suppression of pool fires by water mist in

SUPPRESSION OF POOL FIRES BY WATER MIST
IN ENCLOSURES
MEENAKSHI GUPTA
DEPARTMENT OF MECHANICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY DELHI
OCTOBER 2015
© Indian Institute of Technology Delhi (IITD), New Delhi, 2015
SUPPRESSION OF POOL FIRES BY WATER MIST
IN ENCLOSURES
by
Meenakshi Gupta
Department of Mechanical Engineering
Submitted
in fulfillment of the requirements of the degree of
Doctor of Philosophy
to the
INDIAN INSTITUTE OF TECHNOLOGY DELHI
OCTOBER 2015
…………….dedicated to my family
ii
CERTIFICATE
This is to certify that the thesis entitled "Suppression
Enclosures"
being submitted
by Ms. Meenakshi
of Pool Fires by Water Mist in
Gupta
to Indian Institude of
Technology Delhi for award of the degree of Doctor of Philosophy,
is a record of
original bonafide research work carried out by her. She has worked under our guidance
and supervision, and has fulfilled the requirements for the submission of this thesis,
which has attained the standard required for a Ph.D. degree of this institute.
The results presented in this thesis have not been submitted elsewhere for the award of
any degree or diploma.
Dr Sunil R. Kale
Dr Anjan Ray
Professor,
Professor
Dept. of Mechanical Engineering
Dept. of Mechanical Engineering
Indian Institue of Technology Delhi
Indian Institue of Technology Delhi
Date: 07
OGTos ER.
2015
Place: New Delhi
iii
Acknowledgements
The work presented here is carried out at Centre for Fire Explosives and
Environment Safety (CFEES), Defence R&D Organisation, Ministry of Defence and I
owe my sincere thanks to Director CFEES and all my colleagues who were involved
with me at various staqes of this work. Thanks to all my project team members at
CFEES, a special mention goes to Sh Rajesh Rajora, Sh Sandeep Dubey, Sh
Ravishankar and Sh Sandeep Sahai for experimental support and Sh Sio Kumar for the
art-work required for the thesis. My special thanks are also due to Sh J C Kapoor, ex
Director CFEES for useful discussions and encouragement during my experimental
study.
I owe the greatest debt of gratitude and admiration to my mentors, professors
and guides, Dr S R Kale and Dr Anjan Ray, for their valuable guidance, continuous
support, patience and belief in me. I also wish to thank Ms. Akanksha Mathur and Ms.
Ankita, research scholars at liT Delhi, who have helped me a lot during the course of
my thesis work and presentations.
I would like to thank my Husband, Dr. Sharat Chandra Agarwal and my sons,
Arpit and Nitish, for their understanding and continuous support during my thesis work
and study at home. It has not been easy and I could not have completed it without their
love and encouragement. I wish to thank all those who have helped me directly or
indirectly in this journey of my life.
Finally, it's the God's grace and blessings that has given me the strength to
complete this highest degree in the engineering disciple in my life.
~.
(Meenakshi Gupta)
iv
Abstract
The international ban on use of Halons as fire suppressants due to their adverse
environmental impact has resulted in the development of water mist fire suppression
technology. Based on a series of experiments, data has been generated to quantify the
extinguishing performance of a mist in an enclosure.
The experiments were conducted in three enclosures, viz.: (a) Scale-1: 1 m3 (1 x
1 x 1 m), (b) Scale-3: 39 m3 (3.5 x 3.4 x 3.3 m), and (c) Scale 5: 345 m3 (9.2 x 7.5 x 5
m) using two different types of twin fluid nozzles (operating pressure < 10 bar(g)). In
Scale-1 enclosure, a pair of low capacity twin fluid nozzles of external mixing type
(Type A) were used which generated a mist with DV50 ~ 23 µm and total discharge of
225 ml/min. A pool fire was generated with circular pan (65, 100, 125, 190 mm
diameter) or 150 x 150 mm square pan; all with n-heptane. In Scale-3 and Scale-5
enclosures, a set of twin fluid nozzles (Type B) were used which internally mixes
pressurized water with air and discharges through multiple orifices; the mist DV50 ~ 34
µm (SMD ~ 16 µm) and discharge rate 1.5 l/min. In Scale-3 enclosure, eight nozzles
were mounted in a circular ring assembly placed centrally near the ceiling and fire was
generated with a circular pan (300, 350, 550 and 650 mm diameter) with n-heptane;
some experiments were with one pan and some with two pans. In Scale-5 enclosure,
fifty-four nozzles were placed uniformly on grids installed near the ceiling and on the
sides. Experiments were conducted with either one, two or three pool fires produced by
burning Light diesel oil (LDO) or high speed diesel (HSD), in circular pans of diameters
350, 800 and 1460 mm. Temperatures were measured at several locations with
thermocouples. Concentrations of O2, CO2 and CO were measured by sampling at 1/3rd
the height below ceiling at the centre. Suppression performance has been quantified by
a Fire Suppression Performance Index (FSPI).
