H2O Mass Fraction Research Articles

Ablation behavior at full-temperature ranges of C/SiC in combustion gases containing water vapor

In order to clarify the ablation behavior of C/SiC ceramics in the combustion gases containing water vapor, we proposed a novel ablation model of C/SiC at full-temperature ranges and simulated the ablation behavior of C/SiC ceramics under combustion gases environments by using our program developed in MATLAB. The numerical results indicate that the comparison between the calculation and the experimental data is in good agreement. The surface temperature of C/SiC ceramics is positively correlated with heat flux, enthalpy and pressure, while negatively correlated with the mass fraction of H2O in the combustion gases. Furthermore, the surface recession of C/SiC increases with the increase of heat flux or water vapor content but decreases with the increase of pressure. This study can predict the ablation behavior of C/SiC ceramics in combustion gases environments, and then guide for optimization of C/SiC components in scramjet engines.

Experimental and numerical investigation on thermochemical erosion and mechanical erosion of carbon-based nozzles in hybrid rocket motors

In order to enhance energy characteristics of propellants in hybrid rocket motors, aluminum particles are added into the solid fuel. However, these particles may lead to nozzle mechanical erosion, which significantly affects the motor performance. This paper intends to study thermochemical and mechanical erosion mechanism of carbon-based nozzles in hybrid rocket motors with aluminum metallized fuel. A firing test is performed, and 95 % hydrogen peroxide and hydroxyl‑terminated polybutadiene based fuel with aluminum particles are utilized. Experimental results show that many metal particles are ejected from the nozzle, and aluminum oxide deposits heavily on the nozzle inner surface. A method of numerical calculation coupled with two-phase flow, combustion of aluminum metallized fuel, thermochemical ablation reactions, and mechanical erosion is established. The errors of combustion chamber pressure and throat erosion rate between numerical calculation and test results are 0.53 % and 7.76 %, respectively. Simulation results indicate that with the increase of aluminum content, nozzle wall pressure gradually increases, while the mass fraction of H2O, CO2, OH, and O declines. The nozzle wall temperature and thermochemical erosion rate raise first and then reduce as aluminum content increases. The mechanical erosion is mainly distributed in the convergent section, and it raises with the increase of aluminum content. When aluminum content is up to 38 %, the maximum mechanical and thermochemical erosion rates are 0.09185 mm/s and 0.0976 mm/s, respectively. This reveals that effects of mechanical erosion on hybrid rocket nozzles should be carefully considered and evaluated under conditions of high aluminum content.

Positional effect of vortex generators on the combustion efficiency of the micro combustor fuelled with hydrogen/air mixture

The focus of this study is to explore the effect of vortex generator placement in a planar hydrogen combustor. The optimization of vortex generator placement is crucial for improving combustion efficiency and reducing pollutant emissions in the exhaust by achieving higher combustion. A numerical simulation model was developed using ANSYS- Reynolds-averaged Navier Stokes to examine the effect of vortex generators. Vortex generators were placed at four different locations away from the inlet at distances of 0.25 m, 0.30 m, 0.40 m, and 0.60 m such as 0.25S, 0.3S, 0.4S, and 0.6S models, respectively. Parameters such as combustion temperature, mass fraction of H2, mass fraction of H2O, turbulence intensity, and heat of reactions (HOR) were determined. The flow was assumed to be turbulent and steady, with hydrogen and air used as the fuel mixture. Hydrogen was released from the nozzle at a pressure of 300 bar and the velocity of air was 10 m/s. The strategic placement of vortex generators near the air inlet has been shown to have a significant impact on combustion temperatures and mixing, resulting in notable improvements in H2O formation and peak HOR. Furthermore, the utilization of vortex generators has been observed to enhance velocity magnitude and HOR, with the 0.25S model demonstrating the highest HOR values. 0.25S model also exhibited elevated temperatures and turbulent kinetic energy, indicating its potential for achieving optimal combustion efficiency. However, it is crucial to optimize the design and placement of vortex generators to mitigate disturbances in fuel spray patterns and attain the desired performance levels. Overall, these findings strongly suggest that vortex generators represent a promising technology for enhancing combustion efficiency and reducing emissions in planar combustors.

