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The study of sprinkler spray characteristics in domestic premises y Damien Mason – K1110597 pervisor – Dr. Siaka Dembele 1

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Page 1: Dissertation - Presentation

The study of sprinkler spray

characteristics in domestic premises By Damien Mason – K1110597

Supervisor – Dr. Siaka Dembele1

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Introduction• In 2013-14 258 out of 322 fire related deaths where

in domestic premises, which is 80% of fire related deaths within the UK.

• Almost one fifth of total fires in the UK in 2013-14 were in domestic premises.

• Fire suppression systems are not integral in domestic premises.

• Fire sprinklers are fire suppression systems, having a fire sprinkler system installed significantly reduces fatalities and loss of property.

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Aims of study• To select a common house fire scenario and

determine the optimum characteristics required for a fire sprinkler system to extinguish that fire effectively and efficiently.

• To research on fire behavior, fire sprinkler systems and fire suppression

• To produce a typical fire scenario using the CFD software Fire Dynamic Simulator and SmokeView and extinguish that fire using a fire sprinkler with optimum characteristics

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Background• Fire sprinkler systems have been in use for over 100 years with the

recording of the first automatic fire sprinkler being made in the 1870’s by Henry. S. Parmelee.

• With current standards now require the use of fire sprinkler systems in public buildings, it is important that they are optimally designed.

• There are various different types of fire sprinkler which is dependent on the application

• Fire sprinkler systems have developed as the knowledge on fires has grown.

• Fires have different classifications and can behave differently under different circumstances.

Figure 1. Modern fire sprinkler head, Jhun, 2015

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Research: Fires & Fire sprinklers• Classification of fires (ordinary combustibles, flammable liquids,

combustible gasses, combustible metals, electrical equipment and cooking oils)

• The structure of a turbulent fire can be divided into separate regions for analysis (The fuel rich core, intermittent region, plume region and ceiling jet)

• Fires do not all burn in the same way factors affecting this are the fuel, initial conditions, surface area and available fuel and oxygen

• A pool fire is a turbulent diffusion fire resulting from the combustion of a fuel, where the fuel has zero or low initial momentum.

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Research: Fires & Fire sprinklers cont.• There are several different types of fire sprinklers,

which are used for different applications (Wet pipe, Dry pipe, Alternate pipe, Pre-action pipe, Deluge pipe)

• There are different fire suppression by water methods (water mist and water spray)

(Tyco, 2016)

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Fire Dynamic Simulator & Smokeview• Fire Dynamic Simulator (FDS), is a computational fluid dynamics

model of fire-driven fluid flow. FDS solves numerically a form of the Navier-Stokes equations appropriate for low speed, thermally driven flow (Pool fires) with an emphasis on smoke and heat transfer.

• Smokeview is scientific software that comes packaged with Fire Dynamic Simulator (FDS). It is tool designed for visualizing numerical prediction generated by fire models such as FDS.

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Key characteristics• Droplet size (μm)

• Velocity (m/s)

• Volumetric flow rate (L/min)

• Spray angle (o) Figure 2 Spectrum of droplet diameters (G. Grant et al. 2000)

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Selected fire scenario• Within a living room

• Single sofa burning in the centre of a room (to simplify study)

• Room dimensions: 4.0 x 4.0 x 2.5 m

• Class A fire

• Fuel: Butane

• Sofa dimensions: 1.2 x 1.0 x 0.8

• Sofa properties taken from Heat release rate of burning items, 2000.

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Selected fire scenario cont.

Figure 3. Simulation domain, 2016

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Selected fire scenario cont.

Heat release rate = 284.4 kW

Figure 4. Simulation #5 after 33.3 seconds, 2016

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Calculations and specifications• Flow rate for domestic premise is 60 litres/min though any single

sprinkler

• The range of flow rates were therefore 60-180, increasing in increments of 20.

• Velocity range 5, 6.5, 8.5, 10, 11.4, 13.4, 15 m/s

• Orifice diameter is 16mm from Victaulic K11 fire sprinkler specifications (FDS sprinkler is k11)

• The range of droplet sizes for sprinkler should be ideally between fine and average (100-1000μm) (Grant et al., 2000).

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Calculations and specifications

• Heat release rate, Q can be calculated with the following equation:

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Simulations

Figure 5. Activated fire sprinkler after 39.2 secondsFigure 6. Fully extinguished fire

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Simulations Cont.• Initially 49 simulations were ran, which varied in different

characteristics which include volumetric flow rate, velocity and droplet diameter. To keep the simulation close to a real life scenario a dry pipe system was replicated, as this is an ideal system to have in a domestic premise; the fire sprinkler did not activate until roughly around 35-39 seconds after the fire had started

• To simplify the study, heat transfer from the walls was not allowed, only one item was selected to prevent fire spread and the fire was not permitted to increase in heat release rate over time.

