I learned that there are certain materials that when subjected to a changing magnetic field will heat or when the magnetic field is removed they cool. Ge is developing materials to work at refrigerator temps, freezer temps and low temp freezers. "They" suggest this could be in consumers products in 5 years. It will eliminate freon from refrigeration systems. The product could use 25% less electricity but cost a little more to produce.
Sunshine could heat, causing pressure to run a pump. The pump cycles the 'fluid' through the system. The system has regions of magnetic field and regions of no magnetic field. The alloy is pumped through the 'cooling' region with NO field, thus as the molecules scurry back into entropy they 'eat' heat. Then the alloy continues back out into the non-cooling area, the room, where the alloy is subjected to a field and as the molecules are again lined up, generate/give off heat.
Given that heat is far more efficiently produced from sunshine than electricity:
Ammonia Cycle. Well-known established technology, not entirely forgotten yet. Of course, you _might_ want to put the ammonia part exterior to the building envelope and pump a more innocuous fluid into the house heat exchanger.
Lithium salt solutions are another approach - less noxious fluid, but higher temperatures needed to regenerate - concentrating solar collectors can reach those temperatures, but solar collection efficiency drops as required temperature rises.
More generally, absorption cycle refrigeration.
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Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
It's not all that hard to understand. Low temperature physics types have been using it for years.. search under adiabatic demagnetization.
Step one connect magnetic material to heat bath (outside for a refrigerator.)
2.) apply big B field.
3.) wait while spins become polarized along field direction. (There is a loss of energy as the spins polarize... go into a lower enrgy state.. this energy (as heat) is put into the heat bath.)
4.) remove from heat bath and connect to thing you want to cool.
5.) Remove the B field.*
6.) spins are still polarized but now that's a higher energy state. (hmm OK maybe lower entropy... spins are aligned and lower entropy is when they are random.) This depolarization causes the sample to cool. Rinse and repeat.
I may have made a mistake in the above. George H.
*(I'd have to think more about how to remove the B field... do you want it fast or slow??? )
ve been using it for years.. search under adiabatic demagnetization.
ator.)
rgy state.. this energy (as heat) is put into the heat bath.)
mm OK maybe lower entropy... spins are aligned and lower entropy is when th ey are random.) This depolarization causes the sample to cool.
it fast or slow??? )
(I didn't watch the video...) Great question. The answer is YES! So in some sense this is also about NM R and relaxation times. When you put a spin in a B field it doens't polarize instantly. It takes some time.. called the T1 time by NMR types*. And yo u've got to wait several T1 times for the system to come to the new equilib rium.
Well you can't cause it to polarize with E&M. But if it is polarized then you can depolarize it... (cause transitions bet ween the spin states.) with the right frequency B-field. Dat's what NMR is all about!
George H.
*There's a story told by old NMRers (I don't know if it's true.) that the f irst guy to go looking for an NMR signal tried water. Good choice cause th ere are a lot of protons in water. (hydrogen atoms) But also a bad choice because the T1 time in pure water can be several seconds and he was lookin g on too short a time scale. (Of course you don't know the T1 time of wate r til you do the measurement.)
I recall reading about that effect in popsci back in the 70's. It's only taken 40'ish years to advance this far. At that rate we'll be long dead before a useful product emerges. {yawn} Art
I believe I remember that the early prototypes had issues with magnetostriction. The generation of the high-frequency "changing magnetic field" and the flexing it induces in the various metal parts caused the refrigerators to whine and howl :-(
The basic principle, is that some materials have lower heat capacity when in a magnetic field. So, if you apply magnets, then wait for equilibrium with ambient temperature, then remove magnets, the heat capacity goes UP but the thermal energy remains constant (that's the 'adiabatic' part). So, temperature = T_energy/H_capacity goes down.
Simpler, is to stretch a rubber band (and its heat capacity goes down) - try it, you can feel that the rubber band gets hotter. Then, after it reaches ambient temperature, let it relax (and the heat capacity goes UP). The rubber band becomes cooler than ambient temperature.
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