The data show that FSPI increases with increasing gas pressure for all fire
locations in Scale-1 enclosure; the reason being decrease in Dv50 from 26.6 µm to 17.7
µm at 850 mm downstream for gas pressure 4 to 8 bar(g). In all the three enclosures,
the suppression time decreases with the increase in fire size. Temperature profiles also
show that if the fire pool diameter is doubled, the temperature decrease rate becomes
higher by an order of magnitude. With air as atomizing medium, the extinguishing
concentration of mist varied from 50-80 g/m3 for large fires (> 14 kW/m3) to 450-500
v
g/m3 for smaller fires (< 1 kW/m3), depending on the fire-nozzle relative positions. When
atomized with nitrogen, this concentration is less by 30–50 %. With multiple fires, an
individual fire was extinguished at different times with obstructed fires taking the longest
time. With ventilation, the extinguishment time for multiple pool fires was greater by
about 10 %. Nitrogen as atomizing media, in lieu of air, reduced the extinguishing time
by 40–50 % for multiple, obstructed, and ventilated fires. For a single fire (< 1 kW/m3)
the extinguishment time with nitrogen is half that with air. Increase in pre-burn duration
decreases the suppression time by up to 45 %, but as the fire size reduces, the
performance enhancement due to increased pre-burn is less.
Pulsing of mist reduced suppression time and water quantity by about 40–50 %
at the optimum pulsing cycle (ON- OFF duration of 1.3 and 1.0 s, respectively),
provided the mist discharge rate is sufficient enough to remove heat by evaporation in
comparison with that generated for each ON duration. Fires with lower fire point fuel
(e.g. n-heptane) are difficult to extinguish than those with higher values (e.g. light diesel
oil).
Rapid decrease rate of measured temperatures after the mist injection confirm
the role of heat absorption from the hot gases and cooling of the flame as a major
extinguishing mechanism. For larger fire sizes, only 22-29 % of heat removal from the
enclosure was found to be enough to suppress the fire for nitrogen or air assisted mist
indicating the role of other processes in fire suppression. Heat absorption (flame
cooling) is the dominant mechanism for suppression of small fires while cooling and
dilution of oxygen in the flame region are major contributors to suppression of large
fires. The mist induces rapid mixing of hot and cold gas layers which resulted in faster
reduction of the temperature difference between the upper and lower layers.
A correlation between mist extinguishing concentration and the normalized fire
size has been proposed which can be used for designing a total flooding water mist
system.
Keywords: Enclosure fire, Pool fire, Water mist, Twin fluid nozzle, Fire suppression,
Total flooding, pulsed mist, extinguishment, mist system design
vi
CONTENTS
Certificate
........................................................................................iii
Acknowledgements ...................................................................................iv
Abstract
.........................................................................................v
List of Figures
......................................................................................xiii
List of Tables
.......................................................................................xx
Nomenclature
....................................................................................xxiii
Symbols
.....................................................................................xxv
Subscript
.....................................................................................xxv
Abbreviations
................................................................................... xxvi
1. Introduction
.........................................................................................1
1.1
Significance and overview......................................................................... 1
1.2
Fire in an enclosed space ......................................................................... 2
1.3
Fire fighting ............................................................................................... 4
1.4
Engineered water mist system .................................................................. 6
1.5
Objectives and scope of research ............................................................. 6
1.6
Organization of the thesis ......................................................................... 8
2. Pool fires and their extinguishment .....................................................9
2.1
Anatomy of a fire ....................................................................................... 9
2.2
Fire types ................................................................................................ 10
2.3
Pool fire ................................................................................................... 10
2.3.1 Flame character, shape and height ................................................... 11
2.3.2 Flame temperature and heat transfer in flames ................................. 14
2.3.3 Burning rate (or mass loss rate) and heat release rate ...................... 15
vii
2.3.4 Effects of enclosure ........................................................................... 19
2.4
Fire extinguishment ................................................................................. 22
2.5
Water mist characteristics and extinguishing mechanisms ..................... 24
2.5.1 Water mist generation and system configuration ............................... 24
2.5.2 Mist characteristics ............................................................................ 27
2.5.3 Mist characterization techniques........................................................ 30
2.5.4 Extinguishing mechanisms of a water mist ........................................ 31
2.5.5 Effects of an enclosure ...................................................................... 34
2.6
Summary ................................................................................................. 35
3. Literature review ...................................................................................36
3.1
Historical perspective .............................................................................. 36
3.2
Water mist characterization..................................................................... 37
3.3
Extinguishing mechanisms ...................................................................... 38
