Mechanical Sciences Turbines
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Flow of steam is in the direction that is almost parallel to the axis of the turbine shaft.
Axial flow turbine
A velocity-compounded impulse turbine with two rows of moving blades
Steam from the high-pressure turbine enters at the center of the low-pressure turbine and flows outward in both directions through two identical sets of turbine staging.
Flow of steam is at an angle to the rotor. The flow is directed into buckets fixed onto the turbine wheel and then back out of the buckets into stationary reversing chambers to be directed back into the buckets.
Helical flow turbine
Classification for a turbine that has more than one pressure drop.
Classification for a turbine that has combination of pressure and velocity drops.
Pressure-velocity compounded turbine
The flow of steam is directed either toward or away from the rotor. This type turbine may be used for driving some small auxiliary equipment.
Radial flow turbine
A simple impulse stage having one set of nozzles and one row of moving blades.
Steam in a turbine flows in only one direction.
A heat engine in which the thermal energy in steam is converted to kinetic energy and then to work.
Components (i.e., high and low pressure turbine units, steam turbine and main generator) mounted on the same shaft.
A nozzle followed by one or more sets of moving blades in the same section of a turbine (i.e., high pressure, low pressure).
Classification for a turbine that has more than one velocity drop.
Describe the process for converting heat energy to rotational energy in turbines.
- In the turbine, the steam velocity is increased as it passes through a nozzle. This converts the steam thermal
- energy to kinetic energy by expanding the steam from a higher to a lower pressure.
Describe the components that comprise a turbine
- Fixed and Movable blades attached to a shaft.
- One high pressure turbine mounted on the same shaft with two or three low pressure turbines is a common configuration. The electrical generator is mounted at the end of the shaft.
Describe reaction and impulse turbine blading.
- Impulse - High velocity steam striking the turbine blading (an impulse) causes the rotor to turn.
- Reaction - The fixed and moving reaction blades are nozzles. They are shaped like tear drops. The most
- important motive force in a reaction turbine is the jet-like thrust that results when the steam expands through the tail of the tear drop-shaped moving blades.
Describe the function of a nozzle in turbine blading.
In the turbine, the steam velocity is increased as it passes through a nozzle. A fixed blade.
Explain the concept of turbine staging.
A turbine stage is defined as a nozzle followed by one or more sets of moving blades.An impulse turbine stage is one set of nozzles and the succeeding row of moving blades or one set of fixed and moving blades.
Define turbine efficiency.
Turbine efficiency (ηt) is the ratio of work done by a real turbine to the work done by an ideal turbine in accomplishing the same gas expansion.
Describe the steam flow path through a turbine.
- Most turbines are of the single-entry type since the steam only passes once through the blades
- Another commonly used method is the double-flow design. Steam from the high-pressure turbine enters at the center of the low-pressure turbine and flows outward in both directions through two identical sets of turbine staging
DESCRIBE accessories and support systems associated with turbines
- Lube oil system
- Hydraulic control system
- Steam or water seal system
- Exhaust hood cooling system
- Turning gear
- Bearing lift pumps
- Shaft grounding brushes
DESCRIBE failure mechanisms and symptoms associated with turbines.
The primary failure mechanism for the main turbine is water impingement on the main blades. Excessive moisture will erode the blades causing an imbalance leading to a vibration problem.
Another failure would be a failure of the lube oil system.
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