Experimental Investigation of Externally Pressurized Bearings Under High Knudsen Number Conditions

1988 ◽  
Vol 110 (1) ◽  
pp. 144-147 ◽  
Author(s):  
S. Fukui ◽  
R. Kaneko
Keyword(s):  
Experimental Investigation ◽  
Boltzmann Equation ◽  
Knudsen Number ◽  
Numerical Results ◽  
Experimental Results ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Transition Flow ◽  
Lubrication Equation ◽  
Medium Vacuum

The characteristics of the externally pressurized bearings under high Knudsen number conditions were investigated experimentally by the use of surface restriction bearings in a medium vacuum on the order of 0.1 kPa (10−3 atm.). The experimental results agreed well with the numerical results calculated from a generalized lubrication equation based on the Boltzmann equation. Therefore, it would appear that this generalized lubrication equation is valid even when flows are categorized into transition flow or free molecular flow.

scholarly journals Non-equilibrium dynamics of dense gas under tight confinement

2016 ◽  
Vol 794 ◽  
pp. 252-266 ◽  
Author(s):  
Lei Wu ◽  
Haihu Liu ◽  
Jason M. Reese ◽  
Yonghao Zhang
Keyword(s):  
Boltzmann Equation ◽  
Flow Regime ◽  
Mass Flow Rate ◽  
Knudsen Number ◽  
Mass Flow ◽  
Flow Rate ◽  
Transitional Flow ◽  
Molecular Flow ◽  
Parallel Plates ◽  
The Boltzmann Equation

The force-driven Poiseuille flow of dense gases between two parallel plates is investigated through the numerical solution of the generalized Enskog equation for two-dimensional hard discs. We focus on the competing effects of the mean free path ${\it\lambda}$, the channel width $L$ and the disc diameter ${\it\sigma}$. For elastic collisions between hard discs, the normalized mass flow rate in the hydrodynamic limit increases with $L/{\it\sigma}$ for a fixed Knudsen number (defined as $Kn={\it\lambda}/L$), but is always smaller than that predicted by the Boltzmann equation. Also, for a fixed $L/{\it\sigma}$, the mass flow rate in the hydrodynamic flow regime is not a monotonically decreasing function of $Kn$ but has a maximum when the solid fraction is approximately 0.3. Under ultra-tight confinement, the famous Knudsen minimum disappears, and the mass flow rate increases with $Kn$, and is larger than that predicted by the Boltzmann equation in the free-molecular flow regime; for a fixed $Kn$, the smaller $L/{\it\sigma}$ is, the larger the mass flow rate. In the transitional flow regime, however, the variation of the mass flow rate with $L/{\it\sigma}$ is not monotonic for a fixed $Kn$: the minimum mass flow rate occurs at $L/{\it\sigma}\approx 2{-}3$. For inelastic collisions, the energy dissipation between the hard discs always enhances the mass flow rate. Anomalous slip velocity is also found, which decreases with increasing Knudsen number. The mechanism for these exotic behaviours is analysed.

Static Characteristics of Gas-Lubricated Slider Bearings Operating in a Helium-Air Mixture

1989 ◽  
Vol 111 (4) ◽  
pp. 620-627 ◽  
Author(s):  
T. Ohkubo ◽  
S. Fukui ◽  
K. Kogure
Keyword(s):  
Reynolds Equation ◽  
Mean Free Path ◽  
Linear Interpolation ◽  
Numerical Results ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Static Characteristics ◽  
Slider Bearings ◽  
Lubrication Equation ◽  
Modified Reynolds Equation

This paper outlines experimental investigations of the static characteristics of self-acting gas-lubricated slider bearings operating in a helium-air mixture. The experimental results are compared with numerical results obtained by solving a modified Reynolds equation and a generalized lubrication equation based on an equivalent molecular mean free path (MMFP) and on an equivalent viscosity derived from molecular gas dynamics. At any mole ratio of air α, the values of the equivalent MMFP are generally expected to be smaller than those of the MMFP derived from linear interpolation, whereas the values of equivalent viscosity are expected to be larger. The numerical results agree well with the experimental results within the range of α from 1.0 to 0.6. Lower values of α give a bigger difference between numerical and experimental results, and make the experimental results lower than the numerical results. Moreover, results of a generalized lubrication equation based on the Boltzmann equation give a closer prediction or qualitative tendency to the experimental results than do those based on the modified Reynolds equation.

