docs: def wall_factor_fd(mu, mu_wall, turbulent=True, liquid=False):
      r'''Computes the wall correction factor for pressure drop due to friction
      between a fluid and a wall. These coefficients were derived for internal 
      flow inside a pipe, but can be used elsewhere where appropriate data is 
      missing. 
      
      .. math::
          \frac{f_d}{f_{d,\text{constant properties}}} 
          = \left(\frac{\mu}{\mu_{wall}}\right)^n
  
      Parameters
      ----------
      mu : float
          Viscosity (or Prandtl number) of flowing fluid away from the wall,
          [Pa*s]
      mu_wall : float
          Viscosity (or Prandtl number) of the fluid at the wall, [Pa*s]
      turbulent : bool
          Whether or not to use the turbulent coefficient, [-]
      liquid : bool
          Whether or not to use the liquid phase coefficient; otherwise the gas
          coefficient is used, [-]
          
      Returns
      -------
      factor : float
          Correction factor for pressure loss; to be multiplied by the friction
          factor, or pressure drop to obtain the actual result, [-]
  
      Notes
      -----
      The exponents are determined as follows:
          
      +-----------+--------+---------+---------+
      | Regime    | Phase  | Heating | Cooling |
      +===========+========+=========+=========+
      | Turbulent | Liquid | -0.25   | -0.25   |
      +-----------+--------+---------+---------+
      | Turbulent | Gas    | 0.1     | 0.1     |
      +-----------+--------+---------+---------+
      | Laminar   | Liquid | -0.58   | -0.5    |
      +-----------+--------+---------+---------+
      | Laminar   | Gas    | -1      | -1      |
      +-----------+--------+---------+---------+
      
      Examples
      --------
      >>> wall_factor_fd(mu=8E-4, mu_wall=3E-4, turbulent=True, liquid=True)
      0.7825422900366437
  
      References
      ----------
      .. [1] Kays, William M., and Michael E. Crawford. Convective Heat and Mass 
         Transfer. 3rd edition. New York: McGraw-Hill Science/Engineering/Math,
         1993.
      '''
      params = wall_factor_fd_defaults[(turbulent, liquid)]
      return wall_factor(mu=mu, mu_wall=mu_wall, **params)