Transport properties of helium near the liquid-vapor critical point. V. The shear viscosity of3He-4He mixtures

Abstract

A torsional oscillator operating at 158 Hz has been used to measure the shear viscosity for two mixtures,3He0.65-4He0.35 and3He0.80−4He0.20. Data for each mixture are reported along near-critical isochores 0.85<ρ/ρ c <1.18, where ρ c is the critical density. Just as in a previous paper on pure3He and4He, the observed viscosity $$\tilde \eta$$ includes the sum of background and critical contributions and the effect from the earth's gravity nearT c . The analysis of the data provides (1) the background viscosity $$\bar \eta$$ versus density ρ and temperatureT, (2) the viscosity ratio $$\tilde \eta$$ / $$\bar \eta$$ along the various isochores and also along selected isotherms obtained by interpolation, showing the critical contribution, and (3) the shape of the dew-bubble curve for each mixture, as obtained from the maxima in η or from the discontinuities in the slopedη/dT at the transition from the two-phase to the single-phase regime. A comparison between the data of these mixtures and those for pure fluids is presented. The background viscosity data along isotherms and along isochores are found to vary smoothly from3He to4He. The critical viscosity ratio [ $$\tilde \eta$$ / $$\bar \eta$$ ](ρ c ) for mixtures along the critical isochore is comparable with that for the pure fluids, i.e., it diverges weakly asT c is approached. Hence, just as for previously investigated critical transport properties in3He-4He mixtures, there is no significant difference in behavior from that in the pure fluids.