Problem with IAPWS97

[bemoore99]

I have been validating the IAPWS97 code against data published by IAPWS for the purpose of validating computer code implementation. Data is in this report

The International Association for the Properties of Water and Steam
Lucerne, Switzerland
August 2007
Revised Release on the IAPWS Industrial Formulation 1997
for the Thermodynamic Properties of Water and Steam
(The revision only relates to the extension of region 5 to 50 MPa)
The International Association for the Properties of Water and Steam

The routine iapws.IAPWS97 does not return the values published in Table 18 of this report (it does return essentially identical values for other similar tables). I checked the data in Table 18 against other commercial implementation of this code, and that software produced erros as well. However, the implementation on the IAPWS website at this link reproduced Table 18 - http://twt.mpei.ac.ru/mcs/worksheets/iapws/IAPWS-IF97-Region2.xmcd.

I'm wondering if there was some error in the publication which has been addressed by subsequent errata which is not addressed in your code.

[jjgomera]

Hi,
That table is calculated for a different correlation specific for the metastable-vapor region, so, you need use it to get the corrected values in table, in fact, that table is used in testing of library

https://github.com/jjgomera/iapws/blob/master/test.py#L568

If you use the input values in IAPWS97 class, you dont get the values of the table, you get the values of the stable phase at that conditions, the liqpuid phase, to get the metastable-vapor properties you must use directly the specific correlation

[bemoore99]

Juan, Thanks for the prompt reply. Here is an example of how I am using the iapws code # Define pressure (MPa) and temperature (°C) P = 5.0 T = 300 + 273.15 # Temperature in °C x = iapws.IAPWS97(T=T, P = P) My interpretation of the documentation is that this IAPWS97 class can accept combinations of P, T, X etc. and then internally will determine which region the input falls into and then will use the appropriate code for the applicable region. Under this assumption the results from all the other data tables are correctly reproduced. Is this correct use of the class, and it so is this meta-stable region an exception. I have not gone through the code for this class but will do so. if not, then do I need to write code which evaluates the T and P input value and then selects which Region to use for the calculations Note that the commercial software which my company uses and has used for many years (large multinational engineering company) include functions by property which performs in the way I assume your code does i.e. if I pass a function for enthalpy a specific temperature and pressure it determines which region and returns the result. It reproduces all the data tables correctly except for the Table 18 data, I have contacted them and am awaiting a responses. Thanks for your feedback. Bernie Moore

…

On Wed, Feb 5, 2025 at 1:41 PM Juan José Gómez Romera < ***@***.***> wrote: Hi, That table is calculated for a different correlation specific for the metastable-vapor region, so, you need use it to get the corrected values in table, in fact, that table is used in testing of library https://github.com/jjgomera/iapws/blob/master/test.py#L568 — Reply to this email directly, view it on GitHub <#78 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AF4FMDIZ4BZTJTPIFBWX37L2OJZOBAVCNFSM6AAAAABWQA6ROWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMMZXHE3TONZZGQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

-- Regards, Bernie Moore

[jjgomera]

Hi, Bernie,

Juan,

Thanks for the prompt reply. Here is an example of how I am using the iapws
code

# Define pressure (MPa) and temperature (°C)
P = 5.0
T = 300 + 273.15  # Temperature in °C
x = iapws.IAPWS97(T=T, P = P)

My interpretation of the documentation is that this IAPWS97 class can
accept combinations of P, T, X etc. and then internally will determine
which region the input falls into and then will use the appropriate code
for the applicable region. Under this assumption the results from all the
other data tables are correctly reproduced. Is this correct use of the
class, and it so is this meta-stable region an exception. I have not gone
through the code for this class but will do so. if not, then do I need to
write code which evaluates the T and P input value and then selects which
Region to use for the calculations

Your right, metastable states are not added in IAPWS97, you must use it directly to get properties in that metastable state

In [1]: from iapws.iapws97 import _Region2_meta

In [2]: st = _Region2_meta(450, 1)

In [3]: st
Out[3]: 
{'T': 450,
 'P': 1,
 'v': 0.1925165400597291,
 'h': 2768.811151116923,
 's': 6.566603768617397,
 'cp': 2.7634926495107943,
 'cv': 1.958307301714166,
 'w': 498.40810066232143,
 'alfav': 0.0031881982400282847,
 'kt': 1.0936423860609599,
 'region': 2,
 'x': 1}

[bemoore99]

Thanks Juan. Is this meta stable region 2 the only region not included in the IAPSW97 class, or are there other I would be aware of. Sorry if I missed this in the documentation.BernieSent from my iPadOn Feb 6, 2025, at 3:09 PM, Juan José Gómez Romera ***@***.***> wrote: Hi, Bernie, Juan, Thanks for the prompt reply. Here is an example of how I am using the iapws code # Define pressure (MPa) and temperature (°C) P = 5.0 T = 300 + 273.15 # Temperature in °C x = iapws.IAPWS97(T=T, P = P) My interpretation of the documentation is that this IAPWS97 class can accept combinations of P, T, X etc. and then internally will determine which region the input falls into and then will use the appropriate code for the applicable region. Under this assumption the results from all the other data tables are correctly reproduced. Is this correct use of the class, and it so is this meta-stable region an exception. I have not gone through the code for this class but will do so. if not, then do I need to write code which evaluates the T and P input value and then selects which Region to use for the calculations Your right, metastable states are not added in IAPWS97, you must use it directly to get properties in that metastable state In [1]: from iapws.iapws97 import _Region2_meta In [2]: st = _Region2_meta(450, 1) In [3]: st Out[3]: {'T': 450, 'P': 1, 'v': 0.1925165400597291, 'h': 2768.811151116923, 's': 6.566603768617397, 'cp': 2.7634926495107943, 'cv': 1.958307301714166, 'w': 498.40810066232143, 'alfav': 0.0031881982400282847, 'kt': 1.0936423860609599, 'region': 2, 'x': 1} —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>