Vapor-gas Mixture Research Articles

Гідродинамічне дослідження групи струменів рідини в апаратах із циліндричними розподільними пристроями

The analysis of existing studies regarding the process of steam condensation from a vapor-gas mixture on liquid jets allows us to conclude that the vast majority of them are experimental in nature, so the results of these studies can be correctly used only for the appropriate range of parameter changes of the liquid and gaseous phases. Also, the subject of research in them is mainly the hydrodynamic mode of a continuous liquid jet along its entire length. During theoretical and experimental studies, it was established that the shape of the jets flowing out of the cylindrical holes counter to the oncoming steam current differs from cylindrical shape, depends on the flow parameters, and is characterized by their rotation with intense wave formation on the jet surfaces. The jets are combined with each other with their subsequent disintegration along the current, dispersed and carried away with the steam current. Accordingly, it is incorrect to apply existing methods of heat transfer calculation to the analysis of heat transfer in this type of jets, only on solid jets of liquid, outside the investigated range of parameters. That is, using classical equations is impossible due to the complexity of calculating the cross-sectional area of jet groups flowing through cylindrical holes, and accordingly, the area of the heat exchange surface. Namely, it is impossible to use the traditional concept of the heat transfer coefficient as a parameter. Therefore, most of the existing calculation methods are based on using dimensionless complexes that describe the degree of change in the temperature of the liquid along the length of the jets under the appropriate geometric conditions. That is, without finding the limits of changes in the continuity of liquid jets, determining the limiting hydrodynamic modes using the existing methods of heat exchange calculation is incorrect.

Simulation of Bulk Condensation in a Flow of a Vapor–Gas Mixture through a Nozzle by CFD-Methods Using a Special Computational Module

Simulation of Bulk Condensation in a Flow of a Vapor–Gas Mixture through a Nozzle by CFD-Methods Using a Special Computational Module

The Impact of Geometric Parameters on Three-Layer Flow Patterns in a Horizontal Channel: A Comprehensive Study

This paper focuses on studying stationary flows in horizontal layers, taking into consideration the effects of heat and mass transfer. A mathematical model is presented for a three-layer flow in an infinite channel with solid, impermeable walls. The gas-vapor mixture flows over one-component immiscible liquids in the lower and middle layers. The paper considers the processes of heat and mass transfer at the "liquid-gas" and "liquid-liquid" thermocapillary boundaries, respectively. The Dufour and Soret effects are also considered in the upper layer of the system. Mathematical modeling is based on exact solutions of a special form of the Navier-Stokes equations in the Boussinesq approximation. The procedure for determining unknown parameters is explained. The paper derives dependencies of the longitudinal temperature gradients at the system boundaries from each other. The influence of the flow region's geometry on the nature of the process is studied using the "silicone oil-water-air" system as an example. The paper presents longitudinal velocity profiles and temperature distribution for different values of the liquid layer heights while other parameters of the system remain fixed. The paper concludes that, in this case, the thickness of the lower layer is more influential than the thickness of the middle layer.

Plasma Enhanced High-Rate Deposition of Advanced Film Materials by Metal Reactive Evaporation in Organosilicon Vapors.

Dense homogeneous nanocomposite TiSiCN coatings with a thickness of up to 15 microns and a hardness of up to 42 GPa were obtained by the method of reactive titanium evaporation in a hollow cathode arc discharge in an Ar + C2H2 + N2-gas mixture with the addition of hexamethyldisilazane (HMDS). An analysis of the plasma composition showed that this method allowed for a wide range of changes in the activation degree of all components of the gas mixture, providing a high (up to 20 mA/cm2) ion current density. It is possible to widely change the chemical composition, microstructure, deposition rate, and properties of coatings obtained by this method, by changing the pressure, composition, and activation degree of the vapor-gas mixture. An increase in the fluxes of C2H2, N2, HMDS, and discharge current leads to an increase in the rate of coating formation. However, the optimal coatings from the point of view of microhardness were obtained at a low discharge current of 10 A and relatively low contents of C2H2 (1 sccm) and HMDS (0.3 g/h), exceeding which leads to a decrease in the hardness of the films and the deterioration of their quality, which can be explained by the excessive ionic exposure and the non-optimal chemical composition of the coatings.

