Why Is Compressed Air So Cold

Eventually your hand gets cold.

Why is compressed air so cold. A vortex tube turns factory compressed air into two airstreams one very cold and one hot using no moving parts. However that is not true. 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. A gas initially at high pressure cools significantly when that pressure is released.

This is perhaps why compressed air cylinders feel cold even before use. 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. A fluid such as water or air that rotates around an axis like a tornado is called a vortex. Cans of compressed air get cold while they re discharging because of a thermodynamic principle known as the adiabatic effect.

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. Minutephysics knows the actual reason why compressed air cans become so cold and will explain it. Travelling along this pressure gradient the gas expands and does work and this removes energy from the gas. In fact it can become so cold that the cans feature frostbite warnings.

One hot and one cold. It creates a tornado or vortex of compressed air that separates the fluid into two air streams.