Dissertation - Study of sprinkler spray characteristics in domestic premises

Faculty of Science, Engineering and Computing

School of Mechanical and Automotive Engineering

MEng (Hons) Degree in Mechanical Engineering

Module Code: ME6014

Name: Damien Omar Mason

KU Number: K1110597

Project Title: Study of sprinkler spray characteristics in

domestic premises

Date: 22nd April 2016

Supervisor: Dr. Siaka Dembele

WARRANTY STATEMENT

This is a student project. Therefore, neither the student nor Kingston University

makes any warranty, express or implied, as to the accuracy of the data nor

conclusion of the work performed in the project and will not be held responsible

for any consequences arising out of any inaccuracies or omissions therein.

ii

Acknowledgements

I would like to thank Kingston University for giving me the opportunity to study

a MEng in Mechanical Engineering.

I would like to thank my supervisor, Dr. Siaka Dembele, for his continued

support and guidance throughout my project. He ensured that I had a thorough

understanding of the requirements of the project and allowed me to expand my

knowledge on fires, fire suppression and fire sprinklers.

I would like to thank my mother, father and little brother for their support.

I would like to thank my friend Hugh Jones, who has been a great classmate ever

since we met in foundation year. We have a great friendship and have always

supported each other; he has made my university experience very enjoyable.

Finally, I would like to thank my partner Kalifa Coleman-‐Best who has

continually supported me through out my entire degree, has always encouraged

me to be the best I can be and thrive in Engineering. I would not have got this

far without her being by my side.

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Abstract On completion of this dissertation, research was carried out on the classification

of fires, types of fire sprinkler systems, fire statistics in United Kingdom and

characteristics of fire sprinklers. This research is important as it helped to

determine what are the key characteristics of a fire sprinkler, how those

characteristics affected the fire extinguishing process and demonstrated the

importance of their implementation in domestic premises. This research was

completed with both the analysis of research papers and the use of fire statistics

published by the UK government.

Once the optimum characteristics were determined, a real life scenario was

created using the Fire Dynamic Simulator software. Simulations were then

carried out and the results were analyzed; the Fire Dynamic Software was used

as it provides detailed analyses of fire behaviour.

The research indicated that the optimum characteristics were small-‐scale

droplet sizes with low to medium velocities and flow rates. With these

characteristics a variety of fires could be extinguished in seconds, which then

prevent fire growth and fire spread. These results are very important as they

demonstrate and reiterate the effectiveness of fire sprinklers in domestic

premises, the implementation of fire sprinklers in domestic premises can save

hundreds of lives on a yearly basis

iv

Glossary

Term Definition

Frangible

bulb Heat sensitive bulb element

Water flux The rate of flow of water per unit area

Momentum Force of a body or object when it is moving

Atomization The reduction or separation into small particles or fine spray

Inertia The inability of a body to change its state of rest or motion

Buoyant The ability to rise to the top of a liquid or gas

Flashover

The temperature at which the heat generated is high enough to

ignite an object simultaneously

E coefficient

A parameter that is obtained experimentally and is used in Fire

Dynamic Simulator when complicated fuels are being used

Over

engineered

Designing a product more complicated than it needs to be for

its application.

v

List of symbols

Symbol Description

μm Micrometer or Micron (Measurement of length)

m Meter (Measurement of length)

m.s 1/2

Meter seconds to the power of 0.5 (Heat response of element in

seconds)

oC Degree Celsius (Measurement of temperature)

K Degree Kelvin (Measurement of temperature)

L/min Litres per minute (Measurement of volume flow over time)

m/s Meters per second (Measurement of length over time)

J/s Joules per second (Measurement of power over time)

W Watts (Measurement of power)

S Seconds (Measurement of time)

m3/s Cubic meters per second (Measurement of volume over time)

Kg/m3 Kilograms per cubic meters (Weight over volume)

KJ/Kg -‐ K Kilo Joules per kilogram Kelvin (Power per mass in temperature)

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List of figures

Figure 1 Modern fire sprinkler head, (Dr. Jhun, 2015) ..................................................... 3

Figure 2 Henry. S. Parmelee, Automatic fire extinguisher, (Woodford, C. 2014) .. 4

Figure 3 Fire structure and regions, (2015) .......................................................................... 8

Figure 4 Differences in surface area, (2007-‐2009) .......................................................... 10

Figure 5 Spectrum of droplet diameters, (G. Grant et al. 2000) ................................. 16

Figure 6 Water flux, (2015) ....................................................................................................... 18

Figure 7 Sprinkler spray shapes, (Sheppard, 2002) ........................................................ 19

Figure 8 Sidewall sprinkler head, (Archtoolbox, 2016) ................................................ 19

Figure 9 Outer spray angle, (Rein, 2008) ............................................................................. 20

Figure 10 Process of atomization, (Marshall, 2004) ....................................................... 20

Figure 11 Starting FDS using command prompt, (2016) .............................................. 22

Figure 12 FDS input file for burning couch, (2016) ........................................................ 24

Figure 13 Smokeview visual of burning couch & temperature slice file, (2016) 25

Figure 14 Smokeview visual of fire suppression using a fire sprinkler, (2016) . 26

Figure 15 Typical heat releases vs. time in t2-‐fire characterization, (Kim, 2000)

...................................................................................................................................................... 30

Figure 16 International Sprinkler Sensitivity Ranges, Response Time Index

(RTI) versus Conductivity (C). For SI units: 1ft = 0.305m, (Madrzykowski,

2002) .......................................................................................................................................... 32

Figure 17 Distance travelled when droplets achieve 95% of terminal velocity

(m), (Sheppard, 2002) ........................................................................................................ 38

Figure 18 Simulation domain, (2016) ................................................................................... 52

Figure 19 Simulation #5 -‐ Simulation after 33.3 seconds, (2016) ............................ 53

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Figure 20 Simulation #5 -‐ Slice file temperature at 34.4 seconds, (2016) ............ 53

Figure 21 Simulation #5 -‐ Activated fire sprinkler after 39.2 seconds, (2016) .. 54

Figure 22 Simulation #5 -‐ 1 second after activated fire sprinkler, (2016) ........... 55

Figure 23 Simulation #5 -‐ Fully extinguished fire after 5 second after fire

sprinkler activation, (2016) ............................................................................................. 55

Figure 24 Simulation #49 -‐ Spray angle, (2016) .............................................................. 57

Figure 25 Droplet size vs. Time to extinguish (Constant velocity and flow rate

11.4 and 40 respectively), (2016) ................................................................................. 60

Figure 26 Simulation 7 with optimized spray angle, (2016) ....................................... 63

Figure 27 Velocity vs. Time to extinguish (droplet size of 100μm), (2016) ......... 78

Figure 28 Velocity vs. Time to extinguish (droplet size 200μm), (2016) .............. 78


Figure 30 Velocity vs Time to extinguish (droplet size 500μm), (2016) ............... 79



Figure 33 Velocity vs. Time to extinguish (droplet size 1000μm), (2016) ........... 81

Figure 34 Navier-‐Stokes equations (NASA, 2016) ........................................................... 81

List of tables

Table 1 Simulations 1-‐49 results, (2016) ............................................................................ 58

Table 2 Optimized results -‐ Spray angle 20,70, (2016) ................................................. 62

Table 3 Refined mesh results -‐ grid size 0.05m, (2016) ................................................ 64

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Abbreviations

• NIST – National Institute of Standards and Technology

• USFA – U.S Fire Administration

• BFRS – Bedfordshire Fire and Rescue Service

• HRR – Heat release rate

• RTI – Response time index

• FDS – Fire Dynamic Simulator

• SMV – SmokeView

• ADD – Actual density delivered

ix

Table of Contents

Acknowledgements ......................................................................................................... ii

Abstract ............................................................................................................................. iii

Glossary .............................................................................................................................. iv

Over engineered .............................................................................................................. iv

List of symbols ................................................................................................................... v

List of figures .................................................................................................................... vi

List of tables .................................................................................................................... vii

Abbreviations ................................................................................................................ viii

1.0 Introduction ................................................................................................................ 1

1.1 Background .......................................................................................................................... 3

1.2 Aims of study ....................................................................................................................... 5

1.3 Deliverables ......................................................................................................................... 5

2.0 Fires and Fire sprinklers ........................................................................................ 6

2.1 Fires ........................................................................................................................................ 6

2.2 Fire Sprinklers ................................................................................................................. 11

2.3 Fire suppression method using water ..................................................................... 13

2.4 Spray Characteristics ..................................................................................................... 15

3.0 Fire Dynamics Simulator 6 (FDS) & SmokeView (SMV) ............................ 21

3.1 Introduction to FDS & SMV .......................................................................................... 21

3.2 Integration & application of software ...................................................................... 22

3.3 Case study .......................................................................................................................... 23

4.0 Literature review ................................................................................................... 26

x

4.1 Fire suppression by water sprays ............................................................................. 26

4.2 Heat release rate of burning items ........................................................................... 28

4.3 Residential sprinkler systems .................................................................................... 31

4.4 Overview of sprinkler technology research .......................................................... 33

4.5 Characteristics of pool fire burning .......................................................................... 34

4.6 Computational modeling of fire sprinkler spray characteristics using the

fire dynamics simulator ....................................................................................................... 36

4.7 Spray characteristics of fire sprinklers ................................................................... 37

4.8 Modeling aspects of sprinkler spray dynamics .................................................... 38

5.0 Selected fire scenario ............................................................................................ 40

6.0 Selected Fire Sprinkler System .......................................................................... 41

6.1 Sprinkler system / piping ............................................................................................ 41

