Browsing by Author "Song, Yingru"

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    Probing phonon heat conduction in multi-scaled systems via ray tracing simulation and three omega measurements
    (2024-06-27) Song, Yingru; Wehmeyer, Geoff
    Nanostructured materials display unique thermal and electrical properties, but it can be challenging to scale up the nanoscale phenomena for micro/macroscale applications. In addition to experimental challenges in assembling and controlling multiple nanostructures, it is difficult to model multiscale phonon heat transfer and capture nanoscale size effects for microscale experimental geometries with complex features. In this first half of this thesis, I have developed a Landauer-based phonon Monte Carlo ray tracing simulation methods to determine the phonon mean free path and local temperature/heat flux profiles in realistic micromaterials. I will discuss applications of the ray tracing method to experimentally relevant microstructures that display interesting phonon transport phenomena including locally inverted temperature gradients and ballistic phonon focusing. In the second half of the thesis, I will discuss experimental measurements of high-conductivity carbon nanotube fiber (CNTFs), which consist of long individual carbon nanotubes (CNTs) that are highly aligned along the fiber’s axis. My electrothermal three-omega measurements show that the thermal conductivity increases with increasing CNT molecular aspect ratio (i.e., length to diameter ratio) up to values as large as 380 W/m.K, showing that the interfaces between CNT bundles still impede thermal transport even at high degrees of alignment and with CNT lengths up to 10 μm. Thus, my simulations and experiments focus on understanding and optimizing the relationship between nanoscale phonon physics and macroscale properties in complex geometries.