TurbineFund.txt

The flashcards below were created by user pegwinn on FreezingBlue Flashcards.

1. What is the definition of a turbine?
A multi-blade rotor attached to a shaft that receives steam from the boiler which causes it to rotate. This converts thermal energy (steam) into mechanical energy (rotation / work) which can be used to drive other equipment
2. Briefly describe how a steam turbine works.
Steam, from our boilers enters the steam chest where it is directed via the throttling valves (nozzles) to the blades causing the shaft to rotate. This rotation is used to drive other pieces of equipment to perform work.
3. What is Newtons 1st Law?
A body in motion tends to stay in motion. A body at rest tends to stay at rest. This is inertia. Think of the effect when you are in a car and slam on the brakes. The car decelerates and your body tries to obey the law and continue forward until the seatbelt or windshield absorbs your impact and transfers your energy.
4. What is Newtons 2nd Law?
Force is equal to mass times acceleration. As force on an object increases, acceleration will increase. As mass increases without a change in force, acceleration will decrease. As you are windsurfing, the wind is the force acting on the sail. Assuming your mass is constant an increase in wind will increase the acceleration of the board and impress the onlookers on the beach. If your mass increases, like a shark attaching itself to your leading edge, and the wind doesn’t increase, your acceleration will decrease (slow down) allowing you to desperately dive and try to swim for shore. If the shark adds five times to your mass, then the force will be one fifth of what it was. So, swim like crazy and hope the shark goes for a ride.
5. What is Newtons 3rd Law?
For every action there is an equal or opposite reaction: This means that for every push there is another push going the other way. Consider when you fire your shotgun at a home intruder. The expanding gas from the exploding primer is contained in the chamber and pushes the 00 buck towards the intruder. This expanding gas also acts against the closed end, the chamber, and pushes the shotgun against your shoulder.
6. Describe Bernoulli’s Principle:
An increase in the velocity of a fluid will cause a decrease in pressure.

Picture a four inch pipe with a two inch constriction in the middle. Assume that the pipe is full and the flow is constant. In order to move the same amount of fluid through the constricted section of the pipe the fluid must increase its’ velocity at the expense of pressure. The fluid pressure in the constricted area will measure out to be less than in the unconstricted space. In our case the principle applies when the nozzle directs steam against the blading on the rotor. As the steam impacts the moving blade it will change direction and move to a fixed blade where it will be redirected to the next moving blade in the series. Due to the shaping of the blade, each time it does this there is a velocity increase with a corresponding pressure decrease.
7. Explain this term as applied to turbines:

Kinetic energy:
Energy possessed because it is in motion. In a turbine the primary kinetic energy is contained in the shaft during rotation.
8. Explain this term as applied to turbines:

Potential energy:
The capacity for doing work because of position or condition. An offline turbine is a big ol mass of energy just waiting to be converted.
9. Explain this term as applied to turbines:

Mechanical energy:
The sum of potential energy and kinetic energy. It’s also defined as the ability to do work. The turbine shaft has mechanical energy due to motion (kinetic) when rotating. It has the potential to do work when offline.
10. Explain this term as applied to turbines:

Thermal energy:
The energy related to or caused by heat. Or, the kinetic energy total generated by the movement of atoms. Our turbines thermal energy is provided by superheated steam.
11. Explain this term as applied to turbines:

Velocity:
The time rate of linear motion. In other words; how fast an object or fluid gets from point a to point b.
12. Explain this term as applied to turbines:

Pressure:
A measurement of the force per unit volume. Pressure = force / area. This is normally measured in (PSI) pounds per square inch.
13. Describe the operational theory of the Impulse type of turbine:
Steam is directed against a curved (crescent shaped) blade mounted on the rotor. This directed steam provides a “push” which causes the shaft to rotate.
14. Describe the operational theory of the Reaction type of turbine:
Steam is directed against a series of moving, attached to the rotor/shaft, and fixed blades.

The blades are shaped in such a way that when viewed on end they form a nozzle.

The steam exiting the “nozzle” as it moves from blade to blade creates the “equal and opposite reaction” rather than a simple “push”.
15. Describe the following turbine component:

Nozzle/Nozzle diaphragms:
Used in compound Rateau stages.

This is where we redirect steam to the moving blades, they are shaped like a nozzle and they increase velocity and decrease pressure.