Adsorption purification of drinking water with activated carbons «Gold Carbon» produced from plum pit shells

The process of adsorption of sulfates and residual chlorine, which are the main sources of drinking water pollution, was investigated in the work. The shell of plum seeds activated by a vapor-gas mixture was used as an adsorbent. The shell of plum seeds is pre-carbonized at a temperature of 20 to 800 ° C and activated in a stream of CO2 and H2O in a mass ratio of 90:10 at a temperature of 750-850 ° C. The adsorption characteristics of sulfates and residual chlorine were investigated. The fastest adsorption of sulfates occurred on the adsorbent at a concentration of 500 mg/l. The characteristics of the kinetics of activated carbon adsorption by residual chlorine are found. The dependence of the absorption capacity of chlorine by activated carbons on the equilibrium concentration in water is determined. Upon reaching 90 minutes, we observe adsorption values of the order of 99%. The influence of the water flow speed on the absorption of residual chlorine by activated carbon was determined, where the optimal factor of the regime, the water flow speed, was 0.0022 m/s. The influence of the water flow speed on the turbidity index in the source and purified water was determined, where the maximum degree of purification for the activated shell of plum pits occurred at the water flow speed of 0.0022 m/s. The analysis of the data obtained indicates a satisfactory adsorption capacity of the studied activated carbons from the shell of plum pits and a high degree of water purification. Key words: adsorption, activated carbon, sulfate, residual chlorine, water purification, drinking water, water supply.

The Study of Three-Dimensional Fluid Flow Regimes on the Basis of the Exact Solution to the Convection Equations

We consider the evaporation/condensation process of diffusion type in two-layer fluid flows under the assumption that both viscous heat-conducting incompressible fluids, a liquid and a gas-vapor mixture, have a common interface and occupy an infinite threedimensional rectangular channel. Based on the exact solution to the convection equations, we study the fluid flows arising in the case of a linearly distributed thermal load on the substrate and thermal insulation of the upper and lateral walls of the channel. It is observed that some complex vortex structures are formed under the action of the longitudinal temperature gradient and transversely directed gravity field. For the ethanol–nitrogen system we present the characteristics of hydrodynamic, thermal, and concentration fields, in particular, the profiles of the evaporative mass flow rates and interface tangential stresses, the topology of flows, and the temperature and vapor concentration distributions.

Cooling of a Vapor-Gas Mixture by Evaporating Water Drops: Dependence of the Cooling Time on the Initial Temperature of the Vapor-Gas Mixture

Numerical modeling of the cooling of a vapor-gas mixture by evaporating water drops has been carried out. An expression is proposed using the characteristic temperature, which determines the dependence of the cooling time on the initial temperature of the mixture. A technique for determining the characteristic temperature based on the results of numerical simulation is presented. An estimate of the error in the results of using the obtained expressions is made. Keywords: vapor-gas mixture, thermal relaxation, numerical simulation, heating and evaporation of droplets, vapor-gas mixture cooling time, characteristic temperature.

Высокочастотный разряд между металлическим и жидким (неметаллическим) электродами

The work is devoted to the study of the characteristics of a low-temperature plasma of a high-frequency (HF) discharge (f = 13.56 MHz) ignited between metallic and electrolytic electrodes at atmospheric pressure. Burning of an RF discharge in a diffuse (volumetric) form is observed at the interface between the media between the electrodes. Numerical calculations of the electric field strength and the distribution of the volumetric power density of the Joule heat release before breakdown in a vapor-gas mixture near a metal electrode are presented. The discharge radiation spectrum, plasma composition, and electron density were studied by optical emission spectroscopy. The thermograms of the electrode surface under the conditions of an RF discharge are considered.

Conducting fundamental scientific research and exploratory scientific research

The work is devoted to the study of the characteristics of a low-temperature plasma of a high-frequency (HF) discharge (f=13.56 MHz) ignited between metallic and electrolytic electrodes at atmospheric pressure. Burning of an RF discharge in a diffuse (volumetric) form is observed at the interface between the media between the electrodes. Numerical calculations of the electric field strength and the distribution of the volumetric power density of the Joule heat release before breakdown in a vapor-gas mixture near a metal electrode are presented. The discharge radiation spectrum, plasma composition, and electron density were studied by optical emission spectroscopy. The thermograms of the electrode surface under the conditions of an RF discharge are considered. Keywords: Plasma-liquid systems, high-frequency discharge, electrolytes, numerical methods.

