Why Is Compressed Air So Cold

Anyone who has ever made use of the compressed air can knows that it can get icy cold.

Why is compressed air so cold.

Eventually your hand gets cold. In fact it can become so cold that the cans feature frostbite warnings. Compressed air cylinders are required to be kept out of direct sunlight to avoid gas expansion by direct heating and perhaps also due to phase change although no one seems to mention this explicitly. The cold temperature profile sneaks back towards the can because the air is such a lousy conductor of heat so the heat is all coming from the can.

Minutephysics knows the actual reason why compressed air cans become so cold and will explain it. The reason the can gets cold after being used is due to a process known as adiabatic cooling a property of thermodynamics. One hot and one cold. This is perhaps why compressed air cylinders feel cold even before use.

A vortex tube turns factory compressed air into two airstreams one very cold and one hot using no moving parts. Some of you might falsely believe that this happens because the gas expands upon coming out of the can and thus cools off. A fluid such as water or air that rotates around an axis like a tornado is called a vortex. When you pressurize a gas by compressing it into a container you re putting all those molecules into a smaller volume of space and you re adding potential energy by the compression.

It creates a tornado or vortex of compressed air that separates the fluid into two air streams. Travelling along this pressure gradient the gas expands and does work and this removes energy from the gas.