Assessment of modulated hot wire method for thermophysical characterization of fluid and solid matrices charged with (nano)particle inclusions

Recently we reported on simultaneous thermal conductivity k and thermal diffusivity a measurement of liquids and in particular of nanofluids in a configuration using an ac excited hot wire combined with lock-in detection of the third harmonic (3ω method) [1]. The conductive wire is used as both heater and sensor. The requirements for the asymptotic validity of the line heat source model are fulfilled at low modulation frequencies below a few Hz. The study of the relative sensitivity of signal amplitude and phase to changes in k and a indicates that there is an optimum frequency range for accurate and stable results. We extend by up to two decades the feasible frequency range for 3ω measurements by considering various more elaborate models for the heat transfer between the wire and the fluid. Finally we show that the same ac hot wire method can be applied to soft solid, composite materials. We measured the k enhancement of a poly(ethylene vinyl acetate) EVA polymer matrix charged with various fractions of graphite

A numerical and experimental study on thermal conductivity of particle filled polymer composites

In this study, thermal conductivity of particle filled polymer composites is investigated numerically and experimentally. In the numerical study, the finite-element program ANSYS is used to calculate the thermal conductivity of the composite by using the results of the thermal analysis. Three-dimensional models are used to simulate the microstructure of composite materials for various filler concentrations at various ratios of thermal conductivities of filler to matrix material. The models used to simulate particle filled composite materials are cubes in a cube lattice array and spheres in a cube lattice array. A modified hot wire method is used to measure the thermal conductivity of the composites consisting of a high-density polyethylene (HDPE) matrix filled with tin particles up to 16% by volume. The experimentally measured thermal conductivities are compared with numerically calculated ones by using the spheres in cube model and also with the already existing theoretical and empirical models. At low particle content, up to 10% of volume content of tin filler, numerical estimation and all other models except for the Cheng and Vachon model, predict well the thermal conductivity of the composite. For more heavily filled composites there is an exponential increase in thermal conductivity and most of the models fail to predict thermal conductivity in this region

Effect of particle shape on thermal conductivity of copper reinforced polymer composites

Thermal conductivity of copper powder filled polyamide composites are investigated experimentally in the range of filler content 0-30% by volume for particle shape of short fibers and 0-60% by volume for particle shapes of plates and spheres. The thermal conductivity of polymer composites is measured by the Hot-Disk method. It is seen that the experimental values for all the copper particle shapes are close to each other at low particle content, phi < 10, as the particles are dispersed in the polyamide matrix and they are not interacting with each other. For particle content greater than 10% by volume, a rapid increase occurs in the thermal conductivity for the copper fibers filled polymer composite. As a result of this study, thermal conductivity of copper filled polyamide composites depends on the thermal conductivity of the filler particles, filler particle shape and size, and the volume fraction and spatial arrangement of the filter particles in the polymer matrix

Epoxy- and Polyester-Based Composites Reinforced With Glass, Carbon and Aramid Fabrics: Measurement of Heat Capacity and Thermal Conductivity of Composites by Differential Scanning Calorimetry

The primary purpose of the study is to investigate the temperature dependence of heat capacity and thermal conductivity of composites having different fiber/matrix combinations by means of heat-flux differential scanning calorimetry (DSC). The materials used as samples in this study were epoxy- and polyester-based composites. Noncrimp stitched glass, carbon, and aramid fabric were used as reinforcements for making unidirectional composites. For the heat capacity measurements the composite sample and a standard material are separately subjected to same linear temperature program. By recording the heat flow rate into the composite sample as a function of temperature, and comparing it with the heat flow rate into a standard material under the same conditions, the temperature dependence of heat capacity of the composite sample is determined. Measurements were carried out over a wide range of temperatures from about 20 to 250 degrees C. The differential scanning calorimeter was adapted to perform the thermal conductivity measurements in the direction perpendicular to the fiber axis over the temperature range of 45-235 degrees C. The method used in this study utilizes the measurement of rate of heat flow into a sensor material during its first-order phase transition to obtain the thermal resistance of a composite material placed between the sensor material and the heater in the DSC. POLYM. COMPOS., 30:1299-1311, 2009. (C) 2008 Society of Plastics Engineer

Concentration Effect of gamma-Glycidoxypropyl-trimethoxysilane on the Mechanical Properties of Glass Fiber-Epoxy Composites

WOS: 000269341500008In this study, glass fibers. were modified using gamma-glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of gamma-glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short-beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three-point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat-cleaned glass fiber reinforced composite is enhanced by similar to 59% as a result of the glass fiber treatment with 0.5% gamma-GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% gamma-GPS treatment of glass fibers was observed. POLYM. COMPOS., 30:1251-1257, 2009. (C) 2008 Society of Plastics EngineersResearch Foundation of Dokuz Eylul UniversityDokuz Eylul University [2007.KB.FEN.007]Contract grant sponsor: Research Foundation of Dokuz Eylul University; contract grant number: 2007.KB.FEN.007

FTIR and SEM analysis of polyester- and epoxy-based composites manufactured by VARTM process

Polyester- and epoxy-based composites containing glass and carbon fibers were manufactured using a vacuum-assisted resin transfer molding (VARTM) process. Fourier transform infrared (FTIR) spectroscopy analyses were conducted to determine the interaction between fibers and matrix material. The results indicate that strong interaction was observed between carbon fiber and epoxy resin. However, weak interactions between remaining fiber-matrix occur. Scanning electron microscopy (SEM) analysis was also performed to take some information about strength of interaction between fibers and matrix material. From SEM micrographs, it is concluded that the findings in SEM analysis support to that obtained in FTIR analysis. Another aim of the present work was to investigate the influence of matrix on composite properties. Hence, the strengths of composites having same reinforcement but different matrix systems in axial tension and transverse tension were compared. Short beam shear test has been conducted to characterize the interfacial strength in the composites. (C) 2008 Wiley Periodicals, Inc