Steam Turbine Review

1
Steam Turbine Review

• Steam turbine and its representation on a T-s
  diagram
• (Thermodynamics 4th ed., Cengel and Boles, Figure
  6-50)

2
Basic Equations
3
Engine Basics

• Dynamometer Measures RPM and torque of steam
  turbine shaft and applies load.
• Torque a force acting through a radius common
  units
• ft lbf
• Brake (shaft) horsepower derives its name from
  the fact that the power output of an engine can
  be measured using a dynamometer to apply a torque
  to resist the turning of a shaft

4
Engine Basics

• Efficiency changes with bhp.
• The maximum efficiency will occur at different
  bhps for different RPMs.

5
Temperature and Pressure Measurements

• Temperature
• Thermocouples voltage changes with temperature
• Thermistors and RTDs resistance change with
  temperature
• Thermometers
• Pressure
• Manometers
• Transducers

6
Temperature Sensors
Industrial thermocouples
Various thermocouple bead styles
Thermocouple probes
Thermometers
Thermistors
7
Thermocouple Basics

• Seebeck effect
• If two wires of dissimilar metals are joined at
  both ends and one end is heated, current will
  flow.
• If the circuit is broken, there will be an open
  circuit voltage across the wires.
• Voltage is a function of temperature and metal
  types.
• For small DTs, the relationship with temperature
  is linear
• For larger DTs, non-linearities may occur.

8
Thermocouple Basics

• If you attach the thermocouple directly to a
  voltmeter, you will have problems.
• You have just created another junction! Your
  displayed voltage will be proportional to the
  difference between J1 and J2 (and hence T1 and
  T2). Note that this is Type T thermocouple.

www.omega.com
9
External Reference Junction

• A solution is to put J2 in an ice-bath then you
  know T2, and your output voltage will be
  proportional to T1-T2.
• Handheld thermocouple readers and computer data
  acquisition systems use something called an
  isothermal block instead to perform this task.

10
Comparison of Pressure Instruments
Characteristics Manometer Transducer Dial gauge
Overall Inherently accurate Automation friendly Poor precision
Electronic output No Yes No
Temperature range Approx. -50C to 50C Approx. -200C to 400C Approx. -50C to 50C
Frequency response lt 10 Hz lt 1 MHz lt 10 Hz
Cost 100-2000 50-10,000 10-3000
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Manometer Basics

• Pressure varies with depth for constant density
  fluid

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Manometers/MicromanometersExamples
(b) Micromanometer
(c) Inclined
Source www.dwyer-inst.com
(a) U-tube
13
Pressure Transducer Basics
Diaphram strain

• Strain on a diaphram is linearly proportional to
  pressure difference for the following conditions
• A strain gage changes in resistance with strain.
  
• This resistance change can be indicated by the
  voltage output of a bridge circuit.

Strain gage
Bridge circuit
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Pressure Transducer Examples
(c) General purpose

• Low pressure
• (Validyne DP103)

(d) Miniature
Source www.omega.com
(b) High performance
15
Dial Gauges

• A deformable pressure sensing element is attached
  to a pointer which rotates against a graduated
  dial--like these childrens party blowouts
• Sources of error include human error, hysteresis

Examples from www.omega.com