Accurate and Efficient Models for Microscopic Transport Processes in Gases

先进的微制造技术现在允许在微和纳米尺度上设计和制造设备，例如微传感器和其他微机电系统（MEMS）。微器件过程的计算机模拟对于器件行为的预测和设计性能的优化非常有用。事实上，良好的仿真模型可以减少（昂贵的！）原型制作，而且它们可以详细了解设备中的过程，这是无法测量的。***建议的研究重点是进一步开发和应用微型装置内部和周围气体流动的有效输运模型，从而实现快速准确的气体微流动数值解。同样的模型也可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，传热受到声子气体（量子化晶格振动，类似于光子）的影响，这与经典气体非常相似，在微纳米器件中有相关应用。***气体过程由平均自由程控制，即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尺寸相当，通常的和公认的流体动力学和传热定律就不再有效了。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——已经很好地建立起来了，但由于模拟时间非常长，成本非常高。***在过去的十年中，我们在开发和应用从微观描述推导高级流动模型的方法方面取得了显著的成功，这些方法改进了流体动力学方程，并将其有效性扩展到微观流动。使用铅笔和纸，以及适当的数值解的计算机模型，我们已经表明，精炼方程是微观模型的极好近似，并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人与学生和同事最近建立的方法和模型的基础上，通过考虑更详细，因此更现实的微观描述稀薄多原子气体，气体混合物，以及用于微传热的先进声子模型。将特别考虑有边界的气体和声子的相互作用，有或没有冷凝或吸附过程。虽然计算和模拟可以深入了解稀薄流动的世界，但完全的实验验证是困难的。作为研究的一部分，我们计划确定受稀薄气流显著影响的新实验，以便将其可视化

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.**