Search Results (173)

We surveyed the air quality conditions in 18 homes with gas stoves for PM_2.5, CO₂, NO₂ and CO using calibrated low-cost sensors. In each home, participants were asked to cook as usual, but to record their cooking activities and mitigation efforts (windows, ventilation fans, etc.). All homes showed enhanced pollutants during, and immediately after, times of cooking or stove use. For each home, we quantified the minutes per day and minutes per minute of cooking over known health thresholds for each pollutant. On average, homes exhibited 38 min per day over one or more of these thresholds, with PM_2.5 and NO₂ being the pollutants of greatest concern. Six homes had much higher occurrences over the health thresholds, averaging 73 min per day. We found an average of 1.0 min over one or more of the health thresholds per minute of cooking when no mitigation was used, whereas when mitigation was used (filtration or vent fan), this value was reduced by 34%. We further investigated several mitigation methods including natural diffusion, a commercial HEPA filter unit, a commercial O₃ scrubber and a ventilation fan. We found that the HEPA unit was highly effective for PM_2.5 but had no impact on any of the gaseous pollutants. The O₃ scrubber was moderately effective for NO₂ but had little impact on the other pollutants. The ventilation fan was highly effective for all pollutants and reduced the average pollutant lifetime significantly. Under controlled test conditions, the pollutant lifetime (or time to reach 37% of the original concentration), was reduced from an average of 45 min (with no ventilation) to 7 min. While no commercial filter showed efficacy for both PM_2.5 and NO₂, the fact that each could be removed individually suggests that a combined filter for both pollutants could be developed, which would significantly reduce health impacts in homes with gas stoves. Full article

For cold venting processes frequently employed in oil and gas fields, precisely predicting the instantaneous diffusion process of the vented explosive and/or toxic gases is of great importance, which cannot be captured by the Reynolds-averaged Navier–Stokes (RANS) method. In this paper, the large eddy simulation (LES) method is introduced for gas diffusion in an open space, and the diffusion characteristics of the sulfur-containing natural gas in the cold venting process is analyzed numerically. Firstly, a LES solution procedure of compressible gas diffusion is proposed based on the ANSYS Fluent 2022, and the numerical solution is verified using benchmark experiments. Subsequently, a computational model of the sulfur-containing natural gas diffusion process under the influence of a wind field is established, and the effects of wind speed, sulfur content, the venting rate and a downstream obstacle on the natural gas diffusion process are analyzed in detail. The results show that the proposed LES with the DSM sub-grid model is able to capture the transient diffusion process of heavy and light gases released in turbulent wind flow; the ratio between the venting rate and wind speed has a decisive influence on the gas diffusion process: a large venting rate increases the vertical diffusion distance and makes the gas cloud fluctuate more, while a large wind speed decreases the vertical width and stabilizes the gas cloud; for an obstacle located closely downstream, the venting pipe makes the vented gas gather on the windward side and move toward the ground, increasing the risk of ignition and poisoning near the ground. The LES solution procedure provides a more powerful tool for simulating the cold venting process of natural gas, and the results obtained could provide a theoretical basis for the safety evaluation and process optimization of sulfur-containing natural gas venting. Full article

In gas transmission stations, flame arrestors are typically installed in pipelines and venting systems to prevent the flames resulting from accidental ignition or deflagration of combustible gases during transmission from propagating through the pipelines. During actual operation, the presence of solid particulates in the gas compromises the flame-arresting efficacy and increases the failure rate of current pipeline flame arrestors. This study employs an integrated approach combining theoretical analysis and numerical simulation to establish a numerical model for flame arrestors that accounts for solid particle deposition effects. The model reveals the distribution characteristics of velocity fields, pressure fields, gas phase volumetric concentration fields, and solid deposition rate fields within pipeline flame arrestors. It systematically investigates the influence mechanisms of porosity, flame arrestor core thickness, inlet flame velocity, arrestor length, particle size, particle concentration on pressure drop, flame arrestment velocity, and deposition rate. These findings provide theoretical support for optimizing flame arrestor structural design and reducing operational failure rates. Full article

