https://www.stirlingworks.co.uk/innovation
The use of a kind of spiral planar spring as a displacer is quite interesting.
https://youtu.be/knhXOnILotk?si=k-neaYUVwnu5OXOL
I was excited to see the initial description at the early part of the video, as it appeared to be a method of effectively dispensing with the cold "sink" side of the engine.
The final "two displacer" design, one hot and the other cold, though, was, for me anyway, a bit of a let down.
The hot AND cold together, as animated:
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Aside from the planar spring innovation, I had come up with a similar design way back in 2006 which I had posted a link to here to the forum at that time.
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https://members.tripod.com/prc_projects/stirling.html
The phone # and address on that page are no longer valid, but the email is.
viewtopic.php?f=1&t=77&p=150#p156
Anyway, as I started saying above, the hot AND cold displacers together, as animated, do nothing, as far as I can see, to eliminate "mixing" or intermingling of hot and cold air. The surface area is increased tremendously, but as shown by my 2006 design, there are other ways of accomplishing that.
What I THOUGHT was fantastic about this new planar spring style displacer innovation, as I first imagined it or as first demonstrated in Andrew Hall's video is, or was...
This "coil" or planar spring displacer design used as a kind of HEAT VALVE, with no open spaces between the spirals and no upright fins protruding up through the spaces, could be very effective as an INSULATOR to cover the hot side and prevent heat addition to the working fluid.
Then lifting the spiral would open up numerous passageways, fully exposing the hot plate. Then it could be lowered to again, cleanly cut off heat input. With dwell, the bottom part of the displacer/heat valve could take up heat during the down, dwell period, and provide additional surface area for exchanging heat with the working fluid when raised.
The concave shape would help to eliminate some dead air space, which would be advantageous I think.
Anyway, the exciting news of a new radical ino action, for me, turned into a kind of ho hum, same old same old Carnot fallacy infected concept of removing heat after adding it, dumping the "waste heat" to a cold side, but now a cold side with enormous (unnecessary IMO) surface area designed to eliminate an abundance of "waste heat" that is not actually there, if it was CONVERTED to WORK output as heat engines are supposed to do.
A curved bottom hot plate is hardly necessary IMO, so what I would do with this basic planar spring displacer concept would be something like this:
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As, hopefully, can be seen, the planar spring/spiral "displacer"/heat valve (illustrated in blue) has tight fitting spirals with absolutely minimal air gap, just enough to provide clearance and avoid binding and friction.
If there are prongs or a spiral vane or grove of some sort to increase surface area for heat exchange, this, IMO, only provides benefit for heat INPUT on the hot side
Once the working fluid is heated and expands transferring energy to the piston as WORK output, it naturally drops in temperature, due to the expenditure of energy.
The spiral displacer should be insulating on top and retain heat on the bottom.
The spiral "heat valve" should only "open" or lift, briefly when the piston is down (at "TDC"). To let in a quantity of heat the engine can utilize for each cycle and no more.
I've found that the magnetic displacer design is an effective way to accomplish this and is self regulating.
If the engine slows, the magnet lifts the displacer higher and for a longer period, adding more heat. If the engine speeds up, the displacer is lifted less and more briefly.