Study of Water Droplet Behavior in Hot Air Layer in Fire Extinguishment

Li, Y. F.; Chow, Wan Ki

doi:10.1007/s10694-007-0036-2

Cited by 24 publications

(27 citation statements)

References 28 publications

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“…The results of the analysis using the proposed model are compared with their results and presented in Figure . The results of the proposed model, in first case, are almost identical with the results by Li and Chow . However, the analysis by Li and Chow predicted slower evaporate rate, in second case, compared to the prediction of that by the proposed model.…”

Section: Use Of the Model As A Validation Toolsupporting

confidence: 76%

“…However, the analysis by Li and Chow predicted slower evaporate rate, in second case, compared to the prediction of that by the proposed model. It may be primarily due to the fact that Li and Chow did not consider the contribution of radiation emanating by a flame and the surrounding boundary walls on the evaporation of droplet. However, flame and the boundary walls emanate a substantial amount of energy through radiation.…”

Section: Use Of the Model As A Validation Toolmentioning

confidence: 99%

“…When sprinkler systems are activated at a temperature of 60 °C, say, the relative humidity (RH) of the surrounding air is very low, typically 5%. This is in sharp contrast with the data generated by Li and Chow who assumed that the RH of the air was 53%, yet the dry bulb temperature was 60 °C. Vaari assumed the droplet temperature to be identical to the surrounding air temperature in his transient one‐zone model that described the total flooding water mist fire suppression.…”

Section: Introductionmentioning

confidence: 99%

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Study of water‐mist behaviour in hot air induced by a room fire: Model development, validation and verification

2014

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Summary Water‐mists are emerging as an effective agent for the suppression of fires. However, the mechanisms of suppression are complex and the behaviour of individual water droplets in a smoke layer generated by fires must be quantified. This study investigates the behaviour of individual droplets injected from a nozzle into a hot air environment induced by a room fire. A semi‐empirical model has been developed based on the conservation of mass, momentum and energy to evaluate the heat and mass transfer phenomena in an air‐water droplet system. The model has considered the effect of change of momentum of an evaporating droplet. A forward finite difference approach is applied to solve the governing time dependent ordinary differential equations. The droplets are considered to be ‘lumped mass’ and variable thermo‐physical properties of water and air and the change of Reynolds number of the droplets, due to the change of their diameter and velocity are considered. The effect of high evaporation rate on the mass and heat transfer coefficient and the contribution of radiation emanating by a flame and the surrounding boundary walls are also considered in the model which were not taken into account in the previous studies. Experimental data on terminal velocity and adiabatic saturation temperature are used to validate and verify the model. The validation and verification indicate that the proposed model predicted the terminal velocity within 4% of the experimental data and predicted the saturation temperature within 5% of the adiabatic saturation temperature. This semi‐empirical model is also used as a tool to validate a more comprehensive computational fluid dynamics (CFD) based tool, Fire Dynamics Simulator (FDS). It is found that FDS results agree well with the results of the proposed model. Furthermore, the proposed model can be used to evaluate the temperature, velocity, diameter and other physical properties of a droplet travelling through a layer of hot air. Copyright © 2014 John Wiley & Sons, Ltd.

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Section: Use Of the Model As A Validation Toolsupporting

confidence: 76%

Section: Use Of the Model As A Validation Toolmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of water‐mist behaviour in hot air induced by a room fire: Model development, validation and verification

2014

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“…due to turbulence and non-linear variation of physical properties [18]. However, we do not pursue complex simulations of individual detailed interactions among droplets.…”

Section: Model Assumptionsmentioning

confidence: 99%

“…In the literature, many studies are found on the topic of interaction of water droplets with fire smoke layer [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The cooling effect and drag force produced by water droplets are considered generally to yield smoke logging [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Description and application of an analytical model to quantify downward smoke displacement caused by a water spray

Tao

Vierendeels

Fang

et al. 2013

Fire Safety Journal

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An analytical model is developed from basic principles to quantify the downward smoke displacement as caused by a water spray from e.g. a sprinkler head. The underlying assumptions are identified and the global balance is described between downward drag force, potentially downward buoyancy due to a cooling effect within the water spray envelope in the smoke layer, and the upward buoyant force in the ambient air below the smoke layer. From this balance, the downward smoke displacement is quantified. It is explained that the classical Bullen theory to define a criterion for smoke layer stability is in general not valid. There is always downward smoke displacement, although potentially small, depending on the circumstances. The tracking of individual water droplets leads to the evolution of the spray envelope radius and provides the total downward drag force on the smoke. An extensive sensitivity study is presented, varying the water spray angle at the nozzle, the water droplet diameter, the smoke layer temperature, and inclusion or not of the cooling effect by water and air entrainment in the downward smoke displacement. It is highlighted that the downward smoke displacement is more pronounced for smaller droplets (for fixed water mass flow rate), and for lower smoke layer temperatures. For larger water spray angle at the nozzle, the downward displacement also increases monotonically with initial smoke layer thickness. A smaller spray angle at the nozzle leads to stronger 2 downward smoke displacement and the variation of downward smoke displacement with initial smoke layer thickness is non-monotonic: stronger descent of smoke for thinner smoke layer, but beyond a critical smoke layer thickness also again a stronger descent with increasing smoke layer thickness. The accuracy of the model as presented is illustrated by means of an experimental data set. Keywords:

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Experimental and numerical study of water spray system for a fire event in a confined and mechanically ventilated compartment

2019

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Summary The present work addresses the application of a water spray system in case of a fire event in large‐scale experiments for nuclear safety issues. It focuses on the interaction between a water spray system and a stratified smoke layer due to a pool fire in a mechanically ventilated enclosure. This study is supported by a set of four large‐scale tests and one numerical simulation with a 3D CFD software, named CALIF3S/ISIS, and developed by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The modelling used in this paper is based on an Eulerian‐Lagrangian approach. The fire tests are performed in a 165 −m3 mechanically ventilated single room. The fire is a lubricant oil pool fire of about 400 kW. The ventilation flow rate is 2550 m3.h−1 and corresponds to a renewal rate of 15.5 h−1. The spray nozzles are deluge and sprinkler type. The test parameters are the water flow rate, the time of activation, and the duration of activation. Based on the large‐scale experiments and the numerical simulation, four typical physical mechanisms have been enlightened. The first one corresponds to the cooling of the gas phase that is the straightforward consequence of the heat transfer exchange between the water droplets and the surrounding gas. The second effect is the process of gas mixing and homogenization induced by the water spraying system. The gas concentrations (O2, CO2) in the upper and lower parts of the room tend to the same level. The third effect is the significant increase of the fire heat release rate (HRR), up to 25 %, when the water spray is activated. Then, the last noteworthy effect is the occurrence of gas pressure peaks when the water spray is activated or shut off, consequence of the sudden change of the gas temperature. The processes of gas cooling and fire HRR increase are showed to be the main causes of these variations of gas pressure.

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Study of Water Droplet Behavior in Hot Air Layer in Fire Extinguishment

Cited by 24 publications

References 28 publications

Study of water‐mist behaviour in hot air induced by a room fire: Model development, validation and verification

Study of water‐mist behaviour in hot air induced by a room fire: Model development, validation and verification

Description and application of an analytical model to quantify downward smoke displacement caused by a water spray

Experimental and numerical study of water spray system for a fire event in a confined and mechanically ventilated compartment

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