Search

The flashover mechanism in an aircraft cargo compartment under low pressure was investigated in this study. A series of fire experiments were conducted in a scale model of a one-quarter volume FAA standard aircraft cargo compartment at 96 kPa and 60 kPa. The ignition of single-walled corrugated cardboard was chosen as the criterion of the flashover. The influence of different fire sizes and fuel types on the flashover was studied by comparing the average temperature of the smoke layer, the radiation heat flux at the floor level, and the heat release rate of the fire source. The critical condition and behavior of the flashover were analyzed. The results show that under low pressure, the flashover occurs at a higher temperature and radiation heat flux. Increasing the fire source size brings the flashover forward. At 60 kPa and 96 kPa, the cardboard ignites under a flashover when the average temperature of the smoke layer reaches 551 °C and 450 °C, and the average radiant heat flux at the floor level reaches 19.6 kW/m2 and 14 kW/m2, respectively. In addition, the minimum fire size for a flashover is directly proportional to the heat of evaporation and inversely proportional to the heat of combustion. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Efficient coal mining is essential for ensuring China’s energy security, and the advancement toward intelligent coal mining represents a strategic move to foster high-quality development within the coal industry. The cornerstone of realizing intelligent coal mines lies in underground space positioning technology. Accurate positioning is crucial not only for safeguarding miner safety but also for optimizing mining operations, improving equipment utilization and minimizing operational costs. The unique challenges of underground mining, such as the absence of satellite navigation signals, restricted and confined operating environments, and harsh electromagnetic and lighting conditions, place new requirements on positioning techniques. This paper focuses on the localization issues specific to underground coal mines, offering a systematic overview of four fundamental localization techniques: range intersection, database matching, dead reckoning, and multisource information fusion. Range intersection determines location by utilizing distance measurements obtained through various methods. Database matching employs online measurements to match against characteristics stored in a database. Dead reckoning calculates the current location by integrating measurements over time. Lastly, multisource information fusion enhances positioning accuracy by combining data from multiple sources. The paper further reviews detailed implementation schemes of these four positioning technologies in coal mines, highlighting typical sensors or systems and summarizing current research developments. For range intersection methods, methods such as visible light, ultrasonic, wireless local area network, bluetooth, ultra-wideband, and infrared positioning are examined. Database matching positioning methods include geomagnetic, gravity, and radio fingerprint positioning systems. Dead reckoning techniques cover inertial navigation, pedestrian navigation, and odometers, while multisource information fusion focuses on integrated navigation and simultaneous localization and mapping. Moreover, the paper identifies key challenges confronting underground positioning systems in coal mines. These challenges encompass the increasing inaccuracies in absolute localization methods, difficulties in correcting dead reckoning localizations, performance declines in multisource fusion localization methods, and the absence of comprehensive standardization. Given the complex environment of coal mines, there is still much room for improving the accuracy and reliability of underground positioning. To address these challenges, this paper proposes several avenues for improvement. Enhancing the performance of the positioning systems might involve fostering collaboration across multiple systems, incorporating brain-inspired navigation to explore new localization solutions, and strengthening seamless and emergency localization capabilities. Furthermore, in today’s interconnected intelligent age, the privacy and security aspects of positioning systems warrant careful consideration.

To explore the development characteristics of gas jets generated by pulsed detonation water ramjet engines working underwater in water deflectors, numerical simulations and experimental validations were conducted on underwater detonation gas jets generated by detonation tube within a cylindrical confined space by utilizing the detonation of combustible gases to generate pulsating bubbles in the underwater confined space. A flow field model of a single gas jet in an underwater confined space was established based on the Reynolds-averaged equations, the k-ε two-equation model, and the gas-liquid interface tracking method of the volume of fluid(VOF) coupled with the phase transportation equation. The Compressible Inter Foam solver in OpenFOAM was employed for numerically solving pulsed detonation gas jets in the confined space. The results show that the influence of confined space on the leading shock wave of underwater detonation is slight, and the amplitude of the leading shock wave changes insignificantly compared to that in free underwater space. However, the pressure disturbance caused by the detonation gas jet significantly increases, and its duration is prolonged. Additionally, it leads to a noticeable increase in pressure within the confined space compared to that outside the confined space. The pulsation period of bubbles in the confined space is extended to approximately 60 ms, and the radial dimension of the confined space has little effect on the fluctuation period of the bubbles. Therefore, it can be seen that confined space can increase the near-field pressure at the outlet of the underwater detonation tube and extend the action time of the gas jet. The research results are of important guiding significance for the study of thrust performance improvement methods for pulsed detonation water ramjet engines.

