Hydrogen Fraction Research Articles

Effectiveness-MTU modeling approach for hydrogen separation with dense metallic membranes

As hydrogen gains interest as energy vector, so it happens for its purification techniques. In particular, dense metallic membranes are a promising technology for many high-temperature applications. Modeling of hydrogen permeation is a fundamental support to their commercial development. Permeation through metallic membranes, in particular Pd-alloys, is regulated by a generalized form of the Richarson’s equation, where driving force for permeation is due to the difference in hydrogen partial pressure at the membrane surfaces. From the flux expression it is possible to develop a model for a mass exchanger, in analogy with the mathematical description of heat exchangers. For the latter, a well-known method, called , is used to simplify heat transfer problem. The same approach applies to mass exchangers, where the method had already been transferred to reverse osmosis. In this article, method is applied to ideal mass exchangers for hydrogen separation. Effectiveness showed to be influenced by inlet hydrogen fraction, exponent of partial pressures and pressure ratio. Moreover, a procedure to include concentration polarization losses is presented. A rule-of-thumb approach is proposed for an estimation of hydrogen recovery, validated to reproduced an experimental result with less that 7% relative error. shows to be a fundamental support to membrane module design.

Exploring hydrogen isotope fractionation in lipid biomolecules of freshwater algae: implications for ecological and paleoenvironmental studies

ABSTRACT Understanding the stable hydrogen isotope (δ 2H) composition and fractionation in lipid biomolecules of primary producers, such as terrestrial and aquatic plants, is crucial for deciphering past environmental conditions, as well as applying compound-specific stable isotope analysis for the study of metabolic and ecological processes. We conducted a new tracer experiment to explore the δ 2H composition of algal fatty acid biomarkers, focusing on freshwater algae, which form the base of aquatic food webs. We selected a range of algal species widely found in freshwater ecosystems and cultivated them under controlled conditions. First, we added 2H2O to ambient water as a tracer to investigate the net hydrogen isotope fractionation during algal lipid synthesis at isotopic equilibrium, which is particularly informative for paleo-geochemical studies. Then, we conducted kinetic experiments to quantify the time needed for algal fatty acids to achieve isotopic steady-state conditions in response to the change in ambient water δ 2H values. Our findings revealed substantial variability in hydrogen isotope fractionation among different algal taxa and various fatty acids. Based on taxa, different fatty acids exhibited faster integration of water hydrogen than others, but they were not necessarily in the order of the biosynthetic pathway. This experiment underscores the complexity of hydrogen isotope fractionation and the requirement for controlled laboratory studies to properly apply compound-specific stable H isotope analysis techniques in ecological and paleo-environmental studies.

Experimental and numerical investigation of the Doppler-shifted resonance condition for high frequency Alfvén eigenmodes on ASDEX Upgrade

Abstract The Doppler-shifted resonance condition for high frequency Alfvénic eigenmodes has been extensively studied on ASDEX Upgrade in the presence of one or a combination of two neutral beam injected (NBI) fast ion populations. In general, only centrally deposited NBI sources drive these modes, while off-axis sources globally stabilize the mode activity. For the case of a single central NBI source, the observed trend is: the highest frequency modes are driven by the lowest energy and lowest pitch angle NBI sources, in line with the expectation from the Doppler-shifted resonance condition. The expected mode frequencies are determined analytically from the two-fluid cold plasma dispersion relation and the most unstable frequency relation, while the mode growth rates are estimated using the fast ion slowing down distribution functions from the ASCOT code. The overall mode frequency trend in a source-to-source variation is tracked, although a systematic overestimate of ∼1 MHz is observed. Possible causes of this overestimate include the finite size of the resonant fast ion drift orbit and non-linear effects such as mode sideband formation. Alternatively, the expected mode frequencies are determined by tracking the growth rate maxima trajectories, this method improves the agreement with the experimentally measured values. A combination of two central mode-driving NBI sources results in the suppression of the mode driven by the lowest energy and the lowest pitch angle NBI source. Computing the analytically expected mode frequency following the method outlined above, again, generally tracks the experimentally observed trend. The mode’s Alfvénic nature allows for a practical application to track the core hydrogen fraction by following the mode frequency changes in response to a varying ion mass density. Such application is demonstrated in a discharge where the average ion mass is varied from ∼2m p to ∼1.5m p (where m p is the proton mass) via a hydrogen puff in a deuterium plasma, in the presence of a strong mode activity. The expected mode frequency changes are computed from the existence of the resonance condition, and the values track the measured results with an offset of ∼0.5 MHz. Overall, the results suggest an intriguing possibility to monitor and control the D-T ion fraction in the core of a fusion reactor in real time using a non-invasive diagnostic.

