Experimental study of the effects of
vent geometry on the dispersion of a
buoyant gas in a small enclosure
B.CARITEAU, I. TKATSCHENKO
CEA Saclay, DEN, DM2S, SMFE, LEEF
ICHS 4, San Francisco, California, USA, September 2011
Dispersion in an enclosure : Natural ventilation through one vent
V
X(z)?
U0, Dr0
ICHS 4, San Francisco, California, USA, September 2011
Dispersion in an enclosure : Natural ventilation through one vent
V
X(z)?
U0, Dr0
A wide range of injection velocity
ICHS 4, San Francisco, California, USA, September 2011
Dispersion in an enclosure : Natural ventilation through one vent
V
X(z)?
U0, Dr0
Vent effects
ICHS 4, San Francisco, California, USA, September 2011
Previous results on dispersion regimes without ventilation
r  r0 V
Volume Richardson number: Ri v  g a
r 0 U 02
Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36)
1
ICHS 4, San Francisco, California, USA, September 2011
3
Previous results on dispersion regimes without ventilation
r  r0 V
Volume Richardson number: Ri v  g a
r 0 U 02
Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36)
1
Buoyancy dominated
dispersion
Stratified
Momentum dominated
dispersion
Riv
1
d
H
Homogeneous layer
 H 

Rivc  
 25R0 
3
2
ICHS 4, San Francisco, California, USA, September 2011
RiVc
Fully homogeneous
A simple analytical model for dispersion with 1 vent
Linden, Lane-Serff & Smeed (1990, J. Fluid Mech. Vol. 212)
ICHS 4, San Francisco, California, USA, September 2011
A simple analytical model for dispersion with 1 vent
Linden, Lane-Serff & Smeed (1990, J. Fluid Mech. Vol. 212)
Hypotheses for the analytical model:
P and T Constant
Homogeneous distribution
Pure gravity driven flow through the vent
Boussinesq approximation
ICHS 4, San Francisco, California, USA, September 2011
A simple analytical model for dispersion with 1 vent
Linden, Lane-Serff & Smeed (1990, J. Fluid Mech. Vol. 212)
Hypotheses for the analytical model:
P and T Constant
Homogeneous distribution
Pure gravity driven flow through the vent
Boussinesq approximation
Volume flow rate
through the vent
Qe  C D S ( Xg 0 h)1 / 2
CD=0.25 discharge coefficient
S
h
g 0  g
ICHS 4, San Francisco, California, USA, September 2011
r a  r0
ra
A simple analytical model for dispersion with 1 vent
Linden, Lane-Serff & Smeed (1990, J. Fluid Mech. Vol. 212)
Hypotheses for the analytical model:
P and T Constant
Homogeneous distribution
Pure gravity driven flow through the vent
Boussinesq approximation
Volume flow rate
through the vent
Qe  C D S ( Xg 0 h)1 / 2
CD=0.25 discharge coefficient
S
Steady state volume
fraction in the enclosure


Q0
X 
1/ 2 
 C D S ( g 0 h) 
2/3
ICHS 4, San Francisco, California, USA, September 2011
h
g 0  g
r a  r0
ra
Goals of the present experiments:
Influence of Riv and vent geometry on the
vertical distribution
Compare results to the analytical model
Check the validity of the criterion for
homogeneous filling
ICHS 4, San Francisco, California, USA, September 2011
11
Experimental set-up
Steady state vertical distribution
Volume fraction variations with the flow rate
ICHS 4, San Francisco, California, USA, September 2011
12
