Why Is Compressed Air So Cold

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.

Why is compressed air so cold.

One hot and one cold. Travelling along this pressure gradient the gas expands and does work and this removes energy from the gas. Eventually your hand gets cold. A fluid such as water or air that rotates around an axis like a tornado is called a vortex.

A gas initially at high pressure cools significantly when that pressure is released. However that is not true. 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. 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.

It creates a tornado or vortex of compressed air that separates the fluid into two air streams. Some of you might falsely believe that this happens because the gas expands upon coming out of the can and thus cools off. This is perhaps why compressed air cylinders feel cold even before use. The reason the can gets cold after being used is due to a process known as adiabatic cooling a property of thermodynamics.

Minutephysics knows the actual reason why compressed air cans become so cold and will explain it. In fact it can become so cold that the cans feature frostbite warnings.