Dioxide Mixtures Research Articles

A novel concept of enhanced direct-contact condensation of vapour- inert gas mixture in a spray ejector condenser

An analytical model of direct steam condensation (DCC) in the novel idea of spray ejector condenser (SEC) in the presence of inert gas has been developed. It is based on continuity, momentum and energy equations for the steam-carbon dioxide mixture and direct contact condensation mechanisms due to heat transfer and concentration. Crucial in the process of DCC is atomisation of the motive fluid in the ejector. The effect of atomised droplet size is exhibiting a significant amplification influence with increasing size of the droplet. Motive fluid is driving the secondary fluid-mixture of steam and inert gas in the Venturi nozzle and is cold enough to cause direct condensation. The intensity of heat transfer process from steam to water when the phases are in direct contact is much higher than the heat transfer intensity in surface heat exchangers. The analytical model pertains to a subcritical flow of a mixture of steam and gas in SEC. The model exhibits satisfactory agreement with experimental data. The model of DCC predicts higher values of temperature drop between inlet and outlet from the mixing section for the case of smaller steam-CO2 flow rates. Increasing the flow rate of steam mixture from 1.2 g/s to 3.6 g/s results in a reduction of steam mixture temperature from 25 °C to 14 °C respectively, at CO2 flow rate of 6.8 m3/h. Condensation without presence of CO2 in the same range of steam flow rate, i.e. from 1.2 g/s to 3.6 g/s results in reduction of steam mixture temperature from 56 °C to 25 °C respectively, confirming in such way the effect of CO2 presence on the efficiency of DCC. Such model allow for discussion of parameters affecting process of condensation in SEC and ability of application such condenser in power plants.

5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a carbon dioxide binary mixture based compressed gas energy storage system: A comprehensive research and feasibility validation

Recently, the application of carbon dioxide binary working fluids in compressed carbon dioxide energy storage systems has been proposed to improve the system characteristics, especially for the condensation problem of carbon dioxide. Based on the previous research, a more comprehensive 5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a typical transcritical compressed carbon dioxide energy storage system using carbon dioxide binary working fluid is carried out. Propane, propylene, R32, R161, R1234ze, and R1234yf are chosen to compose the binary working fluid with carbon dioxide, respectively. The effect of changing parameters, including pump pressure ratio, compressor isentropic efficiency, and heat exahcnger1 outlet temperature on system performance, is also analyzed. In addition, the feasibility of applying carbon dioxide binary working fluid at high ambient temperature is investigated. According to the results, the performance of heat exchanger1, heat exchanger2, and pump decreases while the performance of the turbine is improved with a higher refrigerant mass fraction from the point of energy level. The compressor, pump, and turbine show potential for optimization according to their higher process energy level difference. The pump power and system operating pressure is reduced at the cost of reducing round trip efficiency when using carbon dioxide binary working fluid. A 1% improvement in compressor isentropic efficiency leads to an increase of nearly 0.4% in round trip efficiency, albeit with reduced turbine power. Increasing the heat exchanger1 outlet temperature from 305 K to 315 K results in a 1% increase in round trip efficiency but with a decrease in the performance of heat exchanger1. Both increasing compressor isentropic efficiency and heat exchanger1 outlet temperature benefit the system economy and exergetic sustainability. A noticeable decrease in system performance is observed when the ambient temperature shifts from 293 K to 303 K. However, this deterioration can be mitigated by raising the pressure of saturated working fluid gas at the compressor inlet. Propylene, R32, and R1234yf are suitable candidates to address the condensation issue, considering the system performance at high ambient temperatures. This paper extends research on the compressed carbon dioxide energy storage system based on carbon dioxide mixtures and provides a reference for the working fluid selection and system optimization for related research.

