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This study explores the influence of water mist droplet diameter and the spacing between the droplets on the alternating current breakdown characteristics of a water mist-air mixture (WAM) between short ball-ball and rod-plate gaps. The experimental results show that the diameter of the water mist droplets and the electrode structure influence the breakdown while the spacing between the water droplets shows a slight affect. Computations are carried out on various droplet sizes and spacings between the droplets between ball-ball and rod-plate electrodes and it is observed that the maximum electric field in the gap increases with increasing diameter of the water mist droplets. Comparatively, the spacing between the droplets of water mist shows a small influence on the electrostatic field distortion in the gaps. In addition, the effect of water mist droplets on the electrostatic field of the ball-ball electrodes is greater than that of the rod-plate electrodes. [ABSTRACT FROM AUTHOR]

Water mist-based fire-extinguishing systems are gaining acceptance for the protection of ship machinery spaces. The use of simulation tools presents a great potential for taking a performance-based design (PBD) approach to these fire scenarios. The Fire Dynamics Simulator (FDS) is the most frequently used and validated fire modeling software; however, studies of low-pressure water mist fire suppression modeling in ship engine rooms are rare. This paper contributes to the current literature by using the FDS to model a series of fire suppression scenarios defined by the International Maritime Organization (IMO) Circulars, including spray and pool fires with heptane and diesel oil, as well as exposed and obstructed fires. The simulation results are compared to data from full-scale tests conducted at recognized fire testing laboratories. Furthermore, an analysis of both the experimental and model uncertainties is carried out to assess the simulations performance. In general, a good agreement in compartment temperature evolution and fire extinguishing time is found for the modeled fire scenarios. The results support the application of FDS in a PBD approach for the design of water mist fire extinguishing systems for machinery spaces in ships. In this way, designers and engineers could model different machinery volumes and nozzles spacings that differ from those prescribed for a one story square engine room of the IMO, and, thus, predict the evolution of temperatures and extinguishing times for get the authorities approval. [ABSTRACT FROM AUTHOR]

To investigate the efficiency of water mist with additives on suppressing the typical pool fires including gasoline fire, diesel fire and transformer oil fire, a water mist generating system was employed to conduct a series of fire-extinguishing experiments. In this paper, the suppression effectiveness of the pure water mist was used to compare with the water mist containing additives, which comprises of KHCO3, carbamide, cocamidopropyl betaine and Capstone FS-1157. Meanwhile, the corresponding temperature characteristics and flame shape were measured and recorded. Results demonstrated that the fire-extinguishing performance of the water mist was improved significantly by containing additives. Wherein, the suppression efficiency of carbamide was higher than that of KHCO3 and surfactant because its decomposition reaction absorbed a large amount of heat, as a result, leading to reduction in the flame temperature. Also, the flame-retardant gases were generated and they can dilute oxygen concentration in the combustion region. However, the surfactant was better to be selected as the additive of water mist for the transformer oil fires in comparison with other additives. In contrast to the pure water mist, the average fire-extinguishing time was greatly reduced, particularly for the Capstone FS-1157. This is because the emulsification of surface-active agent plays a key role for heavy oil in the suppression process. [ABSTRACT FROM AUTHOR]

• Considering the occurrence conditions of the "wet blockage" of filter media. • Decreasing the liquid content of airflows and increasing the water absorption of filter media significantly alleviate the pressure drop jump of air filters in gas power plants. • The difference in water-holding capacity between the wettable and non-wettable filter media was approximately 42 mg/cm2 under the same pressure drop jump. • The influences of the dust-holding capacity of the filter medium on the pressure drop jump are dependent on the hygroscopic particles. This study aims to quantitatively evaluate the impact of humid airflows (unsaturated and saturated airflows with water mists), water absorption by filters (wood cellulose and polyester fibre filter media) and hygroscopic loading dust (KCl and Al 2 O 3 particles) on the pressure drop jump. Additionally, proposed methods to alleviate this tendency are known as the "wet blockage" of filters in practice. The experimental results demonstrated that the water content of the airflows mainly contributed to the pressure drop jump in the filters. Increasing the water content from 4.2 g/m3 to 11.3 g/m3 resulted in a fourfold decrease in the water-loading capacity of the tested filter medium. However, increasing the water absorption of the filters by a factor of three times caused a reduction in the water-loading capacity of approximately 42 mg/cm2 based on the self-defined parameter t c. Furthermore, the non-hygroscopic particles delayed the pressure drop jump, which is associated with the dust-holding capacity of filters. [ABSTRACT FROM AUTHOR]

