Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
188.8.131.52 Containerized Flow
Once a block of fluid has passed into the interior of a nanodevice, it may be containerized or divergently subdivided and then transported at velocities far higher than diffusive flow (Eqn. 3.1) or Poiseuille flow (Eqn. 9.25) would otherwise permit. The velocities available in containerized flows are largely independent of fluid viscosity and total transport time (unlike diffusive flow), and are nearly independent of fluid pressure and flow channel length (unlike Poiseuille flow).
For easy comparison, consider a disk-shaped container of radius rblock and thickness hblock with useful fractional storage volume fblock (to account for container wall thickness and mechanism overhead). After loading with fluid, the container is transported through a channel of radius rtube ~ rblock and length ltube at a velocity vblock, giving a volumetric flow rate of 'Vblock = p rtube2 fblock vblock (m3/sec) which is superior to the Poiseuille flow rate in a pressurized tube of equivalent size when:
Containerized transport thus may be preferred to Poiseuille flow in narrow, long transport channels, or in cases where fluid pressure is relatively low or fluid viscosity is relatively high, or where containers can be very thin-walled (e.g., high fblock) such as when strong diamondoid containers are used. For example, a containerized transport channel carrying water at 310 K with rtube = 10 nm, ltube = 1 micron, Dp = 1 atm, and fblock = 0.9 produces volume flow rates superior to Poiseuille flow if container transport velocity vblock > 0.002 m/sec. Container/channel sliding interfaces moving up to 1 m/sec have low frictional losses,10 and speeds up to ~100 m/sec can probably be tolerated in internal mechanisms if flow speed (entirely inside nanodevices) is a more important design criterion than minimizing power dissipation in a particular application. An additional consideration is that subdividing a volume of fluid into many smaller blocks of fluid allows these smaller blocks to be transported independently through numerous spatially independent channels of much smaller bore, greatly increasing the number of flow design options and greatly increasing the relative advantage over Poiseuille flow through channels of similar size.
Last updated on 20 February 2003