H2 Mass Fraction Research Articles

Numerical simulation of seasonal underground hydrogen storage: Role of the initial gas amount on the round-trip hydrogen recovery efficiency

Subterranean structures such as aquifers and depleted gas reservoirs (DGRs) offer a scalable, high-pressure, secure, cost-efficient, and ecologically friendly means of hydrogen (H2) storage. Underground H2 storage (UHS) has emerged as a potential solution to alleviate the imbalance between the fluctuating renewable energy generation and the demand for a constant energy supply. Quantifying the recovery efficiency is of paramount importance in the effort toward large-scale UHS. In this numerical simulation study, we employed a high-resolution grid for the discretization of a synthetic (but realistic) heterogeneous anticline intended as a H2 storage facility, and we assessed the H2 recovery efficiency, and the purity of produced gas associated with UHS in natural reservoirs involving different pre-existing gases and their quantities. All of these studies included an initial phase of cushion gas injection, followed by 4 cycles of H2 storage operations composed of injection-idle-withdrawal periods. The simulation results indicated that the H2 round-trip recovery efficiency RH increased (a) with an increasing number of storage cycles, routinely exceeding 90% and providing evidence of a self-enhancement or self-optimization H2 recovery mechanism and (b) with an increasing amount of pre-existing gas in the storage zone prior to the H2 injections — at the end of the 4-cycle test, the highest RH is associated with a DGR with a pre-existing gas consisting of residual CH4 and additional injected N2, and the lowest RH corresponds to an aquifer with no cushion gas. Conversely, the H2 mass fraction of the produced gas FHQ (a) increased with an increasing number of storage cycles, but (b) decreased rapidly with an increasing amount of pre-existing gas. The presence of a pre-existing gas inevitably leads to severe contamination of the produced H2, which never exceeds 40% in the produced gas, can be as low as 4% in early cycles, and cannot be used as a H2 fuel without gas separation. Aquifer storage without a cushion gas may exhibit the lowest H2 recovery (about 75% in the long run), but yields practically pure H2 that does not require further processing before use. A positive conclusion is that, under the conditions of this study, total H2 losses (including H2 escaping into the caprock, and inaccessible H2 dissolved in the aqueous phase of the formation or remaining in the gas storage zone) are limited and manageable, indicating the technical feasibility of geologic H2 storage.

Simulations of early structure formation: Properties of halos that host primordial star formation

Context. Population III (pop III) stars were born in halos characterised by a pristine gas composition. In such a halo, once the gas density reaches nH ∼ 1 cm−3, molecular cooling leads to the collapse of the gas and the birth of pop III stars. Halo properties, such as the chemical abundances, mass, and angular momentum can affect the collapse of the gas, thereby leading to the pop III initial mass function (IMF) of star formation. Aims. We want to study the properties of primordial halos and how halos that host early star formation differ from other types of halos. The aim of this study is to obtain a representative population of halos at a given redshift hosting a cold and massive gas cloud that enables the birth of the first stars. Methods. We investigated the growth of primordial halos in a ΛCDM Universe in a large cosmological simulation. We used the hydrodynamic code RAMSES and the chemical solver KROME to study halo formation with non-equilibrium thermochemistry. We then identified structures in the dark and baryonic matter fields, thereby linking the presence or absence of dense gas clouds to the mass and the physical properties of the hosting halos. Results. In our simulations, the mass threshold for a halo for hosting a cold dense gas cloud is ≃7 × 105 M⊙ and the threshold in the H2 mass fraction is found to be ≃2 × 10−4. This is in agreement with previous works. We find that the halo history and accretion rate play a minor role. Here, we present halos with higher HD abundances, which are shown to be colder, as the temperature in the range between 102 − 104 cm−3 depends on the HD abundance to a large extent. The higher fraction of HD is linked to the higher spin parameter that is seen for the dense gas.

