DescentBB

So if you compress a gas, it cools? That can't be right. When you put pressure on something it’s suppose to heat up.
and
When ammonia is compressed into a liquid at room temperature, it turns right back into a gas, by evaporating. The evaporation requires energy, which is fueled by heat. The heat is stolen from the surrounding objects, making them very cold. If I could see the atoms with my own eyes, what would they be doing?

I think you answered the first question with your second statement. It only \"feels\" cold because the compressed gas is actually a liquid. When it is expelled into a gas, it evaporates, requiring a lot of energy from the surrounding area. This makes it feel cold. At least that's what I recall from Gr 12 chem ...

As for what the atoms are doing in ammonia? Can't help ya there ...

The one I always found cool (pun alert) is when you purse your lips together and blow air. It's cool. When you open wide and exhale it's warm. Although if you hold your hand out in front a ways and blow with your lips together, it's cool but then keep doing it and move your hand toward your lips. It gets warm. No idea although I'm sure google would answer it. I'll look it up later.

Compressing a gas heats it up... evaporating or releasing the pressure causes it to steal heat from the environment and the cooling effect. Essentially how refrigeration works. Here is a little applet to help illustrate the concept;

Big Link Turned Into Little Link

Oh and we aren't going to help you do all the schoolwork, your going to have to come up with some of the answers yourself!

Canuck's right. My compressor heats up when it's compressing the air, but when I release the air via the tank valve at the bottom, ice forms in the valve from the water in the air.

Canuck wrote:Compressing a gas heats it up

So a gas will heat up when getting compressed. BUT will turn into a liquid, because of the pressure. Once the pressure is released, its high temperature causes it to evaporate taking more heat around it. A drop in pressure and an increase of volume is like a sponge to heat. That still doesn’t make any sense.

okay i think you're getting confused. But hang in there. It's a bumpy ride but it can be snoothed out.

when a gas is compressed, it's temperature raises. the heat is dissapated somewhat by the metal in the cylinder, the lines to the tank and the tank itself.

Now if you were to compress it straight into a liquid from gas in one go, you will need some serious heat dissapation. That is the reason why most industries go with a cascading compressor.

This cascading compressor involves at least two compressors. The first stage compresses the gas which heads to a heat exchanger, then to a secnd compressor.

That second stage compresses that gas further to either a highly compressed gas, or if run through a heat exchanger becomes into a liquid.

Three-stage cascade compressors take it one stage further. the heat exchanging components are still there, but that third stage is used for the final product.

You can think of it this way: the lower the boiling point of a gas, the more stages you will need to change the gas to a liquid.

Pretty simple concept: http://en.wikipedia.org/wiki/Refrigerat ... sion_cycle

Some compounds, when forced to become liquids, become endothermic.

There is \"basically\" 2 ways to make a gas (or vapor) a liquid:

1) decrease the temperature

or

2) increase the pressure within a confined space.

Gases that vaporise at low temps when made liquid get very cold and will take in energy. That how refrigerators work. ..erm sorta.

I'm at a good point to learn the rest on my own. It's a very interesting subject to me. Thank you everyone!