IAPWS97_REGION_TP

This function classifies a water state into one of the IF-97 thermodynamic regions using temperature and pressure. The result enables branch logic in formulas that require region-specific equations.

Region identification is:

r = g(T, P)

where r \in \{1,2,3,5\} for valid single-phase IF-97 regions reachable by a T-P input pair.

Excel Usage

=IAPWS97_REGION_TP(T, P, use_ninety_five_boundary)

T (float, required): Water temperature (K).
P (float, required): Water pressure (Pa).
use_ninety_five_boundary (bool, optional, default: false): Use IAPWS-95 vapor-pressure boundary instead of IF-97 boundary (-).

Returns (int): IF-97 region index (1, 2, 3, or 5).

Example 1: Region one liquid-like state

Inputs:

T	P	use_ninety_five_boundary
400	1000000	false

Excel formula:

=IAPWS97_REGION_TP(400, 1000000, FALSE)

Expected output:

1

Example 2: Region two vapor-like state

Inputs:

T	P	use_ninety_five_boundary
700	1000000	false

Excel formula:

=IAPWS97_REGION_TP(700, 1000000, FALSE)

Expected output:

2

Example 3: Region three dense near-critical state

Inputs:

T	P	use_ninety_five_boundary
650	25000000	false

Excel formula:

=IAPWS97_REGION_TP(650, 25000000, FALSE)

Expected output:

3

Example 4: Region five high-temperature state

Inputs:

T	P	use_ninety_five_boundary
1800	1000000	true

Excel formula:

=IAPWS97_REGION_TP(1800, 1000000, TRUE)

Expected output:

5

Python Code

Show Code

from chemicals.iapws import iapws97_identify_region_TP as chemicals_iapws97_identify_region_tp

def iapws97_region_tp(T, P, use_ninety_five_boundary=False):
    """
    Identify the IF-97 region from temperature and pressure.

    See: https://chemicals.readthedocs.io/chemicals.iapws.html#chemicals.iapws.iapws97_identify_region_TP

    This example function is provided as-is without any representation of accuracy.

    Args:
        T (float): Water temperature (K).
        P (float): Water pressure (Pa).
        use_ninety_five_boundary (bool, optional): Use IAPWS-95 vapor-pressure boundary instead of IF-97 boundary (-). Default is False.

    Returns:
        int: IF-97 region index (1, 2, 3, or 5).
    """
    try:
        return chemicals_iapws97_identify_region_tp(T, P, use_95_boundary=use_ninety_five_boundary)
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

T *

Water temperature (K).

P *

Water pressure (Pa).

use_ninety_five_boundary

Use IAPWS-95 vapor-pressure boundary instead of IF-97 boundary (-).