def L_bot(P_mass, R, M_bot, M_dist, F_mass, M_feed, phi):
    """
    Calculates the flow rate liquid at the bottom of column.
    Parameters
    ----------
    P_mass : float
        The mass flow rate of distilliat, [kg/s]
    F_mass : float
        The mass flow rate of feed, [kg/s]
    M_dist : float
        The molar mass  of distilliat, [kg/kmol]
    M_feed : float
        The molar mass  of feed, [kg/kmol]
    phi : float
        The fraction of vapor at the feed point
    R : float
        The actual reflux number, [dismensionless]
    M_bot : float
        The molar mass at bottom of column, [kg/kmol]    
    Returns
    -------
    L_bot : float
        The  flow rate liquid at the bottom of column, [kg/s]
    References
    ----------
    Дытнерский, стр. 229, формула 6.5
    """ 
    return (P_mass * R * M_bot / M_dist) + (F_mass * M_bot * (1 - phi) / M_feed)