Fix error HumidAir.mixing humidity

[c-ortbauer]

Hi

I think I spotted an error in the HumidAir.mixing method. The humidity of the mix was calculated incorrectly.

Here is my derivation:

$$X = \frac{m_W}{m_{dA}}$$ $$= \frac{X_1 m_{dA1}+X_2 m_{dA2}}{m_{dA1}+m_{dA2}} $$ $$= \frac{X_1\frac{m_1}{1+X_1}+ X_2\frac{m_2}{1+X_2}}{\frac{m_1}{1+X_1}+\frac{m_2}{1+X_2}}$$ $$= \frac{X_1 m_1 (1+X_2)+ X_2 m_2 (1+X_1)}{m_1 (1+X_2) + m_2 (1+X_1)}$$

Luckily I implemented my own mixing function before finding this one. While checking my own, they always were just a bit off.

Thanks for the great library!

[portyanikhin]

Hello, @c-ortbauer!

Thank you so much for fixing this bug!
I've refactored a bit and brought the code in line with your formula:

$$\frac{m_1 X_1 (1+X_2)+ m_2 X_2 (1+X_1)}{m_1 (1+X_2) + m_2 (1+X_1)}$$

In my opinion, it will be much more concise this way.

I'm glad that my library turned out to be useful for you😊

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (b09589e) to head (268fea1).
Report is 8 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           22        22           
  Lines         1269      1269           
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  Hits          1269      1269           

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