Kunze Simon, Perrier Pierre, Groll Rodion, Besser Benjamin, Varoutis Stylianos, Lüttge Andreas, Graur Irina, Thöming Jorg
Chemical Process Engineering CVT, University of Bremen, Leobener Str. 6, 28359, Bremen, Germany.
IUSTI UMR 7343, CNRS, Aix Marseille Université, 13453, Marseille, France.
Sci Rep. 2024 Apr 12;14(1):8559. doi: 10.1038/s41598-024-59027-1.
The interaction of rarefied gases with functionalized surfaces is of great importance in technical applications such as gas separation membranes and catalysis. To investigate the influence of functionalization and rarefaction on gas flow rate in a defined geometry, pressure-driven gas flow experiments with helium and carbon dioxide through plain and alkyl-functionalized microchannels are performed. The experiments cover Knudsen numbers from 0.01 to 200 and therefore the slip flow regime up to free molecular flow. To minimize the experimental uncertainty which is prevalent in micro flow experiments, a methodology is developed to make optimal use of the measurement data. The results are compared to an analysis-based hydraulic closure model (ACM) predicting rarefied gas flow in straight channels and to numerical solutions of the linearized S-model and BGK kinetic equations. The experimental data shows that if there is a difference between plain and functionalized channels, it is likely obscured by experimental uncertainty. This stands in contrast to previous measurements in smaller geometries and demonstrates that the surface-to-volume ratio of 0.4 m seems to be too small for the functionalization to have a strong influence and highlights the importance of geometric scale for surface effects. These results also shed light on the molecular reflection characteristics described by the TMAC.
稀薄气体与功能化表面的相互作用在诸如气体分离膜和催化等技术应用中具有重要意义。为了研究功能化和稀薄化对特定几何形状中气体流速的影响，进行了氦气和二氧化碳通过普通微通道和烷基功能化微通道的压力驱动气体流动实验。实验涵盖的克努森数范围为0.01至200，因此包括从滑移流态到自由分子流态。为了最小化微流动实验中普遍存在的实验不确定性，开发了一种方法以最佳利用测量数据。将结果与预测直通道中稀薄气体流动的基于分析的水力封闭模型（ACM）以及线性化S模型和BGK动力学方程的数值解进行比较。实验数据表明，如果普通通道和功能化通道之间存在差异，很可能会被实验不确定性所掩盖。这与之前在较小几何形状中的测量结果形成对比，并表明0.4米的表面积与体积比似乎太小，以至于功能化无法产生强烈影响，突出了几何尺度对表面效应的重要性。这些结果还揭示了由TMAC描述的分子反射特性。
