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The wide application of lithium-ion batteries (LIBs) brings along with it various safety problems, such as fire and explosion accidents. Aiming at the thermal runaway (TR) and fire problems of LIBs, we reviewed the evolution of TR within LIB and the release of TR gases and their hazards, as well as the research progress in recent years in the area of fire separation of LIBs. To begin with, physical, electrical, and thermal abuse are the three main factors leading to TR and the thermal stability of aging batteries significantly deteriorates. Furthermore, the decomposition of the electrolyte and the reaction between the active materials generates CO, CO2, H2, HF, and a variety of hydrocarbons. These TR gases have serious toxic and explosive hazards. In addition, fire separation can effectively delay the occurrence and propagation of TR within LIB modules. As a good heat-absorbing material, phase-change materials are widely used in the thermal management system and have a great prospect of wide applications in the fire separation of LIBs. Finally, the research on the TR gases' hazards of aging LIB and safer and more effective fire separation are prospected. [ABSTRACT FROM AUTHOR]

Due to their high energy density, long calendar life, and environmental protection, lithium-ion batteries have found widespread use in a variety of areas of human life, including portable electronic devices, electric vehicles, and electric ships, among others. However, there are safety issues with lithium-ion batteries themselves that must be emphasized. The safety of lithium-ion batteries is receiving increasing amounts of attention as incidents such as fires and explosions caused by thermal runaway have caused significant property damage and fatalities. Thermal runaway can easily occur when lithium-ion batteries experience issues such as electrical abuse and thermal abuse. This study compares various monitoring, warning, and protection techniques, summarizes the current safety warning techniques for thermal runaway of lithium-ion batteries, and combines the knowledge related to thermal runaway. It also analyzes and forecasts the future trends of battery thermal runaway monitoring, warning, and protection. [ABSTRACT FROM AUTHOR]

To predict pedestrian movement is of vital importance in a wide range of applications. Recently, data-driven models are receiving increasing attention in pedestrian dynamics studies, demonstrating a great potential in enhancing simulation performance. This paper presents a pedestrian movement simulation model based on the artificial neural network, in which two submodels are, respectively, used to predict velocity displacement and velocity direction angle at each time step. Destination information, the pedestrian's historical movement information, neighboring pedestrians, and environmental obstacles within a semicircular-shaped perception area are used as inputs to learn pedestrian movement behavioral rules. In the velocity direction angle submodel, a novel division method on pedestrian's perception area is adopted. Specifically, perception radius is divided into several bands, and perception angle range is divided into a number of sectors, establishing a weighted spatial matrix to represent varied influences of neighboring pedestrians and obstacles. Experiments on two typical scenarios, the unidirectional flow and bidirectional flow in a long straight corridor, were conducted to obtain pedestrian movement datasets. Then, a series of simulation cases were conducted to investigate the proper values for critical parameters, including perception radius, perception angle division, weights of the spatial matrix, and historical movement adoption. In comparison of pedestrian trajectory between simulation results and real data, the mean trajectory error (MTE) and mean destination error (MDE) are, respectively, 0.114 m and 0.171 m in the unidirectional flow scenario, which are, respectively, 0.204 m and 0.362 m in the bidirectional flow scenario. In addition, the fundamental diagram representing density-velocity and density-flow relationships in simulation results agree well with that in real data. The results demonstrate great capacity and credibility of the presented model in simulating pedestrian movement in real applications. [ABSTRACT FROM AUTHOR]

Nowadays, the famous tourist attractions are becoming more and more popular for people from all over the world. Thus, to ensure the safety of tourists is a tough task in such crowded area. The study of pedestrian's characteristics in crowd movement is essential for safety management. In this article, both uni- and bidirectional observational experiments were conducted to quantitatively analyze the movement properties of pedestrians in a zigzag corridor which is located in a tourism area named Yuyuan business district in Shanghai. Several phenomena have been found during the tourists' movement process: congestion at boundary, competing and bypassing behavior, and flow gap. As indicated by the transit time of pedestrians in both uni- and bidirectional scenarios, pedestrians in bidirectional pattern (>10 s) spend more time on going through the corridor than that in unidirectional one (<10 s). Besides, the fundamental diagrams in both uni- and bidirectional scenarios are significantly different from data in a controlled experiment, and obvious differences are observed within the density regime from 1.5 to 2.5 ped/m2 between the uni- and bidirectional scenarios. In addition, spatial distributions of density and velocity demonstrate that pedestrians would like to cluster at the boundary of straight corridors in both uni- and bidirectional scenarios. The results could enrich the database of fundamental diagrams, and then be used for model calibration by taking the actual situation into consideration in similar scenarios. [ABSTRACT FROM AUTHOR]

