Showing papers by "Sarith P. Sathian published in 2012"

Molecular-dynamics study of Poiseuille flow in a nanochannel and calculation of energy and momentum accommodation coefficients.

Abstract: We report a molecular-dynamics study of flow of Lennard-Jones fluid through a nanochannel where size effects predominate. The momentum and energy accommodation coefficients, which determine the amount of slip and temperature jumps, are calculated for a three-dimensional Poiseuille flow through a nano-sized channel. Accommodation coefficients are calculated by considering a " gravity"- (acceleration field) driven Poiseuille flow between two infinite parallel walls that are maintained at a fixed temperature. The Knudsen number (Kn) dependency of the accommodation coefficients, slip length, and velocity profiles is investigated. The system is also studied by varying the strength of gravity. The accommodation coefficients are found to approach a limiting value with an increase in gravity and Kn. For low values of Kn (<0.15), the slip length obtained from the velocity profiles is found to match closely the results obtained from the linear slip model. Using the calculated values of accommodation coefficients, the first- and second-order slip models are validated in the early transition regime. The study demonstrates the applicability of the Navier-Stokes equation with the second-order slip model in the early transition regime.

A molecular dynamics study to determine the solid-liquid interfacial tension using test area simulation method (TASM).

Abstract: Molecular dynamics (MD) studies on heat transfer from a heated nanoparticle into the surrounding fluid have indicated that the fluid next to a spherical nanoparticle can get heated well above its boiling point without observing a phase change, while a contradicting behavior was observed for a flat surface-fluid interface. Another interesting observation is that the critical heat flux was found to increase with increase in the wetting characteristics of solid. Thus, the interfacial tension or free energy of solid-liquid interface could play a pivotal role in the mechanism of heat transfer. A recent study by Gloor et al. [J. Chem. Phys. 123, 134703 (2005)]10.1063/1.2038827 has proposed test area simulation method (TASM) for the determination of interfacial tension. The present study involves the determination and the comparison of solid-liquid interfacial tension for planar and spherical interfaces using MD based on TASM and analyze the results. A higher interfacial tension value is observed for spherical n...

Determination of accommodation coefficients of a gas mixture in a nanochannel with molecular dynamics

Abstract: A molecular-dynamics (MD) study of non-reacting and disparate mass binary gas mixture is conducted. The interaction properties of a typical mixture of gases on the walls of a nanochannel, at moderately rarefied conditions, are investigated with MD. The study discusses the method of calculation of the energy and the momentum accommodation coefficients for a binary gas mixture confined in a nanochannel. The thermal distributions are obtained from the imposed thermal wall conditions using MD. While keeping the bulk number density a constant, the interaction properties of gas mixtures at different molar concentration of individual components are determined. The accommodation properties are found to increase with an increase in concentration of heavier gas component in the gas mixture.

Combining molecular dynamics simulation and transition state theory to evaluate solid-liquid interfacial friction in carbon nanotube membranes.

Abstract: A molecular dynamics (MD) methodology based on Eyring theory of reaction rates is proposed for investigating solid-liquid interfacial properties crucial to the development of many nanotechnology applications. The method involves the calculation of activation energy required for the flow process directly from the MD trajectory information. We have applied this methodology to study the behavior of water in hydrophobic confinement in carbon nanotubes (CNTs) and also between graphene sheets. In the case of confined water molecules in CNTs and between graphene sheets the degree of confinement and curvature effects were found to have more influence on the solid-liquid interfacial friction, with almost negligible friction below a certain characteristic dimension in both the cases. This behavior of confined and unconfined water molecules is explained on the basis of molecular interactions and subsequent changes in the activation energy. Analysis based on this method also revealed that a finite amount of friction does exist at the channel entry and exit region. This could limit the flow of liquid molecules through the nanochannels and hence needs to be taken into account in the design of nanofluidic devices.

Molecular dynamics studies in nanoscale liquid structures: geometry and thermal effects on nanojet development

Abstract: Conventional macroscopic jet theory relies heavily on experimental correlations which cannot be easily extended to the nanoscale regime. Moreover, the fluid dynamic effects at small length scales and their contribution to the development of nanoscale liquid structures are fundamentally different from their macroscopic counterparts. This coupled with the high spatial and temporal resolution requirements at nanoscale domains make molecular dynamics (MD) an excellent tool for studying such structures. In this study, the formation and breakup of nanojets (NJs) developing from high pressure into vacuum is investigated using MD based on non-Hamiltonian formulations. By ejecting the equilibrated argon atoms through various nozzle geometries and diameters, nanoscale jet flows were generated. The dependence of the jet structure on nozzle geometry and diameter is studied. The influence of geometry on NJ formation is also studied along with issues involved in the equilibration and thermostat coupling parameter. Vari...