Gas Generation Rate Research Articles

Honeycombed pomegranate-like sludge ceramsite particles: preparation with fly ash floating beads as the pore-forming template and performance optimization

Ceramsite used in construction and building are typically limited by high water absorption rates, the contradiction between lightweight and high strength, and severe performance fluctuations. This can be attributed to the fact that ceramsites are currently prepared by high-temperature sintering expansion, wherein viscosity and surface tension of the liquid phases shall perfectly match with the gas generation rate. On the other hand, sand washing sludge and fly ash are common solid wastes in construction and building and their environmentally friendly disposal are of great significance. In this study, honeycombed pomegranate-like sludge ceramsites with low density (packing density = 733.2-968.3kg/m3), high strength (cylinder compressive strength = 11.2-18.8MPa), and low water absorption rate (one-hour water absorption rate = 1.2-2.8%) were prepared with sand washing sludge and fly ash floating beads as the raw material and the pore-forming template, respectively. Also, the effects of particle size and content of fly ash floating beads on the structure and performance of the as-prepared ceramsite were investigated. The results indicated that the pore structure of the as-prepared ceramsite was directly dependent on size and content of the fly ash floating beads, suggesting that the performance of the as-prepared ceramsite can be customized by tuning size and content of the beads. Additionally, lightweight aggregate concrete prepared by using the as-prepared ceramsites exhibited improved 7-day and 28-day compressive strengths and reduced thermal conductivity compared with concrete prepared by using commercially available ceramsites. Overall, this study presents the preparation of ceramsite particles with both high strength and low density by using fly ash and sand washing sludge, both of which are abundant solid wastes in constructions, thus contributing to solid waste recycling in construction.

Theoretical Analysis of Landfill Gas Migration in Capillary Barrier Covers Considering Effects of Waste Temperature

The high-temperature and high-humidity conditions arising from the biochemical degradation of landfill waste result in significant temperature gradients within the landfill cover. The effects of waste temperature on landfill gas transport and microbial aerobic methane oxidation are not fully understood. In this study, a fully coupled theoretical model was developed to simulate the interactions of moisture, heat, and gas transport within a capillary barrier cover. A series of parametric studies were carried out to investigate the influence of the combined effects of temperature gradient, initial soil moisture content, and landfill gas generation rate on methane transport, oxidation, and emissions. The simulated results indicated that increasing waste temperature intensified the temperature gradient, leading to higher surface evaporation rates and variations in methane oxidation efficiencies. Additionally, variations in initial soil moisture content and landfill gas generation rates were found to significantly impact gas migration and methane oxidation in the cover. This study demonstrates the critical role of waste temperature in landfill gas migration within landfill cover systems, providing technical methodologies for the optimized design of soil cover systems.

Study on Thermal Runaway Behavior and Early Warning Algorithm of Ternary Lithium Battery Pack Under Preload Force

Overcharging is a primary cause of thermal runaway in ternary lithium‐ion batteries, often leading to serious safety incidents. Early detection of thermal runaway during overcharging is therefore critical. This study investigates a 5 Ah ternary lithium battery pack, applying appropriate preload force to simulate real‐world conditions. Various overcharge experiments are conducted under different conditions, and changes in battery voltage, temperature, and expansion force are thoroughly analyzed. The results indicate that under the same initial conditions, higher charging rates accelerate the temperature rise in the lithium battery. Additionally, the internal gas generation rate increases, causing a faster rise in edge pressure and leading to earlier battery cracking. Building on these findings, a three‐level early warning algorithm is developed, which comprehensively considers voltage, temperature, and expansion force changes. Experimental validation demonstrates that this algorithm can accurately identify the current stage of thermal runaway and detect the transition to the third warning stage 604 s before complete failure, thus providing critical protection for the safe operation of the battery pack. This study offers valuable guidance for enhancing the monitoring and early warning capabilities of battery management systems.