6.2 Sprinkler spray / nozzle ............................................................................................... 41

6.3 Trigger system ................................................................................................................. 41

6.4 Fluid ..................................................................................................................................... 41

7.0 Calculations and specifications ......................................................................... 42

7.1 Flow rate ............................................................................................................................ 42

7.2 Orifice diameter .............................................................................................................. 42

7.3 Droplet diameter ............................................................................................................ 43

7.4 Velocity ............................................................................................................................... 43

7.5 Heat release rate ............................................................................................................. 44

8.0 Writing FDS Input File .......................................................................................... 45

8.1 Specifications ................................................................................................................... 45

8.2 Starting input file ............................................................................................................ 45

8.3 Computational mesh ...................................................................................................... 46

8.4 Miscellaneous parameters ........................................................................................... 48

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8.5 Creating obstruction ...................................................................................................... 48

8.6 Pyrolysis model and Fuel ............................................................................................. 49

8.7 Particles, droplets and size distribution ................................................................. 50

8.8 Introduction of sprinkler & Fire suppression by water .................................... 50

9.0 Running FDS Simulation ...................................................................................... 52

10.0 Analysis of FDS results ....................................................................................... 56

10.1 Results .............................................................................................................................. 56

10.2 Optimization .................................................................................................................. 61

10.3 Accuracy .......................................................................................................................... 63

10.4 Discussion ....................................................................................................................... 65

11.0 Conclusion .............................................................................................................. 67

12.0 Bibliography .......................................................................................................... 69

13.0 References ............................................................................................................. 70

14.0 Appendices ............................................................................................................ 75

14.1 FDS simulation input file ........................................................................................... 75

14.2 Graphical results .......................................................................................................... 78

14.3 Navier-‐Stokes equations ............................................................................................ 81

1

1.0 Introduction

The United Kingdom public sector information website collected fire statistics

in 2013-‐14 which provided a detailed analysis of location of fires, causes of fires,

casualties and other important fire related statistics. In 2013-‐14 there were 322

fire related deaths recorded in the United Kingdom, this is the lowest recording

in the last 50 years. Out of the 322 fire related deaths, 258 of them were in

domestic premises, making 80% of fire related deaths within the United

Kingdom domestic based. Almost one fifth of total fires in the United Kingdom in

2013-‐14 were in domestic premises, this was a total of 39,600. 88% of fires in

domestic premises were caused by the misuse of equipment or house hold

appliances with the main source of ignition being cooking appliances, faulty

appliances, careless handling of hot substances and/or fire, chip pan fires and

incidences of placing fabrics to close to heat or fire (Department of Communities

and Local Government, 2015).

It is an obvious sign that the efforts and research gone into fire suppression and

fire behaviour have improved in the United Kingdom in the last 50 years. New

standards have been incorporated and previous ones have been revised in

order to see a reduction in fatalities and time taken to extinguish fires before

they intensify and spread. However with more than three quarters of fire

related deaths occurring in domestic premises, there is still much needed room

for improvement in this area in particular.

2

At the moment fire suppression systems are not integral in domestic premises

and although most domestic premises have and are advised to have smoke

alarms, the law does not require you to have one installed. Smoke alarms alone

are not an adequate source to reduce the amount of deaths caused by fires and

it is not advised that an individual is to store a fire extinguisher in their home

with the intention of fighting a fire. Smoke alarms are reliant on having fully

charged batteries and fire extinguishers are reliant on an individual locating

them and using the correct one for a specific type of fire. Automatic fire

sprinklers provide an alternative fire suppression system, as the name states,

this type of fire sprinkler will trigger automatically to deliver an effective and

efficient method of fire suppression.

Fire sprinkler systems are fire suppression systems mainly used in industrial

buildings, offices, shops, schools and other important buildings that require fire

protection. These systems are a network of water pipes that run through the

ceiling rooms of buildings, and at targeted locations in the building a hole will

be placed in the pipe as a means of escape for the water into the room below.

These holes will be fitted with sprinkler heads similar in mechanism to water

valves but in place of a hand operated component, a heat sensitive element such

as a frangible bulb or two spring metal arms held together by a metal with a

relatively low melting point is used. The water in the fire sprinkler system is

either supplied from a water mains or a water tank located close by (Woodward,

2016). Fire sprinkler systems are automatic and are active fire protection

systems, which make them the single most effective fire suppression method for

this application. Having fire sprinkler systems installed can extinguish a fire

3

before it spreads, significantly reducing fatalities, and reducing property loss

and insurance costs.

Figure 1 Modern fire sprinkler head, (Dr. Jhun, 2015)

A fire related death in a building protected by a fire sprinkler system is a rare

occurrence anywhere in the world (Davies, 2013). Currently fire sprinkler

systems are not commonly seen installed in domestic premises in the United

Kingdom, as the benefits and potential of domestic sprinklers are still not fully

realized. With such a large number of fire related deaths occurring in domestic

premises, the installation of fire sprinkler systems would be the most effective

fire suppression method, making a significant reduction in deaths.

1.1 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

in the United States. This sprinkler system was based on previous manual

systems that had been developed. In Parmelee’s system the hole which water

would escape was covered with a simple metal cap fixed with a solder that was

specifically designed to melt in a fire, releasing the water (Woodford, 2014).

4

Although this simple design was not perfect, it has been the foundation that

current fire sprinklers are based on.

Figure 2 Henry. S. Parmelee, Automatic fire extinguisher, (Woodford, C. 2014)

With current codes and regulations now requiring the use of these systems in

public buildings, it is of the utmost importance that they are optimally designed.

Current fire sprinkler systems are split into various different types dependent

on the application such as pipe system, nozzles/sprinkler head and water

supply. Sprinkler systems also have key characteristics to be considered such as

velocity, droplet size, flow rate and spray angle.

Fire sprinkler systems have developed over time due to the fact that the

knowledge on fires has grown. It is important to recognize that there are

different classes of fires; fires can behave differently under different

circumstances and in different environments and there are key characteristics

required for a fire to be maintained.

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1.2 Aims of study

The purpose of this study is 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.

In order to do this, research was completed on:

• Fire behaviour

• Fire suppression systems

• House fire statistics

• Fire sprinkler systems

• Fire dynamics simulator (FDS) and Smoke view (SMV)

These will help make an informed decision concerning what the optimum

characteristics should be. Once the key characteristics have been selected, a

simplified real life fire scenario will be simulated in the CFD software FDS; a

detailed analysis of the results will be made.

1.3 Deliverables

By the end this study, the following material will be delivered:

• Description of different types of fires and fire sprinkler systems

• Literature review relating to the optimum characteristics of fire

sprinklers and parameters affecting those characteristics

• Selected fire scenario and fire sprinkler system

• Calculations to select fire sprinkler system characteristics

• FDS & SMV simulation images

• Analysis of results

6

2.0 Fires and Fire sprinklers

2.1 Fires

A fire is the visible result of a chemical reaction between fuel, oxygen and heat.

This chemical reaction is called the process of combustion. The temperature of

the fuel must be high enough for combustion to begin, also known as the

ignition temperature, the fuel will react with oxygen to release heat energy

causing a fire (Science learn, 2009).

Types of fires

Fires are not all the same; they are categorized into different classes, which are

defined by different fuels and different methods of extinguishing:

• Class A –fires that are ordinary combustibles and consist of fuels such as

wood, paper, fabric, plastic and trash. A simple stream of water can be

used for such fires.

• Class B –fires that are flammable liquids such as gasoline, petroleum, oil

and paraffin. Water should not be used for such fires, to extinguish these

fires a Halon extinguishing agent or a foam extinguishing method must

be used.

• Class C – fires that are combustible gasses such as propane, butane,

methane, etc.

• Class D – fires that are combustible metals such as magnesium,

potassium, etc.

• Class E – fires that involve electrical equipment such as motors or

appliances. Water should not be used for such fires as this can causes a

greater hazard.

7

• Class F – fires which involve cooking oils in well-‐insulated cooking

appliances located in commercial kitchens. These fires are characterized

by high flash points. Water mist is the most effective way of

extinguishing such fires.

(Fire equipment manufacturer’s associate, 2015)

A class A fire is a typical type of fire that occurs in domestic premises, therefore

this study focused on this category (Department of Communities and Local

Government, 2015).

Fire structure

The structure of a turbulent fire can be divided into four separate regions for

analysis:

• Fuel rich core – This region is considered as a non-‐reacting region, this is

because the generation of heat release mostly appears in the region

above, the intermittent region. This region is approximately 20% of the

average flame height and is above the surface of the fuel.

• Intermittent region – Above the fuel rich core lays this region, which is a

reacting region, heat is released as decomposition particles caused by the

fire, react with the air that is brought into the fire. Products are then

produced from the combustion such as water vapor, carbon monoxide,

soot particles and carbon dioxide.

• Plume region – This region is also considered as a non-‐reacting region,

this is due to the rapid decrease in chemical reactions, the temperature

drops in this region as air is brought in. There will be some traces of

8

combustion products such as soot or carbon monoxide but due to the

low temperature reactions do not fully take place.

• Ceiling jet – This region appears inside or in confined areas, this region is

a non-‐reacting region. It consists of gases and products from the fire

rising to the ceiling and spreading outwards.

The structure and shape of fires are very important in understanding fire

behaviour and fire suppression. It is known that the shapes of fires will

change with time and the circumstances surrounding it. Typically the shape

of a turbulent fire can be described as a cylindrical or cone link with the

bottom taken as the pool diameter and the top given by the visible flame

height. Figure 3 shows a typical structure and the different regions of a fire

(Hamins et al., 1995).

