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As a highly efficient and environmentally friendly gas fuel, hydrogen has emerged as one of the most promising sources of energy. However, the hydrogen explosion limit is low, the explosion risk is high, and the production, storage and transportation processes are prone to explode. Therefore, it is necessary to explore hydrogen explosion inhibitor to prevent and mitigation hydrogen explosions. In this study, the synergistic effect of the combination of inert gas and ultrafine water mist on the suppression of hydrogen explosion was studied by using a standard 20 L spherical explosive container bomb. The results of the study indicate that the combined use of inert gas and ultrafine water mist yields better suppression effects in terms of explosion pressure, flame propagation speed, and flame cellular structure formation, compared to the use of a single inert gas. Inert gas and ultrafine water mist have synergistic effects, but the synergistic effect of N 2 was significantly stronger than that of CO 2. Through chemical kinetic simulation, it was found that the formation rate of O, H, and OH, which were three active free radicals, decreased significantly compared with that of the single inhibition condition in the process of inhibiting the hydrogen explosion reaction by inert gas and ultrafine water mist. The pairing of nitrogen with ultrafine water mist demonstrates a superior collaborative effect in comparison to the combination of carbon dioxide and ultrafine water mist. • Synergistic explosion suppression effect of inert gas and ultra-fine water mist. • Twin-fluid can effectively slow down the formation of flame honeycomb structures. • Analyzed the synergistic explosion suppression mechanism of twin-fluid. • N 2 is more synergistic than CO 2 with ultra-fine water mist. [ABSTRACT FROM AUTHOR]

The use of external fire suppression systems can reduce the risk of fire spreading between buildings. This study investigated the effectiveness and efficiency of different externally placed water-based fire suppression systems on façade fire safety. A series of large-scale experiments comprising an SP Fire 105 setup equipped with sprinklers and high-pressure water mist nozzles have been performed. A combustible façade, consisting of 2.5 cm thick oriented strand board (OSB) plates, was installed to provide challenging conditions and allow a visual assessment of the post-fire damage. The temperature profile on the façade surface was measured with 34 thermocouples, while five heat flux gauges and two fast-response plate thermocouples were used to measure the heat flux on the façade surface and emitted to the ambient. The sprinklers and the high-pressure water mist system effectively suppressed the upwards flame migration and reduced the heat flux toward adjacent buildings. It was observed that the sprinklers acted as a water curtain and kept the façade wet during the fire, promoting minor damage (the burnt area is less than 1% of the total area). The temperature and heat flux measurements demonstrated that the sprinkler system was the most effective suppression system. However, the high-pressure water mist systems achieved similar effectiveness but a much higher efficiency concerning water consumption. The sprinkler nozzles used four times as much water as the high-pressure water mist nozzles. [ABSTRACT FROM AUTHOR]

As the complexity and the cost of infrastructures have risen, the need for a fast, reliable, cost-effective and clean fire extinguishing system has become important. Water mist is a clean and effective technology to deal with most types of fires. Over the years, chemicals have been added to the water to improve the performance of the mist and deal with new types of fires. This review presents an exhaustive state of the art on additives for water mist technology over the last fifty years. Eleven publishers were reviewed to form the corpus of almost one hundred articles. A systematic review of the articles highlighted that alkali metal compounds have been the main focus of research. Metal-based compounds have also proved to be effective. Surfactants remain an additive of choice in the formulation of fire-fighting foams and as additives for water mist but hydrocarbon surfactants should be preferred to fluor-based ones for environmental reasons. Solvents have proved to be a new, clean and potent class of water mist additives worthy of further investigation. Overall, the toxicology and environmental impacts of most additives have not been addressed or are often overlooked as an important criterion for a water mist additive. [ABSTRACT FROM AUTHOR]

A nanosecond-pulsed laser with a wavelength of 1064 nm was used to irradiate silicon, and the concentration of water mist and smoke was characterized through light transmission. The drift and scattering effects of the laser propagation atmosphere (water mist and smog environment) on the laser and the influence of different ambient atmospheres on the effect of the laser irradiation on silicon were studied. Research has shown that when a laser passes through a water mist environment, as the laser transmission ratio increases, the diameter of the exit spot increases, and the diameter of the damage induced to single-crystal silicon increases approximately linearly. The erosion damage is enhanced, and a mixture of heat and stress damage occurs. Smoke is a simulated haze environment, and the attenuation effect of the aerosol content on the laser in a smoke environment depends on the particle size and concentration. When the laser transmission ratio is the same, the diameter of the particles is small, and the corresponding particulate matter concentration is large. The smaller the particle size, the larger the particle concentration corresponding to a different laser transmission ratio. When the laser energy of the target is the same, the shape and size of the export laser change as the laser passes through fog; furthermore, the damage shape is no longer circular, but it is rather stretched and deformed along a specific direction. This study can provide a reference for laser processing, far-field laser applications, and atmospheric optics. [ABSTRACT FROM AUTHOR]

This paper used full-scale experimental tests to study fine water mist system to extinguish fires in the electrical compartment of utility tunnel after cable fires. It used a 250 kW propane burner to ignite the cable. A high-pressure water mist system was implemented for cable fire extinguishing tests. The volume flow rate of fine water spray varied between 7 L/min and 10 L/min. The effect of different water mist volume flow rates on fire extinguishing in the electrical compartment of utility tunnel was investigated. In four cases, the ventilation speed of utility tunnels varied from 0 m/s to 1.2 m/s. The temperature above the ignition source and the lateral temperature distribution at different positions of the ignition source were measured. The effect of different longitudinal ventilation speeds on the fire extinguishing efficiency in the electrical compartment of utility tunnel were studied. The results showed that high-pressure water mist could reduce the internal temperature of the electrical compartment in utility tunnel to below 100 ℃ within 300 seconds. The high-pressure water mist system had good effects in reducing temperature and preventing re-ignition. Fine water mist system has an important practical significance in the electrical compartment of utility tunnel. [ABSTRACT FROM AUTHOR]