In the confined space of the underground coal mine, which is dominated by transportation lanes, explosion-proof diesel-powered trackless rubber-wheeled vehicles are becoming the main transportation equipment, and the exhaust gas produced by them is hazardous to the health of workers and pollutes the underground environment. In this experiment, a similar test platform is built to study the effects of wind speed, vehicle speed, and different wind directions on the diffusion characteristics of exhaust gas. In this paper, CO and SO2 are mainly studied. The results show that the diffusion of CO and SO2 gas is similar and the maximum SO2 concentration only accounts for 11.4% of the CO concentration. Exhaust gas is better diluted by increasing the wind speed and vehicle speed, respectively. Downwind is affected by the reverse wind flow and diffuses to the driver's position, which is easy to cause occupational diseases. When the wind is a headwind, the exhaust gases spread upwards and make a circumvention movement, gathering at the top. When the wind speed and vehicle speed are both 0.6 m/s, the CO concentration corresponds to the change trend of the Lorentz function when the wind is downwind and the CO concentration corresponds to the change trend of the BiDoseResp function when the wind is headwind. The study of exhaust gas diffusion characteristics is of great significance for the subsequent purification of the air in the restricted mine space and the protection of the workers' occupational health. [ABSTRACT FROM AUTHOR]

Immersed tube tunnel is the main structural form of cross-sea channel, the waterproof and tightness of immersed tube joints are crucial, which directly affects the safety and durability of the whole life of the project. OMEGA waterstop is the second waterproof device of the tube joint, its installation surface space is narrow, the working space is limited, and it has significant cross impact with other construction in the tunnel. Combined with the Shenzhen -Zhongshan Link immersed tube tunnel engineering, this paper introduces the OMEGA waterstop installation and construction technology in confined space of large steel shell immersed tunnel. This technology has the advantages of simple construction, flexible operation, high construction efficiency, and low impact on other processes. It can provide reference and experience for the installation of waterstops in pipe gallery structures such as immersed tunnels, underwater open-cut tunnels, and metro projects in the future. [ABSTRACT FROM AUTHOR]

Gas leakage accidents occur frequently in confined spaces, and heavy gases with a relative density greater than 1.15 among hazardous gases and greenhouse gases are commonly stored in confined spaces. However, atmospheric pollutant emission standards are becoming more stringent, and it is essential to remove heavy gas after accidents while reducing emissions to the atmosphere. This study proposes using a heavy gas collection tank (HGCT) to safeguard the internal environment and minimize emissions to the atmosphere. The capture efficiencies applicable to heavy-gas environments under different ventilation strategies are derived. This research analyzes the impact of the exhaust rate, leakage rate, density of heavy gas, and air supply modes on the indoor concentration distribution. The results demonstrate that the mass flow rate of heavy gas into the exhaust is positively correlated with the exhaust rate, but the gas from the exhaust system contains more air. The exhaust rate should be greater than four times the space volume per hour; otherwise, heavy gas above 1000 ppm accumulates to a height of 0.67 m at ground level. Finally, attachment ventilation as make-up air helps to reduce upstream heavy gas accumulation and reduces the extension of heavy gas along the room width. Combining an HGCT with floor slope and attachment ventilation achieves an efficiency of 96.28%. This study provides valuable insights and references for preventing hazardous heavy gas leakage. [ABSTRACT FROM AUTHOR]

Metal–organic framework (MOF) membranes with rich functionality and tunable pore system are promising for precise molecular separation; however, it remains a challenge to develop defect‐free high‐connectivity MOF membrane with high water stability owing to uncontrollable nucleation and growth rate during fabrication process. Herein, we report on a confined‐coordination induced intergrowth strategy to fabricate lattice‐defect‐free Zr‐MOF membrane towards precise molecular separation. The confined‐coordination space properties (size and shape) and environment (water or DMF) were regulated to slow down the coordination reaction rate via controlling the counter‐diffusion of MOF precursors (metal cluster and ligand), thereby inter‐growing MOF crystals into integrated membrane. The resulting Zr‐MOF membrane with angstrom‐sized lattice apertures exhibits excellent separation performance both for gas separation and water desalination process. It was achieved H2 permeance of ~1200 GPU and H2/CO2 selectivity of ~67; water permeance of ~8 L ⋅ m−2 ⋅ h−1 ⋅ bar−1 and MgCl2 rejection of ~95 %, which are one to two orders of magnitude higher than those of state‐of‐the‐art membranes. The molecular transport mechanism related to size‐sieving effect and transition energy barrier differential of molecules and ions was revealed by density functional theory calculations. Our work provides a facile approach and fundamental insights towards developing precise molecular sieving membranes. [ABSTRACT FROM AUTHOR]

