Showing papers by "Sarith P. Sathian published in 2013"

The effect of system boundaries on the mean free path for confined gases

Abstract: The mean free path of rarefied gases is accurately determined using Molecular Dynamics simulations. The simulations are carried out on isothermal argon gas (Lennard-Jones fluid) over a range of rarefaction levels under various confinements (unbounded gas, parallel reflective wall and explicit solid platinum wall bounded gas) in a nanoscale domain. The system is also analyzed independently in constitutive sub-systems to calculate the corresponding local mean free paths. Our studies which predominate in the transition regime substantiate the boundary limiting effect on mean free paths owing to the sharp diminution in molecular free paths near the planar boundaries. These studies provide insight to the transport phenomena of rarefied gases through nanochannels which have established their potential in microscale and nanoscale heat transfer applications.

Thermal transpiration through single walled carbon nanotubes and graphene channels

Abstract: Thermal transpiration through carbon nanotubes (CNTs) and graphene channels is studied using molecular dynamics (MD) simulations. The system consists of two reservoirs connected by a CNT. It is observed that a flow is developed inside the CNT from the low temperature reservoir to the high temperature reservoir when the two reservoirs are maintained at different temperatures. The influence of channel size and temperature gradient on the mean velocity is analysed by varying the CNT diameter and the temperature of one of the reservoirs. Larger flow rate is observed in the smaller diameter CNTs showing an increase in the mean velocity with increase in the temperature gradient. For the flow developed inside the CNTs, slip boundaries occur and the slip length is calculated using the velocity profile. We examine the effect of fluid-wall interaction strength (e(fw)), diffusivity (D), and viscosity of the fluid (μ) on the temperature induced fluid transport through the CNTs. Similar investigations are also carried out by replacing the CNT with a graphene channel. Results show that the mean velocity of the fluid atoms in the graphene channel is lower than that through the CNTs. This can be attributed to the higher degree of confinement observed in the CNTs.

Effect of Confined Fluid Interaction on the Thermal Transport in Carbon Nanotubes

Abstract: Carbon nanotubes (CNTs) are one of the most commonly used engineering materials. The axial thermal conductivity of CNTs were found to be exceptionally high, which makes them one of the favourable candidates for the next generation thermal management devices. Previous works have indicated that the presence of confined fluid molecules inside the CNT lead to a reduction in the thermal conductivity of the CNT. In the present study, we investigate the effect of confined liquid flow through CNTs on the thermal transport of CNTs. Spectral energy density method is used to predict the phonon properties and lifetimes of the CNT. The phonon mode lifetimes were found to be greater under flow compared to filled condition for smaller diameter CNTs. But the flow does not seem to modify signifcantly the phonon mode lifetimes of larger diameter CNTs. These variations in the thermal transport properties of CNT is explained using the changes occuring in the physical behavior of the confined fluid as the tube diameter changes.

A Molecular Dynamics Study of Energy and Momentum Accommodation Coefficients in the Transitional Knudsen Numbers

Abstract: The principal aim of this work is to study the thermophysical aspects of gas interaction on the walls of nano-channels using a three dimensional Molecular Dynamics (MD) model. The complete physics of gas-surface interaction in micro/nano channels in the non continuum regime is yet to be understood. The important parameters that are relevant to such interactions include energy and momentum accommodation coefficients. The study reported in this paper aims at implementing a relatively simple methodology for calculating different accommodation coefficients. Energy accommodation coefficient (EAC) and normal momentum accommodation coefficient (NMAC) are the main focus of the study. The accommodation coefficients for the different equilibrium states are calculated. Instead of tracking individual collision, a collection of collisions are considered for the calculations. The EAC and NMAC reported here are found to be influenced by gas-wall temperature difference and Knudsen number in the transition regime.