Is it possible to extract thermodynamic data for metastable liquid/gas phases?

[t-brink]

Thank you for this package. I have a question, not a bug. I am using the package to teach a course on thermodynamics, where I demonstrate things based on “real” data. I am not too familiar with the IAPWS formulas, since I only use this for a course. When I calculate, e.g., an isobar with

p = 0.1
T = np.linspace(253.15, 773.15, 100)
G = [iapws.iapws95.IAPWS95_PT(p, T_i).g for T_i in T]

there is obviously a discontinuity in G when the water evaporates (and a corresponding jump in S etc). For didactic reasons, I would like to plot G, S, cp, … in the metastable regions, too. The functions looks like they must be piecewise defined (for liquid and gas), but I cannot find how to access the individual functions. For ice (iapws._iapws._Ice), I can get the free energies over the whole range. I appreciate that these might be unreliable extrapolations, but I just want to demonstrate things like ΔG in undercooling etc. Can this be done with this package?

[jjgomera]

Hi,
you can do easily using iapws97, using directly the different region correlations

In [1]: from iapws.iapws97 import _Region1, _Region2, _Region3

In [2]: _Region1(400, 0.1)   # water liquid  at metastable conditions above boiling point
Out[2]: 
{'T': 400,
 'P': 0.1,
 'v': 0.001066770077006482,
 'h': 532.8467717759336,
 's': 1.601364145433787,
 'cp': 4.259137661887794,
 'cv': 3.6349635158871316,
 'w': 1509.9697825944884,
 'alfav': 0.0008954997036707562,
 'kt': 0.0005482213360900553,
 'region': 1,
 'x': 0}

In [3]: _Region2(360, 0.1)    # vapor below its condesnation temperature
Out[3]: 
{'T': 360,
 'P': 0.1,
 'v': 1.6306206277775008,
 'h': 2647.9037232659953,
 's': 7.284968650485413,
 'cp': 2.186403602666266,
 'cv': 1.6362893769523013,
 'w': 461.97557061124303,
 'alfav': 0.0030930809673336878,
 'kt': 10.209045379140832,
 'region': 2,
 'x': 1}

For region3 there is a little more unusable because need density and temperature as input parameter
For region 2 exist a special correlation for metastable states dont implemented in this library, working of that...

[jjgomera]

Done, now you can use the special correlation for vapor in metastable state:

In [1]: from iapws.iapws97 import _Region2_meta

In [2]: _Region2_meta(360, 0.101325)
Out[2]: 
{'T': 360,
 'P': 0.101325,
 'v': 1.6087447325890363,
 'h': 2647.655107910522,
 's': 7.278320647817223,
 'cp': 2.1680156708391864,
 'cv': 1.619240492418992,
 'w': 462.3206487379948,
 'alfav': 0.0030901404516094693,
 'kt': 10.077472402997257,
 'region': 2,
 'x': 1}

[t-brink]

Wow, thanks for the quick response and implementation. That appears to be exactly what I need, works well in my testing.