Fire suppression and rapid cooling methods are required to reduce the risk of battery fires. However, the liquid and solid residues generated during fire extinguishing pose a risk to the environment and human health. With the aim of correlating the extinguishing efficiency and environmental impact of the residues, fire tests were carried out on NMC lithium-ion pouch cells using different agents, namely water mist, F-500 water additive 2 % (v/v) and CO2. The combination of cell temperature measurements and videos allowed the efficiency of the extinguishing agents to be assessed. It was found that the efficiency of the water-based agents was higher than that of the gaseous agents (cooling rate of 30.5 ± 4.9 °C/s for water mist, 36.5 ± 6.4 °C/s for F-500 and 20.0 ± 1.4 °C/s for CO2). Analysis of solid and liquid residues using gas chromatography and induced coupled plasma showed that the use of F-500 resulted in a higher (one order of magnitude) concentration of VOCs in solid residues compared to the other extinguishing agents. The comparison of these concentrations of VOCs with the limits established for waste (EU Regulation N. 1357/2014) showed that the solid residues did not exceed the concentration limit for classification as hazardous waste. Regarding the concentration of metals, the highest values in the solid and liquid residues are due to Li, Ni and Cu. Based on these values, all solid samples can be classified as carcinogenic and toxic for reproduction. While the concentration of metals in the liquid residues was higher than the limit value that poses a risk to aquatic organisms. The overall results showed the need for site remediation and waste management procedures in the event of a major accident.

ObjectiveThis study focuses on the quasi-static pressure characteristics of a confined cabin in a water mist environment. MethodsFirst, on the basis of the theoretical model of quasi-static pressure in a confined cabin in adiabatic ideal gas, two new assumptions are added to establish a theoretical model of quasi-static pressure in a confined cabin in a water mist environment. Internal explosion experiments in a confined cabin with and without water mist are then performed with the charge as an independent variable, and the quasi-static pressure is measured and used to verify the mitigation effect of water mist on quasi-static pressure and obtain its empirical formula.Results Combined with the theoretical model and experimental data analysis, it is concluded that the ability of water mist to reduce quasi-static pressure increases with the increase in charge-volume ratio, but the increase rate gradually decreases. Both the theoretical formulas of the afterburning correction term and empirical formulas can be used to estimate the quasi-static pressure peak in the cabin.ConclusionsThe experimental results verify the mitigation effect of water mist on quasi-static pressure. The experimental data of this paper and others shows good agreement with the empirical formula of the quasi-static pressure peak of an internal explosion in a water mist environment, and can be used to estimate the quasi-static pressure peak.

Abstract Clean fire extinguishing systems applicable to the pottery jar liquor warehouse are in demand. In this study, taking 53vol% liquor as the research subject, fire models of various clean fire extinguishing systems comprising water mist, liquid carbon dioxide (LCO2) and liquid nitrogen (LN2) were established using a fire dynamic simulator to determine their fire extinguishing effect. A feasibility assessment of systems was performed under different fire source types, fire source sizes, and ventilation conditions. The fire extinguishing efficiency was analyzed in terms of the fire extinguishing time, oxygen concentration, and space temperature. The results showed that the success rate of the LCO2 and LN2 fire extinguishing systems was 100%, whereas the success rate of the water mist fire extinguishing system was 95%. In terms of reducing the oxygen concentration at the bottom of the space and the temperature in the space, the LCO2 system exhibited the best performance, followed by the LN2 system, and lastly the water mist. Under different ventilation conditions and fire source types, the LCO2 fire extinguishing system was least affected, whereas the effectiveness of the water mist fire extinguishing system reduced under natural ventilation conditions, and the extinguishing efficiency of the LN2 fire extinguishing system was affected by the fire source type. Overall, the LCO2 system presented more advantages in extinguishing fires in pottery jar liquor warehouses and can provide a new idea for the development and application of clean and efficient fire extinguishing systems.

Clean fire extinguishing systems applicable to the pottery jar liquor warehouse are in demand. In this study, taking 53vol% liquor as the research subject, fire models of various clean fire extinguishing systems comprising water mist, liquid carbon dioxide (LCO2) and liquid nitrogen (LN2) were established using a fire dynamic simulator to determine their fire extinguishing effect. A feasibility assessment of systems was performed under different fire source types, fire source sizes, and ventilation conditions. The fire extinguishing efficiency was analyzed in terms of the fire extinguishing time, oxygen concentration, and space temperature. The results showed that the success rate of the LCO2 and LN2 fire extinguishing systems was 100%, whereas the success rate of the water mist fire extinguishing system was 95%. In terms of reducing the oxygen concentration at the bottom of the space and the temperature in the space, the LCO2 system exhibited the best performance, followed by the LN2 system, and lastly the water mist. Under different ventilation conditions and fire source types, the LCO2 fire extinguishing system was least affected, whereas the effectiveness of the water mist fire extinguishing system reduced under natural ventilation conditions, and the extinguishing efficiency of the LN2 fire extinguishing system was affected by the fire source type. Overall, the LCO2 system presented more advantages in extinguishing fires in pottery jar liquor warehouses and can provide a new idea for the development and application of clean and efficient fire extinguishing systems. [ABSTRACT FROM AUTHOR]

