A.A. Chernov

New hydrate formation methods in a liquid-gas medium

Conceptually new methods of hydrate formation are proposed. The first one is based on the shock wave impact on a water-bubble medium. It is shown that the hydrate formation rate in this process is typically very high. A gas hydrate of carbon dioxide was produced. The process was experimentally studied using various initial conditions, as well as different external action magnitudes. The obtained experimental data are in good agreement with the proposed model. Other methods are based on the process of boiling liquefied gas in an enclosed volume of water (explosive boiling of a hydrating agent and the organization of cyclic boiling-condensation process). The key features of the methods are the high hydrate formation rate combined with a comparatively low power consumption leading to a great expected efficiency of the technologies based on them. The set of experiments was carried out. Gas hydrates of refrigerant R134a, carbon dioxide and propane were produced. The investigation of decomposition of a generated gas hydrate sample was made. The criteria of intensification of the hydrate formation process are formulated.

Mechanism of growth of a crystalline nucleus in a supercooled melt at large deviations from equilibrium

A nonequilibrium model of the growth of a spherical crystal in a supercooled melt has been presented. The model includes correctly the effect of melt heating near the phase boundary, which considerably affects the growth rate of the crystal. The analytical solution of the problem has been found under the conditions of a strongly nonstationary process and large deviations from equilibrium. It has been shown that the previous solutions found in the quasi-steady-state approximation are the special cases of the solution found in this work. It has been demonstrated that the equilibrium is achieved at the crystallization front after some time if the initial supercooling is below the thermal effect of the phase transition (the Kutateladze criterion is greater than unity). In this case, the solution of the problem becomes self-similar. The crystal grows all the time under essentially nonequilibrium conditions if the initial supercooling is above the critical one. The effect of substance shrinkage on the growth rate of the crystal has been investigated.