def COV_motionless_mixer(Ki, Q1, Q2, pipe_diameters):
    r'''Calculates CoV of a motionless mixer with a regression parameter in
    [1]_ and originally in [2]_.

    .. math::
        \frac{CoV}{CoV_0} = K_i^{L/D}

    Parameters
    ----------
    Ki : float
        Correlation parameter specific to a mixer's design, [-]
    Q1 : float
        Volumetric flow rate of larger stream [m^3/s]
    Q2 : float
        Volumetric flow rate of smaller stream [m^3/s]
    pipe_diameters : float
        Number of diameters along tail pipe for CoV calculation, 0 to 5 []

    Returns
    -------
    CoV : float
        Standard deviation of dimensionless concentration [-]

    Notes
    -----
    Example 7-8.3.2 in [1]_, solved backwards.

    Examples
    --------
    >>> COV_motionless_mixer(Ki=.33, Q1=11.7, Q2=2.74, pipe_diameters=4.74/.762)
    0.0020900028665727685

    References
    ----------
    .. [1] Paul, Edward L, Victor A Atiemo-Obeng, and Suzanne M Kresta.
       Handbook of Industrial Mixing: Science and Practice.
       Hoboken, N.J.: Wiley-Interscience, 2004.
    .. [2] Streiff, F. A., S. Jaffer, and G. Schneider (1999). Design and
       application of motionless mixer technology, Proc. ISMIP3, Osaka,
       pp. 107-114.
    '''
    Cv = Q2/(Q1 + Q2)
    COV0 = ((1-Cv)/Cv)**0.5
    COVr = Ki**(pipe_diameters)
    COV = COV0*COVr
    return COV
r'''Calculates CoV of a motionless mixer with a regression parameter in
    [1]_ and originally in [2]_.

    .. math::
        \frac{CoV}{CoV_0} = K_i^{L/D}

    Parameters
    ----------
    Ki : float
        Correlation parameter specific to a mixer's design, [-]
    Q1 : float
        Volumetric flow rate of larger stream [m^3/s]
    Q2 : float
        Volumetric flow rate of smaller stream [m^3/s]
    pipe_diameters : float
        Number of diameters along tail pipe for CoV calculation, 0 to 5 []

    Returns
    -------
    CoV : float
        Standard deviation of dimensionless concentration [-]

    Notes
    -----
    Example 7-8.3.2 in [1]_, solved backwards.

    Examples
    --------
    >>> COV_motionless_mixer(Ki=.33, Q1=11.7, Q2=2.74, pipe_diameters=4.74/.762)
    0.0020900028665727685

    References
    ----------
    .. [1] Paul, Edward L, Victor A Atiemo-Obeng, and Suzanne M Kresta.
       Handbook of Industrial Mixing: Science and Practice.
       Hoboken, N.J.: Wiley-Interscience, 2004.
    .. [2] Streiff, F. A., S. Jaffer, and G. Schneider (1999). Design and
       application of motionless mixer technology, Proc. ISMIP3, Osaka,
       pp. 107-114.