The ability of water mist to mitigate blast loads has been widely recognized. However, the effects of the mean droplet diameter and volume fraction of water mist on the blast mitigation effect and underlying mechanisms have not been comprehensively examined. In this study, a three-dimensional numerical simulation based on the Euler-Lagrangian approach was carried out to study the dissipation process of blast wave energy and momentum by water mist, as well as the impact of varying mean droplet diameters (255-855 μm) and volume fractions (2.4x10-3-5.4x10-3) on blast mitigation. The numerical model incorporates interphase mass, momentum, and energy exchanges, as well as droplet breakup and size distribution. The results showed that the most efficient transfer of momentum and energy between the blast wave and water mist occurred at the air/water mist interface. Subsequently, the efficiency of momentum and energy transfer decreased as the blast wave propagated within the water mist due to the blast wave mitigation. The reduction in the mean droplet diameter and the increase in the volume fraction result in an increase in both the total the surface area and number of water droplets, thereby enhancing the efficiency of energy and momentum absorption by droplets and improving their ability to mitigate blasts. [ABSTRACT FROM AUTHOR]

In recent years, along with the widespread use of electric vehicles (EV), EV fires have occurred frequently. However, few studies have investigated EV fires in confined spaces. To address this gap, this paper aims to explore the different aspects of fire evolution of EVs as well as examining the suppression effect of different water mist (WM) settings on these fires. Multiple simulations are carried out, using the Fire Dynamics Simulator (FDS) simulation tool, considering different numbers and working pressures of WM devices. The results highlighted that the number of WM devices had a more significant effect on the fire. Peak heat release was reduced by 17 % and peak arrival time was delayed by 26 % using 6 MPa with 3 nozzles compared to 0 nozzles. Additionally, it leads to accelerated mixing of the smoke layer with the air layer. Moreover, it was shown that the closer to the fire source in the vertical direction, the greater the degree of peak temperature decrease. In this regard, the maximum reduction in the measured temperature was around 70 %.

The ability of water mist to mitigate blast loads has been widely recognized. However, the effects of the mean droplet diameter and volume fraction of water mist on the blast mitigation effect and underlying mechanisms have not been comprehensively examined. In this study, a three-dimensional numerical simulation based on the Euler-Lagrangian approach was carried out to study the dissipation process of blast wave energy and momentum by water mist, as well as the impact of varying mean droplet diameters (255-855 μm) and volume fractions (2.4×10-3-5.4×10-3) on blast mitigation. The numerical model incorporates interphase mass, momentum, and energy exchanges, as well as droplet breakup and size distribution. The results showed that the most efficient transfer of momentum and energy between the blast wave and water mist occurred at the air/water mist interface. Subsequently, the efficiency of momentum and energy transfer decreased as the blast wave propagated within the water mist due to the blast wave mitigation. The reduction in the mean droplet diameter and the increase in the volume fraction result in an increase in both the total the surface area and number of water droplets, thereby enhancing the efficiency of energy and momentum absorption by droplets and improving their ability to mitigate blasts.

The water mist (WM) is currently an important environmentally friendly fire extinguishing agent, offering a distinct advantage in efficiently cooling and inhibiting the thermal runaway (TR) behavior of lithium battery (LIB). Numerous studies have explored the additives of WM to extinguish LIB fires more efficiently. However, the inhibition mechanism of WM containing additives on TR of LIB has not been revealed clearly, and the principle of adding additives remains to be further studied. In this study, three types of non-ionic surfactants are examined and their effects on the maximum temperature during TR and the cooling time of WM are compared. The results indicate that foam induced by the additives has certain advantages in mitigating LIB TR. Further the defoamer is used to modify the foaming performance of the additive solution, and it is found that an appropriate increase in the brittleness of the foam can greatly decrease the highest temperature of the battery during TR moment. These findings can serve as a valuable reference for future applications of WM with additives in the design of battery fire suppression systems. [ABSTRACT FROM AUTHOR]

In this study, the thermal runaway (TR) suppression test platform of battery modules was built based on the real power battery pack to reduce the thermal runaway propagation (TRP) of electric vehicle power battery packs. The inhibition effect of different fire extinguishing devices on TRP of ternary lithium-ion battery modules was experimentally investigated. Big scale tests yielded combustion behaviors, TRP intervals, peak temperatures, cooling efficacy of extinguishants, heat transfer, and fire traces of the battery modules. Notably, perfluorohexanone application prolonged the TRP by 427 s relative to the blank control experiment, reducing the cell casing temperature to 267 ℃, although it did not fully arrest TRP between cells. However, water mist application effectively halted inter-cell TRP, ensuring post-spray temperatures at thermocouple sites remained below 100 ℃ and reduced heat transfer best. These findings deliver crucial experimental insights that bolster the development of fire extinguishing strategies for the safety management of electric vehicle power battery assemblies. [ABSTRACT FROM AUTHOR]

Fire extinguishing technologies of fine water mist containing additives have good application prospects. Additives that are efficient, nontoxic, nonpolluting, widely used, economical and reliable provide a reference for the application and promotion of fine water mist fire extinguishing systems containing alkali metal salts. In this paper, six potential alkali metal salt additives were selected: potassium carbonate (K 2 CO 3), sodium carbonate (Na 2 CO 3), potassium oxalate (K 2 C 2 O 4 ·H 2 O), potassium acetate (CH 3 COOK), potassium chloride (KCl), and potassium bicarbonate (KHCO 3); these additives were delivered into the fires as mists of their solutions at certain concentrations, the extinguishing time was recorded, and the minimum fire extinguishing concentration (MEC) of fine water mist containing alkali metal salt was tested by using a cup burner experimental apparatus. In addition, different types of alkali metal salts were compared to determine the anions and cations with better fire suppression performance levels. The suppression efficiencies of different ratios of additive packages for hydrogen-doped natural gas diffusion flames were studied to determine a specific ratio of additive packages. Based on the results of the experiment, in contrast to the pure water mist, the suppression efficiency of alkali metal salt greatly improved. The cation extinguishing ability was K+>Na+, and CO 3 2- and CH 3 COO− were better than other anions in alkali metal salts. An efficient compound additive was identified as 1.5% K 2 CO 3 + 0.5% CH 3 COOK. With increasing hydrogen addition, the MEC of fine water mist with additives increased. • The addition of alkali metal salts improved the suppression efficiency. • With the increase of H 2 addition, the MEC of fine water mist with additive increased. • An efficient compound additive was identified as: 1.5% K 2 CO 3 + 0.5% CH 3 COOK. [ABSTRACT FROM AUTHOR]

