A Molecular Dynamics Study on Energy Accommodation Coefficients in Microchannels

2008 ◽  
Author(s):  
Jun Sun ◽  
Zhixin Li
Keyword(s):  
Temperature Difference ◽  
Wall Temperature ◽  
Gas Flow ◽  
Accommodation Coefficient ◽  
Energy Accommodation ◽  
Micro Gas Flow ◽  
Different Temperatures ◽  
Accommodation Coefficients ◽  
Lower Temperature ◽  
Non Equilibrium

Energy accommodation coefficient (EAC), used in thermal boundary condition in micro gas flow and heat transfer, is reported to be always less than unity and greatly influenced by the wall characters. According to EAC’s definition, the statistical algorithm was described and EAC for argon gas was studied by two dimensional NEMD simulations with heat conduction between two smooth platinum plates at different temperatures. With one wall’s temperature fixed, the non-equilibrium EACs were calculated by changing the other wall’s temperature. Meanwhile, the equilibrium EAC at one temperature can be extrapolated from a series of non-equilibrium EACs as the temperature difference approaches to zero. The effects of wall temperature, wall temperature difference, and Kn on EAC were investigated. Non-equilibrium EAC increases with wall temperature difference decreased, and becomes larger with increased Kn. And equilibrium EAC is larger for lower temperature and larger Kn.

Molecular Dynamics Study on the Effect of Adsorbed Layer on Accommodation Coefficients in Micro Gas Flow

2008 ◽  
Author(s):  
Jun Sun ◽  
Zhixin Li
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Driving Forces ◽  
Adsorbed Layer ◽  
Accommodation Coefficient ◽  
Micro Channels ◽  
Adsorbed Layers ◽  
Micro Gas Flow ◽  
Accommodation Coefficients ◽  
Wall Interactions

Tangential momentum accommodation coefficient (TMAC) is reported to be less than unity in rarefied gas flow and greatly influenced by many factors such as temperature and adsorbed layers. According to the definition, a proper statistical algorithm in NEMD method is described and verified. Adsorbed layers occur on walls due to strong gas-wall interactions and the effect on TMAC are studied in two dimensional isothermal Poiseuille flow in smooth micro-channels under the conditions of various temperatures, driving forces, and Kn. The simulation results indicate that when gas-wall interactions become stronger, TMAC increases to maximum firstly and decreases a little. Besides, the effects of temperature and Kn on TMAC are not monotonous with the existence of adsorbed layer. In addition, normal momentum accommodation coefficient (NMAC) is almost unity for isothermal flow in smooth microchannels.

A quantum mechanical theory of energy exchanges between inert gas atoms and a solid surface

1932 ◽  
Vol 28 (1) ◽  
pp. 136-164 ◽  
Author(s):  
J. M. Jackson
Keyword(s):  
Solid Surface ◽  
Accommodation Coefficient ◽  
Solid Surfaces ◽  
Order Unity ◽  
True Value ◽  
A Value ◽  
Quantum Mechanical Theory ◽  
Different Temperatures ◽  
Accommodation Coefficients ◽  
Energy Exchanges

The interaction between gas atoms and solid surfaces has been studied experimentally for many years. The first detailed study of the nature of this interaction was perhaps due to Knudsen, who in his classical researches introduced the idea of the accommodation coefficients for energy or momentum exchanges between gas atoms and a solid surface, when the gas atoms and the solid are at different temperatures or possess different mass motions. Knudsen and other investigators have given numerical values for these accommodation coefficients for various gases and solid surfaces, which seem to indicate that the accommodation coefficients are never small and are often of the order unity. This means that the gas molecules before reflection accommodate themselves almost completely to equilibrium with the temperature or motion of the wall. Before the recent work of Roberts referred to below, which has inspired this paper, no special precautions had been taken in the preparation of the wall surface, and as we now know the walls used by all previous investigators must have been completely covered with at least a mono-molecular film of gas. Thus the old observations of the accommodation coefficient do not determine it under precise conditions, and find in fact a value many times larger than that found by Roberts for the energy exchanges between the gas and a clean tungsten surface. For helium and metal with a dirty surface the value of the accommodation coefficient is some 6 times as large as the true value for the clean surface. The older values of the coefficients were so large that there were apparently grave difficulties in the way of any simple theory, but this is so no longer.

