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ICHS 4, San Francisco, California, USA, September 2011 Experimental study of the effects of vent geometry on the dispersion of a buoyant gas in a small.

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Presentation on theme: "ICHS 4, San Francisco, California, USA, September 2011 Experimental study of the effects of vent geometry on the dispersion of a buoyant gas in a small."— Presentation transcript:

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

2 ICHS 4, San Francisco, California, USA, September 2011 Dispersion in an enclosure : Natural ventilation through one vent U 0, V X(z)?

3 ICHS 4, San Francisco, California, USA, September 2011 A wide range of injection velocity U 0, V X(z)? Dispersion in an enclosure : Natural ventilation through one vent

4 ICHS 4, San Francisco, California, USA, September 2011 Vent effects U 0, V X(z)? Dispersion in an enclosure : Natural ventilation through one vent

5 ICHS 4, San Francisco, California, USA, September 2011 Volume Richardson number: Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36) Previous results on dispersion regimes without ventilation

6 ICHS 4, San Francisco, California, USA, September 2011 Volume Richardson number: Ri v Buoyancy dominated dispersion Momentum dominated dispersion Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36) 1 Stratified Ri Vc d H Homogeneous layerFully homogeneous Previous results on dispersion regimes without ventilation

7 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)

8 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

9 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 S h C D =0.25 discharge coefficient

10 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 S h C D =0.25 discharge coefficient Steady state volume fraction in the enclosure

11 11ICHS 4, San Francisco, California, USA, September 2011 Goals of the present experiments: Influence of Ri v and vent geometry on the vertical distribution Compare results to the analytical model Check the validity of the criterion for homogeneous filling

12 12ICHS 4, San Francisco, California, USA, September 2011 Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

13 13ICHS 4, San Francisco, California, USA, September 2011 Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

14 ICHS 4, San Francisco, California, USA, September 2011 Vents: (a) 180x900 mm 2 (b) 180x180 mm 2 (c) 35x900 mm 2 Experimental setup and injection conditions Injection tube 930mm 1260mm Vent 180mm 20mm (b) 180mm (a) 35mm (c) 900mm 180mm V=1.1m 3

15 ICHS 4, San Francisco, California, USA, September 2011 Sources : D 0 =5mm or 20mm X 0 =100% helium Q 0 =1 to 300Nl/min Experimental setup and injection conditions Injection tube 930mm 1260mm Vent 180mm 20mm D 0 =5mm D 0 =20mm Ri v = to 75 Ri v =0.2 to 740 Working gases : Helium/Air V=1.1m 3

16 16ICHS 4, San Francisco, California, USA, September 2011 Helium volume fraction measurement : min-katharometers 100mm 220mm 340mm 460mm 580mm 700mm 820mm 940mm 1060mm 1160mm Injection tube katharometers 255mm 625mm 135mm 240mm 930mm 1260mm Vent M2 M4 M2 M4 195mm 230mm M1 7mm

17 17ICHS 4, San Francisco, California, USA, September 2011 Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

18 ICHS 4, San Francisco, California, USA, September 2011 Steady state: vertical profiles 180x900 mm 2 vent (a) Ri v mm source : toward buoyancy dominated flow

19 ICHS 4, San Francisco, California, USA, September 2011 Steady state: vertical profiles 180x900 mm 2 vent (a) Ri v Strong vertical variations 20mm source : toward buoyancy dominated flow

20 ICHS 4, San Francisco, California, USA, September 2011 Steady state: vertical profiles 180x900 mm 2 vent (a) Ri v Auto-similar 20mm source : toward buoyancy dominated flow

21 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 180x900 mm 2 vent (a) 5mm source : toward momentum dominated flow

22 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 180x900 mm 2 vent (a) 5mm source : toward momentum dominated flow Top homogeneous layer

23 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 180x900 mm 2 vent (a) 5mm source : toward momentum dominated flow Homogeneous for Ri v <0.0023

24 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 180x180 mm 2 vent (b) 20mm source : toward buoyancy dominated flow

25 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 180x180 mm 2 vent (b) 5mm source : toward momentum dominated flow

