Nuclear Engineering 470

Modeling a Turbine

with TRACE

TURBINE

• A turbine is a device designed to convert internal energy of a gas to kinetic energy of rotation of a blade-generator system.

• All major reactor systems codes have turbine models.

• They are not widely used because they are unreliable.

• The model in TRACE is fairly new. To the extent it has been tested it appears to be superior to other models (TRAC-P, TRAC-B, and RELAP5).• The current model in TRACE uses a non-conservative form of the energy

equation. Can have energy conservation problems due to large pressure drops across the face representing the turbine.

TURBINE

• 2 Types of Turbines• Reaction Turbine

• Multiple Stages

• Subsonic Flow

• Expansion of gas in rotor blades

• Impulse Turbine• Single Stage (in general)

• Supersonic flow in nozzles

• No expansion of gas in the rotor blades

TURBINE

• The input for the TURB component is the same as the TEE with additional input to simulate a steam turbine

• The flow through the turbine is not treated in detail, momentum and energy convected across cell edged 2 are calculated using a lumped momentum and energy balance for the turbine.

Primary Arm of TURB

Side Arm of Turb

Cell 1 Cell 2

Cell Edge 2

Inlet Outlet

Turbine Internalsnozzles, rotor &stator blades, etc.

Steam tap or liquid drain

idealQ m h

Mechanical energy extracted from the turbine flow (J/s = w)

Mass flow rate through the turbine (kg/s)

Turbine efficiency

Ideal isotropic total enthalpy change across the turbine (J/kg)ideal

Q

m

h

TURBINE

• Turbine efficiency is delivered shaft power as a fraction of available gas kinetic energy after expansion.• This can be misleading since it is not a fraction of the internal enthalpy

flow.

• When the details of the turbine mechanical power output is not important:• Model an Impulse Turbine with a choked nozzle.

• Model a Reaction Turbine with an area change and loss coefficients.

• When necessary, model the fluid temperature change across the turbine indirectly through control blocks (control break temp with a control block).

• You can induce a temperature change with a negative direct heat to the fluid driven by the control system (no break).