Study of hydrogen injection strategy on fuel mixing characteristics of a free-piston engine

The formation of the gas mixture in the cylinder has a significant effect on the combustion and emission of the engine. The main difference between a conventional engine and a free piston engine is that the piston movement mode is different. Therefore, a new coupled iterative method is adopted in this paper to study the injection position and duration of hydrogen fuel in a free piston engine where diesel fuels hydrogen, and reveal its influence on gas mixing and combustion in the cylinder of a free piston engine. The results show that it is suitable to spray hydrogen 55 mm from TDC. At this time, the mass fraction of H2 in the cylinder is relatively uniform, the cumulative heat release is about 620 J, and the pressure and temperature are relatively low, which are 7.2 MPa and 1529 K respectively. The duration of hydrogen injection is 0.4 ms, at this time, the mixing degree in the cylinder and the gas flow speed are better, although there is a little shortage of unburned equivalent ratio, but this has little impact on the overall, and the final cumulative heat release reaches 655 J.

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.

CO and [C ii] line emission of molecular clouds: the impact of stellar feedback and non-equilibrium chemistry

ABSTRACT We analyse synthetic 12CO, 13CO, and [C ii] emission maps of molecular cloud (MC) simulations from the SILCC-Zoom project. We present radiation, magnetohydrodynamic zoom-in simulations of individual clouds, both with and without radiative stellar feedback, forming in a turbulent multiphase interstellar medium following on-the-fly the evolution of e.g. H2, CO, and C+. We introduce a novel post-processing routine based on cloudy which accounts for higher ionization states of carbon due to stellar radiation in H ii regions. Synthetic emission maps of [C ii] in and around feedback bubbles show that the bubbles are largely devoid of [C ii], as recently found in observations, which we attribute to the further ionization of C+ into C2+. For both 12CO and 13CO, the cloud-averaged luminosity ratio, $L_\rm {CO}/L_\rm {[C\, \small {II}]}$, can neither be used as a reliable measure of the H2 mass fraction nor of the evolutionary stage of the clouds. We note a relation between the $I_\rm {CO}/I_\rm {[C\, \small {II}]}$ intensity ratio and the H2 mass fraction for individual pixels of our synthetic maps. The scatter, however, is too large to reliably infer the H2 mass fraction. Finally, the assumption of chemical equilibrium overestimates H2 and CO masses by up to 150 and 50 per cent, respectively, and $L_\rm {CO}$ by up to 60 per cent. The masses of H and C+ would be underestimated by 65 and 30 per cent, respectively, and $L_\rm {[C\, \small {II}]}$ by up to 35 per cent. Hence, the assumption of chemical equilibrium in MC simulations introduces intrinsic errors of a factor of 2 in chemical abundances, luminosities, and luminosity ratios.

Detached eddy simulation of the heat release characteristics of H2-O2 reacting flow in supercritical water

The mild H2-O2 reaction is critical for coal-gasification-based polygeneration of power and heat in supercritical water. Time-averaged methods turbulence studies cannot accurately predict the flow, reaction, and heat release during the start-up of the H2-O2 reaction, which was crucial for the start-up and safe operation of supercritical water environment oxidation reactors (SCOR). In contrast, ordinary time-accurate method studies require a tremendous computational effort. Detached eddy simulation (DES), a hybrid model, could balance numerical simulation's computational accuracy and speed. Consequently, this paper has conducted a DES investigation on the start-up process of H2-O2 reaction in SCW with detailed kinetics. Through this article, the spatio-temporal distribution and reaction structure of the H2-O2 reaction start-up process had been unveiled. The process could be divided into the transition and the steady stage, with H2 mass fraction (XH2) and inlet temperature significantly affecting the H2-O2 reaction start-up process. Moreover, the stability of the H2-O2 reaction start-up process was heavily influenced by the XH2. This numerical study could guide the design, scale-up and optimization of SCOR.

