Article

A computational and experimental study of ultra fine water mist as a total flooding agent

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  • EmberTech,LLC
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Abstract

Computational fluid dynamics (CFD) calculations were carried out to design total flooding fire tests in a 28 m3 compartment for an ultra fine water mist (<10 μm). The exit momentum of the mist produced by a proprietary ultrasonic generator technology was extremely low with a mist discharge velocity below 1 m/s. The mist was discharged with multiple floor outlets equally spaced around the centrally located 120 kW pool-like gas fire. The transport of mist and its interaction with the fire was simulated by Fluent, a commercial CFD model. Lagrangian Discrete Phase Model (DPM) was used for droplets. Simulation predicted extinguishment within 10 s with a mist delivery rate of 1 l/min. However, in total flooding fire tests conducted, extinction times were more than 5 min. Additional computations approximating the ultra fine mist (UFM) as a dense gas agreed well with the observed transport timescales of minutes indicating that UFM behaves like a gas. Further, the mist–fire interaction needs a multi-phase Euler–Euler approach with a droplet vaporization model.

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... More than half a decade of work on ultra fine water mist has shown that, under some selected process conditions, the mist transport and extinction behaviors are comparable or superior to Halon agents. The ultra fine water mist with droplet diameter below 10micron closely resembles gaseous agents in transport behavior in cluttered spaces with a superior ability to diffuse around obstructions without significant loss of mist due to deposition [1][2][3][4][5][6][7]. A considerable amount of work has been reported on characterization, droplet behavior and mist fire suppression behavior under different laboratory conditions [8][9][10][11][12]. ...
... Compare this with the momentum of 100-micron droplet, typical of regular water mist droplet, with a velocity of 10 m/s of 5.23 x 10 -9 (a factor of 10 7 ). Thus, the low velocity combined with an extremely small droplet mass provides the desirable gas-like behavior for ultra fine mist, not contacting and impacting on surfaces causing significant mist loss as shown in prior work [1][2][3][4][5][6][7]. At this limiting flow condition, the convection becomes weak and is comparable to diffusion transport that helps mist droplets go around objects. ...
... This work addresses the requirement of using a convection-diffusion approach to predict the transport behavior of extremely fine mist rather than the generally used Lagrangian DPM approach. This issue was reported in our work published recently in Fire Safety Journal [1]. That work did not address the reasons why the DPM model predicted short time scale (~ 5 seconds) while the tests showed significantly slow mist transport (5-8 minutes). ...
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The last five years of research, development and testing of ultra fine water mist raised significant interest in its application for fire suppression and as an advanced inerting system. The objective of this work was to understand the transport behavior of ultra fine mist (UFM) under controlled discharge momentum which was intended to reduce the number of droplets coming into contact with surfaces and plating. This work was mainly focused on exploring the reasons for requiring dense gas model (DGM) approximation and solving convection-diffusion equations as opposed to the Lagrangian, Discrete Phase Model (DPM) generally applicable to a high momentum spray stream. The work showed that at high convective flow, DPM and DGM model predictions are close and transport time scales are not far off. However, at relatively weak flow conditions, the DPM model under-predicts the transport timescale and does not agree with experimental results. At this flow limit, diffusion transport contributes significantly and the DPM two-phase flow model cannot account for this. The lack of a strong convective field in the current ultra fine mist flow is mainly responsible for its ability to flow around objects without significant deposition. The understanding of the UFM transport behavior provides a robust tool for engineering and integrating the UFM technology into fire protection systems.
... Water mist was studied to suppress methane explosions, pool fires, poly fires, cooking oil fires, and so on [3][4][5][6][7][8]. Some comparisons may be found in the literature on experiments and computations in confined spaces or in pipelines [9][10][11]. The water mist with additives will inhibit the fire effect and will be different from the conventional water mist [12,13]. ...
... This system was composed of five parts: a combustion reaction chamber, fuel supply system, a water mist system, and a computer integrated display system, including test instruments, sensors and working parameters. The experimental system is shown in Figure 2. Experimental system for suppressing gas combustion using water mist: 1 data acquisition unit, 2 computer, 3 signal converter, 4 signal acquisition, 5 ignition device, 6 high speed camera, 7 nozzle, 8 pressure sensor, 9 gas release mouth, 10 temperature sensor, 11 The main body of the combustion reaction chamber is a rectangle, with dimensions of 2.0 m × 0.3 m × 0.3 m. The setup used toughened glass with a pressure-releasing device located at two ends. ...
... The quadratic law of single droplet evaporation for water mist is described in Equation (1) [11]: ...
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To safely mine coal, engineers must prevent gas combustion and explosions, as well as seek feasible and reasonable techniques to control for these types of incidents. This paper analyzes the causes and characteristics of methane combustion and explosions. Water mist is proposed to prevent and control methane combustion in an underground confined space. We constructed an experiment platform to investigate the suppression of methane combustion using water mist for different conditions. The experimental results showed that water mist is highly effective for methane flame inhibition. The flame was extinguished with water mist endothermic cooling. However, the annular regions of water vapor around the fire played a vital role in flame extinction. Water from the evaporating mist replaces the oxygen available to the fuel. Additionally, the time required for fuel ignition is prolonged. For these reasons, the water particle action to flame surface is reinforced and the fuel's reaction with air is delayed. As a result, flame stretching and disturbances occur, which serve to extinguish the flame. Engineering application tests were carried out in the goaf, drill hole and upper-corner to investigate the prevention and control of methane gas combustion, with the results showing a good application effect.
... For a trap boundary condition, nonvolatile material will be lost from the calculation at the point of impact with the boundary and volatile material present in the particle or droplet is released to the vapor phase at this point. Escape boundary condition means that the particle is lost from the calculation at the point where it impacts the boundary [7] . For an inert particle, escape boundary condition is the same with trap boundary condition. ...
... The molecular weight was calculated using ideal gas equation with the density of water, temperature, pressure and gas constant (1000 kg/m3, 293 K, 1 105 N/m2 and 8.314 J/(K mol), respectively). Such a treatment is reasonable for UFM (<10 m) [5,7].The species Dense Gas (DG) has the transport properties of water vapor except for the density. The density of DG is 1000 kg/m3. ...
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Ultra-fine water mist (UFM) is a clean agent with a gas like property. Fire suppression experiemt was conducted in a confined space. Numerical simulation using DPM model and dense gas model were carried out to compare with experiment. Simulaition discovered that dense gas model is more suitable for predicting UFM transportation and flow behavior compared with DPM model. Both experiment and simulation found that fire of a larger size is easier to extinguish in a compartment space, which is because fire sources can promote transportation of UFM in a compartment. Fire location also affects the fire suppression performance by promoting or suppressing the transportation of UFM.
... UFM droplets can follow the fluid flow streamlines and reach behind obstructions [14,15] due to very small inertia. They do not wet surfaces significantly and may cause only a minimal damage to electronics [16] due to significant evaporation in dry air even at ambient temperature. ...
... They measured that about 14.5 mass % water is needed to extinguish the flame. Adiga et al. [15] conducted computational and experimental studies of UFM extinction of a 120 KW heptane pool fire inside a 28 m 3 compartment. The experiments show about 9 mass% water is needed to extinguish the fire in 5 minutes. ...
Article
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Computations are performed to examine the effectiveness of mono-disperse water droplets in extinguishing a co-flow, propane diffusion flame by injecting the droplets into the air stream. The calculations show that the droplets entrained into the reaction kernel at the flame base are crucial for extinction. The reaction kernel detaches from the burner rim and blows-off when the droplet concentration is increased to a critical value (extinction concentration). At the critical value, the maximum chain-branching reaction (H2+O=OH+H) rate in the reaction kernel was found to be reduced by a factor of 5 in our computations. A large decrease in the reaction rate indicates that the maximum heat generations rate and Damkholer number are too low to sustain the flame, and cause the flame blow-off. Large drops are more effective than small drops, and the extinction concentration of water increases from 10.5% to 15% by mass as the size is reduced from 32 to 4 micro m. As the droplet size is increased further (>32 micro m), the trend will reverse as the evaporation rates get too small despite increased penetration of flame core by the drops.
... Relatively little is understood especially regarding the suppression and extinction of fires using UFM. UFM droplets can follow the fluid flow streamlines and reach behind obstructions (Adiga et al., 2006(Adiga et al., , 2007 due to very small inertia. They do not wet surfaces significantly and may cause only a minimal damage to the electronics (Adiga et al., 2005b) due to significant evaporation in dry air even at ambient temperature. ...
... They measured about 14.5 mass% water is needed to extinguish the flame. Adiga et al. (2007) conducted computational and experimental study of UFM extinction of a 120 KW heptane pool fire inside a 28 m 3 compartment. The experiments show that about 9 mass% water is needed to extinguish the fire in 5 minutes. ...
Article
Full-text available
Computations are performed to examine the effectiveness of mono-disperse water droplets in extinguishing a co-flow, propane diffusion flame by injecting the droplets into the air stream. The calculations show that the droplets entrained into the reaction kernel at the flame base are crucial for extinction. The reaction kernel detaches from the burner rim and blows-off when the droplet concentration is increased to a critical value (extinction concentration). At the critical value, the maximum chain-branching reaction (H2 + O = OH + H) rate in the reaction kernel was found to be reduced by a factor of 5 in our computations. A large decrease in the reaction rate indicates that the maximum heat generations rate and Damkholer number are too low to sustain the flame, and cause the flame blow-off. Large drops are more effective than small drops, and the extinction concentration of water increases from 10.5% to 15% by mass as the size is reduced from 32 to 4 μm. This is because of competition between the degree of penetration and the rate of evaporation of the water drops. The large drops penetrate the reaction kernel at the flame base better than the small drops, which evaporate completely before reaching the 600 K isotherm located well outside the reaction kernel as shown by our computations. As the droplet diameter is increased further (> 32 μm), the trend will reverse as the evaporation rates get too small, despite increased penetration of flame core by the drops.
