PSYCHRO_DPSATDT

This function computes the first temperature derivative of saturation pressure from the IAPWS-92 vapor-pressure model.

The derivative describes psychrometric sensitivity of vapor pressure with respect to temperature:

\frac{dP_{sat}}{dT}

and is evaluated using the closed-form IAPWS-92 correlation at the specified temperature.

Excel Usage

=PSYCHRO_DPSATDT(temperature)

• temperature (float, required): Temperature for derivative evaluation (K).

Returns (float): First derivative of saturation vapor pressure with respect to temperature (Pa/K).

Example 1: Derivative near boiling point

Inputs:

temperature
373.15

Excel formula:

=PSYCHRO_DPSATDT(373.15)

Expected output:

3619.22

Example 2: Derivative at moderate temperature

Inputs:

temperature
325

Excel formula:

=PSYCHRO_DPSATDT(325)

Expected output:

662.795

Example 3: Derivative at elevated temperature

Inputs:

temperature
450

Excel formula:

=PSYCHRO_DPSATDT(450)

Expected output:

21774.7

Example 4: Derivative at low positive temperature

Inputs:

temperature
280

Excel formula:

=PSYCHRO_DPSATDT(280)

Expected output:

68.1526

Python Code

Show Code

from chemicals.air import iapws92_dPsat_dT as chemicals_iapws92_dpsat_dt

def psychro_dpsatdt(temperature):
    """
    Compute temperature derivative of saturation pressure using IAPWS-92.

    See: https://chemicals.readthedocs.io/chemicals.air.html

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

    Args:
        temperature (float): Temperature for derivative evaluation (K).

    Returns:
        float: First derivative of saturation vapor pressure with respect to temperature (Pa/K).
    """
    try:
        derivative, _psat = chemicals_iapws92_dpsat_dt(temperature)
        return derivative
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

temperature *

Temperature for derivative evaluation (K).