How refrigerators and air conditioners work

[ProPM]

Hi,

I was looking at how refrigerators and air conditioners work as part of thermodynamics and I came across the expansion valve.

I am a bit confused. From what I understand, there is this expansion valve. When the liquid freon, or ammonia as used as an example in this website, goes through the evaporator it returns to the gaseous state. But, if the gas is allowed to expand, won't it do work at the expense of it's own internal energy, and, therefore, cool, and, if it cools, how come does it become a gas and not a solid?

I think the answer why is pretty simple but I just can't see it!

Thanks in advance!

 

[Antiphon]

It does cool but not enough to turn solid.

(this is why you don't use CO2 as a refrigerant. If you need to get down to really low temps, you use He. It won't solidify until close to zero K.)

 

[ProPM]

But how does it boil and vaporizes? We need to heat a liquid to vaporize it, right?

 

[SteamKing]

In order for the working fluid to expand, it must absorb heat from the surroundings. This is why A/C units and refrigerators cool.

 

[supratim1]

the heat you are talking about is taken from the things (and air) kept in the refrigerator, thus cooling them.