With the advancement of Fuel Cell Vehicles (FCVs), detecting hydrogen leaks is critically important in facilities such as hydrogen refilling stations. Despite its significance, the dynamic response performance of hydrogen sensors in confined spaces, particularly under ceilings, has not been comprehensively assessed. This study utilizes a catalytic combustion hydrogen sensor to monitor hydrogen leaks in a confined area. It examines the effects of leak size and placement height on the distribution of hydrogen concentrations beneath the ceiling. Results indicate that hydrogen concentration rapidly decreases within a 0.5–1.0 m range below the ceiling and declines more gradually from 1.0 to 2.0 m. The study further explores the attenuation pattern of hydrogen concentration radially from the hydrogen jet under the ceiling. By normalizing the radius and concentration, it was determined that the distribution conforms to a Gaussian model, akin to that observed in open space jet flows. Utilizing this Gaussian assumption, the model is refined by incorporating an impact reflux term, thereby enhancing the accuracy of the predictive formula.

In this research, the influence of confined space size on the temperature distribution characteristics of internal window plumes from well-ventilated compartment fires was studied. Theoretical analysis was firstly used to establish a mathematical model for the smoke after ejecting from the window in the space. The study considered fire heat release rate and vertical height as dependent variables. Numerical simulations and experimental methods were carried out to study the temperature variations. A critical distance L2 was obtained. Results show that when the space D between the vertical retaining wall and the building façade is greater than L2, the variation of D has little influence on radial temperature. Once D is less than L2, the radial temperature distribution inside the confined space will tend to be consistent, and the temperature in the confined space sharply increases as D decreases. In addition, a dimensionless model was derived to quantify the relationship between temperature rise and vertical height. The experimental and numerical simulation results were processed, which are in good agreement with the model. The study can provide a framework for managing building safety. [ABSTRACT FROM AUTHOR]

With economic development and the burgeoning need for energy, numerous underground gas pipelines have been deployed for operation. Buried gas pipelines often suffer failures as a result of adverse factors, including corrosion, uneven subsidence, and damage caused by third parties. To investigate and predict the diffusion behavior following a natural gas pipeline leakage, Fluent software is utilized to develop a numerical model for the leakage and diffusion of high-pressure natural gas within a confined space. This model incorporates the Soave–Redlich–Kwong equation of state, which is widely recognized for its exceptional precision in characterizing the behavior of natural gas under high-pressure conditions. The study focuses on the analysis of leakage and diffusion behavior as well as the examination of how pipeline operating pressure and leakage diameter have an impact on the dispersion of leaked gas. Further, the prediction model for the diffusion distance of the hazardous area is developed, employing the least-square method and finite element calculations. The results show that, during the leakage process, a vortex and velocity region emerge, extending along the confined space. The farther away from the leakage hole above the pipeline, the higher the overall concentration of the gas. Moreover, the horizontal diffusion distance of gas at the bottom of the pipeline is considerably smaller than that above it. However, gas tends to readily accumulate in a high concentration area at the bottom of the pipeline. Elevating the leakage diameter and the operation pressure leads to a significant rise in gas concentration and the horizontal diffusion of the hazardous area. It is worth noting that the leakage diameter has a more pronounced effect on gas diffusion than does the pressure. The prediction model proposed in this study effectively anticipates the horizontal diffusion of the hazardous area within confined spaces. [ABSTRACT FROM AUTHOR]

Opposed-flow flame spread over solid materials has been investigated in the past few decades owing to its importance in fundamental understanding of fires. These studies provided insights on the behavior of opposed-flow flames in different environmental conditions (e.g., flow speed, oxygen concentration). However, the effect of confinement on opposed-flow flames remains under-explored. It is known that confinement plays a critical role in concurrent-flow flame spread in normal and microgravity conditions. Hence, for a complete understanding it becomes important to understand the effects of confinement for opposed-flow flames. In this study, microgravity experiments are conducted aboard the International Space Station (ISS) to investigate opposed-flow flame spread in different confined conditions. Two materials, cotton-fiberglass blended textile fabric (SIBAL) and 1 mm thick polymethyl methacrylate (PMMA) slab are burned between a pair of parallel flow baffles in a small flow duct. By varying the sample-baffle distance, various levels of confinement are achieved (H = 1–2 cm). Three types of baffles, transparent, black, and reflective, are used to create different radiative boundary conditions. The purely forced flow speed is also varied (between 2.6 and 10.5 cm/s) to investigate its interplay with the confinement level. For both sample materials, it is observed that the flame spread rate decreases when the confinement level increases (i.e., when H decreases). In addition, flame spread rate is shown to have a positive correlation with flow speed, up to an optimal value. The results also indicate that the optimal flow speed for flame spread can decrease in highly confined conditions. Surface radiation on the confinement boundary is shown to play a key role. For SIBAL fabric, stronger flames are observed when using black baffles compared to transparent. For PMMA, reflective baffles yield stronger flames compared to black baffles. When comparing the results to the concurrent-flow case, it is also noticed that opposed-flow flames spread slower and blow off at larger flow speeds but are not as sensitive to the flow speed. This work provides unique long-duration microgravity experimental data that can inform the design of future opposed-flow experiments in microgravity and the development of theory and numerical models. [ABSTRACT FROM AUTHOR]

