docs: def Nu_vertical_plate_Churchill(Pr, Gr):
      r'''Calculates Nusselt number for natural convection around a vertical
      plate according to the Churchill-Chu [1]_ correlation, also presented in
      [2]_. Plate must be isothermal; an alternate expression exists for constant
      heat flux.
  
      .. math::
          Nu_{L}=\left[0.825+\frac{0.387Ra_{L}^{1/6}}
          {[1+(0.492/Pr)^{9/16}]^{8/27}}\right]^2
  
      Parameters
      ----------
      Pr : float
          Prandtl number [-]
      Gr : float
          Grashof number [-]
  
      Returns
      -------
      Nu : float
          Nusselt number, [-]
  
      Notes
      -----
      Although transition from laminar to turbulent is discrete in reality, this
      equation provides a smooth transition in value from laminar to turbulent.
      Checked with the original source.
  
      Can be applied to vertical cylinders as well, subject to the criteria below:
  
      .. math::
          \frac{D}{L}\ge \frac{35}{Gr_L^{1/4}}
  
      Examples
      --------
      From [2]_, Example 9.2, matches:
  
      >>> Nu_vertical_plate_Churchill(0.69, 2.63E9)
      147.16185223770603
  
      References
      ----------
      .. [1] Churchill, Stuart W., and Humbert H. S. Chu. "Correlating Equations
         for Laminar and Turbulent Free Convection from a Vertical Plate."
         International Journal of Heat and Mass Transfer 18, no. 11
         (November 1, 1975): 1323-29. doi:10.1016/0017-9310(75)90243-4.
      .. [2] Bergman, Theodore L., Adrienne S. Lavine, Frank P. Incropera, and
         David P. DeWitt. Introduction to Heat Transfer. 6E. Hoboken, NJ:
         Wiley, 2011.
      '''
      Ra = Pr * Gr
      Nu = (0.825 + (0.387*Ra**(1/6.)/(1 + (0.492/Pr)**(9/16.))**(8/27.)))**2
      return Nu