We investigated through the scattering kernel kinetic concept the transport of small particles in gaseous media in a free molecular regime. The scattering kernel is generally used to provide gas-surface interaction boundary conditions for Boltzmann kinetic equation in flow problems (Maxwell, Phil. Trans. R. Soc. 170, 231, 1879; Sharipov, 2001). We developed a general expression for the transport force explicitly in terms of the scattering kernel and of gas molecule velocity distribution function. From the general expression, first, we could use the first-order Chapman-Enskog solution for the distribution function of gas molecules f(r, v, t) which shows three types of transportation mechanisms, or forces, such that F = F_D+F_T+F_S. Where F_D is the drag force on the particle due to its relative motion in the gas, F_T is the thermophoretic force due to a gradient of temperature in the gas, and F_S is due to shear forces on the particle. Second, it is possible to use any of the several scattering kernel models published in the literature. The traditional simple reflection kernels, specular, diffuse, and Maxwell, which comprises particular cases of the generalized force, are limited and do not fully describe the real reflection mode of molecule-particle interaction. So, we used the general (Struchtrup, Phys. Fluids. 25, 112001, 2013) reflection kernel model to study the drag force on small particles. The results were compared with available experimental data. We concluded that it is necessary to explicitly include impact velocity and particle surface rugosity effects which are predicted by the Struchtrup reflection kernel thermal activation model of molecule-particle interaction.

我们通过散射核动力学概念研究了气态介质中小颗粒在自由分子状态下的传输。散射核通常用于为流动问题中的玻尔兹曼动力学方程式提供气体-表面相互作用的边界条件（Maxwell，Phil。Trans。R. Soc。170，231，1879； Sharipov，2001）。我们根据散射核和气体分子速度分布函数明确地为传输力建立了一个通用表达式。从一般表达式开始，首先，我们可以使用一阶Chapman-Enskog解来求解气体分子f（r，v，t）的分布函数，该函数表示三种类型的传输机制或力，例如F = ˚F _d + ˚F _Ť + ˚F_小号。其中F _D是由于其在气体中的相对运动而对粒子的拖曳力，F _T是由于气体中的温度梯度而导致的热泳力，而F _S是由于颗粒上的剪切力。第二，可以使用文献中发表的几种散射核模型中的任何一种。传统的简单反射核（镜面反射，漫反射和麦克斯韦）（包括广义力的特殊情况）受到限制，不能完全描述分子-粒子相互作用的真实反射模式。因此，我们使用一般的（Struchtrup，Phys。Fluids。25，112001，2013）反射核模型来研究对小颗粒的阻力。将结果与可用的实验数据进行比较。我们得出结论，有必要明确包括碰撞速度和颗粒表面的皱纹效应，这是由分子间相互作用的Struchtrup反射核热活化模型预测的。