3B2 - Chapter 1: Steam Turbine Principles & Design UPDATED ACTUAL
Questions and CORRECT Answers
Question: What are nozzles usually constructed of?
Correct Answer: Monel metal, formed over special dies
Question: What is Monel?
Correct Answer: nickel-copper alloy with high tensile strength
Question: Define 'critical pressure'.
Correct Answer: The lowest exit pressure from the nozzle that can be used without creating turbulence.
Question: Give the value of critical pressure.
Correct Answer: The critical pressure for a convergent nozzle occurs when the exit pressure is 0.577 times
the inlet pressure.
Question: What nozzle is used for small pressure drops?
Correct Answer: Convergent nozzles
Question: What nozzle is used for large pressure drops?
Correct Answer: Convergent - Divergent nozzles
Question: What part of a convergent - divergent nozzle should be at critical pressure?-
Correct Answer: nozzle throat - narrowest part of the nozzle - outlet of the convergent section
Question: What are the blades in an impulse turbine reffered to as?
Correct Answer: Buckets
Question: The buckets in an impulse turbine convert _________ energy of the steam into __________
energy.
Correct Answer: kinetic, mechanical
Question: What are the disadvantages of an impulse turbine?
Correct Answer: -large centrigual forces due to high rotational speeds - large friction losses due to the high
velocity of the steam
Question: In an impulse turbine, the velocity __________ at the nozzles, then _________ in the blades.
Correct Answer: increases, drops -The kinetic ( velocity ) energy of the steam is transferred to the blades
Question: In an impulse turbine, the pressure _________ in the nozzles, then __________ through the
blades
Correct Answer: Decreases, remains constant
Question: A reaction turbine has rows of __________ blades alternating with rows of __________ blades.
Correct Answer: stationary, moving
Question: In a reaction turbine, what do the stationary blades act as?
Correct Answer: Due to their shape, they act as nozzles
, Question: How are the blades in a reaction turbine characterized?
Correct Answer: large enterance angle, almost 90 degrees, and a small discharge angle
Question: In a reaction turbine the steam pressure _________ across the stationary blades, and _________
across the moving blades.
Correct Answer: decreases, decreases
Question: In a reaction turbine, the velocity _________ in the stationary blades but __________ in the
moving blades.
Correct Answer: increases, decreases
Question: What are the disadvantages of a reaction turbine?
Correct Answer: 1. the drop in pressure across the moving blades ecourages steam flow around the end of
the blades reducing turbine efficiency 2. the difference in pressure between the inlet and outlet side of each
rotor produces an axial thrust towards the exhaust end of the turbine
Question: In an impluse turbine, what must happen for the steam to transfer all its kentic energy to the
moving blades?
Correct Answer: The steam must leave the moving blades at the lowest possible velocity.
Question: The lowest velocity of the steam leaving the blades of an impulse turbine occurs when the
____________.
Correct Answer: The blade velocity is one half the steam velocity.
Question: In an impulse turbine, what is pressure compounding?
Correct Answer: Reduces steam and blade velocty by causing the steam pressure to drop in two or more
stages. Two or more impulse stages are used.
Question: In an impulse turbine, what is velocity compounding?
Correct Answer: Consists of one set of sationary nozzles, a set of moving blades, stationary blades, and
moving blades to reduce the velocity.
Question: In an impulse turbine, recuding the steam velocity in two stages results in what?
Correct Answer: roating blades & shaft being the speed of a simple, single stage impulse turbine
Question: In an impulse turbine, what is pressure - velocity compounding?
Correct Answer: Reduces both steam pressure and steam velocity in stages.
Question: What is the difference between single and double flow turbines?
Correct Answer: Single flow - steam flows in one direction only in relation to the shaft. Double flow -
steam flows in two directioons
Question: What are the advantages of a double flow turbine?
Correct Answer: -elimination of end thrust -large number of stages can be used without excessively large
discs
Question: What is another name for a non-condensing turbine?