For exploring the influence mechanism of fine water mist system parameters on extinguishing mine belt fires, FDS was used to study the cooling characteristics and the fire extinguishing effect of fine water mist under different parameters. From the perspective of particle diameter, spray flow and nozzle spacing, the temperature change and fire extinguishing time in the roadway under fine water mist are compared and analyzed. The results show that the fire extinguishing effect is significantly affected by the system parameters. In a certain range, the fire extinguishing time decreases with the droplet particle size and decreases with the spray flow. Under the same droplet particle size and spray flow rate, the fire extinguishing time becomes larger with the increase of the nozzle spacing. Fine water mist with particle size of 100 m, nozzle flow of 8 L/min, and nozzle spacing of 1 m can quickly reduce the temperature of the fire field and effectively inhibit the spread of fire.

Fire accidents are a source of concern for electric vehicles (EV). The spread of fire caused by thermal runaway (TR) in a scenario with a high concentration of EVs can result in a serious disaster. In this study, a full-scale EV fire experiment was conducted using thermal abuse to investigate response strategies to EV fires caused by TR. The pattern of TR fires spreading in EV was also investigated. The suppression capabilities of fire blankets, water spray, and compressed air foam on EV fires in the early stages were analyzed. During the test, the temperature distributions inside and outside the vehicle were measured. The maximum temperature recorded in the passenger compartment near the roof was 919.7 °C. The length of the jet flow was estimated from the images, with the longest being approximately 2.56 m. The fire suppression test demonstrated that the fire blankets effectively extinguished flames, and the temperature inside the car gradually decreased. A water mist device can reduce temperature and put out flames. The compressed air foam effectively extinguished the fire, with an average cooling rate of −9.8 °C/s. These results provide information on EV fire response strategies.

A previous investigation showed that fire in circular, mechanically-ventilated, horizontal 0.30-m and 0.61-m ducts could be extinguished effectively by discharging water mist in a co-flow manner with the exhaust flow. However, besides horizontal ducts, an exhaust system is likely to also have ductwork in vertical and other orientations. Since the water mist dispersion and transport to the fire could be affected by the duct orientation due to fire buoyancy, there was a need to determine if the established horizontal duct protections would also be applicable to other duct orientations. Considering the fact that the fire buoyancy effect in ducts is bracketed between horizontal and vertical duct orientations, a series of fire tests was therefore conducted to evaluate if the above-mentioned horizontal duct protections would also be applicable when the ducts were to be in the vertical orientation. This paper presents the evaluation of vertical duct protection employing the same nominal spacing of 0.31 m for the water mist application as for the horizontal duct protection. The evaluation included the two protections established previously for the horizontal 0.30-m duct: one provided a minimum water mist concentration of 300 g/m3 with a median droplet size of 77 μm, while the other provided 399 g/m3 with a median droplet size of 88 μm. On the other hand, the protection for the horizontal 0.61-m duct yielded a minimum water mist concentration of 270 g/m3 with a median droplet size of 115 μm. The vertical duct tests showed that, by discharging water mist upward in the co-flow manner with the exhaust flow, both the protections for the horizontal 0.30-m duct could successfully extinguish the fire in the vertical duct, but the protection for the horizontal 0.61-m duct could not completely extinguish the fire in the vertical duct when water mist was discharged upward in the co-flow manner. However, by discharging water mist downward against the exhaust flow, the fire in the vertical 0.61-m duct could be extinguished rapidly. The vertical duct tests showed that, to ensure the applicability of a water mist protection for different duct orientations, the protection should be verified for both the horizontal and vertical duct orientations, with appropriate adjustments if required. [ABSTRACT FROM AUTHOR]

With the implementation of the green energy development strategy, new energy vehicles and related industries have been experiencing rapid growth, leading to an expansion in the market scale of the lithium-ion battery (LIB) industry. While the high energy density of LIB is being pursued, the risk of thermal runaway (TR) cannot be underestimated. Water mist (WM) is currently considered an efficient and environmentally friendly fire extinguishing agent, highly favored for its exceptional cooling capabilities. In this study, an alternative WM control strategy is proposed that capitalizes on the distinct advantages of varying particle sizes of WM during different cooling stages and integrates them to enhance overall cooling effectiveness. The experimental results demonstrate that the utilization of WM with mixed particle sizes not only reduces the peak temperature of TR, but also significantly shortens the cooling time. Compared to using WM with a single particle size, this method greatly reduces water consumption and enhances its utilization rate. This finding can offer valuable suggestions for the future implementation of WM in battery fire suppression systems design. [ABSTRACT FROM AUTHOR]

