BEJAN

Computes the Bejan number as a pressure-drop-based dimensionless group using either a characteristic length or permeability form.

Excel Usage

=BEJAN(bejan_type, dP, L_or_K, mu, alpha)
  • bejan_type (str, required): Calculation type for Bejan number (length-based or permeability-based)
  • dP (float, required): Pressure drop in Pascals (Pa)
  • L_or_K (float, required): Characteristic length (m) for length-based or permeability (m²) for permeability-based
  • mu (float, required): Dynamic viscosity in Pa·s
  • alpha (float, required): Thermal diffusivity in m²/s

Returns (float): Bejan number (float), or error message string.

Example 1: Length-based Bejan number with unit length

Inputs:

bejan_type dP L_or_K mu alpha
length 10000 1 0.001 0.000001

Excel formula:

=BEJAN("length", 10000, 1, 0.001, 0.000001)

Expected output:

10000000000000

Example 2: Permeability-based Bejan number with unit permeability

Inputs:

bejan_type dP L_or_K mu alpha
permeability 10000 1 0.001 0.000001

Excel formula:

=BEJAN("permeability", 10000, 1, 0.001, 0.000001)

Expected output:

10000000000000

Example 3: Length-based Bejan number at smaller scale

Inputs:

bejan_type dP L_or_K mu alpha
length 500 0.5 0.002 0.00001

Excel formula:

=BEJAN("length", 500, 0.5, 0.002, 0.00001)

Expected output:

6250000000

Example 4: Permeability-based Bejan number with low permeability

Inputs:

bejan_type dP L_or_K mu alpha
permeability 2000 0.05 0.005 0.00002

Excel formula:

=BEJAN("permeability", 2000, 0.05, 0.005, 0.00002)

Expected output:

1000000000

Python Code

Show Code 
from fluids import core as fluids_core

def bejan(bejan_type, dP, L_or_K, mu, alpha):
    """
    Compute the Bejan number (length-based or permeability-based).

    See: https://fluids.readthedocs.io/fluids.core.html#dimensionless-numbers

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

    Args:
        bejan_type (str): Calculation type for Bejan number (length-based or permeability-based) Valid options: Length, Permeability.
        dP (float): Pressure drop in Pascals (Pa)
        L_or_K (float): Characteristic length (m) for length-based or permeability (m²) for permeability-based
        mu (float): Dynamic viscosity in Pa·s
        alpha (float): Thermal diffusivity in m²/s

    Returns:
        float: Bejan number (float), or error message string.
    """
    try:
      if not isinstance(bejan_type, str):
        return "Error: bejan_type must be a string."

      bejan_type_lower = bejan_type.lower()
      if bejan_type_lower not in ["length", "permeability"]:
        return "Error: bejan_type must be 'length' or 'permeability'."

      try:
        dP_val = float(dP)
        length_or_perm = float(L_or_K)
        mu_val = float(mu)
        alpha_val = float(alpha)
      except (TypeError, ValueError):
        return "Error: dP, L_or_K, mu, and alpha must be numeric."

      if mu_val <= 0:
        return "Error: mu (dynamic viscosity) must be positive."
      if alpha_val <= 0:
        return "Error: alpha (thermal diffusivity) must be positive."

      if bejan_type_lower == "length":
        return fluids_core.Bejan_L(dP_val, length_or_perm, mu_val, alpha_val)
      return fluids_core.Bejan_p(dP_val, length_or_perm, mu_val, alpha_val)
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

Calculation type for Bejan number (length-based or permeability-based)
Pressure drop in Pascals (Pa)
Characteristic length (m) for length-based or permeability (m²) for permeability-based
Dynamic viscosity in Pa·s
Thermal diffusivity in m²/s