Thermal Conductivity of Graphitic Carbon Nitride Nanotubes: A Molecular Dynamics Study

Graphitic carbon nitride (g-C3N4) nanotubes are recently gaining increasing interest due to their extraordinary physicochemical properties. In the following, we report on simulations using a method of nonequilibrium molecular dynamics and focus on the thermal conductivity variation of g-C3N4 nanotubes with respect to different temperatures, diameters, and chiral angles. In spite of the variation of diameters and chiral angles, the structure of nanotubes possesses high stability in the temperature range from 200 K to 600 K. Although there is little change of the thermal conductivity per unit arc length for nanotubes with the same diameter at different temperatures, it decreases significantly with increasing diameters at the same temperature. The thermal conductivity at different chiral angles has little to do with how temperature changes. Simulation results show that the vibrational density of states of nanotubes distributed, respectively, at ∼11 THz and ∼32 THz, indicating that heat in nanotubes is mostly carried by phonons with frequencies lower than 10 THz.

Theoretical study of Specific heat and thermal conductivity variation in nanomaterials

In the present paper, the authors study the specific heat dependence on shape, size and dimension of the nanomaterials. Using an analytic quantitative model for melting temperature, the expression of specific heat for nanomaterials is deduced. Further, the model is extended to study the shape, size and dimension effect on thermal conductivity of nanoparticles. Phonon scattering term is taken into consideration for calculation of thermal conductivity of nanomaterial to explain the roughness and scattering effect on thermal property. The specific heat is observed to increase from model calculations as size of the nanomaterial decreases. However, the thermal conductivity in nanoparticles is observed to decrease with size decrement of nanoparticle. It is observed that inclusion of phonon scattering term help to better understand the variation in thermal conductivity. The variation in specific heat and thermal conductivity with size is determined for spherical, regular tetrahedral, octahedral nanoparticles, cylindrical and hexagonal nanowires and nanofilms. The results calculated from model are in good consistency with the available experimental and simulated results and help to judge the suitability of the present model.

Characterization of applied tensile stress to carbon epoxy composites by measuring the variation of transverse thermal conductivity using transmission thermography

Using the method of step heating thermography, this study seeks to detect and characterize the existence of stress in a beam sample of carbon epoxy composite with the stacking sequence of [08] aided by empirical and simulation approaches. The applied stress in the longitudinal direction of sample, while considering the Poisson’s ratio, changes the lateral dimensions of sample. Furthermore, it is shown that the thermal conductivity along the sample thickness varies as a result of stress existence. Accordingly, to obtain a relation between transverse thermal conductivity and longitudinal tensile stress, one should calculate and eliminate the effect of lateral deformation caused by stress. To this end, by combining the experimental and simulation results of composite sample under the action of different tensile loads, an equation describing the variation of thermal conductivity along the sample thickness with respect to applied stress is developed. Using the relation of transverse thermal conductivity variation in terms of applied stress, the finite element modeling is again carried out by rectifying the values of thermal conductivity. Simulation results are compared with experimental ones, indicating very good agreement between the two approaches.