Analysis of the behavior of a gas-generating system under runaway conditions in a closed vessel

In the event of a runaway reaction, emergency relief systems (ERS) act as the last line of defense against the vessel explosion. To date, ERS design for scenarios involving the runaway of chemical mixtures that generate gaseous reaction products remains very challenging as it requires the prediction of the gas generation rate under runaway conditions at large scale. Current methodologies for the assessment of the gas generation rate are based on pseudo-adiabatic calorimetric experiments at laboratory scale in which the temperature and pressure profiles resulting from the runaway are used to assess the gas generation rate using the ideal gas law. The gas generation rate needs to be further corrected for the thermal inertia (φ-factor), of the calorimetric cell used (φ>1) to predict large scale behavior (φ≈1). The work described in this paper focuses on evaluating the capability of this approach to accurately assess the gas generation rate. It uses a dynamic simulator tool based on rigorous thermodynamics to calculate the temperature, pressure, and the composition of each component in a closed vessel containing a gas generating reactive mixture (decomposition of 20 % w/w di-tert butyl peroxide in toluene) under runaway conditions over a range of initial vessel fill levels. The results were analyzed to develop a better understanding of the phenomena that govern the thermal behavior of the mixture, the overall pressurization of the vessel, rate of generation of the gaseous products and its distribution in the liquid and vapor phase of the vessel as the runaway reaction occurs. The simulated pressure, temperature and phase composition data rigorously calculated by the simulator were used to assess and highlight the limitations of using the temperature and pressure in a closed vessel and the ideal gas law to evaluate the gas generation rate. The simulations were also used to evaluate the validity of φ-factor correction methods currently available in the literature.

PERIODIC FOAMING DURING SELECTIVE ISOLATION OF HIGHLY PERMEABLE CHANNELS OF POROUS MEDIUM

Selective isolation of watered interlayers by forming barriers formed by highly viscous gels or insoluble precipitates does not always lead to the desired results. Field experience confirms that at some distance from the formed barrier, the filtration flow restores its configuration and the water injected into the formation again moves through highly permeable channels. An increase in the efficiency of flow deflection can be achieved by creating not a single barrier, but a whole sequence of alternating deep-penetrating insulating barriers, separated from each other by a certain distance in highly permeable pores. The paper presents the results of studies of quasi-periodic foaming in order to control mobility under conditions of selective isolation of water in pore channels of high permeability. Foaming occurs due to the in-bulk reaction between concentrated aqueous solutions of gas-generating and gas-generating solutions. Flow pattern of injected aqueous solutions of foaming reagents along current tubes is investigated. The task is to determine the space-time distribution of reagents in given zones of the porous medium. The problem of establishing the correlation between the spatial distribution of the gas formation zone and the dynamics of the gas formation process over time on the one hand, as well as the concentration of reactants, the diffusion rate (mutual diffusion), the gas generation rate and the probability of nucleation on the other hand was solved. The degree of flow blockage in highly permeable zones of the formation depends on the rate of in-situ foam generation and the simulation consists in the fact that it is similar to the law of filtration with a limiting gradient. The paper discusses the process of quasi-periodic gas formation during the movement of mixing solutions in porous media. In stationary filtration in a homogeneous porous medium, the process is described by the proposed system of equations. A system of equations is proposed that describes the movement of a liquid taking into account adsorption of reagents, diffusion and dynamics of the foaming reaction. The results obtained can serve as the basis for developing a method for controlling the water cut of porous media during waterflooding of oil formations. This, in turn, leads to the leveling of the displacement front and an increase in the completeness of coverage.

Research on the Characteristics of Partial Discharge Gas Generation in Typical Defects of Oil Immersed Current Transformers

During the operation of oil-immersed current transformers, they gradually deteriorate due to various factors. In order to study the relationship between partial discharge and gas generation characteristics under different typical defects, this paper measures the unit-time discharge energy, unit-time apparent discharge quantity, pulse repetition rate, and gas generation rate during the discharge development process of three typical defects: protrusion defect, surface defect, and gas gap defect. The study reveals that the generation of hydrocarbon gases and hydrogen in the oil mainly depends on discharges with an apparent discharge quantity above 300pC. Among the discharge characteristics, the unit-time discharge energy and unit-time average discharge quantity significantly impact the gas generation rate. It is found that the content of C2H2 and C2H4 in the oil for protrusion and surface defects increases significantly with discharge intensity, while CH4 and H2 show significant changes for gas gap defects. Additionally, an approximately linear relationship exists between discharge energy per unit time, pulse repetition rate, and the rate of characteristic gas generation for both protrusion and surface defects, as well as for gas gap defects. These findings provide a reference for diagnosing current transformers and highlight the critical role of discharge characteristics in gas generation dynamics.