The hydrogen tube skid container is designed to protect the hydrogen gas cylinder group from insolation, rain, and other environmental factors. However, in the event of a leakage accident, the container becomes a confined space. Therefore, it is essential to assess the risks associated with high-pressure hydrogen leakage in this confined space and determine the effectiveness of various risk mitigation methods under conditions of natural ventilation and forced ventilation, taking into consideration factors such as inlet velocity and vent position. The results showed forced ventilation was more effective than natural ventilation in reducing potential risks associated with hydrogen leakage. Furthermore, the magnitude of inlet velocity and the positioning of the vent were found to play crucial roles in reducing hydrogen concentration within the confined space. The vents on the horizontally symmetrical top (R–UP cases) were the most effective for ventilation. With the inlet air velocity set to 15 m/s, forced ventilation could reduce the average hydrogen molar fraction to the theoretical lower flammability limit (LFL) in approximately 17 s. [Display omitted] • The inlet air velocity and vent positions affect the discharge capability of leaked hydrogen. • Multi-perspective analysis of the distribution of leaked hydrogen at different time periods. • Placing vents on both sides at the top proves to be the most effective ventilation method. [ABSTRACT FROM AUTHOR]

Special work involves hot work, confined space, blinding‐pipeline operation with stop plate, work at height, lifting work, temporary electricity, excavation work, work for road breaking, and other work, which may cause harm or damage to the operators themselves, surrounding buildings, equipment, and facilities. In this article, we conducted a statistical investigation on 154 large and above hazardous chemical accidents that occurred between 2008 and 2021 in China, and found that there were 58 accidents that occurred in special work alone, accounting for 37.7% of the total number of accidents. However, at present, no statistical analysis has been conducted on the characteristics of special work accidents in China. Therefore, this paper analyzes the special work accidents in terms of six aspects: categories of special work, industry distribution, enterprise scales, provincial location distribution, time‐volatility characteristics, and accident causes. Moreover, this article puts forward countermeasures and suggestions, aiming to provide useful information for the prevention of special work accidents in China. [ABSTRACT FROM AUTHOR]

The flashover mechanism in an aircraft cargo compartment under low pressure was investigated in this study. A series of fire experiments were conducted in a scale model of a one-quarter volume FAA standard aircraft cargo compartment at 96 kPa and 60 kPa. The ignition of single-walled corrugated cardboard was chosen as the criterion of the flashover. The influence of different fire sizes and fuel types on the flashover was studied by comparing the average temperature of the smoke layer, the radiation heat flux at the floor level, and the heat release rate of the fire source. The critical condition and behavior of the flashover were analyzed. The results show that under low pressure, the flashover occurs at a higher temperature and radiation heat flux. Increasing the fire source size brings the flashover forward. At 60 kPa and 96 kPa, the cardboard ignites under a flashover when the average temperature of the smoke layer reaches 551 °C and 450 °C, and the average radiant heat flux at the floor level reaches 19.6 kW/m2 and 14 kW/m2, respectively. In addition, the minimum fire size for a flashover is directly proportional to the heat of evaporation and inversely proportional to the heat of combustion.

Nanotechnology has advanced the techniques for elucidating phenomena at the atomic, molecular, and nano-level. As a post nanotechnology concept, nanoarchitectonics has emerged to create functional materials from unit structures. Consider the material function when nanoarchitectonics enables the design of materials whose internal structure is controlled at the nanometer level. Material function is determined by two elements. These are the functional unit that forms the core of the function and the environment (matrix) that surrounds it. This review paper discusses the nanoarchitectonics of confined space, which is a field for controlling functional materials and molecular machines. The first few sections introduce some of the various dynamic functions in confined spaces, considering molecular space, materials space, and biospace. In the latter two sections, examples of research on the behavior of molecular machines, such as molecular motors, in confined spaces are discussed. In particular, surface space and internal nanospace are taken up as typical examples of confined space. What these examples show is that not only the central functional unit, but also the surrounding spatial configuration is necessary for higher functional expression. Nanoarchitectonics will play important roles in the architecture of such a total system. [ABSTRACT FROM AUTHOR]