Evolution of solid residue composition during inert and oxidative biomass torrefaction

Biomass torrefaction is a thermochemical pretreatment that can be used to improve biomass properties, contributing to the energy densification of biomass or increasing its grindability, burning and gasification characteristics, porous structure, etc. While it is typically carried out under inert conditions, oxygen-lean torrefaction of biomass can reduce the process cost and complexity. This work proposes a novel extended 2-step kinetics mechanism capable of accurately predicting the evolution of the chemical composition of torrefied biomass. The model parameters are obtained from data collected from an extensive experimental campaign in which the chemical composition of torrefied biomass was measured at different temperatures, residence times, and oxygen fractions. The carbon mass fraction of the torrefied products was found to increase by up to 50 % under severe inert torrefaction conditions, i.e., high temperatures and long residence times, whereas the hydrogen fraction decreased. In the presence of oxygen during torrefaction, the carbon and hydrogen contents in the solid residue decrease compared with those produced under inert torrefaction. The extended 2-step model can also be used to determine the high heating value and energy densification of the torrefied biomass, with the latter ranging from 1 to 1.4 for the operating conditions tested.

A bio‐reactive transport model for biomethanation in hydrogen underground storage sites

AbstractUnderground biomethanation, which relies on the subsurface microbial activity to convert hydrogen and carbon dioxide into methane, is a promising approach to support carbon capture, utilization, and storage technology. The process involves injecting hydrogen with captured CO2 into depleted oil and gas reservoirs or aquifers colonized by hydrogenotrophic methanogens that can convert these two substrates into methane. Despite the attractiveness of this technology, there are still uncertainties about the efficiency of the conversion process, particularly the impact of microbial parameters. To investigate the efficiency of the hydrogen conversion process, we relied on a bio‐reactive transport model that can mimic microbial growth and decay, consumption of substrates, and transport of reactants and products. It was found that the methane concentration peaks near the injection well when the hydrogen fraction is in the range of 75% to 80% of the injected gas composition. In addition, a noticeable hydrogen sulfide concentration can be produced due to sulfide ions in the brine. Using the Kozeny‐Carman relation, an attempt was made to correlate microbial growth with reduced porosity and permeability. It was then revealed that substrate consumption by microbes leads to a drastic increase in the microbial population in the subsurface, which can reduce the petrophysical properties of the reservoir, especially in the near wellbore area. The results obtained from a series of parametric analyses showed that the hydrogen concentration in the injected gas, pressure, well spacing, and injection rate are some of the most important parameters contributing to the biomethanation process. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Thermodynamic and exergo-economic evaluation of biomass-to-X system combined the chemical looping gasification and proton exchange membrane fuel cell

The resource utilization of biomass is of great significance to the adjustment of energy structure. The syngas produced by biomass gasification can be used for power generation and production of green chemical raw materials. In this paper, a biomass-to-X (BtX) system based on the chemical looping gasification and high temperature proton exchange membrane fuel cell (PEMFC) is proposed to produce methanol, electricity, heating and cooling. The heat produced by the BtX system is harnessed for the regeneration of the carbon capture solution, as well as to drive both the organic Rankine cycle and the double-effect absorption chiller, enabling cascade utilization of the energy. The thermodynamic and exergo-economic models are carried out to evaluate system performance. The relationship between the material, energy and cost flow from biomass to products is analyzed. Finally, the influence of key parameters on system performance is studied. The results show that the energy efficiency of the BtX system is 54.0 % and the exergy efficiency is 35.4 %. The yield rate of methanol with 99.2 wt% purity is 6.48 tons/h. The cost of equipment, propanol and biomass accounts for 34.9 %, 28.9 % and 28.1 % of the total investment cost, respectively, while the cost of the PEMFC stack represents 50.4 % of the equipment costs. The unit exergy cost of the electricity and methanol are 0.068 $/kWh and 0.049 $/kWh, respectively. The methanol, carbon capture and cooling costs are most sensitive to the change in the propanol cost, followed by the biomass cost. For every 0.05 increase in the hydrogen fraction to methanol production, the electricity decreases by 3.1 MW and the methanol yield increases by 0.23 kg/s.

