scholarly journals Drag and Thermal Force on a Spherical Particle in a Rarefied Gas. Effect of the Thermal Conductivity of the Particle.

Shinku ◽  
1994 ◽  
Vol 37 (3) ◽  
pp. 151-154
Author(s):  
Shigeru TAKATA ◽  
Yoshio SONE
Keyword(s):  
Thermal Conductivity ◽  
Spherical Particle ◽  
Rarefied Gas ◽  
Rarefied Gas Effect ◽  
Gas Effect

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.

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.

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 Simulation of thermal conductivity of rare gases by the stochastic method

2021 ◽  
pp. 19-29
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Modeling ◽  
Transfer Process ◽  
Thermal Conductivity Coefficient ◽  
Rarefied Gas ◽  
Molecular Dynamics Method ◽  
Gas Transfer ◽  
Polyatomic Gases ◽  
Dynamics Method

One of the main successes of the kinetic theory of gases is the explicit calculation of the transport coefficients of rarefied gases. However, the greatest problems arise when calculating the thermal conductivity coefficient, especially for polyatomic gases. Also, when using different potentials, it is necessary to systematically calculate the so-called Ω-integrals, which in itself is a rather difficult task. For this reason, direct numerical molecular modeling of the processes of transfer of rarefied gases, in particular, the calculation of their transfer coefficients, is also relevant. A well-known method for such modeling is the molecular dynamics method. Unfortunately, until now this method is not available for modeling the processes of rarefied gas transfer. Under nor-mal conditions, the simulation cell should contain tens or even hundreds of millions of molecules during calculations. At the same time, the numerical implementation of the molecular dynamics method is accompanied by a systematic appearance of errors, which is the reason for the appearance of dynamic chaos. With this simulation, the true phase trajectories of the system under consideration cannot be obtained. Therefore, naturally, the idea of developing a method for modeling transport processes arises, in which phase trajectories are not calculated based on Newton's laws, but are simulated, and then are used to calculate any observables. In our works, we developed a method of stochastic molecular modeling (STM) of rarefied gas transfer processes, where this idea was implemented. The efficiency of the SMM method was demonstrated by calculating the coefficients of self-diffusion, diffusion, and viscosity of both monoatomic gases and polyatomic gases. At the same time, the possibility of modeling the most complex transfer process – the energy transfer process – has not yet been considered. This work aims to simulate the thermal conductivity coefficient by the SMM method. Both monoatomic (Ar, Kr, Ne, Xe) and polyatomic gases (CH4, O2) were considered.

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