Whether you know it or not, compressed air is involved in every aspect of our lives, from the balloons at your birthday party to the air in the tires of our cars and bicycles. It was probably even used when making the phone, tablet or computer you’re viewing this on.
The main ingredient of compressed air is, as you might have already guessed, air. Air is a gas mixture, which means it consists of many gases. Primarily these are nitrogen (78%) and oxygen (21%). It consists of different air molecules that each have a certain amount of kinetic energy.
The temperature of the air is directly proportional to the mean kinetic energy of these molecules. This means that the air temperature will be high if the mean kinetic energy is large (and the air molecules move faster). The temperature will be low when the kinetic energy is small.
Compressing the air makes the molecules move more rapidly, which increases the temperature. This phenomenon is called “heat of compression”. Compressing air is literally to force it into a smaller space and as a result bringing the molecules closer to each other. The energy that gets released when doing this is equal to the energy required to force the air into the smaller space. In other words it stores the energy for future use.
Let’s take a balloon for example. By inflating a balloon, air gets forced into a smaller volume. The energy contained in the compressed air within the balloon is equal to the energy needed to inflate it. When we open the balloon and the air gets released, it dissipates this energy and causes it to fly away. This is also the main principle of a positive displacement compressor.
Compressed air is an excellent medium for storing and transmitting energy. It’s flexible, versatile and relatively safe compared to other methods for storing energy, like batteries and steam. Batteries are bulky and have a limited charge life. Steam, on the other hand, is not cost effective nor user friendly (it gets extremely hot).