MS Defense: John Miller
Thermal Rectification Effect caused by Ballistic Phonon Propagation through Asymmetric Nano-Structures
John P. Miller
Department of Mechanical Engineering
Advisor: Professor Christopher Dames
Abstract: Thermal rectification is a phenomenon where heat is transported though a device more easily in one direction than in the opposite direction. This project begins with the belief that including asymmetric nanostructures in a matrix material will allow energy carriers (in this case, phonons) to travel more easily in one direction than in the reverse. Previous theoretical derivations showed that the heat transfer in such devices is dependent on the forward and reverse phonon transmission functions, which are determined by the device geometry. In this thesis work, a computer model was developed to calculate the transmission functions using a ray tracing method. This numerical model was validated successfully against known analytical solutions for the size-dependent thermal conductivity of nanowires, thin films, superlattices, and bulk materials, as well the transitions between these different regimes. Finally, the model was used to calculate the thermal rectification in materials containing arrays of pyramidal inclusions. The effects of pyramid surface roughness, aspect ratio, number of layers, and material were studied. The modeling concludes that the maximum thermal rectification effect is obtained by using a single layer of pyramids with smooth sides, a high aspect ratio, and made of a material with a phonon velocity much higher than the matrix material.