Ed Huntress wrote:

(...)

It's been a few years since I was studying the things, but the old deLavals
ran at something like 20,000 rpm. I was going for something around 8"
diameter, which, at the time, I calculated at 40,000 to get any decent power
out of it.

That is *fast*! You'd want to gear it *down* to drive the alternator
to limit eddy losses, I guess.

(...)

Yeah, but I was just looking into pneumo-static, bleeding in some steam, or
possibly pneumo-dynamic. At those speeds, fluid-dynamic bearings can work.
But when they don't, and you get contact, stand back. d8-)

I also considered using ceramic ball bearings from a high-speed milling
spindle. I think they would do it, in small diameters, but that's where I
stopped.

I guess that one *could* 'mount' ceramic bearings
'fluid dynamically' so that the balls spin at relatively
low RPM and the outer race floats on a steam cushion
'at speed' Avoiding radial oscillation would be a
challenge, though.

(...)

Now I'm fantasizing about building a thermoacoustic engine:
http://www.youtube.com/watch?v=hu0N7...eature=related

All the thrills for about 1% of the effort!

Oh, I don't know about those. I'll have to look into it. That isn't what you
were calling "thermoacoustic," is it? I thought thermoacoustic engines had
no pistons at all.

I believe you are right. The mechanics are there to show a
way to extract power easily and are not required to demonstrate
thermoacoustics.

A better way to extract power might involve suspending a
plasma in a magnetic bottle at the end of the tube.
http://www.youtube.com/watch?v=DhcBrc-TUgk&NR=1
One coupling coil to pump the plasma, surrounded by
two coils to extract power as the thermoacoustic
engine caused the plasma (and it's associated magnetic
field) to oscillate axially.

Thermoacoustic magnetic hydrodynamics, sort of.
(I want an 'RCM attaboy' for typing that at 7:37 in the morning.)


(Stirling motor lubrication)

The problem is that liquid lubricants get into the hot end of the
displacement cylinder and cook on the hot head, which leaves a carbon layer
that wrecks heat-exchange efficiency and gets carbon into the whole engine.
The hot head runs at around 2,000 deg. F in a high-performance Stirling.
Ouch.

Perhaps modern synthetics would address the issue?

Again, models and demo engines are little problem.
Low-temperature-differential Stirlings just use a graphite power piston. I
have a large block of Poco 3 graphite (about 10" square and 1.5" thick),
from a worn-out EDM electrode, that I'm saving for making some of those. I
don't know how it will work because synthetic graphite is kind of nodular
and not as lubricious as natural graphite, but other people have used it, so
it must be Ok.

I guess one would want to wear a respirator while machining
that stuff, but I have no experience with it.


(little Stirling engine demonstrator)

That's cute. It looks like it's based on an old Popular Mechanics plan
that's around here somewhere.

'Wouldn't surprise me.
I love looking at old PM and Mechanix Illustrated, etc. magazines,
for this kind of thing. They are a reminder of how far we've
fallen as a culture though, so that bit is a little depressing.


--Winston