  Carbon nanotube (CNT) have been known to increase the heat transfer at the
solid-liquid interfaces, but have a limitation due to the interfacial thermal
resistance. Vibrational mismatch at the interface leads to this interfacial
thermal resistance, which plays an important role in energy transfer at the
boundary. Negligible work has been reported on the influence of CNT diameter on
the resistance through the vibrational mismatch study. Molecular dynamics
simulations have been performed to investigate the effect of CNT diameter on
interfacial resistance between carbon nanotube (CNT) and water molecules. This
work is an effort to understand the heat transfer phenomenon at the interface
by quantifying the vibrational mismatch. Analysis of the vibrational spectra of
CNT and water molecules is done to study the effect of CNT diameter on
interfacial resistance. Starting with the initial configuration, and
equilibrating the system of CNT and water molecules at 300 K and 1 atm, the CNT
temperature is raised to 700 K by velocity rescaling. This system is now
allowed to relax as a micro-canonical ensemble. Based on the lumped capacitance
analysis, the time constant of the CNT temperature response is determined,
which is then used to compute the interfacial thermal resistance. The
interfacial thermal resistance is observed to be relatively higher for the
larger diameter nanotube. This is attributed to the higher vibrational mismatch
existing for larger diameter CNT as a result of low overlapping region between
vibrational density states of CNT and water molecules. For smaller diameter
CNT, the interfacial thermal resistance is low which results in the efficient
heat transfer at the interface thus, emphasizing the indispensable role of
larger diameter CNTs in the cooling applications.