Synergy effect of nozzle structure and pre-chamber reactivity on the combustion characteristics of ammonia engines

Ammonia (NH3) offers an attractive opportunity for internal combustion engines (ICE) to be carbon–neutral. An active pre-chamber fueled with hydrogen might be suitable to overcome the poor combustion characteristics of ammonia engines. The primary goal of this work is to numerically study the combustion characteristics of ammonia engines with a hydrogen-fueled pre-chamber, and the synergy effect of nozzle structure and pre-chamber reactivity (hydrogen quantity) are also considered. The results show that the hydrogen fraction is reduced to a low degree in the pre-chamber because of the scavenging process. Thus, it is better to inject hydrogen into the pre-chamber during the compression stroke. Although high pre-chamber reactivity is effective in improving the main chamber combustion, a multi-hole pre-chamber is needed to get the maximum promoting effect of the high reactivity when compared to the single-nozzle pre-chamber. For multi-hole pre-chamber, 2 mm is the recommended nozzle diameter when considering the promoting effect, and the recommended area-volume ratio (nozzle number) is increased with the pre-chamber reactivity. For nitrogen-based emissions, the distribution strongly depends on the flame characteristics. High pre-chamber reactivity can significantly reduce the NH3 emissions, while NO emissions will increase with the pre-chamber reactivity. The current study can give some insights and be a preface for the development of ammonia engines.

The Impact of Hydrogen on Flame Characteristics and Pollutant Emissions in Natural Gas Industrial Combustion Systems

To improve energy savings and emission reduction in industrial heating furnaces, this study investigated the impact of various molar fractions of hydrogen on natural gas combustion and compared the results of the Non-Premixed Combustion Model with the Eddy Dissipation Combustion Model. Initially, natural gas combustion in an industrial heating furnace was investigated experimentally, and these results were used as boundary conditions for CFD simulations. The diffusion flame and combustion characteristics of natural gas were simulated using both the non-premixed combustion model and the Eddy Dissipation Combustion Model. The results indicated that the Non-Premixed Combustion Model provided simulations more consistent with experimental data, within acceptable error margins, thus validating the accuracy of the numerical simulations. Additionally, to analyze the impact of hydrogen doping on the performance of an industrial gas heater, four gas mixtures with varying hydrogen contents (15% H2, 30% H2, 45% H2, and 60% H2) were studied while maintaining constant fuel inlet temperature and flow rate. The results demonstrate that the Non-Premixed Combustion Model more accurately simulates complex flue gas flow and chemical reactions during combustion. Moreover, hydrogen-doped natural gas significantly reduces CO and CO2 emissions compared to pure natural gas combustion. Specifically, at 60% hydrogen content, CO and CO2 levels decrease by 70% and 37.5%, respectively, while NO emissions increase proportionally; at this hydrogen content, NO concentration in the furnace chamber rises by 155%.

Enrichment of Chlorophyta growth via cerium oxide and utilized for hydrogen production via hydrothermal gasification process

Abstract The growing interest in alternative fuels stems from the need to address energy security and economic challenges. Hydrogen fuel is considered a promising solution due to its versatility, efficiency, and potential for zero emissions, as well as continuous technological advancements and increasing policy support. This study intends to enhance Chlorophyta growth by incorporating different volume percentages of cerium oxide (CeO2) as feedstock for hydrogen production through hydrothermal gasification. The research findings indicate that the highest concentration (0.2 vol %) of CeO2 resulted in the maximum growth of 0.63 μ/day, which was utilized for hydrogen extraction. Additionally, the investigation explored the impact of Chlorophyta algae loading (0.05-0.15 g/mL) and processing temperature (500-650°C) on molar fraction, hydrogen yield, gasification efficiency, carbon efficiency, and total hydrogen production. Higher feedstock (0.15 g/mL) and gasification temperature (650°C) were found to improve hydrogen fraction (61.8%), yield (10.2 mol/kg), gasification efficiency (43.8 %), and total hydrogen production (62.5%).

