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

气体在微尺度和纳米尺度受限几何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。只有从根本上理解了气体稀薄对多组分扩散的依赖，才能在宏观尺度上，如膜气体分离、多相催化和微机电系统上取得可观的进步。麦克斯韦-斯蒂芬方程（MSE）对体多组分扩散能给出合理的结果，但对稀薄条件下的输运却不能给出合理的描述。runstedler从2006年开始的方法将体扩散和Knudsen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，在更高阶的稀薄下，表面扩散是主要的扩散机制。目前公认的二元摩擦模型（BFM）包含了一个校正因子，用于解释连续态和自由分子态之间的过渡。这表明BFM还不能完全解释机制，并给出了改进的潜力。此外，文献中所有的多组分扩散的实验和数值分析都局限于均匀管道作为研究对象。这是令人惊奇的，因为“真正的”孔隙大多是锥形的，扩散通量强烈依赖于管道的横截面积，正如我自己早期的工作所显示的那样。该项目旨在建立一种新的、经过实验验证的模型，该模型允许在广泛的气体稀薄范围内预测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.