© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

9.2.7.3 Turbomolecular Gas Pumps

Drexler¹⁰ has briefly reviewed the general design parameters of nanoscale turbomolecular gas pumps. Pump effectiveness depends on the ratio of the blade speed to the characteristic thermal speed of the lightest gas molecule to be pumped. If the blades are constructed of diamondoid materials, then blades may be as thin as ~1 nm and blade speed can exceed the velocities of the fastest gas molecules (e.g., 1960 m/sec for hydrogen at 310 K; Eqn. 3.3), providing a compression ratio of >~10 per blade row.¹²⁰⁴ Turbomolecular pumps are designed to operate under free-flow conditions involving essentially ballistic gas molecule trajectories of length l_gas ~ 10 nm at 20 atm pressure, or l_gas ~ 200 nm at 1 atm (Eqn. 9.23). Taking pump length per blade row ~10 nm for operating pressures up to ~20 atm, a pump assembly consisting of a stack of five blade disks achieves a compression ratio of ~10⁵ in a ~50 nm pump length.

Last updated on 20 February 2003