A Modified Loss Breakdown Approach for Axial Turbines Operating With Blended Supercritical Carbon Dioxide

Abstract In this paper, a modified loss breakdown approach is introduced for axial turbines operating with supercritical carbon dioxide (sCO2) mixtures using computational fluid dynamics (CFD) results. Loss breakdown analysis has been previously developed using two approaches, however each approach has its own uncertainties. The first approach neglects the effects of the cross-interaction between the different loss sources, while the second approach ignores the potential changes to the boundary layer thicknesses and the loss source domains. Although the second methodology accounts for the interactions between the different loss sources, it may produce less accurate predictions for compact machines like sCO2 turbines where the boundary layer may dominate the flow passage. The proposed methodology aims to obtain the turbine loss breakdown using a single CFD model where all sources of aerodynamic loss coexist, while considering variable loss regions defined based on the velocity and entropy distribution results. A steady-state, single-stage, single-passage, three-dimensional numerical model is setup to simulate the turbine and verify the loss audit methodology. The results are verified against the published loss audit methodologies for a 130 MW axial turbine operating with CO2/C6F6 blend, designed using an in-house mean line design code. The results show a good agreement between the proposed approach and the multiple-model approaches from the literature. However, the existing approaches appear to overestimate endwall losses by 13–16% and underestimate the profile losses by 11–31% compared to the proposed approach. Compared to the Aungier mean line loss model, large differences in loss sources are observed from the CFD results, especially for the stator and rotor endwall losses which are found to be 3.2 and 1.6 times the CFD values, respectively. This helps to indicate limitations in existing mean line loss models.

Modeling competitive adsorption and diffusion of CH4/CO2 mixtures confined in mature type-II kerogen: Insights from molecular dynamics simulations

In this study, the adsorption and competitive diffusion of methane (CH4) and carbon dioxide (CO2) mixtures through a molecular model of mature type-2 kerogen was investigated using molecular dynamics simulations. The Dual Control Volume-Grand Canonical Molecular Dynamics method was used to analyze the system and the results were focused on the selectivity of kerogen towards mixtures under a wide range of thermodynamic conditions. The results showed that the adsorption selectivity of CO2/CH4 was around 2–4 and decreased with temperature in the range 350–450 K. The Extended Langmuir (EL) model was found to underestimate the selectivity, and a correction was proposed in the form of the Corrected Extended Langmuir (CEL) model, which improved the estimations of the adsorption of CH4/CO2 mixtures in kerogen with only one adjustable parameter independent of thermodynamic conditions. Interestingly, we noticed that, out of equilibrium, the adsorption selectivity was not affected by the flow conditions when a pressure gradient was imposed, and the CEL model can thus be used to describe the contribution of adsorption to the selectivity under flow conditions. The results showed that the ratio of the collective diffusion coefficients of CH4 and CO2 was around 0.3−0.4, which was about two times lower than other simulations found in the literature. To describe the global selectivity, a simple approach combining the CEL model and the average ratio of diffusion coefficients was proposed, resulting in a selectivity of around 1.

Performance of Various Fuels: Gasoline, Liquefied Petroleum Gas and Biogas from Agricultural Biomass Waste in a Two-Stroke Internal Combustion Engine

The Philippines is an agricultural country with massive agricultural waste. The Biofuels Law (Republic Act 9367) aims to minimize the dependence on fossil fuels and encouraged the use of bio-based fuel sources as an alternative fuel in rural areas where farming is the only source of income, and energy is scarce. Biogas is a renewable energy carrier consisting of methane and carbon dioxide mixture. Because of its improved mixing ability with air, clean-burning nature and high-octane number that resists knocking, biogas is an excellent alternative source of energy for internal combustion engines. The single-cylinder two-stroke spark-ignition (43 cm3) was designed to be fed with a variety of fuel in order to assess engine performance parameters such as brake power, brake speed, brake-specific fuel consumption (BSFC) and thermal efficiency at different throttling positions (low- and high-load throttle). This study evaluated the engine performance of biogas (cow, swine and cow-swine manure), liquefied petroleum gas (LPG) and gasoline with two-stroke engine oil (2T) in a dynamometer without modifying the compression ratio. To optimize its use as a fuel for power generation, biogas was purified using hydrogen sulfide adsorption and carbon dioxide absorption. The results showed that biogas fuel from swine manure generated the highest electrical power load of 761 W with a methane concentration of 51% and a BSFC of 1.4 kg/kW-h. The LPG achieved the highest engine speed at 14,700 rpm with 549 W. In conclusion, the purified biogas fuel can be used in a small-scale internal combustion engine.