3.4
Factors affecting fire extinguishing performance ..................................... 43
3.4.1 Droplet size distribution ..................................................................... 44
3.4.2 Mist concentration or flux density....................................................... 51
3.4.3 Mixing and kinetic effects................................................................... 52
3.4.4 Fire size, fuel type and location ......................................................... 54
3.4.5 Effect of compartment size and geometrical configuration ................ 55
3.4.6 Water mist system characteristics ..................................................... 56
3.4.7 Water mist with additives ................................................................... 58
3.5
Mist system design and implementation ................................................. 58
3.6
Summary ................................................................................................. 60
3.7
Issues addressed in the present work ..................................................... 61
4. Methodology and experimental details ..............................................62
4.1
General methodology .............................................................................. 62
4.2
Experimental details ................................................................................ 63
4.2.1 Test enclosures ................................................................................. 63
viii
4.2.2 Nozzles .............................................................................................. 70
4.2.3 Liquid and gas supply systems .......................................................... 70
4.2.4 Nozzle arrangements......................................................................... 73
4.2.5 Pool fires............................................................................................ 75
4.2.6 Instrumentation .................................................................................. 76
4.3
Mist characterization ............................................................................... 81
4. 4
Control parameters and test matrix ......................................................... 83
4.4.1 Characterization of nozzles ............................................................... 83
4.4.2 Experiments in Scale-1 (1 m3) enclosure........................................... 85
4.4.3 Experiments in Scale-3 (39 m3) enclosure ......................................... 89
4.4.4 Experiments in Scale-5 (345 m3) enclosure ....................................... 90
4.5
Experimental procedure .......................................................................... 94
4.6
Fire suppression performance calculation............................................... 95
4.7
Uncertainty analysis ................................................................................ 96
4.7.1 General procedure ............................................................................. 97
4.7.2 Uncertainty analysis for gas-to-liquid mass flow rate ratio (GLR) ...... 98
4.7.3 Uncertainty estimation in FSPI......................................................... 100
4.7.4 Uncertainty analysis for temperature measurements....................... 101
4.8
Summary .............................................................................................. 103
5. Mist characterization ..........................................................................104
5.1 Type-A nozzle ............................................................................................ 104
5.1.1 Gas-to-liquid mass ratio (GLR) ........................................................ 104
5.1.2 Droplet size distribution ................................................................... 105
5.1.3 Droplets velocity distribution ............................................................ 111
5.1.4 Spray cone angle ............................................................................. 111
5.2 Type-B nozzle ............................................................................................ 113
5.2.1 Gas-to-liquid mass ratio (GLR) ........................................................ 114
ix
5.2.2 Droplet size distribution ................................................................... 116
5.2.3 Spray cone angle ............................................................................. 123
5.2.4 Droplet velocity measurements........................................................ 123
5.2.5 Discharge coefficient ....................................................................... 123
5.2.6 Mist characterisics for Scale-3 enclosure ........................................ 123
5.2.7 Mist characterisics for Scale-5 enclosure ........................................ 124
5.3
Summary ............................................................................................... 126
6. Results of experiments in Scale-1 (1 m3) enclosure.......................127
6.1
Dry runs ................................................................................................ 127
6.2
Effect of atomizing gas pressures ......................................................... 129
6.2.1 Fire suppression time ...................................................................... 129
6.2.2 Temperature profiles........................................................................ 132
6.2.3 Gas concentration profiles ............................................................... 140
6.3
Effect of pulsed mist .............................................................................. 143
6.4
Pulsed mist vs. continuous mist ............................................................ 147
6.5
Effect of atomizing gas .......................................................................... 150
6.6
Effect of pre-burn duration .................................................................... 154
6.7
Effect of pool fire size ............................................................................ 155
6.8
Effect of pool fire location ...................................................................... 157
6.9
Discussion............................................................................................. 159
6.9.1 Fire extinguishment time .................................................................. 159
6.9.2 Temperature profiles during fire suppression .................................. 160