The detection of biomarkers with both high sensitivity and specificity is crucial for the diagnosis and treatment of related diseases. However, many current detections employ ex-situ detection method and non-confined condition, thus have many problems, which may eventually lead to inaccurate detection results. Compared to detection in non-confined space, detection in confined space can better reflect the real in-vivo situation. Therefore, the construction of detection for target molecules in confined space has great significance for both theoretical research and practical application. To realize the detection of target molecules in confined space, the probes should accurately enter the confined space where the target molecules reside and interact with the interface. Thus, how to explore and utilize the properties of the interface (for example, bioinspired superwettability) has always been a hot and difficult topic in this field. Herein, the recent advances and our efforts in recent 10 years on detection of bio-target molecules in confined space with superwettable interface have been introduced from the perspective of the detection methods. The suitable and most widely employed detection methods for target molecules in confined spaces are introduced firstly. Then, recent progresses for related detections based on visual, optical, and electrochemical detection methods are presented successively. Finally, the perspective for detection in confined space is discussed for the future development of biochemical detection. [ABSTRACT FROM AUTHOR]

In this paper, the diffusion characteristics and laws of hydrogen leakage in confined spaces are investigated using a combination of numerical simulations and experiments, and a small-scale cube model (dimensions: 0.47 m×0.33 m × 0.20 m) is used. The effects of leak source location, obstacles, leak hole size and shape on hydrogen diffusion and concentration evolution were investigated. The results show that the top funnel is sprayed vertically downward, the diffusion velocity decreases rapidly under the blocking effect of air and buoyancy force, and the momentum of the airflow is exchanged. During the injection phase, the leaking gas is mainly subjected to strong buoyancy forces and the hydrogen concentration shows a stratification effect. When the injection stops, the concentration difference decreases and eventually the hydrogen concentration reaches a steady state. The obstacle model in turbulence (4.3%) increases the concentration difference by a factor of about three compared to the empty room model (1.7%), which seriously affects the diffusive behavior of hydrogen. The obstacle in laminar flow model (10.4%) has almost the same concentration difference as the empty room model (10.2%). Rectangular leakage holes have a greater initial kinetic energy and diffuse more widely and faster. • Effects of obstacles, leakage hole size and shape on concentration were studied. • The rate of diffusion is reduced due to the blocking effect of air and buoyancy. • Hydrogen concentration shows a stratification effect in the presence of buoyancy. • Obstacles cause loss of gas kinetic energy and delay the averaging time. • Rectangular leakage holes have a large gas diffusion range and fast diffusion rate. [ABSTRACT FROM AUTHOR]

The frequent occurrence of kitchen gas explosion accidents has raised widespread attention to gas safety. This article takes kitchen as the research object, and explores the dispersion law of LPG leakage in kitchens and the influence of ignition at different leakage time on explosion consequences by establishing LPG leakage and explosion models. The results show that the process of LPG leakage in a closed kitchen can be divided into three stages: initial kinetic energy dominant stage, gravity expansion stage, and passive dispersion stage. Propane forms a non-uniform concentration field in the kitchen that gradually decreases from bottom to top, filling the entire kitchen in 583 s. When an explosion occurred in the kitchen center, the initial burst of flame spreads around in a fireball. After 115 ms and 122 ms, the explosion overpressure causes the door and window to be destroyed respectively, and the flames stretch toward the door and window. The flames are then concentrated mainly in the lower area where the fuel is more adequate. In the later stage of the deflagration reaction, the flame propagates toward the upper area of the kitchen under buoyancy. The explosion consequences of LPG non-uniform gas clouds show a pattern of first intensifying and then weakening with the leakage time. The explosion consequences are most severe when ignited about 300 s after the leakage. The maximum explosion overpressures at the center of the kitchen, door, and window were 67.15 kPa, 28.12 kPa, and 27.92 kPa, respectively. The research results can provide reference for emergency response, consequence assessment, and kitchen safety design for kitchen LPG leakage and explosion accidents.. [ABSTRACT FROM AUTHOR]

The oil and gas industry is inherently known for its riskiness, involving numerous activities and a variety of chemicals naturally present in the plant environment. Simultaneously, it has been observed that certain activities classified as critical, such as crane lifting, hydrostatics, excavations, hot work, and confined spaces, pose significant risks. Previous studies have shown that between the years 2009 and 2019, there were many reported incidents, with a total of 46 verified cases of deaths occurring in confined spaces in Malaysia. These incidents underscore deficiencies in the current system that need addressing. Therefore, this study aims to collect data on confined space incidents and issues in the oil and gas industry to propose a new intervention plan for employers and workers. The current working practices in confined spaces were analysed for this purpose. The data were gathered through survey questionnaires distributed to workers employed in confined spaces. The obtained data were analysed using the SPSS system to conduct reliability tests, ANOVA, and Pearson Correlation. The results of the ANOVA analysis indicated that there was no statistically significant difference at the p < 0.05 level for n = 50 concerning Age Categories, Position Categories, Years of Service, and Education Background in their perceptions of confined space work practices at Gas Processing Kertih (GPK). Additionally, Pearson Correlation analysis revealed a strong statistical correlation (r > 0.5, n = 50, p < 0.05) between Incidents in the Workplace and Health or Disease Problems. Based on the findings, suitable intervention plans have been proposed, such as transparency on Incident Reports by Management, quality training for confined space workers, and implementation of an efficient toolbox meeting to assist management in addressing the challenges associated with confined space working practices at GPK. [ABSTRACT FROM AUTHOR]

