Newsgroups: sci.energy
Subject: Flywheel for
From: srgxbhh@grace.cri.nz
Date: Thu,  7 Jan 93 04:44:24 GMT
Organization: Industrial Research Ltd., New Zealand.
NNTP-Posting-Host: grv.grace.cri.nz

 
The following details of the flywheel come from the Nov 1992 IEEE 
Spectrum  which includes a drawing of the proposed 
" Electromechanical battery " ( EMB ) on page 100.
  
The information is from Richard F Post, a senior scientist at the 
Lawrence Livermore National Laboratory. 
   
" the kind that Post has in mind for Electric Vehicle ( EV )
applications is quite small, is made out of a lightweight, ultrastrong
material, and rotates at a velocity in the order of 10,000 radians per
second. An EV would be powered by 20-30 such units, each storing about
1 kWh of energy." .... 
      
" By using composite materials based on graphite fibers, according to 
Post, it should be possible to build EMBs with a specific energy of 
about 150 Wh/kg ( the rotor itself should be able to store 540 Wh/kg; 
but just as with electrochemical batteries, the necessity for 
" inert " construction materials, which do not themselves store 
energy, lowers that theoretical maximum considerably.)"
   
" Although the specific energy of the EMB is impressive, what makes 
the device stand out is its specific power, which is orders of 
magnitude greater than anything acheivable by an electrochemical 
battery or even an internal combustion engine. Where the better 
electrochemical units have specific powers of 200-400 W/kg and 
internal combustion engines check in at about 600-800 W/kg, the EMB 
can deliver a whopping 5000 - 10000 W/kg."....
     
" for a chamber pressure of 10^-3 - 10^-4 pascals, Post calculates 
the rotor should have a rundown time constant of several months."...
       
" Safety is critical any time a lot of energy is stored in a small 
volume. But it is less of a problem for the EMB than might be 
imagined. Unlike massive steel rotors, which can fail in a spectacular 

fashion, throwing off large chunks of shrapnel, fiber-based composite 
rotors tend to fail by disintegrating into a mass of fairly benign 
" cotton candy," to borrow Post's descriptive phrase."
         
" The hot fluff, he told us, could be contained in a box made of three
dimensional composite- that is, a composite  in which the high 
strength
fibers run in all three directions. With such a construction, any 
cracks
that get started in the housing will not be able to propagate."...
           
" Not one to minimise the problems of building a practical EMB, Post
warns that the job is not one to be knocked off over a weekend in 
someone's garage. " It will require a first-class engineering effort," 

he said, " but it definitely can be done." " 
             
The drawing shows a cross-section of a cubical outer containment made 
from 3-D fiber composite anchoring springs providing a gimbal mounting 

of a spherical vacuum chamber made from "stainless steel reinforced 
with fiber composite". Inside the chamber ( supported on top and 
bottom magnetic bearings ) are vertical "concentric rotating 
cylinders, 
with thin walls ( 10% of radius, to prevent delamination) separated by 

an elastic material or coupled by a spring mechanism."  
There is also mention of a Halbach magnet array near the axis for 
generating a rotating dipole field, and generator windings outside 
the vacuum chamber. No dimensions are given, but the article implies 
that individual units will be quite small.
               
       Bruce Hamilton         SRGXBHH@grv.grace.cri.nz