Definition of a Turbomachine

1
Definition of a Turbomachine

• A turbomachine is a device in which energy is
  transferred either to or from a continuously
  flowing fluid by the dynamic action of one or
  more moving blade rows
• The word turbo is a Latin origin and implies that
  which spins or whirls around
• A rotating blade row, a rotor or an impeller
  changes the stagnation enthalpy of the fluid
  moving through it by either ve or ve work. The
  changes in enthalpy are linked with pressure
  changes.
• A pump work is done on fluid
• A turbine work is done by fluid
• The definition precludes consideration of
  positive displacement machines such as piston
  pumps and piston steam engines.

2
Classification of Turbomachines

• Major subdivisions
• A. Power classifications (power is added or
  extracted from the fluid)
• Pumps are power addition machines and include
  liquid pumps, fans, blowers and compressors.
• Fluids are water, fuels, air, steam,
  refrigerants.
• Turbines are power extraction devices and include
  windmills, water wheels, hydroelectric turbines,
  automotive engine turbochargers, gas turbines.
• Fluids gases, liquids, mixtures.

3
Classification of Turbomachines

• B. The manner in which the fluid moves through
  and around a machine
• Open flow
• No casing or enclosure for the rotating devices
• Examples propeller is an open flow pumping
  device.
• Windmill is an open flow turbine
• Enclosed or encased flow devices

4
Classification of Turbomachines

• C. Flow-path or through-flow
• Axial through-flow machines. The flow moves on
  streamlines parallel to the axis.
• Predominantly radial flow.
• Mixed flow machines.

5
Classification of Turbomachines
6
Classification of Turbomachines

• D. Compressibility of the fluid
• Incompressible
• The density is constant through the entire flow
  process liquid pumps.
• Compressible Gas flows compressors.
• E. Impulse or reaction machines
• Impulse pressure changes are absent in the flow
  through the rotor. In an impulse machine, all the
  pressure change take place in nozzles
• Ex. Pelton wheel
• Reaction pressure changes in rotor are absent

7
Classification of Turbomachines

• Pelton wheel

8
Relations of Thermodynamics and fluid mechanics

• The First Law of Thermodynamics (Conservation of
  Energy)
• Enthalpy
• The Second Law of Thermodynamics
• Reversible engines have the best efficiency as
  compared to other engines having the same
  conditions of maximum and minimum temperatures.

9
Relations of Thermodynamics and fluid mechanics

• Adiabatic reversible process
• Stagnation Properties
• Stagnation enthalpy
• Stagnation temperature
• Stagnation pressure
• Stagnation Properties in Adiabatic Process

10
Relations of Thermodynamics and fluid mechanics

• Work and Moment of momentum

Control volume for a generalized turbomachine
11
Relations of Thermodynamics and fluid mechanics

• Work and Moment of momentum
• For a compressor rotor running at an angular
  velocity , the rate at which the rotor
  does work on the fluid is

Thus, the work done on the fluid per unit mass
(or the specific work ) is
For a turbine, the fluid does work on the rotor
and the sign for work is then reversed, thus, the
specific work is