• Compared to pure magnesium dust, the flame preheating zone of the magnesium dust/fine mist water hybrids has widened, with the emergence of a red radiative zone. • The explosion products of the magnesium dust/fine water mist hybrids generate "cubic" oxide products with different structure from those of pure magnesium dust explosions. • This study established the explosion mechanism for the magnesium dust/fine water mist hybrid explosions, providing a research foundation for exploring the three-phase explosion of magnesium dust/fine water mist/hydrogen gas. The primary purpose of this paper is to deeply investigate the impact of water mist on the explosive characteristics of magnesium dust and to broaden the inerting and suppression strategies for magnesium dust explosions. The explosion characteristics and flame propagation behaviors of magnesium dust/water mist mixtures were examined in a 16.2-L visualized closed vessel. The explosion products were further analyzed using SEM and XRD. The results indicate that with the addition of water mist, the explosivity of low-concentration magnesium dust (≤600 g/m3) increases. The explosive strength of three higher concentrations of magnesium dust (800 g/m3, 1200 g/m3, 1600 g/m3) notably decreases, with the P max dropping by 69.86%, 54.08%, and 46.22% respectively compared to pure magnesium dust. The leading edge of the preheat zone exhibits red radiation, the fluctuation range of the instantaneous flame propagation speed decreases, and cubic particles appear in the explosion products. These changes are mainly attributed to the hydrogen produced in the explosion of the magnesium dust/water mist mixture. Under the combined effects of hydrogen and steam, the preheat zone significantly expands. Moreover, as the concentration of hydrogen increases, its presence weakens the suppressing effect of the water mist, manifested by the evident slowing of the average flame speed, the maximum flame speed, and the rate of decrease in explosive strength. The suppression of magnesium dust explosions by water mist mainly relies on physical actions such as heat absorption, blocking thermal radiation, and diluting oxidizer concentration. [ABSTRACT FROM AUTHOR]

Fire tests were conducted to evaluate the efficacy of incorporating nitrogen to enhance water mist's fire-extinguishing capability in an obstructed, naturally-ventilated 1.22 × 0.61 × 1.22 m high enclosure. Water mist and nitrogen were applied from the enclosure ceiling in the respective ranges of 0.35–3.89 lpm and 0.113–0.283 m3/min, with median droplet sizes ranging from 16 to 35 μm. The obstruction was facilitated with horizontal baffles with various vertical spacings to force the transport of water mist and nitrogen to follow an alternating path to a 76- or 152-mm heptane pan fire sitting on the enclosure floor. The enclosure ventilation was provided with a 0.23 × 0.15 m high base opening centered on the enclosure's front wall, together with a 0.33 × 0.05 m high opening centered on the enclosure's front wall or on the enclosure's back wall at the respective elevations of 0.36 m and 0.81 m above the enclosure floor, or with the presence of these two elevated openings. The tests showed that incorporating nitrogen in the water mist application did improve water mist' fire-extinguishing capability in the enclosure. However, the improvement was highly affected by the fire size, obstruction and ventilation conditions. • Evaluate the effects of obstruction, ventilation and fire size on enclosure fire extinguishment. • Improve enclosure fire extinguishment by incorporating nitrogen in water mist application. • Improvement is highly affected by fire size, obstruction and ventilation conditions. [ABSTRACT FROM AUTHOR]

Thermal runaway (TR), as the most critical safety problem of lithium-ion batteries (LIBs), may cause considerable accident consequences, especially for large capacity LIBs, TR hazards should be multiplied. Therefore, effective TR mitigation strategies are needed. Water mist (WM), being widely considered as a clean and efficient fire suppression method, is employed for TR control in this work. TR evolution of the multi-cell large capacity LIBs induced by thermal abuse has been clearly demonstrated for the first time, the disaster characteristics of the LIB before TR are dominated by the successive gas production behaviors of the internal cells, but the battery ultimately triggers the TR as a whole. More than that, the critical signal is identified based on the battery disaster development and is successfully used for TR suppression. Then the reason for TR being suppressed is revealed by elucidating the overall and instantaneous cooling effects of the WM on LIBs. Moreover, it is found that the disaster of large capacity LIBs develops quickly, and 15 s is sufficient to make TR uncontrollable. Even so, the WM still exhibits excellent cooling ability, taking away over 65 % of the battery heat accumulation. The results provide the first comprehensive analysis of TR evolution and clarify the ability of WM in TR suppression of multi-cell LIBs. • Thermal runaway evolution is clarified based on multi-parameter fusion analysis. • The battery disaster significantly intensifies after the activation of safety vent. • Over 75 % of the battery heat is accumulated after the activation of safety vent. • 15 s disaster development is enough to make thermal runaway uncontrollable. • Water mist can remove over 65 % of the heat accumulated by lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The work is a continuation of research concerning the influence of intensive cooling of permanent mold in order to increase the casting efficiency of aluminium alloys using the multipoint water mist cooling system. The paper presents results of investigation of crystallization process and microstructure of multicomponent synthetic hypereutectic alloy AlSi20CuNiCoMg. The study was conducted for unmodified silumin on the research station allowing the cooling of the special permanent sampler using a program of computer control. Furthermore, the study used a thermal imaging camera to analyze the solidification process of multicomponent alloy. The study demonstrated that the use of mold cooled with water mist stream allows in wide range to form the microstructure of hypereutectic multicomponent silumin. It leads to higher homogeneity of microstructure and refinement of crystallizing phases of casting.

This article focuses on the interaction of infrared (IR) radiation with water droplets. The main objective of the article is the production of water mist in order of evaluation the reduction in intensity of IR radiation. In the experiments described in this paper, a set of five different nozzles was used with various spray characteristics. The respective nozzles were gradually located between the IR radiation source and a detector and the attenuation of IR radiation was assessed. The reduction in IR radiation intensity was determined and IR radiation transmittance was calculated for the respective tested nozzles.

