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

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

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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

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

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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

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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

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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)

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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

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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

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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

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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

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

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

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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

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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

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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

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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

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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

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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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