26 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 180x180 mm 2 vent (b) 5mm source : toward momentum dominated flow Homogeneous for Ri v <0.0023

27 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 35x900 mm 2 vent (c) 20mm source : toward buoyancy dominated flow

28 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 35x900 mm 2 vent (c) 5mm source : toward momentum dominated flow

29 ICHS 4, San Francisco, California, USA, September 2011 Ri v Steady state: vertical profiles 35x900 mm 2 vent (c) 5mm source : toward momentum dominated flow Homogeneous for Ri v <0.0023

30 30ICHS 4, San Francisco, California, USA, September 2011 Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

31 ICHS 4, San Francisco, California, USA, September 2011 Average volume fraction Volume fraction variations with the flow rate Filed symbols: 20mm source Vent 35x900 mm 2 (c) Vent 180x900 mm 2 (a) Vent 180x180 mm 2 (b) Model with C D =0.25

32 ICHS 4, San Francisco, California, USA, September 2011 Average volume fraction Volume fraction variations with the flow rate Filed symbols: 20mm source Vent 35x900 mm 2 (c) Vent 180x900 mm 2 (a) Vent 180x180 mm 2 (b) Model with C D =0.25

33 ICHS 4, San Francisco, California, USA, September 2011 Average volume fraction Volume fraction variations with the flow rate Filed symbols: 20mm source Vent 35x900 mm 2 (c) Vent 180x900 mm 2 (a) Vent 180x180 mm 2 (b) Model with C D =0.25 The model over estimate the experimental results In particular for vent (a)

34 ICHS 4, San Francisco, California, USA, September 2011 Average volume fraction Volume fraction variations with the flow rate Filed symbols: 20mm source Vent 35x900 mm 2 (c) Vent 180x900 mm 2 (a) Vent 180x180 mm 2 (b) Model with C D =0.25 The power law is no longer valid for SOME data

35 ICHS 4, San Francisco, California, USA, September 2011 Average volume fraction Volume fraction variations with the flow rate Filed symbols: 20mm source Vent 35x900 mm 2 (c) Vent 180x900 mm 2 (a) Vent 180x180 mm 2 (b) Model with C D =0.25

36 ICHS 4, San Francisco, California, USA, September 2011 Maximum volume fraction Volume fraction variations with the flow rate Filed symbols: 20mm source Vent 35x900 mm 2 (c) Vent 180x900 mm 2 (a) Vent 180x180 mm 2 (b) Model with C D =0.25

37 ICHS 4, San Francisco, California, USA, September 2011 Maximum volume fraction vs normalized flow rate Source flow rate normalized by the expected outflow rate : i.e. only gravity driven outflow Model X=Q/Q e <1 Filed symbols: 20mm source Event 35x900 mm 2 (c) Event 180x900 mm 2 (a) Event 180x180 mm 2 (b) Volume fraction variations with the flow rate

38 ICHS 4, San Francisco, California, USA, September 2011 Filed symbols: 20mm source Event 35x900 mm 2 (c) Event 180x900 mm 2 (a) Event 180x180 mm 2 (b) Maximum volume fraction vs normalized flow rate Volume fraction variations with the flow rate 0.3

39 ICHS 4, San Francisco, California, USA, September 2011 Filed symbols: 20mm source Event 35x900 mm 2 (c) Event 180x900 mm 2 (a) Event 180x180 mm 2 (b) Maximum volume fraction vs normalized flow rate Volume fraction variations with the flow rate 0.3

40 ICHS 4, San Francisco, California, USA, September 2011 Filed symbols: 20mm source Event 35x900 mm 2 (c) Event 180x900 mm 2 (a) Event 180x180 mm 2 (b) Maximum volume fraction vs normalized flow rate Volume fraction variations with the flow rate 0.3 Purely gravity driven flow through the vent

41 ICHS 4, San Francisco, California, USA, September 2011 Filed symbols: 20mm source Event 35x900 mm 2 (c) Event 180x900 mm 2 (a) Event 180x180 mm 2 (b) Maximum volume fraction vs normalized flow rate Volume fraction variations with the flow rate 0.3 Additional pressure effects

42 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/Q e >0.3


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