Thermodynamic Oddities

From a conversation this morning…

Vortex tubes: Put compressed air in the middle, one end emits hot air, one end emits cold air. Reminds me of a mechanical peltier.

Sterling engine: One end gets hot. And it turns.

What other weird things are out there in this space?

I’m familiar with the vortex tubes sold as ‘cold air guns’ for machining parts without cutting fluid where cooling is still needed. What I hadn’t heard of was vests designed to do the same thing-

Friend of mine who’s done some pretty heavy duty structural welding has one, says they’re terrific. 10 CFM at 90 PSI isn’t efficient cooling by any means, but when you’re welding on plate steel in confined spaces efficiency isn’t what you’re after. Interesting where the uses for these things come up.

Nitinol engines. Heat turned to motion by applying it to a nickel-titanium alloy wire. It returns to a ‘remembered’ shape as it cools, applying force.

Nothing that went beyond scientific curiosity, AFAIK. There are some interesting spring and valve applications for the Nitinol material though.

I understand it returns to its remembered shape when it is heated above a threshold temperature. I hadn’t heard of that effect, either - interesting stuff!

Probably old hat to folks here but fun anyway…

Can you use a magnifying glass and moonlight to light a fire?

Answer: You can’t start a fire with moonlight

I’m envisioning the hot and cold sides of a stirling engine being fed by the hot and cold outputs of a vortex tube functioning as a piece of some sort of thermodynamic Rube Goldberg machine.

Don’t think of it as 99% losses! Think of it as 1% gains! :stuck_out_tongue:

I’m sure the efficiency of that system is poor…

And the air compressor for the vortex tube is run from a nitinol engine in hot water, heated from the power produced by the stirling engine…

I ran across this article today: Can nanoscience help make AC more efficient? | Popular Science

Here’s a shorter summary of the ideas: Radiative cooling - Wikipedia

Bonus quote from the article placed next to XKCD:

If all that energy was emitted back into space, it would not have any noticeable effects anywhere at all

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I know that effect can be put to good use at night to generate dozens or hundreds of mW of power between “ground” and “exposed to space,” but using it to chill cooling water for heat rejection is really neat! Plus the general “cool shade panels for the building” thing.

One advantage of rooftop solar is that you get shade, often on the sunniest roof panes - I prefer ground mount for a variety of reasons, but a layer over the roof (with airflow under) can really help reduce cooling loads too. I wonder if I can buy some of these panels to stick on my roof anywhere…

For hot water heating, the engineered black surfaces on the high absorption water heating systems is really unique. It absorbs IR, heats the water, but the emissivity is actually super low, which prevents the captured heat from re-radiating away. It’s not just paint, it’s not just dark, but they figured out how to do that. I read this years and years ago, but don’t recall any of the details. but it’s interesting to think about. Clearly the opposite can be true too; you can engineer a surface that’s really good at emitting IR (black body radiation) at your desired object temperature.