While studying a heat exchanger, I have encountered a hydrogen rich fluid stream (enters at 90° Celsius and exits at 120° Celsius) which has composition given in the following form:

Air Humidity/Fluid composition: 1% (2.5 bar abs)/Mass fraction of hydrogen=0.02

For the heat exchanger analysis, I need to calculate several properties of this mixture like enthalpy, specific heat.

Property reference software like Coolprop and Refprop give data for gas mixtures, but not for air-gas mixtures.

How should I start to calculate the properties of this air-gas mixture? I guess the humidity can be neglected safely because it is just 1%.

  • $\begingroup$ Why exactly can you neglect humidity? $\endgroup$
    – Solar Mike
    Mar 27, 2022 at 16:13
  • $\begingroup$ @SolarMike Honestly, I just wrote the assumption looking at only 1% value of the relative humidity which would imply a very small mole fraction of water vapour. $\endgroup$
    – Avrana
    Mar 28, 2022 at 3:51

1 Answer 1


A molar thermodynamic property $\bar{P}$ for a mixture containing ideal gases can generally be calculated from molar composition (mole fraction $z_j$) and individual component molar property $\bar{P}_j$ as

$$\bar{P} = \sum\ z_j\ \bar{P}_j$$

Composition is given. Reference values for thermodynamic molar properties for pure components abound.

The book The Properties of Gases and Liquids by Poling, Prausnitz, and O'Connell has information on materials properties of fluids such as thermal conductivity and viscosity.

  • $\begingroup$ Thankyou for the answer. An additional question. Can thermal conductivity, viscosity and Prandtl number be also calculated using the molar composition scheme ? $\endgroup$
    – Avrana
    Apr 2, 2022 at 5:55
  • $\begingroup$ @Avrana I can recommend for this the book The Properties of Gases and Liquids by Poling, Prausnitz, and O'Connell. $\endgroup$ Apr 2, 2022 at 13:20
  • $\begingroup$ Thankyou for the suggestion. It is available in our library. $\endgroup$
    – Avrana
    Apr 5, 2022 at 5:42

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