Fix Media.Air.MoistAir.{density_derX, s_pTX, s_pTX_der}

[beutlich]

Back-port of #2932 to fix #2874, #2872 and #2868 in maint/3.2.3 branch.

[casella]

Sounds good!

[wischhusen]

There is another issue with the specific entropy, when the actual pressure is smaller than the reference pressure p < reference_p, the increasing influence on the entropy is clipped:

s := Modelica.Media.IdealGases.Common.Functions.s0_Tlow(dryair, T)*(1 - X[ Water]) + Modelica.Media.IdealGases.Common.Functions.s0_Tlow(steam, T)X[Water] - Modelica.Constants.R(Utilities.smoothMax(X[Water]/MMX[Water]*Modelica.Math.log(max(Y[Water], Modelica.Constants.eps)*p/reference_p), 0.0, 1e-9) + Utilities.smoothMax((1 - X[Water])/MMX[Air]*Modelica.Math.log(max(Y[Air], Modelica.Constants.eps)*p/reference_p), 0.0, 1e-9));

A corrected version, keeping p/reference_p out of the max()-function, looks like this:

s=Modelica.Media.IdealGases.Common.Functions.s0_Tlow(dryair, T)*(1 - X[Water]) + Modelica.Media.IdealGases.Common.Functions.s0_Tlow(steam, T)X[Water]-Modelica.Constants.R(
Utilities.smoothMax(X[Water]/MMX[Water],0.0,1e-9)*Modelica.Math.log(max(Y[Water], Modelica.Constants.eps)*p/reference_p) + Utilities.smoothMax((1 - X[Water])/MMX[Air],0.0,1e-9)*Modelica.Math.log(max(Y[Air], Modelica.Constants.eps)*p/reference_p)
);

[beutlich]

There is another issue with the specific entropy

@wischhusen Sorry, I do not understand. This PR is a backport of your PR #2932 from master to maint/3.2.3 (as we agreed to fix bugs also in the maint branch). Now, if there is another issue with the specific entropy, that is not yet reported, can you please create a new PR for master first. I'll care for the cherry-pick then.