Experimental set-up
Steady state vertical distribution
Volume fraction variations with the flow rate
ICHS 4, San Francisco, California, USA, September 2011
13
Experimental setup and injection conditions
(b)
(c)
20mm
(c) 35x900 mm2
(a)
180mm
(b) 180x180 mm2
180mm
Vents:
180mm
900mm
35mm
(a) 180x900 mm2
Vent
1260mm
930mm
V=1.1m3
930mm
Injection tube
ICHS 4, San Francisco, California, USA, September 2011
Experimental setup and injection conditions
Working gases : Helium/Air
Riv=8 10-4 to 75
D0=20mm
Riv=0.2 to 740
20mm
Sources : X0=100% helium
Q0=1 to 300Nl/min
180mm
D0=5mm or 20mm
D0=5mm
Vent
1260mm
930mm
V=1.1m3
930mm
Injection tube
ICHS 4, San Francisco, California, USA, September 2011
Helium volume fraction measurement : min-katharometers
7mm
M1
M2
M4
1160mm
katharometers
1060mm
Vent
940mm
700mm
580mm
M4
625mm
135mm
930mm
240mm
1260mm
820mm
460mm
M1
340mm
230mm
M2
220mm
255mm
195mm
930mm
100mm
Injection tube
ICHS 4, San Francisco, California, USA, September 2011
16
Experimental set-up
Steady state vertical distribution
Volume fraction variations with the flow rate
ICHS 4, San Francisco, California, USA, September 2011
17
Steady state: vertical profiles
180x900 mm2 vent (a)
20mm source : toward buoyancy dominated flow
1,0
0,8
0,6
z /H
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
180Nl/min
300Nl/min
0,4
0,2
0,0
0,0
0,5
1,0
1,5
2,0
2,5
X/<X>
ICHS 4, San Francisco, California, USA, September 2011
3,0
3,5
Riv
1
0.2
Steady state: vertical profiles
180x900 mm2 vent (a)
20mm source : toward buoyancy dominated flow
1,0
0,8
0,6
z /H
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
180Nl/min
300Nl/min
0,4
0,2
0,0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Riv
1
0.2
3,5
X/<X>
Strong vertical variations
ICHS 4, San Francisco, California, USA, September 2011
Steady state: vertical profiles
180x900 mm2 vent (a)
20mm source : toward buoyancy dominated flow
1,0
0,8
0,6
z /H
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
180Nl/min
300Nl/min
0,4
0,2
0,0
0,0
0,5
1,0
1,5
2,0
2,5
X/<X>
Auto-similar
ICHS 4, San Francisco, California, USA, September 2011
3,0
3,5
Riv
1
0.2
Steady state: vertical profiles
180x900 mm2 vent (a)
5mm source : toward momentum dominated flow
1,0
0,8
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min
z /H
0,6
0,4
0,2
Riv
1
0.05
0.0023
0,0
0,0
0,5
1,0
1,5
2,0
2,5
X/<X>
ICHS 4, San Francisco, California, USA, September 2011
3,0
3,5
Steady state: vertical profiles
180x900 mm2 vent (a)
5mm source : toward momentum dominated flow
1,0
0,8
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min
z /H
0,6
0,4
0,2
Riv
1
0.05
0.0023
0,0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
X/<X>
Top homogeneous layer
ICHS 4, San Francisco, California, USA, September 2011
Steady state: vertical profiles
180x900 mm2 vent (a)
5mm source : toward momentum dominated flow
1,0
0,8
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min
z /H
0,6
0,4
0,2
Riv
1
0.05
0.0023
0,0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
X/<X>
Homogeneous for Riv<0.0023
ICHS 4, San Francisco, California, USA, September 2011
Steady state: vertical profiles