Targeting carbon-neutral waste reduction: Novel process design, modelling and optimization for converting medical waste into hydrogen

This study proposes a novel system designed to turn waste masks (WM) into hydrogen while aiming at carbon neutrality. The system utilizes plasma gasification to primarily convert WM into syngas, which is subsequently upgraded through water gas shift to enhance hydrogen fraction. To mitigate carbon emissions, carbon capture techniques including monoethanolamine-based carbon absorption and oxy-fuel combustion are incorporated into the system. A high-fidelity model of the designed process is developed in Aspen Plus. Machine learning-driven optimization is applied to identify the optimal operating conditions. Utilizing Gaussian process regression-based surrogate optimization, the system achieves around 0.5 kg CO2 eq/kg H2 of levelized emissions per unit hydrogen (LEH) in the reaction stage and the execution time required for optimization is only 4 s, outperforming detailed process models-based optimization. Energy assessment highlights plasma gasification and CO2 absorption as the primary sources of energy loss. Furthermore, life cycle analysis indicates that CO2 absorption is the primary contributor to carbon emissions, accounting for approximately 60% of the total emissions. With levelized emissions of 1.27 kg CO2 eq/kg WM and 5.18 CO2 eq/kg H2, the designed system demonstrates superiority over conventional medical waste treatment and hydrogen production methods.

Thermodynamic investigation of biomass-steam gasification in converter vaporisation flue for synthesis gas production

Biomass gasification for hydrogen production is a highly promising technology for energy conversion and utilisation. This paper proposed a novel technology for the injection of biomass and steam into the flue of a converter vaporisation to produce hydrogen-rich syngas. The feasibility of hydrogen generation through gasification between biomass, steam, and carbon dioxide in the high-temperature flue gas was investigated based on the thermodynamic principle of Gibbs free energy minimisation. The influence of gasification parameters on the composition of syngas was also explored. The results indicate that in the gasification process, biomass and steam injected into the converter vaporisation flue can effectively inhibit the generation of by-products such as tar. As the steam volume increases, the volume fraction of hydrogen in the product also increases, while the concentration of carbon monoxide decreases. By adjusting the steam-to-biomass ratio, syngas with a hydrogen content exceeding 20% can be produced. At a reaction temperature of 1200 °C, with a steam addition of 5%, a biomass addition of 8 g/L, and a [Formula: see text] ratio of 3, the gas products are composed of 25% hydrogen and 67% carbon dioxide. The process has the potential to achieve a hydrogen yield of up to 90%, a syngas yield of 94%, and a CO2 conversion rate of 70%. Additionally, the lower heating value of the syngas is measured at 11.24 MJ/Nm3. The research results have confirmed the viability of the new technology, thus establishing a theoretical foundation for the industrial implementation of injecting biomass and steam into the converter vaporisation flue to produce hydrogen-rich syngas.

Turbulent Burning Velocity of High Hydrogen Flames

Abstract The turbulent burning velocity (ST) is one of the most important combustion properties controlling combustor operability limits, directly influencing blowoff, flashback, and combustion instabilities. Hydrogen has particularly significant influences on the turbulent flame speed. This paper presents new H2/CH4 data of high pressure, high hydrogen turbulent burning velocities. The datasets were designed to address fundamental questions as well as provide engineering/design relevant insights. This paper presents new scaling analysis of fuel composition, pressure, and preheat temperature effects on turbulent burning velocity. We also discuss the importance of considering what is being held constant (temperature, flame speed, Reynolds number, etc.) when one is analyzing these sensitivities. Data show that hydrogen fraction and pressure cause an increase in turbulent flame speed; whether quantified as raw ST,GC or normalized as ST,GC/SL,0 or ST,GC/SL,max (where SL,0 and SL,max are the unstretched and stretched laminar flame speed, respectively). We also propose that observed increases in ST,GC with pressure are due to increases in Reynolds number and not a kinetics/stretch sensitivity effect. With increasing preheat temperature, ST,GC increases while its normalized value (ST,GC/SL,0 and ST,GC/SL,max) can either increase or decrease, depending upon fuel composition. We also show how these sensitivities vary, depending on whether these comparisons are made at constant raw turbulence intensity urms or at constant normalized urms/SL,0 or urms/SL,max.