Unmodified AlSi20 alloy were casted at the research station, allowing for sequential multipoint cooling using a dedicated computer- controlled program. This method allows for the formation of the microstructure of hypereutectic AlSi20 alloy and also increases hardness. Primary silicon dendrites were found in the microstructure of cooled samples. Based on these dendrites, the formation of primary silicon particles is explained. Cooling of casting die with a water mist stream causes changes in solidification, which leads to expansion of the boundary layer with columnar crystals and shrinkage of the core zone with equiaxed crystals. It also causes more regular hardness distribution around pre-eutectic Si crystals, which can lead to tensile strength and machinability improvement.

In this study, the effects of discharge area and atomizing gas type in a twin-fluid atomizer on heptane pool fire-extinguishing performance were investigated under the heat release rate conditions of 1.17 and 5.23 kW in an enclosed chamber. Large and small full cone twin-fluid atomizers were prepared. Nitrogen and air were used as atomizing gases. With respect to the droplet size of water mist, as the water and air flow rates decreased and increased, respectively, the Sauter mean diameter (SMD) of the water mist decreased. The SMD of large and small atomizers were in the range of approximately 12–60 and 12–49 μm, respectively. With respect to the discharge area effect, the small atomizer exhibited a shorter extinguishing time, lower peak surface temperature, and higher minimum oxygen concentration than the large atomizer. Furthermore, it was observed that the effect of the discharge area on fire-extinguishing performance is dominant under certain flow rate conditions. With respect to the atomizing gas type effect, nitrogen and air appeared to exhibit nearly similar extinguishing times, peak surface temperatures, and minimum oxygen concentrations under most flow rate conditions. Based on the present and previous studies, it was revealed that the effect of atomizing gas type on fire-extinguishing performance is dependent on the relative positions of the discharged flow and fire source.

Water mist is considered to be one of the most effective ways to suppress fire in coal mines. The structure of an atomization device for water mist was determined based on preliminary research. By regulating the working conditions, including air pressure and water flow volume, we obtained water mist with varying particle size distributions, which proved to be the most important factor for fire suppression. Particle size distribution, characterized by a V99 and V50, changed from 50 to 1600 µm during the experiment at a given air pressure (0.6–0.16 MPa) and water flow volume (0.6–1.0 m3/h). The particle size distribution along an axial line can be divided into a wavy flow zone and a fully atomizing zone. Based on the experiments, three types of particle size distributions, 98, 498 and 1013 µm, were used to test the fire-suppression characteristics of water mist in a simulated roadway with a self-built platform. The result showed that water mist could suppress fire rapidly and the highest temperature dropped from 205 to 10 °C within 30 s. [ABSTRACT FROM AUTHOR]

Water mist fire fighting has achieved a well established position in fire protection for industrial and civil applications. The performances of water mist nozzles, largely used in water mist production, are deeply influenced by the internal nozzle flow characteristics and CFD modelling is a powerful tool to analyse them in details. The paper focuses on the numerical investigation of the internal flow in pressure swirl injectors for water mist applications. 3D large eddy simulations based on the Volume-Of-Fluid methodology have been implemented. The flow is assumed to be incompressible and under isothermal non-reacting conditions. Validation of the model against available experimental data is performed with satisfactory results. The effect of internal nozzle geometry on the injector behaviour is investigated by modifying the inclined swirling channels (five configurations) and the injection pressure in the range 5 to 320 bar. The effect of the size of cylindrical and conical swirl chambers are also independently investigated. Three different flow regimes can be distinguished as a function of imposed swirl and injection pressure and a map is reported to clarify the effect of these parameters. When a stable hollow cone spray is formed the mass flow rate fluctuations are < 5%, corresponding to a discharge coefficient between 0.34 and 0.50. When no air core is present in the discharge hole, mass flow rate fluctuations as high as 16% are observed, which correspond to discharge coefficient as high as 0.7. A detailed quantification of in-nozzle characteristics, like swirl number and momentum flux distribution along the nozzle and lamella thickness in the discharge hole, is reported and discussed, with particular emphasis on stability and transient behaviour of the atomiser internal flow, which represents the main novelty of the present study. [ABSTRACT FROM AUTHOR]

This work experimentally studied the synergistic effect of fire extinguishing by inert extinguishing of water and chemical fire extinguishing of potassium salts. The effect of the combination of water and potassium salts on the effectiveness of the fire suppression compared with that of water and potassium salts used individually was analyzed by measuring the minimum extinguishing concentration of pure water mist, water mist with potassium salts additive and potassium salts dry powder. Results show that water mist containing potassium salts can enhance the fire extinguishing efficiency of pure water and potassium salt dry powder, and the fire extinguishing efficiency is enhanced with the increase in potassium salt content in the solution. Based on the chemical thermodynamic analysis, the essence of synergistic role of water and potassium salts in flame temperature is the existence of water vapor, which can activate potassium salts, thereby easing the generation of a large number of active substances obtained by thermal decomposition of potassium salts at flame temperature, such as gaseous KOH, for fire extinguishing in the equilibrium products. [ABSTRACT FROM AUTHOR]