... Due to the limitations of such experimental studies, several numerical investigations have been performed to simulate the water mist fire extinguishing mechanisms [7][8][9]. Some primary studies have been accomplished to predict the physical phenomena arising in fire suppression by water mist systems in real scale compartments [10][11][12]. Yang et al. [10] and Kim and Ryou [11] developed and validated numerical models to obtain the temperature, oxygen concentration, and extinguishing time of water mist systems in a room fire. Adiga et al. [12] designed a numerically total flooding fire test for an ultra-fine water mist in a 28 m 3 compartment. ...
... Yang et al. [10] and Kim and Ryou [11] developed and validated numerical models to obtain the temperature, oxygen concentration, and extinguishing time of water mist systems in a room fire. Adiga et al. [12] designed a numerically total flooding fire test for an ultra-fine water mist in a 28 m 3 compartment. Alongside these practical studies, some parametric investigations on fire suppression mechanisms have been done in small test scales [13,14]. ...
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In this paper, the effect of initial water temperature on the cooling performance of a water mist fire suppression system has been investigated. A zero-dimensional analytical model was first developed to study the thermal and dynamic behavior of a single water droplet. The developed model was validated against available experimental data in the literature. The developed model was further extended to simulate the transient heating, evaporation, break-up, and liquid penetration length of a hollow-cone water spray. Results indicated that increasing the initial temperature of the water spray before injection resulted in a decrease in the initial size distribution of the spray droplets. It was further found that the evaporation time of the injected droplets decreased by about 11% and the cooling power of the pre-heated water mist system enhanced by 12% in exchange for increasing the initial temperature of the water spray by 10˚C. It was concluded that pre-heating the sprayed water droplets would likely improve the cooling efficiency of the water mist system. It could be also inferred that at equal cooling power, less water was consumed by the pre-heated spray compared to conventional water mist systems.
... The mixture of air and O 3 mist was modeled as a mixture of ideal gases, considering that the generated mist behaves like a dense gas. This behavior is observed in mists with particles smaller than 10 µm, as ultra-fine water mists produced for fire suppression (Adiga, Hatcher, Sheinson, Williams, Ayers 2007;Liang et al. 2013). Similar behavior is seen in chemicals that are denser than air, such as chlorine gas (Siddiqui, Jayanti, Swaminathan 2012) and Freon-22 (Gilham, Deaves, Woodburn 2000). ...
... The mist fills up the environment around the impact areas of the plume (Figure 12). This behavior is similar to dense gases, previously described in the literature (Adiga, Hatcher, Sheinson, Williams, Ayers 2007;Liang et al. 2013). Over time, the mist also moves toward the frontal region of the room. ...
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The COVID-19 pandemic has demonstrated the demand for more effective procedures for sanitizing environments, especially high-risk ones, such as hospitals. Several products are used as disinfectants , with ozone being one of the strongest oxidants known. High relative humidity helps reduce the contact time required for viruses and bacteria inactivation with ozone. Thus, this work aimed to analyze the dispersion of an ozonized mist by CFD simulation to sanitize a hospital operating room. To our best knowledge, for the first time, the dispersion of an ozonized mist was investigated by CFD. The mathematical and numerical models were validated with results from the literature. The decay kinetics of the ozonized mist was obtained experimentally, resulting in a first order reaction with a kinetic constant of 2.66 × 10 −4 s −1. The numerical results of concentration on the surfaces were analyzed qualitatively and quantitatively, providing relevant information about the fluid dynamics of the sanitizing process. Ozone mist concentrations were higher on the walls close to the generator and lower on the furthest walls and the ceiling. The ozone mist concentration in the room reached an average of 11 mg/L. Five minutes of ozone mist generation and another five minutes of decay by air circulation were sufficient to provide an increase in ozone mist to concentrations above 4 mg/L, considered satisfactory for the sanitization of the operating room surfaces.
... For an enclosed space, ultrafine water mist (<10 μm) generated by ultrasonic atomizer was thought to be a total flooding agent for overcoming obstructions in extinguishing fire. [11][12][13][14] For the gas-like agent, the accurate minimum extinguishing concentration (MEC) is an important parameter for firefighting system design. Fisher et al 13 Their study showed that a fire will be quenched when the adiabatic flame temperature was decreased to the combustion limit temperature (CLT), the oxygen concentration was reduced to the limiting oxygen concentration (LOC), or the fuel vapor concentration was dropped to the lower flammability limit (LFL). ...
... Although water can absorb a significant quantity of heat from flame, it takes more time than 300 seconds to extinguish a fire in an 28-m 3 enclosed space for UFWM. 12 To improve the fire extinguishing performance of UFWM, many chemical additives were examined through experimental researches. [21][22][23][24] Most of these additives are metallic salts, which are not as clean as pure water. ...
Article
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.
... As the major cause of this problem is the size of mist particles, the use of ultra-fine water mist particles called nano-mist humidification is expected to be an effective technique to minimize the problem (Nickolas-Richardson, 2007). Nano-mist is defined as a very low momentum gas-like ultrafine mist (<10 m) (Adiga et al., 2007). Because of being ultrafine particles, it is assumed that the introduced mist particles become vapor before settling on the produce surface. ...
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Anaerobic respiration is a major problem that causes the deterioration of fresh produce packaged under low O2 atmospheres. The problem becomes more severe and causes high losses in the packages handling at ambient conditions, especially in developing countries. In designing modified atmosphere packaging, the risk of anaerobic development greatly depends upon the accuracy of respiration rate prediction; therefore, the respiration rate model for a particular produce has to be identified. In this study, different atmospheric storage conditions in a closed system were realized to examine the adaptability of respiration rate models for spinach storage under low O2 at an expected ambient temperature of 25 °C. Six models were applied and it was found that, for aerobic conditions, the respiration rate could be described with a constant respiratory quotient by three models, viz., (a) Michaelis–Menten model without inhibition, (b) Michaelis–Menten model with uncompetitive inhibition, and (c) Langmuir adsorption model, whereas three other models, viz. (d) Michaelis–Menten model with competitive inhibition, (e) Michaelis–Menten model with noncompetitive inhibition, and (f) Michaelis–Menten with mixed inhibition could not be fitted. Among the three successful models, the Michaelis–Menten with uncompetitive inhibition was found to be the most suitable model for practical applications in developing countries where cold-chain systems are lacking. This model can be applied for the prediction of gas composition and optimize the packages, particularly to ensure the aerobic respiration.
... Most of the available literature is focused on fire suppression and flow-flame interaction: the early works by Rasbash and co-workers on liquid-fire extinction [1,2] serve as major foundations, together with recent studies by Liao et al. [3]. Among the works on more applied subjects, it is worthwhile to mention the long-term research conducted by the US Navy [4] through experimental and computational approaches to evaluate performance in shipboard applications. It is also worthwhile to mention theoretical approaches to extinction [5] and some experimental studies on the innovative challenges of additive-endowed flows [6][7][8]. ...
Article
Pressure-swirl atomizers are often employed to generate a water-mist spray, typically employed in fire suppression. In the present study, an experimental characterization of dispersion (velocity and cone angle) and atomization (drop-size axial evolution) was carried out following a previously developed methodology, with specific reference to the initial region of the spray. Laser-based techniques were used to quantitatively evaluate the considered phenomena: velocity field was reconstructed through a Particle Image Velocimetry analysis; drop-size distribution was measured by a Malvern Spraytec device, highlighting secondary atomization and subsequent coalescence along the spray axis. Moreover, a comprehensive set of relations was validated as predictive of the involved parameters, following an inviscid-fluid approach. The proposed model pertains to early studies on pressure-swirl atomizers and primarily yields to determine both initial velocity and cone angle. The spray thickness is also predicted and a classic correlation for Sauter Mean Diameter is shown to provide good agreement with experimental results. The analysis was carried out at the operative pressure of 80 bar; two injectors were employed featuring different orifice diameters and flow numbers, as a sort of parametric approach to this spray typology.
... Fire suppression performance of water mist, a Halon alternative, has been being studied for decades [1][2][3][4][5][6][7]. Recent researches also demonstrated that gas-like ultrafine water mist (<10 m) has great potential in fire suppression application [8][9][10][11][12][13][14]. Previous work [10] also showed that ultrafine water mist (UFM), a total flooding agent, has the ability to overcome obstructions in fire extinguishing. ...
Article
Two simplified models for predicting minimum extinguishing concentration (MEC) of ultrafine water mist (UFM) (<10 μm) were developed based on limiting oxygen concentration (LOC) and combustion limit temperature (CLT), respectively. Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM. Two typical liquid fuels, n-heptane and ethanol, were used in the experiment. Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time. The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM. Experimental results agree well with the model based on LOC, and disagree with the model based on CLT. The disagreements were explained by analyzing flow behavior of UFM. It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.
... The phenomenon of water mist fire suppression is quite complex [1]. Although numerical simulations of water mist fire suppression [2][3][4] are valuable in providing engineering guidance, these models have not been sufficiently validated, especially for condensed fuels. Thus, the fire protection industry still heavily relies on the expensive large-scale testing approach to develop water mist fire protection systems. ...