Development of a method for assessing the degree of hydrogenation of titanium alloy VT1-0 by acoustic method

In this paper, the possibilities of using a non-destructive acoustic method to determine the degree of hydrogenation of titanium alloy VT1-0 are investigated. The features of the use of various acoustic parameters for the construction of engineering techniques for determining the structural state of a titanium alloy at various stages of its hydrogenation are analyzed. A number of computational and experimental methods for determining the mass fraction of hydrogen in a titanium alloy are proposed, based on the use of its acoustic characteristics, which increase the accuracy and stability of the algorithms underlying the calculation part of the methods. The sources of errors of the proposed methods, the limits of their applicability, as well as the requirements for hardware and software for their implementation are analyzed. The results of acoustic measurements carried out on samples from the VT1-0 alloy are compared with the ideas about the patterns of its structural changes during its hydrogenation. The possibility of creating engineering algorithms for assessing the state of the material of products subjected to hydrogenation on the basis of experimental data obtained in order to prevent dangerous degradation of its operational properties is shown.

Soft X-ray emission from the classical nova AT 2018bej

Context. Classical novae are known to demonstrate a supersoft X-ray source (SSS) state following outbursts. This state is associated with residual thermonuclear burning on the white dwarf (WD) surface. During its all-sky survey (eRASS1), the eROSITA telescope on board the Spectrum-Roentgen-Gamma observatory discovered a bright new SSS, whose position is consistent with the known classical nova AT 2018bej in the Large Magellanic Cloud. There were two eROSITA spectra obtained during the eRASS1 and eRASS2 monitoring epochs and one XMM-Newton grating spectrum close to the eRASS1 epoch. Aims. We aim to describe the eROSITA and follow-up XMM-Newton spectra of AT 2018bej with our local thermodynamic equilibrium (LTE) atmosphere models. We focussed on the evolution of the hot WD properties between the eRASS1 and eRASS2 epochs, especially with respect to the change in carbon abundance. Methods. A grid of LTE model atmosphere spectra was calculated for different values of the effective temperature (from Teff = 525 to 700 kK in steps of 25 kK), surface gravity (six values), and chemical composition, assuming approximately equal hydrogen and helium number fractions, and five different values of carbon and nitrogen abundances. Results. Both eRASS1 and XMM 0.3–0.6 keV spectral analyses yield a temperature of the WD of Teff~ 600 kK and a WD radius of 8000–8700 km. A simultaneous fitting of the eROSITA spectra for two epochs (eRASS1 and eRASS2) with a common WD mass parameter demonstrates a decrease in Teff, accompanied by an increase in the WD radius and a decrease in the carbon abundance. However, these changes are marginal and remain within the errors. The derived WD mass is estimated to be 1.05–1.15 M⊙. Conclusions. We traced a minor evolution of the source on a half-year timescale accompanied by a decrease in the carbon abundance and concluded that LTE model atmospheres can be used to analyse the available X-ray spectra of classical novae during their SSS state.

An experimental study on the flame behaviors of H2/CO/Air mixtures in closed tube with varying number of obstacles

In order to investigate the flame behavior of syngas/air mixtures after leakage in industrial scenarios. A series of fence-type obstacles with a blockage ratio of 0.3 were installed in a closed tube to simulate common blockage scenarios. The stoichiometric mixtures of H2/CO/Air with hydrogen fractions ranging from 10 % to 50 % were used to simulate typical syngas compositions. Results indicate that the increase in hydrogen fractions and the number of obstacles can enhance flame acceleration and oscillation downstream of obstacles. The flame inverts into the tulip shape after it passes the obstacle area, and then the distorted “tulip” flame appears. The obstacles number has no influence on the instant of the planar flame formation, because the flow competition initiates when the flame passes the first obstacle channel. However, the initial instant of the first “tulip” distortion decrease with the increasing obstacle number. The “tulip” flame is a hydrodynamic phenomenon, while the distortion of the “tulip” flame is related to pressure waves. At higher hydrogen fractions, the obstacle number increases the maximum overpressure more significantly. In practical scenarios, it is advisable to limit the number of obstacles as much as possible and prevent syngas leaks with higher hydrogen fractions.

