Thermodynamics Miscellaneous

Thermodynamics Miscellaneous

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Thermodynamics

Thermodynamics Miscellaneous
  1. One side of a wall is maintained at 400 K and the other at 300 K. The rate of heat transfer through the wall is 1000 W and the surrounding temperature is 25°C. Assuming no generation of heat within the wall, the irreversibility (in W) due to heat transfer through the wall is.








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    T0 = 273 + 25 = 298 K
    AE1 = a1 – T0 S1

    AE1 = 1000 - 298 ×
    1000
    		= 225 watts
    400

    AE2 = a2 - T0 S2
    AE2 = 1000 - 298 ×
    1000
    		= 6.67 watts
    300

    ∆ AE = AE2 - AE1

    Correct Option: A

    T0 = 273 + 25 = 298 K
    AE1 = a1 – T0 S1

    AE1 = 1000 - 298 ×
    1000
    		= 225 watts
    400

    AE2 = a2 - T0 S2
    AE2 = 1000 - 298 ×
    1000
    		= 6.67 watts
    300

    ∆ AE = AE2 - AE1

  1. The maximum theoretical work obtainable, when a system interacts to equilibrium with a reference environment, is called








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    Exergy (or) Available Energy: The maximum portion of energy which could be converted into useful work by ideal processes which reduce the system to dead state (a state in equilibrium with the earth and its atmosphere).

    Correct Option: C

    Exergy (or) Available Energy: The maximum portion of energy which could be converted into useful work by ideal processes which reduce the system to dead state (a state in equilibrium with the earth and its atmosphere).

  1. The pressure, temperature and velocity of air flowing in pipe are 5 bar, 500 K and 50 m/s, respectively. The specific heats of air at a constant pressure and at constant volume are 1.005 kJ/kgK and 0.718 kJ/kgK, respectively. Neglect potential energy. If the pressure and temperature of the surroundings are 1 bar and 300 K, respectively, the available energy in kJ/ kg of the air stream is








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    For flow stream,
    A.E. =(h2 – h1) + K.E. – T0 (S2 – S1)

    = cp(T2 - T1) + 1V²T0cplnT2- R / nP2
    2T1p1

    = 187 kJ/kg

    Correct Option: B

    For flow stream,
    A.E. =(h2 – h1) + K.E. – T0 (S2 – S1)

    = cp(T2 - T1) + 1V²T0cplnT2- R / nP2
    2T1p1

    = 187 kJ/kg

  1. Which of the following statements are TRUE with respect to heat and work?
    (i) They are boundary phenomena
    (ii) They are exact differentials
    (iii) They are path functions








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    Since heat and work are energy in transit i.e. heat and work has meaning only when there is process. So both are boundary phenomena and are inexact i.e. path function.

    Correct Option: B

    Since heat and work are energy in transit i.e. heat and work has meaning only when there is process. So both are boundary phenomena and are inexact i.e. path function.

  1. Heat and work are








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    Heat and work are path functions. Since Q and W are dependent on path followed between two given end states of a thermodynamic process undergone by system.

    Correct Option: D

    Heat and work are path functions. Since Q and W are dependent on path followed between two given end states of a thermodynamic process undergone by system.