Gas-driven Machines

Mechanical engineering is a wide field of study. Fluid machinery is one of its most important subjects. Fluid machineries are machines in which fluid is their medium to transfer work. In studying fluid machineries, you must be aware that they are classified according to the types of fluids they used whether liquid such as water and oil, or gas such as air.
In the study of fluid machineries, when we talk about gas, it does not mean a gasoline or a fuel. Gas often pertains to air and other gaseous substance.

Fans and Compressors

Fans and compressors are two common types of fluid machineries that use air as their working medium. Do not get confuse with these two fluid machines. Take note that they work on different pressure difference.

Fans 

Fans are used to control the air movement in a low pressure, commonly at less than 10psi. Typically, a fan is sub-divided into two groups namely blowers and exhausters. A blower is a form of fan in which the air is being driven out to the surroundings through the discharge part of the system. On the other hand, an exhauster is a fan that works in opposite way the blower do. Exhauster is used to withdraw air from the surrounding through its suction part.

Fan performance

In studying fluid machineries, you should know the following concepts of fans:

• Fan static pressure head – the height of the fluid’s surface to the gauge point.
• Velocity head – head necessary to produce the flow of air.
• Total head – the sum of the static head and velocity head of the fan.
• Capacity of a fan – product of the fan area and velocity; the volume flow rate of the air.
• Air power or power output of a fan – power produced by the fan. 
• Brake power or power input to the fan – power being input to the fan usually from a motor.

Compressors

Compressor is also a fluid machine that used to increase air pressure (greater than atmospheric pressure) by decreasing its volume. Compressors, which are commonly powered by electric motor, are typically used in industrial applications that require air or other gases at high pressure. Compressors have two major classifications:

• Positive displacement compressors – these compressors have two types: the reciprocating, which are commonly used in internal combustion engines, and the rotary screw, which are often used in commercial applications. 
• Dynamic compressors – these can be classified as to centrifugal and axial flow compressors.