Article
A series of fire suppression experiments was conducted in two geometrically similar enclosures of 1:3 ratio to evaluate whether the Froude-modeling-based scaling methodology could reasonably reproduce the pool fire development under water mist application in different scales. The parameters considered in the evaluation were: enclosure size, door opening size, water mist spray condition, fire size, fire location and fire-shielding condition. The two enclosures measured 1.22 × 1.22 × 1.22 m and 3.66 × 3.66 × 3.66 m. Two door opening sizes were tested for each enclosure: 0.30 × 0.61 m high and 0.61 × 0.61 m for the Scale-1 enclosure, and 0.91 × 1.83 m high and 1.83 × 1.83 m for the Scale-3 enclosure. Two heptane fire sizes were selected for each enclosure. The quasi-steady heat release rates of the two pool fires for the Scale-1 enclosure were 25 and 57 kW, and the corresponding heat release rates were 380 and 860 kW for the two pool fires used in the Scale-3 experiments. Besides matching the quasi-steady heat release rates according to the scaling requirement, the fire developments under free-burn were also carefully scaled. Two water mist nozzles were used to produce the water mist sprays in the Scale-1 and Scale-3 enclosures; these two nozzles were operated at the designated pressures of 13.8 bar and 41.4 bar, respectively. In each enclosure, nine ceiling-mounted nozzles were arranged in a 3 × 3 pattern with equal nozzle-to-nozzle and nozzle-to-wall spacing. The experiments showed that the fire development in terms of heat release rate could be reasonably reproduced during free-burn and water mist application in the Scale-1 and Scale-3 enclosures, as well as the oxygen concentration inside the enclosure.
... Nano-mist is defined as a very low momentum gas-like ultrafine mist (<10 m) (Adiga et al., 2007). Because of being ultrafine particles, it is assumed that the introduced mist particles become vapor before settling on the produce surface. ...
... In order to determine the optimum water mist droplet size, experiments have been carried out by different researchers. Ultrafine water mists (<10 mm) discharged with multiple floor outlets around a 120 kW gas fire in a 28 m 3 compartment have been studied (Adiga et al., 2007). The work indicated that the ultra-fine water mist behaved like a dense gas which could be used in the case of total flooding situation. ...
Article
With recent developments in sprinkler technology, water mist system is becoming more and more useful in fire suppressions. However, regulations on water mist system are inadequate, because most of them are based on experimental results. The computational method is an efficient way to make validations and optimize droplet size distribution of water mists. In this work, a computational fluid dynamics (CFD) model and a fire dynamics simulator (FDS) code were used to analyze effects of fire suppression using water mists with different droplet sizes. By using numerical methods, the interaction between water mist and fire could be better understood. The range of droplet size was determined based on the NFPA 750 standard. The fire extinguishing times of different droplet sizes were calculated by running the FDS code. After running the FDS code for different droplet size ranges, the optimal droplet size range was obtained. With the increase of droplet sizes, the fire extinguishing time first fluctuated and then increased. An optimal droplet size range was determined to have the best suppression effectiveness with the shortest fire extinguishing time and less water consumption. It should be noted that there are limitations for the CFD study since the real circumstance of fire is more complicated.
... They can easily diffuse around obstructions without significant loss of mist due to plating and deposition. However, they take longer time to suppress the fire [9]. ...
Article
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This paper reports the results of an experimental study of suppression of pool fires in enclosed spaces using water mist. The main objective of the present study is to understand the mechanisms responsible for the suppression of pool fires using water mists. Experiments were conducted in a large compartment with n-heptane pool fires of different heat release rates. The temperature variations in the compartment were measured using K-type thermocouples fixed at two locations. A multi gas analyzer was used to measure gas concentrations. The test results indicate that the water mist suppresses the diffusion flame in an enclosed space mainly through evaporating cooling and oxygen displacement by water vapors, resulting in inefficient combustion. The fire suppression time decreases with a decrease in droplet diameter. It is much easier to suppress a larger fire due to faster rates of evaporation of water droplets and therefore, the total mist requirement decreases with an increase in the fire size. The results of this study can find application in the design of water mist based fire fighting systems for indoor fires.
... Recently, ultrasonic technology is also used to generate ultrafine water mist in the mitigation of fire or explosion. Adiga et al. studied the effects of ultrafine water mist as a total flooding agent in a 28 m 3 compartment experimentally and numerically (Adiga et al., 2007) and the ultrafine water mist was found to be able to successfully extinguish all pool fires with ultrasonic technology. Even the findings was based on the fires, it was very instructive on the application of ultrafine water mist for the explosion mitigation. ...
Article
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The mitigation effect of ultrafine water fog on the methane/air explosions with methane concentrations of 6%, 9%, 11% and 13% were experimentally studied in an entire closed visual vessel. The ultrafine water fog was generated in the vessel directly by ultrasonic atomization method. A high speed camera was used to record the flame propagation processes. The explosion flame evolution processes were discussed. The experimental results indicate that the maximum explosion overpressure (ΔPmax), the pressure rising rate ((dP/dt)max) and the flame propagation velocity decreased after adding water fog. The presentation of flame cellular structures after adding water fog and the stifling effect of water vapor caused the extinguishing of the flame in the burned zone and slowed down the flame propagation. The water fog could mitigate the methane explosion of low concentration (6%) absolutely. When applied at the high concentration conditions (9%, 11% and 13%), the water fog still presented a significant suppression effect. The maximum decreasements of ΔPmax under the three high concentration conditions with water fog were 21.1%, 26.7% and 22.9%, respectively, while the maximum decreasements of (dP/dt)max were 71.7%, 77.1% and 52.0%, respectively.
... Williams [11] conducted experimental and numerical studies with nano-mist technology on the effects of ultrafine water mist as a flooding agent in a 28 m 3 detonation compartment. The ultrafine water mist was found to be able to successfully extinguish all pool fires. ...
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The effects of a fine water mist environment in a semi-confined blast chamber on the chemical and thermodynamic processes following detonation of a 20 g PE4 explosive charge have been investigated. The effects were quantified by the analysis of pressure profiles recorded where several parameters including arrival time of the shock at the sensors, peak overpressures, specific impulse of the positive phase, period of the negative phase and the specific impulse of the multiple reflections were quantified. The effect of the fine water mist on the arrival time, peak pressures and the specific impulse of the positive phase agrees with previous findings in literature. In this paper, the focus is on the implications of the fine water mist on the negative phase and the impulse of multiple pressure reflections. The period of the negative phase was found to have increased by 40% and with higher negative peak pressure in the mist condition compared to the atmospheric condition. The activities of the multiple pressure reflections were found to have decreased considerably, both in number and in amplitude leading to lower impulses (by about 60%) for the water mist conditions.
... Some experiments that have been carried in the past shows the use water mist consisting droplets of diameter ranging from 5μm [9] to few hundreds of microns. The parameters that were studied in large extent were loading fraction, temperature and species. ...
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Interaction of fires with water have been a focus of study for human kind from the times immemorial. With the recent advances in water-based suppression, and restrictions put on halon usage, sprinklers and water-mist based fire suppression systems have become popular for industrial usage. Of this water mist is an interesting candidate, for it has advantages and to name a few would be less water requirement, non-wetting nature, gas phase action on fire. Water mist, as an effective fire suppressant, works on the principle of oxygen dilution and flame cooling. In this work, we are studying the action of water mist on a diffusion flame. The water mist was generated from a Delavan nozzle, fed with high pressure water, which is then directed downward into the raising flame. A circular burner fed with Methane in a controlled manner generated the diffusion flame. The reason to prefer a gas burner is to have a control over heat release rate which will help in simulating various fuel sources of different burning rate. A glass cubicle was used to isolate the experiments from ambient disturbances. A Digital SLR camera was used to record the flame and subsequently the images were processed to obtain flame height. Particle Image Velocimetry was used to study the effect of the flame on the water mist., by imaging the Mie scattered laser light from the droplets. Parameters that were varied were the injection pressure and flow rate of the Methane into the burner. Visual imaging from the camera indicated that there were occasional flame tip flattening during the suppression mechanism. The flame luminosity is diminished and the diffusion flame height is reduced due to the action of the water mist. Moreover, this effect is more pronounced for smaller flame than larger flame, indicating the role of the buoyancy in fire suppression effectiveness. The PIV results show that the droplets are slowed down very close to the nozzle due to the flame. Also, a recirculation zone is observed at the periphery of the spray cone, very close to the nozzle. It is a toroidal vortex that is generated due to the interaction, and the droplets thrown away from the spray cone gets trapped into this flow. The flow structure is present in a highly turbulent region and is identified in the mean field. Another finding is that close to the burner, fine droplets that could make it to the base, gets entrained into the flame. It is expected that the droplets tend to be entrained into the larger flame, as the entrainment is stronger for large flame, compared to the smaller flame. But the PIV results indicate otherwise, which is attributed to the larger size of droplets making its way close to the burner. We believe that these results will enlarge our understanding of the suppression mechanism of water mist and could form a basis for validating various simulation models.
... They employed Eulerian-Lagrangian method to predict the water droplets distribution and the movement trajectories and validated the results against the experimental data. In order to design flooding fire tests in an ultra-fine water mist, Adiga et al. (2007) made numerical simulations using Lagrangian model for liquid droplets. Dhanasekaran and Wang (2012) used computational fluid dynamics (CFD) method to study the influence of various parameters in mist film cooling scheme to the rotating turbine blade. ...
