def Boiling(G, q, Hvap):
    """Calculates Boiling number or `Bg` using heat flux, two-phase mass flux,
    and heat of vaporization of the fluid flowing. Used in two-phase heat 
    transfer calculations.

    .. math::
        \\text{Bg} = \\frac{q}{G_{tp} \\Delta H_{vap}}

    Parameters
    ----------
    G : float
        Two-phase mass flux in a channel (combined liquid and vapor) [kg/m^2/s]
    q : float
        Heat flux [W/m^2]
    Hvap : float
        Heat of vaporization of the fluid [J/kg]

    Returns
    -------
    Bg : float
        Boiling number [-]

    Notes
    -----
    Most often uses the symbol `Bo` instead of `Bg`, but this conflicts with
    Bond number.
    
    .. math::
        \\text{Bg} = \\frac{\\text{mass liquid evaporated / area heat transfer 
        surface}}{\\text{mass flow rate fluid / flow cross sectional area}}
    
    First defined in [4]_, though not named.

    Examples
    --------
    >>> Boiling(300, 3000, 800000)
    1.25e-05

    References
    ----------
    .. [1] Winterton, Richard H.S. BOILING NUMBER. Thermopedia. Hemisphere, 
       2011. 10.1615/AtoZ.b.boiling_number
    .. [2] Collier, John G., and John R. Thome. Convective Boiling and 
       Condensation. 3rd edition. Clarendon Press, 1996.
    .. [3] Stephan, Karl. Heat Transfer in Condensation and Boiling. Translated
       by C. V. Green.. 1992 edition. Berlin; New York: Springer, 2013.
    .. [4] W. F. Davidson, P. H. Hardie, C. G. R. Humphreys, A. A. Markson, 
       A. R. Mumford and T. Ravese "Studies of heat transmission through boiler
       tubing at pressures from 500 to 3300 pounds" Trans. ASME, Vol. 65, 9, 
       February 1943, pp. 553-591. 
    """
    return q / (G * Hvap)
