Hi David!
Thanks for the Coll Prop!

1 Why is there such a big difference?

2 Do you know why there is 23% oxygen in the air?

O2-N2-Air.sm (11,32 KiB) scaricato 576 volta(e).

Hi Valery. There are different reference states, that is, with zero enthalpy and entropy. These could be harmonized using CoolProp_set_reference_stateS or CoolProp_set_reference_stateD, but I don't know how to use them, or they don't work for me. By the way, for any application, the important thing will always be Δs, not s.

This post is 10 years old, where I'm asking about how to use them:
https://smath.com/en-US/forum/topic/gcKGsU/CoolProp-Wrapper#msg111998

Best regards.
Alvaro.

Thanks Alvaro!
And what can you say about the maximum at 20% O2?

Hi Valery. I suppose we would have to apply the Second Law of Thermodynamics δQrev = T*ds. Since it is close to a maximum, ds has to be small, and I don't know if this should be interpreted as a maximum in s implying a maximum in the system's capacity to handle heat reversibly, optimizing the efficiency of systems where air is the working fluid, as in internal combustion engines, or vice versa!

I assume that this also has important consequences in biology, but the flexibility of the walls complicates everything, as in the case of veins, which are not pipes because they expand and contract considerably, and the lungs, where the alveoli are also very flexible.

Best regards.
Alvaro.