NUMERICAL SIMULATION STUDY ON THE REACTION PERFORMANCE OF A METHANOL STEAM REFORMING TO HYDROGEN MICROREACTOR

Hydrogen has received widespread attention as a new clean energy in order to reduce the carbon emissions of fuel vehicles. This paper studies a tubular microreactor based on methanol steam reforming. Methanol and steam are mixed in proportion and the chemical reaction takes place in a porous catalytic bed. For heating purposes, hot gas from the burner penetrates the reactor bed through heating tubes. Energy is supplied through the heating tubes to drive the endothermic reaction system. The microreactor is enclosed in an insulated jacket. In this paper, parameters such as methanol conversion and hydrogen concentration are evaluated by considering microreactor materials, heating gas temperature and flow direction, heating tube distribution, pressure drop and reaction channel length. First of all, choosing a microreactor material with a smaller thermal conductivity can avoid excessive heat loss, and improve heat transfer performance. Increasing the heating gas temperature leads to an increase in the temperature of the reaction zone, thereby increasing the CH3OH conversion rate and H2 mass fraction. Changing the flow direction of the heating gas affects the reaction rate, but has little effect on the reaction result. Through the research on the distribution of the heating tubes, the results show that the hydrogen production rate is higher when the contact area between the heating tubes and the reaction zone is larger. Secondly, through the comparison of the data under different pressure drops, the best parameter [Formula: see text][Formula: see text]pa is obtained, and the CH3OH conversion rate is 80.6% at this time. Finally, increasing the length of the reaction channel can make the reaction more complete. For example, when the reaction channel length [Formula: see text][Formula: see text]m, the CH3OH conversion rate is as high as 83.7%.

Computational fluid dynamics study of Y3+-doped Ba(Ce,Zr)O3 based single channel proton ceramic fuel cell

Theoretical studies using Computational Fluid Dynamics (CFD) modeling have been established in the field of polymer electrolyte membrane fuel cells (PEMFCs) and oxygen ion solid oxide fuel cells (O2-SOFCs). However, its implementation in the proton ceramic fuel cell (PCFC) development is still in progress and very limited literature can be found. Thus, in this simulation study, ANSYS 2022 CFD software has been employed to predict hydrogen mass fraction distribution and power density of a single-channel PCFC operating in 100 % hydrogen fuel. This simulation utilized input data based on previously published experimental works. The mass fraction of H2 was 0.0 at the cathode area indicating that the electrolyte layer is fully dense and no leakage of H2 from the anode area into the cathode area. The maximum power density in 100 % H2 was 0.34 W/cm2 at 800° C. This is in agreement with the power density produced by the in-house fabricated button cell with the configuration of NiO-BCZY|BCZY|LSCF (BCZY=BaCe0.54Zr0.36Y0.1O2.95, LSCF=La0.6Sr0.4Co0.2Fe0.8O3-δ.) that showed a maximum power density of 0.33W/cm2 in 100 % H2. This analysis will contribute to insight information on the relationship between fuel mass fraction distribution and fuel cell performance for future improvements in the field of PCFC.

Flame dynamics of hydrogen/air mixture in a wavy micro-channel

The focus of this work is the numerical study of stable and pulsatory flame burst in an undulating geometry, using premixed hydrogen and air (with an equivalence ratio of φ = 1.0). This work extends other works in the literature by considering a linear temperature profile along the wall. This allows an analysis of the flow dynamics without forcing the location of the flame (as is the case with hyperbolic temperature profiles). The interaction between the flow dynamics and the combustion reaction is then analysed, leading to a better understanding of the physics in more general flows.Simulations were performed in OpenFoam using very detailed chemical reactions and different molecular diffusivities for each species. The results obtained show that at low inlet velocity (4 m/s) the flame became stable, and, at higher inlet velocities, the flame showed pulsatory burst dynamics. The interaction between the fluid dynamics and the combustion response proved to be important, especially because of the vortices that are formed due to the nonlinear geometry of the burner. As the inlet velocity increases, the heat release rate transmitted through the vortices decreases and a delay in ignition occurs, as evidenced by a decrease in the pulsatory burst frequency and an increase in the maximum value of the heat release rate (although not sufficient to increase the maximum temperature amplitude).In addition, we also carried out an analyses of the axial velocity and of the H2 and OH mass fractions of the flame dynamics.

