Transport properties of dilute superfluid mixtures of 3He in 4He

Measurements of the heat transport are reported for dilute superfluid mixtures of 3He in 4He between 1.6 and 2.17 K. The temperature transients leading to relaxation times also are presented. The 3He molar concentration X ranged from 1 x 10-6 to 1 x 10-2. Cells with different fluid layer thicknesses h were used with 0.5 < h < 4.8 mm. The fluid mixture thermal resistance was obtained from the steady state data, after correction for the boundary (Kapitza) resistance Rb measured with pure 4He. The bulk fluid results were found to be in agreement with the predictions by F. London and I.M. Khalatnikov. However there is an additional thermal resistance R0 that dominates for the most dilute mixtures. R0 is compared with Rb and both are found to have nearly the same temperature dependence and a comparable magnitude. A description and discussion of the onset of non-linear behavior at a critical heat current is presented. Analysis of the transient experiments shows that the observed relaxation times are larger than expected for the bulk fluid. This additional bottleneck is ascribed to R0 and possible origins of these effects are proposed. In the Appendix, analysis of observed relaxation times in the normal phase of 4He near Tλ and correction for instrumental contributions are described. The intrinsic fluid relaxation times scale with h2 and agree quantitatively with predictions. This analysis, including the corrections, is then extended to dilute 3He-4He mixtures in the superfluid phase