Aim: The purpose of the research was to determine the parameters of the micro- and macro-structure of the streams generated by nozzles of different types, and to identify potential applications of the tested water nozzles, including firefighting and air pollution removal. Introduction: TF6 FCN, TF6 V, NF 15 and CW 50 water nozzles were tested. At supply pressures of 0.2 MPa, 0.4 MPa and 0.6 MPa, the basic parameters of micro- and macrostructure of the streams were measured and determined: flow rate, spray angle, mass distribution of liquid on the surface (spray intensity), non-uniformity of spray density distribution, and average droplet diameters and spray spectrum. A sputter spectrum analyser, using the photoelectric method, was used to determine the microstructural parameters of the stream. Project and methods: Badaniom poddano dysze wodne TF6 FCN, TF6 V, NF 15 oraz CW 50. Przy ciśnieniu zasilania równym 0,2 MPa, 0,4 MPa oraz 0,6 MPa zmierzono i wyznaczono podstawowe parametry mikro- i makrostruktury strumieni: natężenie przepływu, kąt rozpylenia, rozkład masowy cieczy na powierzchni (intensywność zraszania), nierównomierność rozkładu gęstości zraszania oraz średnie średnice kropel i widmo rozpylenia. Do określenia paramentów mikrostrukturalnych strumienia zastosowano analizator widma rozpylenia, wykorzystujący metodę fotoelektryczną. Results: The tested nozzles generated dispersed streams with different parameters. Among the analysed nozzles, the highest degree of dispersion was obtained for the TF 6 FCN sample, whose average Sauter mean diameter (SMD) reached a value of 217.3 μm. In comparison, for the NF15 nozzle this parameter was 945 μm. The spray spectra indicate a high homogeneity of water dispersion in the stream produced by the nozzles TF 6 FCN and CW 50. From the distribution of mass sprinkling density, the CW 50 nozzle shows the greatest uniformity of spraying. At the same time, however, it reports a small amount of water, since the value of the spray density for this product did not exceed 100 g/( m2 · s), while for the NF 15 nozzle it was more than 2,700 g/( m2 · s). The obtained spray angles were close to those declared by the nozzle manufacturer. In the tests of all samples, a slight effect of supply pressure on the values of this parameter was observed. Conclusions: Among other things, the tests made it possible to conclude that in the range of supply pressures of 0.2÷0.6 MPa, the values of disperse angle and spray area of the analysed nozzles were constant or the recorded differences were insignificant. In addition, it was determined that in the case of nozzles with full spray cones, an increase in supply pressure (within the range of declared operating values) has little effect on changing the parameters of the micro- and macro-structure of the stream. The conducted tests showed the potential use of two nozzles (TF6 FCN, CW 50) in low-pressure fog extinguishing systems producing fog with SMD droplet diameters > 200 μm. For the absorption of hazardous substances, it is recommended to use nozzles with a large spray angle and a full spray cone, which, as tests have shown, produce uniform streams with small droplet diameters. Keywords: water nozzles, water spray, spray spectrum, mass spray density, water mist

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Lithium-ion batteries experience rapid temperature increases with a high risk of combustion and explosion during thermal runaway, and water mist has been considered as one of the most effective cooling strategies. The water mist field can be impacted by the safety valve airflow, subsequently affecting the cooling characteristics. In this paper, the water mist nozzle with a fixed working pressure is located 1 m above the 100 Ah LiFePO4 battery to suppress the thermal runaway, and the cooling characteristics under various stages have been compared and analyzed. The results show that the development of thermal runaway can be inhibited before thermal runaway is initiated, and the water mist presents a better cooling effect after the battery safety valve is opened. The critical accumulation heat density of 155 kJ/kg has been identified, which is the threshold for thermal runaway suppression. The confrontation between water mist and the flame has been analyzed, and the water mist droplets cannot fall on the battery surface, resulting in a poor cooling rate of 0.57 kW. This means the suppression effect of water mist will be affected by the airflow impact of the safety valve. [ABSTRACT FROM AUTHOR]

Drives in belt conveyors are critical components of the conveyor system, susceptible to various factors that can cause disruptions and energy losses. In underground mining conditions, the risk of drive fires is particularly hazardous. Therefore, it is necessary to develop highly effective fire suppression systems. However, there are no guidelines for designing such systems. This study presents a methodology for selecting and verifying the fire suppression systems for belt conveyor drives. The proposed AMIGA system for extinguishing fires on underground coal mine conveyor belts, incorporating spraying and water mist installations, is supported by a theoretical calculation methodology. This enables determining the number of required nozzles and flow rate for complete fire suppression. The development of a methodology for the selection and verification of the sprinkler system components utilized guidelines provided in the standard VdS 2109:2002-03 and the PN-EN 12845+A2 standard from 2010, while a novel approach is proposed for water mist parameters that has not been previously applied anywhere else, and is based on assessing the fire's intensity and the persistent disruption of the energy balance of the combusted coal. The theoretical calculations for potential fire power facilitate the determination of the appropriate water flow rate for the spraying system to protect the upper belt drive. For the proposed AMIGA system, the potential fire power was calculated to be 10.33 MJ / min . Based on this, the water flow rate for the spraying installation to protect the upper drive belt of the conveyor was established to be a minimum 37.5 dm 3 / min , and 21.4 dm 3 / min for the mist installation used to protect the space below the conveyor drive. In order to verify the developed methodology for parameter selection, on-site tests were conducted to verify the results. Tests were conducted on an AMIGA prototype suppression system integrated into a conveyor drive. The results demonstrate that the developed system is effective in extinguishing fires on the belt using the spraying installation, as well as under the conveyor belt drive using the water mist installation, within the entire supply pressure range ( 0.4 MPa to 1.6 MPa ). [ABSTRACT FROM AUTHOR]

Determining the input parameters for the calibration of a water mist extinguishing system in a compartment is important for the evaluation of the performance of the design. Although there is a lot of research on the use of water mist, it is still difficult understand the behavior of the system in terms of safety of people and protection of things. In this study, we aimed to conduct an experimental analysis to evaluate the effectiveness of water mist extinguishing systems in protecting paintings in art gallery museums. We compared onsite tests in a compartment of an art gallery and a numerical analysis carried out with Fire Dynamics Simulator (FDS). Numerical analysis using FDS included the water-cooling effect and the heat power in the simulated environment and the calibration for a model was found by reproducing the onsite results. The temperature trend was monitored as an essential parameter for the protection of the paintings. The study aimed to not only verify the effectiveness of the water mist system but also investigate the reproducibility of real-scale conditions through a simulated environment. The most important result obtained is the possibility of using a simulated environment instead of real-scale tests in order to test water mist capabilities. [ABSTRACT FROM AUTHOR]