Investigation on solid-liquid equilibrium for binary mixtures of carbon dioxide (R744) and alkanes: Propane (R290) and isobutane (R600a)

The solid-liquid equilibrium (SLE) of binary systems containing carbon dioxide (R744) and alkanes propane (R290) and isobutane (R600a) was experimentally investigated. A novel experimental setup using the cooling curve method was designed, built and verified, enabling SLE measurements at temperatures down to 173 K. The temperature and pressure of the triple point of carbon dioxide (CO2) were measured. The results for R744 and the binary mixture of carbon dioxide and propane were in agreement with the available literature data, demonstrating the accuracy of the experimental setup. Activity coefficients were determined for the binary mixtures studied. The Schröder and Wilson equations were used to calculate solubility over various temperatures and compositions. The Wilson model produced a very accurate correlation for the studied non-ideal binary mixtures, while the Schröder equation did not provide satisfactory results. Determined activity coefficients and SLE curves should be useful for the design of low-temperature refrigeration systems operating on carbon dioxide mixtures with low global warming potential.

Design and studies of thick Gas Electron Multipliers fabricated in India

THick Gas Electron Multipliers (THGEMs) are robust and high gain Micro Pattern Gaseous Detectors which are economically manufactured by standard drilling and etching of thin printed circuit boards. In this paper, we present our recent simulation as well as experimental studies on THGEMs which have been fabricated in India using local expertise. Two types of THGEMs have been fabricated; one set has holes without any external rim and another set has holes with rims. These detectors have been characterized using argon-carbon dioxide and argon-isobutane gas mixtures. Electron transmission, effective gain, energy resolution, optimized working range and charging up studies have been presented for both the sets of THGEMs.

Confirmatory evaluation of eFUME for control of brown marmorated stink bug, Halyomorpha halys (Hemiptera: Pentatomidae).

The governments of Australia and New Zealand require a phytosanitary treatment to control adult brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), as overwintering aggregations have been intercepted in the importation pathway of various nonhorticultural consignments, including vehicles. The commercialized fumigant, eFUME, a 16.7% by mass dilution of ethyl formate in carbon dioxide, resulted in complete control of ca. 1,000 field-collected, naturally diapausing adult H. halys in each of 3 independent trials at 10 ± 0.5 °C (x¯±2s) when ethyl formate levels in enclosure headspace were maintained steady-state at ca. 14.5 mg/liter for 4 h to yield Ct exposures ranging from 57.9 to 63.1 mg/liter h. Consistent with previous findings where greenhouse reared H. halys were controlled using laboratory formulations of this ethyl formate-carbon dioxide mixture, these confirmatory methods and results further inform technical and operational features of commercial practice.

Performance analysis of the refrigeration system for improving energy efficiency

Refrigeration system holds an important role in many industrial processes. The global industrial refrigeration system market is expected to grow from USD 19.3 billion in 2019 to USD 25.7 billion by 2025, at a CAGR of 4.7%. The traditional systems (cascade/multistage) as well as hybrid system with non-zeotrope refrigerant blends are widely used for processes where more than one temperature level is required. The optimal utilization of energy saving technologies in industrial processes is a key issue for the rational use of energy resources in the process industry. Among the various existing energy saving means, the refrigeration system is a technology area that introduces several degrees of freedom. The goal is to identify the optimal refrigerant/refrigerant mixtures, the optimal temperature levels, and the best cycle's configuration to satisfy the refrigeration requirements of a technological process. It is common that hydrocarbons have great thermodynamic properties, making them efficient refrigerants. The problem is that hydrocarbons are highly flammable, it has restricted their wider adoption for some applications in the refrigeration industry, mostly for applications demanding large refrigerant charges. Targeting to reduce safety as well as regulatory problems getting up from the use of hydrocarbons, the performance of hydrocarbons and carbon dioxide mixtures as refrigerants in a standard vapor-compression cycle has studied. To take into account all energy losses in the compressor, a technique was used that allows one to assess the energy perfection of a hermetically sealed compressor during experimental studies. The given method contains indicators that estimate certain types of energy losses of a hermetic compressor using the electrical efficiency of the compressor.