Numerical investigation on the performance of PEMFC with rib-like flow channels

An innovative flow channel inspired by the physical structure of the human rib was developed in this paper. The performance of a proton exchange membrane fuel cell (PEMFC) with the proposed rib-like flow channels under different flow patterns and relative humidity of anode (RH_a) was investigated. Compared with the conventional interdigitated flow channel (CIFC) and cross-flow channel (CRFC), the maximum current density of the counter-flow channel (COFC) was 1.06 A/cm2 at 0.4 V, with enhancements of 4.95% and 2.91%, respectively. In addition, the quantity referred to as non-uniformity N was introduced to quantify the concentration distribution of oxygen, the minimum non-uniformity N of 0.17 was obtained for CRFC, and the COFC exhibited a more uniform concentration distribution of temperature as compared with the CIFC and CRFC, indicating that the COFC would prevent the occurrence of local hot spots. The maximum net power density of COFC was 6.0% and 3.0% higher than that of the CIFC and CRFC. Finally, the maximum current density of RH_a = 30% was 1.06 A/cm2, which was 3.9% and 7.1% higher than that of RH_a = 60% and RH_a = 100%. The temperature with RH_a = 100% was more uniform in comparison with RH_a = 30% and RH_a = 60%, and the mass fraction of H2 decreased with the increase of values of RH_a. The proposed rib-like flow channel can further enrich PEMFC flow channel design and afford novel insights into the application of bionics in fuel cells.

Sustainability analysis and optimization of innovative geothermal-driven energy storage system for green production of H2, NH3, and pure O2

Significant increase of greenhouse gas emissions and the emergence of global warming have drawn more attention to the use of renewable energies. In the pursuit of this objective, a novel geothermal-driven system consisting of steam and organic Rankine cycles, high-temperature solid oxide electrolysis cell (SOEC), and thermoelectric generator (TEG), NH3 synthesis unit is proposed for power, NH3/H2/O2 productions. The produced hydrogen is completely consumed. Fraction of hydrogen produced by SOEC is injected into the boiler for power generation through the SRC, and the remaining is fed into an ammonia synthesis unit to produce NH3. Moreover, the TEG is used as the condenser to increase system efficiency through waste heat recovery. The proposed system is comprehensively analyzed from energy, exergy, economic, and sustainability perspectives. Also, parametric analysis is conducted to evaluate the effect of important design parameters such as geothermal mass fraction ratio, H2 mass fraction ratio, N2 feeding rate, ammonia reactor pressure, and temperature on the performance and economic indicators of the power plant. Furthermore, comparative multi-objective optimization via the evolutionary genetic algorithm (NSGA-II) is developed in MATLAB to optimize the energy system. Moreover, two different scenarios for the optimization process were considered to compare the optimum solution points with each other. The results show that considering sustainability index and total cost rate as the target functions, by assigning the (m2˙m˙10) = 250, ΔTpp = 11.83, j = 2400 A/m2 and (m˙24m˙23) = 0.76, the highest achievable sustainability index and minimum cost rate are 1.875 and 328.94 $/h, respectively. In the second scenario, by choosing the (m2˙m˙10) = 80, ΔTpp = 19.37, j = 2400 A/m2 and (m˙24m˙23) = 0.3, the rate of ammonia production and total cost rate are reported to be 522.66 kg/h and 300.59 $/h, respectively, when the rate of ammonia production and total cost rate are considered conflicting objectives.

Study of increasing thermodynamic efficiency and hydrogen amount in the process of solid fuels and biomass gasification