At present, the application of water mist fire extinguishing system in the field of ships has attracted extensive attention, but there are few studies on the fire extinguishing performance of water mist in specific compartments. In order to explore the fire extinguishing effect of water mist on ship fires, the fire extinguishing effect of water mist on two typical ship compartments(large-space storage compartment and small-space living compartment)was simulated using FDS software. The effects of particle size, atomization angle and flow coefficient on fire extinguishing and cooling performance were analyzed. The simulation results show that the fire extinguishing performance of water mist in the large space storage cabin is poor, and the fire extinguishing and cooling can not be carried out. The water mist fire extinguishing and cooling performance in the small living room is relatively good. It is revealed that the fire extinguishing performance of water mist in the living room increases with the decrease of particle size, the decrease of atomization angle and the increase of flow coefficient. [ABSTRACT FROM AUTHOR]

Fire accidents are unpredictable, especially oil fires, which often lead to serious losses because they cannot be extinguished quickly. Accidents are unavoidable, even though it is desirable to prevent them with solid preventative measures. There are two approaches to the study of fire. On the one hand, it is to study the intrinsic safety of hazardous substances; on the other hand, it is to study the energy efficiency of fire extinguishing substances. While the latter tries to investigate effective control conditions, the former aims to prevent the occurrence of fires. In reality, as the most commonly used fire extinguishing carrier, water is an effective weapon for different fires. Therefore, with the purpose of environmental protection and energy conservation, the fire extinguishing effect of the water mist system under pure water and low concentration of green additives is explored. The self-made polymer composite additives and NaCl salt were compared with pure water mist system. The findings show that under this low-pressure system, 1% polymer composite additives had the best extinction efficiency enhancement, pure water under medium and high pressure was more effective, and 1% NaCl salt additive negatively correlated with the extinction efficiency. [ABSTRACT FROM AUTHOR]

A new predictive fire suppression model has been developed and applied to a compartment room environment with various fire locations to clarify the suppression mechanisms of water mist and sprinkler systems. To effectively mitigate the combustion process, an in-depth framework has been developed, which includes the thermal fluidic interactions and utilizes statistical approaches for water droplets characterization. Efficiencies and effectiveness of both systems under different operating conditions were investigated with a multi-parametric approach that uniquely traces the accumulative mass fluxes, penetrability and number counts of droplets. Different fire suppression scenarios were identified based on combustion behaviors, and the suppression systems' performance was evaluated based on spray coverage, penetrability, water utilization rate and potential water damage. The current study finds that water mist systems significantly outperform sprinkler systems in suppressing centered fires from both time (within 0.55 s) and utilization rate (up to 6.78%) perspective, while sprinkler systems can effectively suppress fires within a larger area, but their water utilization rate is as low as 0.07%. For water mist systems, although the water utilization rate can be 37 times higher than sprinkler systems, their effective suppression coverage area is small, which provided directions for future improvement. [ABSTRACT FROM AUTHOR]

The fire hazard resulting from the thermal runaway of lithium-ion batteries constitutes an severe threat for electric vehicles, and discovering an effective and prompt method for suppressing battery fire is still challenging. In this paper, a finite volume model for simulating the process of extinguishing lithium-ion battery fire was established, and the effect of water mist on suppressing battery fire was studied. It was found that the larger the droplet size, the greater the initial spray velocity, or the higher the nozzle height, the worse the fire extinguishing effect. The larger number of nozzles, the greater the spray flow, or the earlier the spray start time, the better the fire extinguishing effect. As the spray duration increased, the suppression effect at the center module gradually increased. When the water mist nozzle faced the center point of the module, the temperature rise was much lower than at other angles, and the fire extinguishing performance was the most effective. [ABSTRACT FROM AUTHOR]

In order to explore the effect of characteristic parameters of water mist nozzle on oil pool fire in confined space, mathematical model and physical model of oil pool fire in confined space were established. The effects of nozzle characteristic parameters such as water mist atomization cone angle, spray speed, droplet size and spray flow on fire extinguishing in a naturally ventilated room were discussed by using large eddy method and Lagrange method. The research illustrates that when atomization cone angle is in a certain range (80°–110°), fire extinguishing time is gradually shortened, and cooling effect of water mist is improved with the increase of atomization cone angle. When spray speed is 5–20 m/s, the greater the spray speed, the better the cooling effect. When droplet size is 100–300 μm, there is a positive correlation between droplet size and fire cooling rate. When the droplet size is greater than 300 μm, there is a negative correlation between droplet size and fire cooling rate. The inhibition of water mist on heat release rate increases with the increase of droplet size. The water mist with small particle size has a good cooling effect on the ceiling because of its overflow effect. In a naturally ventilated room, the water mist with the droplet size of 300 μm has a good cooling effect on the oil surface, and the reasonable droplet size is 300 μm. When the spray flow is 10–20 L/min, the greater the spray flow, the better the extinguishing effect. [ABSTRACT FROM AUTHOR]

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In this study, the effects of water mist spray characteristics on thermal radiation attenuation were experimentally investigated using five types of external and internal mixing twin‐fluid nozzles with a full‐cone spray pattern. To the best of our knowledge, this may be the first attempt to experimentally examine the separate effects of water mist spray characteristics on thermal radiation attenuation. Water and air supply pressures were measured, and their values were 1.3–55.5 and 29.8–316 kPa, respectively. The Sauter mean diameter and volume median diameter of the water mist were measured to be 20–99 μm and 21–108 μm, respectively. The spray angle and width of the water mist were approximately 20° and 110 mm, respectively. The thermal radiation attenuation afforded by the water mist discharged from the twin‐fluid nozzle increased with increasing water and air flow rates and decreasing droplet sizes. Within the experimental range, the thermal radiation attenuation was approximately 6.9%–28.4%. Based on experimental data, the effects of the water flow rate and droplet size on thermal radiation attenuation were examined independently. The dependence of the thermal radiation attenuation on the droplet size was greater than that on the water flow rate. [ABSTRACT FROM AUTHOR]

