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Effects of Water Mist System on a Controlled Fire

Ho, Jasper LU (2015) In LUTVDG/TVBB VBRM05 20151
Division of Fire Safety Engineering
Abstract
Current legislation regarding implementation of water mist system(s) requires full scale testing specific to its intended use which involves extensive funding that discourages potential users. This motivates the desire for accurate water mist simulation. The extent to this possibility is studied for a specific high pressure water mist system, “Danfoss 1910”, and its effect on controlled fires of different heat release rates were studied. Concepts to accurately simulate the water mist system were also looked into, where the combined use of an additional air inlet, obstruction (turbulence) meshes and reduced initial particle velocity showed the best performance. A horizontal water mist orientation was adopted to reduce the direct interaction... (More)
Current legislation regarding implementation of water mist system(s) requires full scale testing specific to its intended use which involves extensive funding that discourages potential users. This motivates the desire for accurate water mist simulation. The extent to this possibility is studied for a specific high pressure water mist system, “Danfoss 1910”, and its effect on controlled fires of different heat release rates were studied. Concepts to accurately simulate the water mist system were also looked into, where the combined use of an additional air inlet, obstruction (turbulence) meshes and reduced initial particle velocity showed the best performance. A horizontal water mist orientation was adopted to reduce the direct interaction between water mist spray and buoyant plumes. The results attained from a quasi steady state extinguishment model, simulations and experimental data were compared and vast discrepancies were discovered. The quarter scale ISO room corner used was found to be too small which created high levels of circulation within the enclosure; hindering the proper assessment of extinguishing mechanisms such as gas phase cooling and oxygen depletion. One of the conclusions is the need to compile larger scale tests validation data to form a baseline reference. (Less)
Popular Abstract
This project identifies the extent of water mist simulation accuracy and its effect on a controlled fire.
The largest hindrance to utilising the full potential of water mist systems is the uncertainty in its simulation accuracy. Here, several simulation concepts were tested and an accurate simulation of a specific water mist system was achieved. These results would hopefully contribute to the long term goal to reduce the dependency of full scale testing for water mist applications.
Various scenarios to study several factors were first identified, these factors include; accurate simulation of water mist spray (in relation to velocity profile at predetermined distances from nozzle), water distribution accuracy and extinguishment... (More)
This project identifies the extent of water mist simulation accuracy and its effect on a controlled fire.
The largest hindrance to utilising the full potential of water mist systems is the uncertainty in its simulation accuracy. Here, several simulation concepts were tested and an accurate simulation of a specific water mist system was achieved. These results would hopefully contribute to the long term goal to reduce the dependency of full scale testing for water mist applications.
Various scenarios to study several factors were first identified, these factors include; accurate simulation of water mist spray (in relation to velocity profile at predetermined distances from nozzle), water distribution accuracy and extinguishment predictions using simulation. In the recent decade, simulation accuracy of water mist sprays in the Computational Fluid Dynamic (CFD) simulation software used (Fire Dynamics Simulator, FDS) has drastically improved where the concept of momentum lost is better captured which in turn improves the water distribution prediction. Several combinations of simulation concepts including the use of additional air inlets, obstruction meshes and reducing the particles’ initial velocity were looked into. The best suited concept was then identified by comparing accuracy with experimental test data of velocity profiles previously performed by Husted for his doctorate study submitted in 2007. Having a spectrum of water mist characteristics, the best suited concept found here is limited to the particular model of water mist nozzle used for this project (Danfoss 1910). However, the simulation accuracy is reduced when enclosure effects are introduced which can be attributed to the lack of computational model between the relationship of turbulence effect and water particle size. This likely affected the water distribution accuracy within the enclosure seen in one of the scenarios where high circulation levels were observed. The simulation’s extinguishment prediction was compared with results from experiments and a quasi steady state extinguishment model introduced by Back et al. The results did not coincide with each other likely due to lack of simulation accuracy on distribution of water particles and effects of input variable “particles per second” used to represent the spray in FDS. (Less)
Please use this url to cite or link to this publication:
author
Ho, Jasper LU
supervisor
organization
course
VBRM05 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Fire, water mist, simulation, experiment, extinguish, extinguishment
publication/series
LUTVDG/TVBB
report number
5498
ISSN
1402-3504
language
English
id
5431547
date added to LUP
2015-05-25 12:02:45
date last changed
2015-05-25 12:02:45
@misc{5431547,
  abstract     = {Current legislation regarding implementation of water mist system(s) requires full scale testing specific to its intended use which involves extensive funding that discourages potential users. This motivates the desire for accurate water mist simulation. The extent to this possibility is studied for a specific high pressure water mist system, “Danfoss 1910”, and its effect on controlled fires of different heat release rates were studied. Concepts to accurately simulate the water mist system were also looked into, where the combined use of an additional air inlet, obstruction (turbulence) meshes and reduced initial particle velocity showed the best performance. A horizontal water mist orientation was adopted to reduce the direct interaction between water mist spray and buoyant plumes. The results attained from a quasi steady state extinguishment model, simulations and experimental data were compared and vast discrepancies were discovered. The quarter scale ISO room corner used was found to be too small which created high levels of circulation within the enclosure; hindering the proper assessment of extinguishing mechanisms such as gas phase cooling and oxygen depletion. One of the conclusions is the need to compile larger scale tests validation data to form a baseline reference.},
  author       = {Ho, Jasper},
  issn         = {1402-3504},
  keyword      = {Fire,water mist,simulation,experiment,extinguish,extinguishment},
  language     = {eng},
  note         = {Student Paper},
  series       = {LUTVDG/TVBB},
  title        = {Effects of Water Mist System on a Controlled Fire},
  year         = {2015},
}