Production of acetone by catalytic hydration of acetylene

Among the known processes for the production of acetone, the most promising is the synthesis by hydration of acetylene in the presence of catalysts. The advantage of this method is the possibility of carrying out the process in existing acetaldehyde production plants. On the other hand, the process of simultaneous production of acetaldehyde and acetone under the action of polyfunctional catalysts and the implementation of the process using flexible technology is promising. To study the influence of various factors on the process of obtaining acetone by the catalytic hydration of acetylene and to create a technology for producing acetone. The specific surface area, crushing strength, total pore volume, and ash content of the samples were determined. Acetylene was saturated with water at a temperature of 70-80 ℃ and a ratio of water: and acetylene = (1:3)-(1:5), mol was passed through the catalyst bed at 360 ℃ with a space velocity of 180-200h-1. The gas-vapour mixture leaving the reactor was cooled in a refrigerator. The reaction products were collected with water. The catalyst contains acetaldehyde, acetone, crotonaldehyde, etc. To maintain the degree of acetylene conversion not lower than 80%, the reaction temperature was raised by 10 ℃ every 20 hours. After 96-120 hours, the degree of acetylene conversion decreases to 75-70%. The reactions of catalytic hydration of acetylene to acetaldehyde and acetone were carried out on the selection of polyfunctional mixed catalysts. As a result, a catalyst with cadmium fluoride and chromium(III) oxide dissolved in alumina promoted with aluminium fluoride was chosen to produce acetaldehyde. Acetaldehyde is formed by the interaction of acetylene: water =1:3–1:5 at 360-440 ℃ in the presence of a catalyst based on cadmium fluoride with a composition of 18% CdF2, 2,0% AlF3, 5% Cr2O3, 75% Al2O3. The addition of zinc oxide or fluoride to the cadmium-chromium-aluminium catalyst (Catalysts No.5) ensures the selectivity of the catalyst and directs the acetylene hydration reaction towards the formation of acetone. As the temperature rises above 450 ℃, the yield of acetone formation and the selectivity of the process decrease due to the transformation of the formed acetone into other substances. In the temperature range of 360-500 ℃, the relationship between the reaction yield and temperature is extreme, and at 450 ℃ the yield was considered to be maximum. Based on the obtained results, a technological scheme for the production of acetone by the catalytic hydration of acetylene was proposed.

Охлаждение парогазовой смеси испаряющимися каплями воды: зависимость времени охлаждения от начальной температуры парогазовой смеси

Numerical modeling of the cooling of a vapor-gas mixture by evaporating water drops has been carried out. An expression is proposed using the characteristic temperature, which determines the dependence of the cooling time on the initial temperature of the mixture. A technique for determining the characteristic temperature based on the results of numerical simulation is presented. An estimate of the error in the results of using the obtained expressions is made.

Effect of Titanium tetrachloride on the rate of chlorination of Yarega quartz-leucoxene concentrate

This paper considers the results of a study that looked at chlorination of the Yarega quartz-leucoxene concentrate in an ebullated bed reactor (EBR) that feeds titanium tetrachloride vapours and their mixture with chlorine to the reaction mass. The experiments were conducted at a temperature of 850 oC and an incoming gas flow rate of 1,600 ml/min. 250–315 μm concentrate grains mixed with 160–250 μm calcined petroleum coke (the carbon to titanium dioxide molecular ratio was 5) were subjected to chlorination. The reaction products were analyzed with the help of inductively coupled plasma optical emission spectroscopy. It was found that, in the absence of chlorine, titanium tetrachloride only interacts with iron oxides. Feeding a mixture of titanium tetrachloride vapours and chlorine into the reactor leads to an intensified chlorination of the main concentrate components, including TiO2, SiO2, Al2O3 and Fe2O3. The TiO2 chlorination rate rises proportionally to the square root of the partial pressure of titanium tetrachloride in the gas-vapour mixture. The risen rate can be attributed to a higher concentration of active chlorine atoms, which in this case occur on carbon surface not only due to dissociation of molecular chlorine but also as a result of decomposition of titanium tetrachloride. A higher partial pressure of chlorine atoms leads to higher rates of reaction between the chlorine atoms and the concentrate components. According to the proposed reaction mechanism, the TiO2 chlorination rate is proportional to the square root of the product of the partial pressure of TiCl4 and the carbon grains surface area. The excessive chlorine does not impact the chlorination rate. It would be advisable to take into account the discovered ability of TiCl4 to intensify the titanium dioxide chlorination process when designing a chlorine feeding unit in the ebullated bed reactor. Feeding chlorine mixed with titanium tetrachloride vapours into the lower section of the reactor can help enhance the process performance while avoiding using too much chlorine.The work weas carried out under financial support of the Russian Foundation for Basic Research grant, the project No. 18-29-24187mk.

