Fire and Materials最新文献

To study the explosion suppression mechanism of nonpremixed inert gas, this paper uses CFD software Simtec to simulate the suppression process of methane explosion by nonpremixed nitrogen in a square tube. The closed square tube includes three sections: ignition section, suppression section, and combustible gas mixture section. The results show that the critical explosion suppression length increases first and then decreases with the increase of methane concentration. When the methane concentration is 11%, the critical explosion suppression length is the biggest, which is 1.6 m. With the increase of the length of the suppression section, the overpressure curve first changes from a high-pressure single peak to a double peak and finally to a low-pressure single peak. After ignition, the nitrogen in the suppression section moves to the right with the flame under the driving effect of thermal expansion of combustion products. When the flame propagates near the suppression section, the nitrogen section stops moving right. Then, under the disturbance of the explosion wave, the suppression section is stretched. When the length of the suppression section is less than the critical explosion suppression length, the flame passes through the suppression section to ignite the combustible mixture, causing a secondary explosion. If the suppression length is greater than the critical explosion suppression length, the flame will gradually extinguish in the suppression section. The feasibility of suppression explosion by nonpremixed inert gas was verified, and the suppression mechanism of nonpremixed inert gas is inertial isolation rather than dilution.

This paper investigates the inhibitory effects and mechanisms of different powder inhibitors on corn starch explosion flame propagation. The results indicate that ABC powder exhibits the strongest suppression effect, followed by Al(OH)₃ powder and dolomite powder. Increasing the inerting ratio progressively suppresses the flame acceleration characteristics of corn starch explosion. The addition of 25 wt.% ABC powder significantly inhibits flame propagation, reducing the average flame propagation velocity by 83.6% and the maximum propagation velocity by 91.7% compared to the uninhibited condition. Compared to Al(OH)₃ and dolomite powder, ABC powder has a lower initial thermal decomposition temperature, a broader pyrolysis temperature range, and greater endothermic efficiency. The thermophysical properties of the powder inhibitors show good consistency with their explosion suppression effectiveness. The inhibitors generate NH₃, H₂O, SO₂, and N₂, which effectively reduce both the laminar burning velocity and heat release rate of corn starch pyrolysis gases. The competition between H + O₂ = O + OH and H + CH₃(+M) = CH₄(+M) dominates the combustion reactions of pyrolytic gases from corn starch. The CO₂, H₂O, and NH₃ generated by the thermal decomposition of inhibitors do not alter the fundamental reactions governing combustion. However, the generated SO₂ introduces two additional key inhibitory elementary reactions: H + SO₂(+M) = HOSO(+M) and H + O₂(+M) = HO₂(+M).

The insulation of electrical cables, exposed to external heat in a high-temperature environment, undergoes thermal decomposition and carbonization, resulting in the loss of insulation performance. Cables without insulation protection were prone to short circuits. Short circuits were one of the common ignition sources in electrical fires. However, research on the ignition of energized wires by arcs was not clarified. In this study, the standardized cone heater was used to simulate high-temperature conditions in order to investigate the occurrence of short circuits in energized cables within a high-temperature environment, as well as the characteristics and correlations of the combustion. The intensity of thermal exposure was accurately controlled through adjustments to the heat flux emitted by the cone heater. The short circuits in thermally exposed cables could be classified as a single arc or multiple arcs based on the fluctuations observed in voltage and current upon the occurrence of an arc. The results indicated that the minimum heat flux leading to a short circuit was 22 kW/m². A short-circuit arc became inevitable once the heat flux surpassed 25 kW/m². Notably, when the heat flux exceeded 26 kW/m², the probability of multiple short circuits within the conductor escalated significantly, reaching 83.7%. Compared to a single arc, multiple arcs exhibited a shorter initial occurrence time, a longer duration, and a higher probability of igniting cable insulation. The spread distance of combustion due to multiple arcs was primarily concentrated within the range of 23–28 cm. Furthermore, the maximum and minimum arc energies generated by multiple arcs were approximately three times higher than those generated by a single arc, respectively. This research provided valuable information for evaluating the fire hazards associated with different short circuits and determining the fire causes.

