Application of Thermal and Cavitation Effects for Heat and Mass Transfer Process Intensification in Multicomponent Liquid Media

In this paper, the authors consider the processes of dynamic interaction between the boiling particles of the dispersed phase of the emulsion leading to the large droplet breakup. Differences in the consideration of forces that determine the breaking of non-boiling and boiling droplets have been indicated in the study. They have been determined by the possibility of using the model to define the processes of displacement, deformation, or fragmentation of the inclusion of the dispersed phase under the influence of a set of neighboring particles. The dynamics of bubbles in a compressible liquid with consideration for interfacial heat and mass transfer has also been analyzed in the paper. The effect of standard and system parameters on the intensity of cavitation processes is considered. Physical transformations during the cavitation treatment of liquid are caused not only by shock waves and radiated pressure pulses but also by extreme thermal effects. At the stage of ultimate bubble compression, vapor inside the bubble and the liquid in its vicinity transform into the supercritical fluid state. The model analyzes microflow features in the inter-bubble space and quantitatively calculates local values of the velocity and pressure fields, as well as dynamic effects.

The role of water in volcanism

Water plays an extremely important role in volcanism: it acts as an evacuator of viscous melts in a variety of ways, which is ensured by the presence of relevant properties of its phase states, which successively changing with the fall of the environmental parameters. In this sense, the supercritical (fluid) state of water is especially significant. The paper provides a summary of fluid properties that are unique in many ways. The properties determine the relationship between water fluid and silicate melt, which in turn explains the cause of volcanic phenomena and the course of eruptions: explosions of different power, the emergence of the so-called fluidized mass, scorching clouds, landslides and breakthroughs on the slopes, the formation of ignimbrites, as well as the mechanism of gas transport to the foot of volcanoes. Both by role and quantity, water is the main volcanic substance, which together with the silicate melt constitutes magma.

Observation of Pinning Strengthening in “MgB2 – CNT – α-Fe” Nanocomposites Studied by Microwave Absorption Technique

Microwave absorption histeresis is measured in superconducting composites, prepared from MgB2 , carbon nanotubes, graphene particles and iron nanoparticles. Iron nanoparticles were synthesized with using of isopropanol in the supercritical fluid state. Measurements showed that the greatest increase in the pinning force is observed in the “MgB2 – (CNT-α-Fe)” composite.

Devulcanization of Sulfur-Cured Isoprene Rubber in Supercritical Carbon Dioxide

A new devulcanization process that utilizes supercritical CO2 (scCO2) along with devulcanizing reagents was studied. Unfilled polyisoprene rubber samples (vulcanizates) with different crosslink distributions were prepared by controlling the cure time and the curatives. Each of the vulcanizates was subjected to the Soxhlet extraction using azeotropic acetone/chloroform to remove residual curatives. The devulcanization was performed at various temperatures (140–200 °C) in the presence of scCO2 for 60 min. The product was fractionated into sol and gel components, and molecular weight of the sol component and the crosslink density of the gel component were determined. Thiol-amine reagent was found to be effective among several devulcanizing reagents; the molecular weight of the resulted sol component was about tens of thousands and the crosslink density of gel component decreased substantially from the initial ones. Yield of the sol component increased with the increase in the CO2 pressure. In the supercritical fluid state of CO2, the vulcanizate was more efficiently devulcanized than in an ordinary gaseous state of CO2. The sol fraction depended considerably on the crosslink distribution in the vulcanizate. These results suggest that the devulcanizing reagents penetrate and diffuse into the vulcanizate in the presence of scCO2.

Developments in CO2 research

CO2 can be a good solvent for many compounds when used in its compressed liquid or supercritical fluid state. Above its critical temperature and critical pressure (Tc = 31 C, Pc = 73.8 bar), CO2 has liquid-like densities and gas-like viscosities, which allows for safe commercial and laboratory operating conditions. Many small molecules are readily soluble in CO2, whereas most macromolecules are not. This has prompted development of several classes of small molecule and polymeric surfactants that enable emulsion and dispersion polymerizations as well as other technological processes.