Experimental Measurement of Energy Accommodation Coefficient by Low-Pressure Method

2009 ◽  
Author(s):  
Hiroki Yamaguchi ◽  
Yuta Aoki ◽  
Kazuaki Kanazawa ◽  
Yu Matsuda ◽  
Tomohide Niimi
Keyword(s):  
Heat Flux ◽  
Knudsen Number ◽  
Characteristic Length ◽  
Low Pressure ◽  
Accommodation Coefficient ◽  
Surface Interaction ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Pressure Method ◽  
Energy Accommodation

Heat transfer in micro flows has received much attention along with the development in micro- and nano-technology. In micro- and nano-flow fields, the Knudsen number, which is defined as a ratio of the molecular mean free path to the characteristic length of the system, becomes large because of the small characteristic length. In these so-called “high Knudsen number flows”, the number of the collision of gas molecules to the surface is much larger than that of intermolecular collisions. Therefore, it is important for the high Knudsen number flows to understand the gas-surface interaction. Since detailed science of the gas-surface interaction is complicated, the empirical parameter called the accommodation coefficient is widely used for flow analyses of the flows. In this study, the energy accommodation coefficient for metal surface has been measured experimentally by the Low-Pressure method, in which the energy accommodation coefficient is obtained from the pressure dependency of the heat flux in the free-molecular flow regime. It is not easy to realize the free-molecular flow condition, and, thus, the relation between the heat flux and the pressure extended to much higher pressure condition was employed in this study. Experimental geometry was designed as concentric cylinders, and heat flux between two cylinders, whose surface temperatures was different, was measured. Experimental results are reported for argon and oxygen in contact with a platinum surface. The surface temperature dependence of the energy accommodation coefficient was also studied, and verified by the results of previous work.

Improvement of performance of bolt–nut connections, Part II: Experimental investigation

2014 ◽  
Vol 228 (17) ◽  
pp. 3078-3089 ◽  
Author(s):  
GH Majzoobi ◽  
M Agh-Mohammad Dabbagh ◽  
P Asgari ◽  
MK Pipelzadeh ◽  
SJ Hardy
Keyword(s):  
Experimental Investigation ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Resistance ◽  
Numerical Results ◽  
Experimental Results ◽  
Axial Hole ◽  
Experiment And Simulation

In this work, bolt and nut geometries are modified for the improvement of fatigue life of the bolt–nut connections. The modifications are aimed at reducing the stress concentration at the thread roots by factors such as reducing the shank diameter, making axial hole in bolt, stepping the nut and their combinations. The effect of modifications is studied by experiment and simulation. The experimental results show that all types of modifications considered result in an improvement in the fatigue resistance of bolt–nut connections but to different extents. However, the effects of the two latter types are more significant. The most improvement is achieved for the case when all types of modifications are combined together. In this case, fatigue life can be increased by almost 100%. Numerical results also show that all types of modifications lead to the reduction of stress concentration.

A Database for Interpolation of Poiseuille Flow Rates for High Knudsen Number Lubrication Problems

1990 ◽  
Vol 112 (1) ◽  
pp. 78-83 ◽  
Author(s):  
S. Fukui ◽  
R. Kaneko
Keyword(s):  
Boltzmann Equation ◽  
Knudsen Number ◽  
Flow Rate ◽  
Poiseuille Flow ◽  
Interpolation Method ◽  
Numerical Calculations ◽  
Flow Rates ◽  
Lubrication Equation ◽  
Linearized Boltzmann Equation ◽  
Rapid Calculation

This paper proposes the use of a Poiseuille flow rate database for rapid calculation of a generalized lubrication equation for high Knudsen number gas films. The database is created by numerical calculations based on the linearized Boltzmann equation. The proposed interpolation method is verified to reduce calculation time to several tenths of that required to perform rigorous calculations with the same accuracy.

Dynamic Characteristics of Gas-Lubricated Slider Bearings Under High Knudsen Number Conditions

1990 ◽  
Vol 112 (1) ◽  
pp. 111-118 ◽  
Author(s):  
T. Hayashi ◽  
S. Fukui ◽  
T. Ohkubo ◽  
R. Kaneko
Keyword(s):  
Boltzmann Equation ◽  
Knudsen Number ◽  
Dynamic Characteristics ◽  
Slip Flow ◽  
Magnetic Disk ◽  
Storage Devices ◽  
Disk Storage ◽  
Slider Bearings ◽  
Lubrication Equation ◽  
Flow Approximation

This paper presents numerical analyses of the dynamic characteristics of gas-lubricated slider bearings under high Knudsen number conditions using a generalized lubrication equation based on the the Boltzmann equation. These analyses are compared with those of the slip flow approximation equations and the differences are clarified. The present analysis is applied to the dynamic response of flying head sliders for magnetic disk storage devices. For a small slider with ultra-thin spacing, the deviations of the slip flow approximation equations are remarkable in regard to steady flying characteristics, but insignificant in regard to dynamic characteristics.