Suppression of high-voltage (HV) electrical fires is difficult because it requires fire-extinguishing agents with good isolation properties as well as high fire-suppression efficiency. In the work presented herein, water mist with and without various water mist additives (WMAs) was utilized to suppress HV transformer oil fires. The WMAs included ionic alkali-metal salt and fluorocarbon surfactant, and nonionic hydrocarbon and fluorocarbon surfactants. At the same concentration, the surfactants were more efficient at extinguishing fires compared with the alkali-metal salt. The fluorocarbon surfactant was more efficient at extinguishing fires than the hydrocarbon surfactant, achieving flame extinction in 18 % of the time required when using natural water (NW). Besides, the effects of WMAs on the insulating properties of the water mist were studied. The gap breakdown test showed that the NW mist could increase the breakdown voltage of air by up to 5 % at 70-cm gap distance. Comparatively, the nonionic WMAs did not affect the insulating property of the NW mist, with the mist containing 1.0 % ionic KHCO3 solution enabling a reduction of up to 16 % in the breakdown at 70-cm gap distance while increasing the leakage current of the simulated insulator by up to 250 % at its nominal voltage. Finally, field tests were performed where NW mists were discharged onto a charged 220-kV high-voltage transformer. This study proves that NW mist and mists with nonionic WMAs are suitable for protecting HV electrical equipment, having important implications for extending the applications of water mist. [ABSTRACT FROM AUTHOR]

Water mist has a good three-dimensional cooling effect; however, its extinguishing effect on oil fires is less than that of foam extinguishing agents. This study aimed to enhance the gasoline fire extinguishing efficiency of water mist by adding KBr, Tween-80, and a dissolved CO 2 solution as multicomponent additives with different suppression mechanisms. The fire extinguishing time was measured to evaluate the extinguishing efficiency of different additives. The test showed that KBr mainly works near the flame base and makes an unstable gap between the flame base and the gasoline surface; the Tween-80 mist and dissolved CO 2 mist make the flame height lower under the test conditions. By analyzing the different extinguishing phenomena, temperature and efficiency of each additive, the multicomponent additives were proposed to enhance the extinguishing efficiency based on different mechanisms. The results showed the water mist with KBr, Tween-80 and dissolved CO 2 resulted in a remarkable improvement in the ability to extinguish a gasoline fire compared with pure water mist. [ABSTRACT FROM AUTHOR]

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Abstract In the present study, the effect of turbulence on extinguishment of counterflow diffusion flame by polydisperse water mist was investigated experimentally. A counterflow methane-air diffusion flame was stabilized in the forward stagnation region of a porous cylinder. Water mist was supplied by a pressure-type atomizer. Uniform turbulence was produced in the airflow by a grid. Mist characteristics were measured by a phase Doppler particle analyzer and turbulence properties by a hot wire anemometer. For laminar flames, the critical stretch rate at extinguishment decreases with the mass fraction of water mist and the extinguishment is not affected by the Sauter mean diameter D 32 even when D 32 is as large as 70 µm. Turbulence reduces significantly the critical bulk (mean flow) stretch rate at extinguishment. Effect of turbulence on extinguishment is relevant to the turbulence stretch rate, which is the inverse of the Kolmogorov time scale. Sum of the bulk stretch rate and the turbulence stretch rate is the total stretch rate that actually exerts on turbulent flame. If the relative turbulence intensity v'/V is as low as 0.06 and D 32 is smaller than 30 µm, extinguishment of turbulent diffusion flame is expressed uniquely by the total stretch rate, which coincides with that of laminar flame. On the other hand, for large water mist, D 32 > 30 µm or high turbulence intensity, v'/V = 0.10, non-uniformity of mist dispersion appears, of which scale is of the order of integral scale of turbulence. The locally extinguished flame by a spot of dense water mist is reignited by surrounding flame and the suppression effectiveness of water mist is deteriorated when the turbulence intensity is high or the mist diameter is large. [ABSTRACT FROM AUTHOR]

Natural gas leakage from gas pipelines usually leads to human intoxication. Further, it may even cause fires and/or explosion accidents or make an indirect chemical contribution to climate change in the long term because of its high global-warming potential. As a clean, potential, and effective method for controlling/mitigating the risk of natural gas leakage, water mist is tested to suppress gas jet leakage from a lab-scale pipe in this study. Based on actual natural gas leakages in pipelines or practical emergency management measures, both tilted and non-tilted gas jet cases were considered to evaluate the performance of gas jet suppression by water mist. A series of small-scale experiments has been conducted to deepen the understanding of the dynamical behavior and mechanisms of the gas jet–water mist interaction by visualizing the two-phase flow via planar particle image velocimetry. The results indicate that different shapes of leakage nozzles with a similar effective diameter are highly consistent regarding the interacting flow field characteristics. In addition, guidelines for optimizing a water mist system for leakage gas suppression/control are presented based on gas–spray momentum ratio and dimensionless gas jet suppression height analyses. Owing to the lack of applications on natural gas leakage with water mist, this study is valuable toward optimizing water mist systems for leakage gas suppression/control of such applications. Image 1 • Water mist as a clean technique is tested to control natural gas leakage. • A tilted gas jet-mist spray interaction is visualized and analysed via 2D-PIV. • The gas-spray interaction was varied with tilt angles and leakage shape. • References based on H∗, Z g ∗ and Φ for optimizing water mist system are presented. [ABSTRACT FROM AUTHOR]

