Thermo-Molecular Gas-Film Lubrication (t-MGL) Analysis in the Free Molecular Limit: Effects of Accommodation Coefficients on Static Pressure

2016 ◽  
Author(s):  
Shigehisa Fukui ◽  
Yuki Okamura ◽  
Hiroshige Matsuoka
Keyword(s):  
Temperature Distribution ◽  
Specular Reflection ◽  
Boundary Surface ◽  
Accommodation Coefficient ◽  
Molecular Gas ◽  
Temperature Distributions ◽  
Accommodation Coefficients ◽  
Molecular Gas Film Lubrication ◽  
Wedge Effect ◽  
Film Lubrication

In order to examine thermo-molecular gas film lubrication (t-MGL) characteristics with a temperature distribution at the disk or slider surfaces for spacings of several nanometers, the free molecular t-MGL equation considering temperature distributions and accommodation coefficients at the boundaries was established. By analyzing pressure generated by the wedge effect (slider inclination) and the thermal wedge effect (boundary temperature distributions), it is revealed that, as the accommodation coefficient, α0, of the running disk or the boundary surface with a temperature distribution decreases, that is, as the ratio of specular reflection increases, the pressure generation decreases, whereas as the accommodation coefficient, α1, of the stationary slider surface or the boundary surface without a temperature distribution decreases, the pressure generation increases.

Thermo-Molecular Gas-Film Lubrication (t-MGL) Considering Temperature Distributions and Accommodation Coefficients: Analyses by Quasi-Free-Molecular t-MGL Equation

2018 ◽  
Author(s):  
Shigehisa Fukui ◽  
Fumiya Shinohara ◽  
Ryota Asada ◽  
Hiroshige Matsuoka
Keyword(s):  
Specular Reflection ◽  
Flow Region ◽  
Molecular Flow ◽  
Molecular Gas ◽  
Gas Temperature ◽  
Accommodation Coefficients ◽  
Ambient Gas ◽  
Molecular Gas Film Lubrication ◽  
Local Temperature Distribution ◽  
Film Lubrication

In the present paper, the flying characteristics of a step slider flying in either air or He with a local temperature distribution of the disk are analyzed using the thermo-molecular gas-film lubrication (t-MGL) equation in the quasi-free-molecular flow region (quasi-free-molecular t-MGL equation: t-MGLqfm eq.). The gas temperature in the t-MGLqfm equation, τG, is assumed to be that in the free molecular limit, τGfm, defined by temperatures and accommodation coefficients at the disk, τW0, α0, and those at the slider, τW1, α1, respectively. The decreases in static spacing for the slider flying in He are significant. Moreover, the spacing decreases as the accommodation coefficients of the disk, α0, decreases, that is, as the ratio of specular reflection increases. The spacing fluctuation caused by a running wavy disk varies according to both the ambient gas (air/He) and the boundary accommodation coefficients.

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