Air-steam Mixture Research Articles

CFD Modeling of Film Condensation from a Steam-Air Mixture in Vertical Channels

Steam condensation in the presence of a noncondensable gas is of vital importance for passive cooling containment systems. The noncondensable gas causes a significant reduction in the condensation rate and heat transfer across the containment, which is important for postulated loss-of-coolant accidents in a nuclear reactor. In this work, computational fluid dynamics models of condensation and the adjacent single-phase steam-air mixture flow are developed for laminar and turbulent flow in vertical channels by two distinct wall condensation modeling approaches using the commercial code STAR-CCM+. The first is the fluid film model available in STAR-CCM+, which solves liquid layer governing equations with connections to the adjacent gas mixture flow. The second is a user-defined wall condensation model that neglects the fluid film and instead accounts for mass, momentum, and heat transfer via user-defined volumetric sink terms adjacent to the cold wall. The condensation models are assessed by first comparing the calculated results with the numerical solution of laminar flow, solved using a complete two-phase model that solves parabolic equations based on conservation of mass, momentum, energy, and species for each phase. Next, the results of a two-dimensional analysis are compared with COPAIN experiments and existing numerical solutions from three-dimensional analyses. The comparisons include new, detailed results that have not been reported in previous analyses of a COPAIN case. These new results include local field profiles of velocity, temperature, and air mass fraction, and local mass flux.

Detonation of H2–Air–Steam Mixtures: A Potential Hazard in Large-Scale Electrolyzer and Fuel Cell Installations

Detonation of H2–Air–Steam Mixtures: A Potential Hazard in Large-Scale Electrolyzer and Fuel Cell Installations

Analyses of Jet Buoyant Flow in a Multicompartment Containment Using an Open-Source Solver

Hydrogen mixing and distribution in a nuclear power plant containment during a postulated severe accident is a phenomenon with high safety relevance for current and advanced light water reactors. The Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) SESAR Thermal-Hydraulics (SETH) project was carried out to generate experimental data on basic containment phenomena with the required instrumentation to assess computational fluid dynamics (CFD) and lumped parameter codes. In this paper, we analyze the PANDA SETH Test 16 of the OECD/NEA SETH project using containmentFOAM, which is a tailored open-source CFD code package for containment analysis developed at Forschungszentrum Jülich GmbH based on OpenFOAM.® SETH Test 16 addressed steam-air mixture transport driven by jets and plumes in the multicompartment PANDA facility (two vessels and an interconnecting pipe) at the Paul Scherrer Institut in Switzerland. Steam as a wall plume was injected at 0.040 kg/s and 140°C in vessel 1, which was initially filled with dry air at 108°C. The steam-air mixture was vented out from the top of vessel 2. The system pressure was constant at 1.3 bar for the whole test duration (4000 s). To simulate SETH Test 16, the k-ω shear stress transport turbulence model was adopted with the generalized gradient diffusive hypothesis buoyancy turbulence model. The simulation represented the experimental phenomenology reasonably well. The trends for the calculated temperature distribution were similar to those of the experiments and only yielded a slight discrepancy of about 2.7%. In addition, the distribution of the steam molar fraction was well predicted above the injection tube in vessel 1. However, below the injection tube in vessel 1, some discrepancies between the simulations and the experimental results were observed. These may have been caused by the higher turbulent mass diffusivity in the physical model and the challenge of the mesh resolution in the middle region of vessel 1.

Thermodynamic equilibrium state calculations for oxidation and corrosion reactions of B4C and oxide-based neutron absorber compounds in reactor control rods

