Steam-gas Mixture Research Articles

Mathematical Modeling of the Transport of H2O–CH4 Steam–Gas Mixtures in Hydrodynamic Devices: The Role of Helical Screws

Mathematical Modeling of the Transport of H2O–CH4 Steam–Gas Mixtures in Hydrodynamic Devices: The Role of Helical Screws

Transport of Steam-Gas Mixture in Hydrodynamic Devices: A Numerical Study of Steam Reforming of Methane

The paper introduces a mathematical model that describes the cavitation process occurring during the passage of a water steam flow in various geometric configurations of a hydrodynamic device. The flow experiences a localized constriction (convergent nozzle) followed by expansion (divergent nozzle), exemplified by a Venturi tube or a Laval nozzle. A narrow flow channel connecting the convergent and divergent sections is equipped with a narrow-section nozzle for injecting methane molecules into the high-speed steam flow. As the steam-gas mixture passes through this zone, it is irradiated with an electron beam and sprayed into a cylindrical chamber at atmospheric pressure, where the distribution of methane molecules in water vapor forms an aerosol. Key geometric parameters of the constriction and expansion zones of the hydraulic system (cavitation-jet chamber) are determined to ensure the uniform distribution of dispersed-phase particles (methane) in the dispersion medium (water vapor). Velocity and pressure distributions of the mixed steam-gas flow are calculated using a turbulent mathematical model, specifically the k-ω model, while the motion of methane particles is simulated using a particle tracing method. The uniformity of methane molecule distribution in water vapor is assessed using Ripley’s K-function. The best performance of the hydrogen-producing chamber was observed when the cavitation-inducing nozzle’s convergence angle exceeded 50 degrees. The divergence angle of the nozzle within the range of 30–40 degrees provided the best distribution in terms of uniformity of the methane particles in the chamber.

USE OF THE WORKING BODY OF THE UNIVERSAL VIBRATORY MILL FOR DRYING GRAIN MATERIAL

One of the most perspective directions of intensification of heat and mass transfer in the processes of drying plant materials and increasing the energy efficiency of drying plants is the application of a vibration field for mixing grain material while moving in the drying chamber. The analysis of existing vibration installations has revealed that the most promising is the usage of vibratory grinding chambers with spatial circulation of material for the implementation of grain heat treatment, in particular drying. As a result, it is proposed to use the proven element base of a vibratory mill as a working body of which grinding chambers with spatial circulation of the load are used. The article presents the structural and technological scheme of a vibratory thermal drying unit, the structural parameters of the unit, and a mathematical description of the grain drying process. The obtained differential equations constitute a mathematical model of the nonstationary process of continuous drying of grain material and determine the change in time, parameters of grain and steam-gas mixture at the outlet of the grain drying chamber. The constructed mathematical model of the drying process makes it possible to determine the modes of heating and dehydration of grain material during circulation in a vibrating chamber with a conductive energy supply and partial vacuuming of the chamber, to expand the technological capabilities of the "vibrating mill" type installations. The graphical dependences of the temperature and moisture content of grain over time, the data for which were determined experimentally, are presented when a monolayer of grain of mass m is heated on a heating surface of area F at a stabilized surface temperature θn. In this work, the kinetics of drying and heating of grain were obtained, which were used to calculate the parameters of the vibrothermal drying unit. Also, using the results of the experiments, the performance indicators of the vibration dryer created on the basis of the grinding chamber of the vibrating mill were determined.

Cogeneration Installations in Degassing Systems of Solid Municipal Waste Polygons

The possibility of using energy and resource-saving power plants of cogeneration type with steam injection into the flow part with deep utilization of high-potential and low-potential heat of the gas-steam mixture in systems for degassing municipal solid waste is investigated. The use of a combined technology of absorption and adsorption purification of landfill gas is proposed. The conclusion is made about the effectiveness of using landfill gas as an energy carrier in a combined contact-type bioenergetic installation with a heat recovery heat exchanger, which will save the national wealth of the country and at the same time solve the problems of modern megacities associated with reducing the negative impact of MSW landfills on the environment.

