The maximum compression varies linearly with circumferential rotor speed. In order to obtain extremely low pressures on the order of 10-10 torr, rotation rates of 20,000 to 30,000 revolutions per minute are often necessary. Unfortunately, the compression ratio varies exponentially with the square root of the molecular weight of the gas. Thus, heavy molecules are pumped much more efficiently than light molecules. Most gases are heavy enough that this isn't really an issue, however hydrogen and helium are not pumped efficiently.
Search Encyclopedia
|
Featured Article
|