协调系数是反映气体与壁面动量和能量交换的重要参数,可通过分子动力学方法进行统计,其二维模拟由于计算量较三维大大减小而逐渐得到应用.法向动量协调系数表达式中的p_(nw)和能量协调系数表达式中的E_w分别表示气体分子在壁面漫反射后的平均法向动量和平均能量,利用气体动理论推导发现,二维的p_(nw)与三维相同,而E_w则由于降维小于三维的结果,导致能量协调系数的表达式在二维计算中有别于三维.依据协调系数的表达式,使用分子动力学方法模拟三维和二维系统中的导热问题,结果表明,二维能量协调系数与三维相比较小,而法向动量协调系数差别不大.
Accommodation coefficients,important parameters in momentum and energy exchange between a gas and wall,are mainly calculated with molecular dynamic(MD) method.Since the computational cost in a two-dimensional(2D) system is highly reduced from the three-dimensional (3D) one,the 2D MD method has been applied in recent researches.p_(nw) in the definition of normal momentum accommodation coefficients(NMAC) and E_w in the definition of energy accommodation coefficients(EAC) are average normal momentum and energy for those diffusively reflected gas molecules,respectively.Expressions of P_(nw) and E_w were deduced from the kinetic theory that,in the 2D system with lower dimension,p_(nw) was equal while E_w was smaller,resulting the different EAC expression.Furthermore,the NMAC and the EAC were calculated in thermal conductions using 2D and 3D MD with corresponding expressions.The results revealed that the 2D EAC were smaller than the 3D ones.while the NMAC was maintained.
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