def DIPPR9B(T, MW, Cvm, mu, Tc=None, chemtype=None):
Cvm = Cvm*<NUM_LIT>  <EOL>if not chemtype:<EOL><INDENT>chemtype = '<STR_LIT>'<EOL><DEDENT>if chemtype == '<STR_LIT>':<EOL><INDENT>return <NUM_LIT>*mu*Cvm/MW<EOL><DEDENT>elif chemtype == '<STR_LIT>':<EOL><INDENT>Tr = T/Tc<EOL>return mu/MW*(<NUM_LIT>*Cvm + <NUM_LIT> - <NUM_LIT>/Tr)<EOL><DEDENT>elif chemtype == '<STR_LIT>':<EOL><INDENT>return mu/MW*(<NUM_LIT>*Cvm + <NUM_LIT>)<EOL><DEDENT>else:<EOL><INDENT>raise Exception('<STR_LIT>')<EOL><DEDENT>
r'''Calculates the thermal conductivity of a gas using one of several
    emperical equations developed in [1]_, [2]_, and presented in [3]_.

    For monoatomic gases:

    .. math::
        k = 2.5 \frac{\eta C_v}{MW}

    For linear molecules:

    .. math::
        k = \frac{\eta}{MW} \left( 1.30 C_v + 14644.00 - \frac{2928.80}{T_r}\right)

    For nonlinear molecules:

    .. math::
        k = \frac{\eta}{MW}(1.15C_v + 16903.36)

    Parameters
    ----------
    T : float
        Temperature of the fluid [K]
    Tc : float
        Critical temperature of the fluid [K]
    MW : float
        Molwcular weight of fluid [g/mol]
    Cvm : float
        Molar heat capacity at constant volume of fluid, [J/mol/K]
    mu : float
        Viscosity of gas, [Pa*S]

    Returns
    -------
    k_g : float
        Thermal conductivity of gas, [W/m/k]

    Notes
    -----
    Tested with DIPPR values.
    Cvm is internally converted to J/kmol/K.

    Examples
    --------
    CO:

    >>> DIPPR9B(200., 28.01, 20.826, 1.277E-5, 132.92, chemtype='linear')
    0.01813208676438415

    References
    ----------
    .. [1] Bromley, LeRoy A., Berkeley. University of California, and U.S.
       Atomic Energy Commission. Thermal Conductivity of Gases at Moderate
       Pressures. UCRL;1852. Berkeley, CA: University of California Radiation
       Laboratory, 1952.
    .. [2] Stiel, Leonard I., and George Thodos. "The Thermal Conductivity of
       Nonpolar Substances in the Dense Gaseous and Liquid Regions." AIChE
       Journal 10, no. 1 (January 1, 1964): 26-30. doi:10.1002/aic.690100114
    .. [3] Danner, Ronald P, and Design Institute for Physical Property Data.
       Manual for Predicting Chemical Process Design Data. New York, N.Y, 1982.