The challenges associated with conventional boron carbide (B4C) control rod materials, including helium gas accumulation and susceptibility to oxidation and corrosion in various environments, have been thoroughly explored. To address these issues, a comprehensive investigation into the potential of oxide-based neutron absorber compounds for control rods has been undertaken. Thermodynamic equilibrium state calculations have been conducted to assess the oxidation and corrosion reactions of various neutron absorber materials (Gd, Hf, Sm, Er, Eu, Dy-based oxide), including B4C, in various environments such as oxygen, steam, air, and air–steam mixtures. The results have unveiled vulnerabilities of B4C in these environments, notably the generation of gases such as H2, CO, and boron compounds. Furthermore, neutron absorber oxide materials have exhibited potential susceptibility to oxidation and corrosion in steam environments. Consequently, the potential of oxide-based neutron absorber compounds, formed by combining neutron absorber oxide materials with highly oxidation-resistant substances (ZrO2, TiO2), has been explored. Thermodynamic equilibrium state calculations indicate that these compounds maintain robust resistance to oxidation and corrosion across various environments. This paper demonstrates the superiority of oxide-based neutron absorber compounds as alternatives to existing boron carbide neutron absorber materials. Additionally, the oxide-based neutron absorber compounds are expected to extend the lifetime of the LWR control rod as well as improve stability and resistance to oxidation and corrosion.

Studying Flotation of Gold Microdispersions with Carrier Minerals and Pulp Aeration with a Steam–Air Mixture

This work is aimed at obtaining new knowledge in the field of interactions of polydisperse hydrophobic surfaces in order to increase the extraction of mineral microdispersions via flotation. The effect of high velocity and the probability of aggregating fine particles with large ones are used to increase the extraction of finely dispersed gold in this work. Large particles act as carrier minerals, which are intentionally introduced into a pulp. The novelty of this work lies in the fact that a rougher concentrate is used as the carrier mineral. For this purpose, it is isolated from three parallel pulp streams by mixing the rougher concentrate, isolated from the first stream of raw materials, with an initial feed of the second stream; accordingly, the rougher concentrate of the second stream is mixed with the initial feed of the third stream, and the finished rougher concentrate is obtained. In this mode of extracting the rougher concentrate, the content of the extracted metal increases from stream to stream, which contributes to the growth in its content in the end product. Moreover, in order to supplement forces involved in the separation of minerals with surface forces of structural origin in the third flotation stream, the pulp is aerated for a short time (about 15%–25% of the total) with air bubbles filled with a heat carrier, i.e., hot water vapor. Within this accepted flotation method, the influence that the surface currents occurring in the wetting film have on its thinning and breakthrough kinetics is proposed to be in the form of a correction to a length of a liquid slip in the hydrophobic gap. The value of the correction is expressed as a fraction of the limiting thickness of the wetting film, determined by the condition of its thickness invariability when the streams are equal in an interphase gap: outflowing (due to an action of the downforce) and inflowing (Marangoni flows and a thermo-osmotic stream). Gold flotation experiments are performed on samples of gold-bearing ore obtained from two deposits with conditions that simulate a continuous process. Technological advantages of this developed scheme and a flotation mode of gold microdispersions are shown in comparison with the basic technology. The purpose of this work is to conduct comparative tests on the basic and developed technologies using samples of gold-bearing ore obtained from the Natalka and Olimpiada deposits. Through the use of the developed technology, an increase in gold extraction of 7.99% and in concentrate quality (from 5.09 to 100.3 g/t) is achieved when the yield of the concentrate decreases from 1.86 to 1.30%, which reduces the costs associated with its expensive metallurgical processing.

Gasification of Egusi Melon (Citrullus lanatus) Shell over a Novel Ni/dolomite/MgO/[formula omitted]Al2O3 Catalyst for the Production of H2-rich gas

Hydrogen-rich gas was produced from Citrullus-lanatus in a fixed-bed reactor using a novel Ni/dolomite/MgO/γ−Al2O3 with air-steam mixture as the gasifying agent. The feed and steam-air flow rates were 3 and 0.8 kg/h with fixed steam-air volume-concentration of 40% v/v. The results displayed a high cracking activity of the hydrocarbons/tar in the biomass by the catalyst with a resultant upgrade in the gas quality/H2 yield. The highest H2 yield was 66.1 g/kg biomass, a minimal tar concentration of 2 g/Nm3 with steam-to-biomass ratio of 2 at 1100 °C. The highest H2 yield (57 vol%) was achieved at 0.28 equivalence ratio.

