Browsing by Author "Toprak, Kasim"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Carbon nanotubes thermal conductivity analysis using molecular dynamics simulations
    (2010) Toprak, Kasim; Bayazitoglu, Yildiz
    Non-equilibrium molecular dynamics simulations are used to determine the thermal conductivities of (5,5) single wall carbon nanotubes. By fixing the temperatures of opposing ends of an armchair single wall carbon nanotube with a Nose-Hoover thermostat, the length dependence of thermal conductivities of single wall carbon nanotubes were studied in vacuum. Specifically, single wall carbon nanotubes of 12.3 nm, 24.6 nm, and 36.9 nm lengths with varying fixed end temperatures were analyzed to determine thermal conductivities. In addition, the fixed end temperature lengths of single wall carbon nanotubes were varied to see convergence of the temperature profiles. The equivalent thermal resistance of single wall carbon nanotube bundle in water was modeled using the one dimensional heat conduction equation. The preliminary effective thermal conductivity of the system was calculated with different nanotube structures for a length ranging from 500 nm to 3000 nm to observe effective thermal conductivity variations. The effective thermal conductivity increases when the volume fraction of SWNTs and the nanotube length increase.
  • Thumbnail Image
    Item
    Thermal Conductivity of Single Wall Carbon Nanotube and Copper Coaxial Nanocomposite
    (2014-01-09) Toprak, Kasim; Bayazitoglu, Yildiz; Vajtai, Robert; Chapman, Walter G.
    Based on non-equilibrium molecular dynamics, a model is developed to study the thermal conductivity of Single Wall Carbon Nanotube (SWCNT) inside filled with Copper (Cu), forming a coaxial composite in the form of a nanowire. The Nose-Hoover thermostat is used to maintain the opposing ends of the SWCNT-Cu nanowire at uniform temperatures of 320 K and 280 K. Firstly, the length dependent thermal conductivities are examined in vacuum using the simulated axial temperature profiles and by applying the Nose-Hoover thermostat. The effective thermal conductivity of copper nanowire is estimated based on the electrical resistance analogy. The calculations showed that the thermal conductivity of a SWCNT-Cu nanowire is up to 24% higher than that of a corresponding pure SWCNT. Secondly, the identical SWCNT-Cu nanowire is placed in water instead of vacuum. The conduction along the radial direction of this coaxial nanocomposite surrounded with water is examined. Due to its simplicity and adaptability, a simple point-charge water model is implemented. Using the Nose-Hoover thermostat, the copper core is kept at a uniform temperature as a heat source, and a circular edge layer of water is kept at a lower temperature as a heat sink in order to impose a radial temperature distribution. The temperature jump due to interface resistance at the SWCNT-water interface is found to be smaller than the temperature jump at the SWCNT-Cu interface.