Data center fires, often caused by continuous high-load operations, result in significant losse. Liquid nitrogen has been proposed as an environmentally friendly cryogenic fluid for data center fire prevention. In this work, the effects of liquid nitrogen on typical integrated circuit chips in data centers were studied through experimental research and numerical simulation, focusing on the environmental parameter characteristics and the effects on structural and electrical performance under the liquid nitrogen actions. Results show that liquid nitrogen spraying has obvious cooling and inerting effects. Numerical simulations revealed that the temperature near the action point under spraying decreases to 0°C at 2.5 s at room temperature, indicating significant local cooling. Under high-temperature combustion conditions, the temperature near the action point decreased to 28°C after 21 s, and the oxygen concentration in the experimental space fell below 5% after 60s, effectively inhibiting combustio. The actions of liquid nitrogen have less harmful effect on the chips, with primary impacts observed in some chips and plastic laminates. In addition, because of the poor temperature change characteristics of quartz, the input and output frequencies of the quartz oscillator are unstable, leading to slight deviations in the IV curve. This work provides valuable insights for the development and application of liquid nitrogen fire prevention technology in data centers, offering a critical reference for enhancing fire safety in such environments.

The European project “European Approach to Assess the Fire Performance of Facades” led by RISE, has been working toward the development of a harmonized European testing and assessment method for façade. In this study, we present numerical predictions of the thermal exposure on a noncombustible façade in the European test. Fire Dynamics Simulator (FDS), version 6.7.9, was employed as numerical model. The temperature inside the combustion chamber was underestimated by approximately 8.9%. The heat flux from the wood crib aligns well with the test results up to around 800 s, after which a deviation was observed, likely due to the way the wood crib was modeled. The heat flux at 1 m above the chamber opening was underestimated by 22.2%, while the plate thermometer temperature at the center of the fictitious window was underestimated by 17.6%. The overall trends along the vertical centerline were captured correctly, though overestimations were observed at most locations, except at 1 and 1.5 m above the chamber, with a maximum overestimation of 17.5% at 4.5 m above the chamber. The flame height was determined based on the predicted temperature, with an overestimation of 29.8%. However, this comparison has inherent limitations, primarily due to differences in the methods used to define the flame tip in experimental tests and numerical simulations. An analysis was conducted to assess the influence of the wood crib model on the fire dynamics in this large-scale test.

To promote sustainability, this study incorporates coarse recycled aggregate (RA) from crushed concrete blocks into high-performance concrete (HPC) to reduce the cost of expensive mineral components and reduce surface flaking and thermal degradation at elevated temperatures. Steel fibers (SF) and nano-silica (NS) were introduced as co-modifying agents to enhance HPC's mechanical and microstructural properties. In total, 36 mixtures with varying proportions were designed and subjected to compressive, splitting tensile, and modulus of elasticity tests, considering different RA replacement rates, SF contents, and NS contents. Microstructural analyses, including SEM, XRD, pore distribution, and thermal conductivity tests, were also conducted. Results revealed that SF and NS significantly improved the residual compressive and splitting tensile strengths of HPC with RA (HPC-RA) at elevated temperatures. As temperature increased, residual compressive strength initially rose but then declined, while splitting tensile strength showed a continuous decrease. SEM and XRD analyses confirmed that NS enhanced C-S-H gel formation, improving heat resistance. However, at 600°C, dehydration and C-S-H decomposition led to strength reduction. Pore analysis indicated that higher RA replacement rates introduced more detrimental pores, impacting thermal conductivity. A linear relationship between compressive and splitting tensile strengths was established, along with a temperature-dependent fitting equation to predict residual properties.