Проявление линии Видома при микроволновых измерениях увлажненных перекисью водорода сорбентов

For deeply supercooled bulk water, anomalies of thermodynamic values are known near the Widom line, the locus of increased fluctuations of entropy and density. In this work, we measured the reflected power of microwave radiation at a frequency of 18 GHz from a silicate sorbent sample moistened with a hydrogen peroxide solution. In the experiment, we observed variations in the recorded reflected radiation power in the range –46 – –47 °С, determined by structural changes in the liquid. Thus, it is shown that fluctuations of water parameters near the Widom line are manifested in changes not only in thermodynamic, but also in electrophysical quantities.

Influence of Liquid Inclusions to Explosive Instability of Ice

The influence of the nuclei of the liquid phase arising during mechanical deformations of polycrystalline ice at temperatures below -40 ... -45 C on its explosive instability is considered. The nucleus of the liquid phase appear in ice when part of the hydrogen bonds are broken when high pressure is applied to ice crystals. The resulting clusters can have characteristics close to those of bulk metastable water. It is known that such water in the region of negative temperatures has anomalous thermodynamic characteristics. In particular, at a temperature of -60 C and a pressure of 100 MPa, there is a second critical point of water for the liquid-liquid transition. It was found that the transition occurs between the two types of water LDL (low density water) and HDL (high density water), with the Widom line coming out into the one-component region of the water phase diagram. This line is the locus of increased fluctuations in entropy and density. Near atmospheric pressure, the temperature on the Widom line is -45 C. If the pressure inside the ice and its temperature turn out to be close to the line of coexistence of LDL and HDL, then liquid inhomogeneities can become a source of mechanical instability of the medium due to the growth of fluctuations in the energy of molecules and destruction of the ice structure. Such conditions can occur at temperatures below -45 C and pressures above 100 MPa.

Supercritical Pseudo Boiling in Cubic Equations of State

Today, modern combustion systems and advanced cycles often reach operating pressures exceeding the working fluid’s or fuel’s critical pressure. While the liquid-gas coexistence line is the dominant feature in the fluid state space at low pressures, a supercritical analog to boiling, pseudo boiling, exists at supercritical pressures. Pseudo boiling is the transcritical state transition between supercritical liquid states and supercritical gaseous states, associated with peaks in heat capacity and thermal expansion. This transition occurs across a finite temperature interval. So far, the relation between the pseudo boiling line of tabulated hi-fi p-v-T data and the behavior of efficient engineering cubic equations of state (EOS) is unclear. In the present paper, we calculate the slope of the pseudo boiling line analytically from cubic equations of state. The Redlich-Kwong EOS leads to a constant value for all species, Peng-Robinson and Soave-Redlich-Kwong EOS yield a cubic dependency of the slope on the acentric factor. For more than twenty compounds with acentric factors ranging from −0.38 to 0.57 calculated slopes are compared with NIST data and vapor pressure correlations. Particularly the Peng-Robinson EOS matches reference data very well. Classical empirical values of Guggenheim or Plank & Riedel are obtained analytically. Then, pseudo boiling predictions of the Peng Robinson EOS are compared to NIST data. Deviations in transition temperature interval, and nondimensional parameters of the distributed latent heat are compared. Especially the different caloric behavior of tabulated fluid data for H2, N2, CO2, and H2O cannot be reproduced by the Peng Robinson EOS. These results may open the way towards new EOS with specific emphasis on Widom line and supercritical transition behavior.

Behavior of a Binary Asymmetric Mixture of Interacting Particles in the Supercritical Region

We propose a method for describing the phase behavior of a system consisting of particles of two sorts. The interaction of each species is described by interaction potentials containing the repulsive and attractive components. Asymmetry is ensured by different values of the interaction potentials of each sort. The grand partition function of a binary mixture is calculated in the zero-mode approximation. A line of critical points, which correspond to different proportions of the components, is calculated for specific values of parameters of the interaction potential. We have obtained an equation that relates the introduced mixing parameter x to the concentration of the system. An explicit expression of the pressure of the binary mixture is derived as a function of the relative temperature and the mixing parameter x to plot the Widom line. It is established that, for boundary values of this parameter (x = 0 and x = 1), the equation of state of a mixture turns into equations of state of its separate species.

Supercritical water anomalies in the vicinity of the Widom line

Supercritical water is used in a variety of chemical and industrial applications. As a consequence, a detailed knowledge of the structure-properties correlations is of uttermost importance. Although supercritical water was considered as a homogeneous fluid, recent studies revealed an anomalous behaviour due to nanoscale density fluctuations (inhomogeneity). The inhomogeneity is clearly demarked through the Widom line (maxima in response factions) and drastically affect the properties. In the current study the physical properties of supercritical water have been determined by classical molecular dynamics simulations using a variety of polarized and polarizable interatomic potentials. Their validity which was not available at supercritical conditions has been assessed based on the ability to reproduce experimental data. Overall, the polarized TIP4P/2005 model accurately predicted the properties of water in both liquid-like and gas-like regions. All interatomic potentials captured the anomalous behaviour providing a direct evidence of molecular-scale inhomogeneity.

Visualization of supercritical water pseudo-boiling at Widom line crossover

Supercritical water is a green solvent used in many technological applications including materials synthesis, nuclear engineering, bioenergy, or waste treatment and it occurs in nature. Despite its relevance in natural systems and technical applications, the supercritical state of water is still not well understood. Recent theories predict that liquid-like (LL) and gas-like (GL) supercritical water are metastable phases, and that the so-called Widom line zone is marking the crossover between LL and GL behavior of water. With neutron imaging techniques, we succeed to monitor density fluctuations of supercritical water while the system evolves rapidly from LL to GL as the Widom line is crossed during isobaric heating. Our observations show that the Widom line of water can be identified experimentally and they are in agreement with the current theory of supercritical fluid pseudo-boiling. This fundamental understanding allows optimizing and developing new technologies using supercritical water as a solvent.