Figure 3 Fire structure and regions, (2015)

Fire behaviour

Another important characteristic of fires is their behaviour; fires do not all

behave in the same way with external factors dictating this. Fires can burn

differently, range in different temperatures, have different color flames and

initiate differently. All fires produce gases but some fires produce deadlier

9

gasses than others. The way in which a fire behaves can depend on the fuel and

other factors that affect the fuel, such as initial conditions, surface area, heat

produced, and availability of fuel and oxygen (Science learn, 2009).

The temperature at which fuels begin combustion varies with different fuels.

For every fuel there is a certain amount of heat energy required to change that

fuel into a gas, if it is not already. After that, more heat energy is required to

create the chemical reaction with oxygen, causing the production of a fire

(Science learn, 2009).

The ambient conditions that affect the fuel relate to the humidity of the

atmosphere; if the air is dry it will contribute in drying the fuel, making ignition

quick and easy alternatively if the air is moist ignition will become difficult

(Science learn, 2009).

The rate at which a fire initiates and burns is dependent on the surface area of

the fuel. Fuels with larger surface areas have faster combustion reactions; this is

due to the fact that more oxygen molecules can collide with the surface of the

fuel per second. You can increase the surface area of a solid by breaking it up

into smaller pieces, this can be seen with wood, small pieces will catch fire

quickly and more easily than larger pieces (Science learn, 2009).

10

Figure 4 Differences in surface area, (2007-‐2009)

The amount of heat energy release varies in different fuels; some fuels retain a

lot of energy while others do not. The amount of energy release dictates how

quickly the fuel burns; more heat energy will allow the reaction with oxygen to

occur very quickly (Science learn, 2009).

The amount of fuel available will dictate the intensity and duration that the fire

will burn at in terms of heat energy output or heat release rate. The more fuel

available the more intense and longer the fire will burn for. The amount of fuel

available is also known as the ‘fuel load’ (Science learn, 2009).

Similarly to the amount of heat energy available, the amount of oxygen available

will depend on how quickly the reaction will occur and the rate of burning. A

low concentration of oxygen also known as the ‘back draught’ will slow down

burning and cause smoldering, if there is then an increase in oxygen the fire will

immediately grow (Science learn, 2009).

11

Pool fires & Jet fires

When fires begin they can start as one of the following:

• A pool fire -‐ a turbulent diffusion fire resulting from the combustion of a

fuel, where the fuel has zero or low initial momentum.

• A jet fire -‐ a turbulent diffusion fire resulting from the combustion of a

fuel continuously released with some significantly high initial

momentum.

(Health and safety executive, 2016)

2.2 Fire Sprinklers

Fire sprinkler systems are fire suppression systems that are commonly used in

industrial buildings, offices, residential buildings and other buildings that are

deemed important. Due to the frangible bulb component in fire sprinklers, they

are classified as active fire protection measures.

Types of fire sprinklers systems

There are several different types of fire sprinklers with different functionality

between them; this is because they have different applications.

Wet pipe

The wet pipe system is the quickest responding system, as per the name this

system always has water within the pipes of the system; this water is also under

a considerable amount of pressure. The combination of these two factors allow

for a rapid response when the sprinkler head is activated. The wet pipe system

is commonly used in buildings such as offices, it is cost effective, easy to

12

maintain, easy to install and reliable. The risks with this system is that if the

pipes are damaged there is the possibility of leaks and if the system is installed

in an environment with extremely cold weather, the water is at risk of freezing

(Tyco, 2016).

Dry pipe

In contrast to the wet pipe system, this system does not have water readily

available within the pipes of the system, instead of water the pipes are filled

with pressurized air; this pressurized air keeps a valve closed that retains the

water. When the sprinkler head is activated, the air is released, which allows the

water to flow through the pipes and then out through the sprinkler head. The

obvious downside to this is that there is a delay before the water actually exits

the sprinkler head however the advantage of this system is that it releases a

large amount of pressurized water. The dry pipe system is a very expensive and

complicated system to install and maintain. These systems are used in buildings

such as warehouses where there is exposure to extremely cold temperatures

that will cause a risk of the water freezing in the pipes (Tyco, 2016).

Alternate pipe

This system is a combination of the wet pipe system and dry pipe system; this

alternation happens between different times of the year; during the summer

time when there is no risk of the water freezing, the system is filled with

pressurized water, achieving a wet pipe system. During the wintertime when

there is a risk of the water freezing the pipes are instead filled with pressurized

air. Of course this system is extremely costly and difficult to install and maintain

13

but can be used across various types of buildings where there is a risk of the

water freezing only during winter (Tyco, 2016).

Pre-‐action pipe

This system is similar to the dry pipe system in which it initially does not have

the system pipes filled with water but with compressed air. What differentiates

this system from a dry pipe system is that this system requires two triggers. The

first trigger being a device such as a smoke detector, once this trigger is

activated, water is then released into the pipe system. The second trigger will be

the fire sprinkler head, once activated will release the water out of the sprinkler

head (Tyco, 2016).

Deluge pipe

Similar in functionality to the pre-‐action pipe system, the deluge pipe system

requires two trigger activations. The difference between the pre-‐action system

and this system is that there is a manual component for the first trigger, such as

a button, a lever or a device that is similar. These systems are commonly seen in

chemical plants or hazardous areas (Tyco, 2016).

2.3 Fire suppression method using water

Water spray

Water spray is the commonly seen mode of spray; which is defined by the size

of droplets released from the sprinkler head. The range is typically between

100-‐1000µm (Grant et al., 2000). Water spray systems can be categorized in

either medium or high velocity.

14

High velocity water sprays provide coverage in wide areas over a short amount

of time. To create this high velocity the system would have an increased flow

rate and pressure.

Medium velocity sprays provide better coverage on a smaller area than high

velocity sprays but are used in different applications where the size and type of

fire risk is not as great (Tyco, 2016).

Water mist

Water mist is defined by the droplet sizes being in the range of 10-‐100 µm. This

mode of spray is highly efficient and effective way of fire suppression, this is due

to the size of the water droplets; the smaller droplets allow coverage of a larger

surface area, this in turn increases the heat absorption of the droplets,

extinguishing the fire quickly. The heat of the fire converts the water mist into

steam, which then covers the fire and prevents oxygen from reaching it; the

steam also reduces the heat output.

Not all types of fires can be easily extinguished with smaller droplets alone,

other characteristics of the fire sprinkler are key to ensure that the droplets get

to the fire core; even then, an increase in droplet size may be necessary (Tyco,

2016).

15

2.4 Spray Characteristics

When designing or selecting a fire sprinkler system it is very important to

consider the characteristics of the spray, all equally as important as the other

contributing to the extinguishment of a fire. The spray characteristics are

dependent on the type of fire, heat release rate and size of the fire that could

possibly grow and the dimensions of the room.

Flow rate (Volumetric)

The flow rate of a fire sprinkler is the rate at which a volumetric measure of

water is released over a given amount of time and is defined by:

Q =V × A (m3 / s) or (l / s)

Where :Q = Flow rateV =VelocityA =Cross− sec tional area

The flow rate is determined by analyzing the type of fire then finding how much

water is required to be stored to extinguish a fire.

Droplet size

The droplet size is defined by:

d = 6×Vtoti×π

3 (mm) or (µm)

16

Where :i = Droplet of equal volumed = Droplet diamaterπ= piVtot = Total volume

(Grant et al., 2000)

This parameter is important as it dictates whether or not the droplets can

efficiently penetrate through the various regions of a fire and reach the fire core

without completely evaporating. It must be noted that increasing droplet size

has an adverse effect on the pressure within the pipe system. However

increasing the droplet size increases the probability of the droplets penetrating

the fire and also increases the velocity (Grant et al., 2000).

Figure 5 Spectrum of droplet diameters, (G. Grant et al. 2000)

The range of droplet sizes for fire sprinklers should be ideally between fine and

average (Grant et al., 2000).

17

Velocity

The velocity of the particles are defined by rearranging the volumetric flow rate

equation:

V =4×Qπ × d 2

(m / s)

Where;Q = Flow rated =Orifice diameterπ = pi

This characteristic plays an important part in whether or not the droplets are

able to reach the core of the fire. Due to gases and products from the fire flowing

upwards, which can be seen in Figure 3, the velocity of the droplets must be

high enough to counteract this upwards movement and penetrate through the

gases. The height of the room must also be considered; higher rooms will have

higher plume regions, which will require higher velocities (Bourque, 2013).

Water flux

The water flux is defined as:

J = QA(l / s /m2 )

Where :J =Water fluxQ = Flow rateA=Cross-sectional area

18

The water flux is a measure of volumetric flow rate over cross-‐sectional area

and is the amount of water that is released under the sprinkler (Bourque, 2013).

It is dependent on the intensity of the fire, if you have a fire with a high power

output, a large amount of water will be required to cover that area and

extinguish the fire.

Figure 6 Water flux, (2015)

Shape of spray (Spray angle)

The shape of spray dictates the spray coverage on the fire. As per Figure 7 and 8

there are different types of spray patterns. The traditional and modern upright

sprinkler head project the spray upwards and have deflectors that spray the

water below, the traditional upright provides ceiling protection by wetting and

cooling the ceiling, opposed to the modern upright. Commonly seen pendant

sprinkler heads hang down from the ceiling and spray the water in a circular

19

pattern, early suppression fast response sprinkler heads provide optimum

water delivery and water flow by spraying water over a small area and direct

the spray downwards (Sheppard, 2002).

