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Multiple fires of unequal heat release rate (HRR) is a common fire scenario in real fire accidents. Differing from most previous research assumption of identical fire sources, the unequal HRR for those fire sources is regarded as more reasonable in reality. To explore the asymmetric flow characteristics surrounding multiple fires under such circumstances, simulations of two square propane burners with the same side length but different HRRs were carried out. The HRR combination and burner separation distance were varied. The results showed that the asymmetric flow characteristic was found in both the flame and the smoke plume zone. In the flame region, the flame morphology in terms of the tilt angle is a good parameter indicating the asymmetric flow characteristic. In general, the tilt angle of the small fire is larger than that of the big fire. The tilt angle of the small fire decreases while that of the big fire increases until equaling to each other under the HRR ratio reaching unity. In the smoke plume region, the smoke plumes from the small and the big fire will converge at a certain height with some shifting distance, which is another parameter indicating the asymmetric flow characteristic. Besides, the smoke plume merging process driven by asymmetric air entrainment can be divided into three stages, namely the I) Separate stage, II) Converging stage and III) Complete coalescence stage. Correlations of the converging & coalescence height suggesting the starting point of the II and III stages were proposed.

Flame merging is deemed to enhance the burning intensity and make the fire more destructive. This paper presents an experimental study on merging behaviors of two same rectangular heptane pool fires with long sides parallel. The pan aspect ratio was set 2–4 and the spacing was changed. The burning rate and flame height were measured. As the spacing decreases, the flame shape was divided into five regions, i.e., (I) no interaction, (II) tilt but non-merging, (III) intermittent merging, (IV) upper flames fully merging but lower flames separated and (V) flames merging from the pan base. The results showed that both the burning rate and flame height increase within the stages I–IV and then decrease in stage V. A normalized parameter ψ is introduced to characterize the air entrainment restriction. A unified correlation between burning rate and ψ is then developed. Connecting with the theoretical force analysis, the criteria of merging from the base and beginning merging are determined as ψ = 0.33 and ψ = 0.61. Then a piecewise correlation of the merging flame height is established. The proposed correlations for burning rate and flame height are verified using present and literature data and their scope of application is further expanded into square pool fires.

Fire-induced smoke is the most lethal threat to the residents in high-rise buildings and it is necessary to understand the smoke rising characteristics for the engineering applications of smoke control system. Previous researches only focused on smoke movement driven by buoyancy and stack effect. It is common, however, that external wind can flow inside the building through broken windows and affect the smoke flow. This paper studies the influence of external wind on smoke characteristics in a stairwell. A series of simulations were conducted in a full-scale staircase with top window open. The ambient wind velocity ranged from 0 m/s to 6 m/s and the heat release rate varied from 500 kW to 1500 kW. Results show that the rise time for plume reaching a given height increases with the wind velocity. For a HRR, smoke cannot overcome the wind force when wind velocity exceeds a critical value. Thus a quantitative model is proposed to predict the rise time of plume front considering the hindrance of wind. Moreover, the mass flow rate at the bottom door decreases with wind velocity due to pressure attenuation. However, the CO concentration increases by about 15% with wind velocity, which is a great danger to trapped victims.

Annular fire source is a common combustion form in fire accidents. Effects of D in / D out (the ratio of inner to outer diameters of the floating-roof tank) on the flame morphology and plume entrainment mechanisms of annular pool fires were studied by numerical simulation. Results show, as D in / D out increases, the area with low combustion intensity near the central axis of the pool surface gradually increases. Combined with the time-series HRR and the stoichiometric mixture fraction line of the fire plume, it reveals that the combustion of annular pool fire is dominated by non-premixed diffusion flame. The pressure near the pool outlet decreases with D in / D out , while the plume turbulence presents an opposite trend. Based on the time-sequential plume flow and the gas-phase material distribution data, the flame merging mechanism of the annular pool fires is revealed. Furthermore, based on the similarity criterion, it verifies that the applicability of the above scaled simulation conclusions could also be extended to guide full-scale fires.

Fire is one of the most common hazards in the process industry. Timely and accurate fire detection is essential. The camera-based technics for fire detection are one of the promising technologies. However, its uncertainty of fire monitoring quality, such as noise artifacts within digital images caused by the inherent interference of hot environments, is always a key defect hindering the further application of this technology. Taking a simple fire scenario of the cable fire as an example, the noise reduction model (SA-DCGAN, Spatial Attention-Deep Convolution Generative Adversarial Network) is discussed for three kinds of typical fire image noise (white, black and mottled). Compared with traditional noise reduction algorithm, the model has greater advantages in restoring flame profile and texture. Through the verification process of applying this method in promoting fire detection based on image recognition, the effectiveness of the theoretical model is confirmed in improving the detection accuracy. It shows that the “True Detection” is increased by 375% and the “Missed Detection” and “False Detection” are decreased by 54% and 587%, respectively. These results show that the proposed theoretical model is of great significance for improving camera-based fire detection performance in thermal environments, which makes possible to further promote the intelligent fire protection in the process industry.

High-quality fire image is essential for fire detection and monitoring. Degraded fire images in the fire field aggravate the difficulties in determining the burning area and assessing the severity of the fire, thus being unable to make scientific firefighting strategies. Therefore, a fire image enhancement model of multi-segment resolution structure, designed to implement image enhancement step by step, is proposed to solve the problem of low-resolution and detail reconstruction. Through testing samples by both the experimental and simulated datasets, the experimental results show that the model significantly improved image quality, with the peak signal-to-noise ratio increasing by 140.66% in the experimental dataset and by 3242.67% in the simulated dataset, while the structural similarity index measurement increased by 525.90% and 3090.07%, respectively. These enhancements led to an 85% improvement in the recognition accuracy of the fire detection model in the experimental dataset and a 55% improvement in the simulated dataset. The model also exhibited strong robustness, effectively restoring flame contours in images with varying smoke concentrations and fire sizes, suggesting its potential for application in complex fire scenarios. The proposed method illustrates the effectiveness of the multi-segment resolution structure in enhancing fire images, providing a novel approach to improving fire monitoring quality. The fire image enhancement method based on artificial intelligence has far-reaching significance for advancing the informatization and intelligence of fire protection.

