Thermal heat transport characterization for macroscale, microscale, and nanoscale heat conduction

Abstract

Several theoretical and experimental methods for predicting the thermal conductivity of thin dielectric ¯lms and carbon nanotubes are presented based on two schools of thought: (1) the physics of the Boltzmann Transport Equation (BTE), and (2) Molec- ular Dynamics (MD) simulations. First, in relation to models based on the BTE, this thesis highlights temporal and spatial scale issues by looking at a uni¯ed theory that bridges physical aspects presented in the Fourier and Cattaneo models. This newly developed uni¯ed model is the so called C- and F-Processes heat conduction model. The model introduces the dimensionless heat conduction model number which is the ratio of thermal conductivity of the fast heat carrier F-Processes to the total thermal conductivity comprised of both fast F-processes and slow heat carrier C-processes. Prior work has claimed that macroscopic heat transfer models cannot explain mi- croscale heat transfer. First, this dissertation provides arguments by showing how the C-F model is able to extend the use of \macroscopic" constitutive relations for the prediction of thermal conductivity at the \microscopic" level for thin ¯lms, mul- tilayer structures, and includes both dielectrics and metals. Second, the in°uence of external mechanical strain on the thermal conductivity of single-wall carbon nan- otubes is studied using direct molecular dynamics simulations with Terso®-Brenner potential for C-C interactions. Three types of external mechanical strain, namely, axial compression, tension, and torsion are studied. In all three cases, the thermal conductivity does not degrade much, i.e., it remains within 10% of the pristine nan- otube values for lower applied strain below the values required for structural collapse. At higher applied strain, structural collapse occurs, and major reductions in the ob- served thermal conductivity for axially compressed and torsionally twisted tubes are observed.