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Why does compressed air get hot or cold?

Compressed air is an optimal source of energy. It can be used to power machines, tools, engines, and other equipment. Changes in volume and pressure can make the air temperature either increase or decrease. Higher temperatures result from air getting forced into a smaller space, which makes the molecules move closer together and in turn causes an increase in temperature. Canned air, in contrast, contains a mixture of nitrogen and gases that are turned to liquid when compressed to 40-70 pounds per square inch (PSI). The air is cooled through a process called adiabatic cooling.

The Process of Adiabatic Cooling

Adiabatic cooling explains why air gets cold with compression. During the process of adiabatic cooling, pressure is released from inside the can, which in turn causes the gas to cool rapidly when it releases pressure. Additionally, the liquid in the can evaporates, which causes the internal heat levels to decrease as well. The air then absorbs a considerable volume of heat from its surrounding environment, which is the can. The gas also captures heat energy as it is released. The air from the can may emerge as either gas or liquid following the cooling process. Sometimes you'll notice a combination of both. Cooling the air is an important part of the overall process of creating compressed air. If the air is too hot, it can cause machinery and equipment to fail, and it can also present a safety hazard. However, air that gets too cold can also damage equipment, and it can also cause frostbite on exposed skin or otherwise cause the skin to freeze.

Isothermal Compression

Isothermal compression, as Engineering Sales Associates can explain, has the opposite effect. While adiabatic cooling lowers air temperature, isothermal compression refers to a method of compression that causes air temperature to rise instead. With isothermal compression, the heat produced through the compression process is removed more slowly than the rate at which it is created. This causes an increase in internal air temperature, which makes the air in a compressed air system hotter. Compressed air can reach very high temperatures of up to 300°F.

Optimal Operating Temperatures

Compressors required the right working environment in order to maximize their efficiency. Air temperature is one of the most critical variables in a compressor room for safety, efficiency, and avoiding mechanical issues. By nature, air compressors generate some degree of heat as they operate, which means installing a ventilation method is essential to help hot air escape. The degree of ventilation required depends on several factors, including whether the compressor that you are using is cooled by air or water. The ventilation system should either redirect air outside or to other locations onsite to be reused. Generally, an operating temperature in a compressor room should be somewhere between 50-85°F in order to allow the compressor to function properly. Keeping temperatures within this range prevents the compressor from freezing if compressed air gets too cold, or overheating if the air gets too hot.

For more information on how compressed air gets hot or cold, contact Engineering Sales Associates (ESA) for further details.

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