Specific Heat Capacities of Air

The nominal values used for air at 300 K are CP = 1.00 kJ/kg.K, Cv = 0.717 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. Potter & Somerton suggest that in those cases one should consult ideal gas tables in Appendix E, which tabulate h(T) and u(T), or integrate using expressions for CP(T) found in Table B-5 (however Table B-5 does not include values for air!). An alternative approach which we find gives results with reasonable accuracy (within around 1%) is to use values of specific heats at the average value of temperature T in each process. This is conveniently done using tables of specific heats vs T, however since Potter & Somerton do not provide these we have provided one here for air:

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.