Thermo-molecular gas-film lubrication (t-MGL) considering temperature distributions and accommodation coefficients: analyses by quasi-free-molecular t-MGL equation
Thermo-molecular gas-film lubrication (t-MGL) considering temperature distributions and accommodation coefficients: analyses by quasi-free-molecular t-MGL equation
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考虑温度分布和调节系数的热分子气膜润滑（t-MGL）：通过准自由分子 t-MGL 方程进行分析
DOI：
10.1007/s00542-019-04642-6
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Hiroshige Matsuoka
中科院分区：
文献类型：
--
作者：
Shigehisa Fukui;Fumiya Shinohara;Ryota Asada;Hiroshige Matsuoka
本文利用热分子气膜润滑（t-MGL）方程，分析了具有局部温度分布和表面调节系数不完全的、表面分子反射为漫反射（α）和镜面反射（1−α）（麦克斯韦型反射）混合的固定平面倾斜滑块（案例1）和在空气或He中飞行的阶梯滑块（案例2）在流动边界壁上的空气承载特性。特别地，由于最小间距超小（~ 1 nm），因此采用准自由分子t-MGL方程，其中气体温度τG假设为自由分子极限τGfm，分别由圆盘处的温度和调节系数τ w0和α0以及滑块处的温度和调节系数τ w1和α1定义。对于平面倾斜滑块（Case 1），数值分析了滑块的基本静动态特性，并与无限承载数（t-MGLqfm，Λ→∞）的近似结果进行了比较。当间隙超小且只有运行边界（盘）有局部温度分布时，局部边界温度分布产生的附加静压近似正比于等效调节系数γα≡α0(2-α1)/[2{1-(1-α0)(1-α1)}]。对于阶跃滑块（情形2），结果表明：(1)随着圆盘调节系数α0的减小，滑块间距减小。在磁盘,镜面反射的比例增加,(2)提高最低间距由于地方在空气温度分布可以忽略不计,他因为加热光斑尺寸很小,(3)的最小间距的减小滑块在他很重要,和(4)的空间波动引起的波浪运行磁盘根据不同表面住宿系数和周围气体(空气/他),可以精确估计。
In the present paper, the air-bearing characteristics of a fixed plane inclined slider (Case 1) and a step slider flying in either air or He (Case 2) over a running boundary wall with local temperature distributions and imperfect surface accommodation coefficients, the molecular reflections at the surface of which are a mixture of diffuse reflection (α) and specular reflection (1−α) (Maxwell-type reflection), are analyzed using the thermo-molecular gas-film lubrication (t-MGL) equation. In particular, since the minimum spacing is ultra-small (~ 1 nm), the quasi-free-molecular t-MGL equation, in which the gas temperature,τG, is assumed to be that in the free molecular limit,τGfm, defined by temperatures and accommodation coefficients at the disk,τW0andα0, respectively, and those at the slider,τW1andα1, respectively, is used. For a plane inclined slider (Case 1), the fundamental static and dynamic characteristics are analyzed numerically and are compared with the approximation results for an infinite bearing number (t-MGLqfm,Λ→∞). When the spacing is ultra-small and only the running boundary (disk) has a local temperature distribution, the additional static pressure produced by the local boundary temperature distribution is approximately proportional to the equivalent accommodation coefficient γα≡α0(2-α1)/[2{1-(1-α0)(1-α1)}]. For a step slider (Case 2), the following results are revealed: (1) the spacing decreases occur as the accommodation coefficient of the disk,α0, decreasei.e., the ratio of specular reflection at the disk increases, (2) the increases in the minimum spacing due to local temperature distribution are negligible in both air and He because the heat spot size is very small, (3) the decreases in the minimum spacing for a slider flying in He are significant, and (4) the spacing fluctuation caused by a running wavy disk varies according to both the surface accommodation coefficients and the ambient gas (air/He) and can be estimated precisely.
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