Slides for ME 115 Steam Turbine Review Steam
Slides for ME 115 Steam Turbine Review Steam turbine and its representation on a T-s diagram (Thermodynamics 4 th ed. , Cengel and Boles, Figure 6 -50)
Slides for ME 115 Basic Equations
Slides for ME 115 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
Slides for ME 115 Engine Basics • Efficiency changes with bhp. • The maximum efficiency will occur at different bhp’s for different RPM’s. Efficiency RPM 1 RPM 2 Rated power
Slides for ME 115 Temperature and Pressure Measurements • Temperature – Thermocouples: voltage changes with temperature – Thermistors and RTDs: resistance change with temperature – Thermometers • Pressure – Manometers – Transducers
Slides for ME 115 Temperature Sensors Industrial thermocouples Various thermocouple bead styles Thermocouple probes Thermometers Thermistors
Slides for ME 115 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 DT’s, the relationship with temperature is linear – For larger DT’s, non-linearities may occur.
Slides for ME 115 Thermocouple Basics • If you attach thermocouple directly to a voltmeter, you will have problems. www. omega. com • You have just created another junction! Your displayed voltage will be proportional to the difference between J 1 and J 2 (and hence T 1 and T 2). Note that this is “Type T” thermocouple.
Slides for ME 115 External Reference Junction • A solution is to put J 2 in an ice-bath; then you know T 2, and your output voltage will be proportional to T 1 -T 2. • Handheld thermocouple readers and computer data acquisition systems use something called an isothermal block instead to perform this task.
Slides for ME 115 Comparison of Pressure Instruments Characteristics Overall Electronic output Temperature range Frequency response Cost Manometer Inherently accurate Transducer Automation friendly Dial gauge Poor precision No Yes No Approx. -50°C to +50°C Approx. -200°C to +400°C Approx. -50°C to +50°C < 10 Hz < 1 MHz < 10 Hz $100 -$2000 $50 -$10, 000 $10 -$3000
Slides for ME 115 Manometer Basics • Pressure varies with depth for constant density fluid P 1 P 2 H Manometer fluid
Slides for ME 115 Manometers/Micromanometers Examples (b) Micromanometer (c) Inclined (a) U-tube Source: www. dwyer-inst. com
Slides for ME 115 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. Bridge circuit Strain gage
Slides for ME 115 Pressure Transducer Examples (c) General purpose (a) Low pressure (Validyne DP 103) (b) High performance (d) Miniature Source: www. omega. com
Slides for ME 115 Dial Gauges • A deformable pressure sensing element is attached to a pointer which rotates against a graduated dial--like these children’s party blowouts: • Sources of error include: human error, hysteresis Examples from: www. omega. com
- Slides: 15
