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The present study focuses on extinction of flames with water mist where surface cooling effects are neglected i.e. water mist as a total flooding system where the direct spray cannot reach and cool all burning items in the protected volume. The study includes a survey of the production and properties of water mist such as different types of nozzles and means to describe droplet size distribution. Properties of jets and sprays are discussed as well as water droplet movement, fall and evaporation. Three different series of experiments were conducted with different hydraulic atomising nozzles. In the first series, droplet size distribution and water spray distribution measurements for the nozzles were conducted. The measurements showed that the droplet size distribution ranged from a Sauter Mean Diameter of approximately 35 - 85 µm, all dependent on the water pressure and the configuration of nozzles. The measurements show that considerably larger droplets are formed when individual nozzles are placed together. This can be explained by a coalescence effect when droplets from the sprays of the nozzles collide. The second series of experiments were done using a tubular propane gas bumer where water and propane were mixed prior to reaching the burner outlet. Based on the tests, the specific amount of extinguishing medium required (Required Extinguishing Medium Portion, REMP = m, / m, i.e. the ratio of the agent quantity to fuel quantity consumed) is given as a quantitative measure of the efficiency of the agent. The lower the REMP value, the more efficient the agent. The water pressure ranged between 40 and 80 bar which provided for droplet sizes with a Sauter Mean Diameter in the order of 35 pm. The results show that the amount of water needed for extinguishment by weight is between 1.2 - 2,2 times the amount of propane gas. The decrease in droplet sizes decreased the amount of water needed. Another observation was that the heat release rate of the fire is not affected until extinction occurs. A REMP-value of 1,2 - 2,2 corresponds to a water content of 100 – 200 g/m3 protected volume which is in agreement with theoretical values. Finally, a series of tests were conducted in a 113 scale room using a propane gas fire. Parameters such as location of the fire, the location of the nozzle, water flow rate and the size of the room opening were varied. In these tests the water content needed was in close agreement with the values obtained from the REh4P experiments and the theoretical values. These tests also highlighted the problem of delivering the droplets to the fire. To achieve "total flooding" in an actual situation, nozzles covering the complete protected compartment, with additional nozzles under obstructions would be needed. To make droplets follow the air flows inside a room and behave more like a gaseous total flooding agent, requires droplets of a size in the order of 1 - 20 µm.

International Conference on Fire Protection in the HVDC Industry: 10 April 1995, Vancouver, B.C., Canada

NFPA 1994 Fall Meeting: 13 November 1994, Toronto, Ontario, Canada

Fourth International Symposium on Fire Safety Science: 13 July 1994, Ottawa, Ont., Canada

Halon Options Technical Working Conference : Proceedings: 03 May 1994, Albuquerque, NM, USA

Also appeared in Fire Research News, no. 74, 1994, p. 1-3., International CFC and Halon Alternatives Conference: 24 October 1994, Washington, D.C., U.S.A.

IMAS '94 : Fire Safety on Ships - Developments into the 21st Century: 26 May 1994, London, UK

Proceedings of the International Conference on Water Mist Fire Suppression Systems: 04 November 1993, Boras, Sweden

Workshop on Water Mist Fire Suppression Systems: 01 March 1993, Gaithersburg, MD, USA

In order to enhance the fire suppression performance of water mist, a new multi-component additive of water mist is produced through physics process for the typical fire (oil pool fires and wood crib fires). To study the effectiveness of the water mist adding this new multi- component additive in fire suppression, a laboratory-scale suppression system was built and a series of tests were conducted in this system. The experimental result reveals that the fire suppression effectiveness of water mist is improved greatly by adding the multi-component additives, Along with increasing the amount of multi-component additives, the fire suppression time of oil pool fire drops rapidly, then increases slightly at some points; but the time of wood crib fire declines gently, then tends to become stable. Finally, the suppression mechanism is discussed so as to find out the deep relationship between the multi-component additive and suppression effectiveness.

Full scale experiments were performed in an underground subway station to investigate the effect of water mist on smoke flow from tunnel area to platform through shield door. Smoke temperature, species concentrations and smoke visibility were measured at different points. Dimensionless variables were introduced to represent the variations of smoke characteristics. The smoke temperature with water mist interaction could be reduced to less than 1/10 of the spill smoke flow. The mass flow rate could be reduced to less than 1/4 of the spill smoke flow. The experimental results indicated that the water mist system could help to reduce smoke temperature and the concentration of toxic species, improving survival conditions for evacuations of passengers.

Experiments of water drops with and without additives impact on wood surfaces were conducted. Three kinds of wood which are Paulownia, Fraxinus mandshurica and Jatoba, were considered, since they are commonly used for architecture and furniture in China. The dynamics of solution drop with additive impact on wood surfaces and the effects of the surface topography on drop spreading were investigated. Comparing to the collision dynamics of a pure water drop, the results show that the additives significantly alter the dynamics of the drop impact on wood surfaces. The maximum and the final spread factor increase as the surface tension decrease. In addition, the surface topography plays an important role on dynamics of liquid drop impact on a solid surface. The drop spreading on different wood surfaces except for Fraxinus mandshurica surface agrees well with the scaling results reported in literature. The grooves comprising in the wood surface can deform the shape of the liquid lamella when the spreading drop reaches the maximum diameter

Statistics shows that the majority of accidents with fatal outcome are caused by methane and/or coal dust explosion. This leads to assumption that contemporary counter-explosion systems of various designs cannot be considered effective. Considering the growing threat of methane explosion in the coming years along with the development of deeper levels, the improvement of a system for protecting people in underground opening appears to be essential. This paper presents the results of the testing of the Automatic System from Methane Explosion in Coal Mines. The protective system consists of a wireless device for the detection of explosions and activation of a protective system, and an absorber with a pyrotechnic device ensuring the discharge of dispersed water. The protective system, at the command of the initiation signal, produces tailored dispersing water mist with droplet sizes in the range of 25–400 μm along selected tunnel sections.

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.Copyright © 2011 by ASME

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. A new approach has been used for the simulations with the LES model in FDS 4.07. In this approach the simulations of the water mist spray is not done in the zone close to the nozzle. Instead the boundary conditions are set further downstream, based on the conducted measurements. This approach resulted in droplets and air moving downwards at relatively high velocities as expected. However, the momentum transfer is limited, and the simulations did not give sufficient mixing. Suggestion are made of how sufficient mixing can be obtained with the new approach, with regards to implementation of spray boundary conditions and treatment of the turbulence model interacting with the movement of the droplets.