Canned air is a common tool used for cleaning electronic devices. The strong blows of compressed air are very useful for removing dust from components. Anyone who uses canned compressed air to clean their computer or keyboard is aware that the canned air quickly becomes cold to touch, but nobody, or few, seems to know why.
The can becomes cold and in some cases, frost forms on the can and the straw attached to the nozzle. This article will provide you with all the relevant information to this question.
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If you didn’t already know, canned air is not the same as the air we breathe. Canned air contains a common mixture of nitrogen and other gases that are compressed to between 40 and 70 PSI (pounds per square inch) which turns them into liquid.
These gases are compressed to a liquid form and a pocket of gas sits at the top of the can which prevents the liquid from spraying out when using it. However, if the canned air is flipped upside down and used, the liquid will come out before it turns to gas.
Why Canned Compressed Air Gets Cold
The main reason the canned compressed air gets cold after use is due to a thermodynamic process called adiabatic cooling. The gas, initially at high pressure will cool significantly when the pressure is released.
The compression required to turn gas to liquid allows a large amount of gas to fit in a relatively small space, and so, when the gas is released to a larger space, it rapidly expands to fill it.
The evaporation of liquid inside a can of compressed air into a gas can result in a drop in its internal heat energy. It absorbs a large amount of heat from the surrounding environment, the metal can. So, when the liquid inside the compressed air can absorb heat energy from the can’s metal body, the can itself cools down rapidly and that is why it becomes cold to touch or hold.
When you use the canned air for prolonged use, you will notice the force of the air stream begins to weaken and maybe the can becomes too cold to hold in your hands. The heat energy from the can have all gone into the evaporating liquid and when the can itself becomes cold, there is not enough heat to vaporize more liquid, resulting in a lack of force of the air stream.
If this happens, you should typically set the can down and let it warm for a few minutes to restore the strength of the air bursts.
You may notice that when you spray something, you initially see a thin white layer of frost for a few seconds. This is because as the expanding gas leaves the can, it is absorbing heat energy from the nozzle and straw or anything else it encounters.
It’s vital that you don’t spray directly onto your skin because the rapid absorption of heat can rather easily cause frostbite. Hence, the warnings on every can!
FAQs (Frequently Asked Questions)
Air duster cans get cold due to adiabatic cooling. The liquid inside the can absorbs a large amount of heat from the canned air to compensate for the loss of heat due to its evaporation into gas. When it does so, the can itself loses heat and therefore, becomes cold to hold or touch.
If you shake a can of compressed air it leads to the possibility that liquid will be propelled when the trigger is pressed instead of gas. If the liquid came in contact with the skin or eyes, the chemicals will freeze the skin and cause frostbite. All compressed air cans specify on the container that you should not shake them for this reason.
If you have any questions regarding compressed air getting cold, please leave a comment below, with a photo if applicable, so that someone can help you!