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In the regular Stirling engine, the expanding heated gas
pushes the rotor, which in turn pushes a 'displacer' which
pushes the heated gas away from the heat source and
into
the cooling chamber, and after cooling and compressing
is
pushed back to the heating chamber for another cycle.
In
the solid Stirling engine the heated metal rod expands
and pushes the rotor, it is then mechanically moved to
the
cooling location, where it is cooled and detracts, only to
be set in place again for the heating cycle.
The movement to and from the heat source and cooling
source, can be controlled mechanically, electrically or
digitally. The action can be done by moving the sources
of
heat and cooling, or by moving the rod(s).
If the source of heat is concentrated sunlight, it can be
directed (and avoided) dynamically along the pathway,
creating a truly rotary Stirling engine.
Malone liquid engine
http://www.douglas-...id/maloneliquid.htm
Bad enough using water, never mind a solid ... [8th of 7, Sep 01 2014]
Bimetal heat engine
http://sci-toys.com...thermo/thermo3.html
[scad mientist, Sep 17 2014]
Rubber band heat engine
https://www.haverfo...and_heat_engine.htm
[scad mientist, Sep 17 2014]
[link]
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Stirling engines work best where the working
fluid has a high coefficient of expansion;
hydrogen gas is the optimum. Compared to
gases, the expansion of solids is very small. |
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The expansion of solids is also rather irresistible. Imagine an associated gear ratio, converting that enormous force into significant motion.... |
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Soiled Sterling Engine. Engine composed of grubby English
pound coins assembled together in such a way as to use
their knurled edges as cog wheels that bear against each
other. |
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[Vern], that's just a matter of leverage - converting a high pressure
short travel to a longer travel at lower force. |
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A "solid" stirling engine might be made to work using a set of long,
very thin wires (to maximise Δl, and allow rapid heating/cooling)
which move in and out of the hot and cold zones, generating power on
contraction, not expansion. |
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//generating power on contraction, not expansion//
They're solid; no reason they can't push AND pull. Or were you thinking wires = too flexible for pull? A "swash plate" style system would be the way to go.
Crazy idea popped into my head - why have multiple independent wires? A piece of pipe (maybe thicker with machined cooling fins) that rotates past the hot source/cold sink, swash plate on a TINY angle at the end. Hmm, I may have to CAD+FEA a model at lunchtime... |
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It's a devil getting those Δl's like you used to, they just can't get the wood. |
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"Poor, poor, poor old Jim Tigernuts .... He couldn't get the wood either.
He had to put 'em in cardboard boxes." |
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Come out of there. Tigers aren't meant to be slept in you know. You mustn't... Come out at once |
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Asked Jutta to run this joke every 24 hours, it's unix server so it can be a crun job. |
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NB the best lines are in Shifting Sands, Series 7, Episode 17. Ironically it's partly about the British Army in Waziristan.. |
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I was able to follow the discussion up to not morrison's first
anno. |
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You silly, twisted boy, you ... |
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Back to the discussion: If instead of a simple solid
rod, the
rod was made from a porous but rigid metallic
material, it
would on the one hand gain and lose heat quickly
while also
quickly expanding or contracting. This can be
exploited in
various ways, generating power from both
contraction and
expansion. |
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[marked-for-tagline] //expanding and detracting// |
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There was a NASA-developed solar motor, that was a heat engine with a solid 'working fluid'. It was mentioned briefly in a sidebar in popular science or something about 30 years ago. It consisted of a metal pipe or tube, horizontal, supported on bearings at each end, and with a round heavy weight (i.e. a flywheel) at midspan. When placed in the sun, the top of the tube would heat and expand, causing the tube to bend upwards and thus to raise the weight, which (as weights do) preferred a lower position which was conveniently made accessible by rotation of the tube. As you might imagine, the cycle would continue as long as the tube was heated on one side, from any direction except directly underneath. |
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This arrangement leverages a small expansion with large force, as noted by Vernon. |
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I imagine the efficiency and power density to be poor, but it's an interesting and simple heat engine (not necessarily strictly a Stirling cycle, but neither are a lot of 'stirlings'). Also, it fits the description in this idea, hence my anno. Thank you for your kind attention. |
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No, you might not, because Nitinol engines
exploit flexion, not the expansion/contraction
ccle of the true Stirling engine. |
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Go to google books and look at Popular Science July 1980, page 112. |
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Hmm, load of nitinol springs on a carousel, pressed up against car radiator, one gets hot, expands, then rotate away to let it cool, as the water in rad is usually 80 degrees c. Mighty expensive way to harvest energy given the price of the metal. |
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Now, if you had a closed circuit sub-atmospheric pressure steam engine, with lots of brass twiddly bits and a small robot Fred Dibnah.. |
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pashute, what substance would you use for the rod? |
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//I was able to follow the discussion up to not morrison's first anno |
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His Borgness was trying to use a character (not Seagoon) that doesn't work on HB, it's strictly boring old ASCII so something he typed ended up as |
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and I was just trying to point out that it didn't work. Unless of course he did mean to type Δl. |
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I can't argue with solids heating up and expanding, so I can only agree with pashute that this would work, but what would be the special advantage? |
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The mechanism does strangely remind me of a gatling gun. |
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Delta-l ; small change in length. Analagous to delta-vee for change in
velocity. |
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Search for bimetal heat engines. Most are pretty
simple lab demonstrations like <link>, but it seems
to me that a motor very similar to the nitinol heat
engine ought to be able to be built using a cheap
bimetallic strip rather than nitinol. I suspect the
reason for the typical demonstrations seen on the
web is the wide availability of cheap
thermometers. If you can't get a bimetallic loop to
duplicate the nitinol engine, you could probably
arrange several of these bimetallic springs in a
rotating contraption to create continuous
rotation. That might look similar to a rubber band
heat engine <link>. |
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// a NASA-developed solar motor // Is it just me or
is it ironic that NASA would develop a solar heat
engine that uses gravity to operate. Of course it
could be useful on the moon or simply by using a
pulley with tensioned belt instead of the weighted
flywheel, but it just struck me as odd. |
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