The Knudsen Compressor is a solid-state micro/meso-scale gas roughing pump based on the rarefied gas phenomena of thermal transpiration. Knudsen Compressors operate by imposing a temperature gradient across a high porosity, low thermal conductivity transpiration membrane, typically a silicon aerogel membrane. Previous optimization studies have concluded that significant reductions of both energy consumption and device volume per unit throughput and pressure difference for a given pressure ratio can be achieved when each stage of the cascade operates with a Knudsen number based on the mean pore radius of approximately one. Perforated aerogels (using the same bulk aerogel material, but with machined arrays of properly sized parallel capillaries) are appealing candidate low-pressure transpiration membranes and are the focus of this investigation. Conventional drilling techniques using micro drills have successfully demonstrated perforated aerogel with pore diameters ranging from 200μm to 500μm. This range of pore sizes corresponds to efficient Knudsen Compressor operation between roughly 500mTorr and 200 mTorr. The performance of a low pressure Knudsen Compressor is clearly affected by rarefaction phenomena including “reverse” thermal transpiration and possible thermally induced internal flow circulation at low pressures due to the relatively large Knudsen number in the connector section.

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