6.9.3 Flame suppression behavior............................................................ 161
6.9.4 Dynamics of pulsed mist .................................................................. 165
6.9.5 Suppression performance with gas pressure................................... 167
6.9.6 Suppression rate variation with fire size .......................................... 167
6.9.7 Effect of nitrogen as atomizing medium ........................................... 169
6.9.8 Effect of pre-burn duration ............................................................... 170
x
6.10
Summary ............................................................................................. 171
7. Results of experiments in Scale-3 and Scale-5 enclosures ..........172
7.1
Results from the Scale- 3 enclosure ..................................................... 172
7.1.1 Dry run ............................................................................................. 172
7.1.2 Fire extinguishment time .................................................................. 175
7.1.3 Temperature profiles during suppression ........................................ 186
7.1.4 Gas concentration profiles ............................................................... 191
7.2
Results from Scale-5 (345 m3) enclosure.............................................. 194
7.2.1 Suppression performance with single pool fire ................................ 197
7.2.2 Temperature and gas concentration profiles ................................... 203
7.3
Discussion............................................................................................. 211
7.3.1 Effect of water flow rate ................................................................... 211
7.3.2 Effect of fire size and pre-burn duration ........................................... 211
7.3.3 Effect of fuel type ............................................................................. 212
7.3.4 Effect of nitrogen atomization .......................................................... 213
7.3.5 Suppression of multiple pool fires .................................................... 213
7.3.6 Suppression of obstructed and ventilated fires ................................ 213
7.3.7 Uncertainty in suppression time ....................................................... 214
7.4
Summary ............................................................................................... 214
8. Scaling analysis ..................................................................................216
8.1
Theoretical basis ................................................................................... 216
8.2
Normalization of experimental parameters and suppression results ..... 216
8.3
Discussion............................................................................................. 220
8.4
Summary ............................................................................................... 223
9. Conclusion and recommendations for future work .......................224
9.1
Conclusions .......................................................................................... 224
9.1.1 Effect of nozzle parameters ............................................................. 224
xi
9.1.2 Influence of fire parameters ............................................................. 224
9.1.3 Effect of enclosure parameters ........................................................ 225
9.1.4 Extinguishing mechanisms .............................................................. 225
9.1.5 Thermal behaviour ........................................................................... 225
9.1.6 Fire suppression performance ......................................................... 226
9.1.7 System design criteria ..................................................................... 226
9.2
Recommendation for further work ......................................................... 227
References
.....................................................................................228
Appendix – A
Fuel properties and Pool fire parameters ...............246
Appendix – B
Uncertainty analysis ..................................................247
B.1
Uncertainty in estimation of gas-to-liquid mass flow ratio (GLR) .......... 247
B.2
Uncertainty in estimation of fire suppression performance index .......... 248
B.3
Uncertainty in flame / near flame gas temperatures .............................. 251
List of Publications .................................................................................253
Brief Biodata of the author .....................................................................254
xii
List of Figures
Fig. no.
Fig. 1.1
Description
A fire in an administrative building [Ref.: Deccan Chronicile, 8th Nov,
Page
1
2012].
Fig. 1.2
A fire in a cargo ship [Ref: Turkey Seanews, 16 Feb 2011].
2
Fig. 1.3
View of an engine compartment of a ship.
3
Fig. 1.4
Interaction of water mist with a fire in an enclosure.
5
Fig.1.5
Suppression of pool fire by a water mist in an enclosure.
8
Fig. 2.1
Essential components for a fire.
9
Fig. 2.2
Plume structure of a pool fire.
12
Fig. 2.3
Time sequence images of a pool fire in an enclosure.
14
Fig. 2.4
Heat transfer in an enclosure containing a fire.
15
Fig. 2.5
Energy transfer inside a liquid pool fire.
17
Fig. 2.6
Idealized temperature - time history in an enclosure fire.
20
Fig. 2.7
High pressure single fluid nozzle.
25
Fig. 2.8
Single fluid impingement nozzle.
25
Fig. 2.9
Twin fluid internal mixing nozzle.
26
Fig. 2.10 Twin fluid external mixing nozzle.
26
Fig. 2.11 Classification of water mist system.
27
Fig. 2.12 A typical droplet size distribution in a mist.
30
Fig. 3.1
Classification of water sprays by drop-size distribution [26]
38
Fig. 4.1
General arrangement of the 1 m3 test enclosure (Scale-1 enclosure).
64
Fig. 4.2
Photograph of the 1  1  1 m enclosure.
64
Fig. 4.3
General arrangement of the 39 m3 enclosure (Scale-3 enclosure).
65
Fig. 4.4
General arrangement of the Scale-5 enclosure (345 m3, 10 m dia x
66
7.5 m length).
xiii
Fig. 4.5
Layout of nozzles in the Scale-5 enclosure.
67
Fig. 4.6
Type-A twin fluid nozzle.
68
Fig. 4.7
Type-B internally mixed twin fluid Nozzle.
69
Fig. 4.8
A sectional view of internally mixed twin fluid Type-B Nozzle.
70
Fig. 4.9
Schematic of water and air/gas supply system for Type-A Nozzle.
72
Fig. 4.10 Schematic of water and air / gas supply arrangement for Type-B
72
Nozzle.
Fig. 4.11 Schematic of a twin fluid water mist system.
73
Fig. 4.12 Arrangement of nozzles in 1 m3 enclosure.