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The influence of water spray from wheels on the ice accumulation in the bogie regions of high-speed train has been studied using the coupling numerical methods of improved delayed detached eddy simulation (IDDES) and Lagrangian Model. The rotation of the wheels was simulated using the moving overset grid technique. The flow field, spatial distribution and surface distribution of droplets on the bogies have been analysed to identify the effect of various speed on the movement of droplets. The results show that the inlet speed between 160 km/h and 250 km/h will lead to the most severe influence on water spray from wheel in the whole bogie regions. A large amount of water droplets gathering on the surface of the bogies and bogie cavities is likely to cause severe ice accretion. The influence of water spray for high-speed train decreases rapidly at the speed of 300 km/h and changes a little as the speed continues to increase. Among all the components of the bogie, the brake clamp is most affected by droplets. Furthermore, the droplets were found to have a severe effect on the draft sill and air spring.
... Andersson and Holmstedt showed that water mist droplets larger than 20 µm would not be able to follow an air stream of 5 m/s and would, due to inertia, hit the obstacle instead [19]. Recent experiments with ultra fine water mist with an uniform droplet size of 10µm have shown promising results, though it is difficult to get the mist distributed and therefore there was only a spacing of 1 m between mist inlets [20]. ...
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The use of water mist for fire extinguishment has increased rapidly in recent years. The main reason is the abandonment of halon-based extinguishing systems in favour of environmentally friendlier systems. Furthermore the use of water mist systems has spread from mainly marine applications to also include the protection of buildings. The main problem in this regard is to verify the effectiveness of the system. At present time this can only by done by full-scale tests. This is however expensive and in some cases also unrealistic and expensive when it comes to water mist systems for buildings. The aim of this thesis is to provide experimental data that can serve as a basis for simulations of the interaction of water mist and a fire and to demonstrate that CFD can predict the performance of a water mist system. The physics of water mist systems has been studied by theoretical considerations as well as experimental work. Measurements of droplet velocities, diameters and volumetric water distribution were carried out on the spray from a high-pressure system of 100 bars. Experiments have been conducted on a hollow cone nozzle without fire and with fire, as well as a full cone nozzle without fire. Relevant measurement results were obtained with Phase Doppler Anemometry and Particle Image velocimetry as well as Laser Tomography and High Speed camera. Suggestions were made for improvement of the water density apparatus. The measurements have been the basis for simulations of water mist with CFD. Initial simulations involving the complex zone around the nozzle resulted in droplets with radial velocities and insufficient transfer of momentum to the air.
... Fire suppression based on the use of water has proved to be effective: they can effectively extract thermal energy through phase change from liquid water to water-vapor, and the latter can reduce the oxygen concentration of a closed environment among other effects [7]. Studies on fire suppression by water mist have been carried out for modeling real-scale fires [8,9] or to characterize the ignition [10] or extinguishment [11] of fires. Richard et al. [12] analyzed the effects of water-vapor addition into small-scale heptane fires, finding that in addition to the important physical influences, there is also a substantial chemical effect that impacts the flames. ...
Article
The effect of water-vapor addition to oxidizer on flame radiation is assessed experimentally and numerically through the study of laminar coflow ethylene-fueled non-premixed flames. Oxygen-deficient conditions were studied to closely represent real confined fire situations. Experimental soot volume fraction distributions, presented in a previous study, are complemented with temperature and radiation measurements. Experimental data are compared and complemented with numerical simulations. The relative importance of the thermal, chemical and dilution effects of water-vapor is also investigated through numerical modeling. Addition of water-vapor to oxidizer leads to a decrease in soot concentration, flame temperature, emitted radiation and radiant fraction, regardless of the Oxygen Index (OI). The measured temperatures in the sooting region by two-color pyrometry are in reasonably good overall agreement with the numerical predictions. Soot is the main radiation emitter in the ethylene flame under all the conditions studied, but its relative importance decreases with the water-vapor addition. CO2 is the second most important contributor. Depending on the OI, the relative importance of the water-vapor addition to flame radiation varies. At lower OI the dominant effect is thermal, while at higher OI (normal air condition) the effect of the water-vapor is shared by the three effects: dilution, chemical, and thermal.
... The high surface-to-volume ratio allows ultrafine water mist to extinguish fires after droplets bypass obstacles. In a 28 m 3 compartment, a total flooding system of ultrafine water mist can extinguish a 120 kW pool-like gas fire in 5 min with a mist delivery rate of 0.64 L/min (Adiga et al., 2007). ...
Article
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Due to its high efficiency and non-pollution, water mist fire extinguishing technology has attracted increasing interest and attention from various fire protection fields, including library fire safety, traffic hub station fire safety, ship fire safety and spacecraft fire safety. To support research and development of water mist fire extinguishing technology and its application in the field of battery fires, this paper begins by detailing the mechanisms by which water mist extinguish fires. The influence of internal and external factors on the fire suppression effectiveness of water mist is then discussed, such as water mist characteristics, additives, obstacles, ventilation conditions, fuel types, flame scales, followed by a review of researches of water mist technology in battery fires. In the final part, based on current research tendency, the paper provides future development direction and research ideas of water mist fire extinguishing technology and foresees the development prospects of its application in the battery fire field.
... Halogen-based compounds are effective fire suppressing agents, however, due to the harmful effects on the ozone layer they have been banned from further production since the last century [1]. In order to find suitable replacement, there has been a notable increasing interest in the use of CO2, inert gas and water sprinkler as substitutes [2]. ...
Preprint
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Water mist fire suppression technology has attracted an increasing interest from the field of fire protection services such as fire safety for buildings, ships, spacecraft, libraries and museums due to its non-toxic and high efficiency in the suppression of a wide variety of fires. To support the technological development of water mist fire suppression system and its application areas, this review introduces the concept of water mist system and discusses its suppression mechanisms in comparison with other fire protection systems. The recent application areas of water mist system are surveyed for class A fires involving combustible solid materials such as wood, paper and textiles; class B fires involving flammable liquids such as petrol, oils, lubricants, paints and waxes; class C fires involving flammable gasses such as natural gas and liquefied petroleum gas; fires involving electrical (class E) equipment such as computers and information technology facilities; and the class F fires involving flammable cooking oils and fats. Finally, the paper concludes the review by identifying the current research trends, and providing the future direction for water mist technology and applications.
Article
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The paper introduced the progress in research and application of electronic ultrasonic water mist fire suppression technology. Several researches showed that the electronic ultrasonic water mist can be as effective as the now-banned gaseous fire suppressant halon 1301. With the further research about electronic ultrasonic water mist technology, there must be more and more electronic ultrasonic water mist extinguishment tools applied in the fire suppression.
Article
Water mist fire suppression systems which use relatively small droplets of water with high injection pressure are increasingly being used in wider applications because of its greater efficiency, low flooding damage and low toxicity. However, the performance of the system significantly relies on the water mist characteristics and fire environment and it requires better understanding of fire suppression mechanism of water mist. In the present study, computational fluid dynamics simulations were carried out to investigate the interactions between water mists and fire fields. The gas phase was prepared with natural convection heat transfer model for incompressible ideal case and then the effects of water mist characteristics on cooling capabilities were numerically investigated upon the basis of the predetermined temperature field. For the simulation of water mist behavior, Lagrangian discrete phase model was employed by using a commercial code, FLUENT. Fire suppression efficiency based on different water mist characteristics such as droplet sizes, injection angles, water flow rates and fire types was investigated.
Article
This article presents a series of experiments on benchmark fire suppression. The experiments were performed in a controlled environment, utilizing a cylindrical object or calorimeter centered above a 2 m diameter pan filled with kerosene-based hydrocarbon fuel, JP8. The experimental setup and procedure for gathering data on water suppression performance are presented. The characteristics of the nozzles used in the experiments are presented as well. The experimental results provide the boundary condition and temporal data necessary for validation of the fire suppression models used. The article also includes simulation results on the fire suppression experimental tests. The suppression simulations were carried out using a numerical model based on a Temporally Filtered Navier-Stokes (TFNS) formulation coupled with a Lagrangian model for droplets, which includes detailed descriptions of the interaction between the water droplets and the fire plume. The results from both experiments and simulations suggest that the criterion for complete suppression depends on a combination of factors including the mass flow rate (or nozzle diameter), nozzle operating pressure, and calorimeter presence. A critical regime which distinguished the regions of suppression and no-suppression in the domain of the mass flow rate versus operating pressure is found.
Article
This paper reports the results of a comparative study of the effects of various salt additives on the flame extinguishing efficiency of fine water sprays. The relative suppression efficiencies are gauged by comparing the extinguishment time of a heptane flame. Preliminary tests are performed in a reduced scale cup-burner; major results are obtained using the closed reduced compartment set-up.The addition of NaCl, KCl or KHCO3 resulted in large improvements of the suppression efficiency of the water mist. Potassium compounds show the greatest effect as 10% solution of KHCO3 reduces the average extinction time by up to 96% compared to pure water. The other additives tested have a less noticeable effects, with aqueous solutions of MnCl2, ZnCl2 and CuCl2 showing minimal improvement over water, whereas (NH4)2HPO4, (NH2)2CO and FeSO4·7H2O actually increasing the time taken to extinguish the flame.
