Thermal Diffusion Measurements near the Liquid-Vapor Critical Point

The authors report measurements of the density and temperature gradients in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures near their liquid-vapor critical point, as induced by a heat flux. From these they deduce the thermal diffusion ratio $k_T$ and the conductivity $\kappa$. They find that $k_T$ and $\kappa$ diverge with respective effective exponents $\varphi \approx 1.2$ and $\psi \approx 0.6$. Both of these results are in contradiction with the asymptotic predictions for binary mixtures and are discussed in the light of the hydrodynamic transport equations.