PROPS_SI

This function evaluates a requested thermophysical property for a pure fluid or mixture string using CoolProp’s high-level SI interface with two independent state inputs. It supports common thermodynamic and transport properties such as density, enthalpy, entropy, viscosity, and conductivity.

The property calculation is represented as:

y = h\left(o,\; n_1, v_1,\; n_2, v_2,\; \text{fluid}\right)

where o is the requested output property code, n_1,n_2 are input property codes, v_1,v_2 are SI values, and y is the computed scalar result.

Excel Usage

=PROPS_SI(props_si_output, props_si_name_one, value_one, props_si_name_two, value_two, fluid)

props_si_output (str, required): Desired property code (e.g., ‘D’ for density, ‘H’ for enthalpy).
props_si_name_one (str, required): Name of the first input property (e.g., ‘T’, ‘P’).
value_one (float, required): Value of the first input property in SI units.
props_si_name_two (str, required): Name of the second input property (e.g., ‘P’, ‘Q’).
value_two (float, required): Value of the second input property in SI units.
fluid (str, required): Fluid name (e.g., ‘Water’, ‘R134a’) or mixture string.

Returns (float): Calculated property value in SI units.

Example 1: Density of Water at STP

Inputs:

props_si_output	props_si_name_one	value_one	props_si_name_two	value_two	fluid
D	T	298.15	P	101325	Water

Excel formula:

=PROPS_SI("D", "T", 298.15, "P", 101325, "Water")

Expected output:

997.048

Example 2: Boiling point of Water at 1 atm

Inputs:

props_si_output	props_si_name_one	value_one	props_si_name_two	value_two	fluid
T	P	101325	Q	0	Water

Excel formula:

=PROPS_SI("T", "P", 101325, "Q", 0, "Water")

Expected output:

373.124

Example 3: Enthalpy of R134a

Inputs:

props_si_output	props_si_name_one	value_one	props_si_name_two	value_two	fluid
H	T	298.15	Q	1	R134a

Excel formula:

=PROPS_SI("H", "T", 298.15, "Q", 1, "R134a")

Expected output:

412334

Example 4: CO2 Supercritical Density

Inputs:

props_si_output	props_si_name_one	value_one	props_si_name_two	value_two	fluid
D	T	350	P	10000000	CO2

Excel formula:

=PROPS_SI("D", "T", 350, "P", 10000000, "CO2")

Expected output:

228.804

Python Code

Show Code

import CoolProp.CoolProp as CP

def props_si(props_si_output, props_si_name_one, value_one, props_si_name_two, value_two, fluid):
    """
    Calculate thermophysical properties of fluids using CoolProp.

    See: https://coolprop.org/coolprop/HighLevelAPI.html#propssi-function

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

    Args:
        props_si_output (str): Desired property code (e.g., 'D' for density, 'H' for enthalpy). Valid options: Temperature (T), Pressure (P), Density (D), Enthalpy (H), Entropy (S), Vapor Quality (Q), Internal Energy (U), Specific Heat Cp (C), Specific Heat Cv (O), Thermal Cond. (L), Viscosity (V), Prandtl (Prandtl), Speed of Sound (A), Phase Index (Phase).
        props_si_name_one (str): Name of the first input property (e.g., 'T', 'P'). Valid options: Temperature (T), Pressure (P), Density (D), Enthalpy (H), Entropy (S), Vapor Quality (Q), Internal Energy (U).
        value_one (float): Value of the first input property in SI units.
        props_si_name_two (str): Name of the second input property (e.g., 'P', 'Q'). Valid options: Temperature (T), Pressure (P), Density (D), Enthalpy (H), Entropy (S), Vapor Quality (Q), Internal Energy (U).
        value_two (float): Value of the second input property in SI units.
        fluid (str): Fluid name (e.g., 'Water', 'R134a') or mixture string.

    Returns:
        float: Calculated property value in SI units.
    """
    try:
        # CoolProp.PropsSI(output, name1, prop1, name2, prop2, Ref)
        result = CP.PropsSI(props_si_output, props_si_name_one, value_one, props_si_name_two, value_two, fluid)
        return float(result)
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

props_si_output *

Desired property code (e.g., 'D' for density, 'H' for enthalpy).

props_si_name_one *

Name of the first input property (e.g., 'T', 'P').

value_one *

Value of the first input property in SI units.

props_si_name_two *

Name of the second input property (e.g., 'P', 'Q').

value_two *

Value of the second input property in SI units.

fluid *

Fluid name (e.g., 'Water', 'R134a') or mixture string.