Article
Water-mist systems have become quite popular over the last two decades as an innovative technology in fire protection. Moreover, insertion of additives to the flow may be applied to provide additional improvements in terms of suppression effectiveness and temperature control. The present work consists of an experimental approach within a real-scale facility, which has been aimed at challenging water mist against severe fire scenarios. Among them, a high-rise storage has been here explored, being it commonly recognized as strongly hazardous even by technical standards in terms of both nominal fire load and designed physical domain. The system configuration presents high-pressure nozzles at the ceiling; the sole-water flow is compared to water endowed with a commercial additive.The thermal transient within the test chamber has been evaluated during the fire development as the main quantitative parameter; moreover, the fire evolution has been visualized through a post-fire estimation of the damages. Despite the large amount of released smoke and smoldering materials, water mist is shown to be efficient in fire control, if endowed with the chosen additive. On the other hand, the sole-water flow does not appear suitable for such hazardous conditions under the designed nozzle arrangement.
Article
Water mist fire suppression systems are starting to be used popularly in large cities in Asia. If designed properly, effective fire extinguishment can be achieved by applying much smaller amounts of water. However, there are still concerns regarding the system performance, particularly when the water mist is not acting at the source of the burning combustibles. The action of water mist in a thermal environment induced by a gasoline pool fire in a room was studied. Experiments on smoke temperatures in the room and heat release rates of the pool fire with and without discharging water mist were performed. Fire suppression and reduction in temperature were discussed. Effect of water mist on the fire environment induced by a gasoline fire was also simulated numerically by a fire field model and a zone model. Discharging water mist at positions away from the pool fire avoided simulating the complicated combustion phenomena. Functional analysis was used to compare predicted results with experimental values. It is observed that the field model predicted results agreed better with experiments than zone model.
Article
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The paper introduced a kind of new ultra-fine water mist extinguisher, and conducted serials total flooding extinguishing test on ultra-fine water mist extinguishing heptane cup fire in 1200mm×1200mm×1200 mm confined space. Test results showed that the ultra-fine water mist extinguisher was effectively in extinguishing 50 ml heptane cup fire when it's theoretically mist flux was 100 ml/min or more.
Article
In order to improve the explosion suppression efficiency, experiments were conducted on a self-built visual half-open explosion pipe to study the synergistic explosion inhibition effect of CO2 twin-fluid water mist containing potassium salt additives. Results showed that: the inhibition effect of CO2 twin-fluid water mist with potassium salt additive increased with the spraying time, the peak overpressure and flame speed declined obviously, and the brightness of the flame was lower or even disappeared, indicating the flame propagation was better blocked. Comparing to 5s CO2 twin-fluid water mist, after the addition of 6% K2CO3, the maximum overpressure and flame speed reduced by 28.87% and 15.07% respectively, and the arrival time of the flame to the end of the pipe prolonged by 21.57%. The inhibition order of CO2 twin-fluid water mist containing four potassium salt additives from high to low is K2CO3> K2C2O4> KCl > KH2PO4. The number of flame free radicals O, H, OH in the whole explosion system decreased significantly under the inhibition of CO2 twin-fluid water mist containing potassium salt additive, indicating potassium salt additive and CO2 twin-fluid water mist have a synergistic effect on inhibiting gas explosion, which can enhance the physical and chemical inhibition effect on flame propagation.
Article
Water-mist systems have gained wide popularity over the last twenty years as an innovative technology in fire protection. Moreover, insertion of additives in the flow is typically applied to provide additional improvements in terms of suppression effectiveness and temperature control. The present work consists of an experimental approach in a real-scale facility, which has been aimed at challenging water mist against severe fire scenarios. The sole water flow is compared to water endowed with a commercial additive, the F-500 by Hazard Control Technologies Inc. As the fire setting, a high-rise storage has been explored: this real scenario is commonly recognized as severely hazardous even by technical standards, because of both its nominal fire load and the designed physical domain. The thermal transient within the test chamber during the fire development has been measured as the main quantitative parameter: K-type thermocouples have been employed to the purpose over a set of remarkable locations. Moreover, the fire evolution has been evaluated through a post-fire estimation of the damages. Despite the large amount of released smoke and smoldering materials, water mist is shown to be efficient in fire control, if endowed with the chosen additive, while the sole water flow does not appear suitable for such hazardous conditions.
Article
Water mist fire suppression systems which use relatively small droplets of water with high injection pressure are increasingly being used in wider applications because of its greater efficiency, low flooding damage and low toxicity. However, the performance of the system significantly relies on the water mist characteristics and it requires better understanding of fire suppression mechanism of water mist. In the present study, computational fluid dynamics simulations were carried out to investigate cooling performance of water mist in heated chamber. The gas phase was prepared with natural convection heat transfer model for incompressible ideal case and then the effects of water mist injection characteristics on cooling capabilities were investigated upon the basis of the pre-determined temperature field. For the simulation of water mist behavior, Lagrangian discrete phase model was employed by using a commercial code, FLUENT. Smaller droplet sizes, greater injection angles and higher flow rates provided relatively higher cooling performance.
Article
The explosion of combustible gas is an urgent problem to be solved in production safety accidents. In this paper, the experiment of methanotroph degradation of CH4 and the experiment of the water mist containing methanotroph-inorganic salt inhibiting the methane explosion were carried out respectively based on a self-designed and built semi-closed small-scale experimental platform. We studied different volumes of the water mist containing methanotroph-inorganic salt to inhibit 5%, 8%, 9.5%, 12%, 15% methane explosion, and analyzed the relationship between time and relevant experimental parameters such as flame structure, flame average propagation velocity, maximum explosion overpressure, and average pressure rise rate, etc. The result showed that the water mist containing methanotroph-inorganic salt had a quite restrain effect on the methane explosion. At the same time, for first spray, when the degradation time is constant, with the increase of spraying volume, the explosion suppression effect is better. And when the spraying volume remains the same, the longer the degradation time is, the better the explosion suppression effect. As for the secondary spray, when spraying volume remains the same, the explosion suppression effect under the condition of Degradation with spray + explosion suppression with spray is superior to that of direct explosion suppression, whose reason is that the first spray mainly plays the biodegradation role of methanotroph, while the secondary spray mainly plays the physicochemical synergistic explosion inhibition role of the water mist containing methanotroph-inorganic salt.
Article
As an effective depressant, ultra-fine water mist has broad application prospects in reducing the loss caused by a gas detonation. Ultra-fine water mist can be sprayed into coal mine roadways or natural gas pipelines when detecting the radiation spectrum signal of the explosion, to prevent further expansion of the explosion. A two-dimensional pipeline model was designed to study the effect and mechanism of methane detonation suppression by monodisperse ultra-fine water mist with a diameter of 10 μm. The methane detonation at the stoichiometric concentration (9.5 %) will decay to a deflagration under the suppression of fine water mist of 160 g/m³. When the concentration of fine water mist is less than 160 g/m³, the detonation wave has a slight attenuation in the water mist area, while it returns to a stable detonation state after passing through the mist area. The results also indicate that a water mist above 800 g/m³ can effectively suppress detonation and eventually lead to flame extinguishment. The critical transition concentration of ultra-fine water mist that can decay a methane detonation to a deflagration and the critical extinction concentration of ultra-fine water mist that completely suppresses a detonation within the explosion limit were obtained, providing a visual reference for the suppression of methane explosion accidents in coal mine tunnels or pipelines.
Article
In order to deeply understand the inhibitory effect of ultrafine water mist containing methane-oxidizing bacteria on methane explosion, a small-sized semi-closed visual experimental platform was built. Five different application mist amounts (0.7 mL, 2.1 mL, 3.5 mL, 4.9 mL, 6.3 mL) of ultrafine water mist containing methane-oxidizing bacteria on 9.5% methane explosion were studied experimentally. Ultrafine water mist was generated by the ultrasonic atomization generator, and mist size was measured by a winner319 laser particle size analyzer. During the methane explosion, a high-frequency pressure sensor collected pressure change data, and a high-speed camera recorded the flame development process. The results indicated that the maximum explosion overpressure (ΔPmax) decreased with time, and the arrival time of the maximum explosion overpressure (ΔPmax) delayed. The appearance time of the “tulip” shaped flame delayed, and the flame propagation speed decreased. The ultrafine water mist and deposition can effectively inhibit the methane explosion. The explosion suppression effect of the second step spraying water mist was better. The improvement of the explosion suppression effect of the ultrafine water mist containing methane-oxidizing bacteria was attributed to the degradation effect of the methane-oxidizing bacteria. Under long-term degradation, methane-oxidizing bacteria in water mist play a role in inhibiting methane explosion.
Article
Fire suppression tests using low pressure twin‐fluid water mist under low pressure environments were carried out to exam the performance of water mist systems at low pressure environments. The experiment results show that the suppression time gets shorter for lower chamber pressure, and relevant total weight of water and nitrogen used decreases as the chamber pressure gets lower. For the case of 30‐cm diameter pool fire, the suppression times are 20.19, 7.5, and 2.24 under the chamber pressure of 60, 38, and 24 kPa, respectively. In case of a cargo compartments fire, it is suggested to open the ventilation valve of the cargo compartment at a high cruising altitude to relieve pressure, so as to achieve rapid fire suppression. When a fire happens at the position off the center below the water mist nozzle, the water mist suppression effects will be weakened. The fire size has little effects on the fire extinguishing process under pressure of 24 kPa. Under the critical atomization condition with the pressure differential between the inlet and outlet of the nozzle for water as 0.05 MPa (5.04 L/min), and the pressure differential for nitrogen as 0.10 MPa (10.97 L/min), the suppression time is the shortest as 18.66 seconds.
