def Fourar_Bories(x, mul, mug, rhol, rhog):
    """Calculates a suggested definition for liquid-gas two-phase flow 
    viscosity in internal pipe flow according to the form in [1]_ and shown
    in [2]_ and [3]_.
        
    .. math::
        \\mu_m = \\rho_m\\left(\\sqrt{x\\nu_g} + \\sqrt{(1-x)\\nu_l}\\right)^2
        
    Parameters
    ----------
    x : float
        Quality of the gas-liquid flow, [-]
    mul : float
        Viscosity of liquid, [Pa*s]
    mug : float
        Viscosity of gas, [Pa*s]
    rhol : float
        Density of the liquid, [kg/m^3]
    rhog : float
        Density of the gas, [kg/m^3]

    Returns
    -------
    mu_lg : float
        Liquid-gas viscosity (**a suggested definition, potentially useful
        for empirical work only!**) [Pa*s]

    Notes
    -----
    This model converges to the liquid or gas viscosity as the quality
    approaches either limits.
    
    This was first expressed in the equalivalent form as follows:
        
    .. math::
        \\mu_m = \\rho_m\\left(x\\nu_g + (1-x)\\nu_l + 2\\sqrt{x(1-x)\\nu_g\\nu_l}
        \\right)
    
    Examples
    --------
    >>> Fourar_Bories(x=0.4, mul=1E-3, mug=1E-5, rhol=850, rhog=1.2)
    2.127617150298565e-05

    References
    ----------
    .. [1] Fourar, M., and S. Bories. "Experimental Study of Air-Water 
       Two-Phase Flow through a Fracture (Narrow Channel)." International 
       Journal of Multiphase Flow 21, no. 4 (August 1, 1995): 621-37. 
       doi:10.1016/0301-9322(95)00005-I.
    .. [2] Awad, M. M., and Y. S. Muzychka. "Effective Property Models for 
       Homogeneous Two-Phase Flows." Experimental Thermal and Fluid Science 33,
       no. 1 (October 1, 2008): 106-13. 
    .. [3] Aung, NZ, and T. Yuwono. "Evaluation of Mixture Viscosity Models in 
       the Prediction of Two-Phase Flow Pressure Drops." ASEAN Journal on 
       Science and Technology for Development 29, no. 2 (2012). 
    """
    rhom = 1.0 / (x / rhog + (1.0 - x) / rhol)
    nul = mul / rhol
    nug = mug / rhog
    return rhom * ((x * nug) ** 0.5 + ((1.0 - x) * nul) ** 0.5) ** 2
