[geeks] crazy stupid idea

[Chris Byrne]

Two words my friend, Shock Cooling. Actually lots of words related to the
issue. Incompressible flow, compressible flow, turbulent flow, laminar flow,
high temperature flow, low temperature flow, steam flash, cavitation, and
aeration.

Shock cooling is an extremely rapid change in the temperature of a solid
causing uneven expansion and contraction throughout the medium, or worse,
across a single shear plane. Basically if cold water ever hits hot turbine
at 25000 RPM then hot turbine shatter into 25 million little pieces
travelling at 500+ miles per hour.

Gas turbine exhaust by its nature is extremely turbulent compressible flow
at a high temperature. Water flow is low temperature laminar incompressible
flow. When the two meet the result can be impressive.

Imagine the highest hotest craziest boil youve ever seen, add a high
pressure air compressor blowing through it, and multiply that by 10000.

Then there's the superheated steam. The exhaust would probably be so hot as
to flash the water rather than propel it. Combine that turbulent flow with
superheated steam and you have a bit of a mess.

Even if none of those is a problem simply directing an extremely high
pressure jet of turbulent air still wont be a good propulson method for two
reasons. First is cavitation. Basically lots and lots of small bubbles form
near the outlet and around any solid surface in the area. When those bubbles
burst a small vacuum is created sucking the boat back just a bit. You'll
still move, it just wont be efficient.

The aeration issue is potentially much more serious. If you end up producing
lots and lots of tiny bubbles you could end up aerating the water around
your hull. Aerated water has almost no bouancy

What you need to do is build two isolated circuits, a hot circuit and a cold
circuit and never the twain shall meet. The cold circuit must be submerged
in the water continuously to avoid extreme cavitation or aeration. You must
also prefent it from running dry or there will be a turbine overspeed
followed by a massive shock when the incompressible water hits the now
oversped impeller.


Chris Byrne

> -----Original Message-----
> From: geeks-admin at sunhelp.org [mailto:geeks-admin at sunhelp.org]On Behalf
> Of Fogg, James
> Sent: 08 May 2002 15:26
> To: 'geeks at sunhelp.org'
> Subject: [geeks] crazy stupid idea
>
>
> I am working on building a gas turbine engine based on an automotive
> turbocharger (not a new idea, there is a big hobby jet engine movement
> around this idea). I finished welding the flame tube last week and am
> working on a fuel injector. My fuel will be propane at first
> (easy injection
> scheme) and kerosene later (I'm looking for oilburner parts for this).
>
> I was trying to figure out how to harness the output power. The
> turbo has no
> output shaft of course, and welding a shaft onto the exotic metals of a
> rotor is out of the question (balance would be a bitch too).
> While pondering
> this I looked over at my boat and had a eureka moment.
>
> Would it work if....
> I routed the thrust of the jet into a tube or a venturi under the
> hull of a
> boat (pointing toward the stern of course)? It seems to me that the water
> would be a good resistive force to "push" against, and a jet
> thrust wouldn't
> have any of the limitations of a prop. It seems to me that it
> should be very
> fast if enough thrust is available. The only downfall I can think of is if
> any "thrust air" is under the hull the displacement/buoyancy of the hull
> might change drastically.
>
> Any ideas? Am I destined for disaster?
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