74
Fig. 4.13 Photographs showing arrangement of nozzles in 1 m3 enclosure.
74
Fig. 4.14 Location of thermocouples at the back wall of the 1 m3 enclosure.
76
Fig. 4.15 Location of thermocouples in the 1 m3 enclosure.
77
Fig. 4.16 Instrumentation layout in the 39 m3 (Scale-3) enclosure.
78
Fig. 4.17 Thermocouple trees at two radial distances from the pool vertical axis
79
in the 39 m3 (Scale-3) enclosure.
Fig. 4.18 Plan view of instruments layout in the 345 m3 (Scale -5) enclosure.
80
Fig. 4.19 Mist characterization using EPCS instrument.
82
Fig. 4.20 Mist characterization using PDIA.
83
Fig. 4.21 Pool fire locations in the 1 m3 enclosure.
86
Fig. 4.22 C800 pan placed between the mockup and platform.
92
Fig. 4.23 C1460 pan placed between the mockup and platform.
93
Fig. 4.24 C800 pan obstructed by a 1 x 1 m plate placed 0.75 m above the fuel
93
surface and two C350 pools placed on the platform in Scale-5
enclosure.
Fig. 4.25 Components of temperature measurement data acquisition system.
103
Fig. 5.1
GLR variation with gas pressure for Type A nozzles.
106
Fig. 5.2
Cumulative volume droplet diameter plot as obtained from LDA
107
xiv
measurement for Nozzle N1 at 7 bar(g) pressure at 850 mm
downstream.
Fig. 5.3
A typical PDIA result image for Type-A nozzle .
108
Fig. 5.4
Variation of droplet diameters with operating pressure at two
110
downstream distances for the nozzle N1 using the PDIA.
Fig. 5.5
Variation of droplets velocity with droplet diameters for nozle N1 for
112
different operating pressures at two downstream distances.
Fig. 5.6
Photograph of the spray from nozzles, N1 and N2, at 7 bar(g)
113
pressure showing the cone angle measurement.
Fig. 5.7
Variation in Gas-to-liquid mass flow ratio (GLR) with air pressure at
114
different water pressures.
Fig. 5.8
Variation in water flow rate with GLR and water supply pressure.
115
Fig. 5.9
Droplet size distribution for water pressure of 25 psig (1.7 bar(g)) and
117
different GLR.
Fig. 5.10 Cone angles at 25 psig (~ 3.5 bar(g)) water pressure and different
117
GLR
Fig. 5.11 Droplet size distribution for 50 psi(g) air pressure and different water
119
pressures.
Fig. 5.12 Spray images for 50 psig (~ 3.5 bar(g)) air pressure at different water
119
pressures.
Fig. 5.13 Variation of Sauter Mean Diameter (SMD) with GLR and water
120
pressure.
Fig. 5.14 Variation of droplet diameter distribution with GLR for 15 psi(g) water
121
pressure.
Fig. 5.15 Variation of SMD with water flow rate for different water pressures.
122
Fig. 5.16 Variation of SMD with air pressure for different water pressures.
122
Fig. 5.17 Characterization of Type-B nozzle for Scale-5 enclosure using the
125
LDA.
Fig. 5.18 Droplet size characteristics data for mist in Scale-5 enclosure
xv
126
Fig. 6.1
Mass loss history and heat release rate profile for 100 mm  circular
127
pan.
Fig. 6.2
Mass loss history and heat release rate profile for 125 mm  circular
128
pan.
Fig. 6.3
Mass loss history and heat release rate profile for 150 x 150 mm pan.
128
Fig. 6.4
Variation of fire extinguishing time and FSPI with nozzle operating
132
pressure for different fire locations (Fire locations as per Fig. 4.21).
Fig. 6.5
Flame temperatures for three experiments at 8 bar(g) nozzle
133
pressure for pool fire location P1.
Fig. 6.6
Temperature histories at the pan centreline, 600 mm above the floor
135
for four locations of 125 mm circular pool fire with 30 s pre-burn time.
Fig. 6.7
Temperature histories at 600 mm above enclosure floor along the
140
centreline (T3 of Fig. 4.15(b)), at 7 bar(g) nitrogen pressure for C125
pool fire at four different locations.
Fig. 6.8
Gas concentration histories during dry run and with mist injection at
142
different operating pressures for fire location P3.
Fig. 6.9
FSPI variation for different ON/OFF pulsing cycles.
Fig. 6.10 Temperature histories at 350 mm from the pan edge for 100 mm pool
145
146
fire at location P3.
Fig. 6.11 Temperature histories at wall mounted thermocouples for C125 Pan
149
(location P3) and pre-burn duration of 20 s.