Figure 7 Sprinkler spray shapes, (Sheppard, 2002)

Sidewall sprinkler heads are attached to walls; they spray water away from the

wall in a semi-‐circular pattern and wet and cool the wall below using a

secondary deflector (Archtoolbox, 2016).

Figure 8 Sidewall sprinkler head, (Archtoolbox, 2016)

One way to define the shape of spray is the spray angle; in every shape of spray

there are two different spray angles that exist. These spray angles are the inner

and outer spray angle. The area inside of the spray where there is no water

20

defines the inner spray angle and the outer area of the spray defines the outer

spray angle (Bourque, 2013).

Figure 9 Outer spray angle, (Rein, 2008)

Spray offset

The distance from the sprinkler head in which water droplets are fully formed is

called the spray offset (Bourque, 2013). The process of which the droplets are

produced is called atomization; the stages of atomization are described in figure

10 (Marshall, 2004).

Figure 10 Process of atomization, (Marshall, 2004)

21

3.0 Fire Dynamics Simulator 6 (FDS) & SmokeView

(SMV)

3.1 Introduction to FDS & SMV

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

(shown in appendix 14.3) appropriate for low speed, thermally driven flow

(Pool fires) with an emphasis on smoke and heat transfer.

FDS was publicly released in February 2000. To date, roughly half of the

applications of the software have been used for the design of smoke handling

systems and sprinkler/detector activation studies. The other half consists of

residential and industrial fire reconstruction. Throughout the years of

development, FDS has been aimed at solving practical fire problems in fire

suppression, while at the same time providing a tool to study fundamental fire

dynamics and combustion

Smokeview is a scientific software that comes packaged with FDS. It is tool

designed for visualizing numerical prediction generated by fire models such as

FDS. FDS and Smokeview are primarily used to model and visualize time-‐

varying fire phenomena. Smokeview performs visualizations by displaying time

dependent tracer particle flow, animated contour slices of computed gas

variables and surface data. Smokeview also presents contours and vector plots

of static data anywhere within a simulation scene at a fixed time (NIST Special

Publication 1019, 2015).

22

FDS & Smokeview must be discussed as the selected simulations are to be

carried out on this software to evaluate the optimum sprinkler spray

characteristics for fire suppression. It is also important to discuss why this

software is being used for this project.

3.2 Integration & application of software

A single text-‐based input file that ends with the file extension is required to start

an FDS simulation. The input file can be written using a text editor such as

Microsoft word or more commonly used notepad. The simulation is started

directly via the command prompt i.e. job_name.fds.

Figure 11 Starting FDS using command prompt, (2016)

Once the simulation has been completed, output files will be produced and

Smokeview will provide a visual aid for the simulation over a specified time,

these output files and visual aid describe the performance of the simulation.

23

In order to create a FDS input file there are certain steps that are required to be

completed, these are described in greater detail in 8.0.

FDS and Smokeview was used in this project as it has ideal applications; these

include fire sprinkler activation study and fire suppression. When using this

software for such applications, it will take the following key characteristics into

consideration that are crucial for this project.

• Sprinkler head

• Droplet diameter

• Activation temperature

• Response time index

• Flow rate

• Spray offset

• Particle velocity

• Spray angle

• Heat release rate

The purpose of the simulation was to create a typical fire scenario in a domestic

premise with real life values and demonstrate how to extinguish that fire with

pre-‐determined characteristics for the fire sprinkler system.

3.3 Case study

To provide a better understanding of FDS and Smokeview and how it relates to

this project, an analysis of two of the existing input files took place.

24

The first example is of a couch situated in a living room that is burning over a

period of 600 seconds. This is a very useful example, which is relative to this

study as it demonstrates a fire scenario that could occur in a domestic premise

and provides output values. The Input file for the burning couch can be seen in

figure 13 where all boundaries and parameters about the scenario are defined.

Figure 12 FDS input file for burning couch, (2016)

25

Once the simulation is completed, the Smokeview visual can be viewed, this is

shown in figure 13; where the couch has been burning for a period of 500

seconds. Everything that can be seen in the Smokeview file has been specified

within the input file.

Figure 13 Smokeview visual of burning couch & temperature slice file, (2016)

Flow patterns can be seen and slices of data can be shown, either in the gas or

solid phase by including the slice file and or boundary file name list group in the

input file. A slice file of the burning couch can be seen in figure 14, which

displays the temperature on a specified plane; this can also be on a line or

volume depending on the boundaries set. Other quantities such as conductivity,

enthalpy and heat release rate can also be specified using the slice file.

The second example is of a fire, which is then suppressed using a fire sprinkler

after a specified amount of time; if required the fire sprinkler can also be

activated when the sprinkler head reaches a temperature that is specified

26

within the input file. This example is relative to this study as it demonstrates

fire suppression with the use of a fire sprinkler. Similarly to the previous

example, all parameters and boundaries of the fire scenario that are seen in the

Smokeview file must be specified within the input file.

Figure 14 Smokeview visual of fire suppression using a fire sprinkler, (2016)

4.0 Literature review

4.1 Fire suppression by water sprays

One of the first key topics researched include fire suppression. Grant et al.

explored the classification of fire types, fire suppression of class A fires, class A

fire characteristics and water spray qualities. This research paper is applicable

27

to my project as it directly relates to fire suppression using water sprays; water

sprays being an integral part of fire sprinkler systems.

A major point that was discussed in this paper was the extinguishment of class

A fires by water; it is important to note that the following are key components

to extinguishing these fires:

• Cooling the fuel surface – This reduces the burning rate and the rate of

fuel available to the fire; this in turn has a reduction on the heat release

rate. This method allows easier extinguishment of the fire.

• Cooling the flame zone directly – This reduces the rate of chemical

reactions for combustion, some of the heat normally used to support the

reaction is transferred into heating and evaporating the water droplets,

and this will provide an insufficient amount of heat needed to aid the

reaction for combustion.

• Volumetric displacement of oxygen – As the fire sprinkler provides water

vapor within the area that the fire exists, it displaces the oxygen away

from the fire, which reduces the rate of chemical reactions for

combustion. This has a similarly result to cooling the flame zone directly.

• Wetting combustible surface to control fire spread – Once the fire

sprinkler has activated, the water sprays distributed can pre-‐wet

combustible surfaces within the immediate range of the fire; this

provides a heat-‐sink which effectively delays ignition.


28

The information provided on class A fires are applicable to this project because

they are a common type of fire that occurs in domestic premises and is the type

of fire that will be used for the analysis.

The second major point discussed was the water spray characteristics, which

are required when considering the properties of fire sprinkler sprays. This

journal provides a quantitative way of calculating, number of droplets, droplet

diameter, total volume and total surface area per litre volume of the resulting

spray, which is defined below (Grant et al., 2000).

Vtot = i×π × d3

6(mm3)

d = 6×Vtoti×π

3 (mm) or (µm)

Stot = i×π × d2 (mm2 )

Where :i = Droplet of equal volumed = Droplet diamaterπ= piVtot = Total volumeStot = Total surface area per litre volume of resulting spray


4.2 Heat release rate of burning items

Another key topic researched was heat release rate. The heat release rate is a

critical parameter for the analysis of fire growth and is typically described as

the heat energy evolving on a per unit time basis. The heat release rate is

defined by:

29

Q.=αg × t

2

or

Q.=m

.×ΔHc

Where :

Q.= Heat release rate

t = Timeαg = Fire growth

m.=Mass− burning rate

Hc = Heat of combustion

The heat release rate is important as it has a major influence on the values

selected for the characteristics of the fire sprinkler systems. If a burning item

has a high heat release rate value, the sprinkler spray characteristics such as the

velocity and droplet size need to be able to accommodate it, otherwise the spray

will not be able to reach the base of the fire (Kim, 2000).

Kim et al. explored heat release rate by examining what it is, how it can be

calculated and providing experimental data on burning rates of typical furniture

in a room. This paper was selected due to the information provided, it was

deemed reliable due to the experimental method and applicability to my project

because of the burning materials used.

30

Figure 15 Typical heat releases vs. time in t2-‐fire characterization, (Kim, 2000)

When finding experimental values for the heat release rate, the value of Q.

m

(Maximum heat release rate) is given. If this value is used as the basis for

designing a fire sprinkler system, the fire sprinkler system will be over

engineered. As previously mentioned heat release rate is energy evolving on a

per unit time basis, which means that as time goes on, the heat release rate will

grow. From the experimental data (Table A, Kim et al., 2000) from this paper it

can be seen that the time it takes to reach this maximum value ranges from 90-‐

1000 seconds; it is not ideal for a fire to be burning for this length of time before

the fire sprinkler system reacts. This paper states that:

Q.=αg × t

2

Where :αg = Fire growth = 1000/(t1mw -t0 )2

t = timet 1mw= time to reach 1MWt0 = time to the onset of ignition

31

(Kim, 2000)

If values for t1MW and tO are provided then αg can be calculated. The value for t

will then be the ideal time for a sprinkler to activate after a fire has started; this

is typically between 30-‐50 seconds. Inserting these values into the heat release

rate equation will provide the heat release rate for the specified time, t.

4.3 Residential sprinkler systems

Madrzykowski et al. discussed the importance of automatic sprinkler systems

being incorporated in residential premise. This paper is relevant to this project

as it discusses the research and development for a solution to fires in homes; it

also contains statistics on fires in homes.