In order to study the gas leakage in a confined space and the effect of venting methods on the subsequent explosion, a major gas accident scene in confined space was constructed based on FLACS software. The leakage, diffusion, and explosion behavior of the leaked gas in the confined space was investigated, and the venting effect on the subsequent explosion was analysed. The results showed that the leaked gas cloud from the closed section of the pipeline diffuses outward along the outer wall of the pipeline, forming an irregular concave shape, and the diffusion speed will be accelerated when encountering obstacles. The maximum overpressure of leaked gas cloud is 660.7 kPa, which can seriously damage the surrounding buildings, and the degree of damage to the buildings at the open end of the restricted space is higher than that at the closed end. When the outlet is installed in the axial position of the flame development, the pressure- venting effect is the best. The maximum explosion pressure in the confined space can be reduced to 312.4 kPa, a reduction of 52.70%. If the outlet is placed on the side of the confined space, the closer it is to the ignition source, the better the venting effect will be. The maximum explosion pressure in the confined space can be significantly reduced by increasing the length-to-width ratio of the outlet to expand the explosion area. When the length-to-width ratio is 34 : 1, the maximum explosion pressure is reduced to 15.4 kPa, a reduction of 97.65%. Reducing the outlet opening pressure can effectively reduce the maximum explosion pressure in the confined space. For the outlet opening pressure at 50 kPa, the maximum explosion pressure is reduced to 351.0 kPa, a reduction of 46.87%. [ABSTRACT FROM AUTHOR]

This study investigates the influence of the opening pressure of the explosion‐venting surface (EVS) of a vertical branch pipeline on the deflagration characteristics of methane at different concentrations. The results indicate that the increase in the opening pressure of the EVS promotes the accumulation of deflagration pressure in the horizontal pipeline, whereas the venting effect in the vertical branch pipeline attenuates the peak value of the deflagration pressure. The vertical branch pipeline has both "promoting" and "inhibiting" effects on the flame propagation speed in the horizontal pipeline. With an increase in the methane concentration and opening pressure of the EVS, the promoting effect gradually plays a dominant role, resulting in an increase in the flame propagation speed. In actual industrial production and daily life, in order to avoid explosion hazards, it is essential to install EVSs or reduce their opening pressure in a confined space. [ABSTRACT FROM AUTHOR]

In this paper, the effects of varying material widths on the propagation of discrete fires within diverse confined space conditions are investigated experimentally. The width-induced mechanisms influencing the flame spread of discrete solid surfaces in distinct confined spaces are comprehensively discussed, encompassing flame characteristics, pyrolysis front dynamics, flame spread rate, and mass loss rate. The findings reveal that the dimensionless flame height and width conform to a negative power relationship at varying restricted distances. Furthermore, a positive correlation between the width of the PMMA in confined spaces and both the flame spread rate and the mass loss rate is established. Notably, when the width is fixed, the confined space plays a dominant role in the propagation of flames. As the restricted distance decreases, the flames become more slender. Additionally, flame height, flame spread rate, and mass loss rate increase with the widening of the material. However, as the restricted distance becomes smaller, the effect of width becomes less pronounced. Under conditions of same restricted distance, an increased width results in a higher radiation factor, thereby enhancing the thermal feedback of the wall to the material, which in turn accelerates the spread rate of discrete flames. Moreover, due to the dominant role of radiant heat feedback provided by the confined walls to the discrete PMMA panels, the proportion of heat transferred by convection in the flames is minimal. Consequently, the influence of the convective coefficient's width variation on flame spread is relatively minor within confined spaces. Ultimately, an energy conservation model under confined spaces was established, which facilitated the analysis of the comprehensive mechanism of flame spread influenced by varying confined spaces and material widths.