Article
This paper investigates the fire-suppression ability of water mists containing various organic solvents—ethanol, 1-propanol, tetrahydrofuran, methyl acetate, and 1,2-dimethyoxyethane—which form minimum-boiling azeotropic mixtures with water. The key factors influencing the suppression efficiencies of the solvent-containing water mists were elucidated by measuring the evaporation rates, flash points, extinguishing times, and spray properties (droplet-size distribution, spray mass-flux density, and droplet velocity) of the mists. Suppression trials indicated that (i) heptane pool fires can be extinguished by aqueous solutions of ethanol and 1-propanol at solvent concentrations of 1.0–20.0 vol%, but are not consistently extinguished by the other three solvents, and (ii) the extinguishing times of aqueous ethanol and 1-propanol (despite their high flammability) are significantly shorter than those of a wet chemical (i.e., conventional fire-extinguishing agent). In a stepwise regression analysis, the fire-suppression abilities of water mists containing ethanol and 1-propanol were positively related to the spray flux density, spray velocity, and flash point, enabling an estimation of the extinguishing times. A correlation analysis demonstrated that a faster evaporation rate improves the fire-suppression ability. The results confirmed that ethanol and 1-propanol are effective additives to fire-extinguishing water mists. The study findings provide useful insights into the development of new water-mist fire suppressants, potentially making a large contribution to the reduction of fire-related fatalities and economic losses in industries.
Article
The present study seeks to measure suppression effects in a canonical experimental configuration, featuring the exposure of a buoyant, turbulent, methane-fueled diffusion flame to a co-flowing oxidizer laden with a fine water mist (Sauter mean diameter of 6.6 µm). The carefully designed facility features well-characterized inlet and boundary conditions suitable for accurate representation in numerical simulations. Suppression performance is monitored via combustion efficiency (ηcomb), measured using species-based calorimetry techniques. As the mass fraction of water mist in the oxidizer is increased, visible flame emissions are reduced due to diminishing soot incandescence coupled with a reduction in visibility due to Mie scattering effects in the mist. Global flame extinction is observed at , a condition corresponding to 44% less water mass in the oxidizer than required for extinction due to dilution effects alone, suggesting that significant latent cooling effects contribute to the observed extinction limit. Despite visually observed suppression effects, across all tested , decreasing abruptly only at the extinction limit. Numerical simulations of the experiments are conducted using FireFOAM, an open source large eddy simulation solver incorporating a flame extinction model based on a critical Damköhler number and a flame reignition treatment based on a critical flame temperature. Though numerical results show qualitative agreement with the observed extinction behavior, the simulated extinction limit of significantly exceeds that measured in the experiment, but is itself consistent with an extinction limit due only to dilution effects.
Article
This study focuses on the fire-suppression capabilities and corrosive properties of ferrocene dispersions. The motivation behind the present study was to develop a high-performance, phosphorus-free fire suppressant. Aqueous dispersions containing micron-sized ferrocene particles and surfactants were prepared using sonication techniques. In this study, Triton X-100 (TX), Noigen TDS-80 (NT), Tween 60 (T60), and Tween 80 (T80) were used as surfactants. Suppression experiments involving pool fires clearly indicated that aqueous ferrocene dispersions containing TX and micron-sized ferrocene with a d50=16.9 μm exhibit shorter extinguishing times than a conventional wet chemical. Corrosion trials using steel plates immersed in ferrocene dispersions containing TX confirmed that there was no pitting corrosion, implying that ferrocene dispersions containing TX do not present a corrosion risk.
Article
Phase distribution and velocity field sketch out hydrodynamics characteristics of flat-sheet MBR (membrane bioreactor), which could be analyzed by multiphase and turbulence models efficiently. Aiming at structure optimization, fouling mitigation and energy reduction for MBR, flat-sheet membranes of three major domestic and abroad companies, including Kubota, Toray and SINAP, were chosen to investigate spatial structure of commercial submerged flat-sheet MBR, and to compare effects of different multiphase and turbulence models on phase distribution, velocity field and computational expense. Results showed that the spatial structure of all three flat-sheet membrane was usually designed according to company's manuals, resulting that ratios of length/width and height/diameter were in the range of 1.37±0.63 and 0.97±0.23, respectively. Multiphase model plays key roles rather than turbulence models in phase distribution and velocity field simulation, and the combination of VOF (volume of fluid) and standard k-ε is more accurate and faster for simulating velocity field of submerged flat-sheet MBR. Multiphase model is the key factor of affecting computational costs. On 6 cores platform, VOF consumes 4.5-2.2 times more CPU time than mixture, and realizable k-ε consumes almost the same time as standard k-ε.
Conference Paper
An experimental approach and parametric analysis are here presented to investigate some dynamic aspects of water-mist sprays operating at high supply pressure. An already proposed methodology (P.E. Santangelo, 2010, Exp. Therm. Fluid Sci., 34, pp. 1353-1366) has been extended to a three-dimensional analysis, that emphasizes the characteristic drop-size evolution along the axial coordinate of the spray. Therefore, an evaluation of coalescence and secondary-atomization phenomena along the spray axis results as the ultimate scope of this study. With regard to dispersion, the initial-velocity field has been experimentally determined both as a contour/vector map and as magnitude profiles at different distances from the injector outlet. In addition, some evaluation of the spray-cone angle has been proposed, resulting from a simple geometric approach to the already mentioned maps. Advanced laser-based diagnostics has been employed to perform experimental measurements: a Malvern Spraytec device has been used to measure drop-size distribution and Particle Image Velocimetry has been chosen to evaluate both velocity and cone angle. Moreover, a mechanical patternator has been employed to introduce flux measurements as an averaging quantity. Two nozzles having different orifice diameter have been employed and operative pressure has been set at a value of interest for fire-protection applications.
Article
The study on fire extinguishing performance has gradually become an international fire research focus. A prediction model of minimum extinguishing concentration is developed in this paper. The minimum extinguishing concentration of UFM and water vapor are calculated based on the combustion limit temperature of 1600 K and 1700 K, respectively. Numerical simulation with a detailed chemical reaction is conducted by FLUENT software. The calculated result (using model by 1600 K) agrees with the simulation result and previous experimental result. By comparing the theoretical result with the simulation result and previous experimental result, it is found that the cooling effect of UFM in fire extinguishing is better than that of water vapor, but lower than that of water. A concentration range of UFM is found in the simulation, which is consistent with the previous experiment. Only when the flame temperature is reduced below 1600 K can stable extinguishing be achieved, which can serve as a guide for the selection of combustion limit temperature in the fire engineering.
Article
This paper introduced a new kind of ultra-fine water mist extinguisher, and study on total flooding extinguishing test of ultra-fine water mist extinguishing combustion of paper in confined space with the size of 2.4m×2.4m×3.5m. The results showed that the ultra-fine water mist extinguisher with the mist flux of 500ml/min was effectively in extinguishing combustion of paper in confined space. Therefore, the device can be used to put out fire in archives room.
Article
Transient simulations with full hydrogen chemistry were performed to reveal the flame structure and extinguishment process of co-flow hydrogen diffusion flame suppressed by ultrafine water mist (UFM). As UFM was added incrementally to the oxidizer stream, the flame experienced a series of destabilization process, i.e., detachment, drifting and blowoff. The simulations predicted that the critical mass flow rate of 10-μm UFM was 6 g/min, which is in agreement with the value calculated by a perfectly stirred reactor model and the value measured by the experiments. The critical mass flow rate exhibited a plateau region as the diameter increased from 5 μm to 20 μm. The optimal diameter for UFM was ≠10 μm. A scrutiny on the extinguishing mechanisms reveals that both the chemical kinetic effect and latent heat play important roles in determining the optimal diameter in this configuration. For the chemical kinetic effect, water molecule inhibits the flame through 1) enhancing the chain-terminating reaction H + O2 (+M) = HO2 (+M) and 2) subsequently scavenging free radicals in the flame. An energy equation was used to investigate the relative importance of extinguishing mechanisms for UFM. It shows that the thermal cooling outweighs the chemical kinetic effect in terms of contributions to flame inhibition although the chemical kinetic effect is obviously enhanced compared with N2.
Article
CFD simulation study on the fire-extinguishing performance of ultra-fine water mist (UFM) and its flow behavior in a small scale tunnel. Numerical simulation using dense gas model were carried outIt is discorvered that simulation shows that the larger size of fire is more difficult to extinguish in tunhenel space; and that the effect of obstruction in extinguishing efficiency depends on the location of obstruction.
Conference Paper
The problem of steady-state mass transport from a spherical mono-component droplet immersed in gaseous environment is addressed to find a solution for the expected vaporisation rate under general ambient conditions. The continuity, momentum and energy equations are written on a radial coordinate system. The effect of thermal gradient in the vapour phase is taken into account, while the viscous and dissipation terms in the momentum and energy equations are neglected. The model yields a non-linear second order ODE that is numerically and analytically solved to calculate the steady-state vaporisation rate. The description in terms of non-dimensional variables introduces some new parameters that are expected to influence the vaporisation rate. The model is then compared to the existing simplified Maxwell equation and the well-known Stefan-Fuchs model. Quantitative comparisons are presented and discussed and an application to water droplets floating in hot gas environment, under the operating conditions typical of fire protection spray scenarios, is presented.
Article
Based on analyzing the reasons and characteristics of gas combustion under coal mine and integrating the situation of gas combustion accident which frequently occured at presentthe authors built the experimental platform with the ultra fine water mist to prevent gas combustion.A series of experiments with the ultra fine water mist to prevent gas combustion was conducted.Finallythe best operation parameter to study the water mist restrained gas combustion was obtained with the methane flow of 150 mL/minthe methane concentration of 90%the atomization quantity of 220 mL/minand the water spray particle size of 5-30 μm.The results show that after release ultra fine water mista closed spray ring is formed around the gas flameand the gas flame interact with ultra fine water mist appears the process of restrained-cut flame-restrained again-cut flame againwith the gas flame gradual becoming smaller until to extinguish.Comparing with free combustionthe temperature and oxygen concentration around gas flame all reduced with different degreeand the whole process of flame extinguish is only 90 s.