УСТАНОВКА ДЛЯ СОЗДАНИЯ ПАРОГАЗОВЫХ СМЕСЕЙ

The problem of the development and research of sensitive elements is posed. To solve it, it is proposed to create an installation of steam-gas mixtures with the specified parameters necessary for sensitive elements. The installation of a saturator and a block diagram of an installation for creating steam-gas mixtures are given. The dependence of the volume concentration of vapors of the investigated organic matter on the pressures created by the installation is given

SIMULATION OF THE PROCESS OF FILLING POLYSTYRENE FOAM FOUNDRY MOLD WITH THE METAL

Modern approaches to prefabrication production consist in the maximum approximation of the shape and size of the blanks to the finished part, which essentially makes the final part cheaper. One of the methods of precision casting is casting in gasified models, or foam models. The basis is the task of developing a theoretical model of filling a polystyrene foam model with liquid metal. The analysis of the process of filling the mold with a gasified model and the process of filling the mold with a closed sprue system are considered. The analysis of the obtained solutions shows that the movement of the metal has the character of aperiodic oscillations. The speed of metal in quantity is maximum at the initial moment of metal processing in the form and happens as it is filled. The pressure of the steam-gas mixture at the initial moment of time exceeds the pressure of the weak metal in the riser, which provides the possibility of metal ejection from the bowl. At the same time, the pressure in the mold cavity changes little with the increase in gas permeability of the mold, which is explained by the small gap between the melting front of the model and the metal mirror. However, with an increase in gas permeability due to a decrease in back pressure, the speed of the metal in the mold cavity and the path traveled by it increase. The analysis of the system of equations allows predicting the behavior of metal during the design of molds for the summer, which reduces the probability of production defects.

The influence of a noncondensable gas on the collapse of a bubble in a stratified steam explosion at NPP

In the present work, the effect of a noncondensable gas on the collapse of a hot bubble in cold water was studied. It is assumed that the bubble consists of a gas mixture of steam, which can condense on cold water, and a noncondensable gas. The dynamics of the bubble was modeled by the integral equations of mass and energy supplemented by the steam diffusion equation. The steam condensation rate was determined by heat fluxes on the interfacial surface from the steam and water sides. It was used a one-dimensional spherically symmetric approach. The water surrounding the bubble was considered as an incompressible fluid, the flow of which was described by the Rayleigh-Plesset. Heat transfer in water is described by a one-dimensional heat equation, which takes into account conductive and convective mechanisms of heat transfer. Calculations performed using this model showed that the presence of a noncondensable gas in a bubble does not significantly affect its collapse in cold water. This means that the noncondensable gas cannot significantly weaken the impact of water on the melt, which occurs when a bubble collapses near the interface, which leads to a stratified steam explosion.

Prevention of Explosive Transformation of an Oil–Steam–Gas Mixture in an 8T-650-01 Boring Pump Casing

Prevention of Explosive Transformation of an Oil–Steam–Gas Mixture in an 8T-650-01 Boring Pump Casing

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.

Experimental investigation on thermal hydraulic interaction of RCS (reactor coolant system) and containment for intermediate break loss-of-coolant accident (IBLOCA) scenario in ATLAS-CUBE test facility

In order to experimentally investigate the thermal hydraulic interaction between the reactor coolant system (RCS) and the containment, the integral effect tests were conducted in a test facility, ATLAS-CUBE. Three tests for an intermediate-break loss-of-coolant accident (IBLOCA) were conducted for simulating the break of a cold leg or a direct vessel injection (DVI) nozzle. The effect of the mass/energy (M/E) supply from the break and the asymmetric phenomena inside the containment according to the break simulation position were investigated with considering its impact on the pressure/temperature (P/T) behavior inside the containment. As the test results, both of the RCS and the containment were effectively cooled down during the transient, by activation of the safety injection system and the containment spray system, respectively. The M/E supply from the RCS increased a pressure and a steam-gas mixture temperature of the containment, while a wall condensation on the passive heat sink and a spray injection contributed to cool down the steam-gas mixture. The two-phase flow characteristics of the break flow such as the quality or the subcooling of the liquid phase could highly affect the P/T build-up of the steam-gas mixture in the containment. The ATLAS-CUBE test data in this study will contribute to evaluate the thermal hydraulic safety analysis codes for the RCS and the containment.

THEORETICAL STUDIES OF THE HEAT TRANSFER PROCESS AND THE HYDRODYNAMICS OF A CONDENSATE FILM BY NUMERICAL EXPERIMENT

The paper presents an analysis of the mathematical description of the process of film condensation of vapors from steam-gas mixtures, taking into account the dependence of the processes of heat transfer and the hydrodynamics of the condensate film. It is established that the presence of an insignificant fraction of non-condensing gases sharply reduces the surface temperature of the condensate film. The numerical experiment has confirmed that the loss of stability of the film and its deceleration are associated with the temperature gradient on its surface. It is established that the influence of non-isothermicity on the characteristics of transfer processes can significantly change their flow mode even with small fluctuations in functional parameters. The influence of temperature on the condensate density leads to a certain increase in the average and local Nusselt numbers. As a result of the conducted studies, it was found that the dependence of the condensate density on temperature contributes to an increase in the average and local Nusselt number. This is confirmed by its fundamentally small effect on heat exchange under condensation conditions for liquids in the following range  ~ 10 10   4 2  .