Abstract Fire disasters occurring in the ventilated places often feature the harmless and pollution-free fire extinguishing methods, one of which is water mist. However, the application of water mist system in the forced-ventilated places is still a controversial issue. The main objective of this study is to present a systematic experimental investigation on water mist suppression performance in the mechanical ventilation conditions. A series of full-scale experiments were conducted in a glass-walled cabin with dimension of 3 m × 3 m × 3 m, measuring instantaneous flame height, smoke temperature, radiative and convective heat flux, and concentrations of oxygen and carbon monoxide. The coupling effect of water mist and mechanical smoke exhaust was revealed. Experimental results show that all the dimensionless maximum temperature rise, dimensionless rising and descending rates decline linearly with exhaust rate. Moreover, the dimensionless maximum temperature rise correlates well with the dimensionless height in a cubical relationship. The inhibitive effect of convective heat transfer is enhanced gradually with the increased mechanical exhaust rate. Both the turbulent mixing and radiation attenuation play significant roles in water mist fire suppression. Furthermore, the minimum value and descending rate of O 2 concentration both tend to increase with exhaust rate, while the maximum value and rising rate of CO concentration change inversely. It is implied that the coupling of mechanical ventilation and water mist system is beneficial for personnel evacuation, and it provides a reference for the clean and sustainable fire-extinguishing system design. Highlights • Coupling effect of water mist and mechanical ventilation was investigated. • Dimensionless maximum temperature rise, rising and descending rate decrease with exhaust rate. • Δ T m a x ∗ correlates well with h* in a cubical relationship. • Turbulent mixing and radiation attenuation play significant roles in water mist fire extinguishment. • Both maximum value and rising rate of CO concentration decrease with exhaust rate. [ABSTRACT FROM AUTHOR]

Highlights • Experimentally investigated impact of laterally sprayed water on methane jet flame. • Studied impact on flame shape, temperature, radiation intensity, and extinguishment. • Developed relationship between the mean flame tilt angle and Froude number. • 3D numerical simulation showed sound agreement with experimental data. Abstract This paper investigates the impact of a laterally sprayed water mist on a methane-air jet flame. An experimental apparatus for suppressing a flame using laterally sprayed water mist was developed and used to investigate the effect of the mist on the flame shape, temperature field, velocity field, radiation intensity, and extinguishment. A 3D numerical simulation was then performed to reveal the underlying mechanisms observed in the experiments, with the simulations showing reasonable agreement with the experimental data. Increasing the pressure of the water mist decreased the flame height and increased its tilt angle. For a given water mist pressure, lower–velocity flames exhibited larger tilt angles, because they were more strongly affected by the transverse shear forces exerted by the water mist; additionally, they were more likely to be extinguished by the mist. A relationship between the mean flame tilt angle, and the Froude number was deduced. Water mist was also discovered to substantially decrease the radiation intensity of the flame. Moreover, the influence of gas velocity and water mist pressure on the turbulence intensity, radiation temperature, and velocity field were discussed numerically. This can theoretically help interpret the suppressing effect of water mist on a methane-air jet flame. [ABSTRACT FROM AUTHOR]

In order to reduce the heat stress caused by urban heat island and local overheating of the city, the spray cooling system is arranged in the streets. The purpose of this study was to reveal the dynamic physiological adjustment and thermal perception response of human body under heat stress with alternating exposure of sunlight and water mist. Fifteen subjects participated in the exposure test at different frequencies. Three kinds of data were collected, including meteorological parameters, skin temperature (T sk), and thermal perception. The results showed that the dynamic thermal perception was affected by the short-term thermal experience based on 2 or 5 min. The change of thermal sensation to cooling stimulation was approximately 1.5 times higher than that to warm stimulation. The increase of water mist exposure rate improved the neutral temperature of the universal thermal climate index (NUTCI) and the neutral temperature of the universal thermal climate index range (NUTCIR). In the step-change stages, air temperature (T a) and relative humidity (RH) were the meteorological parameters that significantly affected the thermal sensation, and the physiological parameter was the skin temperature of lower arm (T Arm). Dynamic models for predicting thermal sensation with T a , RH and T Arm change rate was established. Compared with the traditional regression prediction, BP neural network prediction had higher accuracy (RMSE = 0.229) and better fitting degree (R2 = 0.856). • The dynamic thermal response to microclimate step changes was studied. • A short-term thermal experience of 2 or 5 min affected thermal sensation. • The sensitivity to cooling stimuli was 1.5-fold greater than that to warm stimuli. • The relationship between thermal sensation and multiple parameters was revealed. • Four methods for predicting dynamic thermal sensation were proposed. [ABSTRACT FROM AUTHOR]

The work is a continuation of research concerning the influence of intensive cooling of permanent mold in order to increase the casting efficiency of aluminium alloys using the multipoint water mist cooling system. The paper presents results of investigation of crystallization process and microstructure of synthetic hypereutectic alloys: AlSi15 and AlSi19. Casts were made in permanent mold cooled with water mist stream. The study was conducted for unmodified silumins on the research station allowing the cooling of the special permanent probe using a program of computer control. Furthermore the study used a thermal imaging camera to analyze the solidification process of hypereutectic silumins. The study demonstrated that the use of mold cooled with water mist stream allows in wide range the formation of the microstructure of hypereutectic silumins. It leads to higher homogeneity of microstructure and refinement of crystallizing phases and also it increases subsequently the mechanical properties of casting.