Conference Paper
This study is focused on characterizing the spray released by a water mist injector at high pressure. To this end, an experimental campaign has been performed employing non intrusive techniques to investigate both drop size and initial velocity over a prescribed range of operative pressure. In particular, a laser-diffraction-based instrument (Malvern Spraytec) has been used to determine the characteristic diameter. An alternative method has been developed to reconstruct the drop-size trend in respect to fluid fraction: drop-size data have been averaged through mass flux distribution. This latter parameter has been measured by a mechanical patternator ad hoc built. Moreover a classic predictive formula for Sauter Mean Diameter has been validated through a physical analysis based on inviscid-fluid assumption. Velocity field has been studied by PIV technique. The proposed measurement methodology has been discussed and both maps and values have been finally stressed out. An experimental evaluation of the spray cone angle has been realized as an additional result of the PIV tests.
Article
In order to apply ultra-fine water mist technology on spontaneous coal combustion in the goaf of a coal mine, we built a small scale compartment with ultra-fine water mist for restraining coal combustion in a confined space and then investigated the restraining efficiency and related factors. The study obtained the following results: a descending rate of heat release, an increase in O2, the production of CO2 decreased gradually, while the production of CO increased dramatically and quickly and then decreased; ultimately it tended to become stable after the discharge of an ultra-fine water mist. The technology showed that the ultra-fine water mist can effectively reduce the heat release rate of coal and the rate to generate components. We found that the restraining effect relied on the mist flux, the discharge time and other factors. A sufficient amount of mist has a better effect compared to an insufficient amount of mist. To combat coal combustion, the greater the discharge time, the better coal flames are extinguished.
Article
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The development of ultrafine water mist fire suppression technology for NanoMist Systems, LLC, using computational fluid dynamics (CFD) simulations, is discussed. Simple fire tests were conducted to determine the accuracy of the overall trend predicted by the CFD model. NanoMist™ is the trade names for the proprietary process technology of producing, scaling, transporting, and delivering the ultrafine fine water mist system. The system exhibits extremely high-energy absorption behavior because of the huge droplet surface area combined with the high vaporization rate of nearly micron-sized droplets.
Patent
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The present invention provides a method and device for production, extraction and delivery of an aerosol mist with ultrafine droplets. A high frequency wave generating device or other process generates very small particles or droplets from a reservoir of liquid or material to be atomized. A helical flow of a carrier gas medium such as air is directed into a container and creates a high throughput aerosol of air and fine droplets. The aerosol is delivered through a suitable outlet such as by deflecting the aerosol upwards and providing a tube centrally situated with respect to the helical flow such that the aerosol will discharge through the tube in high quantity of throughput and high quality of stable aerosol of very fine mist droplets. The methods described utilize in-situ extraction of fine mist droplets using helical flow behavior as opposed to forced convection ejection of mist or inertial separation of droplets by separators.
Article
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A non-isothermal, non-homogeneous approach has been developed for radiation analysis of moderate to large scale liquid pool fires, with a special emphasis on soot formation and the absorption and emission processes. The present field approach reveals the phenomenon of radiative energy blockage by the cold fuel and soot particles in the vicinity of the fuel bed, resulting in a variable heat flux distribution at the fuel surface. The convective contribution to the heat feedback at the fuel surface is found to decrease from 54 to 5% as the pool diameter increases from 15 to 50 cm, while the radiative contribution proportionately increases. The estimated mass evaporation rate and the total radiative output from the flame agree closely with experiment.
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The overall objective of this area is to evaluate and understand the fire suppression behavior of a patented ultra-fine water mist technology with the tradename NanoMist™. NanoMist is a dense gas-like, ultra-fine (<10 µm) water mist produced at ambient pressure. The mist exhibits superior ability to readily diffuse around obstructions and has a potential to be a total flooding agent. However, the technology needs research into key issues such as the mist deployment design, the transport behavior of mist within the flooding volume, the optimum conditions for the mist entrainment into the firebase, and the interaction of mist with laminar and turbulent fires. The specific objective of this work is to develop experimental design factors for testing NanoMist total flooding in a 27-m 3 compartment using CFD simulations. The mist is deployed through multiple outlets located on the compartment floor. The number of outlets, their location are determined from the CFD results in order to produce the desired mist flux density. The mist spreads laterally across the compartment floor and rises to fill the compartment volume. The design factors including mist outlet locations, the outlet velocity, and the mist throughput were evaluated for extinction of a turbulent pool-like gas fire located at the center of floor. In the CFD calculations, 120 kW pool-like gas fires were extinguished with a mist throughput of 1 Lpm, which corresponds to a mist flux density of 0.11 Lpm/m 2 . Significant cooling was observed even at lower flux densities. The fire entrains the nearly stagnant mist into its base as seen from stochastic droplet trajectories, and cools before the chamber reaches the total-flooding condition. The time to extinguishment is <10 seconds, which includes mist filling time as well. The mist filling behavior is similar to low momentum dense gas dispersion inside a chamber. Under weak flow conditions, the dispersion time scale is in minutes, while typical flame extinction is in seconds. Additional computations were conducted to understand the transport behavior of dense gas-like mist and its implications on fire suppression times. Using the predicted design factors as guidelines, total flooding fire tests were conducted at the Naval Research Laboratory (NRL) fire test facility at the Chesapeake Bay Detachment (CBD), MD. The tests results are reported in a companion paper presented in this conference.
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The progress on the research and application of water mist technology in fire suppression has been substantial over the last decade. This paper, following our previous review on water mist fundamental studies, reviews recent water mist applications for: the extinguishment of Class B spray and pool fires in machinery spaces, gas turbine enclosures, combat vehicles, and flammable liquid storage rooms; the extinguishment of Class A fires in residential occupancies, marine accommodations and public spaces, heritage buildings and libraries; the extinguishment of Class C fires in electronic equipment and computer rooms; and the protection of aircraft onboard cabin and cargo compartments. Some new applications, such as the use of water mist for the extinguishment of Class K fires in commercial cooking areas; and the use of water mist as a possible total-ship protection method, as well as the use of water mist for the protection of heavy goods vehicle shuttle trains, are also reviewed. Up-to-date development of corresponding test and design criteria for the installation of water mist fire protection systems and for the evaluation of the capabilities and limitations of water mist for fire suppression in some application areas, such as machinery spaces, ship's cabins and corridors, and turbine enclosures, are discussed.
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The FIRE Detection And Suppression Simulation (FIREDASS) project was concerned with the development of water misting systems as a possible replacement for halon based fire suppression systems currently used in aircraft cargo holds and ship engine rooms. As part of this program of work, a computational model was developed to assist engineers optimize the design of water mist suppression systems. The model is based on Computational Fluid Dynamics (CFD) and comprised of the following components: fire model; mist model; two-phase radiation model; suppression model; detector/ activation model. In this paper the FIREDASS software package is described and the theory behind the fire and radiation sub-models is detailed. The fire model uses prescribed release rates for heat and gaseous combustion products to represent the fire load. Typical release rates have been determined through experimentation. The radiation model is a six-flux model coupled to the gas (and mist) phase. As part of the FIREDASS project, a detailed series of fire experiments were conducted in order to validate the fire model. Model predictions are compared with data from these experiments and good agreement is found.
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The FIRE Detection and Suppression Simulation (FIREDASS) project was concerned with the development of water misting systems as a possible replacement for halon based fire suppression systems currently used in aircraft cargo holds and ship engine rooms. As part of this program of work, a computational model was developed to assist engineers optimize the design of water mist suppression systems. The model is based on Computational Fluid Dynamics (CFD) and comprised of the following components: fire model; mist model; two-phase radiation model; suppression model; detector/activation model. In this paper the FIREDASS software package is described and the theory behind the fire and radiation sub-models is detailed. The fire model uses prescribed release rates for heat and gaseous combustion products to represent the fire load. Typical release rates have been determined through experimentation. The radiation model is a six-flux model coupled to the gas (and mist) phase. As part of the FIREDASS project, a detailed series of fire experiments were conducted in order to validate the fire model. Model predictions are compared with data from these experiments and good agreement is found.
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A buoyant, turbulent methane flame with a base diameter of 0.25mm and a heat release rate of 28 kW was numerically modeled. Soot formation was included in the model by a phenomenological soot formation scheme. Gas radiation was treated by a weighted-sum gray-gas model. A non-isothermal, non-homogeneous field approach was utilized and the thermal radiation was included by incorporating a four flux radiation model into a finite-difference scheme.The methane fire did not show appreciable soot concentrations to the extent that the radiation was significantly affected. The radiation present was predominantly due to gaseous species. The centerline flame properties such as the axial velocity, mean temperature, and entrainment behaviors are generally well reproduced by the theory. However, the radial expansion of the flame is underestimated near the flame base because of the neglect of the elliptic behavior in the present approach.An analysis of the thermal radiation behavior revealed a non-uniform heat feedback flux distribution. Unlike in sooting flames, where the flux maximizes usually midway between the centerline and flame edge, we observe the maximum flux at the pool center in the methane fire. In sooting flames, this behavior arises because of radiative energy blockage by the cold fuel vapor and soot in the core. A reduced radiation blockage in the methane flame is a distinguishing feature of the methane fire compared with sooting pool fires.
