Study of the Phase Boundary for C 6 F 6 and SF 6 under Microgravity
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MOPHYSICAL PROPERTIES OF MATERIALS
Study of the Phase Boundary for C6F6 and SF6 under Microgravity V. S. Vorob’eva, E. E. Ustyuzhaninb, *, V. F. Ochkovb, V. V. Shishakovb, Aung Tu Ra Tunb, V. A. Rykovc, and S. V. Rykovc a
Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia National Research University “Moscow Power Engineering Institute”, Moscow, 111250 Russia c University of Information Technologies, Mechanics and Optics (ITMO University), St. Petersburg, 197101 Russia *e-mail: [email protected] b
Received June 6, 2019; revised November 22, 2019; accepted December 24, 2019
Abstract—Two groups of experimental data obtained in the vicinity of the critical point are discussed. Group I describes the level ht of the meniscus separating the two phases of the substance in the cell. The measurements were performed for SF6 under the condition (g = 9.8 m s–2) during an experiment conducted in a space laboratory. Group II includes data on the density of liquid and vapor measured for C6F6 along the saturation curve under terrestrial condition. In both cases, the studied two-phase sample is located in a horizontal cylindrical cell. In the second experiment, the gravitational effect was also measured along the isotherms as the dependence of the sample density on the height h measured from the bottom of the cell. An equation relating the ht level (experiment I) with such functions as the order parameter fs and the average diameter fd is derived in this work. The obtained equation describes the initial experimental data at relative temperatures τ = (T – Tc)/Tc = 2 × 10–6–0.01. An approach is considered that takes into account the influence under microgravity (g = gM ! 9.8 m s–2) on the height h (experiment II). The dependences that represent fs and fd and the density of the liquid and gas phases along the saturation curve of these substances are obtained. These dependences agree satisfactorily with the results of experiments I and II in a wide temperature range and correspond to the scaling theory of critical phenomena. DOI: 10.1134/S0018151X20030190
Introduction The objects of this study are the (ρl, ρg, τ) data and functions ρl(τ), ρg(τ), fd(τ), fs(τ), etc., which are related to C6F6 and SF6. Here, ρl and ρg are the densities of the liquid and gas phases, fd is the average binodal diameter, fs is the order parameter, τ = (T – Tc)/Tc is the relative temperature, and Tc is the critical temperature. The (ρl, ρg, τ) data for C6F6 were first measured in [1]. The density behavior along the SF6 binodal was studied in several works [2–13], including experimental studies [9, 10]. The scaling models proposed in these publications are the functions ρl(τ), ρg(τ), fd(τ), fs(τ), etc., which correspond to the scaling theory (ST) of critical phenomena. We can divide models ρl(τ) and ρg(τ) into two groups: one group generalizes the results [9], and the other is based on the data in [10]. The equations included in the first group and the same type equations of included in the second group differ; this diff
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