Cryogenics Methods of Cooling
The following four things listed are four of the methods of cryogenic cooling.
1. Evaporative Cooling
2. Joule-Thompson Effect
3. Heat Conduction
4. Adiabatic Demagnitization
1. Evaporative Cooling
- Used when atoms are in a gaseous state, they have more energy than they do when they are in a gaseous state
- When a liquid evaporates, atoms or molecules at the surface acquire enough energy from the surrounding liquid to enter the gaseous state. The remaining liquid has relatively less energy,so its temperature drops.
- By encouraging the process of evaporation, the temperature of liquids can be lowered.
- It can be used to reduce the temperature of liquid nitrogen to its freezing point, or to lower the temperature of liquid helium to approximately 1K
- Joule-Thompson effect also called cooling by rapid expansion
- Even though they are different, they are used in conjunction with one another
- Example: Kamerlingh Onnes
- First Step: When he first liquified helium, he cooled the gas through conduction to successively lower temperatures
- Second Step: Brought it into contact with three successively colder liquids: Oxygen, Nitrogen, and Hydrogen
- Last Step: Used a Joule-Thompson valve to expand the cold gas and produce a mixture of gas and liquid droplets
Adiabatic Demagnatization
- Uses salts that are paramagnetic in order to absorb the heat from whatever you are trying to cool
- With this method, it is possible to reach a temperature of that is a thousandth above 0K.
- Paramagnetic magnets are made up of a bunch of tiny magnets that are called magnetic moments
- When the alt is placed in a magnetic field by turning on a nearby electromagnet, the north poles of each magnetic moment are repelled by the north pole of the applied magnetic field, so many of the moments align in the same way, that is, opposite to the applied field. This process decreases the entropy of the system.
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