Comparative Characteristics of Evaporative Convection Regimes in Different Statements of Boundary Value Problem for Convection Equations

We analyze different statements of the boundary value problem for the convection equations in order to use Ostroumov–Birikh type exact solutions for describing the evaporative convection regimes in two-layer systems of liquids and gas–vapor mixtures filling a plane channel. The statements differ in the types of boundary conditions for the vapor concentration and temperature functions on the channel walls. We discuss the boundary value problems modeling two-layer flows in the channel, describe the characteristics of hydrodynamic, thermal, and concentration fields for the working HFE7100-nitrogen system and classify the types of flows by distinguishing three classes: purely thermocapillary, mixed, and Poiseuille type flows.

Heat transfer during condensation of water vapour in the presence of non-condensable gas in vertical tube of small diameter

The paper deals with a detailed analysis of published analytical relations for heat transfer during steam condensation in a vertical tube. The historical development of the approaches and the chronological development of the used analytical relations are presented. Attention is focused on the description of the processes at the gas phase-condensate film interface as well as on the inclusion of the influence of the presence of non-condensable gases. The analytical relations in 12 modifications are compared with each other for the same geometrical configuration of the vertical tube and identical boundary conditions. The authors performed comparative experimental measurements of the heat transfer coefficient during condensation of the vapour-gas mixture in vertical tubes of three diameters, namely 16, 20 and 26 mm. Based on a comparison of the experimental results and analytical relations, recommendations are made on the validity interval of the tested relations.

Simulation of Bulk Condensation during Expansion of a Vapor-Gas Mixture in the Flow Path of a Stage of a Turboexpander Unit

Simulation of Bulk Condensation during Expansion of a Vapor-Gas Mixture in the Flow Path of a Stage of a Turboexpander Unit

Mathematical modeling the ignition of several gas hydrate particles

Gas hydrates are regarded as a high-potential type of alternative fuel for the power industry, transportation, space, and special-purpose equipment. Due to their high conversion rates and safe long-distance transportation by all means of transport, gas hydrates can be widely used as primary and secondary fuels. No one has yet developed a general theory of safe and effective gas hydrate ignition under different thermal conditions reproducing those of promising applications. There are no prediction models for an array of particles with different shapes and porosities. This research aims at studying such conditions. Using the experimental data obtained, we have developed a physical and mathematical model for numerical studies of gas hydrate ignition behavior. Here we consider the most promising compositions of methane-based hydrates. The ignition delay times are determined for the emerging gas-vapor mixture when two and three hydrate particles are heated in variable arrangement schemes and at different distances between them. We also determine how the key factors—size, number, and distance between hydrate particles, temperature of external gaseous medium, component composition of particles, as well as their shape and porosity—influence the ignition speed in the systems of interest. Approximations are obtained to predict the gas hydrate ignition characteristics as a function of the key factors and to extend the modeling results to the thermal conditions of the current and future power plants.

Numerical analysis of evaporation from a falling film in a vertical parallel plate channel

A detailed numerical analysis is performed of evaporation from a laminar falling liquid film with a co-current laminar gas-vapour mixture flow in a vertical parallel plate channel. A finite volume method is used to obtain a fully coupled implicit solution of a complete set of parabolic two-phase two-dimensional governing equations. Comparisons with the previous numerical and experimental studies are made to demonstrate the accuracy and capability of the present numerical model. Water-air and ethanol-air mixtures are used to examine the effects of buoyancy forces on the flow and the thermal characteristics of the evaporation process. The effects on the heat and mass transfer of the system of the wall heat flux, the relative humidity, and the inlet pressure are investigated.