Use of an absorber for the regeneration of hydrotreating catalysts using a steam-air mixture

This article explores the processing of high-sulfur petroleum products into low-sulfur fuels without harming the environment. Specifically, it discusses the implementation of EURO-3 standards at the Bukhara Oil Refinery in Uzbekistan since 2022. The study examines the hydrodesulfurization process used to treat high-sulfur heavy fractions of oil. The primary aim of the research is to improve the method of oxidative regeneration of hydrotreating catalysts. Modern techniques are proposed for restoring the activity of used catalysts, one of which involves regeneration with a steam-air mixture. This new method offers numerous advantages over traditional approaches, including significant savings in energy and materials, reduced process duration, and decreased emissions of harmful gases into the environment. Consequently, this method not only enhances production efficiency but also plays a crucial role in protecting both the environment and human health.

ФОРМУВАННЯ МЕТОДИКИ ДОСЛІДЖЕНЬ ВОДНЕВООРІЄНТОВАНОЇ ТЕХНОЛОГІЇ ПІДЗЕМНОЇ ГАЗИФІКАЦІЇ ВУГІЛЛЯ

Purpose. Establishing correlations between analytical and laboratory research in underground coal gasification with a focus on hydrogen production. Methodology. Analysis of experience in conducting analytical and laboratory research in the field of underground coal gasification in situ. Analysis of the application specifics of the Darcy-Weisbach equation to establish optimal conditions for supplying steam-air mixture to the combustion face considering the relationship between the volumetric flow of the specified mixture through the controlled pipeline and its cross-sectional area. Results. The proposed algorithm for conducting research on underground coal gasification processes focuses on hydrogen production. Analytical formulas are provided to determine optimal parameters for supplying the blowing mixture to the combustion front via the controlled pipeline. An author's technological scheme of a laboratory setup for studying gasification processes and the peculiarities of researching it are presented. A diagram illustrating the relationship between blowing system parameters, which vary depending on the hydrogen raw material requirements, the energy capabilities of the system itself, and the parameters of the controlled pipeline, is provided. Originality: Scientifically grounded development of a methodology for conducting analytical and laboratory research on coal gasification process to determine parameters for supplying the blowing mixture through the controlled pipeline with a focus on hydrogen production. Practical implications: Practical implications: Conducting research according to the developed research methodology of underground coal gasification technology allows for a systematic and structured approach to assessing all aspects of the gasification process. The use of a clear research methodology helps to avoid subjectivity and simplifies the process of data collection and analysis. The research methodology ensures high reliability and accuracy of the obtained data, which is critical for making informed decisions. Effective use of the research methodology minimizes resource usage, such as time, costs, and equipment, by avoiding unnecessary duplications and unjustified expenses. Practical implications: Practical implications: Conducting research according to the developed research methodology of underground coal gasification technology allows for a systematic and structured approach to assessing all aspects of the gasification process. The use of a clear research methodology helps to avoid subjectivity and simplifies the process of data collection and analysis. The research methodology ensures high reliability and accuracy of the obtained data, which is critical for making informed decisions. Effective use of the research methodology minimizes resource usage, such as time, costs, and equipment, by avoiding unnecessary duplications and unjustified expenses. Keywords: underground coal gasification, hydrogen, methodology, analytical research, Darcy-Weisbach equation, laboratory research.

High Temperature Oxidation of Zircaloy-4 Under Conditions Simulating a Loss of Cooling Accident in Spent Fuel Pools Examined with Raman Imaging and 18o Tracer Techniques