180x180 mm2 vent (b)
20mm source : toward buoyancy dominated flow
1,0
0,8
0,6
z /H
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
180Nl/min
300Nl/min
0,4
0,2
0,0
0,8
0,9
1,0
1,1
1,2
X/<X>
ICHS 4, San Francisco, California, USA, September 2011
1,3
1,4
Riv
1
0.2
Steady state: vertical profiles
180x180 mm2 vent (b)
5mm source : toward momentum dominated flow
1,0
0,8
0,6
z /H
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min
0,4
0,2
0,0
0,8
0,9
1,0
1,1
1,2
X/<X>
ICHS 4, San Francisco, California, USA, September 2011
1,3
1,4
Riv
1
0.05
0.0023
Steady state: vertical profiles
180x180 mm2 vent (b)
5mm source : toward momentum dominated flow
1,0
0,8
0,6
z /H
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min
0,4
0,2
0,0
0,8
0,9
1,0
1,1
1,2
X/<X>
1,3
Riv
1
0.05
0.0023
1,4
Homogeneous for Riv<0.0023
ICHS 4, San Francisco, California, USA, September 2011
Steady state: vertical profiles
35x900 mm2 vent (c)
20mm source : toward buoyancy dominated flow
1,0
0,8
Riv
z /H
0,6
5Nl/min
10Nl/min
20Nl/min
40Nl/min
60Nl/min
100Nl/min 1
180Nl/min
300Nl/min 0.2
0,4
0,2
0,0
0,4
0,6
0,8
1,0
X/<X>
ICHS 4, San Francisco, California, USA, September 2011
1,2
1,4
Steady state: vertical profiles
35x900 mm2 vent (c)
5mm source : toward momentum dominated flow
1,0
0,8
Riv
1
0,6
z /H
5Nl/min
10Nl/min
20Nl/min 0.05
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min 0.0023
0,4
0,2
0,0
0,7
0,8
0,9
1,0
1,1
X/<X>
1,2
ICHS 4, San Francisco, California, USA, September 2011
1,3
1,4
Steady state: vertical profiles
35x900 mm2 vent (c)
5mm source : toward momentum dominated flow
1,0
0,8
Riv
1
0,6
z /H
5Nl/min
10Nl/min
20Nl/min 0.05
40Nl/min
60Nl/min
100Nl/min
140Nl/min
180Nl/min 0.0023
0,4
0,2
0,0
0,7
0,8
0,9
1,0
1,1
X/<X>
1,2
1,3
1,4
Homogeneous for Riv<0.0023
ICHS 4, San Francisco, California, USA, September 2011
Experimental set-up
Steady state vertical distribution
Volume fraction variations with the flow rate
ICHS 4, San Francisco, California, USA, September 2011
30
Volume fraction variations with the flow rate
Average volume fraction
100,0
<X> (%)
10,0
Vent 180x900 mm2 (a)
Vent 180x180 mm2 (b)
Vent 35x900 mm2 (c)
Filed symbols: 20mm source
Model with CD=0.25
1,0
0,1
1,E-05
1,E-04
1,E-03
Q
(m 3/s)
ICHS 4, San Francisco, California, USA, September 2011
1,E-02
Volume fraction variations with the flow rate
Average volume fraction
100,0
<X> (%)
10,0
Vent 180x900 mm2 (a)
Vent 180x180 mm2 (b)
Vent 35x900 mm2 (c)
Filed symbols: 20mm source
Model with CD=0.25
1,0
0,1
1,E-05
1,E-04
1,E-03
Q
(m 3/s)
ICHS 4, San Francisco, California, USA, September 2011
1,E-02
Volume fraction variations with the flow rate
Average volume fraction
100,0
<X> (%)
10,0
Vent 180x900 mm2 (a)
Vent 180x180 mm2 (b)
Vent 35x900 mm2 (c)
Filed symbols: 20mm source
Model with CD=0.25
1,0
0,1
1,E-05
1,E-04
1,E-03
Q
1,E-02
(m 3/s)
The model over estimate the experimental results
In particular for vent (a)
ICHS 4, San Francisco, California, USA, September 2011
Volume fraction variations with the flow rate
Average volume fraction
100,0
<X> (%)
10,0
Vent 180x900 mm2 (a)
Vent 180x180 mm2 (b)
Vent 35x900 mm2 (c)
