Accurate and Efficient Models for Microscopic Transport Processes in Gases

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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 descriptionthe gas as an ensemble of atoms or particlesis 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.**