docs: def helical_turbulent_Nu_Mori_Nakayama(Re, Pr, Di, Dc):
      r'''Calculates Nusselt number for a fluid flowing inside a curved 
      pipe such as a helical coil under turbulent conditions, using the method of 
      Mori and Nakayama [1]_, also shown in [2]_ and [3]_.
              
      For :math:`Pr < 1`:
          
      .. math::
          Nu = \frac{Pr}{26.2(Pr^{2/3}-0.074)}Re^{0.8}\left(\frac{D_i}{D_c}
          \right)^{0.1}\left[1 + \frac{0.098}{\left[Re\left(\frac{D_i}{D_c}
          \right)^2\right]^{0.2}}\right]
              
      For :math:`Pr \ge 1`:
          
      .. math::
          Nu = \frac{Pr^{0.4}}{41}Re^{5/6}\left(\frac{D_i}{D_c}\right)^{1/12}
          \left[1 + \frac{0.061}{\left[Re\left(\frac{D_i}{D_c}\right)^{2.5}
          \right]^{1/6}}\right]
          
      Parameters
      ----------
      Re : float
          Reynolds number with `D=Di`, [-]
      Pr : float
          Prandtl number with bulk properties [-]
      Di : float
          Inner diameter of the coil, [m]
      Dc : float
          Diameter of the helix/coil measured from the center of the tube on one
          side to the center of the tube on the other side, [m]
  
      Returns
      -------
      Nu : float
          Nusselt number with respect to `Di`, [-]
  
      Notes
      -----    
      At very low curvatures, the predicted heat transfer coefficient
      grows unbounded.
      
      Applicable for :math:`Re\left(\frac{D_i}{D_c}\right)^2 > 0.1`
  
      Examples
      --------
      >>> helical_turbulent_Nu_Mori_Nakayama(2E5, 0.7, 0.01, .2)
      496.2522480663327
  
      References
      ----------
      .. [1] Mori, Yasuo, and Wataru Nakayama. "Study on Forced Convective Heat 
         Transfer in Curved Pipes." International Journal of Heat and Mass 
         Transfer 10, no. 5 (May 1, 1967): 681-95. 
         doi:10.1016/0017-9310(67)90113-5. 
      .. [2] El-Genk, Mohamed S., and Timothy M. Schriener. "A Review and 
         Correlations for Convection Heat Transfer and Pressure Losses in 
         Toroidal and Helically Coiled Tubes." Heat Transfer Engineering 0, no. 0
         (June 7, 2016): 1-28. doi:10.1080/01457632.2016.1194693.
      .. [3] Hardik, B. K., P. K. Baburajan, and S. V. Prabhu. "Local Heat 
         Transfer Coefficient in Helical Coils with Single Phase Flow." 
         International Journal of Heat and Mass Transfer 89 (October 2015): 
         522-38. doi:10.1016/j.ijheatmasstransfer.2015.05.069.
      '''
      D_ratio = Di/Dc
      if Pr < 1:
          term1 = Pr/(26.2*(Pr**(2/3.) - 0.074))*Re**0.8*D_ratio**0.1
          term2 = 1. + 0.098*(Re*D_ratio*D_ratio)**-0.2
      else:
          term1 = Pr**0.4/41.*Re**(5/6.)*(Di/Dc)**(1/12.)
          term2 = 1. + 0.061/(Re*(Di/Dc)**2.5)**(1/6.)
      return term1*term2