An Estimation in the Recovery factor of Micro Gas Flow by Measuring the Adiabatic Wall Temperature

2018 ◽  
Vol 2018.71 (0) ◽  
pp. B26
Author(s):  
Takayuki SHIGEISHI ◽  
Chungpyo HONG ◽  
Yutaka ASAKO ◽  
Hiroshi KATANODA
Keyword(s):  
Wall Temperature ◽  
Gas Flow ◽  
Recovery Factor ◽  
Adiabatic Wall ◽  
Micro Gas Flow

Thermal Transport Phenomena in Turbulent Gas Flow Through a Tube at High Temperature Difference and Uniform Wall Temperature

1998 ◽  
Vol 120 (3) ◽  
pp. 784-787 ◽  
Author(s):  
Shuichi Torii ◽  
Wen-Jei Yang
Keyword(s):  
Heat Flux ◽  
High Temperature ◽  
Temperature Difference ◽  
Wall Temperature ◽  
Thermal Transport ◽  
Gas Flow ◽  
Uniform Wall Temperature ◽  
Uniform Wall ◽  
Flow Through ◽  
Turbulent Gas Flow

A numerical study is performed to investigate thermal transport phenomena in turbulent gas flow through a tube heated at high temperature difference and uniform wall temperature. A k-ε turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by a Boussinesq approximation in which the eddy diffusivity of the heat is determined by a t2-ε, heat transfer model. The governing boundary layer equations are discretized by means of a control-volume finite difference technique and are numerically solved using a marching procedure. It is disclosed from the study that (i) laminarization takes place in a turbulent gas flow through a pipe with high uniform wall temperature just as it does in a pipe with high unform wall heat flux, and (ii) the flow in a tube heated to high temperature difference and uniform wall temperature is laminarized at a lower heat than that under the uniform heat flux condirion.

Study on Effect of Momentum and Energy Accommodation Coefficient on Flow Properties

2018 ◽  
Author(s):  
Kishore Kumar Kammara ◽  
Arun Kumar Chinnappan ◽  
Rakesh Kumar
Keyword(s):  
Accommodation Coefficient ◽  
Flow Properties ◽  
Energy Accommodation

scholarly journals Modeling of three-dimensional exciplex pumped fluid Cs vapor laser with transverse and longitudinal gas flow

2021 ◽  
Vol 9 ◽  
Author(s):  
Chenyi Su ◽  
Xingqi Xu ◽  
Jinghua Huang ◽  
Bailiang Pan
Keyword(s):  
Wall Temperature ◽  
Laser Power ◽  
Gas Flow ◽  
Particle Density ◽  
Fluid Velocity ◽  
Three Dimensional ◽  
Heat Accumulation ◽  
Vapor Laser ◽  
Output Laser Power ◽  
Output Laser

Abstract Considering the thermodynamical fluid mechanics in the gain medium and laser kinetic processes, a three-dimensional theoretical model of an exciplex-pumped Cs vapor laser with longitudinal and transverse gas flow is established. The slope efficiency of laser calculated by the model shows good agreement with the experimental data. The comprehensive three-dimensional distribution of temperature and particle density of Cs is depicted. The influence of pump intensity, wall temperature, and fluid velocity on the laser output performance is also simulated and analyzed in detail, suggesting that a higher wall temperature can guarantee a higher output laser power while causing a more significant heat accumulation in the cell. Compared with longitudinal gas flow, the transverse flow can improve the output laser power by effectively removing the generated heat accumulation and alleviating the temperature gradient in the cell.

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