Transcript Water Mist Spray Modeling With FDS

Water Mist Spray Modeling With FDS
Fire and Evacuation Modeling Technical Conference 2011
Simo Hostikka, Jukka Vaari, Topi Sikanen, Antti Paajanen
VTT Technical Research Centre of Finland
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SPRAY COMPUTATIONS IN FDS
Droplet momentum
dmd u
 md g  12  g CDrd2 u rel u rel
dt
Size distribution



F d   


d
1
2

1 e
d 

lnd  / d m 2

2 2
0
1 e
0.693
 
d 
dm
dd  d  d m
dm  d
u0
1  C Drd2
u
; B
1  Bu0 t
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DRAG REDUCTION BY WAKE EFFECT
F
CD 
C D0
F0
L
Ramírez-Mũnoz et al. (2007).
 Re
F
1
 W 1  1
F0
16 L / d d  1

2


2
 Re
1
exp  1
 16 L / d d  1
2


 Re1
CD 0 
1
1  exp 
W  1
 16 L / d d  1
2 
2













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INTRODUCING THE DROPLETS INTO THE
COMPUTATION
Segment of a spherical surface
Pf  f f sinf

f f   exp     x2
f

,x 
fmax  f
fmax  fmin
Here:  = 5 and  = 0
Initial velocity: vd , 0  C 2P / d
User specifies the offset distance
f
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EXAMPLE NOZZLES
 Spraying systems LN-2
 High-pressure micronozzles A, B and C from
Marioff.
 Multi-orifice spray heads
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SPRAY PROFILE TESTS
NFPA 750
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RESULTS: SPRAY PROFILES (LN-2 NOZZLE)
• 0.4 m below the nozzle
• 20 bar pressure
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RESULTS: SPRAY PROFILES (A, B, C NOZZLES)
• 1 m below the nozzle
• 70 bar pressure
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AIR ENTRAINMENT TESTS
• Rectangular channel 2.0 m  0.6 m  0.6 m
• Multi-orifice nozzles in the middle of the channel
• Pressures 50…10 bar
• Air speed measurement 0.5 m upstream
(center and 6 cm from wall)
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RESULTS: AIR ENTRAINMENT
Channel center
6 cm from wall
• SH4 and SH5 have different perimeter angles
• Difference in momentum transfer difficult to capture
• Results were sensitive to offset value
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RADIATION ATTENUATION TESTS
 LPG gas heater
 0.2 m  0.3 m
 Temperature 950 C
 Nozzles A, B and C
 50, 70 and 100 bar
 Experimental
uncertainty < 7 %
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RADIATION ATTENUATION SIMULATIONS
Two sets of simulations
 Set 1 = ‘good resolution’
 Set 2 = ‘even better’
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RADIATION ATTENUATION RESULTS
Set 1
Set 2
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RADIATION ATTENUATION SENSITIVITY STUDY
x = 2.0 cm
DROP INSERT RATE = 1105 1/s
x = 1.0 cm
DROP INSERT RATE= 1105 1/s
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ACKNOWLEDGEMENTS
 Spray profile measurements were performed by Maria Putkiranta,
Riina Rajala, Pentti Saarenrinne and Markus Honkanen of the
Tampere University of Technology.
 Co-operation with the members of the FDS development team
 Funding
 Finnish Funding Agency for Technology and Innovation,
 Marioff Corporation Oy,
 Rautaruukki Oyj,
 YIT Kiinteistötekniikka Oy
 Insinööritoimisto Markku Kauriala Ltd.