Summary: Knowledge about the heat release rate (HRR) is essential for studying tunnel fires. The standard method in ISO 9705 is widely applied to calculate the HRR of combustion by measuring the consumption of oxygen in a fire. However, the studies of HRR measurement in full‐scale tunnel fires are rare because of the complication and costs of large experiments. This paper presents a system based on the principle of oxygen consumption calorimetry for the measurement of HRR and total heat release (THR) of full‐scale fires in tunnels. A total of 22 fire experiments are performed in a large‐scale ventilated testing metro tunnel with dimension of 100.0 m × 5.5 m × 5.5 m to validate the reliability and effectiveness of this system. Firstly, four oil spray fire tests are conducted with nozzle flow of 106 L/h at (1 ± 0.1) MW HRR to calibrate the instrumentation. Then, 18 full‐scale fire tests using square diesel pools at five sizes (0.5, 1.0, 2.5, and 5.0 m2) and wood cribs as fire sources are carried out for the measurement of HRR and THR. Results provided by the comparison between the measured HRR and THR values of the fire tests and the theoretically calculated ones show that our system works effectively in the HRR measurement of full‐scale fires in tunnels. [ABSTRACT FROM AUTHOR]

Owing to the wide use of air-conditioning systems, building energy consumption constantly increases, and ventilation pipes account for 15% to 30% of the total consumption. Local resistance component is extensively present in ventilation pipeline systems, and the local resistance these systems produce occupies a large proportion of the total energy consumption of the ventilation systems. [1] Previous studies on the local resistance in pipelines were assumed that the local resistance components are independent and do not influence each other. In practice, if two local resistance components are adjacent, then the flow of fluid in these components falls under mutual influence [2]. In the present work, the structure of the resistance reduction optimization of cambered surfaces of an elbow is studied under coupling conditions. Results are compared with the results of a model test. [ABSTRACT FROM AUTHOR]

Ventilation and air conditioning (VAC) tubes and technologies have been widely applied in modern architecture. In tube systems, local drag generally accounts for 40% of the total drag losses. Thus, optimizing the existing system components is extremely important in improving energy utilization, saving energy, and reducing emissions. Among the local drag components of the systems, 90° elbows are essential. In this study, the drag reduction of 90° elbows in an arc form is numerically simulated and experimentally studied. Factors influencing drag losses are analyzed. Several optimal design schemes for such components are given, and the effect of drag reduction of various optimization schemes is verified by experiments.The optimized elbows can effectively reduce local drag opposite VAC tubes by 9%–10%. [ABSTRACT FROM AUTHOR]

Owing to the limited installation space and duct size, coupled fittings are common in the duct systems of buildings. The coupling effect leads to changes in drag and fan energy consumption. This study investigates duct drag and flow field characteristics under coupling conditions. Experiments and numerical simulations with the Reynolds stress model are conducted. Flow field changes, flow field deformation, and drag changes in the duct are analyzed. Regardless of the coupling form, the velocity near the inner arc is fast, whereas that near the outer arc is slow. Under three different coupling connection conditions (S-shaped, L-shaped, and U-shaped), the outlet velocity gradient of the U-shaped coupling connection is the least obvious. After the fluid flows through the bend, a significant centerline velocity reduction can be observed, even greater than that in the bend. The lowest centerline velocity lies within the range of 2.5 D to 4.5 D after the bend. Coupling connection has an insignificant effect on upstream duct resistance. The resistance of single bend is less than that of the downstream bend for the coupled bend and greater than that of the upstream bend under coupling conditions.Practical application: Coupling effect is common in practical application of ventilation engineering. This effect leads to the change of fluid resistance loss of ducts and pipes. However, few researchers focus on this effect. This study finds that regardless of the coupling form, the velocity near the inner arc is fast, whereas that near the outer arc is slow. It means the guide vane should be set near inner arc. L-shaped coupling connection has the largest downstream piping resistance. The resistance of the downstream piping under S-shaped coupling is the least, thus L-shaped coupling connection should be avoided as far as possible in practical application. [ABSTRACT FROM AUTHOR]