Annular pool fires, frequently happened in chemical industries, have a significant influence on environmental pollution. Air pollution, greenhouse gas emissions, water pollution, and soil contamination are general ways of environmental hazards caused by the annular pool fires. This study built upon our previous study (Environ. Sci. Pollut. Res., 2023, 30(21): 59781–59792.), and extended to investigate the combustion and fire plume flow behaviors of annular pool fires, both with and without air entrainment through the hollow center of the annular pool. Results show that when there is no air entrainment through the hollow center, the low combustion intensity area at the plume’s central axis gradually extends while the high combustion intensity area concentrates at higher places and the flame height increased by nearly 40% from a solid pool ( D in / D out  = 0) to the annular pool ( D in / D out  = 0.80). Additionally, the area with high combustion intensity is more concentrated at a higher position. The combustion of annular pool fires was found to be dominated by non-premixed diffusion combustion. The center of the annular pool fires is dominated by air prior to flame merging and by fuel vapor after the merging occurs. For annular pool fires with air entrainment through the center of the pool, the combustion intensity increases as D in / D out at the plume base increases. And, the flame height decreased by nearly 25% as D in / D out increases. Flame burning occurs both on the outside and inside of the plume, exhibiting a “double layer” combustion characteristic. It reveals that the combustion of the fire plume transitions to premixed diffusion combustion. The center of the annular pool fire is predominantly composed of air. Understanding and controlling annular pool fires can lead to new methods for remediating fuel spills, reducing pollution from combustion, and advancing research in fluid mechanics.

Radial diffusion (RD) induced by ULF waves can contribute to particle acceleration and scattering. Past global simulations that incorporate RD often use dipole magnetic fields, which could not realistically reveal the role of RD. To better understand the effects of RD and identify whether a background magnetic field model matters in understanding the ring current dynamics in response to RD, we simulate a storm event with different magnetic configurations using a global kinetic ring current model. Results indicate that RD can effectively diffuse protons of hundreds of keV to inner regions (L ∼ 3.5), especially in recovery phase. Comparisons with in‐situ observations demonstrate that simulations with TS05 overall capture both the intensity and variations of proton fluxes with the aid of RD, whereas that with a dipole field significantly overestimates low‐L region fluxes. This study implies adopting realistic magnetic fields is important for correctly interpreting the role of RD. Plain Language Summary Ultra‐low‐frequency (ULF) waves in the magnetosphere can scatter particles and diffuse them radially, called radial diffusion, resulting in particle acceleration and scattering and even precipitation down to the upper atmosphere. The interaction between ULF waves and particles is highly dependent on the strength of the magnetic field. This study quantified the role of ULF wave radial diffusions in the ring current dynamics using a global ring current model under different magnetic field configurations. Results indicate that radial diffusion could efficiently migrate energetic particles inward to L ∼ 3.5, especially during storm recovery phase when the convection is weak. With a more realistic magnetic field configuration, distributions of energetic ring current particles agree much better with satellite observations than using a dipolar magnetic field. Adding the radial diffusion process in the simulation helps to accelerate particles and yield better data‐model comparisons. Key Points Radial diffusions are able to effectively diffuse energetic (80 ∼ 300 keV) ring current protons to L ∼ 3.5 especially during recovery phase Simulations with a dipole field may overestimate the role of radial diffusion in low L regions, but underestimate in high L regions Adopting a more realistic magnetic field model is necessary to correctly interpret the role of radial diffusion

SCARF1 (scavenger receptor class F member 1, SREC-1 or SR-F1) is a type I transmembrane protein that recognizes multiple endogenous and exogenous ligands such as modified low-density lipoproteins (LDLs) and is important for maintaining homeostasis and immunity. But the structural information and the mechanisms of ligand recognition of SCARF1 are largely unavailable. Here, we solve the crystal structures of the N-terminal fragments of human SCARF1, which show that SCARF1 forms homodimers and its epidermal growth factor (EGF)-like domains adopt a long-curved conformation. Then, we examine the interactions of SCARF1 with lipoproteins and are able to identify a region on SCARF1 for recognizing modified LDLs. The mutagenesis data show that the positively charged residues in the region are crucial for the interaction of SCARF1 with modified LDLs, which is confirmed by making chimeric molecules of SCARF1 and SCARF2. In addition, teichoic acids, a cell wall polymer expressed on the surface of gram-positive bacteria, are able to inhibit the interactions of modified LDLs with SCARF1, suggesting the ligand binding sites of SCARF1 might be shared for some of its scavenging targets. Overall, these results provide mechanistic insights into SCARF1 and its interactions with the ligands, which are important for understanding its physiological roles in homeostasis and the related diseases.

The switching power supply is widely used in the secondary equipment of the power grid. The failure of the switching power supply will cause the protection device to malfunction, leading to a risk of large‐scale power failure. In this paper, a real‐time monitoring method based on only output voltage information is proposed. The experiment shows that this parameter‐reduced approach, relying only on voltage information, outperforms the existing method in detection accuracy. A real‐time monitoring method based on time series voltage waveform and image analysis for switching power supply is proposed and validated. The two methods, namely voltage waveform deviation assessment and voltage waveform image analysis, are integrated to further improve the fault detection performance for switching power supply by the D‐S evidence theory.