Simulating the behavior of a Turbine

Assignment :

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.

• 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 rotor blades.
• 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 available gas kinetic energy after expansion, not as a fraction of inlet internal enthalpy flow.
• When details of the turbine mechanical power output are not important:
• Model an Impulse Turbine with a choked nozzle
• Model a Reaction Turbine with an Area Change and loss coefficients
• 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 Final project.
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 choked flow.

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 BREAK component.

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 flow rate.

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 information.

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