Efficient oil transportation in field-deployed mobile pipelines is critical, but mixed-oil zones at interfaces reduce quality and increase waste, necessitating effective interface detection and cutting. Existing online densitometers, such as vibrating tube or high-accuracy magnetic suspension types, typically require external power, limiting their use in remote or emergency/temporary field operations. A self-powered device is presented that leverages gravitational force variations acting on a float to detect density changes and trigger automatic cutting. Validated with gasoline, diesel, kerosene, and water, it achieves a 10 kg/${\mathrm{m}}^3$ resolution, deemed sufficient for functional batch separation in its target application, with switching times of 61–395 s for density differences (760–835 kg/${\mathrm{m}}^3$). It supports 20–90% blending ratios, with a vent mitigating gas effects. The modular, robust, self-powered design suits emergency operations, offering a practical alternative to powered systems. Future work targets improved resolution and environmental testing. Full article

The development of deep coalbed methane (CBM) wells faces challenges such as significant reservoir depth, low permeability, and severe liquid loading in the wellbore. Traditional drainage and gas recovery techniques struggle to meet the dynamic production demands. This study, using the deep CBM wells at the Jishen 15A platform as an example, proposes a “cyclic gas lift–wellhead compression-vent gas recovery” composite synergy technology. By selecting a critical liquid-carrying model, innovating equipment design, and dynamically regulating pressure, this approach enables efficient production from low-pressure, low-permeability gas wells. This research conducts a comparative analysis of different critical liquid-carrying velocity models and selects the Belfroid model, modified for well inclination angle effects, as the primary model to guide the matching of tubing production and annular gas injection parameters. A mobile vent gas rapid recovery unit was developed, utilizing a three-stage/two stage pressurization dual-process switching technology to achieve sealed vent gas recovery while optimizing pipeline frictional losses. By combining cyclic gas lift with wellhead compression, a dynamic wellbore pressure equilibrium system was established. Field tests show that after 140 days of implementation, the platform’s daily gas production increased to 11.32 × 10⁴ m³, representing a 35.8% rise. The average bottom-hole flow pressure decreased by 38%, liquid accumulation was reduced by 72%, and cumulative gas production increased by 370 × 10⁴ m³. This technology effectively addresses gas–liquid imbalance and liquid loading issues in the middle and late stages of deep CBM well production, providing a technical solution for the efficient development of low-permeability CBM reservoirs. Full article

The use of a conceptual model of reference and modelling of relevant processes is mandatory to correctly interpret chemical and isotopic data. Adopting these basic guidelines, we have interpretated the unprecedented increase in the H₂S_(g) concentration and the concurrent unexpected decrease in the δ³⁴S value of H₂S_(g) recorded since 2018 in the fumarolic effluents of the Bocca Grande fumarolic vent at Solfatara, Campi Flegrei caldera, in the framework of our conceptual model of the Solfatara magmatic–hydrothermal system. Assuming that the magma chamber situated at depths ≥ 8 km was filled at the end of the 1982–1984 bradyseismic crisis and no refilling episodes took place afterwards, as suggested by gas geochemistry, the concentration and the δ³⁴S value of H₂S_(g) of the Bocca Grande fumarolic effluents are controlled by closed-system degassing of the melt at depths ≥ 8 km and disproportionation of SO₂ in the deep hydrothermal reservoir (6.5–7.5 km depth) hosted in carbonate rocks where H₂S equilibrates. These processes have been active during the last 40 years, but 41.1% (±6.4%) of the sulfur initially stored in the melt (2200 mg/kg) was lost in the 4-year period of April 2018–April 2022. This marked loss of S from the melt in 2018–2022 might be due to the high solubility of sulfur in the melt, which caused its preferential separation during the late degassing stages. These findings are of utmost importance for the surveillance of the Solfatara magmatic–hydrothermal system during the ongoing bradyseismic crisis. Full article

Liquid hydrogen is regarded as a key energy source and propellant for lunar bases due to its high energy density and abundance of polar water ice resources. However, its low boiling point and high latent heat of vaporization pose severe challenges for storage and management under the extreme lunar environment characterized by wide temperature variations, low pressure, and low gravity. This paper reviews the strategies for siting and deployment of liquid hydrogen storage systems on the Moon and the technical challenges posed by the lunar environment, with particular attention for thermal management technologies. Passive technologies include advanced insulation materials, thermal shielding, gas-cooled shielding layers, ortho-para hydrogen conversion, and passive venting, which optimize insulation performance and structural design to effectively reduce evaporation losses and maintain storage stability. Active technologies, such as cryogenic fluid mixing, thermodynamic venting, and refrigeration systems, dynamically regulate heat transfer and pressure variations within storage tanks, further enhancing storage efficiency and system reliability. In addition, this paper explores boil-off hydrogen recovery and reutilization strategies for liquid hydrogen, including hydrogen reliquefaction, mechanical, and non-mechanical compression. By recycling vaporized hydrogen, these strategies reduce resource waste and support the sustainable development of energy systems for lunar bases. In conclusion, this paper systematically evaluates passive and active thermal management technologies as well as vapor recovery strategies along with their technical adaptability, and then proposes feasible storage designs for the lunar environment. These efforts provide critical theoretical foundations and technical references for achieving safe and efficient storage of liquid hydrogen and energy self-sufficiency in lunar bases. Full article

