Structural evolution of PVDF during storage or annealing

The effect of annealing PVDF at temperatures above Tg and below Tm was investigated by differential scanning calorimetry (DSC), thermostimulated current spectroscopy (TSC) and solid-state NMR. This study evidences a progressive structural evolution, taking place during such annealing. Its characteristics (kinetics and its temperature dependence, lack of reversibility at lower temperature over extended periods of time, double organization corresponding to double annealing with unmodified kinetics) point to a mechanism of secondary crystallization as described by Marand et al. In addition to the formation of extra crystalline (hence rigid) material, this phenomenon is believed to generate increasing conformational constraints in the residual amorphous material. Accordingly, a progressive reduction of the molecular mobility was demonstrated by NMR during annealing

Thermographic monitoring of asphalt concrete surface with phase change materials inclusions for icing delays purposes

International audienceIf de-icers still are the main solution to avoid black ice occurrence and snow accumulation on pavements, some alternatives based on transportation infrastructure modifications have been tested over the past years. They aim at the reduction of environmental impacts and at coping with budgets constraints and cuts, including in winter maintenance. Among existing ones, the implementation of phase changes materials (PCM) into the infrastructure was evaluated to delay the occurrence of water in its solid phase on the surface. Additional results were obtained with an asphalt concrete in simulated winter conditions, indicating a tenuous thermal effect at the surface

Étude des propriétés thermophysiques et électriques de matériaux hétérogènes

Ce travail présente une étude comparative des propriétés thermiques, électriques rhéologiques et diélectriques de trois systèmes composites : EVA chargé de billes de verre argentées et non argentées, EVA chargé de poudres de BaTiO3, et PVC chargé de nanotubes de carbone. Cette étude est consacrée dans un premier temps à l élaboration des échantillons et à la détermination de la conductivité électrique ( ), de la conductivité thermique (k), de la viscosité dynamique ( ) et de la permittivité diélectrique relative ( r) (pour certains composites). Il a été démontré dans ce travail que l effet de la taille des charges est significatif sur les propriétés électriques et diélectriques (diminution du seuil de percolation et de r) et négligeable sur les propriétés thermiques et rhéologiques. En outre, l effet de la surface externe des charges est très important sur k et s il existe des contacts entre les charges au sein de la matrice. Par ailleurs, des corrélations ont été constatées entre k et les autres propriétés de transport ( , et r). Parallèlement à ce travail, une amélioration d une méthode radiométrique périodique utilisant la thermographie infrarouge et permettant la mesure simultanée de l'émissivité, de la conductivité et de la diffusivité thermique de matériaux opaques a été mise en place. La méthode et le dispositif de mesure ont été validés en étudiant un matériau de propriétés connues (PVC) à température ambiante. Cette validation comprend une étude de la reproductibilité de la méthode, une comparaison aux résultats de la littérature, une analyse des sources d'incertitudes ainsi qu'une analyse de sensibilité pour l échantillon de PVC.This work presents a comparative study of thermophysical, electrical, dielectric and rheologic properties of three composites: glass and silver coated glass spheres dispersed in EVA matrix, powders of BaTiO3 dispersed in EVA matrix and PVC matrix filled with Carbon NanoTubes. This study is devoted in the first time to the composites preparation and to the measurements of the electrical conductivity ( ), thermal conductivity (k), dynamic viscosity ( ) and the relative permittivity ( r) (for some composites). It was shown that both relative permittivity r and electrical conductivity depend on the fillers size. However, the effect of the particles size on the thermal and the rheologic properties can be neglected. Besides, the fillers surface is an important factor controlling the thermal and the electrical conductivities. It also follows from this study the existence of a correlation between the thermal conductivity and others properties ( , and r). The second objective of this study was the improvement of a measurement method of emissivity, thermal conductivity and diffusivity. The characterisation of a reference sample (PVC) allowed the validation of the measurement protocol. This includes the reproducibility study of the method, the comparison of the results to the literature data, the analysis of the limitations of the measurement protocol and a sensitivity analysis.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF

