Specific Heat Capacities of Air

The nominal values used for air at 300 K are CP = 1.00 kJ/kg.K, Cv = 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

CP
kJ/kg.K

Cv
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.

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