Flame Surface Density and Artificially Thickened Flame Combustion Models Applied to a Turbulent Partially-Premixed Flame

The Sydney Flame provides an excellent framework for systematic analysis of premixed, partially premixed and non-premixed methane/air combustion. It represents (depending on the axial position from the fuel inlet) non-premixed, partially premixed and fully premixed combustion. We simulate the test case FJ200-5GP-Lr75-57, which represents the partially premixed mode. Large-eddy simulations (LES) are conducted using a flame surface density combustion model (FSD) using one-step chemistry and an artificially thickened flame model (ATF) with a global two-step and an analytically reduced multi-step chemistry reaction mechanism. Unity Lewis numbers are assumed (Le=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Le=1$$\\end{document}) at first. The FSD and ATF models are compared using the same computational mesh, numerical scheme and boundary conditions. Both models will be analysed regarding their accuracy and computational efficiency in the regime of partially premixed combustion. A comparison of the results points out the strengths and weaknesses of the FSD models. The FSD model with inclusion of flame stretch effects yields good agreement with mean experimental temperature, CO2 and H2O mass fraction distributions in contrast to the ATF model using the global two-step mechanism, which overestimates downstream temperature, CO2 and H2O mass fractions. The FSD model performs well in all regions, which are dominated first by premixed, then partially premixed and finally non-premixed combustion along the flame. The ATF multi-step chemistry shows good results only in the premixed mode region, while mean temperature, CO2 and mass fractions are overestimated in the non-premixed mode regions at higher mixture fraction values. Including differential diffusion into the transport equations improved the ATF model results in comparison with experiments. A mesh study revealed, that the ATF model performs only after mesh refinement. In particular results are improved in the non-premixed combustion region. In contrast, the FSD model is less resolution sensitive and performs very well for both meshes. An evaluation of the Wasserstein metric provides a quantitative assessment of different ATF model setups on simulation accuracy. Finally, computational times for all simulation setups are compared.

Influences of operating parameters on uniform mixing behaviors of gas-liquid-solid in novel spouted beds with strengthening components

Influences of integral multi jet(IMJ), swirling blade nozzle(SBN) and longitudinal vortex generators(LVGs) on uniform mixing behaviors of ternary mixture during water vaporization in spouted beds were simulated from the perspective of temperature and velocity fields. To quantitative evaluate the mechanism of water vaporization, temperature uniformity index(Tu), mixing index(IM) and coefficient of variation(CV) were used. Simulation results: the bubble-like distribution of particles caused by LVGs, IMJ and SBN strengthen the gas–solid radial mixing and improve flow “dead zone”. In the upper of system, the promotion of uniformity and mixing quality is SBN > LVGs > IMJ, and LVGs has the most obvious promoting effect on Tu. Moreover, the influences of operating parameters on Tu, IM and mass fraction of H2O(g)(MFH) were investigated. Vgas = 11.2 m/s, Tgas = 520 K, and TWater = 300 K, the liquid–solid mixing quality is the best. In terms of Tu and MFH, Vgas = 11.2 m/s, Tgas = 540 K, and Twater = 400 K have the most obvious effect.

Estimation of Entropy Generation in a SCR-DeNOx System with AdBlue Spray Dynamic Using Large Eddy Simulation

In this work, the entropy generation analysis is extended to the multi-phase fluid flow within a Large Eddy Simulation (LES) framework. The selected study case consists of a generic selective catalytic reduction (SCR) configuration in which the water/AdBlue is injected into a cross-flow of the internal combustion (IC) engine exhaust gas. The adopted numerical modules are first assessed by comparing with experimental data for film thickness in the case of AdBlue injection and then with H2O mass fraction and temperature for water injection case. Subsequently, the impact of heat transfer, fluid flow, phase change, mixing and chemical reaction due to AdBlue injection on the entropy generation is assessed. Hence, the individual contributions of viscous and heat dissipation together with the species mixing, chemical reaction during the thermal decomposition of urea into NH3 and dispersed phase are especially evaluated and analysed. In comparison to the shares of the viscous and mixing processes, the entropy generation is predominated by the heat, chemical and dispersed phase contributions. The influence of the operating parameters such as exhaust gas temperature, flow rate and AdBlue injection on entropy generation is discussed in details. Using a suitable measures, the irreversibility map and some necessary inferences are also provided.