MATHEMATICAL DESCRIPTION OF THE PROCESS OF FILM CONDENSATION OF VAPORS FROM STEAM-GAS MIXTURES

This article presents an analysis of the mathematical description of the process of film condensation of vapors from vapor-gas mixtures. Taking into account the considerable variety of effects that occur during the flow of films in processes in which phase transformations occur, the complexity of the mathematical description of the flow of condensate films becomes obvious. This complexity of describing the process is aggravated by the combination of heat and mass transfer, non- isothermic, and changes in such properties as surface tension, viscosity, and density. To describe the flow rate and film thickness during film condensation, a fundamental system of equations is used, and the equations of dynamics and continuity in the long-wave approximation are also taken into account. The estimation of the propagation length of nonlinear waves in condensate films with varying flow rates showed that with an increase in the condensation intensity, the role of the proposed corrections increases, but within the limits of the validity of the thin-film approximation does not become decisive and significant. During the description of the process of film condensation of vapors from steam-gas mixtures, it was found that when the basic conditions are met, the influence of undulation manifests itself mainly through an increase in the heat exchange surface, and the contribution of surface forces to the intensification of the process, i.e., an increase in condensate consumption, is no more than 10-12%

Optimizing Parameters of a High-Efficiency Steam Condenser from a Steam-Gas Mixture with a Large Content of Noncondensing Gases

Optimizing Parameters of a High-Efficiency Steam Condenser from a Steam-Gas Mixture with a Large Content of Noncondensing Gases

Decreasing the Weight-Size Parameters of Gas-Steam Turbine Plant by Increasing the Efficiency of Thermodynamic Processes in the Condenser

The aim of this work is decreasing the weight-size parameters of the contact gas-steam turbine plant and contact condenser elements by increasing the efficiency of thermal-gas dynamic processes of condensation through rational irrigation of countercurrent gas-steam flow. To achieve the goal the total efficiency of water-return drops ranging from 0.1 to 1 mm at different initial velocities from 5 to 35 m/s emitted by the multi-nozzle sprinkler was determined by mathematical modeling of the liquid droplet movement processes, heat and mass transfer between the liquid droplet and gas-vapor mixture, and gas-vapor mixture pressure loss. The effect of increasing the gas-steam mixture velocity from 3.3 to 6 m/s on the overall efficiency of water return was determined. The novelty of the obtained results was defined by an increase in the water return into cycle from 12 to 13% with a droplet diameter of 0.3 -- 0.4 mm and the initial velocity from the sprinkler of 5--10 m/s. The velocity of the mixture was to 6 m/s at rational correlations of the initial velocity of the droplets’ escape, which increased the total amount of heat withdrawn to 11%. The positive effect conditions of irrigation processes on thermogasdynamic and weight-size parameters of the condenser elements for the contact gas and steam turbine plant at full pressure recovery coefficients of over 0.967 were substantiated. The most significant result was the reduction of the weight-size parameters of the marine infrastructure object power plant from 8 to 19%.

Study on CO2 capture upgrading of existing coal fired power plants with gas steam mixture cycle and supercritical water coal gasification

Upgrading instead of phasing out the existing coal fired power plants for CO2 capture with high efficiency is an alternative to the tough task for realizing the commitment for Paris Agreement and carbon neutrality. A gas steam mixture power cycle with syngas from supercritical water coal gasification (GSMC-C) is proposed and studied, using syngas fuel/O2 combustion products mixed with feedwater as working medium to realize power generation with CO2 capture in internal process from the non-condensable gases of condenser. A top-turbine is set before the existing turbine unit for increasing the cycle efficiency with higher turbine inlet parameters and the working medium from the reheating combustor is used for coal gasification heating first. The effects of some key parameters on the performances of the cycle such as net efficiency, specific turbine output and percentage of auxiliary power were studied. The results show that the net efficiency and gross efficiency of GSMC-C system were 41.96% and 48.67% respectively under the conditions of top-turbine inlet parameters of 30 MPa/650°C, condenser parameters of 30 kPa/30°C and ASU specific power consumption of 0.245 kWh·kg−1(O2). The GSMC-C system can provide a reference for retrofitting coal-fired power plants into clean and efficient power plants with nearly zero emissions of CO2 and other pollutants.

