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THERMODYNAMICS - CASE STUDY

    Introduction


paramedics Rescue
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An aircraft powered by a turbojet engine is used to transport seriously injured people to hospitals. The pilot uses the brakes during the loading process to hold the aircraft. How much force that must be applied to the brakes?

What is known:

  • Fuel is burned at a rate of 0.1 kg/s and has a heating value of 42,000 kJ/kg.
  • The compressor has a compression ratio of 10.
  • Air enters the engine at a rate of 8 kg/s.
  • The ambient air is 27oC and 100 kPa.
     
    Question


 

Determine the force that must be applied to the brakes to hold the plane stationary.

     
    Approach


 
  • Model the cycle of the engine as an ideal jet-propulsion cycle.
  • The braking force equals the thrust developed by the engine.
  • Determine the temperature and pressure at each state of the cycle.
  • Model the compressor, turbine and nozzle as steady-flow devices. Use the energy balance of nozzle to determine the exit velocity at the nozzle.