What is Joule-Thomson Effect?

Put your hand near your mouth and slowly exhale. Again, repeat the same thing but this time try to blow air a little more furiously with your lips pursed.

What do you observe? 

Your breath seems colder in the second case. This is a very famous analogy of a process called throttling which is extensively used in refrigeration.

When a real gas is expanded from a higher pressure to lower pressure it becomes cooler.

Also known as the Joule-Thomson Effect.