def uch_leung(us, ut):
    """
    Choking velocity based on Equation 6 from Leung [2]_. All parameters must
    be in units of ft/s or in units of m/s.

    Parameters
    ----------
    us : float
        Solids velocity [ft/s or m/s]
    ut : float
        Terminal velocity of a single particle [ft/s or m/s]

    Returns
    -------
    uch : float
        Choking velocity [ft/s or m/s]

    References
    ----------
    .. [2] L.S. Leung, Robert J. Wiles, and Donald J. Nicklin. Correlation for
       Predicting Choking Flowrates in Vertical Pneumatic Conveying. Ind. Eng.
       Chem. Process Des. Develop., vol. 10, no. 2, pp. 183-189, 1971.
    """
    uch = 32.3 * us + 0.97 * ut
    return uch