def speed_section_bot(speed_limit_bot, D_bot, D):
    """
    Calculates the section speed of vapor at the bottom
    Parameters
    ----------
    speed_limit_bot: float
        The limit speed of the vapor at the bottom of  column, [m/s]
    D_bot : float
        The calculating bottom diameter of column, [m]
    D : float
        The choosing diameter of column, [m]   
    Returns
    -------
    speed_section_bot : float
        The section speed of vapor at the bottom, [m/s]
    References
    ----------
    &&&&&
    """         
    return speed_limit_bot * (D_bot / D)**2