CFD Online Discussion Forums - Sutherland model calculate the thermal diffusion coefficient

Hello everyone;
I was confused about the formula in sutherland model to calculate the alpha (thermal diffusion coefficient).

template<class Thermo>
inline Foam::scalar Foam::sutherlandTransport<Thermo>::mu
(
const scalar p,
const scalar T
) const
{
return As_*::sqrt(T)/(1.0 + Ts_/T);
}

template<class Thermo>
inline Foam::scalar Foam::sutherlandTransport<Thermo>::kappa
(
const scalar p, const scalar T
) const
{
scalar Cv_ = this->Cv(p, T);
return mu(p, T)*Cv_*(1.32 + 1.77*this->R()/Cv_);
}

template<class Thermo>
inline Foam::scalar Foam::sutherlandTransport<Thermo>::alphah
(
const scalar p,
const scalar T
) const
{

return kappa(p, T)/this->Cpv(p, T);
}

Does anybody know mu(p, T)*Cv_*(1.32 + 1.77*this->R()/Cv_) where this formula comes from. Any paper can I refer to?

Thanks a lot in advance.