Abstract

Carbon nanotubes (CNTs) have been a promising material for thermal management applications including micro/nano-electromechanical system (MEMS/NEMS) due to their extremely high thermal conductivity values. CNTs-reinforced Cu/Al (CNT-Cu/Al) composites are attractive to meet all-around requirements on high thermal performance materials to be applied in many areas, such as aerospace, automotive and electronic packaging. However, the experimental results on resultant thermal conductivity of these composites are far from expectation due to the law of mixture. In this research, molecular dynamics (MD) simulation is used to study the thermal conduction of CNT-Cu/Al composites. Before the simulation is conducted, new inter-atomic potentials for the Modified Embedded Atom Method (MEAM), which are important for MD simulation of such materials, are developed for Cu-C and Al-C binary system and are validated by correctly predicting physical properties, such as the cohesive energy, the lattice constants, the surface energy and the institutional energy. Then Two Temperature Model along with the nonequilibrium Molecular Dynamics method (TTM-MD) is used to study the thermal conductivity of CNT-Cu/Al composites. The two-temperature model considers the electrons contribution, which plays a crucial role in energy transfer for calculating metal-based composites. Other than pure MD method which considers only phonons in energy transfer, the TTM-MD deals with all interactions including electron-electron interactions, electron-phonon coupling and phonon-phonon interactions. The resultant thermal conductivity of CNT-Cu/Al composites calculated by TTM-MD method is much higher than that of pure Cu/Al, significantly different from those simulation results obtained with pure MD methods. It has proven that the TTM-MD is more reliable to calculate the thermal conduction of metal-based materials, especially for CNT-Cu/Al composites with high thermal conduction capabilities. Simulation results have also shown that the orientation of embedded CNTs in metal matrices can significantly influence the resultant thermal conductivity of CNT-Cu/Al composites, in addition to the CNT volume fractions. There is optimization in the resultant thermal conductivity of CNT-Cu/Al composites with respect to the CNT additions and the CNT orientation. Interfacial thermal resistance between CNT and Cu/Al substrate are also calculated in this work. Factors including the direction of heat flow, the temperature dependence, the CNT engagement as well as the metal crystal orientations on the resultant interfacial thermal resistance are all investigated. Thermal rectification has been observed due to the change of heat flow directions. Internal metal filling ratio of metal-filled CNT nanowire and the structures of the filled metal substrate are found all important to significantly affect the resultant interfacial thermal resistance.

Notes

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Graduation Date

2020

Semester

Summer

Advisor

Chen, Quanfang

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering

Format

application/pdf

Identifier

CFE0008223; DP0023577

URL

https://purls.library.ucf.edu/go/DP0023577

Language

English

Release Date

August 2023

Length of Campus-only Access

3 years

Access Status

Doctoral Dissertation (Campus-only Access)

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