Another fact is a tangential muffler is a vortex generator.
This vortex is forced to flow aft out of the can due to exhaust
gas pressure build up in the front of the can.
Paul Lamar

"Robinson, Chad" wrote:

Could somebody please explain what the purpose of cooling the exhaust
 gases is? I understand the muffling aspects, but I don't understand
why the cooling effect is valuable.

Regards,
Chad

It is not the exhaust gases we are interested in cooling. It is the
steel the muffler is made out of :) Cooling the gases does not reduce
the noise. Something like the opposite happens. Due to viscosity and

friction

effects the steel is heated by the noise over and above the 1700 degree F
temperature of the exhaust gases and the noise is reduced in the process.

In theory this design could reduce the noise by almost half exiting the

can.

This is because of the concentric shape of the can doubling the steel
area the exhaust gases are rubbing against.

At the same time all the steel sheet exposed to the gas in the can would
also be exposed to cooling air on it's opposite surface.

If this works it could be a revolution in low back pressure mufflers.

Paul Lamar

Mark Wrathall wrote:

Nicely drawn Bill.

I don't really buy the cooling effect. The greatest risk are the welds where
the stacks enter the muffler. This design does nothing for lowering the EGT
until the tailpipe, and no one is having issues with unrestricted tailpipes
cracking.

How do you support that X inch long cantilevered pipe? If you weld struts
into the muffler-tailpipe transition piece to support it, they will fail
(hot vibrating gas, thin section to avoid backpressure, strong thermal
gradient, corrosive environment). If you don't support it, a weld on the
cooling inlet end will fail, giving you a hell of a bad day (fire risk).

Do we have a single example of a muffler with any contents surviving the
Aviation duty cycle 13B gas path?

I thought centering the outlet on a tangiential muffler causes the throat to
choke due to the vortex?

Mark

"I don't really buy the cooling effect." Do you mean the air flowing over the
steel will not cool it or do you mean cooling the exhaust gas reduces the noise?

Yes Tracy is having good luck with a .073 thick  Spin Tech muffler but it 
is outside the cowl and causing drag. His early tangential muffler lasted 
650 hour and it was only .035 thick. Dave Atkins has flown a thin .035 
Inconel tangential muffler for years.

Good point on the inner tube supports. Thick Inconel is the only way to 
go on those. Perhaps they can be welded in at an angle to enhance the vortex.
If they are not welded to the inner tube the thermal gradients would be less
of a problem.

As far as outlet choking is concerned this is an improvement as the outlet
is annular and closer to the main rotating air mass in the vortex.

I think it is well worth making a test piece and I am prepared
to pay for it if Ed Klepeis would read his email once in an while :)

Paul Lamar
 
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