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Over the years, I've often heard of Tesla's ambient heat engine (cold hole) and blown it off as just another one of his wacky schemes (he had many). However, a recent post made me reconsider the possibility.

Which post, Matt?

Not sure how you figure "hot" gas is expanding into the power piston. The cold gas, for the most part, is heated and expanded below the displacer as the displacer raises up and drives cold air down to be heated. Aside from that, we can generally say the gas does not actually heat up that ...

VincentG, the power piston is on the cold, plate and side. There shouldn't be any hot gas there. Right? I don't agree. The displacer is agitating the gas and imo the ideal model of just high pressure cold gas powering the piston is not what actually occurs. The piston is increasing volume and I'd b...

I'm still confused Tom. Why would the power piston NOT be warmer? Hot gas is expanding into it..

Moving this discussion from the Essex thread, I do see the potential of a regenerator. Let's say the regenerator is contained in a separate circuit outside the engine. Then if the regenerator is active(gas flowing through) only when the displacer is moving, and is isolated from the rest of the syste...

Imo the Essex works so good with such a simple design because it makes no attempt at traditional "regeneration" and instead makes an attempt at minimizing thermal mass. I would wager that any attempt at adding on a traditional regenerator would lower specific power output. Again, imo, in p...

Due to the thin brass walls(.015") of the main tube, displacer and power piston, the original Essex has pretty effective regeneration without any additional dead space or flow restriction. I'll try to film a thermal video to show this later.

Not sure if you will find this relevant. https://youtube.com/shorts/AvZ_GvFu8xE?si=Zyp537_zeX7PRnk7 I don't think chasing surface area with complicated design is needed until some other things are figured out. Imo the overall proximity of the heat exchanger to the gas is more important, and most imp...

I think it would be helpful to put pressure and volume values on these ideal PV graphs.

Yes, I actually measured my aluminum plate, painted black over boiling water and saw 250 degrees f. They are good for comparison but definitely dont seem accurate in all circumstances.

Hey Tom have all your below ambient results been with an acrylic hot plate? I just realized that and it explains why my engine with metal plate always heat soaks the cold plate.

I know the metal hot plate is way overkill for these small ltd engines and have been meaning to test a plastic hot end.

No the point I was making is that the claims of inaccuracies due to the different emissivity of various materials is perhaps negligible. (I and others have made these claims.)


I'm just suggesting that these models are just too small to sway anyone's belief.

Is this right or have I fouled up? 9072 Watts in to get 145 Watts shaft power out seems very poor. Surely they'd have been better off slapping electric underfloor heating elements all over the base of the displacer cylinder than running heated Ethylene glycol round a small area of the sidewalls? Ag...

Tom, in the name of science I spray painted half of a Pyrex bowl flat black and tested with the thermal gun at room temperature and after hot water exposure. There was no discernable difference except for a small variation where the paint transitioned to clear glass. I also tested a piece of black p...