[CompelTechnic]

A few thoughts after reading this as a mechanical engineer:

1. My understanding: this material relies on mechanical work (force x distance = work energy) to add energy to the material by compressing (or tensioning, or "magnetically stressing", which I don't understand) it. Some fraction of this energy is converted phase transitions which absorb heat, and some fraction is retained as spring potential energy. If the material is then heated by ambient air, and then the material is allowed to expand, it will now be at a temperature above the ambient temperature at the start of the cycle. In this way it is similar to a standard refrigeration cycle- just without pipes.

2. The cycle described in point 1 is not particularly unique to this material. You could do a similar process with any mechanical spring (google "rubber band heat engine"), and achieve similar results. This material is likely uniquely well suited to this application because it has usefully large amounts of heat associated with phase transitions at temperatures that correspond well with the temperatures used in a refrigeration cycle.

3. You want the material to dump heat to a hot reservoir while hot and suck heat from a cold reservoir while cold. Standard, fluid based refrigeration cycles do this by pumping the refrigerant to different locations (the condensor and evaporator). (I am assuming) This process would have to open and close dampers to get the hot reservoir air and the cold reservoir air to flow across the material; otherwise you have to move the material between the two locations. Both of these sound expensive/tricky to me.

4. A large challenge here is creating an electrical actuator that can compress the material. It would the following design objectives/constraints:

4a. The material should be shaped into long, narrow rods, or another shape with a large surface area, to be ideal for maximum heat transfer with the air of the hot and cold reservoirs.

4b. The actuator must recover the work energy provided when the material is allowed to expand.

4c. The actuator will have a very short stroke (solids do not compress very far), and large force.

4d. The actuator must last many thousands or millions of cycles without wearing out.

5. This style of refrigeration does not have any higher theoretical or actual efficiency than a fluids-based cycle. However, refrigerants have historically been environmentally damaging when released to the atmosphere. R-12 kills ozone, and is obselete/ outlawed. R-134a is currently in a lot of new systems, there are also newer refrigerants being put into new cars. The only thing particularly bad about R-134a is that 1 kg of R-134a equals several thousand kg's of CO2 in terms of global warming effect.

[cr0sh]

I have a couple of thoughts on how this material might be able to be used - but I'm not a mechanical engineer, so what I mention might be (probably is) worthless:

1. Mechanical compression using hydraulic fluid and electric pumps? 2. Could the hydraulic fluid be used as the heat transference mechanism? 3. Could this material be used in a liquid Sterling cycle pump?

I'm thinking a combination of these might be the answer; the material at one end of a closed cylinder with a piston compressing hydraulic fluid, and the reciprocating motion through some means (and the hydraulic fluid) moving the heat from the material one end to the other end of the cylinder (where it could be dumped).

[pariahHN]

Yeah, I read another article about this material a few days ago and I was trying to figure out how exactly to handle actually moving the heat. Easy to do with a liquid, you can pump it fairly easily and piping can be pretty flexible with routing. Maybe some sort of rotating disk design, with rods rotating from cold zone to hot zone and static blowers in each zone?

[CompelTechnic]

I like that design idea for the rotating disc. It makes me wonder the best way to stress the material while on the "compressed side."

1. Make the edge of the disc rub against a low friction, spring-loaded compressing element (similar to commutator brushes, but designed to really transfer a large load). This is probably infeasible because friction would eat more energy than your cycle would move.

2. Have electric actuators that are mounted on the disk itself. These would have to be powered by slip rings via the shaft. These would be active for half of the cycle and inactive for the other half. Not sure whether they should be radial, azimuthal, or axial mounted. Seems kludgey.

3. Have the disk pass through a magnetic field, exploiting the magnetic effects the article mentions. I have no idea of any of the implementation details of this, but it sounds like a better idea than 1 or 2...

[zaarn]

Put a heat sink on the outside and a water cycle on the inside of the pump.

If you want to cool, you pump heat outside by stopping the water cycle when the material is cold, thus allowing the water to dump it's heat into it.

If you want to heat, you pump heat inside by stopping the water cycle when the material is hot, thus allowing the water to absorb the heat from the material.

You can increase the efficiency of this by having more water touch bot the inside and outside phases (increase material surface area in contact with water and increase surface area of water cycle heatsink).

If you want to allow sub-zero temperatures, add anti-freeze to the water.