docs: def Nu_vertical_cylinder_Touloukian_Morgan(Pr, Gr, turbulent=None):
      r'''Calculates Nusselt number for natural convection around a vertical
      isothermal cylinder according to the results of [1]_ correlated by [2]_, as
      presented in [3]_ and [4]_.
  
      .. math::
          Nu_H = 0.726 Ra_H^{0.25},\; 2\times 10^{8} < Ra < 4\times 10^{10}
  
          Nu_H = 0.0674 (Gr_H Pr^{1.29})^{1/3},\; 4\times 10^{10} < Ra < 9\times 10^{11}
  
      Parameters
      ----------
      Pr : float
          Prandtl number [-]
      Gr : float
          Grashof number [-]
      turbulent : bool or None, optional
          Whether or not to force the correlation to return the turbulent
  		 result; will return the laminar regime if False; leave as None for
          automatic selection
  
      Returns
      -------
      Nu : float
          Nusselt number, [-]
  
      Notes
      -----
      Cylinder of diameters 2.75 inch, with heights of 6, 18, and 36.25 inch.
      Temperature was controlled via multiple separately controlled heating
      sections. Fluids were water and ethylene-glycol. Transition between ranges
      is not smooth. If outside of range, no warning is given. [2]_, [3]_, and
      [4]_ are in complete agreement about this formulation.
  
      Examples
      --------
      >>> Nu_vertical_cylinder_Touloukian_Morgan(.7, 2E10)
      249.72879961097854
  
      References
      ----------
      .. [1] Touloukian, Y. S, George A Hawkins, and Max Jakob. Heat Transfer by
         Free Convection from Heated Vertical Surfaces to Liquids.
         Trans. ASME 70, 13-18 (1948).
      .. [2] Morgan, V.T., The Overall Convective Heat Transfer from Smooth
         Circular Cylinders, in Advances in Heat Transfer, eds. T.F. Irvin and
         J.P. Hartnett, V 11, 199-264, 1975.
      .. [3] Popiel, Czeslaw O. "Free Convection Heat Transfer from Vertical
         Slender Cylinders: A Review." Heat Transfer Engineering 29, no. 6
         (June 1, 2008): 521-36. doi:10.1080/01457630801891557.
      .. [4] Boetcher, Sandra K. S. "Natural Convection Heat Transfer From
         Vertical Cylinders." In Natural Convection from Circular Cylinders,
         23-42. Springer, 2014.
      '''
      Ra = Pr*Gr
      if turbulent or (Ra > 4E10 and turbulent is None):
          return 0.0674*(Gr*Pr**1.29)**(1/3.)
      else:
          return 0.726*Ra**0.25