def DIPPR9H(ws, ks):
if not none_and_length_check([ks, ws]):  <EOL><INDENT>raise Exception('<STR_LIT>')<EOL><DEDENT>return sum(ws[i]/ks[i]**<NUM_LIT:2> for i in range(len(ws)))**(-<NUM_LIT:0.5>)<EOL>
r'''Calculates thermal conductivity of a liquid mixture according to
    mixing rules in [1]_ and also in [2]_.

    .. math::
        \lambda_m = \left( \sum_i w_i \lambda_i^{-2}\right)^{-1/2}

    Parameters
    ----------
    ws : float
        Mass fractions of components
    ks : float
        Liquid thermal conductivites of all components, [W/m/K]

    Returns
    -------
    kl : float
        Thermal conductivity of liquid mixture, [W/m/K]

    Notes
    -----
    This equation is entirely dimensionless; all dimensions cancel.
    The example is from [2]_; all results agree.
    The original source has not been reviewed.

    DIPPR Procedure 9H: Method for the Thermal Conductivity of Nonaqueous Liquid Mixtures

    Average deviations of 3%. for 118 nonaqueous systems with 817 data points.
    Max deviation 20%. According to DIPPR.

    Examples
    --------
    >>> DIPPR9H([0.258, 0.742], [0.1692, 0.1528])
    0.15657104706719646

    References
    ----------
    .. [1] Reid, Robert C.; Prausnitz, John M.; Poling, Bruce E. The
       Properties of Gases and Liquids. McGraw-Hill Companies, 1987.
    .. [2] Danner, Ronald P, and Design Institute for Physical Property Data.
       Manual for Predicting Chemical Process Design Data. New York, N.Y, 1982.