Solvation structure and electron isolation synergy of piperidine ionic liquid additives inspires high performance lithium metal batteries

The safety concerns associated with lithium metal stand as the foremost barrier preventing widespread application of lithium metal batteries, especially due to lithium dendrite growth and gas evolution from electrolyte decomposition. This study employed N‑butyl‑N-methyl-piperidinium bis(trifluoro-methyl-sulfonyl) imide (PP14TFSI) as an additive in the electrolyte, aimed at improving the safety attributes of lithium metal batteries. The assessment conducted on the protective mechanism of the PP14TFSI additive unveiled its capability to control create robust and rapidly ion-conductive SEI by adjusting the solvation structure. Simultaneously, PP14+ intercepts free electrons, inhibiting the decomposition of DME and subsequent gas generation. Due to the synergistic effects of these two mechanisms, the rate of gas generation was reduced by half. A comprehensive investigation of lithium metal-based cells exhibited promising performance, maintaining stable cycling for 2160 h at 25 °C, 0.5 mA cm−2, displaying consistently high CE > 98.5 % in a Li||Cu cell. Moreover, at 60 °C, 2 mA cm−2, the cells maintaining stability for 240 cycles while still exhibiting relatively high CE > 98.5 %. In addition, at a low N/P ratio of 4:1, the Li-S battery maintains a high capacity of 673.4 mA h g−1 after 200 cycles, while the Li-LFP battery maintains a capacity of 131.16 mA h g−1 and capacity retention of 91.02 % after 300 cycles at 1 C. This research lays groundwork for the exploration of ionic liquids as additives in lithium metal battery electrolytes to further enhance battery safety performance.

Experimental Research on Thermal-Venting Characteristics of the Failure 280 Ah LiFePO4 Battery: Atmospheric Pressure Impacts and Safety Assessment

With the widespread application of lithium-ion batteries (LIBs) energy storage stations in high-altitude areas, the impact of ambient pressure on battery thermal runaway (TR) behavior and venting flow characteristics have aroused wide research attention. This paper conducts a lateral heating experiment on 280 Ah lithium iron phosphate batteries (LFPs) and proposes a method for testing battery internal pressure using an embedded pressure sensor. This paper analyzes the battery characteristic temperature, internal pressure, chamber pressure, and gas components under different chamber pressures. The experiment is carried out in a N2 atmosphere using a 1000 L insulated chamber. At 40 kPa, the battery experiences two instances of venting, with a corresponding peak in temperature on the battery’s side of 136.3 °C and 302.8 °C, and gas generation rates of 0.14 mol/s and 0.09 mol/s, respectively. The research results indicate that changes in chamber pressure significantly affect the center temperature of the battery side (Ts), the center temperature of the chamber (Tc), the opening time of the safety valve (topen), the triggering time of TR (tTR), the time difference (Δt), venting velocity, gas composition, and flammable limits. However, the internal pressure and gas content of the battery are apparently unaffected. Considering the TR characteristics mentioned above, a safety assessment method is proposed to evaluate the TR behavior and gas hazard of the battery. The results indicate that the risk at 40 kPa is much higher than the other three chamber pressures. This study provides theoretical references for the safe use and early warning of energy storage LIBs in high-altitude areas.