Fig. 6.12 Temperature variations at 500 mm (T6) above the edge of the fuel
150
pan, S150, for continuous and pulsed mist (Pre-burn duration: 20 s).
Fig. 6.13 Fire suppression performance (FSPI) of continuous mist.
151
Fig. 6.14 Fire suppression performance (FSPI) of pulsed mist.
152
Fig. 6.15 Temperature profiles at 350 mm height from the pan for continuous
153
mist, with air and nitrogen (Pool size: 125 mm, Pre-burn: 30 s).
Fig. 6.16 Temperature profiles at 350 mm height from the pan for pulsed mist
xvi
153
with air and nitrogen (Pool size: 125 mm, Pre-burn: 30 s).
Fig. 6.17 Temperature variations at 350 mm from circular pool (diameter 125
155
mm) for different conditions in Scale-1 enclosure.
Fig. 6.18 Variation in water usage and time for extinguishment with fire size,
156
pre-burn and atomizing medium in Scale-1 enclosure.
Fig. 6.19 Centreline temperature-time histories for dry run and mist at 7 bar(g)
159
for 125 mm pool fire at different locations from the nozzle.
Fig. 6.20 Sequential images of flame at different intervals for continuous mist
163
on a pool fire placed at a corner of the enclosure.
Fig. 6.21 Schematic showing steps in flame extinguishment process by water
164
mist.
Fig. 6.22 A plot showing ratio of heat absorption to heat generated at
170
suppression vs specific heat release rate for air and nitrogen as
atomizing media.
Fig. 7.1
Temperature histories at a radial distance of 500 mm from vertical
173
axis of the C350 pool (Fuel: 500 ml n-heptane).
Fig. 7.2
Temperature histories at a distance of 500 mm from vertical axis of
174
the C550 pool (Fuel: 500 ml n-heptane).
Fig. 7.3
Temperature histories at a distance of 1000 mm from vertical axis of
174
the C650 pool (Fuel: 1000 ml n-heptane).
Fig. 7.4
Temperature histories at a height of 2850 mm from the enclosure
175
floor for the C650 pool (Fuel: 1000 ml n-heptane).
Fig. 7.5
Variations in extinguishment time and amount of water used with fire
181
sizes and water flow rates for different pre-burn durations and fire
locations.
Fig. 7.6
Variation in FSPI values with pool size and pre-burn duration for two
183
water flow rates.
Fig. 7.7
Variation in water consumption with fire size for different experimental 184
conditions and mist discharge at 8 l/min.
xvii
Fig. 7.8
Variation of FSPI with pool size and pre-burn for two locations of the
185
pool in Scale-3 enclosure with mist generation rate at 8 l/min.
Fig. 7.9
Temperature history for dry and mist runs for C350 fire placed in
188
Scale-3 enclosure corner (pre-burn 30 s, TC tree at 500 mm from
pool centre).
Fig. 7.10 Temperature history for dry and mist runs for C350 fire placed in
188
Scale-3 enclosure corner (pre-burn 30 s, TC tree at 1000 mm from
pool centre).
Fig. 7.11 Temperature history for dry and mist runs for C550 fire placed in
190
Scale-3 enclosure corner (pre-burn 30 s, TC tree at 500 mm from
pool centre).
Fig. 7.12 Temperature history for dry and mist runs for C550 fire placed in
190
Scale-3 enclosure corner (pre-burn 20 s, TC tree at 1000 mm from
pool centre).
Fig. 7.13 Temperature history for dry and mist runs for C650 fire placed in
191
Scale-3 enclosure corner (pre-burn 20 s, TC tree at 1000 mm from
pool centre).
Fig. 7.14 Gas concentration profiles for C550 pool fire in a corner during dry
194
and mist runs in Scale-3 enclosure (Pre-burn 30 s).
Fig. 7.15 LDO pool fire, C1460, in Scale-5 enclosure (pool on floor between
195
mock-up and platform).
Fig. 7.16 Obstructed C800 LDO pool fire in Scale-5 enclosure.
196
Fig. 7.17 Temperature profiles for C1460 pool fire at 1.5 m (Pre burn = 30 s).
204
Fig. 7.18 Temperature profiles at 1 m from C800 LDO pool (Pre burn = 30 s).
205
Fig. 7.19 Temperature profiles at 1 m from C800 HSD pool (Pre burn = 60 s).
205
Fig. 7.20 Gas concentration profiles during the suppression of C800 LDO pool
207
fire.
Fig. 7.21 Gas concentration profiles during the suppression of C800 HSD pool
fire.
xviii
207
Fig. 7.22 Temperature variations at a distance of 1 m from the obstructed
209
C800 LDO pool in Scale-5 enclosure (Pre burn = 30 s).