An Engineering Model of Steam Condensation from a Flowing Steam-Gas Mixture on a Bundle Made of Horizontal Tubes

An Engineering Model of Steam Condensation from a Flowing Steam-Gas Mixture on a Bundle Made of Horizontal Tubes

Improving energy efficiency of the systems for obtaining water from atmospheric air

This paper outlines the prospect of obtaining water from atmospheric air by cooling it to the dew point temperature using refrigeration machines in order to partially reduce water scarcity in the arid regions of our planet. To minimize energy costs in the systems for obtaining water from atmospheric air, it is proposed to utilize solar energy with absorption refrigeration units (ARUs) acting as a source of artificial cold. The characteristic thermodynamic processes have been analyzed in a modernized ARU, capable of working at a lower thermal energy source's temperature than its analogs. The possibility has been studied to reduce the temperature of the heat source by including a solution vaporizer in the ARU scheme. The analysis involved an authentic method based on the balance of specific streams of ARU working body components and actual boundary conditions at characteristic points of the cycle. A limit was shown for the level of a minimum boiling temperature in the ARU generator (from 90 °C) when the systems for obtaining water from atmospheric air are operated under current climatic conditions. The simulation of heat-and-mass exchange processes during contact interaction between a steam-gas mixture and ammonia water solution was carried out. Based on variant calculations, it has been shown that the proposed ARU structure with an adiabatic solution vaporizer could work as part of systems to obtain water from atmospheric air at a hot spring temperature above 100 °C and constructively enough fits into the element base of standard models. It has been proposed to use two types of solar thermal energy sources to operate ARU. In a tropical climate, with vacuum solar collectors or solar energy hubs; in a temperate climate zone, with solar collectors with water as a heat carrier

Exergy and exergoeconomic analysis of hydrogen and power cogeneration using an HTR plant

This paper proposes using sodium-cooled fast reactor technologies for use in hydrogen vapor methane (SMR) modification. Using three independent energy rings in the Russian BN-600 fast reactor, steam is generated in one of the steam-generating cycles with a pressure of 13.1 MPa and a temperature of 505 °C. The reactor's second energy cycles can increase the gas-steam mixture's temperature to the required amount for efficient correction. The 620 ton/hr 540 °C steam generated in this cycle is sufficient to supply a high-temperature synthesis current source (700 °C), which raises the steam-gas mixture's temperature in the reactor. The proposed technology provides a high rate of hydrogen production (approximately 144.5 ton/hr of standard H2), also up to 25% of the original natural gas, in line with existing SMR technology for preparing and heating steam and gas mixtures will be saved. Also, exergy analysis results show that the plant's efficiency reaches 78.5% using HTR heat for combined hydrogen and power generation.

Experimental investigations of the parameters of liquid evaporation process under acoustic-vacuum exposure

Experimental investigations of the process of liquid evaporation under conditions of acoustic-vacuum exposure were conducted. Based on the obtained values of the evaporating liquid mass and the liquid vapor pressure in a closed container, a resonance effect is revealed. The emergence of the resonance effect is characterized by the active boiling of the liquid when the frequency of the system “steam-gas mixture + cupola + vacuum chamber + liquid layer” coincides with the frequency of the acoustic exposure under conditions of reduced external pressure. To measure the vapor pressure of the liquid, a cupola was introduced into the experimental stand, which makes it possible to increase the vapor pressure of the liquid and register its value with the equipment used. The calibration characteristic of laboratory scales is obtained as a dependence of the change of cargo weight on the pressure values in the vacuum chamber. Using the obtained calibration characteristic of laboratory scales operating under acoustic-vacuum exposure, the values of liquid mass change are obtained at different values of external pressure in the vacuum chamber. The results obtained can be applied in the field of acoustic-vacuum drying and cleaning of different surfaces.

Integral effect test for steam line break with coupling reactor coolant system and containment using ATLAS-CUBE facility

To improve safety analysis technology for a nuclear reactor containment considering an interaction between a reactor coolant system (RCS) and containment, this study aims at an experimental investigation on the integrated simulation of the RCS and containment, with an integral effect test facility, ATLAS-CUBE. For a realistic simulation of a pressure and temperature (P/T) transient, the containment simulation vessel was designed to preserve a volumetric scale equivalently to the RCS volume scale of ATLAS. Three test cases for a steam line break (SLB) transient were conducted with variation of the initial condition of the passive heat sink or the steam flow direction. The test results indicated a stratified behavior of the steam-gas mixture in the containment following a high-temperature steam injection in prior to the spray injection. The test case with a reduced heat transfer on the passive heat sink showed a faster increase of the P/T inside the containment. The effect of the steam flow direction was also investigated with respect to a multi-dimensional distribution of the local heat transfer on the passive heat sink. The integral effect test data obtained in this study will contribute to validating the evaluation methodology for mass and energy (M/E) and P/T transient of the containment.