Tree-inspired semiconductor-on-ceramic 2D/1D heterostructure for efficient CO2 photoreduction

Two-dimension nanosheets are ideal photocatalysts for CO2 reduction due to their high exposure of active sites and short charge transfer pathway. However, 2D photocatalysts have a tendency to agglomeration, thus compromising the performance of photocatalytic CO2 reduction. Trees, one of the most important plants for photosynthesis, have a unique “leaf-on-branch” structure. This unique two-dimension/one-dimension (2D/1D) configuration maximizes the adsorption of CO2 molecules and light harvesting. Herein, a tree-inspired semiconductor-on-ceramic 2D/1D heterostructure for efficient photocatalytic CO2 reduction is reported. The cobalt silicate (CoSi) nanosheets (∼0.68 nm) are in situ grown on the surfaces of hydroxyapatite (HAP) nanowires, creating a well-defined 2D/1D hierarchical structure. The vertical alignment of ultrathin CoSi nanosheets on the HAP nanowires effectively suppresses their agglomeration, leading to a large BET surface area (106.45 m2/g) and excellent CO2 adsorption (8.00 cm3 g−1). The results of photoelectrochemical characterization demonstrate that the 2D/1D hierarchical structure is powerful to expedite charge transfer. As a result, the gas generation rate of CO is as high as 28780 μmol g−1 h−1 over the CoSi-on-HAP 2D/1D heterostructure. In addition, the electron transfer mechanism and reaction pathways of CO2 reduction are revealed by in situ irradiated XPS and in situ DRIFT spectra.

Prediction of anaerobic degradation kinetics based on substrate composition of lignocellulosic biomass

This study presents a comprehensive biochemical predictive approach for assessing biogas production kinetics across ten lignocellulosic substrates in batch operation. The methodology employs a range of kinetic and regression models, all grounded in the substrates' chemical composition. Among the kinetic models, the cone model demonstrated superior performance, achieving an average error of 1.67 % in describing biogas production from all substrates. The quadratic Monod type model followed closely, with an error of 1.96 %. Among the regression models, on the other hand, the logistic function model exhibited enhanced predictive capabilities, yielding an average error of 6.02 %, while the Chen and Hashimoto one showed a higher error of 60.54 %. The findings underscore the potential of precise biogas production forecasting and tracking the daily rates of gas generation, rather than solely relying on cumulative gas yields at the end of the process.

Comparative study on the thermal runaway characteristics of Li(NixCoyMnz)O2 batteries

Lithium-ion batteries (LIBs) generate substantial gas during the thermal runaway (TR) process, presenting serious risks to electrochemical energy storage systems in case of ignition or explosions. Previous studies were mainly focused on investigating the TR characteristics of Li(NixCoyMnz)O2 batteries with different cathode materials, but they were conducted in isolation. In this study, the thermal runaway characteristics of prismatic cells that use Li(NixCoyMnz)O2 (with x ranging from 0.33 to 0.9) cathode materials in an inert environment, which are commonly used or proposed for energy storage applications, are examined. The findings of this research show that the normalized gas generation rate remains consistent, regardless of the battery capacity or experimental chamber volume, with a value of 0.1 ± 0.03 mol∙Ah⁻1. High-capacity cells have short jetting durations, and a high nickel content leads to increased mass loss rates. The flammability limits of the gases expelled during thermal runaway, represented by the lower flammability limit (LFL), remain stable at 8 ± 1.8 % with minimal variations. However, the upper flammability limit (UFL) varies significantly, ranging from 30 % to 60 %. Increasing the battery capacity or reducing the experimental chamber volume increases the explosion index. The explosive, combustibility, and jetting duration characteristics of the emitted gases from five different battery chemical compositions provide valuable insights for risk assessment in future electrochemical energy storage systems.

Influence of mudstone on coal spontaneous combustion characteristics and oxidation kinetics analysis

To explore the spontaneous combustion characteristics and hazards of the low-temperature oxidation (LTO) stage in the process of spontaneous combustion of coal and mudstone, the pore structure, spontaneous combustion characteristic parameters, and exothermic characteristics of coal and mudstone were tested and studied, and the oxidation kinetic parameters were calculated. The results show that mudstone has a larger specific surface area and pore volume than coal. From the fractal characteristics, the pore structure of mudstone is more complex than that of coal. According to the comparison of theoretical and actual gas generation and oxygen consumption rate curves, it is found that there is an interaction between coal and mudstone in the LTO process. With the increase of mudstone mass ratio, gas production, and its oxygen consumption rate increase. Among them, CM-4 (Coal:Mudstone = 1:1) has the highest exothermic intensity and the exothermic factor (A) and fire coefficient (K) increase with the increase of mudstone content. The apparent activation energy of the mudstone sample is lower than that of the raw coal, indicating that the sample after adding mudstone is more likely to have spontaneous combustion in the LTO stage.

