Brayton cycle

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Brayton cycle

• Uses
• Auxiliary power generation
• Stand-alone power generation
• Naval propulsion
• Jet engine

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Gas Turbine

• Advantages
• High powerweight ratio
• Compact
• One-direction motion vibration
• Fewer moving parts
• Better reliability
• Variety of fuels
• Low emissions

• Disadvantages
• Higher cost

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Brayton cycle

• Working fluid air
• Ideal gas
• Specific heats steady
• High temperature reservoir
• Open or closed model
• Steady pressure heat exchange

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Cycle Analysis

• Net work
• Heat in
• Thermal efficiency
• Back work ratio

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Brayton cycle

• 1?2 Isentropic compression
• 2?3 steady pressure heat addition
• 3?4 isentropic expansion
• 4?1 steady pressure heat rejection

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Brayton cycle

• Work in work out
• Heat in heat out
• Thermal efficiency
• Pressure ratio
• Back work ratio

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Brayton Cycle

• Approaches
• Variable specific heats Table h, pr
• Steady specific heats ?h Cp ?T
• P,v,T relationships T2 T1(P2/P1)(k-1)/k

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Compressor

• Essential to compress large volumes of air for
  efficiency of cycle
• Centrifugal
• Axial more common rotor and stator blades

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Example

• A simple Brayton cycle has a rp 12, a
  compressor inlet at 300K, and a turbine inlet at
  1000K. Determine the mass flow of air needed
  when the net power output is 70MW. Specific
  heats are constant.

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Example

• An ideal air-standard Brayton cycle has air
  entering the compressor at 100kPa,300K, 5m3/s.
  The compressor ratio is 10 the turbine inlet is
  at 1400K.
• Find power generated, bwr, and thermal efficiency.

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Brayton cycle

• Irreversibilities isentropic efficiency
• Gas turbine power plant operating at steady state
  receives air at 100kpa 300K. Air is compressed
  to 500kPa and reaches a maximum cycle temperature
  of 920K. The isentropic efficiencies of the
  compressor and turbine are both at 83.
• Find the thermal efficiency and bwr of the cycle.

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Brayton cycle

• Regenerator
• Effectiveness

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Regeneration

• Capital costs
• Pressure losses

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Brayton cycle

• Ideal
• ?th 45.6
• With regenerator
• ?th 57

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Practice problem

• A gas turbine power plant operates on a Brayton
  Cycle between 100 1200kPa. Air enters the
  compressor at 30oC, 150 m3/min and leaves the
  turbine at 500oC. Isentropic efficiencies of 82
  and 88 apply to the compressor turbine
  respectively. Assume specific heats are
  variable.
• Find net power output, bwr, thermal efficiency
  (659kW, 0.63, 31.9)

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Practice Problem

• A gas turbine has a regenerator. Air enters the
  compressor at 100kPa 20oC. Compressor ratio is
  8. Maximum cycle temperature is 800oC. The cold
  air stream leaves the regenerator 10oC cooler
  than the hot air stream entering the regenerator.
  The engine produces 150kW.
• Find heat added heat rejected from the cycle
  303kW 153kW.

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Assignment

• Chapter 9 sections 9.5 through 9.10

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Brayton cycle

• Isentropic compression power
• Isothermal power
• Intercooler

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Chapter 9 Gas Power Systems / F9-18To save, right click on the image and choose "Save As" from the pop-up menu.
              
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Brayton cycle

• Reheat

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Brayton cycle

• Ideal
• ?th 45.6
• With irreversibilities
• ?th 24.9
• With regenerator
• ?th 56.8