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

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

6.2.2.3 Pressurized Fluids

Compressed fluids can store mechanical energy limited only by the tensile strength and aspect ratio of their container (Section 10.3.1) and the rupture strength of their valving system. A "conservative" working stress for diamondoid pressure containers is s_w ~ 10¹⁰ joules/m³ (~100,000 atm). Gases or liquids, either of which are compressible, may be used as the working fluid depending on energy density and design buoyancy requirements (Section 10.3.6). For example, cycling between 1-1000 atm of pressure at 310 K the density of compressed water varies from 993.4-1038.0 kg/m³ while the density of compressed oxygen varies from 1.26-670 kg/m³ (Table 10.2). The energy stored in a compressed fluid is ~the integral of PdV; thus at the ~1000 atm cycle limit, the compressed water stores ~2 x 10⁶ J/m³ and the compressed gas stores ~1 x 10⁸ J/m³. (Materials are thermodynamically forbidden to have negative volume compressibilities. However, lanthanum niobate and a few other crystals exhibit negative linear compressibilities; such materials may be used to fabricate porous solids that either expand in all directions when hydrostatically compressed with a penetrating fluid or behave as if they are incompressible.¹²⁹⁷)

For safety reasons, fluid pressures in excess of 1000 atm (10⁸ joules/m³) should rarely be used in nanomedical systems (Chapter 17). Any mechanical energy storage system with readily accessible catastrophic energy release modes that is operated near maximum capacity (e.g. fluids >10⁵ atm) in vivo risks causing significant damage to nearby tissue cells in the event of device malfunction or rupture.

Last updated on 18 February 2003