Lithium-ion batteries (LiBs) are a proven technology for energy storage systems, mobile electronics, power tools, aerospace, automotive and maritime applications. LiBs have attracted interest from academia and industry due to their high power and energy densities compared to other battery technologies. Despite the extensive usage of LiBs, there is a substantial fire risk associated with their use which is a concern, especially when utilised in electric vehicles, aeroplanes, and submarines. This review presents LiB hazards, techniques for mitigating risks, the suppression of LiB fires and identification of shortcomings for future improvement. Water is identified as an efficient cooling and suppressing agent and water mist is considered the most promising technique to extinguish LiB fires. In the initial stages, the present review covers some relevant information regarding the material constitution and configuration of the cell assemblies, and phenomenological evolution of the thermal runaway reactions, which in turn can potentially lead to flaming combustion of cells and battery assemblies. This is followed by short descriptions of various active fire control agents to suppress fires involving LiBs in general, and water as a superior extinguishing medium in particular. In the latter parts of the review, the phenomena associated with water mist suppression of LiB fires are comprehensively reviewed.

Summary: Ultrafine water mist (UFWM) (<10 μm), as a total flooding agent, has been proven to overcome obstructions in extinguishing fire. To examine the efficacy of UFWM extinguishing pool fires and reveal the primary fire extinguishing mechanisms of heat adsorption, a predictive model of minimum extinguishing concentration (MEC) is developed based on heat extraction, and the experimental data of MECs were obtained with an improved cup burner. The contribution of heat adsorption is about 25% to 50%, and turbulence effect also plays an important role in extinguishing fire. To improve fire inhibition effectiveness of UFWM by turbulence effect, CO (NH2)2, NH4HCO3, and (NH4)2HPO4 were selected as additives; KCl and KH2PO4 were also chosen for comparison purpose. It is discovered that CO (NH2)2 and (NH4)2HPO4 in the low concentrations can improve the fire extinction effectiveness except NH4HCO3. CO (NH2)2 has the most contribution to fire extinction at the optimum concentration (about 0.01 mol L−1 for n‐heptane fire and 0.03 mol L−1 for ethanol fire). Moreover, CO (NH2)2 (at 0.03 mol L−1) was dramatically better than KH2PO4 in extinguishing ethanol fire, and its effect is very close to that of KCl (at 0.067 mol L−1) for ethanol fire. [ABSTRACT FROM AUTHOR]

Recent research has shown that acoustics can be used to suppress flames from a liquid fuel source. The results of these experiments indicated that acoustics alone are insufficient to control flames beyond the incipient stage. Recent research has also shown that variations in the delivery of water mist to a fire can enhance the mist’s efficiency. Therefore, the addition of acoustics to water mist may be an effective means of enhancing an established fire protection technology. For the first time, acoustics and water mist have been combined and studied as a flame suppression strategy. A series of experiments were conducted that explored the potential for coupling acoustics with water mist as means of flame suppression. Heptane fueled flames were created from two different sized ceramic fiber wicks: 30 mm × 50 mm with 5 mL of fuel, and 60 mm × 100 mm with 20 mL of fuel. The flames were then exposed to water mist delivered at a constant rate, which was found to be incapable of suppressing the flames. Next, low frequency sound waves at 62 Hz and 80 Hz were used to suppress flames from both wicks, with each frequency being generated by a different resonator. Finally, acoustics from both resonators were combined with water mist, and used to suppress flames from both wicks. The results showed that a combination of acoustic waves and water mist suppressed the flames more effectively than each individual technique on its own. This finding opens the possibility of developing more efficient ways to use water mist technology. [ABSTRACT FROM AUTHOR]

This paper reports the preparation and fire-suppression efficiency of oil-in-water microemulsions containing ferrocene. In this work, oil-in-water emulsions containing 0–1000 ppm ferrocene and four surfactants (Surfynol 465, Olfin E1020, Triton X-100 (TX), and Noigen TDS-80 (NT)) were prepared by homogenizing n-octane solutions of ferrocene and aqueous surfactant solutions at ambient temperature. Four emulsion parameters were then characterized: emulsion stability, oil-droplet size in emulsion, flash point, and capability of extinguishing n-heptane pool fires. Emulsion stability experiments and droplet-size measurements clearly demonstrated that the oil-in-water emulsions containing ferrocene and TX/NT were thermodynamically stable microemulsions. Flash-point measurements confirmed that no oil-in-water microemulsions tested ignited below 93 °C. Suppression trials involving microemulsions containing 0–1000 ppm ferrocene and NT revealed the relationship between their fire suppression efficiency and the concentrations of ferrocene and NT, and also demonstrated that the microemulsions tested in this study have a higher ability to suppress pool fires compared with a conventional wet chemical agent. [ABSTRACT FROM AUTHOR]

