Elastocaloric materials are a class of materials that exhibit a big change in temperature when exposed to mechanical stress. This could potentially make them useful as solid-state replacement for both vapor-compression refrigeration systems and Peltier coolers.
So far one issue has been that reaching freezing temperatures was impossible, but a recently demonstrated solution (online PDF via IEEE Spectrum) using NiTi-based shape-memory alloys addressed that issue with a final temperature of -12°C achieved within 15 minutes from room temperature.
In the paper by [Guoan Zhou] et al. the cascade cooler is described, with eight stages of each three tubular, thin-walled NiTi structures. Each of these stages is mechanically loaded by a ceramic head that provides the 900 MPa mechanical stress required to transfer thermal energy via the stages from one side to the other of the device, alternately absorbing or releasing the energy with CaCl2 as the heat-exchange fluid.
NiTi alloys are known as about the ideal type of SMA for this elastocaloric purpose, so how much further this technology can be pushed remains to be seen. For stationary refrigeration applications it might just be the ticket, but we’ll have to see as the technology is developed further.
Yeah paywall!
PDF is not paywalled.
https://hackaday.com/2016/08/25/a-refrigerator-cooled-by-rubber-bands/
I remember when i used to repeatedly strech and loosen rubber bands and hold them against my upper lip as a kid. i was fascinated by the cooling effect when releasing the tension
How can it be both solid state and elasto?
compliant mechanisms? At least in the cooling part. So no parts that wear.
The actuator could be non-solid state at the moment.
900 MPa to get a temperature change of a lousy 16.3 C !!!?! Yeesh.
900 MPa is higher than the yield strength of most common steels.
Compressing even just plain air would pump a lot more heat, and get much higher temperature differentials at much lower pressures, and wouldn’t exceed the yield strength of most materials.
A diesel engine compression stroke gets hot enough to instantly ignite fuel at less than 3 MPa.
If you try to put 900 MPa into air it will get hot enough to become plasma. Actually, it will become a supercritical liquid first, but probably rupture your containment vessel even earlier.
900 MPa is insane. That’s starting to approach diamond-making pressures.
(Though, yes, strain is the correct term to use to determine the heat input here, not stress. But stress is what determines when your hardware will turn into a worthless warped lump of waste metal.)