B.CARITEAU, I. TKATSCHENKO CEA Saclay, DEN, DM2S, SMFE, LEEF

ICHS 4, San Francisco, California, USA, September 2011

Experimental study of the effects Experimental study of the effects of vent geometry on the of vent geometry on the

dispersion of a buoyant gas in a dispersion of a buoyant gas in a small enclosuresmall enclosure

B.CARITEAU, I. TKATSCHENKOCEA Saclay, DEN, DM2S, SMFE, LEEF


Dispersion in an enclosure : Natural ventilation through one vent

U0,

V

X(z)?


A wide range of injection velocity

U0,

V

X(z)?



Vent effects

U0,

V

X(z)?



Volume Richardson number: 2

00

031

UVgRi a

v

Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36)

Previous results on dispersion regimes without ventilation


Volume Richardson number:

RivBuoyancy dominated dispersion

Momentum dominated dispersion

200

031

UVgRi a

v

Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36)

1

Stratified

RiVcd

H

Homogeneous layer

Fully homogeneous

Previous results on dispersion regimes without ventilation

2

025

RHRivc


A simple analytical model for dispersion with 1 ventLinden, Lane-Serff & Smeed (1990, J. Fluid Mech. Vol. 212)



Hypotheses for the analytical model: P and T ConstantHomogeneous distributionPure gravity driven flow through the ventBoussinesq approximation




2/10 )( hgXSCQ De Volume flow rate

through the ventS h

a

agg

00

CD=0.25 discharge coefficient




2/10 )( hgXSCQ De Volume flow rate

through the ventS h

a

agg

00

CD=0.25 discharge coefficient

3/2

2/10

0

)(

hgSC

QXD

Steady state volume fraction in the enclosure

11ICHS 4, San Francisco, California, USA, September 2011

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


Experimental set-upExperimental set-up

Steady state vertical distributionSteady state vertical distribution

Volume fraction variations with the flow Volume fraction variations with the flow raterate


Experimental set-upExperimental set-upExperimental set-upExperimental set-up




Vents: (a) 180x900 mm2

(b) 180x180 mm2

(c) 35x900 mm2

Experimental setup and injection Experimental setup and injection conditionsconditions

Injection tube

930m

m

930mm

1260mm

Vent

180m

m20m

m

(b)

180m

m

(a)

35m

m (c)

900mm 180mm

V=1.1m3


Sources :D0=5mm or 20mmX0=100% heliumQ0=1 to 300Nl/min

Experimental setup and injection Experimental setup and injection conditionsconditions

Injection tube

930m

m

930mm

1260mm

Vent

180m

m20m

m

D0=5mmD0=20mm

Riv=8 10-4 to 75 Riv=0.2 to 740

Working gases : Helium/Air

V=1.1m3


Helium volume fraction measurement : min-katharometers

100mm

220mm

340mm

460mm

580mm

700mm

820mm

940mm

1060mm

1160mm

Injection tube

katharometers

255mm

625mm

135m

m

240mm

930m

m

930mm

1260mm

Vent

M2 M4

M2

M4

195mm

230mmM1

M1

7mm


Steady state: vertical profilesSteady state: vertical profiles

180x900 mm2 vent (a)

0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

X/<X>

z /H

5Nl/min10Nl/min20Nl/min40Nl/min60Nl/min100Nl/min180Nl/min300Nl/min

Riv

10.2

20mm source : toward buoyancy dominated flow




0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

X/<X>

z /H


Riv

10.2

Strong vertical variations





0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

X/<X>

z /H


Riv

10.2

Auto-similar



0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5X/<X>

z /H


Riv1

0.05

0.0023



5mm source : toward momentum dominated flow


0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5X/<X>

z /H


Riv1

0.05

0.0023




Top homogeneous layer


0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5X/<X>

z /H


Riv1

0.05

0.0023




Homogeneous for Riv<0.0023


0,0

0,2

0,4

0,6

0,8

1,0

0,8 0,9 1,0 1,1 1,2 1,3 1,4

z /H

X/<X>


Riv

10.2


180x180 mm2 vent (b)



0,0

0,2

0,4

0,6

0,8

1,0

0,8 0,9 1,0 1,1 1,2 1,3 1,4

z /H

X/<X>


Riv1

0.05

0.0023





0,0

0,2

0,4

0,6

0,8

1,0

0,4 0,6 0,8 1,0 1,2 1,4

X/<X>

z /H 5Nl/min

10Nl/min20Nl/min40Nl/min60Nl/min100Nl/min180Nl/min300Nl/min

Riv

10.2


35x900 mm2 vent (c)



0,0

0,2

0,4

0,6

0,8

1,0

0,7 0,8 0,9 1,0 1,1 1,2 1,3 1,4X/<X>

z /H 5Nl/min


Riv1

0.05

0.0023


35x900 mm2 vent (c)



0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

<X>

(%)

Q (m3/s)

Average volume fraction


Filed symbols: 20mm source

Vent 35x900 mm2 (c)

Vent 180x900 mm2 (a)Vent 180x180 mm2 (b)

Model with CD=0.25


0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

<X>

(%)

Q (m3/s)




Vent 35x900 mm2 (c)


Model with CD=0.25

The model over estimate the experimental resultsIn particular for vent (a)


0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

<X>

(%)

Q (m3/s)




Vent 35x900 mm2 (c)


Model with CD=0.25

The power law is no longer valid for SOME data


0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

<X>

(%)

Q (m3/s)




Vent 35x900 mm2 (c)


Model with CD=0.25


0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

Xm

ax(%

)

Q (m3/s)

Maximum volume fraction



Vent 35x900 mm2 (c)


Model with CD=0.25


Maximum volume fraction vs normalized flow rate

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,0 0,5 1,0 1,5 2,0

Xm

ax

Q/Qe

2/10max )( hgXSCQ De

Source flow rate normalized by the expected outflow rate :

i.e. only gravity driven outflow

ModelX=Q/Qe<1


Event 35x900 mm2

(c)

Event 180x900 mm2

(a)Event 180x180 mm2

(b)



0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,0 0,5 1,0 1,5 2,0

Xm

ax

Q/Qe


Event 35x900 mm2

(c)

Event 180x900 mm2


(b)



0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

Xm

ax(%

)

Q (m3/s)

0.3


0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,0 0,5 1,0 1,5 2,0

Xm

ax

Q/Qe


Event 35x900 mm2

(c)

Event 180x900 mm2


(b)



0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

Xm

ax(%

)

Q (m3/s)

0.3

Purely gravity driven flow through the vent


0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,0 0,5 1,0 1,5 2,0

Xm

ax

Q/Qe


Event 35x900 mm2

(c)

Event 180x900 mm2


(b)



0,1

1,0

10,0

100,0

1,E-05 1,E-04 1,E-03 1,E-02

Xm

ax(%

)

Q (m3/s)

0.3

Additional pressure effects


ConclusionsConclusions

Strong vertical stratificationStrong vertical stratification

Highly dependent on the vent geometryHighly dependent on the vent geometry

Source momentum effects : homogeneous layerSource momentum effects : homogeneous layer

Criterion for complete homogeneity still Criterion for complete homogeneity still validvalidHomogeneous model gives fairly good resultsHomogeneous model gives fairly good results

Pressure effects are significant when Q/QPressure effects are significant when Q/Qee>0.3>0.3

B.CARITEAU, I. TKATSCHENKO CEA Saclay, DEN, DM2S, SMFE, LEEF

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