Numerical simulations reveal the combustion dynamics of hydrogen-blended natural gas (H-BNG) in semi-open spaces. In the typical semi-open space scenario, increasing the hydrogen blending ratio from 0% to 60% elevates peak internal pressure by 107% (259.3 kPa → 526.0 kPa) while reducing pressure rise time by 56.5% (95.8 ms → 41.7 ms). A vent size paradox emerges: 0.5 m openings generate 574.6 kPa internal overpressure, whereas 2 m openings produce 36.7 kPa external overpressure. Flame propagation exhibits stabilized velocity decay (836 m/s → 154 m/s, 81.6% reduction) at hydrogen concentrations ≥30% within 2–8 m distances. In street-front restaurant scenarios, 80% H-BNG leaks reach alarm concentration (0.8 m height) within 120 s, with sensor response times ranging from 21.6 s (proximal) to 40.2 s (distal). Forced ventilation reduces hazard duration by 8.6% (151 s → 138 s), while door status shows negligible impact on deflagration consequences (412 kPa closed vs. 409 kPa open), maintaining consistent 20.5 m hazard radius at 20 kPa overpressure threshold. These findings provide crucial theoretical insights and practical guidance for the prevention and management of H-BNG leakage and explosion incidents. Full article

The venting process is one of the most important events during the thermal runaway (TR) of lithium-ion batteries (LIBs) in determining fire accidents, while different ambient pressures will exert an influence on the venting events as well as the TR. Ternary nickel–cobalt–manganese (NCM) batteries with a 75% state of charge (SOC) were employed to conduct TR tests under different ambient pressures in a sealed chamber with dilute oxygen. It was found that elevated ambient pressure results in milder ejections in terms of jet temperature and mass loss. Gas venting characteristics were also obtained. Additionally, the amount of carbon dioxide (CO₂), hydrogen (H₂), methane (CH₄), and ethylene (C₂H₄) released increase with ambient pressure, while carbon monoxide (CO) varies inversely with ambient pressure. The higher the ambient pressure is, the greater the flammability risk is. The molar amount of C, H, O, and total gases released shows a positive correlation with the maximum battery temperature and ambient pressure. This study will support the design of safety valves and help reveal the effects of venting events on the evolution of TR. Full article

Liquid hydrogen (LH2) is a promising energy carrier to decrease the climate impact of aviation. However, the inevitable formation of hydrogen boil-off gas (BOG) is a main drawback of LH2. As the venting of BOG reduces the overall efficiency and implies a safety risk at the airport, means for capturing and re-using should be implemented. Metal hydrides (MHs) offer promising approaches for BOG recovery, as they can directly absorb the BOG at ambient pressures and temperatures. Hence, this study elaborates a design concept for such an MH-based BOG recovery system at hydrogen-ready airports. The conceptual design involves the following process steps: identify the requirements, establish a functional structure, determine working principles and combine the working principles to generate a promising solution. Full article

Thermal runaway (TR) has become a critical safety concern with the widespread use of lithium-ion batteries (LIBs) as an energy storage solution to meet the growing global energy demand. This issue has become a significant barrier to the expansion of LIB technologies. Addressing the urgent need for safer LIBs, this study developed a comprehensive model to simulate TR in cylindrical 18650 nickel cobalt manganese (NMC) LIBs. By incorporating experiments with LG^®-INR18650-MJ1 cells, the model specifically aimed to accurately predict critical TR parameters, including temperature evolution, internal pressure changes, venting phases, and mass loss dynamics. The simulation closely correlated with experimental outcomes, particularly in replicating double venting mechanisms, gas generation, and the characteristics of mass loss observed during TR events. This study confirmed the feasibility of assuming proportional relationships between gas generation and the cell capacity and between the mass loss from solid particle ejection and the total mass loss, thereby simplifying the modeling of both gas generation and mass loss behaviors in LIBs under TR. Conclusively, the findings advanced the understanding of TR mechanisms in LIBs, providing a solid foundation for future research aimed at mitigating risks and promoting the safe integration of LIBs into sustainable energy solutions. Full article

