Determination of Condensation Coefficient and Boundary Condition for Kinetic Theory of Gases by Molecular Dynamics Simulations of Evaporation of Argon Into Vacuum

2003 ◽  
Author(s):  
Tatsuya Ishiyama ◽  
Takeru Yano ◽  
Shigeo Fujikawa
Keyword(s):  
Molecular Dynamics ◽  
Boundary Condition ◽  
Kinetic Theory ◽  
Molecular Dynamics Simulations ◽  
Triple Point ◽  
Kinetic Theory Of Gases ◽  
Condensation Coefficient ◽  
Point Temperature ◽  
Dynamics Simulations ◽  
Triple Point Temperature

Molecular dynamics simulations at liquid-vapor equilibrium condition and evaporation condition into vacuum were carried out to investigate the boundary condition for the kinetic theory of gases. The determination method for condensation coefficient α consistent with the kinetic theory is also proposed. It was found that α for argon at an equilibrium state is close to unity near the triple point temperature of the bulk liquid, and decreases gradually as the temperature rises. The velocity distribution of molecules evaporating into vacuum becomes nearly half-Maxwellian near the triple point temperature, and is deformed as the temperature rises.

Heat Transfer on Walls in Molecular Dynamics Simulations: Modelling With Vibrating Reflective Walls

2008 ◽  
Author(s):  
E. A. T. van den Akker ◽  
A. J. H. Frijns ◽  
A. A. van Steenhoven ◽  
P. A. J. Hilbers
Keyword(s):  
Heat Transfer ◽  
Molecular Dynamics ◽  
Boundary Condition ◽  
Heat Exchange ◽  
Molecular Dynamics Simulations ◽  
A Priori ◽  
Computation Time ◽  
Good Choice ◽  
Competitive Model ◽  
Dynamics Simulations

In simulations of micro channel cooling, the heat exchange from fluid to channel wall is an important aspect. Hence the heat exchange should be included in the model. Although numerically very expensive, it can be done by using a molecular wall. Numerically cheap implementations of a wall are the reflective wall and the thermal wall, and the combination of both, the diffusive-specular wall. In this paper we introduce the concept of a vibrating reflective wall as a boundary condition for molecular dynamics simulations. It is shown that the heat transfer with the vibrating reflective wall is the same as with a molecular wall, and that computation time is reduced greatly. As a competitive model, the diffusive-specular boundary condition is analyzed; it is shown that a good choice of parameters can give similar results in the same computation time, but the choice of parameters is not known a priori, therefore the vibrating reflective wall boundary condition is preferable.

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