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Advances in Water-Based Fire Suppression Modeling:

Evaluating Sprinkler Discharge CharacteristicsJune 24, 2008

7th International Fire Sprinkler Conference and Exhibition Copenhagen, Denmark

Students: Ning Ren, Andrew Blum, Di Wu, and Chi Do

Faculty Advisor: Andre Marshall

Sponsors: NFSA, FM Global, NSF

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Overview

Introduction Motivation Project History Previous Work

Global Objective Evaluate Discharge

Characteristics

Advanced Measurements

SAM Development

Approach Experimental Modeling (SAM)

Results Sheet Formation (Deflector) Sheet Breakup Drop Formation Dispersion

Summary

Plans Experimental Modeling

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Motivation

Gain New Knowledge

Physical models characterizing the break-up process and the associated initial spray in fire suppression devices have yet to be developed.

Develop Injector Technology

The absence of this analytical capability impedes the development of fire suppression injectors/systems.

Understanding the relationship between atomization physics and

injector control parameters would facilitate a transition away from ‘cut

and try’ injector development.

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Motivation

D

D

D

L

L

D

def

boss

space

tine

boss

o

inlet

jet

inlet

A A

Section A-A

tarm

‘Cut and Try’ ‘Characterization’

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Motivation

Advance Fire Protection Engineering Practices

CFD modeling tools of fire phenomena are becoming increasingly popular for fire protection analysis and performance based design.

The absence of physical models describing atomization in sprinklers and water mist injectors results in uncertainties in CFD simulation of suppressed fires.

Errors in the specification of the initial spray will be propagated and amplified during dispersion calculations.

The atomization model represents a critical missing link in the

modeling of suppressed fires.

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Project History

NFSA

Betatti -U. Modena

Sprinkler Atomization Modeling and FDS Integration

DuPontSurfactant Effects on Fire Suppression

FY2005 FY2006 FY2007 FY2008 FY2009

FM GlobalScaling Laws and Models for Fire Suppression Devices

HP Mist Modeling

UM Fire Suppression Spray Research

FY2010 FY2011 FY2012

NSF CAREER AwardExploring Atomization and Jet Fragmentation in Combustion and Fire Suppression Systems

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Previous Work

Dundas, 1974

K = 7.2 (0.5)

K = 27.4 (1.9)

K = 62.0 (4.3)

K = 110 (7.6)

K = 245 (17.0)

K = 435 (30.2)

Yu, 1986

K = 179 (12.4)

Widmann, 2001

43 < K < 81

Sheppard, 2002

40 < K < 363

Putorti, 2003

11 < K < 49

1

3

Previous Research

FDF

We ~FD

F

U 2D

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Global Objective

Evaluate discharge characteristics from fire suppression devices using measurements and models.

Parameter Space

based on varied injector geometry and injection conditions.

Experiments based on state-of-the art diagnostics focused on the initial spray.

Analysis based on physics based models using semi-empirical approaches (e.g. scaling

laws and wave dispersion analysis).

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Approach

HP Nozzle100 bar ~ 60 m

Gr ow th of W aves

Ligament Dr op

Sh eet For mation

Jet

Def le ctor

Sheet L igamen t

Injected Flow

LP Nozzle2 bar ~ 700 m

TYCOTY4211

MP Nozzle15 bar ~ 225 m

TYCOAM4

Injectors

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Approach

Geometric parameter space w/n LP injector (sprinkler) configuration

‘Basis’ Nozzle ‘Tined’ Nozzle(Tyco D3 Nozzle)

‘Standard’ Nozzle(Tyco D3 Nozzle)Sprinkler

38 mm

3.2, 6.7, 9.7 mm

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Trajectory Measurements (PLIF)

Camera FOVtexp = 900 s

Cooke 16-bit cooled 2.0Mpixel High-Speed Digital Video Camera.

Approach

(12.7 mm)

(22.7 mm)

(62.7 mm)

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Approach

Sheet Break-up Measurements

Canon 12-bit 3.4 MpixelDigital SLR Camera

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Approach

Drop Size Measurements

Malvern Spraytec Analyzer(Light Diffraction Technique)

P = 2.07 barr/R = 0.45

Local

Local Measurements Local Drop Size Distribution

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Approach

Volume Flux Measurements

1.0 m

3.0 m 1.0 m

Patternator

30º

15º

Nozzle

3.0 m 5.0 m1.0 m

2.0 m4.0 m

8.6 m

7.2 m 0º

Qi q j r VFi ,jj1

N

QT q j r VFi , jj1

N

i1

M

QFi Qi /QT

BasisDo = 9.7 mmP = 2.07 bar

BasisDo = 9.7 mmP = 2.07 bar

dv50 = 780 μm

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Approach

Transport equations for mass and

momentum provide the sheet

trajectory.

