- Canned air is a common tool when working around computers. It is used for cleaning out peripherals such as the mouse and keyboard, for cleaning dust out of the back of the monitor and for cleaning the dust that collects on the fans and the various cards that attach to the motherboard. It is also a common tool for use in other electronic applications. The advantage of using canned air is that it can remove dust from sensitive electrical circuits and components without the risk of causing any unintentional scratches that can damage a circuit board. Anyone who has used canned air before has noticed the peculiar reaction that occurs after it is used for even a relatively brief amount of time: the can begins to get cold and, in some cases, frost even forms on the exposed metal surfaces of the can and the straw attached to the nozzle.
- Canned air is actually not the same as the air we breathe. Canned air is commonly a mixture of nitrogen and other relatively harmless gases that are compressed to 40 to 70 psi (pounds per square inch) until they convert to fluid form. Some of the gases are actually heavier than air, and when they are sprayed out, they will fall to the floor. Some of these gases can also displace the oxygen in the air, so it is always best to use them with proper ventilation. Because these gases are compressed to liquid form, when the can is turned upside down and sprayed, liquid will actually come out of the nozzle before it has a chance to convert to a gas. The reason this doesn't occur when the can is right side up is that there is a pocket of gas at the top of the can.
- The reason the can gets cold after being used is due to a process known as adiabatic cooling. Adiabatic cooling is a property of thermodynamics that states that when a gas is placed under a high amount of pressure, a significant drop in temperature will occur when that pressure is released. The high level of compression necessary to convert a gas into a liquid allows a massive amount of gas to be stored in a relatively small space, and when that gas is released to a large space, it rapidly expands to fill the space. This results in a drop in its internal energy, and it absorbs a large amount of heat from the surrounding air. This heat absorption results in the cooling effect. This is one of the reasons that every can is labeled with a warning stating that it should never be sprayed onto skin due to the fact that this rapid absorption of heat can easily cause frostbite. The frost that forms on the can is a result of the condensation of water vapor in the surrounding air.
