查看更多>>摘要：Ensuring adequate safety during the production, transportation and storage of ammonium nitrate (AN) has always been a matter of concern. In particular, the combustion and explosion of other chemicals in fire conditions could lead to secondary explosions of AN. An understanding of the effect of fire conditions on the blast characteristics of AN and an estimate of the blast characteristic parameters of AN, such as the critical detonation pressure and fragment impact response, are necessary for minimising risks associated with the large-scale storage of AN and AN-based fertilisers at ports and for avoiding secondary explosions. In this study, the blast characteristic parameters of AN were determined by conducting the UN gap test and fragment impact test. An increase in the AN temperature from ?20 °C to 140 °C was found to be accompanied by a gradual decrease in the critical detonation pressure from 5.444 GPa to 1.741 GPa. Furthermore, bombardment by high-speed fragments caused the ignition of AN below 60 °C, and when the temperature reached 100 and 140 °C, deflagration and explosion occurred, respectively. When combined with the results of an assessment of an explosion event at Tianjin Port, these results indicate that the bombardment of AN by metal fragments produced by an explosion is likely to trigger secondary explosions.
查看更多>>摘要：Based on the prediction of the equipment residual useful life, important decisions are made in oil industry to ensure a safe and profitable management. Atmospheric storage tanks are particularly critical from the safety point of view as their bottom is affected by localised corrosion (pitting), which is not easy to be monitored. The prediction of the useful lifetime defines the time up to which the equipment can continue to be in-service before the formation of holes where the greatest thinning is observed. In this study, the thickness data collected in subsequent inspections of the bottom of twenty-three large storage tanks of petroleum products has been processed by adopting an improved probabilistic approach. The method is unconventional and combines the consolidated extreme value theory and Bayes’ formula to quantify the probability of thinning below a fixed limit and, thus, predict the remaining useful lifetime, as well as the optimal time for the next full inspection. Data collected allowed the validation of the forecast model.
查看更多>>摘要：Medical gas systems are safety-critical systems due to their association with critical care situations. In particular, the oxygen gas supply system contains many complications represented in the interactions between human and equipment while operating the system and managing emergencies. Therefore, it contains many hazards that require high safety standards to maintain the integrity of the system. The traditional hazard analysis methods suffer from weaknesses as their linear reasoning assumption cannot adequately describe the actual behavior of modern socio-technical systems that are characterized by tight couplings and complex interactions among technical, human and organizational aspects. Alternatively, Systems Theoretical Process Analysis (STPA) is a new hazard analysis approach that accounts for the causal relationships between system components and their unsafe interactions, allowing the integration of both occupational and process safety. STPA is widely used in the automotive, aviation, and aerospace industries whereas there are a few applications of STPA in healthcare domain. This paper proposes the use of STPA methodology in analyzing the hazards related to the medical gas pipeline and oxygen supply systems in a low-medium income country. Specifically, the analysis considers the emergencies that stem from the total or partial failure of oxygen supply and the hazards related to temporary restoration of the medical oxygen system. The results indicate that STPA contributes to identifying the hazards resulting from the interference between the human, machines, and equipment, and studying the unsafe effect of the system elements on each other. This research suggests control measures to prevent the unsafe interaction of the system components and improve the response time to oxygen failure incidents, which greatly reduces the potential consequences.
查看更多>>摘要：Large-capacity lithium batteries are being widely used as the power sources of new energy vehicles due to the advantages of easy assembly and simplified electrical connections. However, the temperature rise and thermal safety issues would become more severe for larger capacity batteries with smaller specific areas due to more concentrated heat generation and accumulation thereof. In this paper, an experimental study is presented for the thermal characteristics and thermal performance of a commercial large-capacity lithium battery over 100 Ah. The orthogonal experiment protocol was designed to obtain the direct current internal resistance and entropy coefficient of battery under varying working conditions involving the temperature and depth of discharge. It was found that the discharge rate had little effect on the entropy coefficient and direct current internal resistance, and the average entropy coefficient of a battery with high nickel content and specific energy was lower. Meanwhile, the electrochemical impedance spectroscopy of a battery in different placement orientations was also tested. The results indicated that the ohmic impedance and charge transfer impedance of the battery in the upright orientation were slightly smaller than that in the lying-down orientation, which is preferred in practical operation. The battery heat generation rate is gained by combining the measured internal resistance and entropy coefficient terms. A third-order surrogate model of heat generation rate is correlated under different working conditions with the depth of discharge, temperature, and discharge rate by the response surface analysis (RSA). In addition, the volumetric heat generation rate of the present large-capacity prismatic battery is compared with a smaller 18650 battery. The battery temperature rise under natural convection condition was experimentally measured, together with the measured specific heat, to examine the validity of the present heat generation model. Finally, the heat generation surrogate model was applied in WLTC conditions, and the temperature rises of the battery under different depths of discharge were obtained and discussed.
查看更多>>摘要：As the most concerning failure event of lithium ion batteries (LIBs), thermal runaway (TR) often causes considerable damage, such as fire or even explosion. Therefore, an efficient cooling method is essential after LIBs are triggered into TR. In this study, a series of experiments are performed on LIBs TR using water mist containing different additives to investigate the cooling performance of additives; furthermore, its cooling mechanism is described. The results show that water mist containing Tween 20 or 1-heptanol can enhance heat transfer, whereas FS-51 inhibits heat transfer. The heat dissipation of Tween 20 is 12.46 ± 0.20 kJ, which exhibits the best cooling effect, and it is increased by 23.6% compared with the test with pure water. However, the binary mixture of Tween 20 and 1-heptanol does not exhibit a better cooling performance than the water mist with a single additive. Moreover, the enhanced cooling effect of water mist with additives is closely related to the surface tension and foamability of additives. The additive with lower surface tension and foamability exhibits a better cooling effect of water mist. These results demonstrate that water mist containing specific additives improves the cooling effect, which may provide a reference for the design of battery safety.
