Russell Kent wrote:

Russell Kent wrote:

You need a liquid to conduct the heat from the shaft to the dry ice (air makes a
poor thermal conductor).  I prefer rubbing alcohol to acetone, but either will
work.  Obviously you need a liquid compatible with the parts, and that does not
freeze at -78C (the melting point of dry ice at standard pressure).

Paul Lamar responded:

Ahh so! Very simple. A liquid that will not freeze. duh. What is that in F?

-78 * (9/5) + 32 = -108 F

The liquid to air intercoolers guys are going to love it.

Eh? Don't follow, but whatever...

Paul responded:
The lower the temp of air going into the engine, the higher the density,
the more power.....

Rick Girard wrote:

Try hitting up your local market for some dry ice.  Get enough to encase the shaft
and don't be surprised when it rings like a bell as the shaft shrinks.  When the
singing stops the shaft has reached the temp. of the dry ice.

Russell responded:

Yes, the metal will "sing" if you touch dry ice to it directly, but I would hesitate
to do that.  If one lays a bar across dry ice, the bar will arch/curve because of the
extreme thermal gradient causing a corresponding coefficient of expansion gradient.
The bar may re-straighten after thermal equilibrium is reached, but then again it
might not.  Using an alcohol or acetone bath allows the bar to cool more uniformly,
avoiding the thermal gradient issue.

BTW, pieces assembled using the hot/cold technique (as John Gibbons is doing) use
enormous pressures; pressures so great that intermetallics can be formed.  The
individual parts become one whole piece and will not willing come apart ever again
(you'll likely destroy it before you get them apart). So don't do it unless you're
willing to forgo *ever* taking them apart.

Russell Kent

Sounds like a good home grown way to put a prop flange on a PSRU output
shaft.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org