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arXiv 0709.1055cond-mat.stat-mech
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强剪切下麦克斯韦分子二元混合物的质量输运

Mass transport in a strongly sheared binary mixture of Maxwell molecules

Vicente Garzo

摘要:

从Boltzmann动力学方程精确地确定了均匀剪切流下Maxwell分子二元混合物的输运系数。一个正常的解决方案是通过一个Chapman-Enskog样的扩展周围的局部剪切流分布,保留所有的流体动力学订单的剪切速率。在第一阶的膨胀的质量通量是成比例的摩尔分数,压力和温度的梯度,但由于各向异性引起的系统中的剪切流,相互扩散,压力扩散和热扩散张量的识别,而不是传统的标量系数。这些张量是根据剪切速率和混合物的参数(颗粒质量、浓度和力常数)获得的。在计算机模拟中引入外部恒温器以补偿粘性加热的情况下和存在外部恒温器的情况下进行描述。正如预期的那样,分析表明,有和没有恒温器的结果之间没有简单的关系。在示踪剂极限情况下,说明了三个扩散张量对剪切速率的依赖关系,结果表明广义输运系数偏离其平衡形式在一般情况下是相当重要的。最后,广义输运系数与动量和热量输运的玻尔兹曼方程的模型动力学方程进行评估。

英文摘要:

Transport coefficients associated with the mass flux of a binary mixture of Maxwell molecules under uniform shear flow are exactly determined from the Boltzmann kinetic equation. A normal solution is obtained via a Chapman--Enskog-like expansion around a local shear flow distribution that retains all the hydrodynamics orders in the shear rate. In the first order of the expansion the mass flux is proportional to the gradients of mole fraction, pressure, and temperature but, due to the anisotropy induced in the system by the shear flow, mutual diffusion, pressure diffusion and thermal diffusion tensors are identified instead of the conventional scalar coefficients. These tensors are obtained in terms of the shear rate and the parameters of the mixture (particle masses, concentrations, and force constants). The description is made both in the absence and in the presence of an external thermostat introduced in computer simulations to compensate for the viscous heating. As expected, the analysis shows that there is not a simple relationship between the results with and without the thermostat. The dependence of the three diffusion tensors on the shear rate is illustrated in the tracer limit case, the results showing that the deviation of the generalized transport coefficients from their equilibrium forms is in general quite important. Finally, the generalized transport coefficients associated with the momentum and heat transport are evaluated from a model kinetic equation of the Boltzmann equation.

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