Détection d’éléments de structures ou de fissures non émergentes dans des parois revêtues

National audienc

Determination of anisotropic properties of carbon fiber composites for civil engineering applications using infrared thermography with periodic excitation

International audienc

Measurement of the thermal conductivity of liquids by hot wire method: comparison between transient and stationary approaches

This work concerns the characterization of the thermal conductivity of liquids by hot wire method. A measuring cell has been specially developed for this study. The method of analysing the transient response makes it possible to obtain values of conductivity close to those expected (deviations <4%) for two reference fluids and measurement uncertainties in the order of 5%. The use of the so-called steady state method (ASTM D 2717) leads to relative deviations and uncertainties of the measurements about 3 times higher

Diagnosis of Insulated Building Walls Using Passive Infrared Thermography and Numerical Simulations

International audienceThis work presents the thermal monitoring of a multi-layered wall of a restored building (PANISSE platform). Surface temperatures measured by infrared thermography are corrected by taking account of the influence parameters. Then they are compared with thermocouple measurements and numerical simulations

Novel in situ measurement methods of the total heat transfer coefficient on building walls

International audienceThe performance gap between the design and the as-built energy performance of buildings is considered a significant risk that may compromise the efforts on meeting the carbon reduction targets set by governments in Europe. The relative importance of irregularities or defects within building walls is more prominent when the thermal insulation level increases. It is thus necessary to quantify the global thermal insulation level of building walls (i.e., including thermal bridges). Classical contact measurement methods only allow local measurements and would thus require the use of a high number of sensors which would limit their applicability. Besides, the presence of thermal bridges prevents the use of contact heat flux measurements because of the 2D or 3D nature of the associated heat transfers through the building walls. To overcome these limitations, the present study proposes an alternative approach consisting in measuring the heat flux on one location and extrapolating its value on the whole building wall through the measurement of the total heat transfer coefficient. Therefore, we developed and/or further improved five different in situ measurement methods of the total heat transfer coefficient on building walls. The measurement methods were thoroughly tested indoor thanks to lab-scale experiments carried out both in steady-state and transient regimes. The results obtained demonstrated the accuracy and the robustness of the proposed methods, as well as their intrinsic limitations. These in situ methods can be used to assess the heat losses on a whole building wall, including the contribution of thermal bridges

Utilisation de matériaux à changement de phase pour lutter contre les îlots de chaleur urbains

National audienceAfin de choisir les paraffines les mieux adaptées pour lutter contre les îlots de chaleur urbains, trois paraffines vendues comme ayant des températures de fusion de 28, 31 et 35°C ont été caractérisées en Analyse ThermoGravimétrique et Analyse Thermique Différentielle. La conductivité et la diffusivité thermique des paraffines à l’état solide ont également été mesurées. Les paraffines ont une bonne stabilité thermique et permettent de stocker de grandes quantités d’énergie thermique dans une large gamme de température. La particularité des paraffines est l’existence de phases rotatoires intermédiaires entre la phase liquide et la phase solide qui sont responsables des dédoublements des pics de cristallisation pendant leur refroidissement

Use of phase change materials for frost protection applications

International audienceTransportation and infrastructure sectors face difficulties during the winter season. When road's temperature drops below 3°C, the risk of ice formation increases, leading to reduced traction and snow accumulation. The use of phase change materials (PCMs) can be a potential solution. However, it is important to consider various factors when selecting PCMs, including phase change temperature, latent heat, and long-term stability. In this study, our focus was on RT5HC, a paraffin with a melting temperature of 5°C. Various thermal analysis techniques were employed to characterize its thermophysical properties, particularly its thermal stability and latent heat. The results of the study demonstrated that the RT5HC paraffin reveals good thermal stability for the intended application. Moreover, its high latent heat provides an advantage for thermal energy storage. These findings contribute to advancements in the field of PCMs and offer promising prospects for their use in preventing ice formation and freezing during winter periods