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Twenty-three fire tests were conducted to determine the ability of current fine-spray (water mist) technologies to extinguish fires specified in the International Maritime Organization (IMO) fire test procedure for engine rooms greater than 3000 m3. The tests were conducted using nozzle installed at a 5 m height and 1·5 m spacing in a large test facility (2800 m2 area and 18 m height). Two types of nozzles were tested: a low pressure nozzle operating between 1·2 and 1·5 MPa with flow per nozzle between 12·0 and 13·41/m and a multi-nozzle high-pressure prototype consisting of seven nozzles operating at 6·9 MPa flowing at 5·3 1/m per prototype. These nozzles were selected because they had been shown to extinguish IMO fire tests in enclosures with a protected area of 83 m2 and a ceiling height of 4·5 m. The fire tests selected from the IMO procedure included 6 MW diesel spray fires on top of the IMO engine mock-up, a shielded 6 MW diesel spray fire adjacent to the mock-up, a 1 MW shielded diesel spray fire adjacent to the mock-up, and a wood crib within a 2 m2 pan filled with heptane. In tests in which no additional enclosure surrounded the nozzles other than the test facility, fires were not significantly affected by the water mist using either nozzle. To further investigate mist-system capabilities, a ceiling was then placed directly over the nozzles at a 5 m height covering an area of 188 m2. Using 90 high-pressure prototype nozzles, the test fires were not extinguished. A 940 m3 enclosure was then formed by dropping tarpaulins to the floor from the ceiling. A 4 m2 vent was placed in the wall. With the 90 high-pressure prototype nozzles, the 6 MW spray fire on top of the mock-up was extinguished. When the 6 MW fire was shielded beside the mock-up, the fire was not extinguished. With the vent closed, the 6 MW shielded spray fire was extinguished. Under the same test conditions, a 1 MW shielded diesel spray fire and a 0·1 m2 heptane pool fire were not extinguished. The fire test results indicated that protection of engine rooms with volumes of about 1000 m3 is possible by optimizing current fine-spray technology while significantly larger volumes will require improved discharge characteristics.
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This paper presents the results of an experimental parametric study of water mist suppression of large-scale liquid pool fires. The experiments were conducted with 50cm diameter pan heptane and JP8 pool fires. Mist was injected into the fire from the base at 90 and 45 and from the top at 90. The results show that base injection of droplets enhanced their suppression effectiveness by as much as two times. Secondly, optimum suppression effectiveness is obtained with small droplets injected at the base of the fire. This is because the droplets evaporated quickly within the lower region of the fire where a greater effect of oxygen dilution and water vapor higher heat capacity is fully realized. Finally, a comparison of the results with the two fuels show that water mist is more effective in suppressing the JP8 fires than the heptane fires. It is concluded that the additional effects of direct surface cooling contributed significantly to the observed difference.
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Turbulent, buoyant pool-like propane flames with heat release rates of 15.8, 22.9 and 37.9 kW are numerically modeled. The model assumes a parabolic flow field, α κ–ϵ turbulence model, and an eddy-dissipation concept for the interaction of the chemistry and turbulence. Radiative heat transfer is incorporated by the flux model with the absorption and emission coefficients evaluated using a temperature-weighted gray gas model. Predictions are made for the flame shapes, axial velocity, axial mean temperature and various scalar properties along the centerline, the radial distribution of temperature and velocity at various axial heights, and the air entrainment behavior. The overall agreement between the predicted and experimental flame behavior is seen to be good; however, the radial expansion of the flame is underestimated in the combustion zone.
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This paper presents of an experimental study of the effects of ultra fine water mist (~3 µm) and regular spray nozzle mist (~30 µm) on forced flow boundary layer combustion of a poly methylmethacrylate plate, where mist was introduced with the incoming air. With the spray nozzles, burning rate downstream was enhanced due to spray-induced turbulence, which enhanced heat feedback rate to the plate in this region. Because of the higher heat feedback rate, the downstream achieves steady state burning rate faster with mist than without mist. On the other hand, the ultra fine mist has no induced turbulence and burning rate was suppressed everywhere along the plate due to mist cooling and dilution effects. Transient burning rate downstream lasts longer in this case due to the lower heat feedback rate.
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A preliminary investigation on the effectiveness of water mist as a suppressant in electrical fires under normal-gravity conditions for spacecraft applications is presented. Water-mist suppression experiments of a fire involving an overheated wire are conducted inside a container similar to the Space Shuttle mid-deck locker. Direct and indirect water-mist injection is used with various droplet-size distributions and flow rates. Water mist quickly extinguishes a fire that is directly impacted by the droplets, while much longer spraying times and larger amounts of water are required to suppress fires burning behind a baffle. Smaller droplet size distributions appear to be the most effective. A numerical model enables the simulation of a polydispersed spray, while still providing enough droplet scale resolution for the high-gradient fire suppression scenarios. The preliminary numerical results accurately predict droplet penetration, evaporation, and dispersion into the container as observed in the normal-gravity tests. These qualitative comparisons contribute to the on-going validation process of the model.
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A quasi-steady-state model was developed to predict the effectiveness of a water mist system for extinguishing fuel spray and pool fires. The model was developed for obstructed fires where extinguishment primarily occurs as a result of a reduction in oxygen concentration due to the consumption of oxygen by the fire and due to dilution of the oxygen with water vapor. Interactions between the mist and the flame are neglected resulting in limiting case predictions. The model is based on conservation of energy and requires the following input parameters: fire size, compartment geometry, vent area, and water flow rate. The steady-state temperatures and oxygen concentrations predicted by the model can be used to determine the smallest fire that can be extinguished. The predictions made by the model compared favorably to the results of three full-scale test series conducted for the US Coast Guard. These tests were conducted in shipboard machinery spaces with compartment volumes ranging from 100 to 500 m3 with a wide range of ventilation rates and openings. The model was able to accurately predict the compartment temperatures during the tests where steady-state conditions were produced. The model was also able to accurately predict the extinguishment times for a wide range of fire sizes and was used to identify the smallest fire that could be extinguished for a given set of conditions.
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Suppression of methane/air and propane/air nonpremixed counterflow flames, and n-heptane and methanol cup burner flames by fluorinated hydrocarbons was investigated. Four fluorinated ethanes, 10 fluorinated propanes, four bromine- or iodine-containing halons, and the inert agents CF4, SF6, and N2 were tested in some or all of the flames. Laser Doppler velocimetry (LDV) determinations of peak velocity gradients in the oxidizer flow of the counterflow flames were found to be linearly correlated with the expression for global strain rate derived for plug flow boundary conditions. This correlation was used to estimate strain rate values at extinction. The bromine- or iodine-containing agents are more effective on a molar basis than the fluorinated propanes, followed by the fluorinated ethanes, and finally SF6, CF4, and N2. Agent effectiveness increases with the number of CF3 groups present in the agent molecular structure. Numerical investigations of the flame speed reduction of methane/air mixtures doped with either CHF2CHF2 or CF3CH2F predict that the latter is the better agent, in accord with experimental observations. Chemical contributions to suppression account for less than 35% of the total suppression offered by fluorinated hydrocarbons not containing bromine or iodine. At strain rates below 100 s−1, suppression effectiveness rankings in methane and propane counterflow flames are similar to those obtained in n-heptane and methanol cup burner flames. Methanol flames are more difficult to extinguish than the alkane flames investigated, particularly with the chemical agent CF3Br.
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Numerical simulations have been performed to optimize various water-mist injection characteristics for flame suppression. A two-continuum formulation is used in which the gas phase and the water mist are both described by equations of the eulerian form. The effects of droplet diameter, mist injection angle (throw angle), mist density, and velocity on water-mist entrainment into the flame and flame suppression are quantified. Droplet sectional trajectories and density contours are used to identify the regions of the flame where the droplets evaporate and absorb energy. Numerical results are presented for symmetric and asymmetric spray pattern geometries resulting from base injection and side injection nozzle orientation. Results indicate that smaller droplet diameters produce optimum suppression under base injection configuration, while larger droplet diameters are needed for optimum suppression for the side injection configuration. For all cases, the model is used to determine the water mist required for different levels of suppression, and this is reported in terms of the ratio of the water-mist supply rate to the fuel flow rate.
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Extinction in open space of flames from pool fires by downwardly directed water sprays has been investigated on two linear scales, one three times larger than the other. Circular pool fires were employed as fire sources, mostly in the form of gas discharge (methane) from a horizontal sand surface but also, to a limited extent, in the form of heptane pools. The results are presented in normalized plots based on scaling theory verified in a previous study. Extinction data from the methane fires are insensitive to the initial spray angle of the nozzle discharge. The data are consistent with an engineering relation showing extinction water flow rate approximately proportional to an effective nozzle diameter, and to the 0.4-power of both nozzle height and freeburn heat release rate. This result has been interpreted to indicate that spray-induced dilution of the flammable gas is a major factor in extinguishing fires from gaseous discharge. Extinction data of liquid pool fires from this study (n-heptane) and previous investigations (gasoline, JP-5) are consistent with the methane data, except for somewhat higher water rates at extinction.
Article
We performed what we believe are the first simultaneous in situ measurements of liquid water and oxygen concentrations in a dense water mist environment. Direct absorption tunable diode laser absorption spectroscopy was used to make oxygen concentrations and simultaneously quantify the liquid water via optical density measurements. This spectrometer with an absorption path length of only 36.8 cm was successfully tested during full-scale fire suppression tests with scattering losses up to 99.9%. The simultaneous oxygen and liquid water concentration measurements agree with fire suppression model calculations.
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