As the succedaneum of halon extinguishing agent, water mist is absolutely green, harmless, and sustainable which does not cause the ozone depletion. In order to investigate the fire extinguishment performance of water mist system with both continuous and cycling discharge modes, a series of full-scale pool fire suppression experiments (including gasoline and diesel) with the two discharge modes were conducted in a confined compartment (3 m × 3 m × 3 m) under different mechanical exhaust rates. Some characteristic parameters, such as the smoke temperature, radiative and total heat flux, fire-extinguishing time, and carbon monoxide and oxygen concentration under the influences of both water mist and mechanical ventilation, were obtained, and their variation mechanisms were analyzed in detail. The experimental results show that pool fires could be extinguished more quickly using cycling water mist with shorter turn-off time. The reduction coefficient of carbon monoxide concentration increases exponentially, while the extinguishing time of both gasoline and diesel pool fires decreases first and then increases with the ventilation rate. With cycling discharge mode, the smoke temperature and heat flux both fluctuate with alternate activation of water mist. The application of cycling discharge mode substantially improves the fire suppression efficiency, especially in the condition that the pool fire is difficult to extinguish utilizing continuous discharge mode. The cycling discharge water mist system can be applied in some ventilated spaces when mechanical ventilation is unavoidable, and is helpful for personnel security and evacuation. [ABSTRACT FROM AUTHOR]

Pressure swirl nozzles are often employed in water mist fire suppression systems. In the present work, a single head full cone simplex nozzle with X-type swirl-insert and an orifice diameter of 1.2 mm is used to produce water mist. The objectives are to experimentally measure different characteristics of the spray and investigate extinction performance of diesel pool fires of size 0.1, 0.2, and 0.3 m. Discharge coefficient and spray cone angle are measured and correlations are presented as functions of Reynolds numbers ( Re , based on orifice diameter). Mass flux density of the spray is measured with a patternator designed considering possible asymmetry in the spray. Droplet size and velocity distributions are measured using a particle droplet image analyser ( PDIA ) system for 28,850 ≤  Re  ≤ 35,800 and axial distances from the nozzle (0.75 ≤  z  ≤ 1.75 m). Experimentally measured droplet number distributions are characterized by modified log-normal distribution. Rosin-Rammler and modified Rosin-Rammler model are presented to predict droplet volume distributions. Correlations are presented for calculating parameters of these models in order to describe droplet size distribution ( DSD ) for any combination of Re and z . Relative span factor ( RSF ), Sauter mean diameter ( SMD ), and average velocity of the spray are measured. Correlations for SMD and average velocity are presented as functions of experimental variables. The extinction performances are investigated through video recording for 28,850 ≤  Re  ≤ 35,800 and various vertical distances between the nozzle and the fuel surface (0.75–2 m). Extinction performance of the nozzle in the present work is compared with the other performances of different water mist systems reported in the literature. [ABSTRACT FROM AUTHOR]

In order to analyze the mitigating effect of water mist on the explosive shock wave inside a cabin, a series of TNT explosion experiments in the center of a cabin were carried out, from which the wall pressure and quasi-static pressure inside the cabin in different cases with and without water mist were measured. Results show that water mist truly has an evident effect on attenuating the overpressure peak of blast wave and the quasi-static pressure. In the experiment of 27.5g TNT exploding in cabin, the attenuation rate of initial shock wave overpressure is 26.47%, the attenuation rate of secondary reflected wave pressure is is about 27.27%, and the attenuation rate of quasi-static pressure is about 31.82%. For the same water mist density, the mitigating effect of water mist on the blast wave decreases with the increase in TNT charge. [ABSTRACT FROM AUTHOR]

The combustion of premixed gas mixtures containing micro droplets of water was studied using one-dimensional approximation. The dependencies of the burning velocity and flammability limits on the initial conditions and on the properties of liquid droplets were analyzed. Effects of droplet size and concentration of added liquid were studied. It was demonstrated that the droplets with smaller diameters are more effective in reducing the flame velocity. For droplets vaporizing in the reaction zone, the burning velocity is independent of droplet size, and it depends only on the concentration of added liquid. With further increase of the droplet diameter the droplets are passing through the reaction zone with completion of vaporization in the combustion products. It was demonstrated that for droplets above a certain size there are two stable stationary modes of flame propagation with transition of hysteresis type. The critical conditions of the transition are due to the appearance of the temperature maximum at the flame front and the temperature gradient with heat losses from the reaction zone to the products, as a result of droplet vaporization passing through the reaction zone. The critical conditions are similar to the critical conditions of the classical flammability limits of flame with the thermal mechanism of flame propagation. The maximum decrease in the burning velocity and decrease in the combustion temperature at the critical turning point corresponds to predictions of the classical theories of flammability limits of Zel'dovich and Spalding. The stability analysis of stationary modes of flame propagation in the presence of water mist showed the lack of oscillatory processes in the frames of the assumed model. [ABSTRACT FROM AUTHOR]

To guarantee the stable and quantitative adding of surfactant into the pressure pipe and not be affected by the inlet and outlet pressure changing, the method utilizing jet pump cavitation characteristics to add surfactant was proposed. Keeping pressure ratio lower than the critical pressure ratio, the adding quantity could remain unchanged. In order to improve the stabilities, reduce the pressure loss and improve the critical pressure ratio of the jet cavitation adding method, a new two-stage cavitation jet adding method and device were proposed, and the performance was investigated experimentally under different working flows and outlet pressures, and compared to the cavitation jet pump in this paper. The results showed that the negative pressure remained unchanged within a certain range of outlet pressure, then decreased gradually with the increase of outlet pressure for the new device, which was similar with the traditional one. Furthermore, the critical pressure ratio of the new device was larger than the traditional one, which indicated that the pressure loss for the new device was smaller and it was more stable as the adding amount of surfactant was constant. In addition, the critical pressure ratio could increase by reducing the additive proportion of surfactant. Based on the above contributions and field investigation, it is believed that the study will play an important role for automatic quantitative control. [ABSTRACT FROM AUTHOR]