A numerical study of the urban wood waste gasification

Biomass gasification is currently considered a promising technology with regard to the sustainable use of bioenergy to produce power due to its renewable character and relative availability. In this work, an Eulerian model was used to study numerically the behavior of the temperature and velocity fields, as well as the mass fraction of H2O and wood inside of a gasifier under specific conditions. Two-dimensional simulations were carried out, with the software Ansys Fluent, for turbulent flows with different velocities and temperatures imposed on the entrances of the gasifier. Furthermore, the influence of the viscosity on the temperature and velocity fields was also studied. The results reveal that the maximum temperature inside the gasifier increases slightly with the inlet velocity and the turbulence viscosity ratio is lower in the zones with higher velocity. For the inlet temperature of 300 K, the temperature at the center of the gasifier between the two inlets decreases from 647 K to 612 K as the inlet velocity increases from 0.2 to 0.6 m/s.

Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-poor K Dwarf

Abstract Using radial-velocity measurements from four instruments, we report the mass and density of a 2.043 ±0.069 R ⊕ sub-Neptune orbiting the quiet K-dwarf Wolf 503 (HIP 67285). In addition, we present improved orbital and transit parameters by analyzing previously unused short-cadence K2 campaign 17 photometry and conduct a joint radial-velocity-transit fit to constrain the eccentricity at 0.41 ± 0.05. The addition of a transit observation by Spitzer also allows us to refine the orbital ephemeris in anticipation of further follow-up. Our mass determination, 6.26 − 0.70 + 0.69 M ⊕ , in combination with the updated radius measurements, gives Wolf 503 b a bulk density of ρ = 2.92 − 0.44 + 0.50 g cm−3. Using interior composition models, we find this density is consistent with an Earth-like core with either a substantial H2O mass fraction (45 − 16 + 19 %) or a modest H/He envelope (0.5% ± 0.3%). The low H/He mass fraction, along with the old age of Wolf 503 (11 ± 2 Gyr), makes this sub-Neptune an opportune subject for testing theories of XUV-driven mass loss while the brightness of its host (J = 8.3 mag) makes it an attractive target for transmission spectroscopy.

Numerical Investigation on the Effect of Inflow Mach Numbers on the Combustion Characteristics of a Typical Cavity-Based Supersonic Combustor

The air-breathing engines, commonly known as Supersonic Combustor Ramjet (SCRAMJET) engines, are one of the most prominent technologies among researchers due to their high thrust-to-weight ratio. The researchers are constantly making efforts for improved performance of the combustor under the required boundary conditions. The present working computational model studies a hydrogen-fueled parallel cavity scramjet combustor to recognize the complex flow field characteristics and performance of the combustor in Ansys 15.0. The computational model developed is a replica of an experiment conducted in China which slightly modified the boundary conditions. The standard two-equation K- ε turbulence model and Reynolds averaged Navier Stokes (RANS) equation with finite-rate/eddy dissipation species reaction model are used to simulate the problem. The validation of the present model is achieved by comparing the results with already available experimental data in conformity with the literature. The results of the simulations are in satisfactory accord with the experimental data and images. Furthermore, to achieve the stated objective, different incoming Mach numbers, namely, 2.25, 2.52, and 2.75, are considered for a more clear understanding of variables that affects the characteristics of the flow field. The temperature, Mach number, density pressure, and H2O mass fraction contours were studied to facilitate proper understanding. The maximum temperature rise observed is 2711.467 K for M = 2.25. Additionally, the performance parameters, namely, combustion and mixing efficiencies, are also studied. The maximum combustion and mixing efficiencies are 87.47% and 98.15% for M = 2.25 and 2.75, respectively.