Since the Fukushima accident, an increased attention is continuously paid to the vulnerability of the Spent Fuel Pools (SFPs). In SFPs, for different reasons, degradation of the fuel rods induced by oxidation in air-steam mixtures after dewatering is a major safety concern: (i) the cladding material is the only barrier left against fission product dissemination, (ii) the heat released by the oxidation reactions can overcome the residual decay heat of the fuel and may become the main driving force to the accident escalation, (iii) hydrogen production is a strong concern because of the presence of steam, (iv) presence of air in the atmosphere is known to be an aggravating factor because of the “catalytic” role of nitrogen on the oxidation mechanism.In this study, high temperature oxidation tests in oxygen, air and air - steam atmospheres were performed with Zircaloy-4 cladding tubes and plates specimens. Because spent fuels are concerned, the presence of the corrosion oxide scale formed in reactor during in-service operation was also considered. The tests described in this study were restricted to the 700 – 950°C range, and mostly performed at 850°C. Raman imaging was used to examine the specimens after the oxidation tests, either directly at the oxide surface, or on metallographic preparations for cross-section examinations.We first used new opportunities given by Raman imaging to analyze, at least qualitatively, the structural and mechanical phenomena involved in this particular corrosion phenomena. Indeed, this method can provide information on the nature of phases that are present in the scale and on the stress level with sub-micron spatial resolution. The different methods used to extract this information that is present in the Raman data will be described and discussed.Moreover, isotopic substitution was also considered. Actually, Raman spectroscopy has also the ability to quantitatively extract the 18O distribution in a zirconia oxide scale after a two stage experiment with a fair accuracy. Raman imaging gave clear evidence for different characteristic distributions of 18O in the scales. Some of them have been correlated with the development of cracks and porosity in the oxide which allows the corroding medium to penetrate locally in the scales. Nitrogen appears to have no or limited influence on the oxygen diffusion, but is observed to reach the metal/oxide interface much faster than oxygen. Thus, we also emphasize the potential of this method to investigate the 18O distribution in such complex corrosion scales.

Condensation enhancement experiment investigation of pure steam and steam-air mixture over the chrome-plated tube with different plating thickness

The condensation enhancement research of pure steam and steam with non-condensable gas is of great significance for reactor safety. In this study, to evaluate the influence of chrome-plated tubes on condensation enhancement, pure steam and steam with air condensation heat transfer experiments are conducted, and the plating thicknesses of 1 μm (tube #1) and 10 μm (tube #2) are considered. The results show that dropwise condensation (DWC) occurred in the part of tube #1 surface, while tube #2 surface is filmwise condensation (FWC). For the pure steam condition, the steam condensation heat transfer coefficient (HTC) of tube #2 is higher than that of tube #1, and both are greater than the theoretical analysis of Nusselt. Thus, the condensation enhancement effect of the chrome-plated tubes is remarkable. For the steam with air condition, a new condensation HTC expression is proposed, which is related to gas pressure, wall subcooling, and air mass fraction. Compared with the widely used experimental correlations and the experimental data of polishing tubes, it is found that the condensation enhancement performance is not significant. This is because the dominant thermal resistance affecting heat transfer is the air layer at the gas-liquid interface. Thus, enhancing the disturbance of the gas layer is the key to the condensation enhancement of steam with non-condensable gas.

European Green Deal: An Experimental Study of the Biomass Filtration Combustion in a Downdraft Gasifier

This study presents the experimental results obtained from hybrid filtration combustion using biomass pellets. The experiments were carried out using a porous media gasifier filled with pellets and inert material. The gasifying agent used was an air–steam mixture, with 40% being steam. The dependence of the temperature in the gasifier’s reaction zone from the volume percentage of inert porous material in the gasifier, the specific heat capacity of this material, as well as the air–steam blowing rate, was investigated. The multifactor experiment method was used. A maximum temperature of 1245 °C was achieved using 28 vol% of porous material with a heat capacity of 1000 J/(kg·°C) and at a blowing rate of 42 m3/h. The maximum hydrogen content in the syngas was 28 vol%. This was achieved at an air–steam blowing rate of 42 m3/h and 40 vol% porous material, with a heat capacity of 1000 J/(kg·°C). The calorific value of the syngas was 12.6 MJ/m3. The highest CO content in the gas was 28 vol% and was obtained at 20 vol% porous material with a heat capacity of 1000 J/(kg·°C) and a blowing rate of 42 m3/h. The obtained information is applicable in the design, management, and control of gas production by way of a hybrid filtration combustion process in a downdraft gasifier.

