You may not know it, but compressed air is involved in every aspect of your life, from birthday party balloons to air in the tires of our cars and bicycles. It is even used in the manufacture of telephones, desktop computers and laptops.

As you probably guessed, the main ingredient of compressed air is air. Air is a gaseous mixture, consisting of many gases, including nitrogen (78%) and oxygen (21%). In fact, it consists of different air molecules and each of them has a certain amount of kinetic energy.

Air temperature has a direct relationship with the average kinetic energy of these molecules. That is, if the average kinetic energy is high (and the air molecules move faster), the air temperature will be high, and when the kinetic energy is low, the air temperature will be low.

Compressing the air causes the molecules to move faster, resulting in an increase in temperature. This phenomenon is called “heat of compression”. Compressing air literally means locking it in a smaller space and of course bringing the molecules closer together. The energy released when doing this is equal to the energy required to get air into the smaller space. In other words, it stores energy for future use.

For example, consider a balloon. By inflating the balloon, the air has to become less dense. The energy contained in the compressed air inside the balloon is equal to the energy needed to inflate it. When we open the balloon and the air is released, this energy dissipates and makes the balloon fly. This is the basic principle of the positive displacement compressor.

Compressed air is an excellent medium for storing and transferring energy. Compared to other energy storage methods such as batteries and steam, it is flexible, versatile and relatively safe. Batteries are bulky and have a limited charge life. On the other hand, steam is neither economical nor user-friendly (it gets very hot).