[scientizscht (OP)]

Can you explain how to heat and cool using magnetic fields?

What materials and magnetic fields are used? What is the efficiency? What are the limitations?

Thank you

[Bored chemist]

Do you mean this sort of thing?
https://en.wikipedia.org/wiki/Magnetic_refrigeration#Room_temperature_devices

[scientizscht (OP)]

Do you mean this sort of thing?
https://en.wikipedia.org/wiki/Magnetic_refrigeration#Room_temperature_devices

Yes please, can you explain the basics?

So specific materials under magnetic field get cold. What are the properties of this magnetic field? How effective that is? If I understood well, under the magnetic fields they release heat, so the environment gets warm. How can they get cold in a warm environment? I don't really understand how this works, can you explain please? In few sentences. Almost everything can be explained in few sentences.

[Kryptid]

I had not heard about using magnetic fields to cool things before, but heating objects up with them is pretty easy and commonplace (inductive cooking, for example). You can look into that here: https://en.wikipedia.org/wiki/Induction_heating

Here is a video displaying magnetic induction heating a metal to white-hot temperatures, causing it to melt:

[scientizscht (OP)]

I had not heard about using magnetic fields to cool things before, but heating objects up with them is pretty easy and commonplace (inductive cooking, for example). You can look into that here: https://en.wikipedia.org/wiki/Induction_heating

Here is a video displaying magnetic induction heating a metal to white-hot temperatures, causing it to melt:

how does heating work in few words?

[Kryptid]

how does heating work in few words?

Changing magnetic fields induce electric currents in conducting materials. When the material has a finite resistance (i.e. anything other than a superconductor), there is resistance to the flow of electrical energy and some of that energy is dissipated as heat. Changing the magnetic field quickly increases the amount of induced electric current and therefore the amount of heat generated.

[scientizscht (OP)]

how does heating work in few words?

Changing magnetic fields induce electric currents in conducting materials. When the material has a finite resistance (i.e. anything other than a superconductor), there is resistance to the flow of electrical energy and some of that energy is dissipated as heat. Changing the magnetic field quickly increases the amount of induced electric current and therefore the amount of heat generated.

Is that more efficient than just applying alternating voltage to the metal?

[Kryptid]

Is that more efficient than just applying alternating voltage to the metal?

Unfortunately, I'm not sure. My intuition tells me that it would be at least a little bit less efficient, since there are more steps of energy conversion involved with magnetic heating than there are with taking a source of electricity and applying it directly to the metal you are trying to heat.

[Bored chemist]

Yes please, can you explain the basics?

If I could explain it better than the WIKI page does...
I'd rewrite the page.

[scientizscht (OP)]

Is that more efficient than just applying alternating voltage to the metal?

Unfortunately, I'm not sure. My intuition tells me that it would be at least a little bit less efficient, since there are more steps of energy conversion involved with magnetic heating than there are with taking a source of electricity and applying it directly to the metal you are trying to heat.

So why bother?

[scientizscht (OP)]

Yes please, can you explain the basics?

If I could explain it better than the WIKI page does...
I'd rewrite the page.

Try your best, I am dyslexic

[Kryptid]

So why bother?

There are definitely some advantages, such as safety and convenience. For applications like inductive cooking, it's significantly safer than hooking wires up to a metal pan and then trying to fry an egg with it. It's also easier to do if all you have to do is put the object you want heated into the field instead of trying to find somewhere to attach electrodes to it. I'm guessing that the heating is also more evenly distributed throughout the material via magnetic induction.

[evan_au]

The first thing to say is that the most common application of magnetic refrigeration today is for cryogenic applications, trying to produce temperatures very close to absolute zero.
- It is very hard to cool things below the temperature of liquid Helium, so exotic and expensive techniques like magnetic refrigeration and laser cooling have been developed to achieve temperatures very close to absolute zero.
- But for household use, the use of a conventional gas/liquid refrigerator is likely to remain common

So specific materials under magnetic field get cold.

Actually, it's the opposite. When you put elements like Gadolinium in a magnetic field, they heat up.

But heat is good in a refrigerator!
- I recall my surprise as a teenager at seeing a refrigerator used in remote locations away from the electricity grid, driven by a flame!
- The first step in a home refrigerator is to compress a gas, making it hot.
- The important thing is that the heat is radiated away (eg into the air) before the refrigerant is introduced into the "cold" chamber

What are the properties of this magnetic field?

It depends on the refrigerant and how much cooling you want.
For some applications you need a 1-3 Tesla magnetic field, which is really quite strong. Magnetic fields this strong are often generated by superconducting magnets.

If I understood well, under the magnetic fields they release heat, so the environment gets warm. How can they get cold in a warm environment?

