Mean Free Path Effect in Spiral-Grooved Thrust Bearings

1969 ◽  
Vol 91 (1) ◽  
pp. 69-78 ◽  
Author(s):  
F. C. Hsing ◽  
S. B. Malanoski
Keyword(s):  
Free Path ◽  
Thrust Bearing ◽  
Ambient Pressure ◽  
Slip Flow ◽  
Substantial Reduction ◽  
Mean Free Path ◽  
Slip Boundary Conditions ◽  
Thrust Bearings ◽  
Slip Boundary ◽  
Steady State Performance

The objective of this paper is to study the effect of molecular mean free path on the steady-state performance characteristics of a spiral-grooved thrust bearing operating in extremely thin film and/or low ambient pressure environments. Numerical results for the most popular three versions of the spiral-grooved designs are presented. These results reveal that the effect of slip boundary conditions could contribute substantial reduction, in performance. Helium is the worst gas lubricant in this sense because of its high Knudsen number. The slip-flow corrected results check well with recently published experimental data [11].

The Influence of Ambient Pressure on the Measured Load Capacity of Bump-Foil and Spiral-Groove Gas Thrust Bearings at Ambient Pressures up to 69 Bar on a Novel High-Pressure Gas Bearing Test Rig

2019 ◽  
Author(s):  
Jason Wilkes ◽  
Ryan Cater ◽  
Erik Swanson ◽  
Kevin Passmore ◽  
Jerry Brady
Keyword(s):  
Power Loss ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Ambient Pressure ◽  
Spiral Groove ◽  
Test Rig ◽  
Thrust Bearings ◽  
Order Of Magnitude ◽  
Foil Thrust Bearing ◽  
Thrust Load

Abstract This paper will show the influence of ambient pressure on the thrust capacity of bump-foil and spiral-groove gas thrust bearings. The bearings were operating in nitrogen at various pressures up to 69 bar, and were tested to failure. Failure was detected at various pressures by incrementally increasing the thrust load applied to the thrust bearing until the bearing was no longer thermally stable, or until contact was observed by a temperature spike measured by thermocouples within the bearing. These tests were performed on a novel thrust bearing test rig that was developed to allow thrust testing at pressures up to 207 bar cavity pressure at 260°C while rotating at speeds up to 120,000 rpm. The test rig floats on hydrostatic air bearings to allow for the direct measurement of applied thrust load through linkages that connect the stationary thrust loader to the rotor housing. Test results on a 65 mm (2.56 in) bump-foil thrust bearing at 100 krpm show a marked increase in load capacity with gas density, which has not previously been shown experimentally. Results also show that the load capacity of a similarly sized spiral-groove thrust bearing are relatively insensitive to pressure, and supported an order-of-magnitude less load than that observed for the bump-foil thrust bearing. These results are compared with analytical predictions, which agree reasonably with the experimental results. Predicted power loss is also presented for the bump-foil bearing; however, measured power loss was substantially higher.

Poiseuille Number Correlations of Gas Flow in Concentric Micro Annular Tubes

2008 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Boundary Conditions ◽  
Gas Flow ◽  
Slip Flow ◽  
Tube Length ◽  
Slip Boundary Conditions ◽  
Slip Boundary ◽  
Rarefaction Effect ◽  
Wide Range ◽  
Poiseuille Number ◽  
Fast Flow

Poiseuille number, the product of friction factor and Reynolds number (f · Re) for quasi-fully developed concentric micro annular tube flow was obtained for both no-slip and slip boundary conditions. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The compressible momentum and energy equations were solved for a wide range of Reynolds and Mach numbers for both isothermal flow and no heat conduction flow conditions. The detail of the incompressible slip Poiseuille number is kindly documented and its value defined as a function of r* and Kn is represented. The outer tube radius ranges from 50 to 150μm with the radius ratios of 0.2, 0.5 and 0.8 and selected tube length is 0.02m. The stagnation pressure, pstg is chosen in such away that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure is fixed at the atmospheric pressure. In the case of fast flow, the value of f · Re is higher than that of incompressible slip flow theory due to the compressibility effect. However in the case of slow flow the value of f · Re is slightly lower than that of incompressible slip flow due to the rarefaction effect, even the flow is accelerated. The value of f · Re obtained for no-slip boundary conditions is compared with that of obtained for slip boundary conditions. The values of f · Re obtained for slip boundary conditions are predicted by f · Re correlations obtained for no-slip boundary conditions since rarefaction effect is relatively small for the fast flow.

Photoelectron spectroscopy of wet and gaseous samples through graphene membranes

Nanoscale ◽  
2014 ◽  
Vol 6 (23) ◽  
pp. 14394-14403 ◽  
Author(s):  
Jürgen Kraus ◽  
Robert Reichelt ◽  
Sebastian Günther ◽  
Luca Gregoratti ◽  
Matteo Amati ◽  
...  
Keyword(s):  
Free Path ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Mean Free Path ◽  
Electron Spectrometer ◽  
Dense Media ◽  
Electron Mean Free Path ◽  
Sample Environment ◽  
Graphene Membranes

Due to the short electron mean free path in dense media samples in liquid or ambient pressure environment cannot be easily characterized by photoelectron spectroscopy. We overcome this limitation by employing electron transparent graphene membranes to separate the sample environment from the vacuum conditions in the electron spectrometer.

