Specific Heat Capacities of Air

    The nominal values used for air at 300 K are C P = 1.00 kJ/kg.K, C v = 0.718 kJ/kg.K,, and k = 1.4. However they are all functions of temperature, and with the extremely high temperature range experienced in internal combustion and gas turbine engines one can obtain significant errors. The table following gives the values of specific heat capacities as a function of temperature. We find that choosing values of specific heat capacities at the average temperature of each process gives results with reasonable accuracy (within around 1%).

    Ideal gas specific heat capacities of air

    Temperature
    K

    C P
    kJ/kg.K

    C v
    kJ/kg.K

    k

    250

    1.003

    0.716

    1.401

    300

    1.005

    0.718

    1.400

    350

    1.008

    0.721

    1.398

    400

    1.013

    0.726

    1.395

    450

    1.020

    0.733

    1.391

    500

    1.029

    0.742

    1.387

    550

    1.040

    0.753

    1.381

    600

    1.051

    0.764

    1.376

    650

    1.063

    0.776

    1.370

    700

    1.075

    0.788

    1.364

    750

    1.087

    0.800

    1.359

    800

    1.099

    0.812

    1.354

    900

    1.121

    0.834

    1.344

    1000

    1.142

    0.855

    1.336

    1100

    1.155

    0.868

    1.331

    1200

    1.173

    0.886

    1.324

    1300

    1.190

    0.903

    1.318

    1400

    1.204

    0.917

    1.313

    1500

    1.216

    0.929

    1.309

    The values up to 1000 K were originally published in "Tables of Thermal Properties of Gases", NBS Circular 564,1955. The last five rows were calculated from a formula by B G Kyle "Chemical and Process Thermodynamics", Englewood Cliffs / Prentice Hall, 1984, and have <1% error.


    Engineering Thermodynamics by Israel Urieli is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

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