Coefficient of Thermal Expansion (CTE) is a measure of the expansion or contraction of a material as a result of changes in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure.
Several types of coefficients have been developed: volumetric, area, and linear.
Author(s): Arun Kumar, Joydipta Banerjee, K. Ravi, M. R. Nair, R. P. Singh, Santu Kaity, Smruti Dash, T. R. G. Kutty
Thermophysical properties of a uranium-6 wt. % zirconium alloy were investigated at high temperatures to evaluate the performance of the alloy as a driver fuel for a liquid-metal cooled fast reactor. Of particular interest to the authors were the coefficient of thermal expansion, the specific heat, and the thermal conductivity of the alloy.
Author(s): I. Firkowska, K. Gharagozloo-Hubmann, M. Lisunova, V. Datsyuk
As nanotechnology becomes increasingly important, researchers are investigating methods to decrease the size of electronics. Carbon nanotubes (CNTs) have potential applications in nanoelectronics because of their high thermal conductivity and miniscule size. This study had many focuses, but the transient plane source method was used to specifically measure the thermal conductivities of CNT-fabricated thermal pastes. Results showed that the thermal conductivities varied depending on filler content, but were comparable to commercial pastes.
Thermal properties and moisture absorption of nanofillers-filled epoxy composite thin film for electronic application
Author(s): L. C. Sim, M. Mariatti, Richard Voo
The effects of the addition of three different fillers to a polymer matrix on the thermo-physical properties of the resulting composites were investigated by the authors. Boron nitride, synthetic diamond, and silicon nitride were used as the fillers (up to 2 vol. %), and it was found that their addition did increase the thermal conductivity relative to that of the pure epoxy matrix. Furthermore, it was determined that the thermal conductivities of the composites increased with increasing filler content, and the maximum thermal conductivity observed in the composites prepared in this work was 78 % higher than that of the pure epoxy matrix. The synthetic diamond filled composites were found to be more thermally stable than the other two types of composites; however, they were found to absorb more moisture than the other composites.
Author(s): Sonali Kand, Venkatesh Kodur, Wasim Khaliq
High-strength steel used in bolts was tested for its thermo-physical properties in order to determine how steel bolts would respond in a fire. It was determined that the thermal and mechanical properties of the steel were dependent on temperature, and that the thermal conductivity of the steel was also dependent on carbon content. The thermal conductivity of the three types of steel that were tested was found to be the same at a given temperature in both the heating and cooling phases of a fire. Significant thermal strain was observed in all three types of steel at elevated temperatures. There was no significant change in the yield and ultimate strength of the steel samples at temperatures up to 400oC, but above this temperature, both properties decreased rapidly.
Synthesis and Characterization of Multifunctional Nanocomposites of Toughened Epoxy Reinforced With Carbon Nanotubes
Author(s): Dimitris C. Lagoudas, Patrick J. Klein, Piyush R. Thakre
The authors have developed a method for the functionalization of single-walled carbon nanotubes (SWCNTs). The functionalization of the SWCNTs is useful in helping to produce a better dispersion of nanotubes throughout a polymer matrix. Better dispersion of nanotubes was thought to result in an improvement in the mechanical, electrical, and thermal properties of nanocomposite polymers. It was determined that the method produced effective surface modification of the nanotubes. The elastic modulus and thermal conductivities of the nanocomposites seemed to be unaffected by the functionalization of the SWCNTs; however, the flexural strength of the nanocomposites was reduced.
Determining the thermal conductivity of liquids using the transient method. Part I: Establishing transient thermal-fluid constraints
Author(s): Amy S. Fleischer, Ronald J. Warzoha
The authors look into problems with accurately measuring thermal conductivity of liquid samples. Among these problems is the onset of natural convection during the measurement of thermal properties, which may lead to skewed values reported after characterization. The effect of natural convection is analyzed numerically for the transient method in order to determine at what time during an analysis the convection causes incorrect output data. The effect of the liquids thermal conductivity, diffusivity, Rayleigh number and Prandtl number on the sensor temperature response is studied. Also, a correlation is developed between the onset of convection and a wide range of Prandtl numbers.
Towards Thermoconductive, Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers
Author(s): C. Tang, C. Zhi, D. Golberg, H. Kuwahara, T. Terao, Y. Bando
In this experiment, the thermal conductivity of several composites, with varying matrix composition and boron nitride nanotubes fillers, was investigated. Poly(methyl methacrylate), polystyrene, poly(vinyl butyral) and poly(ethylene vinyl alcohol) were the matrix compositions analyzed. The results indicated that with the addition of the boron nitride nanotube fillers, there was a 20-fold increase in the thermal conductivity of the polymer. Several other properties were analyzed alongside of thermal conductivity.