The possibility to precisely control reaction outcomes for pursuing materials with well-defined features is a main endeavor in the development of inorganic materials. Confining reactions within a confined space, such as nanoreactors, is an extremely promising methodology which allows to ensure control over the final properties of the material. An effective room temperature inverse miniemulsion approach for the controlled synthesis of undoped and Eu3+-doped calcium molybdate crystalline nanophosphors was developed. The advantages and the efficiency of confined space in terms of controlling nanoparticle features like size, shape, and functional properties are highlighted by systematically comparing miniemulsion products with calcium molybdate particles obtained without confinement from a typical batch synthesis. A relevant beneficial impact of space confinement by miniemulsion nanodroplets is observed on the control of size and shape of the final nanoparticles, resulting in 12 nm spherical nanoparticles with a narrow size distribution, as compared to the 58 nm irregularly shaped and aggregated particles from the batch approach (assessed by TEM analysis). Further considerable effects of the confined space for the miniemulsion samples are found on the doping effectiveness, leading to a more homogeneous distribution of the Eu3+ ions into the molybdate host matrix, without segregation (assessed by PXRD, XAS, and ICP-MS). These findings are finally related to the photoluminescence properties, which are evidenced to be closely dependent on the Eu3+ content for the miniemulsion samples, as an increase of the relative intensity of the direct f–f excitation and a shortening of the lifetime (from 0.901 ms for 1 at. % to 0.625 ms for 7 at. % samples) with increasing Eu3+ content are observed, whereas no relationship between these parameters and the Eu3+ content is evidenced for the batch samples. All these results are ascribed to the uniform and controlled crystallization occurring inside each miniemulsion nanodroplet, as opposed to the less controlled nucleation and growth for a classic nonconfined approach. [ABSTRACT FROM AUTHOR]

In this research, the influence of confined space size on the temperature distribution characteristics of internal window plumes from well-ventilated compartment fires was studied. Theoretical analysis was firstly used to establish a mathematical model for the smoke after ejecting from the window in the space. The study considered fire heat release rate and vertical height as dependent variables. Numerical simulations and experimental methods were carried out to study the temperature variations. A critical distance L2 was obtained. Results show that when the space D between the vertical retaining wall and the building façade is greater than L2, the variation of D has little influence on radial temperature. Once D is less than L2, the radial temperature distribution inside the confined space will tend to be consistent, and the temperature in the confined space sharply increases as D decreases. In addition, a dimensionless model was derived to quantify the relationship between temperature rise and vertical height. The experimental and numerical simulation results were processed, which are in good agreement with the model. The study can provide a framework for managing building safety.

Helical structure in catalysts has attracted attention and been recently investigated for various catalytic reactions. However, helical transition metal oxides suffer from uncontrollable crystallization processes at high temperatures when being transformed from an amorphous phase into a crystalline structure. Herein, we report a helical anatase TiO2 nanotube for the first time, which has been prepared using a protected crystallization strategy in the confined space of silica. A single chirality of helical TiO2 has been used to track the ordering of the twisted structure. The twisted structure in helical anatase TiO2 nanotube is maintained after a vigorous crystallization process. Helical anatase TiO2 nanotubes possess more accessible active sites and abundant defects of oxygen vacancy and Ti3+ species owing to the twisted structure. The obtained helical anatase TiO2 nanotube exhibits superior photocatalytic activity for hydrogen production without adding any co‐catalysts. This work provides new insights into the role of helical structure in transition metal‐based catalysts. [ABSTRACT FROM AUTHOR]

Developing a new strategy to improve the self‐assembly efficiency of functional assemblies in a confined space and construct hybrid functional materials is a significant and fascinating endeavor. Herein, we present a highly efficient strategy for achieving the supramolecular self‐assembly of well‐defined metallacages in microdroplets through continuous‐flow microfluidic devices. The high efficiency and versatility of this approach are demonstrated by the generation of five representative metallacages in different solvents containing water, DMF, acetonitrile, and methanol in a few minutes with nearly quantitative yields, in contrast to the yields obtained with the hour‐scale reaction time in a batch reactor. A ring‐opening catalytic reaction of the metallacages was selected as a model reaction for exploring supramolecular catalysis in microdroplets, whereby the catalytic yield was enhanced by 2.22‐fold compared to that of the same reaction in the batch reactor. This work illustrates a new promising approach for the self‐assembly of supramolecular systems. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to reveal the ignition characteristics and explosion propagation characteristics of coal dust, a kind of coal dust cloud is studied through the experiment and numerical simulation in confined space. The result indicated that the particle size of coal dust has a significant impact on the ignition characteristics of coal dust cloud. CFD theory is used to simulate the explosion propagation characteristics in the straight and bifurcated pipelines. It is found that the flame propagation simulation result is consistent with the experimental result. In the bifurcated pipeline, from the time of 0.2 s to 0.8 s after the explosion, the flame propagates through the bifurcated pipeline. It also revealed that the flame propagation intensity of coal dust explosion in the bifurcated pipeline is affected by the structure of the pipeline, which provides a reference for the study of the propagation characteristics of coal dust explosion. [ABSTRACT FROM AUTHOR]

