Fluid Machinery Classification, Fluid Machines

Fluid Machines

The device which converts the energy which has been stored by a fluid into mechanical energy and vice versa. The various energy stored in a fluid are Potential energy, Kinetic energy and intermolecular energy. Machines that use liquid for its operation are known as the Hydraulic machine, and those uses gas/pressurized air are known as Pneumatic machines.


Fluid machines are classified as follows

1. Based on the direction of energy conversion:

  1. The device in which fluid energy gets converted into mechanical energy is called Turbine.
  2. The device in which mechanical energy is transferred to a fluid to increase its stored energy is generally called Pump, Compressor, Fan or Blower.

2. Based on the principle of operation:

1.Positive displacement machine: In such type of machine there is a change in volume of fluid within the machine.
Example: Reciprocating Pump, Reciprocating engine
2.Rotodynamic machine: Its functioning depends upon Principles of fluid dynamics. There is a relative motion between the fluid and the moving part of the machine. The rotating element of the machine consists of a number of vanes/ blades which is known as Impeller, and the fixed part is known as Stator.
Depending upon the main direction of fluid path in the rotor the machine are classified as
  1. Radial flow machine: These are classified into two types
Radially inward flow machines:
Generally, in case of the Francis turbines, the fluid enters radially and then turned into axial direction. so such type of machines is denoted as Radially inward flow machines.
        Radially outward flow machines:
In case of Centrifugal pump/compressor, the flow is radially away from the centre of the pump, hence such type of hydraulic machines are denoted as Radially outward flow machine. In case of the Ljungstrm turbine, the flow is outward. It is a steam turbine, consisting of concentric rows of blades attached to the opposite faces of two rotor discs that rotate in opposite direction.
2. Axial flow machine
In such type of machines, the fluid flow is along the axis of the channel. Example of such type of machine is Kaplan turbine
3. Axial and radial flow machine:
It is a combination of both axial and radial flow machine.It is also known as mixed type machine. Example of such type of machine is: Modern Francis Turbine
4.Tangential flow machine
In this type of machine, the flow is tangential to the rotating part. In case of Pelton turbine, the flow is tangential to the rotor.

3. Classification based on Type of fluid used:

In case of pump generally, the working fluid is liquid and in case of compressor, fan or blower the working fluid is Gas/ air. The compressor increases the static pressure of gas by converting the mechanical energy into pressure energy. Fan/blower increases the kinetic energy of the fluid .

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