Sliding of water droplets onto a textured metal surface

Technologies for catching fluid from a steam mixture in the form of small droplets using the lattices or metal plates located at a certain angle are used in many industrial installations. Conducting experimental studies of the processes of collision and draining the drops of fluid on the surfaces of the metal is relevant for increasing the efficiency of gathering fluid from the steam-air mixture in industrial plants. Accordingly, the purpose of this work was to analyze the effect of the texture of the metal surface on the characteristics of the process of spreading water drops after their fall. The experiments were carried out at the setup, which is based on the shadow technique. The height of liquid droplets and the angle of the substrate inclination were varied. To assess the effect of texture on the characteristics of the spreading of water drops on the surface of brass substrates, microgrooves were applied by a grinder. It was found out that after dosing, the drop stretched along the grooves. The left and right contact angles (LCAs and RCAs), measured perpendicular to the grooves, increased by 15% compared to the angles measured on the polished surface of the substrate. It was established that after pinning the drops on the tilted surface, the difference between the LCAs, measured in parallel and perpendicular to the grooves, increased by more than 35%.

Технология использования чернового концентрата в качестве минералов-носителей

Технология использования чернового концентрата в качестве минералов-носителей

Thermal-hydraulic characteristics analysis of steam–air condensation in vertical porous-wall corrugated tubes

In the passive containment cooling systems (PCCS) of Generation III nuclear power plants, the condensation performance of steam containing non-condensable gas (NCG) in condensate tubes is critical for removing heat from the nuclear power plant containment. By applying a novel porous-wall corrugated structure in the condenser tubes of this system, it was found that under certain conditions, a double vortex is formed inside and outside the porous layer, which is conductive to the transportation and condensation of steam to the condensing wall. The VOF multiphase relation and Brinkman–Forchheimerextended Darcy model in combination of local heat balance, condensation and species transport equations are employed to describe the heat and mass transfer in the porous-wall corrugated tube during condensation. The numerical analysis are conducted to investigate the effects of waveform channel, porous layer and its thicknesses, subcooling of cooling wall and inlet air mass fractions on flow and condensation under different inlet velocities, in which simulations agree with the experimental data. The results show that the condensation heat transfer is greatly influenced by the vortex distribution and air accumulation. At inflowing velocity of 1 m/s, the waveform with amplitude of 1 mm and wavelength of 18 mm can achieve the highest performance evaluation factor, φ (about 67.5 % enhancement than the smooth tubes). The ratio of waveform amplitude to wavelength needs to be chosen properly in consideration of convection between solid matrix and steam–air mixture in porous layer, and non-condensation gas distribution near cooling wall of condensation tube.

Simulation of high-temperature zirconium alloy oxidation in a nitrogen, oxygen and steam mixture

The paper presents a correlation model of high-temperature zirconium alloy oxidation in a mixture of gases (steam, nitrogen and oxygen) for the weight gain calculation of the oxidized sample. The essence of the model consists in using the linear interpolation between the kinetic constants of oxidation in pure gases to describe the oxidation kinetics in gas mixtures. The approach allows one to describe the oxygen weight gain with different contents of gases in steam, nitrogen and oxygen mixtures. The model was validated against experimental data on oxidation in an air-steam mixture in a proportion of 50% to 50% of the volume. For temperatures of 1200 °C and 1400 °C, prior to the 625th second, the deviation between the experimental data and the simulation results is not more than 18%; for 800 °C, prior to the 14th hour, the deviation between the experimental data and the simulation results is not more than 40%. Besides the air-steam mixture, the paper presents the results of the weight gain calculation using the proposed model for oxidation in an oxygen-nitrogen mixture and in a steam-oxygen mixture at 800 °C and 1400 °C.

Modeling of Cooling Tower Operation with Consideration for the Chemical Work in the Steam–Air Mixture

Modeling of Cooling Tower Operation with Consideration for the Chemical Work in the Steam–Air Mixture

MATHEMATICAL MODELING AND NUMERICAL STUDY OF BIOMASS FIXED CARBON GASIFICATION IN A DENSE BED AT ATMOSPHERIC PRESSURE. PART 2. ANALYSIS OF NUMERICAL RESULTS