Gaseous Slip Flow Mixed Convection in Vertical Microducts With Constant Axial Energy Input

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Arman Sadeghi ◽  
Mostafa Baghani ◽  
Mohammad Hassan Saidi
Keyword(s):  
Nusselt Number ◽  
Pressure Drop ◽  
Boundary Conditions ◽  
Mixed Convection ◽  
Cross Sections ◽  
Slip Flow ◽  
Constant Heat Flux ◽  
Slip Boundary Conditions ◽  
First Order ◽  
Slip Boundary

The present investigation is devoted to the fully developed slip flow mixed convection in vertical microducts of two different cross sections, namely, polygon, with circle as a limiting case, and rectangle. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first-order slip boundary conditions. The method considered is mainly analytical in which the governing equations in cylindrical coordinates along with the symmetry conditions and finiteness of the flow parameter at the origin are exactly satisfied. The first-order slip boundary conditions are then applied to the solution using the point matching technique. The results show that both the Nusselt number and the pressure drop parameter are increasing functions of the Grashof to Reynolds ratio. It is also found that, with the exception of the H2 Nusselt number of the triangular duct, which shows an opposite trend, both the Nusselt number and the pressure drop are decreased by increasing the Knudsen number. Furthermore, the pressure drop of the H2 case is found to be higher than that obtained by assuming an H1 thermal boundary condition.

The Effect of Viscous Dissipation on Two-Dimensional Microchannel Heat Transfer

2006 ◽  
Author(s):  
Jennifer van Rij ◽  
Tim Ameel ◽  
Todd Harman
Keyword(s):  
Heat Transfer ◽  
Viscous Dissipation ◽  
Slip Flow ◽  
Second Order ◽  
Slip Boundary Conditions ◽  
Pressure Work ◽  
Axial Conduction ◽  
Slip Boundary ◽  
Nusselt Numbers ◽  
Slip Flow Regime

Microchannel convective heat transfer characteristics in the slip flow regime are numerically evaluated for two-dimensional, steady state, laminar, constant wall heat flux and constant wall temperature flows. The effects of Knudsen number, accommodation coefficients, viscous dissipation, pressure work, second-order slip boundary conditions, axial conduction, and thermally/hydrodynamically developing flow are considered. The effects of these parameters on microchannel convective heat transfer are compared through the Nusselt number. Numerical values for the Nusselt number are obtained using a continuum based three-dimensional, unsteady, compressible computational fluid dynamics algorithm that has been modified with slip boundary conditions. Numerical results are verified using analytic solutions for thermally and hydrodynamically fully developed flows. The resulting analytical and numerical Nusselt numbers are given as a function of Knudsen number, the first- and second-order velocity slip and temperature jump coefficients, the Peclet number, and the Brinkman number. Excellent agreement between numerical and analytical data is demonstrated. Viscous dissipation, pressure work, second-order slip terms, and axial conduction are all shown to have significant effects on Nusselt numbers in the slip flow regime.

Method of Submerged Stokeslets for Slip Flow About Ensembles of Particles

2008 ◽  
Vol 8 (7) ◽  
pp. 3790-3801
Author(s):  
Shunliu Zhao ◽  
Alex Povitsky
Keyword(s):  
Boundary Conditions ◽  
Self Assembly ◽  
Slip Flow ◽  
Chemical Vapor ◽  
Partial Slip ◽  
Slip Boundary Conditions ◽  
Slip Boundary ◽  
Singularity Method ◽  
Low Reynolds Number Flows ◽  
Micro Pump

A boundary singularity method with submerged Stokeslets is applied to the low Reynolds number flows about a set of spheres. Newtonian fluid is considered with no slip or partial slip boundary conditions at the wall. The validity of the method for Stokes flows about representative sets of spheres is investigated. The considered cases include (i) a uniform flow about a stationary set of particles typical for filtration and chemical vapor deposition, (ii) a flow induced by particles moving toward each other typical for self-assembly processes and (iii) a flow induced by spinning particles typical for micro-pump applications. The dependence of the flowfield on the number of Stokeslets is investigated in order to establish the needed number of Stokeslets. Comparison of flow field for the no-slip (Kn = 0) and partial-slip boundary conditions (Kn = 0.1) shows that the partial slip at the particles' surface significantly affect the velocity field and pressure distribution.

Rayleigh Problem in Slip Flow With Modified Initial Conditions

1967 ◽  
Vol 34 (4) ◽  
pp. 833-836 ◽  
Author(s):  
K. C. Reddy
Keyword(s):  
Temperature Jump ◽  
Initial Conditions ◽  
Slip Flow ◽  
Velocity Slip ◽  
Slip Boundary Conditions ◽  
Flow Conditions ◽  
Slip Boundary ◽  
Rayleigh Problem ◽  
Molecule Flow ◽  
The Continuum

The initial conditions of the linearized Rayleigh problem in slip flow are modified so as to satisfy the free molecule flow conditions at the start of the motion. Approximate initial profiles for velocity and temperature are chosen which would yield correct values of velocity slip, temperature jump, and so on, at the start of the motion. The continuum solutions with the modified initial conditions and slip boundary conditions are found to be uniformly valid for all times of motion and agree well with the results of the kinetic theory analyses of the problem.

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