Turbomachanies & Classification

TURBOMACHINES AND THEIR CLASSIFICATION

TURBOMACHINES 

  We classify as  turbomachines  all those devices 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 or  turbinis   is of Latin origin and implies that which spins or whirls around. Essentially, a rotating blade row, a rotor   or an impeller   changes the stagnation enthalpy of the fluid moving through it by either  doing positive or negative work, depending upon the effect required of the machine.

CLASSIFICATION TURBOMACHINES

 ABSORB POWER TO INCREASE FLUID PRESSURE OR ENERGY

PRODUCE POWER BY EXPANDING THE FLUID TO A LOWER PRESSURE

DUCTED FANS, COMPRESSORS, PUMPS

HYDRAULIC STEAM & GAS TURBINES

CLASSIFICATION BASED ON FLOW DIRECTION 

Categorisation according to the nature of the flow path through the passages of the rotor.  –  Whenthe path of the through-flow   is wholly or mainly parallel to the axis of rotation, the device is termed an   axial flow  turbomachine  (e.g. Pelton Wheel turbine & axial flow pumps or compressors). There is no significant change of radius between the flow entry and exit i.e. u1 = u2  –  When the path of the   through-flow   is wholly or mainly in a plane perpendicular to the rotation axis, the device is termed a   radial flow turbomachine   (e.g. centrifugal pump or  compressor)  –   Mixed flow turbomachines are widely used. The term  mixed  flow   in this context refers to the direction of the through-flow at rotor outlet when both radial and axial velocity components are present in significant amounts e.g a mixed flow pump and a mixed flow Francis hydraulic turbine.

CLASSIFICATION BASED ON DEGREE OF REACTION 

  Degree of   reaction ( R ) is defined as the rate of   energy transfer  by virtue of   change of   static pressure to the total energy transfer .

 – IMPULSE MACHINE : NO CHANGE OF STATIC PRESSURE IN THE ROTOR. R = 0 ; ENERGY TRANSFER IS WHOLLY   AFFECTED BY A JET OF FLUID STRIKING THE BLADE. E.g. PELTON WHEEL TURBINE.

 –  RECTION TURBINE: R = 1; ALL ENERGY TRANSFER OCCURS BY VIRTUE OF CHANGE   OF STATIC PRESSURE IN THE ROTOR e.g. ROCKET PROPULSION, LAWN SPRINKLER

CLASSIFICATION BASED ON PRINCIPLE OF OPERATION 

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  POSITIVE DISPLACEMENT: The fluid is drawn or  forced into  finite  space by mechanical  parts & is sealed in it by mechanical means (plunger  cylinder  arrangement). The fluid is then  forced out of  the space by means of mechanical thrust e.g. reciprocating pump   ROTODYNAMIC MACHINES: They have arotating part known as runner   (Turbine) , impeller   (Pump) and rotor   (Compressor) which rotate continuously and freely in the fluid.

CLASSIFICATION BASED ON TRANSFER OF ENERGY 

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The device in which the kinetic, potential or  intermolecular energy held by the fluid is converted to mechanical energy of a rotating member  is known as TURBINE.   When mechanical energy from the moving parts is transferred to a fluid to increase its stored energy by   increasing either  its   pressure or   velocity are known as pumps, compressors, fans or  blowers.