Neutronics analysis of the ion cyclotron resonance heating antenna of the China Fusion Engineering Test Reactor

Ion cyclotron resonance heating (ICRH) is an important auxiliary heating method applied to the China Fusion Engineering Test Reactor, which can effectively heat the ions and electrons in plasma. Owing to the harsh nuclear environment, neutronic analyses are required to verify tritium self-sufficiency and neutron-shielding requirements. In this study, a neutronics analysis of the ICRH antenna was conducted using the COre and System integrated engine for Reactor Monte Carlo (cosRMC) code to estimate the neutron flux, radiation damage, nuclear heating, gas generation rate of key components, and tritium breeding ratio (TBR), providing data support for the subsequent optimization of the shielding design. In addition, the neutron flux of the coils around the antenna was calculated to prevent the entry of neutrons that damage the magnetic field coils through the gaps between the port plugs and antenna, and the shielding effects of the port-plug antenna on the surrounding components were analyzed. Finally, the results obtained using the cosRMC and MCNP codes were compared, which and presented good agreement, thus verifying the reliability of the neutronic analysis using the cosRMC code.

APPLICATIO STUDY ON KINETICS OF BIOMASS PYROLYSIS IN THE FIXED BED. 1. SIMULATION AND NUMERICAL ANALYSIS OF LIGNIN THERMAL DECOMPOSITION

A non-stationary model of the biomass thermolysis process was built based on three primary independent parallel reactions of the biomass active part conversion into gas, liquid phase and char, taking into account the secondary reactions of tar decomposition into char and light gas. It is shown that the main role in the production of mixed pyrolysis gas (primary gas and light gas) is played by the light gas generation rate due to the secondary reaction of tar decomposition into light gas. This reaction rate significantly exceeds the primary gas production rate due to the fact that the activation energy of the primary gas formation reaction lignin → gas is higher than the activation energy of the lignin → tar reactions. It was found that the rate of generation of the primary reaction lignin → char significantly outweighs the rate of tar → char production, so the latter reaction can be neglected. It is shown that as the temperature of lignin pellets increases, CO and light hydrocarbon C1.16H4 increase and carbon dioxide CO2 and H2О decrease. The consumption of volatile components in the pyrolyzer depends on the temperature distribution of biomass pellets across the pyrolyzer cross-section, which decreases towards the center of the retort, following the consumption of gaseous components decreases as they approach the axis of the pyrolyzer. The amount of mixed pyrolysis gas released and char depends on the radial coordinate r. At r = 0.047 m and time τ = 380 s, the amount of mixed pyrolysis gas is 90 % and char is 10 %, at r = 0.016 m and τ = 380 s = 83 % and = 17 %. Bibl. 13, Fig. 7.

Production Characteristics of Volatiles from Anthracite Cracking via Microwave-Induced Discharge.

The ignition of anthracite with arc plasma has not been applied due to its low chemical effect and volatile content in anthracite. The nonequilibrium plasma generated by a microwave-induced discharge has the ability to break branch chains and aromatic ring structures by kinetic effects, which has the potential for anthracite cracking and ignition. This work investigated anthracite cracking by microwave-induced discharges under an Ar/N2 atmosphere. Results showed that the maximum levels of CO production, total gas production, and total gas generation rate occur in 20% argon content due to an increase in the number of electrons and a decrease in the total electronic states excitation rate constant with an increase in the argon content. The total gas production in plasma cracking is larger than that by pyrolysis, indicating the crack of polycyclic aromatic hydrocarbon by plasma. In addition, we attempted anthracite combustion under an 80% N2 and 20% O2 atmosphere.

