Experimental and theoretical study on multicomponent diffusion of gases under rarefied conditions

气体在微米和纳米尺度受限几何形状中的多组分扩散决定了许多自然和技术过程的整体行为和效率。在这样的小系统中，气体处于一种被称为稀薄的状态，其中扩散是主要的，因此限制了传输机制。只有在从根本上理解气体稀薄对多组分扩散的依赖时，才有可能在宏观尺度上显著增强，例如膜气体分离、多相催化和微电子机械系统。Maxwell-Stefan方程(MSE)对多组分扩散给出了合理的结果，但不能描述稀薄条件下的输运。Runstedtler从2006年开始的方法将整体扩散和努森扩散叠加到MSE。然而，在这种方法中，表面扩散被忽略了，根据我自己的工作，在稀疏性较高的情况下，表面扩散是主要的扩散机制。目前公认的二元摩擦模型(BFM)包含一个修正因子，它解释了连续体区和自由分子区之间的转变。这表明BFM还没有完全解释这些机制，并给出了改进的潜力。此外，在文献中，对多组分扩散的实验和数值分析都局限于以均匀管道为考察对象。这是奇妙的，因为“真正的”毛孔大多是锥形的，扩散流量强烈地依赖于管道的横截面面积，正如它在自己的早期工作中所显示的那样。该项目的目标是建立一个新的、经过实验验证的模型，该模型能够预测多种稀薄气体在均匀和锥形管道中的多组分扩散。

Multicomponent diffusion of gases in micro scale and nanoscale confined geometries is determining the integral behavior and efficiency of many natural and technical processes. In such small systems the gas is in a state referred to as rarefied where diffusion is the dominating, and hence limiting, transport mechanism. Considerable enhancement on the macroscale in, e.g., membrane gas separation, heterogeneous catalysis, and microelectromechanical systems is only possible when understanding the dependence of gaseous rarefaction on multicomponent diffusion fundamentally. The Maxwell-Stefan equations (MSE) yield reasonable results for bulk multicomponent diffusion but fail for the description of transport under rarefied conditions. Runstedtler's approach from 2006 superimposes bulk diffusion and Knudsen diffusion to the MSE. However, in this approach surface diffusion is disregarded which, according to my own work, under higher orders of rarefaction is the dominating diffusion mechanism. The nowadays accepted Binary Friction Model (BFM) contains a correction factor that accounts for the transition between the continuum regime and the free molecular regime. This indicates that the BFM does not fully explain the mechanisms yet, and potential for improvement is given. Furthermore, in literature all experimental and numerical analysis on multicomponent diffusion confine on uniform ducts as object of examination. This is wondrous since 'real' pores are mostly tapered and diffusive flux strongly depends on the duct's cross-sectional area as it was shown in an own earlier work. This project aims for a new, experimentally validated model that allows for the prediction of multicomponent diffusion in uniform and tapered ducts over a wide range of gaseous rarefaction.