In order to study the effectiveness of smoke retaining vertical wall combined with water mist as smoke prevention separation in the pipe gallery, the coupling effect of smoke retaining vertical wall and water mist in the pipe gallery was studied through the numerical simulation software FDS. The results show that when the water mist flow rate is 0. 5 L/ min, four kinds of fine water mist with average particle size of 50, 100, 200 and 300 μm are compared, water mist of 50 μm has the most obvious effect on the reduction of flue gas temperature. This is because the vertical velocity of flue gas is reduced by the smoke baffle wall, and the water mist can overcome the longitudinal inertia force without large particle size. Therefore, the appropriate particle size range of the smoke baffle water mist coupled with the smoke baffle wall should be between 50 μm and 100 μm. When the flow rate is 0. 5 ~3. 0 L/ min, the reduction rate of heat flux downstream of the nozzle under the action of the water mist curtain is 46. 6%, 60. 7%, 82. 9%, 85. 7%, 87. 0% and 87. 3%, respectively. The greater the flow rate of the nozzle, the less the heat passing through the cross section of the pipe gallery downstream of the nozzle, but the continuous increase of the flow rate, the heat flux reduction is no longer obvious, it can be seen that there is an optimal flow rate. The water mist and the smoke retaining vertical wall have a synergistic effect, and the combined effect has a good effect on blocking the spread of smoke in the pipe gallery. [ABSTRACT FROM AUTHOR]

Interest in water mist fire suppression has increased within the fire protection industry due to its ability to control the spread and development of fire without using environmentally damaging agents. Water mist fire suppression has been used for many years in various applications such as machinery spaces, combustion turbine enclosures, and onboard passenger sea vessels. Now there is a demand to use this firefighting method to protect other fire risks such as cooking areas, commercial buildings, residential buildings, electrical equipment, road tunnels, bushfire (wildland fire) protection, and nuclear power generation facilities. To support this industry demand, this review covers the fundamentals of water mist, its suppression mechanisms, areas of application, existing research and development, and the codes and standards related to design. This comprehensive review provides a clear history of water mist suppression. It is able to identify the issues and challenges related to the technology to help pave the way for future research and development that will improve these systems to a level so that they are suitable for these new applications and meet the industry demand for nontoxic fire suppression systems. [ABSTRACT FROM AUTHOR]

Mist cannon trucks have been widely applied in megacities in China to reduce the road dust. Their practical effect on controlling the formation of secondary organic aerosol and fine particles remains unknown. We characterized the chemical composition variations in PM2.5 collected on the road sides with the simulated operations of mist cannon truck and traditional sprinkling truck via Fourier transform ion cyclotron resonance mass spectrometry and ion chromatography. The mass concentrations of water-soluble organic carbon in PM2.5 showed a significant increase (62–70 %) after air spraying. Further, we found that secondary organic aerosols, particularly organic nitrates, increased significantly via the interactions of reactive gas-phase organics, atmospheric oxidants, and aerosol liquid water after air spraying, although the air spraying had a better effect on suppressing road dust than the ground aspersion. Moreover, the formation of PM2.5 in the road segment where the mist cannon truck passed was promoted, with an increase of up to 13 % in mass concentration after 25–35 minutes, on average. The application of mist cannon trucks undoubtedly worsens the road atmospheric environment and causes health hazards to walking residents. The overall results provide not only valuable insights to the formation processes of secondary organic aerosols associated with aerosol liquid water in the road environment but also management strategies to regulate the mist cannon truck operation in China. [ABSTRACT FROM AUTHOR]

In this paper, to reflect a real fire combustion situation of stilted buildings with a typical wooden structure, we used FDS numerical simulation software to study the suppression effect of a fine-water-mist fire-extinguishing system under different working conditions. The influences of different mist droplet diameters, spray flows, and nozzle densities on the temperature change in the combustion area were analyzed and compared. The particle sizes of fog droplets exhibited a significant impact, indicating that the smaller the particle size, the faster the vaporization rate and the better the cooling effect. The cooling effect was better when the particle size was 150 μm or less when compared to the particle sizes of 200 and 300 μm. As the spray flow rate and nozzle density were increased, the fire field temperature decreased, and the cooling effect was enhanced, optimal at a water-mist flow rate of 8 L/min. Therefore, given the possible working conditions, the spray flow rate and the nozzle density should be high, while a suitable droplet size should be selected to achieve the best fire-extinguishing effect. [ABSTRACT FROM AUTHOR]

Numerical model was built with fire dynamic simulator and theocratical simulation was carried out to investigate the suppression effect of water mist on ignition and combustion process of typical solid material polymethyl methacrylate under external radiant heat flux. Characteristic parameters such as ignition time, surface temperature, heat release rate and temperature distribution of flame central plane during ignition and combustion process under different thermal radiant fluxes were obtained and compared with experimental results. The suppression effect of spray droplets on ignition and combustion process was analyzed and discussed. The results show the theoretical calculations of combustion characteristic parameters are in good agreement with experimental measurements. Water mist droplets can effectively delay the ignition time. Quantitative data proves that the water mist flow rate at 0.9 L/(min·m2) can delay the ignition time of samples by about 1,100 s while the radiant heat flux is 50 kW/m2. The simulation results can provide theoretical support and data reference for typical solid material fire prevention and fire extinguishment in practice.