Experimental and numerical study of H[formula omitted] enrichment on swirl/bluff-body stabilized lean premixed n-butane/air flame

This study focused on the stabilization of lean premixed flames of n-butane/H2/air with swirl/bluff-body. The research explored four different hydrogen fractions (0, 20%, 40%, and 80%) at a constant equivalence ratio and Reynolds number. The turbulent reacting flow was resolved using a combination of Delayed Detached Eddy Simulation (DDES) and Flamelet Generated Manifold (FGM) model. The velocity fields and reaction zones were obtained through Particle Image Velocimetry (PIV) and OH* chemiluminescence measurements respectively. H2 addition to n-butane significantly enhanced flame characteristics. The chemiluminescence imaging showed that the flame base became stronger with increasing hydrogen addition, reducing the risk of flame lift-off. Hydrogen addition not only increased the overall reaction rate but also changed the combustion intensity at the nozzle exit from weak to strong, which is crucial for flame stabilization. Interestingly, no flashback was observed even at 80% H2 addition to n-butane at the same level of power rating. The flow strain rate analysis of the PIV measurements showed that the inclusion of hydrogen skewed the strain rate probability density functions towards the positive side, indicating an increase in the burning rate. The results demonstrate a progressive increase in preferential diffusion of H2 from reactants to products as the H2 enrichment in the fuel rises and resulted in a more intense flame. Also, the present simulation results were validated with the PIV data, and they showed good agreement. Specifically, an 80% H2 blend exhibited a 16% peak enhancement in flame surface density compared to pure n-butane while concurrently reducing CO2 emissions by 23.2%. The incorporation of H2 also led to the increased vortex strength and strain rate within the flame.

Spontaneous ignition and flame propagation in hydrogen/methane wrinkled laminar flames at reheat conditions: Effect of pressure and hydrogen fraction

Direct numerical simulations (DNS) with detailed chemical kinetics and chemical explosive mode analysis (CEMA) are performed to investigate the effect of operating pressure and hydrogen–methane blending on laminar wrinkled flames at reheat combustion conditions. Building upon previous three-dimensional DNS datasets of reheat hydrogen flames, the present work considers two-dimensional configurations that render computationally-feasible simulations of high-pressure combustion and significantly more complex hydrocarbon chemistry. A geometrically-simplified representation of the reheat combustor is adopted and the thermodynamic states considered in the simulations are carefully chosen to mimic gas turbine operation conditions, which are constrained to achieve a target flame position and flame temperature. The two-dimensional DNS results are first assessed against the available three-dimensional data and then analyzed to extract the main trends exhibited by the reheat combustion process with respect to the fraction of the fuel consumed by spontaneous ignition and flame propagation, for increasing pressures and hydrogen fractions. Due to significant differences in the characteristic features of the velocity and thermal boundary layers between the three-dimensional and the two-dimensional configurations, a different global flame shape is observed (V-shaped flame vs W-shape flame) together with a ∼10% bias in the fraction of fuel consumed by spontaneous ignition. Crucially, results from the scaling studies reveal very clear trends with a significant decrease in the fuel consumption by spontaneous ignition for increasing pressures and hydrogen fractions, at the conditions investigated. Finally, this study highlights the important role that first-principle direct numerical simulations, even when conducted in computationally affordable two-dimensional simplified geometrical configurations, can play in obtaining detailed insights and quantitative trends useful for the characterization of complex reactive flows.Novelty and significanceThe reheat burners of the two-stage sequential gas turbine combustors are designed to stabilize flames primarily due to spontaneous ignition. However, prior numerical simulations revealed the presence of an additional assisted-ignition mode aided by recirculation zones. In this study, we used practically feasible two-dimensional direct numerical simulations of premixed hydrogen–air mixtures under lean conditions to quantify the roles of the two flame stabilization modes at different operating pressures. Achieving fundamental understanding of the effect of pressure and hydrogen fraction on flame stabilization is crucial to the development of two-stage sequential combustion and the present two-dimensional calculations provide important new insights. We show that at high pressures, both modes consume fuel to a similar extent. We also investigated the effect of methane blending on flame stabilization. This study also discusses how two-dimensional direct numerical simulations can be leveraged in the design optimization of reheat burners at low technology readiness levels.

