S. Ya. Misyura

Two-phase nonisothermal flows of LiBr water solution in minichannels

Two-phase flows of LiBr water solution in minichannels with heat exchange is experimentally investigated. Six flow patterns have been revealed: a bubble flow, plug flow, separate and wavy separate flow, dispersed flow, and flow blocking. Contrary to one-component liquids, an additional third phase may appear in desorption of salt solutions, that is, a crystal-hydrate shell on channel walls. The maximum desorption efficiency corresponded to minichannels of 3 mm in diameter and in the presence of a dispersed flow. The desorption rate depends not only on the ratio of liquid, gas, and heat flux velocities, but also on the overall interface area. The maximal interfacial evaporation surface corresponds to the dispersed flow due to the presence of a high concentration of fine-dispersed droplets. Minichannels with a high desorption rate can be effectively applied for high-temperature desorbers of thermal pumps.

Bubble boiling in droplets of water and lithium bromide water solution

The dynamics of growth and interaction of vapor bubbles in droplets of pure water and LiBr water solution on a horizontal wall were investigated in a wide superheating range. The growth rates of bubbles were determined both in a distillate droplet and in a salt solution droplet. The bubble growth rate in a pure water droplet at the final stage is somewhat lower than in pool boiling. The bubble growth rate in a salt solution is substantially lower than for pure water. Due to the bubble density maldistribution, the vapor flow density is appreciably higher at the droplet edges than on the droplet axis. Collective behavior of the bubbles possesses both stochastic character and elements of self-organization. The thermal measurements were carried out by means of high-speed video and blowup thermal imager.

Combustion of methane hydrates

Gas hydrates of methane were obtained under the laboratory conditions, and their structural characteristics were determined there. Kinetics of methane hydrate dissociation in the air atmosphere was studied experimentally. The combined effect of high temperature and pressure gradients was studied and it was shown that in practice it is necessary to take into account the nonstationary heat and mass transfer processes together. The direct measurements of clathrate mass and thermal imaging allowed distinguishing for several typical stages of dissociation with significantly different dissociation rates. The weakly expressed mechanism of self-preservation (the maintenance of residual state of gas in the crystalline lattice at the temperature, which exceeds significantly the equilibrium temperature) was observed in experiments.

Effects of flow turbulence on film cooling efficiency

Abstract Results of experimental investigations on film cooling effectiveness in high-turbulent flow are represented in this paper. The turbulence intensity changed within the range Tu o = 0.2–15% and the injection parameter was 0.1 m m m > 1) the turbulence effect weakens. The experimental data generalization and its comparison with the results of the calculation carried out by asymptotic theory are given.

Peculiarities of nonisothermal desorption of drops of lithium bromide water solution on a horizontal heated surface

The behavior of a drop of lithium bromide solution on a heating surface is investigated in a wide range of surface temperatures and solution concentration. Substantial peculiarities of evaporation and boiling of single drops in the lithium bromide solution are revealed.

Boiling crisis in droplets of ethanol water solution on the heating surface

Evaporation of droplets of ethanol water solution on a heated surface is studied experimentally at high heat fluxes. The behavior of water-alcohol mixtures was examined under the conditions of heat transfer crisis. Direct measurement of the current mass of evaporating droplets allows us to study the behavior of liquid batches in significantly nonstationary processes. An insignificant alcohol admixture to water increases significantly the transitional area of the crisis. The maximal length of transitional area corresponds to a mass concentration of alcohol of about 30%. For this concentration the heat transfer coefficient of the water-alcohol solution is maximal. It is shown that addition of highly volatile liquids to water allows efficient control of evaporation rate, which can be used for engineering processes.

Methane combustion in hydrate systems: Water-methane and water-methane-isopropanol

Kinetics of dissociation of synthetic and natural methane gas hydrates, and also double isopropanol-methane hydrate is investigated. Thermal fields of the sample surfaces are measured by means of thermal imaging in combustion of released methane with clathrate dissociation. The dissociation rates of natural hydrate and double hydrate with isopropanol are many times lower than those of synthetic methane hydrate. Methane combustion is accompanied by formation of a thin water film on the powder surface, which has a strong effect on the heat and mass transfer mechanisms. The experiments demonstrated partial self-preservation for methane hydrate and the absence of self-preservation for double isopropanol-methane hydrate. The experimentally observed dissociation rate of double isopropanol-methane hydrate is considerably lower than that of methane hydrate.

DSC and thermal imaging studies of methane hydrate formation and dissociation in water emulsions in crude oils

The processes of methane hydrate formation from 50 mass% water-in-oil emulsion from the Mamontovskoe, Sovetskoe, Van-Eganskoe, and Vakhskoe oil deposits (East Siberia) were studied using differential scanning calorimetry. It was shown that different types of thermal effects may be observed in curves corresponding to the formation of hydrate (and/or ice) in different emulsions. In particular on the curves, we observed the appearance of a single asymmetric thermal effect or a set of a large number of separate small thermal effects. The analysis of the results allowed us to conclude that hydrate formation (ice freezing) in the studied emulsions occurs as a collective process, which involves a lot of water droplets in the emulsions. This process occurs in some space inside the emulsion sample. The volume of this space determines the type of curve recorded in experiment. Secondary nucleation (nucleation of the solid phase due to the contact of a drop of water with the neighboring hydrate or ice particle) enables fast formation of gas hydrate in all droplets inside this space.

Kinetics of methane hydrate dissociation

The methane hydrate dissociation at an external pressure of 1 bar has been experimentally studied. The methane dissociation rate depends on the heat transfer intensity in the course of dissociation. Quasi-isothermal and nonisothermal conditions of clathrate dissociation have been compared. Under nonisothermal conditions, the dissociation rate depends on the heat flux density. The lowest heat flux was achieved in a quasi-stationary mode, and the highest heat flux was achieved through combustion of methane released from the clathrate powder. The 54-fold increase in heat flux leads to the ninefold increase in the methane dissociation rate. Depending on the heat flux density, the following variants of clathrate dissociation were observed: without self-preservation, partial self-preservation with one dissociation rate minimum, and partial self-preservation with two minima.

Non-isothermal Evaporation of Salt Solutions on a Microstructured Surface

ABSTRACT Heat transfer of a droplet and layer during evaporation of aqueous solutions of salts has been studied. The behavior of salt solutions on a smooth and microstructured surface is compared here. Evaporation rate of aqueous salt solutions is greater for a microstructured surface than for a smooth wall. The behavior of heat transfer coefficient α can be described by two time regimes: quasi-constant values of α and significant increase in heat transfer at a multiple decrease in the liquid layer height. Measurements made with application of the particle image velocimetry showed that the structured surface increases liquid speed inside the sessile drop. The largest value of the heat transfer coefficient α on the structured surface corresponds to water for the final stage of evaporation. For salt solutions, the heat transfer coefficient is lower than that for water in the entire period of evaporation on the structured surface. The maximal excess (20–30%) of α of the structured wall above the smooth surface corresponds to the maximal height of the liquid layer at the beginning of evaporation. With increasing time, the excess is reduced. A drop of heat transfer intensification with a decrease in the layer height relates to suppression of free convection (a multiple decrease in the average velocity in the drop).