What I learned today

??

Thermodynamics is a notoriously difficult subject to teach, and I didn't fi nd making sense of it any picnic.

The quantum-theoretical definition of temperature depends on the relative p opulation of the progressively higher energy quantised states.

If every atom is in the ground state, you are at absolute zero, and as the temperature rises, some atoms get promoted to higher energy states.

What's tricky about magnetic ordering is that changing the magnetic field c hanges the energy difference between states that differ in magnetic orienta tion.

With no magnetic field, the orientation is random. If you apply a magnetic field instantly, half the atoms are in the high energy state and half in th e low, which corresponds to an infinitely high temperature.

Laser operation depends on setting up similarly 'inverted' energy distribut ions, but here the energy just redistributes itself to other modes - rotati on and translation - and the magnet as a whole heats up (but not to infinit y or anything like it - there's not a lot of energy stored by being oriente d against the magnetic field) .

Given enough time in the high magnetic field, most of this extra heat will radiate, conduct and convect away, leaving the magnet at ambient.

Subsequently taking away the magnetic field shrinks the energy difference b etween the magnetic orientations, and for these energy states.This results in a temperature that is lower than the environment.

Again this redistributes itself to other modes, and the magnet as a whole b ecomes cooler than the environment.

Think of it happening sequentially. Starting at some base temperature, place the material in the magnetic field. The domains align and the temperature rises. Leave it in the magnetic field and give it some way to cool off, back down to the original base temperature. Pump liquid coolant over the material, blow air on it, give it time to radiate the heat away, whatever. Now take it out of the magnetic field. The domains randomize and this absorbs heat so the material cools down to a temperature colder than when you started. Let it absorb heat as it cools some load until it gets back up to the original base temperature, then put it back in the magnetic field and start the cycle over. If you just put the material in the magnetic field but keep it insulated it will warm up and stay at the new, hotter temperature. Turn the magnetic field off and it will cool back down to the original temperature so there would be no net cooling or pumping of heat. Clear (as mud :-))?

I'm not refuting that 'a' process will cool, just that they worded it very badly.

They said, "Gadolinium alloy heats up inside the magnetic field and loses thermal energy to the environment, ..."

It made no sense to me that a material could heat up AND lose thermal energy to the environment. It is true that if it did lose heat to the environment it would exit cooler than when entering the field. How do you 'heat up' a material and have it lose heat? I thought heat up a material means it takes up heat. [Is that 'generate' heat? AHA!]

Again, to me they should have said the phrase simply, Gadolinium alloy has its molecules line up inside the magnetic field and loses thermal energy to the environment, so it exits the field cooler than when it entered. Which coorelates to your statement, "Remove the field and the spins start shift absorbing heat as they do so."

I still say, poorly worded due to the phrase 'heats up' to describe the molecular alignment. To me, heats up means it would exit hotter than when went in AND etc. Perhaps, the concept is that applying a magnetic field causes the material to lose heat, which 'feels' like heating up. arrrggg! Perhaps that is "...heats up inside the magnetic field and..." THUS "..loses thermal energy to the environment,..." or, Gadolinium allow 'generates' heat inside the magnetic field... now THAT I could buy. It's much easier to understand *if* I ignore what they said and simply envision the process. I give up.

A bit embarrassing to be so dense about this when English is my first language.

Oh :(

Works ok here, gives a "download" button and format selector, but thanks for the detailed error report :)

Seems to link through to "savefrom.net" to do the work, if that helps.