Fig. 7.23 Temperature profiles at 1 m from the C800 LDO pool fire during two
210
pool fires test (Test no. 46).
Fig. 7.24 Temperature profiles at 1 m from the C350 n-heptane pool fire during
210
two pool fires test (Test no. 46).
Fig. 8.1
Plot of mist extinguishing concentration (MEC) and normalized heat
release rates for the three scale enclosures.
xix
219
List of Tables
Table no.
Description
Page
Table 2.1
Burning modes of pool fires defined by fire sizes [15,14].
18
Table 2.2
Values of  for different growth rates [19].
21
Table 2.3
Comparison of fire extinguishing technologies.
23
Table 2.4
Optical methods for measurement of droplet sizes and velocities.
30
Table 3.1
Summary of studies for fire extinguishing mechanisms of a mist.
42
Table 3.2
Investigation of droplets size effects in fire extinguishment.
46
Table 3.3
Summary of full-scale experimental studies.
49
Table 3.4
Summary of small scale experiments.
50
Table 3.5
Scaling relations for different Reynolds number regimes [165].
60
Table 4.1
Test matrix for characterization of mist from Type-A nozzle.
84
Table 4.2
Test matrix for characterization of mist from Type-B nozzle.
84
Table 4.3
Test matrix for evaluation of the effects of nozzle operating
86
conditions and pool fire locations for Scale-1 enclosure.
Table 4.4
Test matrix for pulsed mist in Scale-1 enclosure.
87
Table 4.5
Test matrix for comparison of continuous and pulsed mist for
88
different pre-burn durations in Scale-1 enclosure.
Table 4.6
Test matrix for experiments in Scale-3 (39 m3) enclosure.
89
Table 4.7
Test matrix for single pool fire experiments in Scale-5 enclosure.
90
Table 4.8
Test matrix for experiments with two fires in Scale-5 (345 m3)
91
enclosure.
Table 4.9
Test matrix for experiments with three/four fires in Scale-5 (345
91
m3) enclosure.
Table 5.1
Liquid-to-air mass ratio for the mist from Type-A nozzles.
105
Table 5.2
Droplet diameter data at 850 mm from the nozzle using the LDA.
106
xx
Table 5.3
Droplet diameter data for nozzle N1 using the PDIA.
109
Table 5.4
Mist characteristics of Type-B nozzle for Scale – 3 enclosure.
124
Table 6.1
Fire suppression performance index for different nitrogen
130
pressures and four pool fire locations.
Table 6.2
Fire suppression performance in terms of rate of temperature
137
decrease for a pool fire at four different locations.
Table 6.3
Fire suppression times for pulsed mist in Scale-1 enclosure (Pool
143
fire: C100; Pre-burn: 10 s; Water flow rate = 3.8 ml/s).
Table 6.4
Fire suppression performance for different pulsing cycles (Pool
144
fire: C100; Pre-burn: 10 s; Water flow rate = 3.8 ml/s).
Table 6.5
Fire suppression performance of nitrogen generated mist in
148
continuous and pulsed discharge modes.
Table 6.6
Fire suppression performance with air generated mist in
151
continuous or pulsed discharge modes.
Table 6.7
Droplets
life-time
at
various
temperatures
and
humidity
165
Estimate of heat absorption and heat generation during fire
168
conditions.
Table 6.8
suppression.
Table 7.1
Suppression times for different conditions in Scale-3 (39 m3)
177
enclosure.
Table 7.2
Average values of FSPI for different conditions in Scale-3 (39 m3)
178
enclosure.
Table 7.3
Fire suppression performance for single fire in Scale-5 (345 m3)
198
enclosure.
Table 7.4
Fire suppression performance with two fires in Scale-5 (345 m3)
199
enclosure.
Table 7.5
Fire suppression performance with three/four fires in Scale-5
200
(345 m3) enclosure.
Table 8.1
Summary of experimental parameters in the three enclosures.
xxi
217
Table 8.2
Summary of fire suppression results for the three enclosures.
218
Table A.1
Thermal properties data for different fuels.
246
Table A.2
Heat release rate, fire duration and flame height for pool fires.
246
Table B.1
Combined uncertainty in GLR estimation for Type-A nozzle.
247
Table B.2
Combined uncertainty in GLR estimation for Type-B nozzle for air
248
supply pressure of 60 psig and water flow rate of 1.0 l/min.
Table B.3
Uncertainty in estimation of FSPI for Scale-1 enclosure.
249
Table B.4
Uncertainty in estimation of FSPI for Scale-3 enclosure.
249
Table B.5
Uncertainty in estimation of FSPI for Scale-5 enclosure.