Numerical Simulation of Nasal Airflow Aerodynamics, and Warming and Humidification in Models of Clival Chordoma Pre and Post-Endoscopic Endonasal Surgery

ObjectivesTo study the effect of endoscopic endonasal surgery on nasal function for the treatment of clival chordoma. MethodsPre and post-operative computed tomography (CT) scans of a case of chordoma treated with an endoscopic endonasal approach (EEA) were collected retrospectively, and models of the nasal cavity were reconstructed so that a subsequent numerical simulation of nasal airflow characteristics, warming, and humidification could be conducted. ResultsMiddle turbinectomy resulted in redistribution of airflow within the nasal cavity, and the most significant changes occurred in the middle section. Consistent with the results of airflow evaluation, it was found that the change in nasal anatomical structure significantly reduced warming and humidification. Nasal humidification decreased substantially when postoperative loss of mucosa was taken into consideration. The H2O mass fraction of pharynx in inspiration phase were significantly correlated with airway surface-to-volume ratio (SVR). ConclusionsThe EEA for chordoma significantly affected nasal function. Attention should be paid to the protection of nasal structure and the associated mucosa.

Performance analysis of AS-SOFC fuel cell combining single and sinusoidal flow field: numerical study

The performance of a solid oxide fuel cell (SOFC) was examined using 3D computational fluid dynamics to model mass and heat flows inside the channels. In the present investigation, a SOFC fuel cell with a new flow field based on a sinusoidal flow has been studied. The latter was tested and compared with a single flow using ANSYS FLUENT. The obtained results showed that at a given operating voltage, the maximum power for the sinusoidal and the single flow fields were 1.43 and 1.35 W/cm2, respectively. By taking in addition, into account the concentration, activation and Ohmic losses; it was noticed that the distribution of velocity and temperature for the sinusoidal flow led to bettered results. Furthermore, it was observed that the maximum use of H2mass fraction consumed in sinusoidal and single flow field designs were 60% and 55% respectively. Similarly, the highest H2O mass fraction values produced for the sinusoidal and single flow designs were 42% and 34% respectively. This model was validated and confronted to previous data. The present results agree well with reported studies in literature.

Fuel properties, dry matter losses and combustion behavior of wood chips stored at aerobic and anaerobic conditions

Aerobic and anaerobic storage of wood chips from coniferous forest residues, coniferous energy roundwood and short rotation coppice were investigated regarding dry matter losses, energy losses and changes in fuel properties using several approaches, i.e. a field trial with 90 m3 wood chip piles, small-scale storage containers (0.5 m3) incl. greenhouse gas measurements and miniature bunker silos (1.5–2 m3). After storage, selected fuels were combusted in a 30 kW wood chip boiler and emissions (CO, NOX, TPM) were measured.Dry matter losses in fleece-covered piles were 7%–9% after 153 days of storage. Drying compensated for energy losses. Container trials achieved full anaerobic conditions in the lab reducing dry matter losses to 0.4–2% while preserving fuel properties. Methane emissions during anaerobic storage in containers were low. Anaerobic conditions could not be achieved in outdoor bunker silos due to insufficient airtightness. The mass fraction of H2O in fuels increased in bunker silos by 4.2–10.4% due to precipitation and dry matter losses up to 22% were recorded. During combustion, CO and TPM emissions were often increased significantly with materials that were stored in silos or piles compared to technically dried fuels, most likely due to changes in their woody or physical-mechanical structure and their mass fraction of H2O.Anaerobic storage might in theory be an interesting option to reduce dry matter losses but could not sufficiently be realized during this study using miniature bunker silos. For many applications, aerobic storage in fleece-covered piles seems preferable to anaerobic storage.

Disclosure of the internal transport phenomena in an air-cooled proton exchange membrane fuel cell—Part I: Model development and base case study

