Knudsen number

About: Knudsen number is a research topic. Over the lifetime, 5052 publications have been published within this topic receiving 104278 citations.

Effects of nonlocal elasticity and Knudsen number on fluid–structure interaction in carbon nanotube conveying fluid

Abstract: In this paper, we investigate the effect of nano-size of both fluid flow and elastic structure simultaneously on the vibrational behavior of a pinned–pinned and a clamped–clamped nanotube conveying fluid, using both Knudsen number (Kn) and nonlocal continuum theory. Euler–Bernoulli plug flow (EBPF) theory is used for modeling fluid–structure interaction (FSI). It is observed that nonlocal parameter has more effect than Kn on the reduction of critical velocities of a liquid nano-flow. This effect has considerable impact on the reduction of critical velocities for a clamped–clamped beam in comparison with a pinned–pinned one. We concluded that the dimensionless nonlocal parameter, had more impressive effect on the dimensionless critical flow velocity of the second mode divergence and coupled mode flutter instabilities. However, in a gas nano-flow, the situation is totally different and Kn causes more reduction in critical velocities. Furthermore, it is emphasized that ignoring nano-size effects on liquid and gas nano-flow might cause non-conservative design of nano-devices.

Mass and heat transfer between evaporation and condensation surfaces: Atomistic simulation and solution of Boltzmann kinetic equation.

Abstract: Boundary conditions required for numerical solution of the Boltzmann kinetic equation (BKE) for mass/heat transfer between evaporation and condensation surfaces are analyzed by comparison of BKE results with molecular dynamics (MD) simulations. Lennard-Jones potential with parameters corresponding to solid argon is used to simulate evaporation from the hot side, nonequilibrium vapor flow with a Knudsen number of about 0.02, and condensation on the cold side of the condensed phase. The equilibrium density of vapor obtained in MD simulation of phase coexistence is used in BKE calculations for consistency of BKE results with MD data. The collision cross-section is also adjusted to provide a thermal flux in vapor identical to that in MD. Our MD simulations of evaporation toward a nonreflective absorbing boundary show that the velocity distribution function (VDF) of evaporated atoms has the nearly semi-Maxwellian shape because the binding energy of atoms evaporated from the interphase layer between bulk phase and vapor is much smaller than the cohesive energy in the condensed phase. Indeed, the calculated temperature and density profiles within the interphase layer indicate that the averaged kinetic energy of atoms remains near-constant with decreasing density almost until the interphase edge. Using consistent BKE and MD methods, the profiles of gas density, mass velocity, and temperatures together with VDFs in a gap of many mean free paths between the evaporation and condensation surfaces are obtained and compared. We demonstrate that the best fit of BKE results with MD simulations can be achieved with the evaporation and condensation coefficients both close to unity.