Relaxation of temperature and concentration in superfluid 3He-4He mixtures. Effective thermal conductivity

The relaxation of temperature and concentration is investigated in superfluid 3He-4He mixtures with initial molar concentration 9.8% 3He at various thermal flows in the temperature range 100-500 mK. It is shown that the kinetics of temperature change in the liquid can be described by an exponential function and the time constants obtained have a weak temperature dependence. The relaxation of concentration is similar to that of temperature only in the single-phase mixture. Below the separation temperature, the change of concentration with time is non-monotonous and can be described by a superposition of two exponential functions. This kinetic behavior of the mixture is explained in the framework of the simple model for distribution of concentration as a function of cell height at different instants of time after switching on the thermal flow. It is shown that the relaxation of concentration in the diluted phase consists of two processes: the growth of concentration due to the involvement of the impuritons 3He in the normal motion and the decrease of concentration due to the formation and growth of the concentrated phase. The time relaxation data obtained are used to estimate the effective thermal conductivity of the mixture. The data are in reasonable agreement with the results of the phonon-impuriton theory of superfluid mixtures