A series of mesoporous silica (MS) materials, including rod-like and spherical SBA-15, spherical MCM-41, and MCM-48, was successfully synthesized and modified by silane coupling agent γ-aminopropyltriethoxysilane. The modified MS was utilized as a microreactor for solution reversible addition–fragmentation transfer (RAFT) polymerization of methyl methacrylate (MMA) using xanthate as a chain transfer agent and azodiisobutyronitrile as an initiator. Notably, modified MS had a low specific surface area and pore volume while maintaining the original morphological structure. Given to the confinement effects, poly(methyl methacrylate) (PMMA) prepared from internal mesoporous channels had higher molecular weight and initial thermal decomposition temperature than those from conventional RAFT polymerization. Moreover, PMMA obtained from spherical SBA-15 and modified MCM-48 exhibited the highest molecular weight (Mn = 8.78 × 104 and Mn = 7.43 × 104, respectively). This work provided a novel approach in designing a polymer microstructure for a more comprehensive application, such as in drug release. [ABSTRACT FROM AUTHOR]

Copyright of Forensic Science & Technology is the property of Institute of Forensic Science, Ministry of Public Security and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The zebrafish model is an emerging model for the study of the complex behavioural patterns noted in depression and neurological disorders. Confinement and memory loss are linked with cognition and mental health impairment, where confinement paradigms are assessed using other behavioural responses based on novel tanks or T tanks. Since zebrafish are exploratory animals, the impact during confinement cannot be evaluated using a novel tank or T tank. The present study investigates the response of the zebrafish to acute confinement and assesses its memory-based learning behaviour through parameters such as movement, swimming speed, and time spent inside the confined space. The movement and swimming speed of the fishes in confinement showed no significant difference. When confined inside a space, the fish showed their anxiety with erratic movements or bouts of freezing, which declined by 83%, during the six days of confinement and the escape time from the confinement space also decreased by 58%. The impact of anxiety, resulting in clockwise and counter-clockwise movement, also reduced after three days. Our results summarise that the decrease in anxiety can help the fish in habituating itself to a forced condition. This experiment on zebrafish behavioural biology is used to assess the cognitive behaviour against confinement, and it emphasizes the learning of behavioural adaptions under both crowded and solitary conditions.

The introduction of enhanced functionalization is a key aspect in the current design of cage chemistry. At the moment, several approaches are intensively investigated. The synthesis of cage compounds that display endohedral functionalization plays a key role among them. Here, the studies of reactions that occur in endohedral‐functionalized cage compounds is reviewed. After an introduction in current trends in cage‐chemistry the discussion of reactions in endohedral‐cage compounds is divided into three sections. These are: 1) Endohedral groups that are by themselves functional, 2) endohedral groups that can bind to a transition‐metal complex and 3) endohedral groups that can bind by themselves to a metal. The article closes with an outlook on additional current developments in the field of endohedral‐functionalized cage‐compounds, which may contribute in the future towards reactivity in cage compounds. [ABSTRACT FROM AUTHOR]

As an advanced energy storage medium, lithium-ion batteries (LIBs) are being used in aircraft and other aviation fields owing their unique advantages. The thermal runaway (TR) behaviours of LIBs used in aircraft are more complicated and dangerous due to the special operating environments, such as low pressure and enclosed environments. Therefore, a special test platform was designed to study the effect of low pressure on the TR characteristics of 2.2 Ah 18,650 type LIBs in this work. Some critical parameters of TR were obtained, such as onset temperature of TR, maximum temperature, voltage drop time, pressure, and the explosion limit of gases, etc. The results show that with the pressure increasing, the TR onset temperature, maximum temperature, and pressure increase in the test chamber, and the voltage drop time postpones. In addition, the amount of released gas and the explosion limitation range of gases increase with the decrease of the initial pressure. This means it's easier to occur but with weaker hazard of TR at lower pressure. Besides, the SEM results reveal that deformation and structural damage of cathode materials, which is attributed to the increase of the large amount of gas released at the electrode material level. These results provide the basis for the safe application and storage of LIBs in a confined space under different pressures. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Flame shapes, flame tip velocities and pressure oscillations with turbulent jet ignition (TJI) combustion were studied comprehensively in a newly designed constant-volume combustion bomb (CVCB) by employing high-speed Schlieren photography. In the CVCB, the pre-chamber was effective at accelerating the flame and promoting turbulent flame formation. The results show that when the jet flame departs from the jet orifice, the flame tip velocity naturally decreases, mainly due to the fluid dynamic mechanism. And a temporal acceleration due to the emergence of additional flame wrinkles is observed at high pressures. When the initial pressure is sufficiently high, pressure waves can be distinguished clearly. The continuous wavelet transform suggests that a 1–3 kHz bandpass filter can be used to filter the pressure oscillation. Comparing pre-chambers with different holes reveals that intense pressure waves are formed with an increase in the number of jet orifices, and the propagating flame can be pushed backward during the interaction between the forward flame and the reflected pressure wave due to the reduced flame tip velocity and increased pressure wave intensity. [ABSTRACT FROM AUTHOR]