Induced Partial Saturation Using Pseudomonas stutzeri Biogas for Mitigate Structure Settlement

Induced partial saturation (IPS) is a new foundation treatment method for mitigating soil liquefaction using biogas. A series of laboratory tests were performed to demonstrate the influencing factors of IPS using Pseudomonas stutzeri biogas. On the basis of the optimal biogas production conditions, the intervention effect of Pseudomonas stutzeri biogas on the foundation deformation under buildings was investigated based on shaking table tests. The test results showed that the best carbon source in the denitrification process of Pseudomonas stutzeri biogas is sodium citrate. The most effective initial value of optical density-based concentration was 0.1. The carbon–nitrogen ratio (C/N) of the bacterium suspension was used as the index to control the saturation. The degree of saturation reduction showed a good linear correlation with the C/N. The optimum temperature of this method was between 20 °C and 30 °C. The most suitable pH value was between 7 and 9. The environmental factors had minimal influence on the degree of saturation reduction but had a significant effect on the average rate of gas generation and the period of initial stagnation. After Pseudomonas stutzeri biogas desaturation, the settlement of the building was greatly reduced. The settlement of saturation of 92.5% sand foundation reached 17.1 mm, and the 85% saturation was only 10.6 mm. These results provide a good foundation for the feasibility of utilizing Pseudomonas stutzeri biogas mitigation of the liquefaction hazard of sand.

Molecular Mechanisms of the Generation and Accumulation of Gas at the Interface.

Gas-evolving reactions are widespread in chemical and energy fields. However, the generated gas will accumulate at the interface, which reduces the rate of gas generation. Understanding the microscopic processes of the generation and accumulation of gas at the interface is crucial for improving the efficiency of gas generation. Here, we develop an algorithm to reproduce the process of catalytic gas generation at the molecular scale based on the all-atom molecular dynamics simulations and obtain the quantitative evolution of the gas generation, which agrees well with the experimental results. In addition, we demonstrate that under an external electric field, the generated gas molecules do not accumulate at the electrode surface, which implies that the electric field can significantly increase the rate of the gas generation. The results suggest that the external electric field changes the structure of the water molecules near the electrode surface, making it difficult for gas molecules to accumulate on the electrode surface. Furthermore, it is found that gas desorption from the electrode surface is an entropy-driven process, and its accumulation at the electrode surface depends mainly on the competition between the entropy and the enthalpy of the water molecules under the influence of the electric field. These results provide deep insight into gas generation and inhibition of gas accumulation.

Investigation on gas generation and corresponding explosion characteristics of lithium-ion batteries during thermal runaway at different charge states

This study investigates the gas generation characteristics and explosion limits of the gas generated by 18650-type LiNi1/3Co1/3Mn1/3O2 (NCM) cells during thermal runaway (TR) at different states of charge (SOCs). An accelerating rate calorimeter is employed to initialize TR, together with an airtight jar for gas measurement. Based on the detected gas composition for NCM cells, the corresponding explosion limits are computed and further compared with those of LiFePO4 (LFP) and LiNi0.80Co0.15Al0.05O2 (NCA) cells. The results reveal that the gas generation rates are slightly higher for NCM cells with lower SOCs prior to the violent TR processes compared to those for high-SOC cells, primarily due to the elevated reaction temperature. Moreover, during violent TR, multiple-peak features are observed for the gas generation rate curves, especially at high-SOC conditions. On the other hand, typical Z-shaped explosion limit curves are observed for all generated mixtures. As the cathode material varies from NCM to LFP and NCA, the explosion limits shift from high-temperature regions to low-temperature regions. In contrast to common beliefs that the generation gas at high SOCs is more explosive, non-monotonic responses of the explosion limit curves are found with respect to cell SOC. The significance of minor components of the generated gas, including ethylene and ethane, in reducing the explosivity of the mixture, is highlighted through sensitivity analyses.

