docs: def Nu_Swenson(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]_.
          
      .. math::
          Nu_w = 0.00459 Re_w^{0.923} Pr_w^{0.613}
          \left(\frac{\rho_w}{\rho_b}\right)^{0.231}
  
          \bar{Cp} = \frac{H_w-H_b}{T_w-T_b}
          
      Parameters
      ----------
      Re : float
          Reynolds number with wall fluid properties, [-]
      Pr : float
          Prandtl number with wall 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 wall fluid properties, [-]
  
      Notes
      -----
      The range of examined parameters is as follows: 
      P from 22.8 to 27.6 MPa; G from 542-2150 kg/m^2/s; 
      Re from 7.5E4 to 3.16E6; T_b from 75 to 576 degrees Celsius and T_w from
      93 to 649 degrees Celsius.
      
      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 most accurate correlation in 
      [2]_ with a MAD of 18.4%. On the overall database in [3]_, it was the 
      9th most accurate correlation.
      
      If the extra density information is not provided, it will not be used.
  
      Examples
      --------
      >>> Nu_Swenson(1E5, 1.2, 330, 290.)
      217.92827034803668
  
      References
      ----------
      .. [1] Swenson, H. S., J. R. Carver, and C. R. Kakarala. "Heat Transfer to 
         Supercritical Water in Smooth-Bore Tubes." Journal of Heat Transfer 87, 
         no. 4 (November 1, 1965): 477-83. doi:10.1115/1.3689139.
      .. [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.
      .. [3] Yu, Jiyang, Baoshan Jia, Dan Wu, and Daling Wang. "Optimization of 
         Heat Transfer Coefficient Correlation at Supercritical Pressure Using 
         Genetic Algorithms." Heat and Mass Transfer 45, no. 6 (January 8, 2009): 
         757-66. doi:10.1007/s00231-008-0475-4.
      .. [4] Jäger, Wadim, Victor Hugo Sánchez Espinoza, and Antonio Hurtado. 
         "Review and Proposal for Heat Transfer Predictions at Supercritical 
         Water Conditions Using Existing Correlations and Experiments." Nuclear 
         Engineering and Design, (W3MDM) University of Leeds International 
         Symposium: What Where When? Multi-dimensional Advances for Industrial 
         Process Monitoring, 241, no. 6 (June 2011): 2184-2203. 
         doi:10.1016/j.nucengdes.2011.03.022. 
      '''
      Nu = 0.00459*Re**0.923*Pr**0.613
      if rho_w and rho_b:
          Nu *= (rho_w/rho_b)**0.231
      return Nu