They are attached to the turbine casing and are also known as fixed blades.
16. Describe the following turbine component:

Shaft:
A machined metal shaft that holds the rotor/blades. This is the component that rotates and converts its’ energy to work by driving another piece of equipment. It is sealed by interstage seals as well as the gland sealing system.
17. Describe the following turbine component:

Shrouding:
A metal strip that is attached to the tops of the moving blades lending stability/rigidity to the assembly. The shrouding is close enough to the casing to provide a seal that prevents the steam from leaking by and not getting redirected to the next fixed/moving blade.
18. Describe the following turbine component:

Steam chest:
The area of the turbine that receives the steam from the boiler. It contains the throttle valve assembly. It holds the steam until it is needed for use. The throttle valves (poppets) are attached to a lifting bar that is controlled externally by the governor.
19. Describe the following turbine component:

Interstage seals:
Nozzle diaphragms and fixed blades on a Reaction turbine are fitted with labyrinth type inter-stage seals around the shaft. They reduce steam leakage around the shaft.
20. Describe the following turbine component:

Nozzle block:
The nozzle block contains the nozzles. When steam passes through the nozzles the velocity increases and the pressure will decrease.

On an impulse turbine, the only time a pressure drop takes place is by passing through the nozzles.

On a reaction turbine pressure drops occur each time steam passes the moving blades.

In all turbines, when steam passes through the nozzle block it will move through the first set of moving blades.
21. Describe the following turbine component:

Throttle valve:
A poppet type of valve lifted by a lifting bar, controlled by a governor, which admits steam in the steam chest to the nozzle block.
22. Describe the following turbine component:

The combination of rotor, blade, and shrouding permanently affixed to the turbine shaft. Either thru impulse or reaction, the moving blade physically causes the shaft to rotate.
23. Describe the following turbine component:

Attached to the casing in between moving blades. Fixed blades provide the change of direction to the steam needed to properly engage the next moving blade.

Impulse turbine fixed blades do not incur an increase in acceleration or decrease in pressure.

Reaction turbine fixed blades form as a nozzle thus increasing acceleration and decreasing pressure.
24. Describe the following turbine component:

Rotor/wheel:
Steel component attached to the shaft that supports the blades and shrouding.
25. Describe and draw the three types of divisional flows within a turbine:

Single flow:
The motive force, in our case steam, goes through the blades once and is inline (parallel) to the turbine shaft.
26. Describe and draw the three types of divisional flows within a turbine:

Double flow:
The steam flow splits 90 degrees, and goes through the blades in line with the turbine shaft.
27. Describe and draw the three types of divisional flows within a turbine:

Cross-compound flow:
Steam goes through a single flow turbine and the exhaust is sent as the intake to a double flow turbine. If you combine the two pictures above you’ll get the idea.
28. Describe the two types of repetition of steam flows through turbines
Single entry: The steam goes thru the blades once.

Re-entry: The steam goes thru the blades more than once.
29. Describe the three types of directional flow within a turbine:

Axial flow:
Tangential or helical flow:
• Axial flow: The steam passes through the turbine parallel to the shaft. Single flow is also Axial flow.
• Radial flow: Steams enters in a nonparallel direction relative to the Shaft.
• Tangential or helical flow: Steam flow is directed through the same set of blades more than once. Reversing Buckets attached to the rotor create a swirl effect that redirects the steam “exhaust” right back into the “intake” side.
30. Describe the operational theory of the following types of nozzles. Which nozzle is more efficient and why?

Convergent-divergent nozzle:

Convergent nozzle:
Convergent-divergent nozzle: When the steam/fluid flow enters the nozzle the velocity increases (thus pressure decreases) on the outlet side until it hits the widened portion at the outlet. Then it does a change-up as the velocity will drop out and the pressure rises. It is more efficiently used in applications where the outlet pressure is more than 55% of the inlet pressure. A sprayer head on a garden hose uses this principle.

Convergent nozzle: When the steam/fluid flow enters the nozzle the velocity increases (thus pressure decreases) on the outlet side. It is more efficiently used in applications where the outlet pressure is less than 55% of the inlet pressure. Think of a garden hose for sweeping dirt off the sidewalk. It only appears as if the pressure is increased when you restrict it with your thumb, only the velocity has changed.
31. What is a stage of an impulse turbine? What is a stage of a reaction turbine?
An impulse turbine stage goes from pressure drop to pressure drop between nozzles.

A reaction turbine stage is from fixed blade to fixed blade.
32. Define compounding as applied to turbines.
A turbine is considered to be compounded if the kinetic energy is converted to work in more than one row of moving blades which causes a series of pressure drops, and/or a series of velocity drops.
 Author: pegwinn ID: 56897 Card Set: TurbineFund.txt Updated: 2010-12-21 10:50:41 Tags: Steam turbine fundamentals Folders: Description: Steam Turbine Fundamentals Show Answers: