What is Adiabatic Compression ?

While air compressors don’t fully use adiabatic compression, understanding the concept is essential to ensuring smooth operations for several reasons:

• Efficiency: If all the heat generated remains in the hot air, you will get lower efficiency, since hot air is less dense and holds less oxygen per unit volume.
• Cooling: Compressed air rises in temperature, so it must be cooled down using intercoolers or aftercoolers. These systems help manage heat to protect equipment and enhance efficiency.
• Design: Knowledge of adiabatic compression effects can help you choose the right compressor size and design for your application.

Here’s the formula representing adiabatic compression:

PV^γ = k

In the context of air compressors, the variables represent:

• P: The force air exerts per unit area inside the compressor, otherwise known as the pressure.
• V: The volume of the air, or the amount of space it occupies. This value decreases during compression.
• γ: Gamma represents the specific heat ratio at a constant pressure to specific heat at constant volume. Typically, this ratio is 1.4 for dry air.
• k: This variable is a constant value for the air mass during the adiabatic process and does not represent heat exchange.

This formula describes how pressure and volume change as air undergoes adiabatic compression inside an air compressor. Engineers might use this formula to estimate how pressure and volume change during compressor operation, which helps in system design.

Adiabatic compression means heat generated during compression remains in the air, but why does air heat up when compressed? Several chemists and physicists determined that as volume decreases, pressure increases. This fact means you can increase air pressure by forcing the air into a smaller space. They also discovered that you can increase the volume when the temperature rises to maintain the same pressure.

Combining these two discoveries shows that when air is compressed, the temperature and pressure increase as the volume decreases. In other words, forcing air into a smaller space naturally causes it to become hotter and more pressurized.

There are several types of compression. Isothermal and adiabatic compression describe ideal conditions, while polytropic compression represents real-world conditions. Here’s an overview of the difference in more detail:

• Isothermal compression: This term describes compression with a heat transfer. The air warms up during the compression process, but compression happens slowly enough that heat has time to escape, so the compressed air returns to its original temperature.
• Adiabatic compression: During adiabatic compression, temperature rises because the heat generated stays in the compressed air. In real-world situations, some heat escapes into the air, but piston and screw compressors get the closest to adiabatic compression.
• Polytropic compression: This type of compression has a partial heat exchange and covers all real-world scenarios. The temperature of the compressed air rises moderately, but not as much as it would during adiabatic compression.