Accurate and Efficient Models for Microscopic Transport Processes in Gases

先进的微加工技术现在可以设计和制造微米和纳米级的设备，例如微型传感器和其他微电子机械系统(MEMS)。微器件中工艺的计算机模拟对于预测器件行为和优化设计性能非常有用。事实上，好的模拟模型可以减少(昂贵的！)*拟议的研究重点是进一步开发和应用微设备内及其周围气体流动的有效传输模型，从而实现气体微流动的快速、准确的数值解。同样的模型可以用于模拟低压气体流动，例如在真空工业中的应用。*在固体中，热传递受到声子气体(量子化晶格振动，类似于光子)的影响，这可以被描述为非常类似于经典气体，在微型和纳米设备中的相关应用。*气体中的过程由平均自由程控制，这是气体粒子与其他粒子或障碍物碰撞之间的平均距离。如果平均自由程与装置的大小相当，那么通常和公认的流体动力学和热传递定律就不再有效。因此，必须使用替代模型来模拟微器件中的气体流动。微观描述--气体是原子或粒子的集合--已经建立得很好了，但由于模拟时间非常长，成本非常高。*在过去的十年里，我们成功地开发和应用了从微观描述推导高级流动模型的方法，这些方法完善了流体动力学方程，并将有效性扩展到微观流动。使用铅笔和纸，以及数值解的适当的计算机模型，我们已经证明精化的方程是对微观模型的极好的近似，并且描述了稀薄气体中所有有趣的输运机制。*计划的研究建立在申请者最近与学生和同事建立的方法和模型的基础上，通过考虑对稀薄多原子气体、气体混合物和用于微观热传递的高级声子模型的更详细、更现实的微观描述。将特别考虑气体和声子与边界的相互作用，有或没有凝结或吸附过程。*尽管计算和模拟对稀薄流动的世界有了深刻的洞察，但全面的实验验证是困难的。作为研究的一部分，我们计划确定受到稀薄流动显著影响的新实验，以便这些实验可以可视化。**

Advanced microfabrication techniques now allow to design and build devices on the micro- and nano-meter scale, e.g., micro sensors and other micro-electro-mechanical systems (MEMS). Computer simulations of the processes in microdevices are extremely useful for the prediction of device behavior, and for optimization of design performance. Indeed, good simulation models allow the reduction of (costly!) prototyping, moreover they give detailed insight into the processes in the device, which are not accessible to measurements.***The proposed research centers on the further development and application of effective transport models for gas flows in, and around, microdevices, which allow for fast and accurate numerical solutions of gas microflows. The same models can be used for simulation of low pressure gas flows, e.g., for applications in the vacuum industry.***In solids, heat transfer is affected by the phonon gas (quantized lattice vibrations, similar to photons), which can be described very similar to classical gases, with relevant applications in micro- and nano-devices.***Processes in gases are governed by the mean free path, which is the mean distance a gas particle travels between collisions with other particles or obstacles. If the mean free path is comparable to the size of the device, the usual and well established laws of fluid dynamics and heat transfer cease to be valid. Therefore, alternative models must be used for the simulation of gas flows in microdevices. The microscopic description—the gas as an ensemble of atoms or particles—is well established, but very costly due to extremely long simulation times.***In the past decade, we had outstanding success in developing and applying methods to derive advanced flow models from the microscopic description which refine the equations of fluid dynamics, and extend the validity towards microflows. Using pencil and paper, as well as appropriate computer models for the numerical solutions, we have shown that the refined equations are excellent approximations of the microscopic models, and describe all of the the interesting transport regimes in rarefied gases.***The planned research builds up on the methods and models established by the applicant with students and co-workers in the recent past, by considering more detailed, and thus more realistic, microscopic descriptions of rarefied polyatomic gases, gas mixtures, and advanced phonon models for micro heat transfer. Special consideration will be given to the interaction of gases and phonons with boundaries, with and without condensation or adsorption processes.***While calculations and simulations give deep insight into the world of rarefied flows, full experimental verification is difficult. As part of the research we plan to identify new experiments which are markedly influenced by rarefied flows, so that these can be visualized.**