The effect of fuel composition such as hard coal and biomass in fluidized bed on the thermodynamic efficiency of three gasifier types, low heating value (LHV) and syngas composition was studied by simulation in CFD program. The paper presents various small gasification systems with fluidized bed of water-coal mixture and water-biomass mixture both with oxygen (air) and without oxygen. The work presents the extended mathematical model of gasification process taking into account also 13 kinetic chemical reactions enabled to apply them in CFD program. The chemical model is based on surface reactions given in the model of Equivalent Reactor Network (ERN) in Ansys Energetico. Simulation of gasification of different reactor designs enabled to obtain the mass concentration of chemical compounds in the syngas which influenced on thermodynamic efficiency and LHV. Additionally, heating of the gasifier walls by electrical system without air gives higher mass ratio of hydrogen (15%) and carbon monoxide (75%) in the syngas than in the oxidized gasification system. The simulation tests showed high thermodynamic efficiency, taking into account the exergy above 80%, both for the oxygen gasification of hard coal-slurry and biomass as well as for the externally heated gasifier without the supply of oxygen. The highest thermodynamic efficiency 90.5% was obtained during gasification of energy willow in the oxidation reactor due to the large difference in LHV of syngas and fuel. Obtaining the maximum possible mass ratio of H2 in syngas and a high thermal efficiency for the OXGR system from the gasification of subbituminous coal dust occurs at a ratio C/O2 = 0.314 and at almost stoichiometric ratio of C/H2O = 0.63. In the case of gasification of biomass in the form of finely ground energy willow in the OXGR system, these ratios were respectively: O2/C = 1.82 and C/H2O = 0.47. While maintaining the almost stoichiometric ratio C/H2O = 0.75, resulting from the water-gas shift reaction, low heating value of the syngas for the analysed gasification systems was over 25 MJ/kg. The paper shows comparison of mass fractions of CO, H2, H2O, H2S, CO2, O2, CH4, tar and other chemical compounds in the syngas. Application of the gasification reactor with external heated walls and without oxygen inflow produces the syngas without tar and volatile species in comparison to the systems with additional oxygen supply. In oxidized reactors the syngas contains a large amount of CO2 about 25–30% of total mass.

Soret effects on the diffusion-chemistry interaction of hydrogen-air edge flames propagating in transverse gradient evolving mixing layers

The effects of Soret diffusion (SD) on the hydrogen-air edge flame propagation and the diffusion-chemistry interaction are investigated through simulation facilitated by the numerical code MultiDiffFOAM. The edge flames in this study gradually develop from a flame kernel into a tri-brachial structure in a hydrogen-air mixing layer that temporally evolves due to transverse reactant concentration gradient. We demonstrate that the responses of flame displacement speed Sd to flame curvature K, stretch rate κ and scalar dissipation rate χ are distinctly influenced by SD. For the linear Sd-K and Sd-κ correlations, SD would result in a smaller Markstein length. Moreover, SD is shown to lead to shifting of the Sd-χ curve towards the regime with larger χ. Compared with the weak influences of SD on the tangential diffusion component Sd,t and normal diffusion component Sd,n, the chemical reaction component Sd,r is significantly weakened by SD. The important chemical reactions for edge flame propagation are identified based on sensitivity analysis and their rates are found to be smaller when SD is considered. For the local composition at the flame marker, the mass fraction of H2 is slightly larger and that of H is obviously smaller when SD is considered. The SD flux of H2jH2SD and that of H jHSD are both coupled with the driving force ∇(lnT) along the mixture fraction coordinate. However, the jH2SD is mainly concentrated on the unburnt side while the jHSD is on the burnt side. The analyses on decomposed fluxes of H2 and H along the flame normal direction further suggest that SD would enhance the H2 mass diffusion but weaken the H mass diffusion. Such opposite effects stem from the distribution features that H2 is mainly on the unburnt side while H on the burnt side.

Spiral Structure Boosts Star Formation in Disk Galaxies

Abstract We investigate the impact of spiral structure on global star formation using a sample of 2226 nearby bright disk galaxies. Examining the relationship between spiral arms, star formation rate (SFR), and stellar mass, we find that arm strength correlates well with the variation of SFR as a function of stellar mass. Arms are stronger above the star-forming galaxy main sequence (MS) and weaker below it: arm strength increases with higher log ( SFR / SFR MS ) , where SFRMS is the SFR along the MS. Likewise, stronger arms are associated with higher specific SFR. We confirm this trend using the optical colors of a larger sample of 4378 disk galaxies, whose position on the blue cloud also depends systematically on spiral arm strength. This link is independent of other galaxy structural parameters. For the subset of galaxies with cold gas measurements, arm strength positively correlates with H i and H2 mass fraction, even after removing the mutual dependence on log ( SFR / SFR MS ) , consistent with the notion that spiral arms are maintained by dynamical cooling provided by gas damping. For a given gas fraction, stronger arms lead to higher log ( SFR / SFR MS ) , resulting in a trend of increasing arm strength with shorter gas depletion time. We suggest a physical picture in which the dissipation process provided by gas damping maintains spiral structure, which, in turn, boosts the star formation efficiency of the gas reservoir.