A very important topic discussed by Madrzykowski et al. is the measuring of

sprinkler sensitivity. The research and testing for sprinkler sensitivity was done

by several fire research institutes, which include FM Global Research, USFA,

BFRS and NIST.

In 1990 an agreement was reached within the International Standards

organization – sprinkler and water spray equipment group, to create a standard

for sprinkler sensitivity requirements and testing; this produced the standard

“Requirements and methods for sprinklers”. The standard was created by using

tests completed in labs that established ranges of sprinkler sensitivity

characteristics. These ranges of sensitivity are based both on the response time

index (RTI) of the device and on its conductivity (C). RTI is a measure of pure

32

thermal sensitivity, which indicates how fast the sprinkler can absorb heat from

its surroundings to cause activation. The conductivity factor is important in

measuring how much of the heat picked up from the surrounding air will be lost

to the sprinkler fittings and waterway. Figure 17 shows the ranges of sprinkler

sensitivity, which include standard, special, and fast response (Madrzykowski et

al, 2008).

Figure 16 International Sprinkler Sensitivity Ranges, Response Time Index (RTI) versus

Conductivity (C). For SI units: 1ft = 0.305m, (Madrzykowski, 2002)

Standard response sprinklers are the traditional sprinklers used in common

applications such as warehouses and offices; fast response sprinklers are the

newer type of sprinklers, which are used for very important and emergency

33

situations. Special response sprinklers are bespoke sprinklers that conform to

appropriate installation standards.

Sprinkler response time as a function of the temperature rating of the heat

sensitive element is well understood; that is, a 74°C rated sprinkler will operate

when its temperature reaches 74°C, plus or minus a few degrees.

The Response Time Index (RTI) gives a good measure of sprinklers sensitivity.

The smaller the RTI is the faster the sprinkler operation will be. Standard-‐

response sprinklers have an RTI range of 180 to 650 sec1⁄2ft1⁄2 (100 to 350

sec1⁄2m1⁄2), but the RTI range for residential sprinkler systems is around 50

to 90 sec1⁄2ft1⁄2 (28 to 50 sec1⁄2m1⁄2).

The conductivity describes the loss of heat from the sprinkler heat sensitive

element to the sprinkler frame; it’s mounting, and even the water within the

system (Madrzykowski et al, 2008).

It is important to understand the RTI as it is a parameter that can be adjusted in

the FDS input file.

4.4 Overview of sprinkler technology research

Yao examined an overview of continuing sprinkler technology research and

practical applications. The aforementioned research consists of the controlling

of variables of a fire sprinkler and development of tools and deterministic

computer models to predict fire protection performance. Similarly to the

previous paper on residential fire sprinklers, this paper discusses and explains

the response time index (RTI). Most importantly this paper provides a

34

quantifiable method of calculating the Response Time Index This is important to

the project as the response time index is a characteristic for fire sprinklers and

is a considered variable in the FDS software.

The response time index can be calculated as:

RTI =U12 ×m× ch× A

Wherem =mass of the elementc = specific heat of the elementh = convective heat transfer coefficient of the elementA = surface area of the element

(Yao, 2015)

The response time index is a given value on stock heat sensitive elements such

as frangible bulbs, but if it was necessary to improve the sprinkler system by

using a new or custom heat sensitive element, it may be required to calculate

this.

4.5 Characteristics of pool fire burning

In order for a fire sprinkler system to be designed and optimized it is important

to know the potential type of fire risk. Most common fires are pool fires, more so

in domestic premises therefore it is important to research the characteristics of

pool fire burning. Hamins et al. reviewed the characteristics, structure and

behaviour of pool fires with special regard to the flame shape, flame pulsation

frequency, flame height and detailed flame structure (Hamins et al., 1995).

35

Pool fires are fires resulting from the combustion of a fuel, where the fuel has

zero or low initial momentum and are configured horizontally. The fuel in pool

fires can be a liquid, gas or solid; the base of the fuel may be of non-‐uniform

geometry. Pool fires can be characterized by several parameters, which include

heat release rate and power radiated to the surroundings, pool fires can also be

affected by ambient conditions such as humidity and surrounding temperature.

The conditions affecting the fire influence the structure and potential risk of a

fire (Hamins et al., 1995).

Hamins et al. provided a detailed explanation on the flame shape and height. It

is commonly accepted that the more fuel available to the fire, the larger the heat

release rate will be and the higher the flame will be. Pool fire Froude modeling

suggest that the ratio of inertia to buoyant forces are the key in simulating the

fluid dynamic aspects of pool fires. Four regions can describe the structure of a

buoyant fire; a fuel rich core, the intermittent region, the plume region and the

ceiling jet; these regions are further explained in section 4.2. The shape and

height of a fire have important implications in terms of fire hazard. If a fire is in

an enclosed area, direct heat transfer to a ceiling may have dramatic

consequences in terms of time to flashover (NIST, 1995).

Knowledge of these factors is essential to understanding the structure and

behaviour of fires, this knowledge will aid in understanding how the fire

sprinkler characteristics has an affect on extinguishing a fire.

36

4.6 Computational modeling of fire sprinkler spray characteristics

using the fire dynamics simulator

Bourque et al. focused on the necessity for a fire sprinkler’s performance to be

tested and assessed before it can become a listed and approved fire sprinkler. In

reality when a fire sprinkler is produced, it will under go an actual density

delivered (ADD) test. An ADD test requires the use of large labs, many staff and

expensive equipment; to perform these tests can be time consuming and costly.

In order to reduce costs and time spent, computational fluid dynamics software,

namely fire dynamic simulator is used to simulate the fire sprinklers

performance. Bourque and Svirsky’s aim was to determine the accuracy of the

fire dynamic simulators prediction of water distribution of a fire sprinkler, and

compare these results to a test conducted in real life (Bourque et al. 2013).

Bourque et al. discussed the characteristics of a fire sprinkler and their

importance which directly relate to the project, it describes and acknowledges

that the major characteristics for characterizing a spray were shape of spray

(spray angle), velocity, droplet size, water flux and spray offset; these

characteristics are further described in section 5.2. It is also important to know

how accurate the fire dynamic software is, as this will support the use of the

software and the final results of the project.

Bourque et al. concluded that after the simulations and tests were conducted to

receive an accurate result from FDS for comparison, better approximations

must then be selected to have a better replication of the real scenario (Bourque

37

et al. 2013). Therefore to receive accurate results, the simulation must be as

close to the real life scenario as possible.

4.7 Spray characteristics of fire sprinklers

Sheppard discussed the lack of progression towards developing analytical

methods of calculating fire sprinkler effectiveness; this paper acknowledged

that this is mainly due to the lack of available information about initial spray

characteristics of fire sprinklers. Sheppard chose a wide selection of sprinklers

and conducts experiments on these, analyzing the results. Sheppard

acknowledged and discussed the key initial spray characteristics as the spray

velocity, droplet size and water flux (Sheppard, 2002).

Sheppard found that the average radial droplet velocity at a distance 0.2m from

the sprinkler orifice is 53% of the water velocity; the maximum spray velocities

ranged from 62% to 120% of the orifice water velocity with a statistically

significant trend for higher maximum velocities from pendant sprinklers .The

median droplet diameter increases with elevation angle and decreases with

increasing pressure. The water flux distribution varies with pressure and

sprinkler type that it is impossible to determine a universal flux distribution

(Sheppard, 2002).

Another useful topic discussed included the distance the droplets travelled

before it reached its highest attainable velocity. Figure shows that droplets

smaller than 0.001m reach their terminal velocity very close to the sprinkler,

38

where as droplets larger than 0.001m may travel a significant distance before

reaching their terminal velocity (Sheppard, 2002).

Figure 17 Distance travelled when droplets achieve 95% of terminal velocity (m),

(Sheppard, 2002)

This was important to know because if the droplet sizes do not have high

enough velocity, it will prove to be more difficult when extinguishing the fire;

the size of the droplets needed are dependent on the height of the room.

This research project acknowledges this project as it provides detailed

information about the sprinkler spray characteristics, including its behaviour of

these characteristics and the variety of factors, which may affect this. This is

very useful to know when designing a fire sprinkler and will prove to be useful

when extinguishing house fire.

4.8 Modeling aspects of sprinkler spray dynamics

Marshall et al. analyses the sprinkler spray performance, which depends on the

initiation, formation, dispersion and surface cooling characteristics of the sprays

created by fire sprinklers. While these mechanisms are clearly understood,

physical models detailing their behaviour are only now becoming available.

Marshal et al. characterizes sprinkler spray behaviour in a fire and presents

39

mathematical models describing the important physical processes for sprinkler

fire suppression (Marshall et al., 2014)

One of the key topics that are discussed within by Marshall et al. was how

sprinkler spray is formed. In order to have a good understanding of the key

characteristics of a fire sprinkler, the formation of the sprinkler sprays must be

understood (Marshall et al., 2014).

Atomization is the process that produces the formation of sprinkler sprays, this

is done by breaking up a stream of liquid into droplets (Marshall et al., 2014).

The process of atomization can be split into three different phases:

• Phase 1 -‐ The jet of liquid exiting the sprinkler will impact the deflection,

which creates a thin sheet of liquid and guides the liquid away from the

sprinkler towards the fire. The purpose of the thin sheet being produced

is due to the fact that the thin sheet will break up more easily than the

liquid jet.

• Phase 2 -‐ As the thin sheet is in the air, it becomes subject to small

disturbances, the disturbances grow until they reach a critical and

unstable state, which creates ligament waves from the liquid sheet, and

the ligament waves are also subject to disturbances as it is in the air.

