def chung(target, temperature='pore.temperature',
          mol_weight='pore.molecular_weight',
          critical_temperature='pore.critical_temperature',
          critical_volume='pore.critical_volume'):
    r"""
    Uses Chung et al. [1] model to estimate viscosity for gases at low
    pressure (much less than the critical pressure) at conditions of interest.

    Parameters
    ----------
    target : OpenPNM Object
        The object for which these values are being calculated.  This
        controls the length of the calculated array, and also provides
        access to other necessary thermofluid properties.

    temperatre: string
        The dictionary key containing the temperature values (K)

    critical_temperature : string
        The dictionary key containing the temperature values (K)

    mol_weight: string
        The dictionary key containing the molecular weight values (kg/mol)

    critical_volume : string
        The dictionary key containing the critical volume values (m3/kmol)

    [1] Chung, T.H., Lee, L.L., and Starling, K.E., Applications of Kinetic Gas
        Theories and Multiparameter Correlation for Prediction of Dilute Gas
        Viscosity and Thermal Conductivity”, Ind. Eng. Chem. Fundam.23:8, 1984.

    """
    T = target[temperature]
    MW = target[mol_weight]
    Tc = target[critical_temperature]
    Vc = target[critical_volume]
    Tr = T / Tc
    Tstar = 1.2593*Tr
    A = 1.161415
    B = 0.14874
    C = 0.52487
    D = 0.77320
    E = 2.16178
    F = 2.43787
    omega = (A*(Tstar)**(-B)) + C*(sp.exp(-D*Tstar)) + E*(sp.exp(-F*Tstar))
    sigma = 0.809*(Vc**(1/3))
    value = 26.69E-9*sp.sqrt(MW*T)/(omega*sigma**2)
    return value
r"""
    Uses Chung et al. [1] model to estimate viscosity for gases at low
    pressure (much less than the critical pressure) at conditions of interest.

    Parameters
    ----------
    target : OpenPNM Object
        The object for which these values are being calculated.  This
        controls the length of the calculated array, and also provides
        access to other necessary thermofluid properties.

    temperatre: string
        The dictionary key containing the temperature values (K)

    critical_temperature : string
        The dictionary key containing the temperature values (K)

    mol_weight: string
        The dictionary key containing the molecular weight values (kg/mol)

    critical_volume : string
        The dictionary key containing the critical volume values (m3/kmol)

    [1] Chung, T.H., Lee, L.L., and Starling, K.E., Applications of Kinetic Gas
        Theories and Multiparameter Correlation for Prediction of Dilute Gas
        Viscosity and Thermal Conductivity”, Ind. Eng. Chem. Fundam.23:8, 1984.