WALL_FACTOR

This function calculates a wall-property correction factor used to adjust ideal heat-transfer or momentum-transfer correlations for property variation between bulk fluid and wall conditions. It supports viscosity-, Prandtl-number-, or temperature-based ratios with separate exponents for heating and cooling.

The generic structure is:

ext{factor} = \left(\frac{\phi_{\text{bulk}}}{\phi_{\text{wall}}}\right)^n

where \phi is the selected property and n is chosen from the corresponding heating or cooling coefficient.

Excel Usage

=WALL_FACTOR(mu, mu_wall, Pr, Pr_wall, T, T_wall, mu_heating_coeff, mu_cooling_coeff, Pr_heating_coeff, Pr_cooling_coeff, T_heating_coeff, T_cooling_coeff, property_option)

• mu (float, optional, default: null): Bulk fluid viscosity (Pa*s).
• mu_wall (float, optional, default: null): Wall fluid viscosity (Pa*s).
• Pr (float, optional, default: null): Bulk fluid Prandtl number (-).
• Pr_wall (float, optional, default: null): Wall fluid Prandtl number (-).
• T (float, optional, default: null): Bulk fluid temperature (K).
• T_wall (float, optional, default: null): Wall fluid temperature (K).
• mu_heating_coeff (float, optional, default: 0.11): Viscosity heating coefficient (-).
• mu_cooling_coeff (float, optional, default: 0.25): Viscosity cooling coefficient (-).
• Pr_heating_coeff (float, optional, default: 0.11): Prandtl heating coefficient (-).
• Pr_cooling_coeff (float, optional, default: 0.25): Prandtl cooling coefficient (-).
• T_heating_coeff (float, optional, default: 0.11): Temperature heating coefficient (-).
• T_cooling_coeff (float, optional, default: 0.25): Temperature cooling coefficient (-).
• property_option (str, optional, default: “Prandtl”): Property basis for correction factor (-).

Returns (float): Wall correction factor, or an error message if invalid.

Example 1: Prandtl correction with default option

Inputs:

mu	mu_wall	Pr	Pr_wall	T	T_wall
0.0008	0.0003	1.2	1.1	300	350

Excel formula:

=WALL_FACTOR(0.0008, 0.0003, 1.2, 1.1, 300, 350)

Expected output:

1.00962

Example 2: Viscosity correction option

Inputs:

mu	mu_wall	Pr	Pr_wall	T	T_wall	property_option
0.0009	0.0004	1.5	1.3	310	360	Viscosity

Excel formula:

=WALL_FACTOR(0.0009, 0.0004, 1.5, 1.3, 310, 360, "Viscosity")

Expected output:

1.0933

Example 3: Temperature correction option

Inputs:

mu	mu_wall	Pr	Pr_wall	T	T_wall	property_option
0.00075	0.00035	1.1	1	290	330	Temperature

Excel formula:

=WALL_FACTOR(0.00075, 0.00035, 1.1, 1, 290, 330, "Temperature")

Expected output:

0.985887

Example 4: Explicit Prandtl correction option

Inputs:

mu	mu_wall	Pr	Pr_wall	T	T_wall	property_option
0.001	0.00045	1.4	1.2	320	370	Prandtl

Excel formula:

=WALL_FACTOR(0.001, 0.00045, 1.4, 1.2, 320, 370, "Prandtl")

Expected output:

1.0171

Python Code

Show Code

from ht.air_cooler import wall_factor as ht_wall_factor

def wall_factor(mu=None, mu_wall=None, Pr=None, Pr_wall=None, T=None, T_wall=None, mu_heating_coeff=0.11, mu_cooling_coeff=0.25, Pr_heating_coeff=0.11, Pr_cooling_coeff=0.25, T_heating_coeff=0.11, T_cooling_coeff=0.25, property_option='Prandtl'):
    """
    Compute wall property correction factors for heat transfer correlations.

    See: https://ht.readthedocs.io/en/latest/ht.air_cooler.html

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

    Args:
        mu (float, optional): Bulk fluid viscosity (Pa*s). Default is None.
        mu_wall (float, optional): Wall fluid viscosity (Pa*s). Default is None.
        Pr (float, optional): Bulk fluid Prandtl number (-). Default is None.
        Pr_wall (float, optional): Wall fluid Prandtl number (-). Default is None.
        T (float, optional): Bulk fluid temperature (K). Default is None.
        T_wall (float, optional): Wall fluid temperature (K). Default is None.
        mu_heating_coeff (float, optional): Viscosity heating coefficient (-). Default is 0.11.
        mu_cooling_coeff (float, optional): Viscosity cooling coefficient (-). Default is 0.25.
        Pr_heating_coeff (float, optional): Prandtl heating coefficient (-). Default is 0.11.
        Pr_cooling_coeff (float, optional): Prandtl cooling coefficient (-). Default is 0.25.
        T_heating_coeff (float, optional): Temperature heating coefficient (-). Default is 0.11.
        T_cooling_coeff (float, optional): Temperature cooling coefficient (-). Default is 0.25.
        property_option (str, optional): Property basis for correction factor (-). Valid options: Viscosity, Prandtl, Temperature. Default is 'Prandtl'.

    Returns:
        float: Wall correction factor, or an error message if invalid.
    """
    try:
        return ht_wall_factor(
            mu=mu,
            mu_wall=mu_wall,
            Pr=Pr,
            Pr_wall=Pr_wall,
            T=T,
            T_wall=T_wall,
            mu_heating_coeff=mu_heating_coeff,
            mu_cooling_coeff=mu_cooling_coeff,
            Pr_heating_coeff=Pr_heating_coeff,
            Pr_cooling_coeff=Pr_cooling_coeff,
            T_heating_coeff=T_heating_coeff,
            T_cooling_coeff=T_cooling_coeff,
            property_option=property_option,
        )
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

mu

Bulk fluid viscosity (Pa*s).

mu_wall

Wall fluid viscosity (Pa*s).

Pr

Bulk fluid Prandtl number (-).

Pr_wall

Wall fluid Prandtl number (-).

T

Bulk fluid temperature (K).

T_wall

Wall fluid temperature (K).

mu_heating_coeff

Viscosity heating coefficient (-).

mu_cooling_coeff

Viscosity cooling coefficient (-).

Pr_heating_coeff

Prandtl heating coefficient (-).

Pr_cooling_coeff

Prandtl cooling coefficient (-).

T_heating_coeff

Temperature heating coefficient (-).

T_cooling_coeff

Temperature cooling coefficient (-).

property_option Optional Viscosity Prandtl Temperature

Property basis for correction factor (-).