In this study, the internal transport phenomena and mechanism inside an air-cooled proton exchange membrane fuel cell (PEMFC) are investigated. It helps to understand the factors that affect the performance of an air-cooled PEMFC and optimize the design of Membrane Electrode Assembly (MEA) and the flow field. This series article contains two parts. In this paper, i.e., Part Ⅰ of this series, a three-dimensional, two-phase flow, non-isothermal, steady-state Computational Fluid Dynamics (CFD) model is established to investigate the liquid water generation mechanism and the species distributions inside an air-cooled PEMFC single cell with a Base Case flow field design. Dry hydrogen and ambient air (the relative humidity and the stoichiometry are 60% and 150 separately) are considered for the simulation and validation. It is found that the liquid water appears mostly inside the cathode electrode underneath the cathode rib. Inside the anode gas diffusion layer (GDL), the mass fraction of H2 underneath the cathode ribs is lower than that underneath the cathode channels, while the mass fraction of H2O shows the opposite. The distributions of O2 mass fraction and H2O mass fraction inside the cathode GDL have the same trend as those of H2 mass fraction and H2O mass fraction inside the anode GDL. The membrane water content is periodically distributed from channel to channel and its value underneath the cathode rib is much larger than that underneath the cathode channel. The current density distribution is affected by the distribution of water content, i.e., the part underneath the cathode rib shows a larger current density than that underneath the cathode channel.

Numerical Investigations on the Impact of Turbulent Prandtl Number and Schmidt Number on Supersonic Combustion

The flow field inside the combustor of a scramjet is highly complicated and the related turbulent Prandtl and Schmidt numbers have a significant impact on the effective numerical prediction of such dynamics. As in many cases researchers set these parameters on the basis of purely empirical laws, assessing their impact (via parametric numerical simulations) is a subject of great importance. In the present work, in particular, two test cases with different characteristics are selected for further evaluation of the role played by these non-dimensional numbers: Burrows-Kurkov case and DLR case. The numerical results indicate that these parameters influence ignition location. Moreover, the temperature distribution is more sensitive to them than to H2O mass fraction and velocity distributions.

Thermodynamics of Sea Ice Phase Composition Revisited

AbstractPure ice, brine and solid minerals are the main contributors to sea ice mass. Constitutional changes with salinity and temperature exert a fundamental control on sea ice physical, chemical, and biological properties. However, current estimation methods and model representations of the sea ice phase composition suffer from two limitations—in a context of poorly quantified uncertainties. First, salt minerals are neglected. Second, formulations are inconsistent with international standards, in particular with the International Thermodynamic Equation of Seawater (TEOS‐10). To address these issues, we revisit the thermodynamics of the sea ice phase composition by confronting observations, theory, and the usual computation methods. We find remarkable agreement between observations and the Gibbs‐Pitzer theory as implemented in FREZCHEM, both for brine salinity (RMSE = 1.9 g/kg) and liquid H2O mass fraction (RMSE = 8.6 g/kg). On this basis, we propose expanded sea ice phase composition equations including minerals, expressed in terms of International Temperature Scale 1990 temperature and absolute salinity, and valid down to the eutectic temperature (−36.2 °C). These equations precisely reproduce FREZCHEM, outcompeting currently used calculation techniques. We also suggest a modification of the TEOS‐10 seawater Gibbs function giving a liquidus curve consistent with observations down to the eutectic temperature without changing TEOS‐10 inside its original validity range.

Numerical study of mixed working fluid in an original oxy-fuel power plant utilizing liquefied natural gas cold energy

Oxy-fuel combustion is considered one of the most promising technologies for carbon capture and storage (CCS) in power plant. The working fluid, which is composed of CO2 and H2O, is obligatory to moderate the combustion temperature in oxy-fuel systems. The content of H2O in the working fluid has a significant influence on system performance. An original oxy-fuel power plant with the utilization of liquefied natural gas (LNG) cold energy is proposed, and the H2O content in the working fluid is adjustable in the work. The results reveal that when the H2O mass fraction is less than 0.3, the system efficiency increases with the increase of the H2O content in the working fluid. When the H2O mass fraction in the working fluid rises over 0.3, the system efficiency decreases with the increase of H2O content due to the decrease of the recycling heat carried by H2O. The optimum heat transfer effect of the recirculating H2O is obtained when the H2O mass fraction is 0.3, and the optimal thermal efficiency is 58.3%. Compared to dry cycle, the thermal efficiency of the proposed system is increased by 17.3% under the optimum condition.

