Effect of Adsorbed Layer on Methane Flow in Silicon Nano Slits for Different Channel Heights

Abstract

The pressure-driven flow of methane in silicon nano slits is analytically studied by using Zhang’s multiscale scheme for the wide channel heights ranging between 8.6nm and 1444 nm when there is the intermediate (continuum or quasi-continuum) fluid film between the two adsorbed layers and no wall slippage occurs. The values of the characteristic parameters of the adsorbed layer required by Zhang’s approach was found from molecular dynamics simulation, and they are considered as independent on the channel height. According to the calculation results, the adsorbed layer encumbers the flow in the whole channel especially for the low channel heights which give the ratio of the thickness (h_bf) of the adsorbed layer to the thickness (h) of the intermediate continuum fluid film no less than 0.1, and this makes the total volume flow rate through the channel about 35% smaller than the classical Hagen-Poiseuille equation calculation. The flow is not sensitive to the variation of the value of the ratio (q₀) of the neighboring fluid molecule separations across the adsorbed layer thickness once the thickness of the adsorbed layer is fixed. With the increase of the channel height, the effect of the adsorbed layer is weakened. When h_bf/h<=0.01, the reduction of the total flow rate through the channel owing to the adsorbed layer is no more than 5.5% and the effect of the adsorbed layer can be considered as negligible. These disciplines of the Poiseuille flow in nanochannels renders the great application values of the adsorbed layer in improving the load-carrying capacity of micro bearings with very low clearances.