Filed symbols: 20mm source
Model with CD=0.25
1,0
0,1
1,E-05
1,E-04
1,E-03
Q
1,E-02
(m 3/s)
The power law is no longer valid for SOME data
ICHS 4, San Francisco, California, USA, September 2011
Volume fraction variations with the flow rate
Average volume fraction
100,0
<X> (%)
10,0
Vent 180x900 mm2 (a)
Vent 180x180 mm2 (b)
Vent 35x900 mm2 (c)
Filed symbols: 20mm source
Model with CD=0.25
1,0
0,1
1,E-05
1,E-04
1,E-03
Q
(m 3/s)
ICHS 4, San Francisco, California, USA, September 2011
1,E-02
Volume fraction variations with the flow rate
Maximum volume fraction
100,0
Xmax (%)
10,0
Vent 180x900 mm2 (a)
Vent 180x180 mm2 (b)
Vent 35x900 mm2 (c)
Filed symbols: 20mm source
Model with CD=0.25
1,0
0,1
1,E-05
1,E-04
Q (m 3/s)
1,E-03
ICHS 4, San Francisco, California, USA, September 2011
1,E-02
Volume fraction variations with the flow rate
Maximum volume fraction vs normalized flow rate
0,7
Source flow rate normalized by the
expected outflow rate :
0,6
Xmax
Model
X=Q/Qe<1 0,5
Qe  CD S ( X maxg0 h)1/ 2
i.e. only gravity driven outflow
0,4
0,3
0,2
0,1
0,0
0,0
0,5
1,0
Q/Qe
1,5
2,0
Event 180x900 mm2 (a)
Event 180x180 mm2 (b)
Event 35x900 mm2 (c)
Filed symbols: 20mm source
ICHS 4, San Francisco, California, USA, September 2011
Volume fraction variations with the flow rate
Maximum volume fraction vs normalized flow rate
100,0
0,7
Xmax (%)
10,0
0,6
1,0
Xmax
0,5
0,4
0,1
1,E-05
0,3
0,2
0,1
0,0
0,0
0.3
0,5
1,0
Q/Qe
1,5
2,0
Event 180x900 mm2 (a)
Event 180x180 mm2 (b)
Event 35x900 mm2 (c)
Filed symbols: 20mm source
ICHS 4, San Francisco, California, USA, September 2011
1,E-04
Q (m 3/s)
1,E-03
1,E-02
Volume fraction variations with the flow rate
Maximum volume fraction vs normalized flow rate
100,0
0,7
Xmax (%)
10,0
0,6
1,0
Xmax
0,5
0,4
0,1
1,E-05
0,3
0,2
0,1
0,0
0,0
0.3
0,5
1,0
Q/Qe
1,5
2,0
Event 180x900 mm2 (a)
Event 180x180 mm2 (b)
Event 35x900 mm2 (c)
Filed symbols: 20mm source
ICHS 4, San Francisco, California, USA, September 2011
1,E-04
Q (m 3/s)
1,E-03
1,E-02
Volume fraction variations with the flow rate
Maximum volume fraction vs normalized flow rate
100,0
0,7
Xmax (%)
10,0
0,6
1,0
Xmax
0,5
0,4
0,1
1,E-05
0,3
0,2
1,E-04
Q (m 3/s)
1,E-03
1,E-02
Purely gravity driven
flow through the vent
0,1
0,0
0,0
0.3
0,5
1,0
Q/Qe
1,5
2,0
Event 180x900 mm2 (a)
Event 180x180 mm2 (b)
Event 35x900 mm2 (c)
Filed symbols: 20mm source
ICHS 4, San Francisco, California, USA, September 2011
Volume fraction variations with the flow rate
Maximum volume fraction vs normalized flow rate
100,0
0,7
Xmax (%)
10,0
0,6
1,0
Xmax
0,5
0,4
0,1
1,E-05
0,3
0,2
1,E-04
Q (m 3/s)
1,E-03
1,E-02
Additional pressure
effects
0,1
0,0
0,0
0.3
0,5
1,0
Q/Qe
1,5
2,0
Event 180x900 mm2 (a)
Event 180x180 mm2 (b)
Event 35x900 mm2 (c)
Filed symbols: 20mm source
ICHS 4, San Francisco, California, USA, September 2011
Conclusions
Strong vertical stratification
Highly dependent on the vent geometry
Source momentum effects : homogeneous layer
Criterion for complete homogeneity still valid
Homogeneous model gives fairly good results
Pressure effects are significant when Q/Qe>0.3
ICHS 4, San Francisco, California, USA, September 2011