Analysis and Comparison of the Models for the Rarefied Gas Effect on Gas Lubrication

2014 ◽  
Vol 577 ◽  
pp. 289-292
Author(s):  
Shuai Zhang ◽  
Peng Yun Song
Keyword(s):  
Knudsen Number ◽  
Flow Rate ◽  
Dynamic Viscosity ◽  
Effective Viscosity ◽  
Rarefied Gas ◽  
Viscosity Coefficients ◽  
Gas Lubrication ◽  
Rarefied Gas Effect ◽  
Gas Effect ◽  
Inverse Knudsen Number

Ultrathin gas film lubrication has been widely used in recent years, such as dry gas seal face gas lubrication, gas lubrication in the hard disk drive, etc. The rarefied gas effect must be considered when the gas film thickness is very thin. In order to analyze, compare, and select the appropriate rarefied effect model on gas lubrication, a comparative analysis has been carried out on the influence laws of the Poiseuille flow rate and the ratio of the effective viscosity coefficients and the dynamic viscosity, μeff/μ, with inverse Knudsen number, D ,or Knudsen number, Kn, as to different models. The results show that when inverse Knudsen number increases or Knudsen number decreases, the Poiseuille flow rate and the ratio of the effective viscosity coefficients and the dynamic viscosity,μeff/μ, of different models approach to each other. However, there are significant differences as to different models when the Knudsen number is large, and only several models from Hwang, Veijola, Peng etc agree with Fukui’s model.

scholarly journals Simulation of Gas Flow Over a Micro Cylinder

2009 ◽  
Author(s):  
Yuan Hu ◽  
Quanhua Sun ◽  
Jing Fan
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Drag Coefficient ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Low Reynolds Number ◽  
Pressure Drag ◽  
Low Reynolds ◽  
Rarefied Gas Effect ◽  
Gas Effect

Gas flow over a micro cylinder is simulated using both a compressible Navier-Stokes solver and a hybrid continuum/particle approach. The micro cylinder flow has low Reynolds number because of the small length scale and the low speed, which also indicates that the rarefied gas effect exists in the flow. A cylinder having a diameter of 20 microns is simulated under several flow conditions where the Reynolds number ranges from 2 to 50 and the Mach number varies from 0.1 to 0.8. It is found that the low Reynolds number flow can be compressible even when the Mach number is less than 0.3, and the drag coefficient of the cylinder increases when the Reynolds number decreases. The compressible effect will increase the pressure drag coefficient although the friction coefficient remains nearly unchanged. The rarefied gas effect will reduce both the friction and pressure drag coefficients, and the vortex in the flow may be shrunk or even disappear.

Plane Thermal Transpiration of a Rarefied Gas Between Two Walls of Maxwell-Type Boundaries With Different Accommodation Coefficients

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Toshiyuki Doi
Keyword(s):  
Boltzmann Equation ◽  
Mass Flow Rate ◽  
Knudsen Number ◽  
Mass Flow ◽  
Flow Rate ◽  
Poiseuille Flow ◽  
Rarefied Gas ◽  
Thermal Transpiration ◽  
Wide Range ◽  
Accommodation Coefficients

Plane thermal transpiration of a rarefied gas between two walls of Maxwell-type boundaries with different accommodation coefficients is studied based on the linearized Boltzmann equation for a hard-sphere molecular gas. The Boltzmann equation is solved numerically using a finite difference method, in which the collision integral is evaluated by the numerical kernel method. The detailed numerical data, including the mass and heat flow rates of the gas, are provided over a wide range of the Knudsen number and the entire range of the accommodation coefficients. Unlike in the plane Poiseuille flow, the dependence of the mass flow rate on the accommodation coefficients shows different characteristics depending on the Knudsen number. When the Knudsen number is relatively large, the mass flow rate of the gas increases monotonically with the decrease in either of the accommodation coefficients like in Poiseuille flow. When the Knudsen number is small, in contrast, the mass flow rate does not vary monotonically but exhibits a minimum with the decrease in either of the accommodation coefficients. The mechanism of this phenomenon is discussed based on the flow field of the gas.

Rarefied gas effect in hypersonic shear flows

2021 ◽  
Vol 37 (1) ◽  
pp. 2-17
Author(s):  
Jie Chen ◽  
Heng Zhou
Keyword(s):  
Shear Flows ◽  
Rarefied Gas ◽  
Rarefied Gas Effect ◽  
Gas Effect

scholarly journals Объемная вязкость суспензии наночастиц оксида кремния

2020 ◽  
Vol 46 (12) ◽  
pp. 37
Author(s):  
М.И. Пряжников ◽  
А.В. Минаков
Keyword(s):  
Attenuation Coefficient ◽  
Bulk Viscosity ◽  
Dynamic Viscosity ◽  
Aqueous Suspension ◽  
Sio2 Nanoparticles ◽  
Nanoparticle Concentration ◽  
Viscosity Coefficients ◽  
Wide Range ◽  
First Time ◽  
Mass Concentrations

Data on the bulk viscosity of an aqueous suspension of SiO2 nanoparticles (Ludox TM-50) were obtained using an acoustic spectrometer for the first time. A wide range of mass concentrations of nanoparticles (from 1 to 50 wt.%) was considered. The spectra of the attenuation coefficient of ultrasound and the coefficients of longitudinal and dynamic viscosity were measured. The dependences of the dynamic and bulk viscosity coefficients of the suspensions on the nanoparticle concentration were obtained.

Study of methods for estimating the viscosity coefficient of metals

2021 ◽  
Author(s):  
S.V. Serikov ◽  
I.K. Ustinov ◽  
O.V. Sulina
Keyword(s):  
Dynamic Viscosity ◽  
Theoretical Study ◽  
Human Life ◽  
Viscosity Coefficient ◽  
Practical Significance ◽  
Accurate Assessment ◽  
Viscosity Coefficients ◽  
Dynamic Yield Strength ◽  
Dynamic Yield ◽  
Problem Setting

Problem setting. The coefficient of dynamic viscosity of metals is used in many branches of human life, but its search, for a more accurate assessment and interpretation, is currently insufficiently studied due to the variety of its application [1-4], as well as due to the uncertainty of the constant parameters of the environment in which it is applied or investigated. Target. Consider a number of known methods for estimating the viscosity coefficients of metals at different ranges of strain patterns. Results. The methods considered for estimating the viscosity coefficient of metals, during their scientific and theoretical study, did not give an unambiguous answer for determining the viscosity of metals. Practical significance. Further study of the dynamic yield strength and the dynamic viscosity coefficient of metals is necessary to achieve more complete results of the method of evaluating the viscosity coefficient of metals.

Sign in / Sign up

Export Citation Format

Share Document