docs: def wall_factor_Nu(mu, mu_wall, turbulent=True, liquid=False):
      r'''Computes the wall correction factor for heat transfer 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. It is
      also useful to compare these results with the coefficients used in various
      heat transfer coefficients.
      
      .. math::
          \frac{Nu}{Nu_{\text{constant properties}}} 
          = \left(\frac{\mu}{\mu_{wall}}\right)^n
  
      Parameters
      ----------
      mu : float
          Viscosity (or Prandtl number) of flowing fluid away from the heat
          transfer surface, [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 heat transfer; to be multiplied by the Nusselt
          number, or heat transfer coefficient to obtain the actual result, [-]
  
      Notes
      -----
      The exponents are determined as follows:
          
      +-----------+--------+---------+---------+
      | Regime    | Phase  | Heating | Cooling |
      +===========+========+=========+=========+
      | Turbulent | Liquid | 0.11    | 0.25    |
      +-----------+--------+---------+---------+
      | Turbulent | Gas    | 0.5     | 0       |
      +-----------+--------+---------+---------+
      | Laminar   | Liquid | 0.14    | 0.14    |
      +-----------+--------+---------+---------+
      | Laminar   | Gas    | 0       | 0       |
      +-----------+--------+---------+---------+    
      
      Examples
      --------
      >>> wall_factor_Nu(mu=8E-4, mu_wall=3E-4, turbulent=True, liquid=True)
      1.1139265634480144
      
      >>> wall_factor_Nu(mu=8E-4, mu_wall=3E-4, turbulent=False, liquid=True)
      1.147190712947014
      
      >>> wall_factor_Nu(mu=1.5E-5, mu_wall=1.3E-5, turbulent=True, liquid=False)
      1.0741723110591495
      
      >>> wall_factor_Nu(mu=1.5E-5, mu_wall=1.3E-5, turbulent=False, liquid=False)
      1.0
  
      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_Nu_defaults[(turbulent, liquid)]
      return wall_factor(mu=mu, mu_wall=mu_wall, **params)