The duster can I use always gets really cold whenever I use it for long enough. Can someone explain in the simplest way possible the reason why it gets cold?
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When all the particles are compressed, they bump into each other a whole lot. When they get sent out of the can, they can’t bump into each other as much because they have so much more space. It’s boosted by the fact that in the can, it’s a liquid, and it exits as a gas. When it transitions between the two states, it has to absorb a certain amount of energy (or release it in the case of gas to liquid).
When you compress something, it gets hot, and when you release that pressure, it gets cold. It’s the basis on which air conditioners and refrigerators work.
Heat on the atomic scale is atoms moving around. The faster they move around, the hotter they are. When something hot is sitting buy itself it’s kind of like a [newton’s cradle](https://78.media.tumblr.com/09d9c6e81fb491101b642fe068a80775/tumblr_nz9eg301um1qdewlro1_500.gif). Atoms like the balls are transferring their momentum to each other as they move about. When it reaches the edge of the object it’s atomic bonds swing it back in like the strings holding the balls on the newton’s cradle.
Now what would happen if you took some scissors and cut the string just as the edge ball of the newton’s cradle swings out? It’ll take it’s momentum and continue flying off instead of bringing that momentum back to retransfer it’s energy to the rest of the balls. This leaves the remaining balls relatively still compared to when they were swaying back and forth.
That’s what happens when air leaves the spray can. It’s also what happens when sweat leaves your skin, or when condensed coolant is uncompressed inside your air conditioner. It leaves the atoms that remain cooler than before.
This is a prime example of boils law.
think about temperature as a concentration of energy. When you spray the duster you are lowering the concentration of energy and the temperature. This is how your AC works in your home and car.
Also the ideal gas law PV=nRT
This is a prime example of boils law.
think about temperature as a concentration of energy. When you spray the duster you are lowering the concentration of energy and the temperature. This is how your AC works in your home and car.
Actually, this cooling phenomenon is called “joule-thomson effect” and it is rather difficult for ELI5, if you want to be technically correct.
You know how you can boil water by adding heat to it? The reverse is also true; if you force it to turn into a gas by putting it in a vacuum chamber, it “sucks” heat from the surroundings. This is true for all matter.
The liquid they put in duster cans boils at a very low temperature, but is kept under pressure by the can, so it stays liquid. When you release gas from the can, the liquid starts boiling off, and as it goes from a liquid to a gas, it “sucks” heat from its surroundings!
1. There is liquid in the can.
2. This liquid evaporates creating gas in the can, which puts the contents under pressure.
3. At this certain pressure, the amount of liquid and gas remain constant.
4. When you use the duster gas, it comes out of the can reducing the pressure.
5. To keep the pressure in constant, the liquid evaporates into a gas.
6. Energy is needed for a liquid to turn into a gas so the can goes cold.
When you squeeze a wet sponge, it leaks a bunch of water so it feels very wet, but you just squeezed a bunch of water out so it is holding less water, despite feeling more wet.
When you release a clenched sponge, it feels very dry because it now has a bunch of space for more water and thus absorbs moisture from its surroundings.
Gases do the same thing with heat under pressure. When you squeeze a gas, it releases a bunch of heat and when you decompress gas, it has more room for heat and absorbs a bunch from its surroundings.
The important observation here is that how hot a gas feels is actually not related to how much heat it is holding, but rather how much heat is leaking out of it.
Imagine the duster can as a magic spray bottle. When you press the button, the magic inside the can starts to come out. But this magic isn’t like the usual water or juice you might spray from a bottle.
Inside the can, there is a special kind of gas that is squeezed really tightly. When you press the button, the gas gets released and starts to expand, just like a balloon being blown up. But when the gas expands, it needs more space, so it takes the space around it.
But here’s the interesting part: When the gas takes up more space, it actually needs to use some energy to do that. It’s like doing a little bit of exercise for the gas. And when it uses energy, it starts to feel colder.
So, when you use the duster can for a while, the gas inside keeps expanding and using energy, which makes it get colder and colder. That’s why you feel it getting chilly when you hold the can for too long.
But remember, even though it gets cold, the duster can isn’t meant to be used for cooling things. It’s designed to blow away dust and dirt, so be careful and use it only for its intended purpose
When gas under pressure loses pressure, it’s temperature drops, the volume expands, or both.
Since the can has a fixed volume, the only thing that can happen is the temperature going down.
This is also how air conditioners work, more or less.
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