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Thermodynamics - compressor

  1. Jan 30, 2012 #1
    Air at 1 bar and 25°C continuously flows through a rigid compressor at a low velocity of 1 m/s. The air exits the compressor at 3 bar, and then enters a nozzle in which it expands adiabatically to a final velocity of 600 m/s at the initial conditions of temperate and pressure. Assume no change in elevation, and that the inlet and outlet conditions are constant with time. If the compressor transfers 240 kJ/kg of mechanical work to the air, how much heat must be removed from the compressor?

    I am completely confused. Adiabatic means no heat transfer?.. Please help
  2. jcsd
  3. Jan 31, 2012 #2

    Andrew Mason

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    What is the mechanical kinetic energy of one kg of air before compression? What is the mechanical kinetic energy of the same air at the outlet. What is the difference, then, in energy of that kg of air between inlet and outlet? (Since the adiabatic expansion causes the gas to return to its initial temperature and pressure, is there any difference in the internal energy of the air between inlet and outlet?).

    How much work was done by the compressor on that kg of air? What is the difference between the work done to and the mechanical energy imparted to that kg of air? What happens to that difference?

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