Robust multi-objective optimization of methanol steam reforming for boosting hydrogen production

Methanol steam reforming (MSR) has been considered as a promising method for producing pure hydrogen in recent decades. A comprehensive two-dimensional steady-state mathematical model was developed to analyze the MSR reactor. To improving high purity hydrogen production, a triple-objective optimization of the MSR reactor is performed. Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is employed as a robust optimization approach to maximize the three objectives, termed as, methanol conversion, CO selectivity, and H2 selectivity. The Pareto optimal frontier has also been provided and the ultimate solution of the Pareto front has been found by the three decision-making methods (TOPSIS, LINMAP, and Shannon's Entropy). Among the three distinct decision-making approaches, LINMAP presents better results according to the deviation index parameter. It has been shown that a perfect agreement is available between the plant and simulation data. Operating under the optimum values based on the LINMAP method confirms an almost 47.04% enhancement of H2 mass fraction compared to the conventional industrial MSR reactor. The predicted results advocate that the key superiority of the optimized-industrial reactor is the remarkable higher production rate of hydrogen compared to the conventional MSR reactor which makes optimized-industrial reactor both feasible and beneficial.

Computational design of H 2 SO 4 decomposer combined with SOFC for thermochemical hydrogen production

Thermochemical methods, such as the sulfur-iodine cycle and hybrid sulfur cycle, are more advantageous than conventional hydrogen production methods, such as fossil fuel reforming and water electrolysis, for large-scale hydrogen production. Sulfuric acid decomposition is a highly endothermic reaction of the sulfur-iodine cycle. To sustain this endothermic process using high-temperature waste heat from solid oxide fuel cells (SOFCs), we propose an integrated thermochemical reactor combined with SOFC by taking a computational approach. First, a thermodynamic analysis was performed to evaluate the heat production of SOFC to sustain the thermochemical reaction in the combined reactor, resulting in a required waste heat of 0.565 kW from the SOFC that was obtained by consuming 0.0241 kg‧h−1 of H2 to process 1.0 kg‧h−1 of the H2SO4 mixture for the H2SO4 decomposer. For the SOFC inlet temperatures 923, 1023, and 1173 K, the corresponding SO3 conversions of the combined reactor were 72.1%, 77.3%, and 85.1%, respectively. A further increase of over 1200 K in the operating temperature led to a minor improvement in the SO3 conversion efficiency. In the SOFC section, the H2 mass fraction decreased from 67.9% to 10.8% in the anode channel, and 0.169 kW of electrical power was generated when the operating cell voltage and energy efficiency were 0.7 V and 53.71%, respectively.

A Phase-space View of Cold-gas Properties of Virgo Cluster Galaxies: Multiple Quenching Processes at Work?

Abstract We investigate the cold-gas properties of massive Virgo galaxies (>109 M ⊙) at <3R 200 (R 200 is the radius where the mean interior density is 200 times the critical density) on the projected phase-space diagram with the largest archival data set to date to understand the environmental effects on galaxy evolution in the Virgo cluster. We find lower H i and H2 mass fractions and higher star formation efficiencies (SFEs) from H i and H2 in the Virgo galaxies than in the field galaxies for matched stellar masses; the Virgo galaxies generally follow the field relationships between the offset from the main sequence of the star-forming galaxies [Δ(MS)] and the gas fractions and SFEs, to the slight offset to lower gas fractions or higher SFEs compared to field galaxies at Δ(MS) < 0; lower gas fractions in galaxies with smaller clustocentric distance and velocity; and lower gas fractions in the galaxies in the W cloud, a substructure of the Virgo cluster. Our results suggest the cold-gas properties of some Virgo galaxies are affected by their environment at least at 3R 200 maybe via strangulation and/or preprocesses, and H i and H2 in some galaxies are removed by ram pressure at <1.5R 200. Our data cannot rule out the possibility of other processes such as strangulation and galaxy harassment accounting for gas reduction in some galaxies at <1.5R 200. Future dedicated observations of a mass-limited complete sample are required for definitive conclusions.