In Vitro Photo-Catalytic Degradation of Chloramphenicol Using Pharmaceutical Wastewater

Abstract: In this work, the performance of composite membranes for the treatment of Chloramphenicol (CAP) pollutants was investigated from pharmaceutical industrial wastewater. The composite membrane was under operated with different concentrations of CAP with Titanium dioxide (TiO2) in 10mg/L, 20mg/L and 30 mg/L. The composite membranes were cross-linked with glutaraldehyde for the elimination of H2SO4. Characterizations of synthesized composite membranes were carried out to analyze functionality, morphology, and hydrophilic behaviours. In continuous operation, the different time intervals of TiO2 were removed in centrifuging. The performance of the composite membrane is the removal of pollutant CAP by UV analysis, and kinetics model at different concentrations. The degree of swelling and contact angle were measured in different concentrations of CAP at TiO2. Liquid Chromatography (LC) is used to CAP with Titanium dioxide mixtures. Mass Spectrometry (MS) can be used for structural identity with high specificity. The MS is also used to analyze CAP from pharmaceutical industrial wastewater. The membranes were subjected to filtration of pharmaceutical wastewater which gave a maximum rejection of 95% of Chloramphenicol.

In Vitro Photo-Catalytic Degradation of Chloramphenicol Using Pharmaceutical Wastewater

Abstract: In this work, the performance of composite membranes for the treatment of Chloramphenicol (CAP) pollutants was investigated from pharmaceutical industrial wastewater. The composite membrane was under operated with different concentrations of CAP with Titanium dioxide (TiO2) in 10mg/L, 20mg/L and 30 mg/L. The composite membranes were cross-linked with glutaraldehyde for the elimination of H2SO4. Characterizations of synthesized composite membranes were carried out to analyze functionality, morphology, and hydrophilic behaviours. In continuous operation, the different time intervals of TiO2 were removed in centrifuging. The performance of the composite membrane is the removal of pollutant CAP by UV analysis, and kinetics model at different concentrations. The degree of swelling and contact angle were measured in different concentrations of CAP at TiO2. Liquid Chromatography (LC) is used to CAP with Titanium dioxide mixtures. Mass Spectrometry (MS) can be used for structural identity with high specificity. The MS is also used to analyze CAP from pharmaceutical industrial wastewater. The membranes were subjected to filtration of pharmaceutical wastewater which gave a maximum rejection of 95% of Chloramphenicol.

Experimental Determination of a Chiral Ternary Solubility Diagram and Its Interpretation in Gas Antisolvent Fractionation

Although crystallization has been widely applied for the enantiomeric enrichment of non-racemates both in research and in industrial applications, the physical-chemical background of chiral crystallizations is not as frequently discussed. A guide for the experimental determination of such phase equilibrium information is lacking. In the current paper, the experimental investigation of chiral melting phase equilibria, chiral solubility phase diagrams and their application in atmospheric and supercritical carbon dioxide-assisted enantiomeric enrichment is described and compared. Benzylammonium mandelate is a racemic compound; it shows eutectic behavior when molten. A similar eutonic composition was observed in its methanol phase diagram at 1 °C. The influence of the ternary solubility plot could be unequivocally discovered in atmospheric recrystallization experiments, which proved that the crystalline solid phase and the liquid phase were in an equilibrium. The interpretation of the results obtained at 20 MPa and 40 °C, using the methanol-carbon dioxide mixture as a pseudo-component, was more challenging. Although the eutonic composition was found to be the limiting enantiomeric excess value in this purification process as well, the high-pressure gas antisolvent fractionation results were only clearly thermodynamically controlled in certain concentration ranges.

