Scavenging and turbocharging

Q. With reference to large T/C state

a) How air & gas tightness between rotor & casing achieved?

b) Explain how the gas can raise the pressure of air higher than its own?

c) What is the purpose of nozzle ring?

Ans: a) Air & gas tightness between rotor & casing achieved by allowing some of the air from compressor outlet through a labyrinth arrangement which act as a seal.

b) The gas can raise the pressure of air higher than its own because of T/C.

• The inducer guides the air flow smoothly into the eye of impeller which throws the air outwardly increasing velocity due to centrifugal force at high rotational speed.

• The diffuser reduces velocity by converting kinetic energy into pressure energy and leads the air to the volute casing.

• The volute casing further decreases the velocity and increases the air pressure.

c) Purpose of nozzle ring:

• Expand the exhaust gas and direct exhaust gas to turbine blade.

• Convert the pressure energy of gas to kinetic energy giving a high velocity.

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