Gas solubility in water Good morning,
I know that Henry's law describes the gas solubility in water with partial pressure of a specific gas.
For example the oxygen concentration in water, under atmospheric pressure, is

$\mathrm{C = P_{O_2} * k}$, where $\mathrm{P_{O_2}}$ is $\mathrm{0.21}$ bar.

But if I have a steam-water mixure, how I can calculate the solubility (for example in a deaerator)?
What data I need to calculate that solubility?
Thanks
You need to know the oxygen content (partial pressure) of the steam-water mixture with which you are purging the system.  

The water being purged will come to equilibrium with the purge gas based on Henry's law, just as in your example of atmospheric conditions, except that the partial pressure of oxygen in the steam should be much lower.