Knudsen number

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

Monte Carlo simulation of diffusion of gases in a porous solid: Calculations for a new class of solids

Abstract: In a previous paper, a Monte Carlo simulation of the Knudsen diffusion of a gas in a porous solid was carried out The simulated porous solid had pore walls that were convex In the present paper, the simulation is repeated using simulated solids whose pore walls are concave It was found that the results of both studies could be correlated by a single equation This equation enables the prediction of the Knudsen diffusiveness from the porosity and mean pore size without resort to a tortuosity factor

Modeling of rarefied gas heat conduction between wafer and susceptor

Abstract: Gas-assisted wafer cooling/heating system is one of the key technologies for manufacturing microelectronic devices. The heat conduction in the gap between wafer and susceptor is modeled here as a one- or two dimensional (1-D or 2-D) rarefied gas problem. The simulation is performed for monatomic and diatomic gases by means of the Direct Simulation Monte Carlo (DSMC) method. In the 1-D case the gas heat conductivity is obtained for various factors (gas species, surface temperature, energy accommodation coefficient) as a function of the Knudsen number. All numerical data obtained can be summarized by a simple equation: Smoluchowski's equation extended to the free molecular regime. In the 2-D case, the DSMC method is applied to the heat transfer between rough and smooth surfaces. The effect of surface roughness on heat conduction is clarified.

Sound wave resonances in micro-electro-mechanical systems devices vibrating at high frequencies according to the kinetic theory of gases

Abstract: The mechanism leading to gas damping in micro-electro-mechanical systems (MEMS) devices vibrating at high frequencies is investigated by using the linearized Boltzmann equation based on simplified kinetic models and diffuse reflection boundary conditions. Above a certain frequency of oscillation, the sound waves propagating through the gas are trapped in the gaps between the moving elements and the fixed boundaries of the microdevice. In particular, we found a scaling law, valid for all Knudsen numbers Kn (defined as the ratio between the gas mean free path and a characteristic length of the gas flow), that predicts a resonant response of the system. This response enables a minimization of the damping force exerted by the gas on the oscillating wall of the microdevice.

Nonlinear vibration of coupled nano- and microstructures conveying fluid based on Timoshenko beam model under two-dimensional magnetic field

Abstract: Nonlinear vibration response of coupled viscoelastic carbon nanotubes (CNTs) conveying viscous fluid is investigated based on nonlocal and modified couple stress theories. The CNTs are placed in a uniform two-dimensional (2D) magnetic field and modeled by a Timoshenko beam. The effect of slip boundary condition is considered in the Navier–Stokes relations based on the Knudsen number correction factor. The higher-order governing equations of motion are derived based on the energy method and Hamilton’s principle where the differential quadrature (DQ) approach is applied to obtain the nonlinear frequency of coupled system. A detailed parametric study is conducted, focusing on the combined effects of 2D magnetic field, Visco-Pasternak foundation, Knudsen number, surface effect, velocity of conveying viscous fluid, and different theories. Also, the Galerkin method is applied to compare our linear results to those that are obtained by the DQ approach. The results of this article could be useful in designing and manufacturing of double nano-/micromechanical systems that are usually used in advanced biomechanics and optics.