查看更多>>摘要：The motivation for this work is to ensure explosion safety when working with flammable gases. One of the passive methods for suppressing combustion of gases, consisting of the use of porous materials, is considered in this work. The propagation of a flame front of hydrogen-air and acetylene-air mixtures when passing through polyurethane foam was experimentally studied. To reduce the velocity of the unburned mixture ahead of the flame front, the initiation was carried out at the open end of the channel. In this event, the foam skeleton has a general effect on the propagation of the flame and not on the flow of the unburned mixture. The flame front velocity was determined with a high-speed camera using the shadow method. It was shown that the flame front does not pass through polyurethane foam containing 45 and 80 pores per inch (ppi). However, the use of foam with 10 and 30 ppi resulted in an acceleration of the flame front, up to 200 m/s for acetylene-air and 550 m/s for hydrogen-air mixtures. It was shown that the relative increase in the velocity of the flame front varied exponentially depending on the length of the foam. The exponent was determined for both mixtures.
查看更多>>摘要：The natural working fluid ammonia has once again attracted widespread attention due to its environmental performance. However, the flammability of ammonia will lead to some potential safety hazards in practical applications. In this paper, the flammability characteristics of ammonia mixed with R125 and R227ea were studied experimentally. Firstly, the flammability limits of the binary mixture in dry air were measured in a 12 L spherical glass flask. The results showed that when the volume ratios of R125/NH3 and R227ea/NH3 were 0.65 and 0.63, respectively, the binary mixture reached the critical flammability ratio. And the inhibition mechanism of R125 and R227ea was discussed by the density functional theory. It was found that the flame retardants are easy to produce F and CF3 inhibition radicals. Finally, the inhibitory effects of R125 and R227ea were compared by the comprehensive analysis of environmental and safety performance. Under the premise of meeting the requirements of environmental protection, R227ea has a stronger inhibitory effect on the flammability of ammonia than R125. This paper is of great significance for the safe application of ammonia in the process industries.
查看更多>>摘要：The purpose of this work is to evaluate hydrogen cloud explosion using large eddy simulation. The LES model combined with acoustical theory is firstly established and validated. Then the effects of cloud scale on flame dynamics and explosion pressure are explored. Finally, the effects of obstacle-induced turbulence on hydrogen cloud explosion are analyzed. The research works indicated that the LES model combined with acoustical theory could be able to reproduce flame acceleration and explosion pressure evolution. Maximum explosion pressure and maximum flame front velocity continue to increase with increasing cloud scale. The deviation values of flame radius of four cloud scales are 0.25 m, 0.5 m and 0.75 m, once beyond the critical value, the flame front velocity of larger cloud scale is lower than that of smaller cloud scale. The increase rate of flame front velocity and explosion pressure, not their peak value, will be certainly increased by built-in obstacles, which could be attributed to the couplings of turbulent vortex and moving flame.
查看更多>>摘要：The effects of connected vessels structure (pipe bending position and angle, vessel shape and volume) and bifurcated pipe on methane explosion characteristics were experimentally researched. Six explosion vessels with different volumes and shapes and a series of bending pipes were adopted respectively. Results indicate that the explosion pressure inside the whole connected vessels presented a trend of rising firstly and then decreasing with the decrease of pipe bending angle. And the increases of primary and secondary volumes could result in the greater explosion pressure inside the two vessels, and the effect of spherical vessel was more significant compared with the cylindrical vessel of same volume. Although the effect of spherical vessel on the pressure rising rate was greater than that of the cylindrical vessel, the effect of smaller volume vessel was more significant. As bifurcated pipe existed, part of the flame and pressure wave was shunted, resulting in the energy weakening, after flame propagation to the secondary vessel. Due to the combined effect of the turbulence enhancing and shunt weakening, different explosion pressures were presented inside the connected vessels under T-L-R, T-L-B and S-T connection forms. Besides, the bending angle of bifurcated pipe also could affect the shunt extents of flame and pressure wave, further affecting the explosion pressure and flame propagation inside the main pipe.
查看更多>>摘要：To effectively examine the influence of elbow structures on hydrogen explosion characteristics, this paper conducts a numerical study of flame propagation during hydrogen explosions in bend pipes with different elbow angles. When the elbow angle is large, the flow field movement caused by the pressure difference can separate the “tongue” flame from the outer wall (concave wall), forming a cavity area. The influence of the elbow structure on flame propagation is mainly concentrated in the middle and later stages. In the middle stage, the elbow structure creates a relatively closed space in advance so that the speed peak-2 occurs earlier than it does in the straight pipe. When the elbow angle is α = 90°, the speed peak-2 is the largest at 245.8 m/s. In the later stage, the acceleration effect produced by the outer wall (concave wall) plays a leading role, and the flame accelerates for the third time after passing through the elbow. When the elbow angle is α = 120°, the best acceleration effect is obtained when the flame passes through the elbow. There is an interactive relationship between the development of explosion overpressure and flame propagation in bend pipes. In the middle stage, the interaction between the compression wave, reflected wave and shear wave causes the overpressure to rise in an oscillatory manner. The elbow structures shorten the reflection distance of the pressure wave, and the oscillation frequency and growth range of the explosion overpressure can be much higher than those in a straight pipe.
NSTL
Elsevier