Turbidity Data of Weightless SF6 Near its Liquid–Gas Critical Point

Abstract

Light transmission measurements performed in SF 6 close to its liquidgas critical point are used to obtain turbidity data in the reduced temperature rangeAutomatic experiments (ALICE 2 facility) were made at a near critical density, i.e., ρ −ρ c ρ c = 0.8 %, in the one-phase homogeneous region, under the microgravity environment of the Mir Space Station ( ρ is the average density, ρ c is the critical density). The turbidity data analysis verifies the theoretical crossover formulations for the isothermal compressibility κ T and the correlation length ξ . These latter formulations are also used to analyze very near T c thermal diffusivity data obtained under microgravity conditions by Wilkinson et al. (Phys. Rev. E 57, 436, 1998).

Weightless experiments to probe universality of fluid critical behavior

“…These turbidity measurements along a non-critical path, comparable to the ones reported in Ref. [14], can now be analyzed with a much improved theoretical understanding than in earlier OZ framework studies. The two data sets are in fact different and independently essential in testing our novel crossover models of the equation-of-state [12] based on the RG approaches of the critical phenomena universality.…”

“…have also added our previous turbidity data (as the form of red full circles) obtained from the ALICE2 turbidity experiments [14], using a cell with off-density criticality δρ ALICE2 = (0.8 ± 0.1) %.…”

“…As a result, the experimental control of the exact value of the second relevant field was never carefully accounted for in the expected asymptotic Ising-like behavior of the fluid in the close vicinity of its gas-liquid critical point. For instance, in our previous light transmission and turbidity (τ ) measurements [14] performed in near-critical SF 6 under microgravity environments, it was noted that the finite small value (∼ 0.8%) of the off-density criticality could be one of the reasons to explain the increasing small differences between the experimental data and the theoretical estimates referring to the so-called OrnsteinZernike (OZ) theory [15] along the critical isochoric path.…”

“…The temperature difference T c − T coex ≃ 55 µK was estimated using the power law ∆ρ LV = B (∆τ * ) β describing the symmetrized top of the coexistence curve, with ∆ρ LV = δρ and ∆ρ LV = ρL−ρV 2ρc , B = 1.596, β = 0.32575 and T c (SF 6 ) = 318733.000 mK [14]. ρ L and ρ V are the coexisting liquid and vapor densities, respectively.…”

“…Note that the methodology for performing these ALI-DECLIC turbidity experiments remains similar to the one for ALICE2 experiments in the MIR station (see Ref. [14]). The major improvement results from the use of an upgraded temperature timeline in DECLIC, which has taken great benefit of the CADMOS and NASA teleoperational managing of this facility.…”