Study on the influence of the hydrogen–oxygen stoichiometric ratio on the power performance improvement in a large-scale PEMFC stack

This study aims to determine the optimized hydrogen–oxygen stoichiometric ratio for power performance improvement in a large-scale proton exchange membrane fuel cell (PEMFC) stack by analyzing the characteristics of internal heat and mass distributions. The power performance of a large-scale PEMFC stack consisting of the designed stack cells with the counter flow directions of hydrogen and oxygen and a coolant flow channel was experimentally evaluated. Temperatures in the central stack cell were monitored. The coupled numerical simulation model was built to analyze the power performance as well as heat and mass distribution characteristics inside a stack cell. It was found that the greatest power performance of the PEMFC stack occurred at a specific hydrogen–oxygen stoichiometric ratio, and this performance had good uniformities of the temperature and water mass fraction distributions at the proton exchange membrane (PEM). The distribution characteristics of the hydrogen and oxygen mass fractions at the interfaces between the gas diffusion layer (GDL) and the catalytic layer (CL) due to the diffusion effect were analyzed. The mechanism of enhancing power performance from an electrochemical reaction was revealed by the greater gas distribution uniformities. Furthermore, a parameter of energy conversion ratio was employed to quantify the hydrogen utilization degree.

Optimizing heat transfer predictions in HCNG engines: A novel model validation and comparative study via quasi-dimensional combustion modeling and artificial neural networks

Heat transfer from the walls of engine has a significant role on engine combustion, performance and emission characteristics. The study objectives to showcase the efficacy of the new model through an analysis by comparison with existing heat transfer models. New model is based on woschni model in which pressure and temperature is replaced by other fluid properties like density, thermal conductivity and dynamic viscosity. A series of experiments were conducted on a compressed natural gas internal combustion engine across varying hydrogen fractions, EGR ratios, engine speeds and different loads under stoichiometric conditions. The study demonstrates the efficacy of the proposed model by constantly achieving high prediction quality across a wide range of engine calibration coefficients by using Quasi-dimensional Combustion Model (QDCM) on MATLAB. Comparative analyses of new model with different heat transfer models were undertaken to validate the heat transfer rates with experimental results across a broad spectrum of operational conditions. It is observed that heat transfer rate is increased by increasing the engine load as 25%, 50%, 75% and 100% as 90.57J/deg, 130.12J/deg, 200.02J/deg, and 260.26J/deg with new model correspondingly. Heat transfer rate reduced by rise in engine speed with 1100 rpm, 1200 rpm, 1500 rpm and 1700 rpm is as 32.91 kW, 32.16 kW, 25.36 kW and 18.03 kW by new heat transfer model respectively. Artificial neural network (ANN) popular backpropagation algorithm is adopted to predict the heat transfer rate of HCNG engine, the five-input and one-output network structure are used. The values of correlation coefficient (R) and mean square error (MSE) were 0.99957 and 0.22667, 0.99998 and 0.010776, 0.99253 and 4.4762, 0.9961 and 1.2329, 0.99994 and 0.025108 for Woschni, New_Model, Chang, Sitkei and experimental respectively. This research work offers that ANN is a wise option for conventional modeling systems. In this way, the heat transfer rate of hydrogen-added CNG engines may be precisely predicted using ANN modeling.

Analysis of hydrogen leakage behavior and risk mitigation measures in a hydrogen refueling station

With the wide application of hydrogen, the research related to 70 MPa pressure level hydrogen storage tank is very important. This paper takes the 70 MPa hydrogen storage tank in the hydrogen refueling station as the research object, and analyses the diffusion characteristics of hydrogen after leakage from the tank under different wind conditions by FLUENT. Studies find that after hydrogen ejects to the obstacle by the effect of high-pressure, it transforms to be dominated by the simple diffusion and the wind condition. The ambient wind helps to reduce the volume fraction of hydrogen. This paper proposes risk mitigation measures based on the distribution of the flammable clouds — installing nitrogen outlets and reducing the height of the enclosure. The volume of flammable clouds is reduced from about 2.72 m3 to less than 0.045 m3 after adding measures, which proves the feasibility of the measures.