This article focuses on the interaction of thermal radiation with water droplets and the creation of water mist for the purpose of evaluating the decrease of heat flux when positioning a water curtain of various parameters between a radiation source and a radiometer. The change of water curtain parameters, affecting the passing through of thermal radiation, was performed using five nozzles with a variable spray characteristics. For the respective nozzles the attenuation of thermal radiation was determined and the thermal radiation transmittance was calculated. Water mist was created using a high‐pressure pump and nozzles with a different size of the orifice. The measurement of droplet size was performed using the time‐shift technique. The Omegalux radiant panel was used as the radiation source and the Hukseflux SBG01 radiometer with a working range of 0–5 kW.m−2 was used as the detector. © 2017 American Institute of Chemical Engineers Process Process Saf Prog 37:18–24, 2018 [ABSTRACT FROM AUTHOR]

The paper presents the experimental results about fire extinction in the model fire sites of forest combustible materials. We use the high-speed video recording tools during the experiments, as well as the system of multiphase media diagnostics based on panoramic optical flow visualization techniques. The presented experiments prove that it is possible to extinguish the forest combustible material (FCM) by small amount of water. The study considers several ways to stop FCM thermal decomposition: by individual large water droplets (1-3 mm), by an aerosol flow (the droplet size is from 0.05 mm to 0.12 mm), or through water film formation on the FCM surface. Typical durations of the FCM thermal decomposition and time of fire suppression are determined for various conditions of interaction with water. The experimental results identify which amount of water is enough to extinguish the FCM by different ways of water transfer to the reacting surface layer. Furthermore, it is estimated how the component composition and the properties of the tested FCM mixtures effects onto the characteristics of the investigated processes. The residual fraction of the FCM was evaluated by comparison of initial and final (after extinguishing) mass of the sample. [ABSTRACT FROM AUTHOR]

The leaking of hazardous, flammable hydrocarbons, such as methane, possesses potential risk to generate accidents of fire or explosion. The conventional technique is water mist which can reduce the environment concentration of flammable gas and manage accidents of fire caused by hazardous hydrocarbons leaking, but pure water mist extremely restricts its popularization and application due to the poor solubility of hydrocarbons. Therefore, the mixed surfactant is used as water mist additive for its excellent physical and chemical nature, and its performance is investigated and evaluated experimentally. A formula of mixed surfactant additive has been developed and the physicochemical properties of water mist with mixed surfactant additive were measured. Additionally, the present work establishes a series of lab-scale experiments to study absorption capacity and gasoline pool fire suppression performance of water mist with mixed surfactant additives and the effect factors. The concentration transient within the test chamber has been evaluated during the absorption experiment. Results showed that water mist with mixed surfactant additives is shown to be efficient in absorbing methane, especially under the condition of low methane concentrations, water mist with 5% mixed surfactant, absorbing time less than 150s had best absorption capacity. Furthermore, the addition of mixed surfactant in water mist can shorten fire suppression time and restrain fire enhancement effectively at the beginning when extinguishes the oil pool fire. The water mist with mixed surfactant additives will greatly promote the large-scale application of water mist technology used to manage accidents of hazardous hydrocarbons leakage or fire. [ABSTRACT FROM AUTHOR]

On account of the fire development rules with great complexity and uncertainty in hot and high humid confinement spaces, fire suppression effects and mechanisms by water mist of different pressures in confined space with one opening at surroundings of different temperature (40 o C/26.5 o C) and different humidity (RH 90% / 37.5%) were simulated by FDS. The flame and the smoke layer temperature, the heat radiation received by the floor and the oxygen near the flame were analyzed. It is concluded that under the experimental and simulated conditions in this paper, in hot and high humid environment, the flame cooling effect by the water mist is less significant than that in normal surroundings, and decreasing with the increase of the water mist pressure. The reason is the stronger perturbation to airflow near the flame root by the higher pressure water mist, so the average flame temperature decreases slowly. With the increase of pressure, the cooling effect on smoke layer is enhancing. At hot (40 o C) and high humidity (RH90%) environment, the cooling effect on smoke layer by water mist is weaker than that in normal temperature and humidity environment, but the gap is reduced with the increase of water mist pressure. The heat radiation attenuation effect is more significant in hot and high humid surroundings than that in normal environment, and increasing with the increase in pressure. With the increase of water mist pressure, the temperature and humidity of surroundings, the oxygen concentration reduction rate will be greater, and the oxygen suffocation effect will be more significant. The researches have important theoretical and application value for application of water mist fire suppression technology. [ABSTRACT FROM AUTHOR]

In order to study the effect of water mist on fire smoke disorder and sinking in road tunnels, it is studied that the influence of water mist particle size on the thickness and temperature distribution and carbon monoxide concentration distribution of fire smoke in the absence of ventilation and longitudinal ventilation. The study is conducted on the road tunnel fire smoke migration characteristics research experiment system. And then preliminary analysis of coupling effect of water mist and ventilation is carried on. The result shows that the release of water mist can make the smoke layer thickening and sinking. The particle size has significant effect on thickness of smoke layer and distribution of temperature, but has less influence on the concentration of CO. [ABSTRACT FROM AUTHOR]