• Phases 3 -‐ The disturbances on the ligament waves then grow to a critical

and unstable state, which causes the ligament waves to break up into

small spherical droplets.

(Marshall et al., 2014)

40

5.0 Selected fire scenario

In order to provide an effective study of fire sprinkler spray characteristics in

domestic premises, it was necessary to analyze the performance of the fire

sprinkler within a fire scenario situated in a domestic premise. For this study a

living room was used as the setting for the fire scenario; typically within this

space there would be several combustible items such as sofas, televisions,

carpet, curtains, etc. To simplify this study, it focused on a single sofa burning in

the center of a room to remove the possibilities of fire spread, the dimensions of

the room are 4.0 x 4.0 x 2.5 m to replicate a typical room size and the room will

not have any doors or windows to remove any external heat transfer.

The selected fire type will be a class A fire for this fire scenario as these types of

fires are the commonly seen in domestic premises and correspond to a typical

living room fire with ordinary combustibles.

The specifications of the sofa selected aimed to replicate a wood frame,

polyurethane foam with olefin fabric; which was experimentally tested by Kim,

H & Lilley, D (heat release rate of burning items, 2000). However the dimensions

of the sofa have been fabricated for this study and are 1.2 x 1.0 x 0.8 m to

replicate a real life sofa size.

41

6.0 Selected Fire Sprinkler System

6.1 Sprinkler system / piping

For the purpose of this study and to replicate an ideal scenario, a dry pipe

sprinkler system was used, this is because there will be no risk of leaking and

there will be a large amount of pressurized water released when the sprinkler is

activated. However, there will be a slight delay before the water is released, as

the water has to travel from its supply, through the system and out of the

sprinkler head, the delay is usually 30 seconds.

6.2 Sprinkler spray / nozzle

The sprinkler head used in this study will be a K-‐11 pendant sprinkler head; this

sprinkler head is commonly seen and is the default sprinkler head in the FDS

and Smokeview software.

6.3 Trigger system

The trigger system was a frangible bulb with an activate temperature of 79oC

and a RTI of 50 (m.s) 1/2. This replicates readily available frangible bulbs to help

the study replicate a real life scenario.

6.4 Fluid

The suppression fluid was water. Water is commonly used for fire suppression

but in extremely hazardous areas such as chemical plants where water cannot

be used foam is often seen as a replacement but in the case of a domestic

premise fire, water is appropriate.

42

7.0 Calculations and specifications

7.1 Flow rate

The British Standard BS9251: 2005 5.2.5.1 System flow rates dictates that a

sprinkler system should be capable of providing flow rates at the sprinkler head

of no less than:

a) For domestic premises

1. 60 litres/min through any single sprinkler; or

2. 43 litres/min through each of two sprinklers operating

simultaneously in a single room

Therefore for this study the range of flow rates that was simulated are;

Q = 60 L /minQ = 80 L /minQ =100 L /minQ =120 L /minQ =140 L /minQ =160 L /minQ =180 L /min

7.2 Orifice diameter

Specifications from Victaulic K11 fire sprinkler standard spray pendant

specifies that the nominal orifice diameter is 16mm, this remained constant

throughout all simulations as FDS only has this model of fire sprinkler head.

do =16mm

(Victaulic, 2014)

43

7.3 Droplet diameter

The range of droplet sizes for fire sprinklers should be ideally between fine and

average (100-‐1000μm) (Grant et al., 2000). Several different droplet sizes were

selected between these values to see what is the ideal droplet diameter.

1. 100μm

2. 200μm

3. 400μm

4. 500μm

5. 600μm

6. 800μm

7. 1000μm

7.4 Velocity

Velocity is related to flow rate, therefore as flow rate changes, velocity changes.

The equation for velocity is:

V =4×Qπ × d 2 (m / s)

Where :Q = Flow rate (L /min)d =Orifice diameter = 16mm =16×10−3mπ = pi = 3.14

The range of velocities that were simulated are:

1. 5 m/s

2. 6.5 m/s

3. 8.5 m/s

44

4. 10 m/s

5. 11.4 m/s

6. 13.4 m/s

7. 15 m/s

7.5 Heat release rate

The heat release value can be calculated with the following equation:

Q.=αg × t

2

Where :αg = Fire growth = 1000/(t1mw -t0 )2

(Kim, 2000)

To replicate a real life scenario data was used from Hyeong-‐Jin Kim’s (2000)

paper on heat release rates of burning items. The sofa used was the F32 sofa,

wood frame with polyurethane foam, which had a time to the onset of ignition,

t0 of 75 and a time to reach 1 MW, t1 MW of 150.

Therefore :

αg = Fire growth = 1000/(150-75)2 = 0.17•

or 845

(Kim, 2000)

The ideal time for a sprinkler to activate after a fire has started is between 40-‐

50 seconds. The lower value was selected; therefore the heat release rate after

40 seconds would be calculated.

Q.=

845× 402 = 284.4 kW or j

s

45

(Kim, 2000)

FDS requires the heat release rate per unit area, this can be found by dividing

the heat release rate by the area the fire is covering.

Area, a = 0.5×1m2 = 0.5m2

HRRPUA = 284.4÷ 0.5= 568.8kW /m2

(Kim, 2000)

8.0 Writing FDS Input File

8.1 Specifications

To help reproduce a real life fire scenario, it is important to ensure that all

aspects were as close to a real life as possible.

Scenario – A fire on a sofa in the center of a living room

Room dimensions – 4.0 x 4.0 x 2.5 m

Resolution –10 cm grid cells

Simulation time – 60 seconds

Boundary conditions – Open boundary on one side and ambient temperature of

20oc

Quantities – Wall temperature, net heat flux, radiative heat flux and slice

temperatures.

8.2 Starting input file

The FDS input file must be named, this is defined by ‘&HEAD CHID’ and was

called ‘living_room’. It is also convenient to have a description of the input file so

46

other users to know what the input file consists off; this is defined by ‘TITLE’

and was described as ‘Domain Creation’.

&HEAD CHID='living_room', TITLE='Domain Creation'/

It is important to set a run time, ‘TIME T_END’, for the simulation, for this

simulation the run time was 60 seconds. Setting the simulation time to zero will

only perform initial set up; this will allow the checking of the geometry of the

domain in Smokeview.

&TIME T_END=60.0 /

8.3 Computational mesh

All FDS calculations are completed within the created domain that is

constructed from rectilinear volumes called meshes. Each individual mesh is

divided into rectangular cells; the quality of the results is dependent on the size

of the mesh. The mesh can be coarse, medium or fine.

A measure of the quality of results is given by the non-‐dimensional expression

D*/δx, where D* is the characteristic fire diameter and δx is the nominal size of

the mesh cell in meters. The cell size is dependent on the value of the

characteristic fire diameter, if this value is small then the cell size should also be

small in order to sufficiently resolve the fluid flow and fire dynamics. A

reference within the FDS user guide suggest a D*/δx ratio between 4 and 16 to

accurately resolve fires in several different situations.

47

For this study the mesh cell size was 10cm or 0.1m. This value was taken from

one of the inbuilt examples with similar geometry to what I require. Therefore

δx = 0.1m.

D* is calculated by the following equation:

D*= Qp∞ × cp ×T∞ × g

#

$%%

&

'((

Where :Q = Heat release rate = 284.4kWp∞ = density of air =1.225kg /m3

cp = Specific heat of air =1.005kJ / kg− kT∞ = Ambient temperature = 293Kg = acceleration due to gravity = 9.81D*= 0.58

(NIST, 2015)

Therefore, D*∂x

=0.580.1

= 5.8

This value is between 4 and 16 and means my selected cell size is adequate.

The code written to define this mesh is:

&MESH IJK=40,40,25 XB=0.0,4.0,0.0,4.0,0.0,2.5 /

The number of cells within the domain can be calculated:

40 x 40 x 25 = 40,000

48

8.4 Miscellaneous parameters

There are miscellaneous parameters that can be included in the input file these

parameters include ambient temperature. For this simulation the ambient

temperature was 20oC / 293oK, the code for this was:

&MISC TMPA=20.0/

8.5 Creating obstruction

The sofa has been situated in the centre of the room. The sofa must be of the

dimensions 1.2 x 1.0 x 0.8 m; these dimensions have been taken from a real life

sofa to help replicate a real life scenario. To have this inserted the following

code has been built into the input file.

&OBST XB=1.5,2.5,2.0,2.5,0.0,0.8, SURF_ID='SOFA'/




It is also necessary to assign properties of the sofa, these properties are

necessary for FDS to calculate the combustion and determine how the sofa

burns; the properties selected were taken from an FDS example with a sofa.

&MATL ID='FABRIC', CONDUCTIVITY=0.1, SPECIFIC_HEAT=1.0, DENSITY=100.0

/

49

&SURF ID='SOFA', MATL_ID='FABRIC', COLOR='BROWN', THICKNESS=1.0,

BURN_AWAY=.TRUE. /

8.6 Pyrolysis model and Fuel

To create a fire a heat release rate must be inserted into the input file, to have

this heat release rate it is necessary to specify material properties, (which was

previously mentioned in section 8.5). A specified fire is modeled as the injection

of a gaseous fuel from a solid surface. This is essentially a burner, with a

specified heat release rate per unit area. For this study the heat release rate per

unit area has been calculated to be 568.8 kW/m2.

To input the fire, the location of the fire, heat release rate and e coefficient must

be inserted; the location of the fire is on top of the sofa.