Correct Answer: back pressure turbine
Questions and CORRECT Answers
Question: What are nozzles usually constructed of?
Correct Answer: Monel metal, formed over special dies
Question: What is Monel?
Correct Answer: nickel-copper alloy with high tensile strength
Question: Define 'critical pressure'.
Correct Answer: The lowest exit pressure from the nozzle that can be used without creating turbulence.
Question: Give the value of critical pressure.
Correct Answer: The critical pressure for a convergent nozzle occurs when the exit pressure is 0.577 times
the inlet pressure.
Question: What nozzle is used for small pressure drops?
Correct Answer: Convergent nozzles
Question: What nozzle is used for large pressure drops?
Correct Answer: Convergent - Divergent nozzles
Question: What part of a convergent - divergent nozzle should be at critical pressure?-
Correct Answer: nozzle throat - narrowest part of the nozzle - outlet of the convergent section
Question: What are the blades in an impulse turbine reffered to as?
Correct Answer: Buckets
Question: The buckets in an impulse turbine convert _________ energy of the steam into __________
energy.
Correct Answer: kinetic, mechanical
Question: What are the disadvantages of an impulse turbine?
Correct Answer: -large centrigual forces due to high rotational speeds - large friction losses due to the high
velocity of the steam
Question: In an impulse turbine, the velocity __________ at the nozzles, then _________ in the blades.
Correct Answer: increases, drops -The kinetic ( velocity ) energy of the steam is transferred to the blades
Question: In an impulse turbine, the pressure _________ in the nozzles, then __________ through the
blades
Correct Answer: Decreases, remains constant
Question: A reaction turbine has rows of __________ blades alternating with rows of __________ blades.
Correct Answer: stationary, moving
Question: In a reaction turbine, what do the stationary blades act as?
Correct Answer: Due to their shape, they act as nozzles
, Question: How are the blades in a reaction turbine characterized?
Correct Answer: large enterance angle, almost 90 degrees, and a small discharge angle
Question: In a reaction turbine the steam pressure _________ across the stationary blades, and _________
across the moving blades.
Correct Answer: decreases, decreases
Question: In a reaction turbine, the velocity _________ in the stationary blades but __________ in the
moving blades.
Correct Answer: increases, decreases
Question: What are the disadvantages of a reaction turbine?
Correct Answer: 1. the drop in pressure across the moving blades ecourages steam flow around the end of
the blades reducing turbine efficiency 2. the difference in pressure between the inlet and outlet side of each
rotor produces an axial thrust towards the exhaust end of the turbine
Question: In an impluse turbine, what must happen for the steam to transfer all its kentic energy to the
moving blades?
Correct Answer: The steam must leave the moving blades at the lowest possible velocity.
Question: The lowest velocity of the steam leaving the blades of an impulse turbine occurs when the
____________.
Correct Answer: The blade velocity is one half the steam velocity.
Question: In an impulse turbine, what is pressure compounding?
Correct Answer: Reduces steam and blade velocty by causing the steam pressure to drop in two or more
stages. Two or more impulse stages are used.
Question: In an impulse turbine, what is velocity compounding?
Correct Answer: Consists of one set of sationary nozzles, a set of moving blades, stationary blades, and
moving blades to reduce the velocity.
Question: In an impulse turbine, recuding the steam velocity in two stages results in what?
Correct Answer: roating blades & shaft being the speed of a simple, single stage impulse turbine
Question: In an impulse turbine, what is pressure - velocity compounding?
Correct Answer: Reduces both steam pressure and steam velocity in stages.
Question: What is the difference between single and double flow turbines?
Correct Answer: Single flow - steam flows in one direction only in relation to the shaft. Double flow -
steam flows in two directioons
Question: What are the advantages of a double flow turbine?
Correct Answer: -elimination of end thrust -large number of stages can be used without excessively large
discs
Question: What is another name for a non-condensing turbine?
Correct Answer: back pressure turbine
