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

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. Dispersion in an enclosure : Natural ventilation through one vent. V. X(z)?. U 0 , Dr 0.

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

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  1. 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. Dispersion in an enclosure : Natural ventilation through one vent V X(z)? U0, Dr0

  3. Dispersion in an enclosure : Natural ventilation through one vent V X(z)? U0, Dr0 A wide range of injection velocity

  4. Dispersion in an enclosure : Natural ventilation through one vent V X(z)? U0, Dr0 Vent effects

  5. Previous results on dispersion regimes without ventilation Volume Richardson number: Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36)

  6. Previous results on dispersion regimes without ventilation Volume Richardson number: Cleaver et. al. (1994, J. Hazardous Mater. Vol. 36) Buoyancy dominated dispersion Momentum dominated dispersion Riv d RiVc 1 H Homogeneous layer Fully homogeneous Stratified

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

  8. 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 Constant • Homogeneous distribution • Pure gravity driven flow through the vent • Boussinesq approximation

  9. 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 Constant • Homogeneous distribution • Pure gravity driven flow through the vent • Boussinesq approximation CD=0.25 discharge coefficient S h Volume flow rate through the vent

  10. 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 Constant • Homogeneous distribution • Pure gravity driven flow through the vent • Boussinesq approximation CD=0.25 discharge coefficient S h Volume flow rate through the vent Steady state volume fraction in the enclosure

  11. 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

  12. Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

  13. Experimental set-up Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

  14. 180mm 900mm Experimental setup and injection conditions (a) (b) (a) 180x900 mm2 (b) 180x180 mm2 (c) 35x900 mm2 180mm Vents: (c) 35mm 20mm 180mm Vent 1260mm 930mm V=1.1m3 930mm Injection tube

  15. Experimental setup and injection conditions Working gases : Helium/Air D0=5mm Riv=8 10-4 to 75 D0=5mm or 20mm X0=100% helium Q0=1 to 300Nl/min D0=20mm Riv=0.2 to 740 20mm Sources : 180mm Vent 1260mm 930mm V=1.1m3 930mm Injection tube

  16. Helium volume fraction measurement : min-katharometers M1 M2 M4 1160mm katharometers 1060mm Vent 940mm 820mm 7mm 700mm 1260mm 240mm 580mm M4 930mm 625mm 460mm 135mm 340mm 230mm M1 M2 220mm 255mm 195mm 100mm 930mm Injection tube

  17. Experimental set-up Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

  18. Steady state: vertical profiles 180x900 mm2 vent (a) 20mm source : toward buoyancy dominated flow Riv 1 0.2

  19. Steady state: vertical profiles 180x900 mm2 vent (a) 20mm source : toward buoyancy dominated flow Riv 1 0.2 Strong vertical variations

  20. Steady state: vertical profiles 180x900 mm2 vent (a) 20mm source : toward buoyancy dominated flow Riv 1 0.2 Auto-similar

  21. Steady state: vertical profiles 180x900 mm2 vent (a) 5mm source : toward momentum dominated flow Riv 1 0.05 0.0023

  22. Steady state: vertical profiles 180x900 mm2 vent (a) 5mm source : toward momentum dominated flow Riv 1 0.05 Top homogeneous layer 0.0023

  23. Steady state: vertical profiles 180x900 mm2 vent (a) 5mm source : toward momentum dominated flow Riv 1 0.05 Homogeneous for Riv<0.0023 0.0023

  24. Steady state: vertical profiles 180x180 mm2 vent (b) 20mm source : toward buoyancy dominated flow Riv 1 0.2

  25. Steady state: vertical profiles 180x180 mm2 vent (b) 5mm source : toward momentum dominated flow Riv 1 0.05 0.0023

  26. Steady state: vertical profiles 180x180 mm2 vent (b) 5mm source : toward momentum dominated flow Riv 1 0.05 Homogeneous for Riv<0.0023 0.0023

  27. Steady state: vertical profiles 35x900 mm2 vent (c) 20mm source : toward buoyancy dominated flow Riv 1 0.2

  28. Steady state: vertical profiles 35x900 mm2 vent (c) 5mm source : toward momentum dominated flow Riv 1 0.05 0.0023

  29. Steady state: vertical profiles 35x900 mm2 vent (c) 5mm source : toward momentum dominated flow Riv 1 0.05 Homogeneous for Riv<0.0023 0.0023

  30. Experimental set-up Experimental set-up Steady state vertical distribution Volume fraction variations with the flow rate

  31. Volume fraction variations with the flow rate Average volume fraction Filed symbols: 20mm source Vent 180x900 mm2 (a) Vent 180x180 mm2 (b) Model with CD=0.25 Vent 35x900 mm2 (c)

  32. Volume fraction variations with the flow rate Average volume fraction Filed symbols: 20mm source Vent 180x900 mm2 (a) Vent 180x180 mm2 (b) Model with CD=0.25 Vent 35x900 mm2 (c)

  33. Volume fraction variations with the flow rate Average volume fraction Filed symbols: 20mm source The model over estimate the experimental resultsIn particular for vent (a) Vent 180x900 mm2 (a) Vent 180x180 mm2 (b) Model with CD=0.25 Vent 35x900 mm2 (c)

  34. Volume fraction variations with the flow rate Average volume fraction Filed symbols: 20mm source The power law is no longer valid for SOME data Vent 180x900 mm2 (a) Vent 180x180 mm2 (b) Model with CD=0.25 Vent 35x900 mm2 (c)

  35. Volume fraction variations with the flow rate Average volume fraction Filed symbols: 20mm source Vent 180x900 mm2 (a) Vent 180x180 mm2 (b) Model with CD=0.25 Vent 35x900 mm2 (c)

  36. Volume fraction variations with the flow rate Maximum volume fraction Filed symbols: 20mm source Vent 180x900 mm2 (a) Vent 180x180 mm2 (b) Model with CD=0.25 Vent 35x900 mm2 (c)

  37. Volume fraction variations with the flow rate Maximum volume fraction vs normalized flow rate Source flow rate normalized by the expected outflow rate : ModelX=Q/Qe<1 i.e. only gravity driven outflow Event 180x900 mm2 (a) Event 180x180 mm2 (b) Event 35x900 mm2 (c) Filed symbols: 20mm source

  38. Volume fraction variations with the flow rate Maximum volume fraction vs normalized flow rate 0.3 Event 180x900 mm2 (a) Event 180x180 mm2 (b) Event 35x900 mm2 (c) Filed symbols: 20mm source

  39. Volume fraction variations with the flow rate Maximum volume fraction vs normalized flow rate 0.3 Event 180x900 mm2 (a) Event 180x180 mm2 (b) Event 35x900 mm2 (c) Filed symbols: 20mm source

  40. Volume fraction variations with the flow rate Maximum volume fraction vs normalized flow rate Purely gravity driven flow through the vent 0.3 Event 180x900 mm2 (a) Event 180x180 mm2 (b) Event 35x900 mm2 (c) Filed symbols: 20mm source

  41. Volume fraction variations with the flow rate Maximum volume fraction vs normalized flow rate Additional pressure effects 0.3 Event 180x900 mm2 (a) Event 180x180 mm2 (b) Event 35x900 mm2 (c) Filed symbols: 20mm source

  42. 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

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