docs: def Nu_Mokry(Re, Pr, rho_w=None, rho_b=None):
      r'''Calculates internal convection Nusselt number for turbulent vertical
      upward flow in a pipe under supercritical conditions according to [1]_,
      and reviewed in [2]_.
          
      .. math::
          Nu_b = 0.0061 Re_b^{0.904} \bar{Pr}_b^{0.684}
          \left(\frac{\rho_w}{\rho_b}\right)^{0.564}
          
          \bar{Cp} = \frac{H_w-H_b}{T_w-T_b}
          
      Parameters
      ----------
      Re : float
          Reynolds number with bulk fluid properties, [-]
      Pr : float
          Prandtl number with bulk fluid properties and an average heat capacity
          between the wall and bulk temperatures [-]
      rho_w : float, optional
          Density at the wall temperature, [kg/m^3]
      rho_b : float, optional
          Density at the bulk temperature, [kg/m^3]
  
      Returns
      -------
      Nu : float
          Nusselt number with bulk fluid properties, [-]
  
      Notes
      -----
      For the data used to develop the correlation, P was set at 20 MPa, and D 
      was 10 mm. G varied from 200-1500 kg/m^2/s and q varied from 0 to 1250
      kW/m^2.
      
      Cp used in the calculation of Prandtl number should be the average value
      of those at the wall and the bulk temperatures.
  
      For deteriorated heat transfer, this was the four most accurate correlation  
      in [2]_ with a MAD of 24.0%. It was also the 7th most accurate against
      enhanced heat transfer, with a MAD of 14.7%, and the most accurate for the
      normal heat transfer database as well as the top correlation in all 
      categories combined.
      
      If the extra density information is not provided, it will not be used.
  
      Examples
      --------
      >>> Nu_Mokry(1E5, 1.2, 330, 290.)
      246.1156319156992
  
      References
      ----------
      .. [1] Mokry, Sarah, Igor Pioro, Amjad Farah, Krysten King, Sahil Gupta, 
         Wargha Peiman, and Pavel Kirillov. "Development of Supercritical Water 
         Heat-Transfer Correlation for Vertical Bare Tubes." Nuclear Engineering
         and Design, International Conference on Nuclear Energy for New Europe 
         2009, 241, no. 4 (April 2011): 1126-36. 
         doi:10.1016/j.nucengdes.2010.06.012.
      .. [2] Chen, Weiwei, Xiande Fang, Yu Xu, and Xianghui Su. "An Assessment of
         Correlations of Forced Convection Heat Transfer to Water at 
         Supercritical Pressure." Annals of Nuclear Energy 76 (February 2015): 
         451-60. doi:10.1016/j.anucene.2014.10.027.
      '''
      Nu = 0.0061*Re**0.904*Pr**0.684
      if rho_w and rho_b:
          Nu *= (rho_w/rho_b)**0.564
      return Nu