docs: def Ravipudi_Godbold(m, x, D, rhol, rhog, Cpl, kl, mug, mu_b, mu_w=None):
      r'''Calculates the two-phase non-boiling heat transfer coefficient of a 
      liquid and gas flowing inside a tube of any inclination, as in [1]_ and 
      reviewed in [2]_.
  
      .. math::
          Nu = \frac{h_{TP} D}{k_l} = 0.56 \left(\frac{V_{gs}}{V_{ls}}
          \right)^{0.3}\left(\frac{\mu_g}{\mu_l}\right)^{0.2} Re_{ls}^{0.6} 
          Pr_l^{1/3}\left(\frac{\mu_b}{\mu_w}\right)^{0.14}
      
      Parameters
      ----------
      m : float
          Mass flow rate [kg/s]
      x : float
          Quality at the specific tube interval [-]
      D : float
          Diameter of the tube [m]
      rhol : float
          Density of the liquid [kg/m^3]
      rhog : float
          Density of the gas [kg/m^3]
      Cpl : float
          Constant-pressure heat capacity of liquid [J/kg/K]
      kl : float
          Thermal conductivity of liquid [W/m/K]
      mug : float
          Viscosity of gas [Pa*s]
      mu_b : float
          Viscosity of liquid at bulk conditions (average of inlet/outlet 
          temperature) [Pa*s]
      mu_w : float, optional
          Viscosity of liquid at wall temperature [Pa*s]
  
      Returns
      -------
      h : float
          Heat transfer coefficient [W/m^2/K]
  
      Notes
      -----
      If the viscosity at the wall temperature is not given, the liquid viscosity
      correction is not applied.
      
      Developed with a vertical pipe, superficial gas/liquid velocity ratios of 
      1-90, in the froth regime, and for fluid mixtures of air and water, 
      toluene, benzene, and methanol.
      
      Examples
      --------
      >>> Ravipudi_Godbold(m=1, x=.9, D=.3, rhol=1000, rhog=2.5, Cpl=2300, kl=.6, mug=1E-5, mu_b=1E-3, mu_w=1.2E-3)
      299.3796286459285
  
      References
      ----------
      .. [1] Ravipudi, S., and Godbold, T., The Effect of Mass Transfer on Heat
         Transfer Rates for Two-Phase Flow in a Vertical Pipe, Proceedings 6th 
         International Heat Transfer Conference, Toronto, V. 1, p. 505-510, 1978.
      .. [2] Dongwoo Kim, Venkata K. Ryali, Afshin J. Ghajar, Ronald L. 
         Dougherty. "Comparison of 20 Two-Phase Heat Transfer Correlations with 
         Seven Sets of Experimental Data, Including Flow Pattern and Tube 
         Inclination Effects." Heat Transfer Engineering 20, no. 1 (February 1, 
         1999): 15-40. doi:10.1080/014576399271691.
      '''
      Vgs = m*x/(rhog*pi/4*D**2)
      Vls = m*(1-x)/(rhol*pi/4*D**2)
      Prl = Prandtl(Cp=Cpl, mu=mu_b, k=kl)
      Rels = D*Vls*rhol/mu_b
      Nu = 0.56*(Vgs/Vls)**0.3*(mug/mu_b)**0.2*Rels**0.6*Prl**(1/3.)
      if mu_w:
          Nu *= (mu_b/mu_w)**0.14
      return Nu*kl/D