Using the constructed two-dimensional model of aerodynamics, heat-mass transfer and chemical reaction of coke-ash residue in a steam-air mixture at a pressure of 1 atm, taking into account interphase convective heat transfer, radiative-conductive heat transfer of the solid phase, radiative and conductive heat transfer of the bed with the reactor wall, gravitational forces and aerodynamic resistance, the unsteady process of lignin gasification in a fixed bed was theoretically investigated. It is shown that: 1) the maximum value of biomass temperature of 887 °С is reached in the oxidation zone, where exothermic reactions prevail over endothermic reactions; 2) the specified temperature turns out to be lower than the temperature of the beginning of ash deformation of 1050 °С, which indicates the slag-free operation of the gas generator; 3) the largest yield of gasification products occurs in the redox reaction zone, where heat absorption dominates over heat release; 4) a slag pad is formed near the grate, protecting the grate from overheating; 5) the largest changes in discrete phase movement speeds are observed in the oxidizing and reducing zones of the gas generator from –5.791.10−5 m/s до –1.86.10−5 m/s due to the change in particle diameter from 10 mm to 6.83 mm (ash). Bibl. 12, Fig. 6.

A universal correlation development for film-wise condensation in the presence of non-condensable gases on vertical walls under turbulent free convection

Accurate prediction of steam condensation in the presence of non-condensable gases is essential for accident analysis in nuclear reactor containments. This study uses the steam–air mixture to illustrate the effect of the mixture's compressibility in analyzing steam condensation. Then, a consolidated database of steam condensation on vertical walls was established, and seven typical empirical and semi-empirical correlations were evaluated. Based on heat and mass transfer analogy and curve fitting, a new universal correlation for predicting steam condensation on vertical walls in the presence of non-condensable gases, including binary and ternary mixtures, under turbulent free convection is established, and this correlation can well handle the transition from binary to ternary mixtures using the same formula. More than 90% of predicted results compared with 1027 data points are within the ± 25% error band, and the mean absolute error is 10.6%. The similarity of helium and hydrogen in analyzing steam condensation is discussed.

Financial viability of hydrogen-enriched gas produced adopting air-steam gasification for power generation: A detailed comparative study and sensitivity analysis with air gasification systems

The financial viability of an air-steam gasification system coupled to an internal combustion engine for power generation application was studied. An experimental set-up established key parameters were identified, and a baseline was created using air as an oxidising agent. Air steam mixtures were used as an oxidising agent, emphasising the enrichment of the hydrogen fraction in the syngas, thereby increasing the energy density. The financial analysis was performed based on the experimental data collected from a prototype. An increase in hydrogen fraction has significantly reduced the specific fuel consumption, i.e., from 1.25 to 0.94 kg per kWh. The levelised cost of electricity generation through air gasification is INR 8.85 per kWh. The payback period of air-steam gasification-based power plants is 4.16 years, whereas it is 5.35 years for air-gasification power plants. Adopting an air-steam gasification system improves the financial performance of biomass power plants.

Experimental research on aerosol scrubbing characteristics under steam-air mixture submerged jet condition

The occurrence of severe accidents in nuclear power plants may lead to the leakage of radioactive aerosol. And the scrubbing efficiency of aerosol contained in the air-steam mixture submerged jet is important for assessing the radioactivity in the containment during a severe accident. Several experiments were carried out to analyze the effect of inlet pressure, aerosol diameter, submergence, and steam fraction on the scrubbing efficiency of aerosol in the jet regime. Then, the scrubbing effects of steam and different flow regimes under submerged jet conditions were investigated by comparing the experimental results. The scrubbing efficiency increased with the increase of the aerosol diameter in the air jet regime while the most penetrating region of the aerosol in the steam-air mixture jet regime is 0.2–0.4 μm. When the gas flow characteristic is subcritical flow, as the inlet pressure increases, the scrubbing efficiency increases rapidly. When the critical flow is reached, the inertial effect was the dominant factor in aerosol scrubbing due to the sufficient gas velocity, the scrubbing efficiency under different steam fractions is close to 100%. The scrubbing efficiency increases with the increase of the steam fraction, which may be caused by the increase of the temperature gradient field under subcritical flow conditions. Additionally, the increase the submergence can increase the residence time and improve the scrubbing efficiency. However, due to the decrease of the gas velocity during the gas floating, the scrubbing efficiency in the flow region of the same height is gradually decreasing.