Carbon dioxide and acetone mixtures as refrigerants for industry heat pumps to supply temperature in the range 150–220 oC

Industry decarbonization is a key a challenge towards the transition to climate neutrality. Indeed, there is a need to satisfy heat at temperatures higher than 150 °C in relevant industrial sectors by upgrading lower temperature heat flows, such as heat from renewable heat sources, ambient heat or industrial waste heat. High temperature heat pumps (HTHP) can upgrade such heat flows enabling great savings in carbon emissions. New refrigerants are needed to develop HTHPs achieving high performances at high temperatures. This paper proposes the use of a new zeotropic mixture composed of carbon dioxide and acetone as the refrigerant of HTHPs working in the temperature range of 150–220 °C. The new fluid is compared with existing pure refrigerants currently used. The thermodynamic characterization of the CO2/acetone mixtures shows temperature glides below 50 K for CO2 mass fractions up to 10%. The best HTHP performance is shown for the mixture 5% CO2/95% acetone in mass fraction. For instance, such a mixture obtains a COP of 5.63 when the target outlet sink temperature is 200 °C and the temperature difference between the outlet heat sink and the inlet heat source is 70 K, showing an improvement of 46% compared to pure acetone.

Effect of Steam to Carbon Dioxide Ratio on the Performance of a Solid Oxide Cell for H2O/CO2 Co-Electrolysis

The mixture of H2 and CO, the so-called syngas, is the value-added product of H2O and CO2 co-electrolysis and the feedstock for the production of value-added chemicals (mainly through Fischer-Tropsch). The H2/CO ratio determines the process in which syngas will be utilized and the type of chemicals it will produce. In the present work, we investigate the effect of H2O/CO2 (steam/carbon dioxide, S/C) ratio of 0.5, 1 and 2 in the feed, on the electrochemical performance of an 8YSZ electrolyte-supported solid oxide cell and the H2/CO ratio in the outlet, under co-electrolysis at 900 °C. The B-site iron doped lanthanum strontium chromite La0.75Sr0.25Cr0.9Fe0.1O3-δ (LSCF) is used as fuel electrode material while as oxygen electrode the state-of-the art LSM perovskite is employed. LSCF is a mixed ionic-electronic conductor (MIEC) operating both under a reducing and oxidizing atmosphere. The cell is electrochemically characterized under co-electrolysis conditions both in the presence and absence of hydrogen in the feed of the steam and carbon dioxide mixtures. The results indicate that under the same concentration of hydrogen and different S/C ratios, the same electrochemical performance with a maximum current density of approximately 400 mA cm-2 is observed. However, increasing p(H2) in the feed results in higher OCV, smaller iV slope and Rp values. Furthermore, the maximum current density obtained from the cell does not seem to be affected by whether H2 is present or absent from the fuel electrode feed but has a significant effect on the H2/CO ratio in the analyzed outlet stream. Moreover, the H2/CO ratio seems to be identical under polarization at different current density values. Remarkably, the performance of the LSCF perovskite fuel electrode is not compromised by the exposure to oxidizing conditions, showcasing that this class of electrocatalysts retains their reactivity in oxidizing, reducing, and humid environments.

Mapping of Greenhouse Gas Concentration in Peninsular Malaysia Industrial Areas Using Unmanned Aerial Vehicle-Based Sniffer Sensor

The increasing concentration of greenhouse gas (GHG) emissions due to increased fossil fuel consumption for manufacturing activities to support population growth is worrisome. Carbon dioxide (CO2) and methane (CH4) remain the two GHGs that contribute to the impact of global warming, and inventorying their concentrations is important for monitoring their changes, which can be used to infer their emissions over time. Hence, this article highlights sniffer4D, an unmanned aerial vehicle (UAV)-based air pollutant mapping system that visualise and analyse three-dimensional (3D) air pollution data in real time, for mapping GHGs concentrations within industrial areas. Consequently, GHGs concentrations for two industrial and adjacent residential areas in Johor, Peninsular Malaysia were mapped. The GHGs concentrations were validated using a ground-based portable gas detector. The results revealed that CO2 has the highest concentration mean of 625.235 mg/m3, followed by CH4 with a mean of 249.239 mg/m3. The mapped UAV GHG concentration also reported good agreement with the in situ observations with an RMSE of 7 and 6 mg/m3 for CO2 and CH4 concentration, respectively. Ozone and nitrogen dioxide mixture (O3 + NO2) with a mean concentration of 249 μg/m3 and an RMSE of 9 μg/m3 are the remaining significant concentrations reported. This approach shall assist in fast-tracking the United Nations climate change mitigation agenda.