&SURF ID='FIRE', HRRPUA=570, E_COEFFICIENT=4.0 /

&VENT XB=1.5,2.5,1.5,2.0,0.4,0.4 SURF_ID='FIRE'/

Specifying fuel is required; this will cause FDS to use the built-‐in thermo

physical properties for that species when computing quantities. The fuel that

was used is butane; because this is a fuel that can cause fires in a domestic

premise.

50

It is also necessary to insert ‘SOOT_YIELD’, this is the fraction of fuel mass

converted into smoke particles, and this helps to provide a good visual analysis

of the fire. The code for this was below:

&REAC SOOT_YIELD=0.01, FUEL='BUTANE' /

8.7 Particles, droplets and size distribution

To define an evaporating liquid droplet, the gaseous species must be explicitly

specified via the ‘SPEC’ name list group and then the appropriate ‘SPEC_ID’

designated on the part line. The ‘SPEC_ID’ specifies a water vapor, which is a

predetermined species in FDS; the particle will be assigned the thermal

properties of water, the radiation absorption of water and will be colored blue

in SmokeView.

The ideal droplet size for fire suppression is between 100-‐1000μm. Testing will

determine the optimum droplet size but this study began with an initial value of

100μm; the ‘DIAMETER’ name list specifies the droplet size.

&SPEC ID='WATER VAPOR' /

&PART ID='water drops', SPEC_ID='WATER VAPOR',DIAMETER=100 /

8.8 Introduction of sprinkler & Fire suppression by water

To insert a sprinkler into the simulation, it must be inserted into the input file.

The default sprinkler type is a ‘K 11’ sprinkler; the location and properties of the

sprinkler must be specified.

51

&PROP ID='K-‐11', QUANTITY='SPRINKLER LINK TEMPERATURE', RTI=100,

ACTIVATION_TEMPERATURE=79, OFFSET=0.10, PART_ID='water drops',

PARTICLE_VELOCITY=10., SPRAY_ANGLE=30.,80., FLOW_RATE=180 /

&DEVC XYZ=2.0,2.0,2.5, PROP_ID='K-‐11', ID='Spr_1' /

The complete input file can be seen in appendix 14.1.

52

9.0 Running FDS Simulation

In total 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.

Figure 18 shows the domain that the simulation was in; this is a room with a

sofa in the centre of it. 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.

Figure 18 Simulation domain, (2016)

53

Figure 19 Simulation #5 -‐ Simulation after 33.3 seconds, (2016)

Figure 20 Simulation #5 -‐ Slice file temperature at 34.4 seconds, (2016)

54

Figure 19 and 20 shows the fire on the sofa and the max temperature reached

by the fire, these images were taken from simulation #5 using a temperature

slice file.

Figure 21 Simulation #5 -‐ Activated fire sprinkler after 39.2 seconds, (2016)

55

Figure 22 Simulation #5 -‐ 1 second after activated fire sprinkler, (2016)

Figure 23 Simulation #5 -‐ Fully extinguished fire after 5 second after fire sprinkler

activation, (2016)

56

Figure 21, 22 and 23 shows the point at which the fire sprinkler was activated

and how the water droplets are suppressing the fire over time until the fire has

been completely extinguished.

10.0 Analysis of FDS results

10.1 Results

The simulations carried out went positively, this is because various different

simulations were carried out with different characteristics, which provided a

range of results to give an adequate analysis. It can be seen from the tabulated

results (shown below) and the graphical results (shown in appendix 14.2) that

during the simulations as the droplet size increases, the time to extinguish the

fire becomes longer; which replicates real life. This is because a reduced droplet

size provides an improved cooling effect on the fire; this is due to the small

droplets covering a larger surface area. This in turn gave an increased rate of

evaporation.

The study indicated that an increase in velocity and flow rate led to prolonged

fire extinguishment. Increasing the flow rate and the velocity will directly

increase the amount of water being used to extinguish the fire and in normal

cases it would be expected that the fire would extinguish quicker. During the

simulations it can be seen that due to the spray angle a large amount of water is

not being sprayed on the fire directly and this water is being distributed on the

surrounding area (shown in figure 24). Although a certain amount of the water

spread to the surrounding area is considered positive, as it prevents fire spread,

57

the goal here is to extinguish the fire as soon as possible before an opportunity

for the fire to spread arises.

If the spray angle were changed so that a large majority of the water coming out

of the fire sprinkler went directly on the fire, a decrease in the time to

extinguish the fire would be seen.

Figure 24 Simulation #49 -‐ Spray angle, (2016)

As anticipated the fastest set of results are when the droplet size is between

100-‐200μm with times to extinguish ranging from 5-‐8 seconds. This range of

times is suitable as any time longer than 10 seconds would allow the heat

release rate to increase, which would in turn make the fire harder to extinguish

in a real life scenario.

58

Table 1 Simulations 1-‐49 results, (2016)

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 #1 100 5 60 7 7.00

Simulation #2 100 6.5 80 6 8.00

Simulation #3 100 8.5 100 6 10.00

Simulation #4 100 10 120 6 12.00

Simulation #5 100 11.4 140 5 11.67

Simulation #6 100 13.4 160 6 16.00

Simulation #7 100 15 180 6 18.00

Simulation #8 200 5 60 6 6.00

Simulation #9 200 6.5 80 6 8.00

Simulation #10 200 8.5 100 6 10.00

Simulation #11 200 10 120 6 12.00

Simulation #12 200 11.4 140 6 14.00

Simulation #13 200 13.4 160 7 18.67

Simulation #14 200 15 180 8 24.00

Simulation #15 400 5 60 10 10.00

Simulation #16 400 6.5 80 8 10.67

Simulation #17 400 8.5 100 8 13.33

Simulation #18 400 10 120 9 18.00

Simulation #19 400 11.4 140 12 28.00

59

Simulation #20 400 13.4 160 13 34.67

Simulation #21 400 15 180 13 39.00

Simulation #22 500 5 60 10 10.00

Simulation #23 500 6.5 80 10 13.33

Simulation #24 500 8.5 100 10 16.67

Simulation #25 500 10 120 11 22.00

Simulation #26 500 11.4 140 16 37.33

Simulation #27 500 13.4 160 16 42.67

Simulation #28 500 15 180 19 57.00

Simulation #29 600 5 60 13 13.00

Simulation #30 600 6.5 80 13 17.33

Simulation #31 600 8.5 100 16 26.67

Simulation #32 600 10 120 17 34.00

Simulation #33 600 11.4 140 19 44.33

Simulation #34 600 13.4 160 22 58.67

Simulation #35 600 15 180 29 87.00

Simulation #36 800 5 60 28 28.00

Simulation #37 800 6.5 80 23 30.67

Simulation #38 800 8.5 100 35 58.33

Simulation #39 800 10 120 40 80.00

Simulation #40 800 11.4 140 53 123.67

Simulation #41 800 13.4 160 61 162.67

Simulation #42 800 15 180 76 228.00

60

Simulation #43 1000 5 60 71 71.00

Simulation #44 1000 6.5 80 72 96.00

Simulation #45 1000 8.5 100 119 198.33

Simulation #46 1000 10 120 151 302.00

Simulation #47 1000 11.4 140 173 403.67

Simulation #48 1000 13.4 160 208 554.67

Simulation #49 1000 15 180 256 768.00

The speed in which the fire is extinguished has a direct impact on the amount of

water used to extinguish the fire. As expected the results that provided the

fastest extinguishing time used the least amount of water used, ranging between

6-‐24 litres, this is ideal information and determines whether or not the

optimum characteristics of the fire sprinkler has been found.

Figure 25 Droplet size vs. Time to extinguish (Constant velocity and flow rate 11.4 and 40 respectively), (2016)

61

10.2 Optimization

The fastest time to extinguish the fire was simulation #5 with a droplet

diameter of 100μm, velocity of 11.4 m/s and a flow rate of 140 L/min but the

simulation that used the least amount of water was simulation #8 with 6 litres

of water. Despite results showing a relatively quick time to extinguish the fire

and a low amount of water used, there is room for optimization. Ideally the best

characteristics would use the least amount of water and have the fastest time to

extinguish. To achieve this the simulations that had the fastest time to

extinguish and used the least amount of water (simulations #1-‐8) will be

optimized.

To optimize the simulations with the intention on receiving improved results a

tighter spray angle will be selected to ensure that the there is an adequate spray

coverage over the fire and to prevent a large amount of water being distributed

on the surroundings. Previously the spray angle was 30, 80 but now will be

20,70.

The results of the optimized simulations are shown below.

62

Table 2 Optimized results -‐ Spray angle 20,70, (2016) Optimized results -‐ Spray angle 20,70

Simulation

No.

Droplet

diameter,

d (μm)

Velocity, v

(m/s)

Flow rate,

Q (L/min)

New time

to

extinguish

fire (s)

New total

water

used

(Litres)

Simulation #1 100 5 60 6 6.00

Simulation #2 100 6.5 80 5 6.67

Simulation #3 100 8.5 100 5 8.33

Simulation #4 100 10 120 5 10.00

Simulation #5 100 11.4 140 5 11.67

Simulation #6 100 13.4 160 5 13.33

Simulation #7 100 15 180 5 15.00

Simulation #8 200 5 60 6 6.00

63

Figure 26 Simulation 7 with optimized spray angle, (2016)

As expected we can see a reduction in the time to extinguish the fire, which in

turn causes a less amount of water to be used. As shown in figure 26 the spray

angle is tighter but still maintaining some coverage to the surroundings; this

means more water is being concentrated on the fire than previously.