Annular Sheets (Ibrahim, 2004)

sin

cos

sincos2

cos

0

2

d

dz

d

dr

gd

d

rTT

p

d

dU

gSd

dUU

d

dTUr

d

drUT

d

dUrT

Lg

L

LL

Sheet Angle

Curvilinear Coordinate Along Sheet

Gas-liquid Interfacial Friction

P Across Sheet

Velocity

Surface Tension

Thick

RadialLocation

VerticalLocation

Mass

r-mom

z-mom

Jet Radius

Radius where Wall EffectsReach Free Surface

Jet Flow RateKinematic Viscosity

Arbitrary Length ScaleDetermined from Matching

Deflector Radius

hd

ro

2

2rd

0.016597 l

Uo

1/ 5

rd

4 / 5 rd rl

0.0211 l

Q

1/ 4rd

9/ 4 l9/ 4

rd

rd rl

Impinging Jet (Watson, 1964)

Viscous interactions with deflector

important for initial thickness and

velocity of unstable free liquid

sheet.

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Approach

f

t

2

l

l

n 2 f

t

2(anU 2 n 2)

lT0

f

t

2

2(anU 2 n 2)

lT0 nbu ,sh

2bu ,sh

aU

2

2

Viscous

InviscidMost

UnstableWavelength

Fastest Growing Wave

DimensionlessWave Growth Rate

f

t

2

3l

l

n 2 f

t

n 2

ldlig

1n 2dlig

2

4

0

ViscousWave Growth(Sterling and Sleicher, 1975; Weber, 1931)

The most unstable wave is determined, which

breaks up the sheet at rbu,lig into a fragment

having characteristic length bu,lig.

The most unstable wave is determined, which

breaks up the sheet at rbu,sh into a fragment

having characteristic length bu,sh/2.

Wave Growth (Dombrowski, 1963)

p-

p+ p+p-p-

U

Gas

Vjet

p+ p-

r

Sinusoidal Waves

r

z

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Results

hd

* 1

4Dd

*

Region II

0.0141Dd

* 4 / 5Reo

1/ 5 rd

* rl

*

Region III +

0.0094Dd

* 5/ 4Reo

1/ 4 rd

* rl

*

Governing Equations

Dimensionless Solution

1

r

(rur )

ruz

z0

ur

ur

r uz

ur

z

2ur

z2

• The thickness and velocity of the sheet is reduced by viscous effects depending on the nozzle geometry (not yet accounting for spaces).

SheetFormation

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Results

• Two distinct streams are formed: the jet is deflected radially outward along the tines and the jet is forced downward through the spaces

• The flow split between these streams governs the sheet thickness and the resulting drop size.

SheetFormation

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ResultsSheet

Breakup

• Sheet breakup locations occur several jet diameters away from the sprinkler.

• Data collapses well with appropriate theory

Xsheet 3 f0

*Dd*

2hd* cosWe

3 f 0

*

f (Re)cos2We (Dd

* )3

Standard Nozzle, Do = 6.35 mm, p = 2 bar

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ResultsDrop

Formation

• Drop size in the space stream are siginificantly smaller than tine stream, but follow Rosin-Rammler

• Testing scaling law for drop size

Xdrop 4.5rd

*hd* cos 2

(* )1/ 2 foWeD

imen

sion

less

Dro

p S

ize,

dv5

0/D

o

C 3

p = 2 bar

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Results

The radial coordinate has been normalized with the maximum theoretical radial value for each condition.

K = 7.2 (0.5) K = 25.9 (1.8) K = 54.7 (3.4)

R (vo)r

2h

g

1/ 2

1(vo)z

2

2gh

1/ 2

(vo)z

2

2gh

1/ 2

Dispersion

Spatial DropSize Distributions Spatial Volume Flux Distributions

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Summary

Viscous effects along the deflector can be important (for small K-factors).

Two well characterized sheets (radially expanding and orthogonal fan) are formed through the tines and the spaces.

SAM successfully models the tine stream. Space stream submodel in SAM currently under development.

Sheet breakup locations are predicted well by SAM with We-1/3.

‘Ligament’ break-up (high We) modes and ‘rim’ break-up modes (low We) are observed. The We transition depends on nozzle geometry.

Drop size predicted well by SAM when nozzle operates in ‘ligament’ breakup mode with We-1/3.

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Experimental Plans

SpaceStream

TineStream

QUANTITATIVESHADOWGRAPH / PTV

BREAKUP IMAGING

DROP SIZE / VELOCITY

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Experimental Plans

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SAM Modeling Plans

Basis NozzleStandard Nozzle(Tyco D3 Nozzle)

FundamentalModels

ToInner

ToOuter

Splitter

Space Stream Submodel

CFD Integration

Device Characterization

Expanding ValidatedParameter Space

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Questions?