S. L. Elistratov

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.

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.

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.

Experimental investigation of heat transfer of helium-xenon mixtures in cylindrical channels

Correlations are obtained for resistance and heat transfer of a helium-xenon mixture with a helium weight concentration from 5.2 to 10.5% in a cylindrical channel for Reynolds numbers from 2 · 103 to 105 and thermal fluxes up to 4 kW/m2. It is shown that with increasing Reynolds numbers in a long cylindrical channel the heat transfer intensity grows to maximum and then substantially decreases.

Experimental investigation of the nonstationary desorption of water-salt solutions in the spheroidal state

Results of experimental investigating the nonstationary desorption of water-salt solutions in the conditions of boiling crisis on a horizontal surface are represented. Current values of mass and average salt concentration in bubble-free spheroids are measured. The influence of the salt solubility and concentration on the evaporation conditions is shown.

Heat Transfer in a Flow of Gas Mixture with Low Prandtl Number in Triangular Channels

We investigated heat transfer in a channel with a triangular cross-section. The working medium is a helium–xenon mixture with a low Prandtl number. This channel configuration corresponds to one of possible cases of fuel cells layout in a gas-cooled nuclear reactor. New experimental data on heat transfer in helium–xenon mixtures were obtained. Results of numerical modeling were compared with the experimental data and the known empirical correlations.

The 2D method for determining the temperatures field of the gas flow at the outlet of a multi-channel heat exchanger

The method for experimental determination of energy efficiency in the multichannel heat exchanger was tested. The visualization of a temperatures field has been performed to determine the thermal structure of gas flows with the use of fast-response fine- meshed wire. Thermograms of the temperature fields of the multi-channels assembly at the outlet were registered by thermal imaging camera. Results show that the 2D method provides a sufficient time resolution for the temperature field for the steady-state gas flow regime, heat generation, and nonsteady regime. The 2D method allows us to determine the gas stream parameters at the channel outlet in real time, which are necessary for determining the efficiency of the heat exchanger. Qualitative and quantitative characters of temperature changes in the thermograms are consistent with modern physical understanding of the gas flow in channels.

Intensification of hydrate formation by means of explosive boiling incipience of rarefied gas in a bulk of water

The experiments on obtaining gas hydrate of refrigerant 134a were carried out by the method, based on explosive boiling-up of a layer of liquefied gas in a bulk of water at decompression. It is shown that this method combines several factors, leading to intensification of hydrate formation process, resulting in the fast gas hydrate growth. The effect of the decompression rate on the volume of produced hydrate was studied experimentally.