def Nu_vertical_cylinder_Hanesian_Kalish_Morgan(Pr, Gr):
    """Calculates Nusselt number for natural convection around a vertical
    isothermal cylinder according to the results of [1]_ correlated by
    [2]_, also as presented in [3]_ and [4]_.

    .. math::
        Nu_H = 0.48 Ra_H^{0.23},\\; 10^{6} < Ra < 10^{8}

    Parameters
    ----------
    Pr : float
        Prandtl number [-]
    Gr : float
        Grashof number [-]

    Returns
    -------
    Nu : float
        Nusselt number, [-]

    Notes
    -----
    For air and fluoro-carbons. If outside of range, no warning is given.
    Laminar range only!

    Examples
    --------
    >>> Nu_vertical_cylinder_Hanesian_Kalish_Morgan(.7, 1E7)
    18.014150492696604

    References
    ----------
    .. [1] Hanesian, D. and Kalish, R. "Heat Transfer by Natural Convection
       with Fluorocarbon Gases." IEEE Transactions on Parts, Materials and
       Packaging 6, no. 4 (December 1970): 147-148.
       doi:10.1109/TPMP.1970.1136270.
    .. [2] Morgan, V.T., The Overall Convective Heat Transfer from Smooth
       Circular Cylinders, in Advances in Heat Transfer, eds. T.F. Irvin and
       J.P. Hartnett, V 11, 199-264, 1975.
    .. [3] Popiel, Czeslaw O. "Free Convection Heat Transfer from Vertical
       Slender Cylinders: A Review." Heat Transfer Engineering 29, no. 6
       (June 1, 2008): 521-36. doi:10.1080/01457630801891557.
    .. [4] Boetcher, Sandra K. S. "Natural Convection Heat Transfer From
       Vertical Cylinders." In Natural Convection from Circular Cylinders,
       23-42. Springer, 2014.
    """
    Ra = Pr * Gr
    return 0.48 * Ra ** 0.23