10.3 Accuracy

To improve the accuracy of the results a finer mesh could be used. Refinement is

important as it allows the software to more accurately analyze smaller sections

of the domain, which in turn provides more accurate results regarding the

simulation. Though more accurate results will be produced this will come at a

computational cost, because of this only simulation #2 will be selected as this

64

had a fast time to extinguish (5 seconds) and used the second least amount of

water (6.67 litres).

The number of divisions can be seen in the new input code below:

&MESH IJK=80,80,50 XB=0.0,4.0,0.0,4.0,0.0,2.5 /

The cell size is now:

0.05m

The number of cells is now:

80 x 80 x 50 = 320,000

Table 3 Refined mesh results -‐ grid size 0.05m, (2016) Mesh refined results -‐ grid size 0.05m

Simulation

No.

Droplet

diameter,

d (μm)

Velocity, v

(m/s)

Flow rate,

Q (L/min)

New time

to

extinguish

fire (s)

New total

water

used

(Litres)

Simulation #2 100 6.5 80 7 9.33

We can see from the results that with a refined mesh, that it has 8 times more

grid cells than the initial simulation, the time to extinguish the fire has increased

slightly to 7 seconds but is still within an acceptable time. Considering that the

mesh has been refined significantly but the results have changed marginally, it

65

can be said that mesh independency has been achieved; therefore the results

will not change anymore with a finer mesh.

Due to the fact that a finer mesh is used, more accurate results are provided

these results can be deemed as reliable. The results from the initial simulations

to the simulations with a finer mesh all show that the optimum sprinkler spray

characteristics are sprinklers with small droplet diameters and with a low to

medium velocity and flow rate in domestic premises.

10.4 Discussion

All simulations ran show that having small droplet sizes and having a low to

medium velocity and flow rate is key in extinguishing a fire. The spray angle was

critical in this scenario as the study focused on a sofa in the centre of a room; in

a real life scenario combustible items may be spread in any particular way

around a room and it may become more essential to have a wider spray angle.

As demonstrated in table 1 the selection of increasing droplet sizes (with flow

rate and velocity remaining constant), ranging from 100 to 1000μm, showed a

large increase in time to extinguish the fire between the minimum and

maximum sizes. In comparison, when the droplet size is kept at a constant, with

flow rate and velocity increasing, the change in time to extinguish the fire is not

as large. This shows that droplet size was the dominant characteristic as it made

the biggest difference.

To further support the results from this study a wide range of simulations

would have been run which would include a variety of different characteristics,

66

that are not limited to a maximum velocity of 15m/s and a maximum flow rate

of 180 L/min (minimum velocity and flow rate cannot be below 5m/s and

60L/min respectively as British Standard BS9251: 2005 5.2.5.1 dictate).

Additionally these simulations could be run with fires that have a variety of

different heat release rate values, these values would be taken from objects

within a domestic premise.

To further improve the accuracy of the results all the simulations could have

been run with a fine mesh opposed to a coarse or medium mesh although this

will result in an increase in computational cost.

Another way to provide improved results is to create a more realistic fire

scenario that is a true representation of an average UK room at risk of fire

including more combustible items, such as several sofas, carpet, curtain etc. This

would complicate the study as several separate heat release rates will have to

be included as well as a fire spread phenomena and different fire behaviours to

be considered. In turn this will have an effect on what the optimum sprinkler

spray characteristics should be and several fire sprinklers may have to be

involved opposed to just one.

Another way to support the results of this study is to compare them with

experimental data. This experimental data would consist of a real life fire

scenario, which replicates the simulations i.e. a room with a single burning sofa.

The optimum characteristics of the fire sprinkler would be tested in this setting.

It should be noted that this method would only be used to support already

67

gathered data and it would be unrealistic to calculate the optimum

characteristics for every domestic premise as there would be a range of

circumstances that would affect the characteristics i.e. different orientation and

different combustible items which result in different heat release rates.

Finally another way to support and improve the accuracy of results gathered is

to investigate how adjusting other characteristics and parameters of the fire

sprinkler system can affect the time to extinguish i.e. RTI, frangible bulb

activation temperatures, sprinkler head, sprinkler offset and allowing FDS to

increase the heat release rate over time, which replicates real life. Although

individually these characteristics may not be deemed as key characteristics,

combined they would provide important information and improved results. In

addition to this altering the ambient conditions may have an affect on the

results.

It should be noted that the results of this study do not reflect what the key

sprinkler spray characteristics should be in all living rooms within the UK, in

order to gather very accurate results, the domain and conditions should

replicate the real life scenario as much as possible.

11.0 Conclusion

Although there has been a significant reduction in fire related deaths in Britain

over the last 50 years, there is still a large amount of fire related deaths

occurring on a yearly basis. This study shows the importance of implementing a

fire sprinkler system in a domestic premise and how the implementation can

68

occur by analyzing rooms within a domestic premise that are at most risk of

having a fire. After the analysis the key characteristics the fire sprinkler needed

to extinguish such fires would need to be determined. By doing this there can

be an even larger reduction in fire related deaths with the possibility of

eliminating them completely.

This project shows that fires in domestic premises could be extinguished within

seconds if the key characteristics of a fire sprinkler system, namely droplet

sizes, flow rate, velocity and spray angle are appropriately selected. This project

shows that the optimum droplet sizes should be on the small end of the water

spray scale, 100-‐200μm and the velocity and corresponding flow rate is

dependent on the spray angle, a tight spray angle (slightly larger than fire area)

on the fire would perform better with a high flow rate and a wider spray angle

(considerably larger than fire area) would perform better with a low to medium

flow rate. With the optimum values selected it will be seen that a fire can be

extinguished before the maximum heat release rate is achieved and can also

prevent fire spread and fire growth from occurring.

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

sprinklers in homes, this would save hundreds of lives and in the long term

would be cost effective.

69

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14.0 Appendices

14.1 FDS simulation input file

FDS code for living

Study of sprinkler spray characteristics in domestic premises.

&HEAD CHID='living_room', TITLE='Domain Creation'/

*Domain dimension, 4 x 4 x 2.5 m, cell dimensions, 0.1 x 0.1 x 0.1 m, 40,000 cells

&MESH IJK=40,40,25 XB=0.0,4.0,0.0,4.0,0.0,2.5 /

*Run time of simulation is set to zero to allow quick checking of geometry

&TIME T_END=60.0 /

*Defines evaporating liquid droplets as water, providing the thermal properties,

radiation absorption and coloured blue in smokeview

&SPEC ID='WATER VAPOR' /

&PART ID='water drops', SPEC_ID='WATER VAPOR', DIAMETER=<value> /

*Adds a sprinkler within the computational domain and specifies characteristics

of the sprinkler

&PROP ID='K-‐11', QUANTITY='SPRINKLER LINK TEMPERATURE', RTI=100,

ACTIVATION_TEMPERATURE=79, OFFSET=0.10, PART_ID='water drops',

PARTICLE_VELOCITY=<value>, SPRAY_ANGLE=30.,80., FLOW_RATE=<value> /

&DEVC XYZ=2.0,2.0,2.5, PROP_ID='K-‐11', ID='Spr_1' /

76

*&RAMP ID='spray', T=30.0, F=0. /

*&RAMP ID='spray', T=40.0, F=1. /

*&RAMP ID='spray', T=50.0, F=0. /

*Fire located on top of sofa with a heat release rate per unit area (285/0.5) of

570kW/m^2 and allow a parameter to allow the reduction of the burning rate

&SURF ID='FIRE', HRRPUA=570, E_COEFFICIENT=4. /

&VENT XB=1.5,2.5,1.5,2.0,0.4,0.4 SURF_ID='FIRE'/

*Fuel for fire is butane, with fraction of fuel mass converted into smoke

particulate

&REAC SOOT_YIELD=0.01, FUEL='BUTANE' /

*The ambient temperature is required to be 20 degrees C/293 degrees K

&MISC TMPA=20./

*Assign properties of sofa

&MATL ID='FABRIC', CONDUCTIVITY=0.1, SPECIFIC_HEAT=1.0, DENSITY=100.0

/

&SURF ID='SOFA', MATL_ID='FABRIC', COLOR='BROWN', THICKNESS=1.0,

BURN_AWAY=.TRUE. /

*A sofa in the centre of a room with the dimensions 1.2 x 1.0 x 0.8 m

&OBST XB=1.5,2.5,2.0,2.5,0.0,0.8, SURF_ID='SOFA' /


77



*Defines boundaries on all four sides (left, right, front and back)

*&VENT MB='XMIN', SURF_ID='OPEN'/

*&VENT MB='XMAX', SURF_ID='OPEN'/

&VENT MB='YMIN', SURF_ID='OPEN'/

*&VENT MB='YMAX', SURF_ID='OPEN'/

&SLCF PBX=2.0, QUANTITY='TEMPERATURE' /

&SLCF PBY=2.0, QUANTITY='TEMPERATURE' /

&BNDF QUANTITY ='WALL TEMPERATURE' /

&BNDF QUANTITY ='NET HEAT FLUX' /

&BNDF QUANTITY ='RADIATIVE HEAT FLUX' /

&TAIL /

78

14.2 Graphical results

Figure 27 Velocity vs. Time to extinguish (droplet size of 100μm), (2016)

Figure 28 Velocity vs. Time to extinguish (droplet size 200μm), (2016)

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Figure 30 Velocity vs Time to extinguish (droplet size 500μm), (2016)

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14.3 Navier-‐Stokes equations

Figure 34 Navier-‐Stokes equations (NASA, 2016)

Dissertation - Study of sprinkler spray characteristics in domestic premises

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