Numerical investigation of subcooled two-phase flow and heat transfer characteristics in a liquefied natural gas cargo containment system

The increase demand in liquefied natural gas (LNG) leads to an increase in the import and export of LNG cargo using LNG carriers with composite insulation and double-hull structures for membrane-type storage tanks. Therefore, the transient characteristics of cryogenic heat transfer in LNG cargo containment systems have become important for understanding the physics when LNG vaporizes into the gas phase to minimize the cargo loss of boil-off gas (BOG). However, public papers on fundamental research on long-term computational fluid dynamics (CFD) simulations are still lacking. In the present study, the transient flow behaviors of LNG fluids and the heat transfer characteristics were numerically studied by applying the simplified single-layer insulation in an LNG cargo containment system, based on an initial temperature of TLNG,0 = 110.5 K and saturation temperature of TLNG,sat = 111.5 K in the boundary condition of IGC code. The proposed analysis procedure can serve as a reference for relative comparison of predicted BOG difference in LNG cargo holds.Consequently, the heat transfer mode between the two-phase methane and the solid insulation could be typically classified into two different regimes: (1) a subcooled regime before reaching the saturation temperature from the initial temperature, and (2) a boiling regime after reaching the saturation temperature. In the subcooled regime, the subcooled liquid exhibited bulk flow motion induced by natural convection. The loss rate of LNG mass per time interval was extracted from the best-fit correlations as −0.0448 kg/s at 1 d (105 s) to cool down the insulation system and −0.0072 kg/s at 5 d (5 × 105 s) to reach the LNG saturation temperature. When the predicted value of the loss rate of LNG mass by the CFD simulation was regarded as the generation rate of boil-off gas, it was smaller than the designed value of the boil-off gas of 0.464 kg/s corresponded to boil-off rate (BOR) about 0.2 %/day. In the boiling regime and under sufficiently cooled conditions, the loss rate of LNG mass per time interval did not consistently exceed the BOR value. The liquid flow exhibited a turbulent-like motion despite the relatively low velocity at 10 d (106 s). Especially, the increase in the effective thermal conductivity was a good indicator for distinguishing between the boiling and subcooled regimes.

Spectroscopy electrochemical impedance characterization of membranes electrode assemblies for PEM electrolyzers

Abstract Hydrogen is projected as a key energy vector to achieve aspiring global decarbonization goals mainly for those sectors where greenhouse gas emissions are highly challenging to reduce. Therefore, green hydrogen production using water PEM electrolysis has become the aim of numerous recent studies. One of the crucial challenges for improving hydrogen production is reaching a deep knowledge of the role of anodes electrocatalysts. In this investigation we studied and modeled the effect of different anode electrocatalysts and solid electrolyte’s configurations in a single-cell PEM electrolyzer performance, using EIS. We assembled and tested PEM electrolysis MEAs with two different configurations. MEA-1 comprises in catalyst-coated membrane (MEA)-type with a geometric area of 25 cm2 containing Nafion™ 115, 3.0 mg cm−2 IrRuOx as the anode, and 3.0 mg cm−2 PtB for the cathode. MEA-2 involves catalyst-coated membrane (MEA)-type with a geometric area of 25 cm2 containing Nafion™ 117, and 3.0 mg cm−2 PtB both for the anode and cathode. Sintered Ti plates were used as gas diffusion layers. After hydration and activation steps at room temperature, the polarization curve was performed. Hysteresis curves were achieved to provide information on thermal equilibrium during the measurements. The oxygen and hydrogen production rate were measured and compared to theoretical values. Experiments were carried out at 20 and 40 °C. EIS measurements were performed at different points of the polarization curve, sweeping a frequency range between 10 kHz and 10 mHz, with an amplitude of 5 mV and taking 10 points per decade. To avoid electrocatalysts area effects in charge transfer reaction, time constants were calculated. It can be clearly observed the trend of resistances and overpotentials according to different process control. Low onset potential for oxygen evolution reaction depicts for MEA-1 means that there will be less power consumption to achieve the same efficiency or same amount of gas generation rate compared to high onset potential case depicted for MEA-2. Although different membrane thicknesses would result in different electrochemical performances due to the change in the ionic resistance, for the thickness studied we did not observe a change in the ionic resistance. The experimental results show an increase in efficiency with temperature, reflected in higher currents for a given potential and lower time constants resulting in the EIS runs.