Numerical simulation study on different spray rates of three-area water distribution in wet cooling tower of fossil-fuel power station

A coal-burning power plant’s cooling tower can take away about 55% of the heat that the steam absorbs in the boiler, which represents a big energy saving potential. This paper presents a three-dimensional numerical model to analyze the influence of non-uniform water distribution on the cooling performance of a counter-flow wet cooling tower with different spray rates, while providing thermal calculation of a large cooling tower. In addition, the user-defined function in the fill zone is compiled. The heat and mass transfer in the fill zone is solved by UDF. This study covers a three-area water distribution structure in the water distribution system. Cooling tower data verified the accuracy of the model. The influence of the inner, middle and outer areas in relation to their location on the cooling tower and effect on spray rate on the outlet water temperature was investigated in detail. The effect of the three-area water distribution structure on the velocity field, temperature field and the mass fraction of H2O in the tower are analyzed. The water flow rate that makes the temperature drop to its maximum low point has been given. The results show that the outlet water temperature of the tower can be effectively reduced by adopting the three-area water distribution structure and proper water distribution flow. Consequently, it can improve the efficiency of the cooling tower and generate enormous economic benefits.

Numerical analysis on centrifugal compressor with membrane type dryer

Moisture content is a common phenomenon in industrial processes especially in oil and gas industries. This contaminant has a lot of disadvantages which can lead to mechanical failure DEC (Deposition, Erosion & Corrosion) problems. To overcome DEC problem, this study proposed to design a centrifugal compressor with a membrane type dryer to reduce moisture content of a gas. The effectiveness of such design has been analyzed in this study using Computational Fluid Dynamics (CFD) approach. Numerical scheme based on multiphase flow technique is used in ANSYS Fluent software to evaluate the moisture content of the gas. Through this technique, two kind of centrifugal compressor, with and without membrane type dryer has been tested. The results show that the effects of pressure on dew point temperature of the gas change the composition of its moisture content, where high value lead more condensation to occur. However, with the injection of cool dry gas through membrane type dryer in the centrifugal compressor, the pressure and temperature of moisture content as well as mass fraction of H2O in centrifugal compressor show significant reduction.

Effect of gas-phase reaction on catalytic reaction for H2/O2 mixture in micro combustor

The catalytic reaction characteristics of the hydrogen and oxygen mixture in the catalytic micro-combustor were detected by thermocouple, infrared thermal imager and OH-PLIF. The equivalence ratio of transition stage from coupling reaction (coupled homogeneous-heterogeneous combustion) to pure catalytic reaction (heterogeneous combustion) was obtained. The three-dimensional pure catalytic reaction model with detailed catalytic reaction mechanism was established in a rectangular catalytic micro-combustor. The simulation model was validated with experimental data. The effects of the intermediate and final products from gas-phase reactions on the pure catalytic reaction were discussed as well as the effects of gas-phase reactions on the catalytic reaction in the process of coupling reactions were studied. The intermediate product OH radical can improve the hydrogen conversion of the surface reaction, and the effect of O radical is not obvious. The final product H2O has an inhibitory effect on the surface reaction. Since the mass fraction of H2O is much higher than other gas-phase reaction products, the dominant effect of the gas-phase reaction on the catalytic reaction is suppression. In the coupling reactions, the fuel consumed by the gas-phase reaction weakened the catalytic reaction.

Numerical Study of Dynamic Response of Different Fuels Jet Diffusion Flame to Standing Waves in a Longitudinal Tube

In this work, the dynamic response of jet diffusion flame of burning hydrogen and propane respectively in a longitudinal tube to acoustic standing waves produced from a loudspeaker are studied. For this, 2-D numerical simulations are conducted by using FLUENT to investigate the interaction of acoustics-flow-flame. And acoustic fluctuations are generated by using User Defined Function (UDF). The numerical model is validated first by comparing the numerical results with the experimental measurements. To gain insight on the difference between combustion flame of propane and hydrogen, 19 monitors points are set to gain the data of their distribution of pressure, temperature, mass fraction of H2O and velocity in the longitudinal tube. The result indicates that their difference concentrates on the pressure and mass fraction of H2O. The phase diagrams of pressure and velocity show that the hydrogen combustion flame is more stable than propane, which is beneficial for combustion systems.