Shear viscosity measurements of liquid 4He and 3He-4He mixtures near the tricritical point

Abstract

A torsional oscillator cell is described, by means of which simultaneous precision measurements of (prl) and of the molar volume can be made in liquid 4He-4He mixtures over the temperature range between 0.5 and 3 K. Here p is the mass density, rl the shear viscosity and in the superfluid phase they become the contributions p, and qn of the normal component. The results of ;l for 4He near the superfluid transition are compared with the predictions by Schloms, Pankert and Dohm, and by Ferrell. Measurements of (P~l) are reported for mixtures with 0.64 < X < O. 74, where X is the 3He mole fraction. Those for X =0.67 and 0.70 are compared with data by Lai and Kitchens. The viscosity experiments show no evidence of a weak singularity at the tricritical point.

Critical phenomena in microgravity: Past, present, and future

“…The thermal diffusion ratio and its scaling have been measured in this region as well ͑Ruppeiner et al, 1980͒. Second-sound measurements have been made by Ahlers and Greywall ͑1972͒ near the tricritical point, and shear viscosity measurements in this region have been reported by Howald et al ͑1992͒. The EXACT experiment ͑Larson, 2000͒ was designed to measure second-sound propagation in microgravity to avoid stratification of the 3 He-4 He mixture under the Earth's gravitational acceleration. Measurements of the second-sound velocity as a function of temperature would permit a more precise determination of the critical exponent , which is the critical exponent of the order parameter which corresponds to the superfluid frac- Griffiths, 1970a.…”

Phase transitions and perfectness of fluids in weakly coupled real scalar field theories

“…Theoretically, it is argued that η has a mild divergence (and hence η/s) at QCD CEP [30] as in the Model H according to Hohenberg and Halperin's classification [31] (but see [32] for a caveat). Experimentally, divergence of η in 3 He liquid-gas transition critical point was observed [33] but not for the tricritical point of 3 He-4 He binary fluid [34]. Both cases belong to Model H and were predicted to have the same weak divergence by Ref.…”

Phase Transitions and the Perfectness of Fluids

“…Experimentally, divergence of η in 3 He liquid-gas transition critical point was observed 29) but not for the tricritical point of 3 He-4 He binary fluid. 30) Both cases belong to Model H and were predicted to have the same weak divergence by Ref. 27).…”