Three-Dimensional CFD Modeling of Serpentine Flow Field Configurations for PEM Fuel Cell Performance

A complete three-dimensional Proton Exchange Membrane Fuel Cell (PEMFC) model is proposed to study the influence of right-angle turn single serpentine (RAT1S), right-angle turn double serpentine (RAT2S), right-angle turn triple serpentine (RAT3S), and right-angle turn 3–2–1 serpentine (RAT321S) flow fields configuration on PEMFC performance with a commercial CFD code (ANSYS FLUENT). Simulations have been performed to envisage the pressure drop in the channel, the mass fraction of H2 and O2 along the anode and cathode channels, current flux density dispersion on the catalyst layer (CL), the membrane water content and proton conductivity as well as cell performance for proposed 4 flow field designs. A comparison of the simulation results of the four models was carried out. It has been found that the output of RAT321S flow field has improved compared to the RAT1S, RAT2S, and RAT3S flow field designs for the flow of the fixed-flow reactants, and RAT321S flow field model has been validated with experimental literature evidence. The results also show that the pressure drop losses are reduced as the number of passes increases.

Evaluation of manifold representations of chemistry in stratified, swirl-stabilized flames

The validity of assuming that a simple, low-dimensional manifold can sufficiently accurately represent the chemical state in a turbulent flame is investigated. The experimental data from the Cambridge/Sandia stratified swirl burner working in nine different configurations are post-processed to explore the effects of coordinate, swirl flow ratio, and stratification factor on the conditionally-averaged reactive scalars. First, the mixture fraction and thermal progress variable are employed to construct a two-dimensional conditional manifold by using all of the data – regardless of the coordinate in the physical domain, swirl ratio, and stratification factor. Moreover, one-point, one-time measurements are utilized to compute the exact joint Probability Density Function (PDF) of the conditioning variables at each point. Having the conditional averages of temperature and mass fractions of CO2, CO, CH4, H2, and H2O in addition to the joint PDF of the conditioning variables, the low-dimensional manifold is applied to calculate the unconditional averages for each of the scalars. The mean values are also obtained by ensemble averaging all of the data available for each of the measuring points, and the discrepancies between the values calculated from the two approaches are reported in order to assess the validity of the assumptions underlying the low-dimensional chemistry representations. The results suggest that the two chosen conditioning variables are not sufficient to make the manifold independent of the real domain, so, the normalized total enthalpy is introduced as the third conditioning variable and the process repeated. Results obtained from the three-condition manifold demonstrate that the discrepancies for prediction of the reactive scalars, more significantly for CO2 and CO mass fractions, decrease when using the third condition. The discrepancies with three conditions show that a three-dimensional manifold is sufficient to assume the conditional averages are independent of swirl and stratification. A normalized accumulated discrepancy is used as a metric for each of the cases so one can see the overall effect of each assumption that is made for constructing the conditional manifold. Decoupling the manifold from the coordinate, swirl ratio, and stratification level makes it possible to obtain the filtered chemical source-terms from a static lookup table for many flames which will considerably reduce the computational cost for simulating turbulent reacting flows.

Large eddy simulation of the Cambridge/Sandia stratified flame with flamelet-generated manifolds: Effects of non-unity Lewis numbers and stretch

The Cambridge/Sandia turbulent stratified flame (SwB5) is simulated with the LES and Flamelet-Generated Manifolds (FGM) combustion model. Three 3D FGM manifolds are adopted. With the purpose to examine the influence of transport properties, unity and non-unity Lewis numbers (Le) are included in the first two manifolds, respectively. The combined effects of non-unity Le and stretch are investigated in the third manifold. Heat loss to the wall is also modeled. Good agreement is found between the simulation and experiment. The equivalence ratio, temperature and mass fractions of CO and H2 are all well reproduced in contrast with previous simulations. It is found that using non-unity Le can even deteriorate the near-wall temperature modeling. Non-unity Le is proposed to be crucial for the CO prediction as well, besides H2. The equivalence ratio modeling is observed to be very important, which accounts for several non-unity Le effects. Flame stretch shows almost no impact on the velocity fields, whereas its effects on the species, equivalence ratio and temperature are identified, although to a limited extent for the Cambridge/Sandia flame.