Fire safety is a changing science for which the dominant parameters that affect fire suppression are still not well defined. The aim of this work is to show that sensitivity analysis techniques can speed up and improve the design process of fire suppression experiments by water mists. The important parameters that play a role in the performance of water mists were confirmed using the CFD code FDS. Various sensitivity analysis methods based on the factorial design and variance decomposition are used with four input parameters (flow rate, spray cone angle, discharge duration and droplet diameter). In our case, results highlight the importance of the discharge duration for the performance of water mists in a confined environment and a strong non-linear effect of the spray cone angle on temperature when variance decomposition methods are used. Further works will be conducted in order to confirm that sensitivity analysis can be used for application in fire suppression by water mist. [ABSTRACT FROM AUTHOR]

In this article, a collective database from validated numerical simulation has been established to study the suppression effects of water-based suppression systems under a single-compartment fire scenario at various suppression configurations and fire locations. Five fuel locations along the axis between the centre and corner of the room were configurated to dynamically analyse how the horizontal distance between the nozzle and fuel pan affects the heat release rate (HRR), temperature cooling phenomena at different heights and also the velocity profile. Throughout the fuel pan relocations, the water-mist system has achieved an average suppression time of 25 s for all the locations, it was found that the water mist system can effectively control the fire under 200 °C that is distanced over 2 m spanwise displacement from the nozzle against the fire, while the sprinkler has exhibited an excellent fuel surface cooling effect due to large momentum and heat capacity within the coverage area with an average suppression time of 50 s. The results of this study have further explored the spray coverage and droplet penetrability of different suppression systems at different locations corresponding to the fire source, and the quantitative assessment of fuel locations could also contribute to the future development of performance-based fire safety designs. [ABSTRACT FROM AUTHOR]

It is commonly assumed in fire modelling that suppression systems can control the heat release rate of a fire. However, many performance-based assumptions are derived from experimental data for sprinklers, and uncertainty remains for their application to water mist systems. In the UK, residential water mist systems are usually tested to the BS 8458:2015 standard, but the heat release rate in these tests is not quantified and focus is instead placed on thermocouple temperatures. This paper details a series of fire tests to the BS 8458:2015 standard for an electronically controlled water mist system. The paper also includes B-RISK zone modelling of these tests to estimate the suppression performance of the system, comparing model outputs to thermocouple test data. Three traditional suppression assumptions, historically derived from experimental data for sprinklers, have been adopted in the zone modelling to examine whether their application following system activation can be extended to the tested water mist system. The work indicates that applying these suppression assumptions remains reasonable in the context of the performance of the tested water mist system, noting the constraints of the test methods in representing a limited number of fire scenarios. [ABSTRACT FROM AUTHOR]

Exposure of LIB to high temperatures may cause certain damage or even fail to work. In this study, the electrochemical performance, the thermal stability and the critical heat of 18650 LIBs with/without water mist after high-temperature impact are experimental investigated. The results demonstrate that water mist raises the critical temperature of battery damage by about 40 °C. With increasing temperature, the electrochemical performance of the battery decreases, primarily caused by loss of lithium-ion. Moreover, water mist also improves the thermal stability of batteries after high-temperature impact, as demonstrated by the higher onset temperature of thermal runaway and activation barriers. Under the use of water mist, the critical heat that the battery performance is not affected and the critical heat for battery damage are obtained based on the increase and distribution of temperature and double integral, which are 2489.46 ± 47.7 J and 4777.63 ± 71.55 J, respectively. This work reveals that water mist could alleviate the damage to the battery caused by high-temperature impact, but when the heat exceeds the critical heat, the damage is irreversible. These findings could provide suggestions for the use of water mist in the thermal safety design of batteries in the future. [ABSTRACT FROM AUTHOR]

Water mist plays an indispensable role in various fire extinguishing scenarios, but its efficiency is restricted by the interaction area of droplets and the flame. With the characteristics of simple operation and limited environmental pollution, acoustic waves can deliver water droplets to flame and have the potential to enhance the fire extinguishing efficiency of water mist. However, our understanding of the synergistic effect of acoustics and water mist on suppressing flame is still limited. In this study, the enhancement mechanisms of acoustic waves in extinguishing ethanol fueled flames are experimentally investigated. The effects of critical parameters related to sound pressure and acoustic-induced air speed on flame behaviors are comprehensively discussed. Initially, the flames cannot be extinguished by the pure water mist. Coupling with acoustic waves, the response of the flames significantly changes. For the acoustic wave of a sine signal, the frequency of 30 Hz induces a greater air speed, which is superior to the frequency of 40 Hz and 50 Hz in suppressing the flame. The acoustically enhanced mechanism is perhaps related to the acoustic-induced wind, which causes the flame oscillation. The flame and the wick expose the larger area to be cooled directly by the water mist when the flame is “pulled” and “pushed” by the acoustic-induced wind. A dimensionless number θ is finally estimated for determining the critical flame extinction condition for this collaborative system. These results could advance our understanding of the underlying enhancement mechanisms in coupling acoustics with water mist and provide scientific insights into applying this novel suppression strategy.

Lithium-ion batteries experience rapid temperature increases with a high risk of combustion and explosion during thermal runaway, and water mist has been considered as one of the most effective cooling strategies. The water mist field can be impacted by the safety valve airflow, subsequently affecting the cooling characteristics. In this paper, the water mist nozzle with a fixed working pressure is located 1 m above the 100 Ah LiFePO4 battery to suppress the thermal runaway, and the cooling characteristics under various stages have been compared and analyzed. The results show that the development of thermal runaway can be inhibited before thermal runaway is initiated, and the water mist presents a better cooling effect after the battery safety valve is opened. The critical accumulation heat density of 155 kJ/kg has been identified, which is the threshold for thermal runaway suppression. The confrontation between water mist and the flame has been analyzed, and the water mist droplets cannot fall on the battery surface, resulting in a poor cooling rate of 0.57 kW. This means the suppression effect of water mist will be affected by the airflow impact of the safety valve.