1. Yes, the magnet gets warmer when you put it in a magnetic field. So you do this step outside the cold chamber, and carry the heat away by conduction or convection (or by another type of refrigerator, operating at higher temperatures, like a liquid helium refrigerator).
2. After the refrigerant has cooled down again, you move it into the cold chamber, and now remove the magnetic field. This makes the refrigerant cooler than it was before, and it absorbs heat from the cold chamber. This reduces the temperature of the cold chamber. When the refrigerant has absorbed all the heat it can, you take the refrigerant outside the cold chamber.

To make a refrigerator, repeat steps 1 & 2 forever. This moves heat from inside the cold chamber to outside the cold chamber.

[syhprum]

Albert Einstein and a collaborator took out patents on a magnetic refrigerator.
I am in error here it was an adsorbtion type refrigerator with a magnetic commpressor

[scientizscht (OP)]

The first thing to say is that the most common application of magnetic refrigeration today is for cryogenic applications, trying to produce temperatures very close to absolute zero.
- It is very hard to cool things below the temperature of liquid Helium, so exotic and expensive techniques like magnetic refrigeration and laser cooling have been developed to achieve temperatures very close to absolute zero.
- But for household use, the use of a conventional gas/liquid refrigerator is likely to remain common

So specific materials under magnetic field get cold.

Actually, it's the opposite. When you put elements like Gadolinium in a magnetic field, they heat up.

But heat is good in a refrigerator!
- I recall my surprise as a teenager at seeing a refrigerator used in remote locations away from the electricity grid, driven by a flame!
- The first step in a home refrigerator is to compress a gas, making it hot.
- The important thing is that the heat is radiated away (eg into the air) before the refrigerant is introduced into the "cold" chamber

What are the properties of this magnetic field?

It depends on the refrigerant and how much cooling you want.
For some applications you need a 1-3 Tesla magnetic field, which is really quite strong. Magnetic fields this strong are often generated by superconducting magnets.

If I understood well, under the magnetic fields they release heat, so the environment gets warm. How can they get cold in a warm environment?

1. Yes, the magnet gets warmer when you put it in a magnetic field. So you do this step outside the cold chamber, and carry the heat away by conduction or convection (or by another type of refrigerator, operating at higher temperatures, like a liquid helium refrigerator).
2. After the refrigerant has cooled down again, you move it into the cold chamber, and now remove the magnetic field. This makes the refrigerant cooler than it was before, and it absorbs heat from the cold chamber. This reduces the temperature of the cold chamber. When the refrigerant has absorbed all the heat it can, you take the refrigerant outside the cold chamber.

To make a refrigerator, repeat steps 1 & 2 forever. This moves heat from inside the cold chamber to outside the cold chamber.

You are confusing.
You put a magnet under changing magnetic field. This will heat up the magnet through induction. What's the next step to achieve refrigeration?
It doesn't make sense.

[evan_au]

You put a magnet under changing magnetic field. This will heat up the magnet through induction.

Not necessarily.
Inductive heating occurs if there are large volumes of electrically conductive material within the changing magnetic field, which can carry an electric current.
- You can reduce the amount of inductive heating by reducing the frequency of magnetic field changes.
- You can reduce the electrically conductive volume by using fine particles of the magnetic medium which are in an insulating matrix.
- You can eliminate the electrical current by using a magnetic medium which is an electrical insulator.

You would select a material and construction so that the cooling effect is greater than any inductive heating effect.

[chiralSPO]

I hadn't heard of these before (so I might be wrong), but it makes sense to me--it's completely analogous to a standard refrigeration strategy, except instead of using pressure to change between two states of matter (gas and liquid), one can use a magnetic field to change spin states. In both cases there are two states, A and B. Going from state A to state B releases heat, and going from state B to state A absorbs heat. If one can force the system to go from state A to state B in "chamber one", and then allow it to return from B to A in "chamber two," and then move it back to "chamber one" before forcing it back into state B again, etc. etc. then "chamber one" will get hotter, and "chamber two" will get colder. You have to put energy into the device to move the heat around (no such thing as a free lunch), but ultimately magnetic refrigeration is only another way of moving the heat.

[scientizscht (OP)]

I hadn't heard of these before (so I might be wrong), but it makes sense to me--it's completely analogous to a standard refrigeration strategy, except instead of using pressure to change between two states of matter (gas and liquid), one can use a magnetic field to change spin states. In both cases there are two states, A and B. Going from state A to state B releases heat, and going from state B to state A absorbs heat. If one can force the system to go from state A to state B in "chamber one", and then allow it to return from B to A in "chamber two," and then move it back to "chamber one" before forcing it back into state B again, etc. etc. then "chamber one" will get hotter, and "chamber two" will get colder. You have to put energy into the device to move the heat around (no such thing as a free lunch), but ultimately magnetic refrigeration is only another way of moving the heat.

Ok and you didn't thank me for informing you that you can cool with magnetic field

[chiralSPO]

Thank you