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.