- Conference date: 10-16 July 2004
- Location: Bari (Italy)
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 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 210μm to 1mm. This range of pore sizes corresponds to efficient Knudsen Compressor operation between roughly 1 Torr and 10 mTorr. The other issue at low pressures is the larger Kn of the connector section which can introduce “reverse” thermal transpiration. Two conventionally perforated carbon doped aerogel membranes, with the mean pore diameters of 210 μm and 380 μm, have been tested at the operating pressure range of 2 Torr to 10 mTorr. Comparison with the predicated results showed the evidence of rarefied gas effects such as “reverse” thermal transpiration.
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