250
Table B.6
Summary of temperature uncertainty components and total
252
uncertainty.
xxii
Nomenclature
A
empirical constants
area of discharge orifice
Ad
surface area of water droplet
Af
burning area of the fuel
glr
an estimate of measurand GLR
C
a constant
CD
drag coefficient
Cs
scattering area of a particle
c
sensitivity coefficients
cpd
specific heat of water droplet
cp
specific heat of water at constant pressure (~ 4.2 kJ/kg).
Cxxx Circular pool with xxx mm diameter
D
diameter for a circular pool (m)
Dm
mass diffusivity of the droplets
d
droplet diameter
E
activation energy of chemical reaction
Fr
Froude number
f
number of particles for a given mass fraction of mist
g
gravitational acceleration (m/s2)
Hc heat of combustion
Hc,eff effective heat of combustion (kJ/kg) of the volatiles,
h
convective heat transfer coefficient
hm
mass transfer coefficient
hfv
latent heat of evaporation of water (~ 2260 kJ/kg at ~1 bar)
Ks
Attenuation coefficient for a mono-disperse particle cloud
k
thermal conductivity of the gas phase
Mw
mass flow rate of water mist
Lf
flame height (m)
mf
mass fractions of the fuel
mox mass fractions of oxygen
md
mass of a water droplet
xxiii
̇ . burning rate or mass loss rate of solid or liquid fuel as it is vaporized
̇
mass flux, i.e., mass flow rate per unit area
̇
asymptotic diameter mass loss rate per unit area for a pool fire
̇
mass flow rate of gas (kg/s)
̇
mass flow rate of liquid (kg/s)
̇
water flow rate (l/min)
N0
number of particles
Nu
Nusselt number
p
probability
pg
gas pressure
ps(Td) saturated vapour pressure at droplet temperature
Pw
water supply pressure
Pgi
absolute pressure of the gas flow
Pstd pressure at standard atmospheric conditions (1 atm.)
Pr
Prandtl number
Q̇
total heat release rate of fire (kW)
Q g
corrected volumetric flow rate of gas (l/min)
Q w
measured volumetric flow rate of water (l/min)
Q g
measured volumetric flow rate of gas (l/min)
Qw
quantity of water discharged in text time (in litres)
QR
heat released during the fire(kW)
QA
heat absorbed by the droplets for total evaporation (kW)
qg
estimate of Qg from N multiple measurements
qw
estimate of Qw, from N multiple measurements
qe
latent heat of evaporation of water
R
ideal gas constant (0.082 L.atm.K-1.mol-1)
Rer Relative Reynolds number, based on the relative velocity between droplet
and gas
Rf
combustion rate of a fire
Sh
Sherwood number
Sxxx Square pool with dimensions as xxx mm.
T
Temperature (C)
xxiv
T
temperature difference between droplet and surrounding gas
text
extinguishment time ( seconds)
tα/2, t-statistics, α =1-p
U
Expanded uncertainty associated with the measurement result
u
Standard uncertainty due to an error
uc
Combined standard uncertainty in the measurement result
V
enclosure volume (m3).
Vf
volume of fuel (litres)
Vd
droplet’s velocity
Vg
velocity of the hot gas
Vp
characteristic vapour phase velocity at the pool surface (m/s),
vg
kinematic viscosity of the gas phase
xv
volume fraction of water vapour in the gas
Symbols

fire growth factor (kW/s2) - an empirical constant

mean beam length correction factor - an empirical constant.

combustion efficiency
regression rate specific to the fuel (m/s).


fluid density (kg/m3)

pulsing factor

degree of freedoms
Subscript
w
water
a
air
d
droplet
f
fuel
g
gas
i
inlet
o
orifice
ox
oxygen
xxv
p
pool
v
vapour
Abbreviations
GLR
Gas-to-Liquid mass flow rate Ratio.
DVX
Diameter of a droplet distribution (mist) such that x % of the volume of the
spray is in droplets smaller (or (100-x) % larger) than this value.
FSPI
Fire Suppression Performance Index: Defined as the inverse of the product
of extinguishment time (in seconds) and quantity of water consumed per unit
enclosure volume (litres/m3).
FTSI
Fire temperature suppression index: Defined as the rate of decrease of flame
temperature from peaking state to the suppression state after mist injection.
HRR
Heat release rate: The rate at which the combustion reactions produce heat
energy, usually given in kW (= kJ/s) and denoted as Q .
MEC
Minimum extinguishing concentration (g/m3): Quantity of agent required per
unit volume of enclosed space to affect extinguishment of fire.
SMD
Sauter Mean Diameter: The diameter of a droplet whose volume to surface
area ratio is equal to the total volume of the droplet population divided by the
total surface area of that population.
VMD
Volume Mean Diameter (or DV50): The midpoint droplet size (median), where
half of the volume of spray is in droplets smaller or larger than the median.
xxvi