Accurate and efficient models for microscopic transport processes in gases

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Advanced microfabrication techniques allow to design and build devices on the micro and nanometer 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 to reduce the amount of (costly!) prototyping, moreover they give detailed insight into the processes in the device, which are not accessible to measurements. The goal of this research program is the development and application of effective transport models for gas flows in, and around, microdevices, which allow for fast and accurate solutions of gas microflows. The same models will be used for simulation of low pressure gas flows, e.g., for applications in the vacuum industry. Processes in gases are governed by the mean free path, i.e., the mean distance a gas particle travels between collisions with other particles. If the mean free path is comparable to the size of the device, the well established laws of fluid dynamics 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 particles--is well established, but very costly due to huge simulation times. The following steps will be taken: (1) Advanced flow models are derived from the microscopic description; the models refine the equations of fluid dynamics, and are valid for microflows. (2) Appropriate computer models are designed for the numerical solutions of the derived equations. (3) The derived flow models are tested and validated against benchmark experiments and accurate microscopic simulations. (4) Applications to flows in microdevices and vacuum flows. The research program builds extensively on a model established by the applicant, with students and co-workers, in the last few years. The present model will be extended to include more detailed physics of the gas, and for the implementation to complex geometries.