Study of glass wool : microscopic scale investigation of heat transfer between glass fibers

Reducing the environmental footprint of the building sector is a key element of today's political and environmental issues. The poor quality of the building stock insulation is pointed out. It is therefore crucial to improve the performance of the existing insulation products. Glass wool, one of the main insulation product, is made of a glass fiber matrix surrounded by gas or vacuum. However, there is a need for microscopic measurements of heat transfer at the fiber scale. The collaborative project CarISOVERRE, funded by the Agence Nationale pour la Recherche, intends to investigate these transfer. This thesis, as part of the CarISOVERRE project, aims at providing experimental measurement of the conductive, convective and radiative heat transfer in a single fiber at microscopic scale along with the measurement of thermal resistance of contact between fibers. To this end, we developed several characterizing tools to study microscale heat transfer. First, the emission properties of single glass fibers with sub­wavelength diameter (given the thermal wavelength of 10 µm) is measured using the infrared spectroscopy method based on the spatial modulation of the sample in the field object plan of the microscope. Then, the thermal resistance of contact between two glass elements is studied under vacuum and under ambient conditions. A glass microsphere is placed into contact with a glass slide using a SThM probe which allows to heat the top of the sphere by Joule effect and to record the temperature at this point. With this information it is possible to identify the different heat channels through the SThM probe and/or through the air to extract the thermal resistance of contact. Finally, a non­contact method for the measurement of thermal emission of a single fiber heated by short laser pulses is presented. This microthermography method is the Flash method coupled with an infrared microscope to meet the specifics of our sample. The identification of the heat transfer parameters ­ exchange with the surrounding air, thermal resistance of contact between fibers – is obtained by studying the spatial and temporal dynamic of the signal along with simple analytical models. The results presented in this thesis are expected to be used as input parameters in future numerical simulations of the heat transfer in a glass wool sample.; La réduction de la consommation d'énergie liée au secteur du bâtiment est au cœur des enjeux politiques et environnementaux actuels. L'isolation du parc immobilier est remise en cause. C'est la raison pour laquelle il est important d'améliorer les performances des matériaux isolants existant comme la laine de verre. La laine de verre, qui est un des matériaux d'isolation thermique les plus courants, est composé d'une matrice solide faite de fibres de verre entourées par du gaz ou de vide. Il manque cependant une caractérisation microscopique du transfert de chaleur à l'échelle de ces fibres. C'estdans ce contexte que s'inscrit cette thèse qui s'est déroulée dans le cadre du projet collaboratif CarISOVERRE financé par l'Agence National pour la Recherche. Le but de cette thèse expérimentale est d'effectuer une caractérisation microscopique des transferts de chaleur ­ transfert conductif, convectif, radiatif ­ intervenant au sein d'une fibre de verre, et de mesurer la résistance thermique de contact entre fibres de verre. Pour cela, nous avons développé différents outils de caractérisation du transfert de chaleur à l'échelle micrométrique. Dans un premier temps, les propriétés d'émission thermique de fibres de verre dont le diamètre est plus faible que la longueur d'onde d'émission thermique (