Which of the following statements are correct? 1) Velocity compounded impulse turbine gives less speed and less efficiency. 2) For an ideal centrifugal compressor, the pressure produced depends on impeller velocity and diameter. 3) While flowing through the rotor blades in a gas turbine, the relative velocity of gas continuously decreases. 4) While flowing through the rotor blades in an axial flow compressor, the relative velocity of air continuously decreases.

Which of the following statements are correct? 1) Velocity compounded impulse turbine gives less speed and less efficiency. 2) For an ideal centrifugal compressor, the pressure produced depends on impeller velocity and diameter. 3) While flowing through the rotor blades in a gas turbine, the relative velocity of gas continuously decreases. 4) While flowing through the rotor blades in an axial flow compressor, the relative velocity of air continuously decreases. Correct Answer 1 and 4

Concept:

• In the velocity compounding of turbines, there are more friction losses due to very high velocity in nozzles and less efficiency because the ratio of blade velocity to steam velocity is not optimum.
• In this type of turbine, compounding is used to reduce the velocity only. It is also called as Curtis turbine.
• For an ideal centrifugal compressor, the pressure rise depends only on the peripheral velocity or The tip speed of the blade is proportional to the rotational speed (RPM) of the impeller and the impeller diameter.
• As the fluid enters the axial flow compressor, the rotor reduces the relative kinetic head of the fluid and adds it to the absolute kinetic head of the fluid i.e. the impact of the rotor on the fluid particles increases their absolute velocity and thereby reduces the relative velocity between the fluid and the rotor.

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Pressure compounding: In this type of turbine, compounding is used for reducing the pressure of fluid in more than 1 stage. Its efficiency is higher than the velocity compounding. It is also called a Rateau turbine.