Static and dynamic properties of helium near the liquid-vapor critical point: Comparison of experiments in mixtures with predictions

Several static and dynamic properties for ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He mixtures near the liquid-vapor critical line, measured along their critical isochores, are compared with predictions made via the formalism developed by Onuki. Theory predicts reduced temperatures for the crossover from pure-fluid to mixture behavior and to the asymptotic behavior, as the critical point is approached. For the static properties, the magnitude of the predicted crossover temperatures $t_{S1}$ and $t_{S2}$ is consistent with the experiments. However, for the transport properties, namely, the thermal conductivity and the thermal diffusion ratio, the predicted crossover temperature $t_D$ is much larger than that inferred from experiments. In fact, no qualitative difference in the critical behavior of measured transport properties is found between pure fluids and mixtures, implying $t_D$≲${10}^{\mathrm{-}5}$ for any mixture.