def METHOD_NAME(
    phase,
    mus='pore.viscosity.*',
    MWs='param.molecular_weight.*',
):
    r"""
    Computes the viscosity of a gas mixture using the correlation in [1]
    Parameters
    ----------
    %(phase)s
    %(mus)s
    %(MWs)s
    Returns
    -------
    mu : ndarray
        An ndarray of Np length containing the viscosity of the mixture in
        each pore
    References
    ----------
    [1] Herning and Zipperer
    """
    MWs = phase.get_comp_vals(MWs)
    mus = phase.get_comp_vals(mus)
    xs = phase['pore.mole_fraction']
    num = 0.0
    denom = 0.0
    for k in xs.keys():
        num += xs[k]*mus[k]*MWs[k]**0.5
        denom += xs[k]*MWs[k]**0.5
    mu = num/denom
    return mu