When you use a can of compressed-air dust remover continually or for an extended period at once, the can gets cold due to a phenomenon called the "Joule-Thomson effect" or "Joule-Thomson cooling." This effect is a thermodynamic process that occurs when a gas expands rapidly without the addition or removal of external heat.
Here's a simplified explanation of the process:
Compressed air: Inside the can, the air is compressed to a high pressure and is in a liquid state. This compression is what allows the air to be stored in the can and released forcefully when the nozzle is pressed.
Rapid expansion: When you press the nozzle, the compressed air rapidly expands as it is released from the can. During this process, the gas experiences a decrease in pressure, causing it to expand and turn into a gas from its liquid state.
Energy exchange: As the air rapidly expands, it requires energy to maintain the same level of internal energy (a thermodynamic property). In this case, it takes energy from its surroundings, which includes the can itself and the air around it.
Cooling effect: As the compressed air absorbs energy from its surroundings, the temperature of the air drops significantly. This cooling effect is what causes the can to get cold.
The same principle is applied in refrigeration and air conditioning systems, where a compressed gas is allowed to expand rapidly to cool down the surroundings.
It's important to note that while the cooling effect is generally harmless, using the can continuously for an extended period can lead to excessive cooling and potential damage to the can or the mechanism inside. For proper and safe usage, follow the manufacturer's guidelines and use the can in short bursts with breaks in between to avoid overheating the can or causing any damage.