Gas-Discharge Point Source of UV Radiation Based on a Gas-Vapor Mixture of Argon and Copper

The characteristics of a pulse periodic source of a long-range UV radiation with overvoltage pumping by a bipolar discharge of nanosecond duration between copper electrodes in argon at atmospheric pressure are investigated. Copper vapors were introduced into the discharge due to the ectonic mechanism, in which a sufficient amount of the electrode material vapors is introduced into the discharge gap due to microexplosions of inhomogeneities of the surface of metal electrodes in a strong electric field of an overvoltage high-current nanosecond discharge. The characteristics of an overvoltage nanosecond discharge at a distance between the electrodes of 2 mm are studied. The emission spectra of the discharge were analysed, and the intensity of the UV radiation of a point emitter was optimized depending on the supply voltage of the high-voltage modulator and the repeti-tion rate of discharge pulses. The identification of the emission spectra of plasma made it possible to establish the main excited plasma products that form the spectrum of the UV radiation of the plas-ma. The study of the spectral characteristics of plasma based on gas-vapor mixtures "copper – ar-gon" showed that the most intense were the spectral resonance spectral lines of the copper atom and ion. It was found that a space-uniform overvoltage nanosecond discharge was ignited between copper electrodes at an inter-electrode distance of 2 mm. It was found that the maximum value of the average UV power at p(Ar) = 101 kPa was observed for the UV-A range.

COGENERATION DEVICE BASED ON INNOVATIVE TECHNOLOGY ORGANIZATION OF ORGANIC WASTE

This work considers the issue of creating efficient and environmentally friendly energy systems based on cogeneration technology. In industrialized countries, work is underway to develop and implement innovative technology for supercritical hydrothermal destruction of industrial and household waste and highly toxic substances. An extremely important urgent task is the complex solution of the problems of creating an autonomous energy complex based on the technology of cogeneration and utilization of organic waste and their use as renewable energy sources. Theoretical and experimental studies have shown that the method of supercritical hydrothermal destruction has high environmental and economic efficiency and demonstrates versatility, providing complete one-stage disposal of any organic waste. It is established that the reaction of supercritical aqueous oxidation of organic matter is exothermic and in the presence of only 15-20% of organic matter the waste processing process becomes autothermal. Autothermal modes of destruction of organic waste at supercritical parameters of the aquatic environment lead to a high-enthalpy vapor-gas mixture, which can be used in the schemes of the autonomous energy complex. Cogeneration units are offered on the basis of a steam power plant operating on the Rankin cycle and on the basis of a heat engine with external heat supply, which operates on a closed thermodynamic Stirling cycle. A non-standard equipment of supercritical hydrothermal destruction technology is a quasi-flow reactor. The conducted research testifies to the possibility of further development of supercritical hydrothermal destruction technologies, both in terms of providing increased process parameters and in terms of developing increasingly reliable, productive and safe types of reactors. The development is based on the replacement of a single-pipe coaxial (two-pipe) reactor. This reactor design significantly expands the temperature and barometric performance characteristics, allows to increase the heat transfer surface and the temperature inside the reactor, bringing it closer to the external temperature of the reactor wall surface while maintaining performance. The cogeneration unit can be used to solve energy efficient and environmentally friendly disposal of organic waste. Allows to solve problems of autonomous electricity and heat supply of industrial and residential facilities and has significant market potential.

Restoration of the heat exchange surface under conditions of its contamination during condensation of a vapor-gas mixture

THE PURPOSE. Determine the operating mode of a heat exchanger designed to transfer heat from a vapor-gas mixture containing solid particles. Get a dependency for calculating the time after which it is necessary to restore the surface by washing it with water. To carry out estimated calculations of the operating mode of the heat exchanger installed at the PULP Invest enterprise. To increase the stability of the heat exchanger and reduce environmental pollution by cellulose particles.METHODS. In solving this problem, the laws of heat and mass conservation, balance ratios in the calculation of economic costs were used.RESULTS. The article describes the relevance of the topic, discusses the features of the operation of a heat exchanger in which heat is transferred from a condensing vapor-gas mixture containing solid particles. An assumption is made about the mechanism of deposition of these particles on the heat exchange surface. A dependence is obtained that allows us to determine the time after which the surface needs to be restored, taking into account the cost of water and electricity.CONCLUSION. Studies have suggested the mechanism of sediment formation on the heat exchange surface. Choosing a rational mode of operation of the heat exchanger will significantly save water consumption for surface restoration, as well as extract the greatest amount of heat from the steam-gas mixture. The release of particles into the air can be reduced.