Techno-economic and environmental assessment of a novel co-generation system integrating heat pump with Allam cycle

Allam cycle is known as a promising alternative cycle for power generation, which combines the advantage of both oxygen-enriched combustion technology and supercritical carbon dioxide technology. In this study, an integrated energy system consisting of an Allam cycle and a heat pump is proposed to co-generate power and heat. The heat of carbon dioxide in the compression train of the Allam cycle is recovered by the heat pump system, which is used for space heating. The techno-economic and environmental performances of the co-generation system are analyzed and compared with those of the single systems. The results show that the net electrical efficiency of the Allam cycle is improved by 1.56 %, and the coefficient of performance of the heat pump in the combined system is increased by 42.02 %. The lowest and highest investment-increment payback periods are 0.26 and 5.80 years, which indicates the proposed integrated system is economically feasible. Meanwhile, the sensitivity analysis of key economic parameters is also conducted. Finally, the carbon emission of different generation configurations are compared and the results indicate that the integration of the heat pump with the Allam cycle can effectively reduce system carbon emission. The proposed concept provides a new approach to efficient utilization of the heat from the carbon dioxide mixture cooling process for heat and power generation with nearly zero emission, and it would be a better choice for cold regions.

Study of impact strength of C-Mn-Si composition metal after wire-arc additive manufacturing (WAAM)

The results of study of impact strength of C-Mn-Si composition metal after wire-arc additive manufacturing (WAAM) are presented. It was established that destruction of the samples of such composition at the temperatures below tough-brittle transition occurs both via tough and brittle mechanisms. The samples manufactured in the direction along built-up welding are characterized by essentially lower impact strength comparing with those manufactured in vertical direction of samples cutting. Impact strength of the samples made of 09G2SA standard steel is substantially lower than for C-Mn-Si composition metal which was obtained via additive technology. Fractographic analysis of fractures for C-Mn-Si compositions manufactured via additive technology using carbon dioxide and gas mixture displays tough pit destruction type. The samples with high impact strength are characterized by forming of cleavage facets after tough crack propagation to the sample middle, what is accompanied by significant widening opposite to a notch and narrowing under a notch. The samples with low impact strength are characterized by forming of brittle fracture directly under a notch without essential sample plastic deformation. It is shown that built-up welding with partial or complete recrystallization of rolls is required for forming of cold-resistant metal structure. In this case, order of rolls location, heat input and parameters of welding conditions make the direct effect on shape, geometrical dimensions, fusion penetration and number of rolls, as well as on size and morphology of the structural components, percent relation between cast and recrystallized microstructure of seam metal. The complex of these factors finally determines structural state and cold resistance of seam metal. The materials for this publication were prepared using the results of investigations, which were conducted within the framework of the program of activity of "Baikal" interregional educational center of global level, according to the priority direction "Processing of industrial wastes", with use of equipment of the Shared knowledge center of isotope and geochemical researches of the Institute of Geochemistry of RAS Siberian branch.