scholarly journals Simulation of Gas Transport in Tight/Shale Gas Reservoirs by a Multicomponent Model Based on PEBI Grid

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Longjun Zhang ◽  
Daolun Li ◽  
Lei Wang ◽  
Detang Lu
Keyword(s):  
Shale Gas ◽  
Slip Flow ◽  
Gas Production ◽  
Darcy Flow ◽  
Molecular Flow ◽  
Flow Transition ◽  
Free Molecular Flow ◽  
Transition Flow ◽  
Gas Reservoirs ◽  
Fracture Length

The ultra-low permeability and nanosize pores of tight/shale gas reservoir would lead to non-Darcy flow including slip flow, transition flow, and free molecular flow, which cannot be described by traditional Darcy’s law. The organic content often adsorbs some gas content, while the adsorbed amount for different gas species is different. Based on these facts, we develop a new compositional model based on unstructured PEBI (perpendicular bisection) grid, which is able to characterize non-Darcy flow including slip flow, transition flow, and free molecular flow and the multicomponent adsorption in tight/shale gas reservoirs. With the proposed model, we study the effect of non-Darcy flow, length of the hydraulic fracture, and initial gas composition on gas production. The results show both non-Darcy flow and fracture length have significant influence on gas production. Ignoring non-Darcy flow would underestimate 67% cumulative gas production in lower permeable gas reservoirs. Gas production increases with fracture length. In lower permeable reservoirs, gas production increases almost linearly with the hydraulic fracture length. However, in higher permeable reservoirs, the increment of the former gradually decreases with the increase in the latter. The results also show that the presence of CO2in the formation would lower down gas production.

Heat flux correlation for high-speed flow in the transitional regime

2016 ◽  
Vol 792 ◽  
pp. 981-996 ◽  
Author(s):  
Narendra Singh ◽  
Thomas E. Schwartzentruber
Keyword(s):  
Heat Flux ◽  
Flow Regime ◽  
Stagnation Point ◽  
High Speed ◽  
Higher Order ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Burnett Equations ◽  
Transition Flow ◽  
Stagnation Point Heat Flux

An analytical correlation is developed for stagnation-point heat flux on spherical objects travelling at high velocity which is accurate for conditions ranging from the continuum to the free-molecular flow regime. Theoretical analysis of the Burnett and super-Burnett equations is performed using simplifications from shock-wave and boundary-layer theory to determine the relative contribution of higher-order heat flux terms compared with the Fourier heat flux (assumed in the Navier–Stokes equations). A rarefaction parameter ($W_{r}\equiv M_{\infty }^{2{\it\omega}}/Re_{\infty }$), based on the free-stream Mach number ($M_{\infty }$), the Reynolds number ($Re_{\infty }$) and the viscosity–temperature index (${\it\omega}$), is identified as a better correlating parameter than the Knudsen number in the transition regime. By studying both the Burnett and super-Burnett equations, a general form for the entire series of higher-order heat flux contributions is obtained. The resulting heat flux expression includes terms with dependence on gas properties, stagnation to wall-temperature ratio and a main dependence on powers of the rarefaction parameter $W_{r}$. The expression is applied as a correction to the Fourier heat flux and therefore can be combined with any continuum-based correlation of choice. In the free-molecular limit, a bridging function is used to ensure consistency with well-established free-molecular flow theory. The correlation is then fitted to direct simulation Monte Carlo (DSMC) solutions for stagnation-point heat flux in high-speed nitrogen flows. The correlation is shown to accurately capture the variation in heat flux predicted by the DSMC method in the transition flow regime, while limiting to both continuum and free-molecular values.

THE INFLUENCE OF SURFACE ROUGHNESS ON SCATTERING OF FREE-MOLECULAR FLOW BY SOLID BODIES

2016 ◽  
Vol 47 (4) ◽  
pp. 367-388 ◽  
Author(s):  
Alexander Ivanovich Erofeev ◽  
Alexander Petrovich Nikiforov ◽  
Sergei Borisovich Nesterov ◽  
Ramul'ya Amirovna Nezhmetdinova
Keyword(s):  
Surface Roughness ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Solid Bodies

Study of drag molecular dynamics in the range of free-molecular flow.

Shinku ◽  
1990 ◽  
Vol 33 (3) ◽  
pp. 98-100
Author(s):  
N. LIU ◽  
S. J. PANG
Keyword(s):  
Molecular Dynamics ◽  
Molecular Flow ◽  
Free Molecular Flow
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