Abderrahim Boudenne

A simultaneous characterization of thermal conductivity and diffusivity of polymer materials by a periodic method

A periodic method is used to determine simultaneously both thermal conductivity and diffusivity of various polymer materials at room temperature. The sample is placed between two metallic plates and temperature modulation is applied on the front side of one of the metallic plates. The temperature at the front and rear sides of both plates is measured and the experimental transfer function is calculated. The theoretical thermal heat transfer function is calculated by the quadrupole method. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of the experimental transfer function. The thermophysical parameters of several polymer samples (PTFE, PVDF and PA11) with different thicknesses (respectively, 5 mm, 2 mm and 300 µm) were studied and compared with values from the literature. The values identified for the thermal parameters are in good agreement with values from the literature for PTFE and PVDF samples; however, we show that the method reaches its limit for the thinner PA11 sample, owing to inadequacy of the thermal model.

Infrared emissivity measurement device : principle and applications

Infrared emissivity is a necessary parameter for computing models to predict road surface status and pavement temperature irrespective of the weather situation. In this work a new experimental device based on the indirect method was developed for the measurement of surface emissivities. The surface is exposed to modulated isotropic infrared radiation. The intensity reflected by the surface of the sample in a given direction is measured by a detector operating in the spectral range 1–40 µm. This large spectral range allows measurement of the total hemispheric emissivity defined in this case as emissivity. The effect of the temperature modulation frequency, surface composition and surface roughness on the emissivity measurements was investigated. The results show good ability of the device for the determination of emissivities at room temperature.

Analysis of uncertainties in thermophysical parameters of materials obtained from a periodic method

In the present work, we are interested in the improvement and the validation of the identification procedure for the simultaneous estimation of thermophysical parameters and their uncertainties using a periodic method. The effect of the statistical uncertainties on the estimation procedure and the reproducibility study of experimental device and measurement method are presented. In addition, the effect of the uncertainties of supposedly known model parameters on the identification procedure was investigated. The results show good reproducibility of the experimental results, and the uncertainty related to reproducibility is negligible. However, conductivity and diffusivity of the copper plate, and heat coefficient exchange, are parameters that strongly affect the result of the identification procedure.

Transport properties of polyester composite reinforced with treated sisal fibers

Thermal conductivity, diffusivity, relative permittivity, specific heat, and tensile properties of sisal/polyester composites were investigated as a function of fiber volume fraction and fiber surface modification. The composites were prepared by resin transfer molding (RTM) technique. Sisal fibers were subjected to various chemical and physical modifications such as mercerization, heating at 100°C, permanganate treatment, benzoylation, and silanization to improve the interfacial bonding with matrix. All treatments used in this study improved the relative permittivity, tensile strength, Young’s modulus, and reduced the elongation at break. The use of NaOH and silane treatments decreased the thermal conductivity. Beside these, a comparison between dielectric, mechanical, and thermal behaviors of the composites was reported in this paper. A linear dependence of the relative variation of dielectric permittivity, Young’s modulus, and thermal conductivity was also shown for untreated systems.

Numerical modelling of the effective thermal conductivity of heterogeneous materials

The effective thermal conductivity of several series of polymer composite materials constituting two polymeric matrixes: ethylene vinyl acetate (EVA) filled with micrometric particles of barium titanate (BaTiO3) and polypropylene (PP) filled with copper (Cu) particles were investigated. The finite-element software COMSOL 3.5a was used to model the thermal heat transport for an elementary cell in order to estimate the effective thermal conductivity of the composites. The effect of the filler concentrations and the nature of the particles on the effective thermal conductivity were also numerically investigated. The present work compares the numerically calculated and the measured thermal conductivities for various samples.

Recent Advances in Green Composites

This review aims at reporting on very recent developments in the, properties and applications of Green Composites. One very important aspect of green composites is that they can be designed and tailored to meet different requirements. Recent advances in natural fiber development offer significant oppurtunities for improved materials from renewable resources. Biocomposites offer a significant non-food market for crop-derived fibres and resins. Considerable growth has been seen in the use of biocomposites in the automotive and decking markets over the past decade or so, but application in other sectors has hitherto been limited. Recent developments of different biodegradable polymers and biocomposites are discussed in this review article.

Thermophysical and mechanical properties of TiO2 and silica nanoparticle-filled natural rubber composites

The mechanical and thermophysical properties of natural rubber filled with titanium dioxide (TiO2) and nanosilica composites have been investigated at room temperature for several filler concentrations. It is observed that the thermal conductivity and thermal diffusivity of the composites increase with filler loading, independent of the nature of the filler. We show that the thermal heat transport through composites is affected by the geometry of the fillers as well as the particle size and specific surface area of the fillers. The measured values of thermal conductivity have been compared to some theoretical models. The mechanical properties of the composites have also been studied and results have been correlated with thermal conductivity data.

Mechanical Properties and Morphology of Composites Based on the EVA Copolymer Filled with Expanded Graphite

Polymeric composites were prepared using ethylene-vinylacetate (EVA) matrix and expanded graphite (EG). Mechanical properties were investigated and it was found that Youngs modulus and the yield stress of EVA-EG composites significantly increased with graphite content. However, for higher EG content the composites became brittle. The dependence of stress at the break of composites reached maximum at 30 vol.% of the filler. The morphology of both EG filler and composites were investigated using transmission electron microscopy and Raman spectroscopy. All these structural characterizations indicated partial exfoliation of EG within EVA matrix, which leads to the increase of the reinforcement effect.

Thermal Conductivity of Polymer/Carbon Nanotube Composites

As one of the most important field of current nanoscience, the polymer nanocomposites is a promising and efficient way for new generation materials with high performances and multifunctionalities. The incorporating of nanofillers in a polymer matrix may improve mechanical, thermal, electrical or dielectric properties of the composites. The current paper focuses on the thermal conductivity of polymer/carbon nanotube composites. These last, are considered to be ideal candidates for the development of nanocomposite materials. Clarifying the role of the factors, influencing the properties of the composites, enable us to choose the suitable processing method for obtaining the composites and to improve the different properties of these systems. This article reviews the dependence of thermal conductivity of carbon nanotubes on the tube size and the effect of interface on the equivalent property. The relationship between the thermal conductivity and the nanostructure of composites are discussed.

Parametric estimation of thermoradiative properties of materials based on harmonic excitation

A simple device for the measurement of emissivity, thermal conductivity, and diffusivity of opaque materials is described. The measurement method is based on the use of a harmonic excitation of a material sample plate. The front surface of the sample is heated periodically and its temperature is measured using a thermocouple. The sample back surface temperature is obtained by infrared thermography. Half of the sample back surface is covered by a black paint of known emissivity used as a reference to compute the sample surface directional emissivity. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of experimental and theoretical heat transfer functions. Results are presented for a thermally thick sample of PVC, where the sample thickness is greater than the thermal diffusion length. The identified thermophysical properties are in agreement with literature values and reproducible results are obtained. Moreover, some limitations of the method are consider...