-gel route, and then directly washed and dried with supercritical CO2. In order to characterise as precisely as possible the apparent thermal conductivity of such superinsulating materials, two methods were developed (so-called hot-band and micro-fluxmeter techniques) and the results obtained at room temperature and atmospheric pressure were compared with the standard hot-wire measurements under the same conditions. A reproducibility study showed no large deviations between the thermal conductivities obtained by these different techniques. This leads to the conclusion that aerogels prepared in this way present a good thermal and optical compromise (low thermal conductivity, high light transmission, and no significant radiative heat transport component at room temperature) and can be considered as transparent superinsulating materials

Drying kinetics and heat flux in thin-layer conductive drying

International audienceThin-layer drying by coating of a viscous product on a hot metallic surface is studied from the point of view of heat and mass transfer. An experimental device has been built up in order both to provide and to estimate the heat flux density at the interface between the hot plate and the drying sample. Results are presented for alumina sludge drying. The determination of the interfacial heat flux is obtained from temperature measurements in the metallic plate and the solution of an inverse conduction problem. An analytical direct model is made using the quadrupole formalism and the system transfer function is calculated. The inverse problem is solved using Beck's sequential function specification method. Intrinsic drying kinetics are obtained by an energy balance

Extension of the hot wire method to the characterization of stratified soils with multiple temperature analysis

International audienceThe aim of this article is to develop a practical device able to estimate a thermal conductivity profile in stratified media such as burned soils in Chile. The classical hot wire method consists of measuring the temperature response of a heat step imposed on a thin cylindrical probe by Joule effect. The main characteristic of the extension of the method consists of analyzing the two-dimensional temperature response of multiple thermo-couples equally spaced along the heating cylinder. A semianalytical method (quadrupole method) is then implemented in order to obtain a transfer matrix between the heat flux excitation and the temperature response vectors. Such method is suitable to obtain asymptotic expansions in order to investigate the sensitivity analysis and the estimation strategy. A complete two-dimensional model is used in order to define a time window in which the one-dimensional radial heat transfer assumption is valid. Some experiments and estimation results are presented in a case where the characteristic diffusion times in the radial direction are small compared to the inter-layers diffusion time

Mise au point de dispositifs de caracterisation thermophysique de materiaux isolants solides ou pateux - extensions aux fluides cisailles

We develop a new simple device based on existing methods to estimate thermophysical properties of insulating materials. We determine the thermal conductivity and the volumic heat of a sample. The classical probe offers all the advantages of a sensor. In a compact device, we have a no intrusive instrument, which can by calibration determine many properties of a material (moisture, density, etc). The new device proposed here tries to combine all the advantages of the previous methods. The main idea is to control the heat flux diffusion inside the insulating sample by addition of a highly conductive metal support. The conducting layer is then a simple technological means to impose boundary conditions. No regulated heat sink and flux meter is then needed. The thermal excitation is applied with a heating disc or ribbon. A development of this kind of device is considered for the thermal characterization of a fluid layer sheared (in Couette flow) by a brass cylindrical block in rotation. It is not necessary to instrument the moving parts on the experimental device. The modeling developed using an extension of the quadripole formalism, takes account of the twodimensional conductive transfer in the sample, and the semi-infinite medium. The comparison of the more or less simplified models, and the study of sensitivity, proves it is possible to estimate 3 parameters : the inertia of the probe (estimated on a material of reference), the volumic heat of the sample, and the thermal conductivity of the sample. An experimental study on materials of reference validate our methods and some examples of applications are presentedNous developpons, a partir de methodes existantes (fil chaud, plan chaud,), des nouvelles techniques de mesure de proprietes thermophysiques adaptees aux materiaux super isolants. Il s'agit de determiner la conductivite thermique et la chaleur volumique de l'echantillon. La sonde a choc thermique offre tous les avantages d'un capteur. En un dispositif compact, on realise un instrument peu intrusif, qui peut, par etalonnage, permettre de remonter a de nombreuses proprietes d'un materiau (humidite, densite etc). Nous associons une couche tres isolante a une couche conductrice semi-infinie afin de concevoir un instrument de mesure de conductivite thermique de super-isolant d'epaisseur finie. La couche conductrice est alors un moyen technologique simple pour imposer des conditions limites. L'excitation thermique est appliquee avec un ruban ou une pastille chauffante. Un developpement de ce type de dispositif est envisage pour la caracterisation d'une couche fluide cisaillee (en ecoulement de couette) par un bloc de laiton cylindrique en rotation. L'interet, sur le plan experimental, est ici de ne pas avoir a instrumenter les parties en mouvement. La modelisation, developpee a l'aide d'une extension du formalisme des quadripoles thermiques, tient compte du transfert conductif bidimensionnel dans l'echantillon, et le milieu semi-infini. La comparaison des modeles plus ou moins simplifies, ainsi que l'etude de sensibilite permettent de choisir le jeu de 3 parametres pertinents identifiables : l'inertie de la sonde (estimee sur un materiau de reference), la chaleur volumique de l'echantillon, et la conductivite thermique de l'echantillon. Une etude experimentale sur des materiaux de reference permet de valider nos methodes et quelques exemples d'applications sont presentes

Effect of homogeneous and heterogeneous source terms on the macroscopic description of heat transfer in porous media

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A new simple device to estimate thermophysical properties of liquids in couette flow

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