METHODS TO REDUCE NOX FORMATION DURING GAS COMBUSTION IN BOILERS

A study of reduction of nitrogen oxides emissions using various methods and their combinations on operational typical steam and water heating boilers of Ukraine during combustion gas fuels was conducted. The experimental research of the power steam TGMP-314 boiler showed that when volume thermal stress of the firebox was reduced to qv » 0.09 MW/m3 (55 % of the nominal power), and the flue gas recirculation factor r = 17 %, the nitrogen oxides emissions were reduced by 75 % and they almost meet the requirements of the IED directive. This measure to reduce emissions of nitrogen oxides is also possible for other types of boilers, and it is advisable to implement for those combustion plants with an excess capacity of about 40–50 % and which have exhausted their factory-designated resource. On the water heating boiler KVGM-180, equipped with standard gas recirculation smoke exhauster, the research was conducted with aim to reduce of NOx emissions at combustion natural gas with recirculation of flue gases into the blowing air. NOx emissions were reduced by 67% to European standards, and the concentration of carbon monoxide in flue gases was below СО≤100 mg/Nm3 (at 3% O2) by a recirculation factor was of about r = 30%. The standard burners in the KVGM-180 boiler are two flow of air and can be considered a type of staged combustion burners. That is, in this case, a combination of the staged combustion burners and flue gas recirculation into blowing air was used. The research of combustion a methane and carbon dioxide mixture in the ratio of CH4 (76 %) and CO2 (24 %) (biogas) with regard to reduce the formation and emissions of nitrogen oxides in the DKVR-6.5-13 steam boiler was conducted. The obtained level of NOx in the flue gases is within the range of 63–76 mg/Nm3 (at 3 % O2), which fully complies with the EU standards for the operation of CP from 1 MW on natural gas and other gas fuels. Bibl. 34, Fig. 3, Tab. 1.

Impact of carbon dioxide and nitrogen addition on the global structure of hydrogen flames

Investigations into the combustion characteristics and flame structure of hydrogen/carbon dioxide/air flames have been carried out experimentally and numerically. The aim was to determine the variations of the combustion properties and flame shape for different carbon dioxide dilutions in the H2-air mixtures. For this purpose, premixed flames at various compositions of hydrogen-carbon dioxide mixtures are investigated experimentally in a heat flux burner configuration at varying equivalence ratios from 0.5 to 1.1, fresh gas temperatures and under atmospheric conditions. Optical investigations are performed to detect the number of cellular structures on the flame front. Furthermore, the laminar burning velocity and the influence of carbon dioxide addition were examined numerically. A detailed kinetic mechanism was implemented for the identification of the most representative intermediates via a reaction path analysis, and the most influential species and reactions are identified through sensitivity analyses at conditions relevant to the studied application. Considering the nature of the adopted mechanism, the presence of CO2 has the potential to shift the production/consumption rate of some hydrogen-containing radicals. Hence, numerical investigations employing an inert species having the same thermodynamic and transport properties as CO2 (referred to as fictitious CO2, FCO2) were compared and discussed in this work. To investigate the effect of CO2 on the dynamics of the hydrogen flames, one-dimensional and two-dimensional detailed simulations of the flame structure have been carried out. The addition of CO2 makes the flame more prone to thermo-diffusive instabilities through a decrease in the mixture’s thermal diffusivity. This results in a decrease of the Markstein number and an enhanced formation of characteristic cellular structures on spherically expanding flames. Overall, the comparison between the experimental and numerical investigations reveals similar conclusions.

Simulation of complex transient flows in geothermal wells

In a recent paper we discussed the development of a new transient geothermal wellbore simulator. In the present paper we discuss the application of this simulator to the modelling of challenging and interesting flows that occur in a geothermal wellbore. The first group of problems involve the opening and closing of hot geothermal wells with rapid transient flows. In some cases, this involves counter-flow with steam flowing upwards and liquid water flowing downwards. The final test case in this category is the simulation of a completion test which involves four stages: cold water injection, heating up of a shut-in well, discharge of the well to the atmosphere, connection of the well to a separator.Simulation of well stimulation by air-lifting and air-compression demonstrate the capability of the simulator for modelling flows of air-water mixtures with a moving interface between the phases.Finally, we demonstrate the ability of the simulator to model injection of water-carbon dioxide mixtures, with an increasing proportion of CO2. This is of particular importance as operators look to carbon sequestration as a way of mitigating green-house gas emissions from geothermal power plants.These are a selection of the more interesting problems of the many test cases that were used during the development of our simulator to ensure that it is robust and can simulate the full range of complex transient flows that can occur in a geothermal well.