Micro-floating method of high-altitude determination of pressure in the critical fluid and condition of its equilibrium under the Earth gravity

Abstract

Based on the analysis of the experimental data of the effect of gravity obtained by optical methods of light scattering and refractometry, it has been shown that the range of changes in the thermodynamic parameters of the manifestation of the effect of gravity in the critical fluid coincides with the coordinates of the fluctuation critical region. From the point of view of the authors of this paper, the obtained result indicates that the phenomenon of the effect of gravity ∆ρ(z) and the magnitude of the altitude change in pressure |∆P*(z)|>>|h| in the inhomogeneous critical fluid are related with the presence in the condensed system of largescale fluctuations of the order parameter in the region of abnomally large compressibility of the substance near the critical point. In continuation of studies of the phenomenon of the effect of gravity, a new experimental method for altitudinal determination of pressure in inhomogeneous critical fluid namely micro-floating manometer has been presented. Using this method, it has been shown that the altitudinal change in the reduced pressure ∆P*(z)=(P(z)−Pc)/Pc in inhomogeneous critical fluid is significantly, by one - two orders of magnitude, greater (|∆P*|>>|h|) than the magnitude of the altitudinal change in hydrostatic pressure |h|=ρcg|z|/Pc. Here P(z) is the altitudinal change in pressure, Pc is the critical value of pressure of the substance, ρc is the critical value of density of the substance, g is the acceleration of Earth's gravity. Based on earlier studies using optical light scattering and refractometric methods, the condition of equilibrium for the inhomogeneous critical fluid under the Earth's gravity field |∆P * (Tc, L, ρ |=|∆U(Tc, L, ρ )| >> |h| has been confirmed. This condition of equilibrium depends on the critical temperature of the substance Tc, on the macroscopic linear size L of the sample cell with substance, and on the average density ρ of its filling with substance. Here |∆U*|>>|h| is the change in the reduced internal field along the height of the inhomogeneous system. This condition of equilibrium is qualitatively different from the condition of equilibrium, |∆P*(z)|=|h|, of the inhomogeneous substance far from the critical point.