2002 Spring Newsletter
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RMI Helping the Cutting Edge of "Turbo-machinery"
by Cameron M. Burns
Although RMI's Amory Lovins is perhaps best known for his role as a
cross-fertilizer of energy and resource efficiency, he's also a recovering
experimental physicist and likes to stay abreast of the latest technical
developments in efficiency.

Recently he became an advisor to Pax Fluid Systems, Inc., of San
Rafael, California. Founder Jayden Harman is " an Australian naturalist who is
an avid diver, and a cutting-edge designer using biomimicry," according to
Lovins.

After decades of study of the plant and animal kingdom, including
thousands of hours underwater, Harman developed and patented a completely new
type of impeller (a spinning shape that moves the fluid around it). Lovins
suspects it could revolutionize such fluid-moving machinery as pumps, fans,
propellers, mixers, and turbines. Pax's impeller design is based on a
logarithmic spiral known as a Phi Ratio, Fibonacci Sequence, or Equiangular
Spiral. In three dimensions, these patterns are called recessive spirals. They
occur in many places in nature, yet few designers have ever mimicked them. ("To
visualize a recessive spiral, picture the inside of a conch shell," Harman
noted). Two of the many such shapes are shown above.

When rotated in water or air, the impeller makes the fluid flow
smoothly in a vortex, like water exiting a bathtub. In contrast, the most common
kinds of conventional pumps and fans sling the fluid outward and bounce it off a
curved wall to make some of it move in the desired direction. This more violent
and indirect method causes turbulence and hence is inherently less efficient
than laminar flow.

By smoothly accelerating the fluid centripetally (towards the
center) with very little turbulence, Pax's impellers lessen vibration and reduce
or even reverse heat gain, while delivering more thrust with virtually no
cavitation (causing flow so turbulent that the water is torn apart and bubbles
form). While design optimization continues, Harman has already found that an
impeller based on a recessive spiral can spin at 6,000 rpm underwater with no
cavitation. "You can't do that even with a smooth cylinder because of the
surface drag!" Lovins said.

Harman has also been exploring some counterintuitive applications.
When one of his impellers is attached to the front of a submarine hull, rather
than slowing down the craft due to increased surface area, it makes it go about
11 percent faster.

Lovins has been advising Harman informally for several years and is
now an inaugural member of Pax's Advisory Board, helping get the concept widely
applied. Pax has also supplied prototype impellers to a natural design exhibit
at Nike headquarters organized by RMI board member Janine Benyus, the author of
Biomimicry. (www.biomimicry.org)

"Not only are impellers of this shape potentially far more
efficient," noted Lovins, "they are remarkably quiet, and gentle on anything
that goes through them—like, say, fish through a hydroelectric turbine. This
could be very big, and has many obvious applications. If this invention—or
rather, rediscovery of nature's genius—fulfills its promise, it could be one of
the greatest technical breakthroughs in energy efficiency in a long time."





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