纳米尺度下气体薄膜润滑理论研究

Ultrathin Gas Film Lubrication Theory at Nanoscale

提出了依赖于逆Knudsen数的纳米尺度影响因子NP,修正了目前应用较为普遍的FK-Boltzmann模型,并给出了其数值计算结果.结果表明:当膜厚小于单个空气分子平均自由程时,由于纳米尺度效应的影响,流量因子有所减小,承载能力略微增加.

The current thickness of the gas film in air bearing of modern hard disk drives is only one order of magnitude larger than the diameter of gas molecules. At such a small thickness, the nanoscale effect cannot be neglected. Therefore, it is essential to understand the behavior of the ultrathin gas film lubrication. Thus a nanoscale effect function, N_p, is proposed, with the unidirectional flow of the rarefied gas between two parallel plates to be investigated based on the kinetic theory and the gas behavior in the near boundary regime to be focused on. The function N_p is dependent on the inverse Knudsen number, D, which characterizes the gas rarefaction. The FK-Boltzmann lubrication model in current use is therefore modified by taking into account N_p. And the numerical calculations with respect to a rarefied gas system confined between two infinite flat plates are carried out based on the modified Reynolds equations. It has been found that the nanoscale effect is minute and can be ignored when the inverse Knudsen number is larger than 1.772. However, when the inverse Knusden number is smaller than 0.886,the nanoscale effect is prominent, which leads to a significant reduce of the flow rate and slight increase of the pressure gradient and load capacity. This indicates that the nanoscale effect plays an important role in ultrathin gas film lubrication.