Simulating the behavior of a Turbine
The basic objective of a turbine is to convert as much internal
energy of a gas to kinetic energy
of the gas as possible, and then to convert that to kinetic energy of
rotation of the blade-generator
system. The good news is that all major reactor systems codes
have turbine components. The bad news is that they are hardly
ever used, and can be expected to be unreliable. The model in
TRACE is relatively new and to the extent tested superior to those in
its predecessors TRAC-P, TRAC-B, and RELAP5. However, keep in
mind that the model currently works from a non-conservative form of the
energy equation and is susceptible to energy conservation problems due
to the large pressure change across the face representing the turbine.
The remainder of the class has two purposes. The first is to to
create an appreciation for the methodology introduced to accelerate the
process of setting a system parameter to achieve a desired
result. The second is to give you a practical appreciation for
- Types of turbines
- A Reaction Turbine is standard on large power plants. It
has multiple stages, subsonic flow, and expansion of the gas is in the
- An Impulse Turbine is standard on smaller power systems.
Generally it has only a single stage (single set of rotating blades).
Expansion is in a set of supersonic nozzles with no expansion in the
blades. Good for
high power density applications.
- Quoted values of turbine efficiency can be misleading.
Turbine efficiency is delivered shaft power as fraction of
kinetic energy after
expansion, not as a fraction of inlet internal enthalpy flow.
- When details of the turbine mechanical power output are not
- Model an Impulse Turbine with a choked nozzle
- Model a Reaction Turbine with an Area Change and loss
- When necessary, model fluid temperature change across the
turbine indirectly through
control blocks, and if
necessary (no break) induce temperature change with a negative direct
heat to the fluid, driven by a control system.
- Remember to reference a description of a turbine model in your
Download a copy of choke1.inp .
This deck is intended to
simulate the flow behavior of a Reaction Turbine, but the underlying
exercise has broader application. Check the results for the value
of mass flow at the outlet break. Adjust the flow area and
rerun the problem
until you get a mass flow of 5 kg/s to the accuracy of the value
printed in choke1.out (or trcout). Keep a record of each value of area
that you try and the resulting mass flow. You will need this for homework 11. What you have
done is to tune your
system so that the model produces a desired mass flow at the inlet
conditions fixed by the inlet
Now change the exit pressure to half the value of the inlet pressure,
and look at the calculated mass flow. Increase the exit pressure
toward the inlet pressure until you see a significant change in mass
Spend time remaining in the class period getting organized as a group
to chose a PWR as a basis for your final project. Define the data
you need to model that plant's steam generators, and reactor vessel
(including core geometry). Assign tasks for collecting the data
and implementing it with the SNAP model editor. Feel free to ask
me questions during class or via email about need for specific
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