Browsing by Author "Balasubramanian, Ganesh"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Heat conduction across a solid-solid interface: Understanding nanoscale interfacial effects on thermal resistance
    Balasubramanian, Ganesh; Puri, Ishwar K. (AIP Publishing, 2011-07-01)
    Phonons scatter and travel ballistically in systems smaller than the phonon mean free path. At larger lengths, the transport is instead predominantly diffusive. We employ molecular dynamics simulations to describe the length dependence of the thermal conductivity. The simulations show that the interfacial thermal resistance R-k for a Si-Ge superlattice is inversely proportional to its length, but reaches a constant value as the system dimension becomes larger than the phonon mean free path. This nanoscale effect is incorporated into an accurate continuum model by treating the interface as a distinct material with an effective thermal resistance equal to R-k. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3607477]
  • Thumbnail Image
    Modeling nanoscale transport phenomena: Implications for the continuum
    Balasubramanian, Ganesh (Virginia Tech, 2011-04-20)
    Transport phenomena at the nanoscale can differ from that at the continuum because the large surface area to volume ratio significantly influences material properties. While the modeling of many such transport processes have been reported in the literature, a few examples exist that integrate molecular approaches into the more typical macroscale perspective. This thesis extends the understanding of nanoscale transport governed by charge, mass and energy transfer, comparing these phenomena with the corresponding continuum behavior where applicable. For instance, molecular simulations enable us to predict the solvation structure around ions and describe the diffusion of water in salt solutions. In another case, we find that in the absence of interfacial effects, the stagnation flow produced by two opposing nanojets can be suitably described using continuum relations. We also examine heat conduction within solids of nanometer dimensions due to both the ballistic propagation of lattice vibrations in small confined dimensions and a diffusive behavior that is observed at larger length scales. Our simulations determine the length dependence of thermal conductivity for these cases as well as effects of isotope substitution in a material. We find that a temperature discontinuity at interfaces between dissimilar materials arises due to interfacial thermal resistance. We successfully incorporate these interfacial nanoscale effects into a continuum model through a modified heat conduction approach and also by a multiscale computational scheme. Finally, our efforts at integrating research with education are described through our initiative for developing and implementing a nanotechnology module for freshmen, which forms the first step of a spiral curriculum.
  • Thumbnail Image
    Reducing thermal transport in electrically conducting polymers: Effects of ordered mixing of polymer chains
    Pal, Souvik; Balasubramanian, Ganesh; Puri, Ishwar K. (AIP Publishing, 2013-01-01)
    Reducing the phonon thermal conductivity of electrically conducting polymers can facilitate their use as potential thermoelectric materials. Thus, the influence of the coupling between the longitudinal and transverse phonon modes on overall thermal conductivity is explored for binary mixtures of polyaniline (PANI) and polyacetylene (PA) chains by considering various geometric polymer mixture configurations. The molecular simulations reveal that an increase in the interfacial area available for transverse interactions between dissimilar chains enhances atomic interactions that are orthogonal to the heat transfer direction. As transverse collisions between PA and PANI chains are enhanced, the motion of longitudinal phonons is disrupted, impeding thermal transport. This enhances phonon scattering and reduces longitudinal thermal transport. While there is a nonlinear decrease in the phonon thermal conductivity with increasing interfacial contact area, there is a corresponding linear growth in the nonbonded interaction energies between the different polymers. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4776676]
  • Thumbnail Image
    Unsteady nanoscale thermal transport across a solid-fluid interface
    Balasubramanian, Ganesh; Banerjee, Soumik; Puri, Ishwar K. (American Institute of Physics, 2008-09-15)
    We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liquid-vapor Ar mixtures adjacent to warmer Fe walls. The equilibration of the system towards a uniform overall temperature is investigated using nonequilibrium molecular dynamics simulations from which the heat flux is also determined explicitly. The Ar-Fe intermolecular interactions induce the migration of fluid atoms into quasicrystalline interfacial layers adjacent to the walls, creating vacancies at the migration sites. This induces temperature discontinuities between the solid-like interfaces and their neighboring fluid molecules. The interfacial temperature difference and thus the heat flux decrease as the system equilibrates over time. The averaged interfacial thermal resistance R(k,av) decreases as the imposed wall temperature T(w) is increased, as R(k,av) alpha T(w)(-4.8). The simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2978245]