To bridge rarefied gas flow phenomena between macro- and microscale - Model development and experimental validation

连接宏观和微观尺度之间的稀薄气流现象 - 模型开发和实验验证

• 批准号: 316976850
• 负责人: Dr.-Ing. Christian Day
• 金额: --
• 依托单位: Institut für Technische Physik (ITEP)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/316976850?language=en
• 关键词: bridge; rarefied; gas; flow; phenomena

For rarefied gas flows the continuum theory fails since molecules collide more frequently with the duct walls than with each other. Themass flow rate measured under low pressure or in very small ducts is significantly higher than predicted by the classical Poiseuille equation - an effect traditionally referred to as slip flow. In the past century several approaches were conceived to phenomenologically explain this effect by means of momentum accommodation (boundary conditions for models derived from kinetic theory) which is incomplete since forces imposed on gas molecules by the duct surfaces are neglected. The questions what slip is and how it depends on either the rarefaction or also on the characteristic length scale of confinements remain unanswered. With increasing rarefaction anddecreasing characteristic length, gas-wall interactions dominate the flow which, at identical rarefaction, is differently described by different scientific communities: the "Rarefied Gas Community" (vacuum) uses kinetic theory and the "Porous Media Community" (that comprises, e.g., catalysis and membrane research) describes gaseous flows by means of superimposed diffusion mechanism (convection, diffusion). The bridge between different phenomena at macro-scale and at micro/nano-scale is not built up yet. This results in the fact that the reliable prediction of flows over the whole range of gaseous rarefaction and size scales is definitely beyond the current state-ofart. In the proposed work we want to experimentally detect and theoretically describe phenomena that occur under rarefied conditions but in situations, in which both rarefaction variables, the inverse pressure and the inverse characteristic length, are in a moderate range. Gas flow phenomena in this area cannot be described properly by neither of the two approaches mentioned above. The theoretical work includes further development of the preliminary developed surface diffusion model in order to obtain a predictive approach for the whole range of gaseous rarefaction and all size scales when adsorption properties and surface diffusivity are known from, e.g., MD simulations or corresponding experiments. The second pillar of this work is given by the corresponding experimental activities. We want to investigate steel-made macro- and micro-channels, which are geometrically similar to each other and comparisons of dimensionless mass flow rate versus Knudsen number will be carried out for different temperatures and functionalized channel surfaces. As a byproduct, this broad parametric work will produce an unprecedented data base for model validation for future research in the field of rarefied gas dynamics.

对于稀薄气体流动，连续介质理论失败了，因为分子更频繁地与管壁碰撞，而不是彼此碰撞。在低压下或在非常小的管道中测得的质量流量明显高于经典泊松公式预测的流量--这种效应传统上被称为滑移流。在过去的一个世纪里，人们设想了几种方法，通过动量调节(动量调节模型的边界条件)来现象学地解释这种效应。动量调节是不完全的，因为忽略了管道表面对气体分子施加的力。什么是滑移，以及它如何取决于稀疏性或限制的特征长度范围，这些问题仍然没有答案。随着稀疏度的增加和特征长度的减小，气壁相互作用主导着流动，不同的科学界对此有不同的描述：“稀薄气体共同体”(真空)使用动力学理论，而“多孔介质共同体”(包括催化和膜研究)通过叠加扩散机制(对流、扩散)描述气体流动。宏观尺度和微观/纳米尺度的不同现象之间的桥梁还没有搭建起来。这导致了这样一个事实，即对整个气体稀薄和尺寸范围内的流动的可靠预测肯定超出了当前的最新水平。在这项拟议的工作中，我们想要从实验上探测和理论上描述在稀薄条件下发生的现象，但在稀薄变量、反压力和反特征长度都处于中等范围的情况下。上述两种方法都不能很好地描述该区域的气体流动现象。理论工作包括进一步发展初步开发的表面扩散模型，以便在从例如MD模拟或相应的实验中得知吸附性质和表面扩散系数时，获得对整个气体稀薄范围和所有尺寸尺度的预测方法。这项工作的第二个支柱是相应的实验活动。我们要研究的是钢制的宏观和微观通道，它们在几何上是相似的，并将在不同的温度和功能化的通道表面下进行无量纲质量流量与克努森数的比较。作为副产品，这项广泛的参数工作将为稀薄气体动力学领域未来研究的模型验证提供前所未有的数据库。