def Nusselt(h, L, k):
    """Calculates Nusselt number `Nu` for a heat transfer coefficient `h`,
    characteristic length `L`, and thermal conductivity `k`.

    .. math::
        Nu = \\frac{hL}{k}

    Parameters
    ----------
    h : float
        Heat transfer coefficient, [W/m^2/K]
    L : float
        Characteristic length, no typical definition [m]
    k : float
        Thermal conductivity of fluid [W/m/K]

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

    Notes
    -----
    Do not confuse k, the thermal conductivity of the fluid, with that
    of within a solid object associated with!

    .. math::
        Nu = \\frac{\\text{Convective heat transfer}}
        {\\text{Conductive heat transfer}}

    Examples
    --------
    >>> Nusselt(1000., 1.2, 300.)
    4.0
    >>> Nusselt(10000., .01, 4000.)
    0.025

    References
    ----------
    .. [1] Green, Don, and Robert Perry. Perry's Chemical Engineers' Handbook,
       Eighth Edition. McGraw-Hill Professional, 2007.
    .. [2] Bergman, Theodore L., Adrienne S. Lavine, Frank P. Incropera, and
       David P. DeWitt. Introduction to Heat Transfer. 6E. Hoboken, NJ:
       Wiley, 2011.
    """
    return h * L / k