With the accelerated application of lithium-ion batteries, the design and optimization of their safety features have become increasingly important. However, the mechanisms by which different safety vent bursting pressures affect thermal runaway and its product compositions remain unclear. This study comparatively investigates the effects of safety vent bursting pressures of 1 MPa, 2 MPa, and 3 MPa on thermal runaway characteristics and product compositions. The results indicate that, under these three conditions, the safety vent bursts at approximately 800 s, 1000 s, and 1300 s after heating begins, with gas volumes of 5.3 L, 6.1 L, and 6.5 L, respectively. Additionally, higher bursting pressures lead to increased H₂ production during thermal runaway. The characterization of solid product compositions reveals that the aluminum current collector participates in internal thermal runaway reactions, resulting in substances such as LiAlO₂ or metallic Al in the solid products under different bursting pressures. This study provides important references for improving existing battery safety standards and optimizing battery safety designs. It also provides insights and references for metal recovery from batteries and investigations into battery fires. Full article

Lithium-ion batteries have been increasingly demonstrated in reuse applications for environmental and economic reasons, and stationary energy storage systems (ESS) and mobile ESS are emerging as reuse applications for electric vehicle batteries. Most mobile ESS deployments are at large scales, necessitating experimental data on thermal runaway (TR) to ensure comprehensive safety. In this study, TR induction and suppression experiments were conducted using fully charged NCM-based batteries at the cell (750 Wh), module (7.5 kWh), and pack (74 kWh) levels. The stepwise TR experiments measured changes in temperature, voltage, heat release rate, volatile organic compound concentrations, and vent gas composition. The suppression experiments assessed the effective water injection rate, timing, and volume required to mitigate TR propagation. The results demonstrate that in the case of TR caused by thermal abuse, early detection of battery abnormalities is possible through monitoring pre-TR indicators, such as temperature and vent gas concentration. It was also confirmed that CO₂ injections can effectively cool the battery without causing damage. Furthermore, it is proposed that rapid water injection, directly contacting the battery immediately after the onset of TR, can successfully prevent TR propagation. Full article

This study analyzes the shortcomings of South Korea’s current evaluation method of ventilation performance for apartment buildings and suggests improvements. The current Korean regulations rely on the air change rate method, which is a prescriptive method and thus inadequately measures indoor air quality practically. Therefore, this study reviews various standards, finding that these standards can be categorized into those evaluating the mechanical performance of ventilators and those assessing indoor ventilation performance. This study highlights that the standards evaluating indoor ventilation performance are based on the tracer gas method but lack clear testing procedures and boundary conditions. This research also reviews the various previous research articles, noting that Korean research places emphasis on system design parameters, while international research focuses on architectural factors. It also identifies inconsistencies in the experimental setups across studies. To improve the current evaluation methods, the research suggests enhancing the tracer gas method with clear testing procedures and introducing indicators such as the age of air and uniformity coefficient together. Since the air change rate method does not consider the actual airflows and distribution in indoor spaces, this method is limited to deriving improvements in indoor ventilation performance. However, the suggested tracer gas method and indicators can be used to discover the optimal locations of vents for better indoor air quality or to drive a better building design to achieve better indoor ventilation performance. In other words, these enhancements aim to provide more accurate and comprehensive insights into the effectiveness of indoor ventilation systems, helping engineers, designers, and residents better understand and improve indoor air quality. Full article

Gas emissions from lithium-ion batteries (LIBs) have been analysed in a large number of experimental studies over the last decade, including investigations of their dependence on the state of charge, cathode chemistry, cell capacity, and many more factors. Unfortunately, the reported data are inconsistent between studies, which can be explained by weaknesses in experimental methodologies, the misinterpretation of data, or simply due to the comparison of datasets that build on different prerequisites. In the present work, the literature on gassing from battery components and battery cells is reported, with a focus on vent gas composition resulting from internal chemical processing in the battery and excluding studies where the gases are combusted after venting. The aim is to identify datasets of high quality that contribute to the advancement of our understanding of gas emissions from LIBs. Gas compositions from different stages in the gassing process are included, starting with the slow formation of gases during normal operation via mild thermal events to a thermal runaway (TR) with extensive gas production. Available published data are used to map gas quantity and composition from LIBs undergoing venting, with or without a TR, and to identify gaps in understanding and the need for further research. Full article