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ResultsSimulation No.

Droplet diameter, d (μm)

Velocity, v (m/s)

Flow rate, Q (L/min)

Time to extinguish fire (s)

Total water used (Litres)

Simulation #1 100 5 60 7 7.00Simulation #2 100 6.5 80 6 8.00Simulation #3 100 8.5 100 6 10.00Simulation #4 100 10 120 6 12.00Simulation #5 100 11.4 140 5 11.67Simulation #6 100 13.4 160 6 16.00Simulation #7 100 15 180 6 18.00Simulation #8 200 5 60 6 6.00Simulation #9 200 6.5 80 6 8.00Simulation #10 200 8.5 100 6 10.00Simulation #11 200 10 120 6 12.00Simulation #12 200 11.4 140 6 14.00Simulation #13 200 13.4 160 7 18.67Simulation #14 200 15 180 8 24.00Simulation #15 400 5 60 10 10.00Simulation #16 400 6.5 80 8 10.67

Simulation #17 400 8.5 100 8 13.33Simulation #18 400 10 120 9 18.00Simulation #19 400 11.4 140 12 28.00Simulation #20 400 13.4 160 13 34.67Simulation #21 400 15 180 13 39.00Simulation #22 500 5 60 10 10.00Simulation #23 500 6.5 80 10 13.33Simulation #24 500 8.5 100 10 16.67Simulation #25 500 10 120 11 22.00Simulation #26 500 11.4 140 16 37.33Simulation #27 500 13.4 160 16 42.67Simulation #28 500 15 180 19 57.00Simulation #29 600 5 60 13 13.00Simulation #30 600 6.5 80 13 17.33Simulation #31 600 8.5 100 16 26.67Simulation #32 600 10 120 17 34.00

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Results cont.Simulation No.

Droplet diameter, d (μm)

Velocity, v (m/s)

Flow rate, Q (L/min)

Time to extinguish fire (s)

Total water used (Litres)

Simulation #33 600 11.4 140 19 44.33Simulation #34 600 13.4 160 22 58.67Simulation #35 600 15 180 29 87.00Simulation #36 800 5 60 28 28.00Simulation #37 800 6.5 80 23 30.67Simulation #38 800 8.5 100 35 58.33Simulation #39 800 10 120 40 80.00Simulation #40 800 11.4 140 53 123.67Simulation #41 800 13.4 160 61 162.67Simulation #42 800 15 180 76 228.00Simulation #43 1000 5 60 71 71.00Simulation #44 1000 6.5 80 72 96.00Simulation #45 1000 8.5 100 119 198.33Simulation #46 1000 10 120 151 302.00Simulation #47 1000 11.4 140 173 403.67Simulation #48 1000 13.4 160 208 554.67Simulation #49 1000 15 180 256 768.00

Figure 7. Simulation #4 Spray angle

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• Additional simulations were ran with optimization and increased accuracy

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Results cont.

0 200 400 600 800 10000

20

40

60

80

100

120

140

160

180

Droplet size vs Time to extinguish

Droplet size vs time to extinguish

Droplet size (μm)

Tim

e to

ext

ingu

ish

fire

(s)

• Droplet sizes all have a constant velocity and flow rate of 11.4 m/s and 140 L/min respectively

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Figure 8. Simulation #4 optimized spray angle

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Discussion and recommendations• Simulations show that having small droplet sizes and having a low to

medium velocity and flow rate is key in extinguishing the fire in this situation

• To further support the results from this study a wider range of simulations would have been run, which would include a variety of different characteristics and values.

• To further improve the accuracy of the results all simulations could have been run with a fine mesh opposed to a coarse/medium mesh but this would be at a computational cost

• In addition, creating a more realistic fire scenario that is a true representation of an average living room would improve the accuracy of the results.

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Conclusion• This study shows the importance of implementing

a fire sprinkler in a domestic premise

• Fires in domestic premises could be extinguished within seconds if the optimum characteristics are selected

• Hopefully in the future we can see progression for the implementation of fire sprinklers in homes

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Thanks for listening

Any questions?

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References• Bourque, M. J & Svirsky, T.A. (2013). Computational modeling of fire sprinkler spray characteristics using the fire dynamics

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References cont.