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Advances in Water-Based Fire Suppression Modeling: Evaluating Sprinkler Discharge Characteristics

Advances in Water-Based Fire Suppression Modeling: Evaluating Sprinkler Discharge Characteristics. June 24, 2008. 7 th International Fire Sprinkler Conference and Exhibition Copenhagen, Denmark Students: Ning Ren, Andrew Blum, Di Wu, and Chi Do Faculty Advisor: Andre Marshall

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Advances in Water-Based Fire Suppression Modeling: Evaluating Sprinkler Discharge Characteristics

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  1. Advances in Water-Based Fire Suppression Modeling: Evaluating Sprinkler Discharge Characteristics June 24, 2008 7th International Fire Sprinkler Conference and Exhibition Copenhagen, Denmark Students: Ning Ren, Andrew Blum, Di Wu, and Chi Do Faculty Advisor: Andre Marshall Sponsors: NFSA, FM Global, NSF

  2. Overview • Introduction • Motivation • Project History • Previous Work • Global Objective • Evaluate Discharge Characteristics • Advanced Measurements • SAM Development • Approach • Experimental • Modeling (SAM) • Results • Sheet Formation (Deflector) • Sheet Breakup • Drop Formation • Dispersion • Summary • Plans • Experimental • Modeling

  3. Motivation Gain New Knowledge • Physical models characterizing the break-up process and the associated initial spray in fire suppression devices have yet to be developed. Develop Injector Technology • The absence of this analytical capability impedes the development of fire suppression injectors/systems. Understanding the relationship between atomization physics and injector control parameters would facilitate a transition away from ‘cut and try’ injector development.

  4. Motivation D inlet L inlet D o L jet A A  boss Section A-A D boss t  tine arm  space D def ‘Characterization’ ‘Cut and Try’

  5. Motivation Advance Fire Protection Engineering Practices • CFD modeling tools of fire phenomena are becoming increasingly popular for fire protection analysis and performance based design. • The absence of physical models describing atomization in sprinklers and water mist injectors results in uncertainties in CFD simulation of suppressed fires. • Errors in the specification of the initial spray will be propagated and amplified during dispersion calculations. The atomization model represents a critical missing link in the modeling of suppressed fires.

  6. Project History UM Fire Suppression Spray Research FY2005 FY2006 FY2007 FY2008 FY2009 FY2012 FY2010 FY2011 NFSA Sprinkler Atomization Modeling and FDS Integration Betatti - U. Modena DuPont Surfactant Effects on Fire Suppression HP Mist Modeling FM Global Scaling Laws and Models for Fire Suppression Devices NSF CAREER Award Exploring Atomization and Jet Fragmentation in Combustion and Fire Suppression Systems

  7. Previous Work Previous Research 1 3 FD Fs

  8. Global Objective Evaluate discharge characteristics from fire suppression devices using measurements and models. Parameter Space • based on varied injector geometry and injection conditions. Experiments • based on state-of-the art diagnostics focused on the initial spray. Analysis • based on physics based models using semi-empirical approaches (e.g. scaling laws and wave dispersion analysis).

  9. Approach Injectors Injected Flow J e t TYCO TY4211 Gr ow t h o f W a v e s D e f le ct o r LP Nozzle 2 bar ~ 700 m Sh e e t F or m a t io n TYCO AM4 Sh e e t L igamen t  Li g a m e nt Dr o p  MP Nozzle 15 bar ~ 225 m HP Nozzle 100 bar ~ 60 m

  10. ‘Standard’ Nozzle(Tyco D3 Nozzle) ‘Tined’ Nozzle (Tyco D3 Nozzle) Approach Geometric parameter space w/n LP injector (sprinkler) configuration 3.2, 6.7, 9.7 mm 38 mm ‘Basis’ Nozzle Sprinkler

  11. (12.7 mm) (22.7 mm) (62.7 mm) Approach Trajectory Measurements (PLIF) Camera FOV texp = 900 s Cooke 16-bit cooled 2.0Mpixel High-Speed Digital Video Camera.

  12. Canon 12-bit 3.4 Mpixel Digital SLR Camera Approach Sheet Break-up Measurements

  13. Approach Drop Size Measurements Malvern Spraytec Analyzer (Light Diffraction Technique) Local Measurements Local Drop Size Distribution P = 2.07 bar r/R = 0.45 Local

  14. 30º Patternator 15º Nozzle 7.2 m 0º 2.0 m 4.0 m 3.0 m 5.0 m 1.0 m 8.6 m Approach Volume Flux Measurements BasisDo = 9.7 mm P = 2.07 bar BasisDo = 9.7 mmP = 2.07 bar 3.0 m 1.0 m 1.0 m dv50 = 780 μm

  15. Mass Thick r-mom Gas-liquid Interfacial Friction Velocity z-mom Surface Tension Radial Location P Across Sheet Sheet Angle Vertical Location Curvilinear Coordinate Along Sheet Approach Impinging Jet (Watson, 1964) Radius where Wall Effects Reach Free Surface Viscous interactions with deflector important for initial thickness and velocity of unstable free liquid sheet. Jet Radius Deflector Radius Arbitrary Length Scale Determined from Matching Kinematic Viscosity Jet Flow Rate Annular Sheets (Ibrahim, 2004) Transport equations for mass and momentum provide the sheet trajectory.

  16. Wave Growth (Dombrowski, 1963) The most unstable wave is determined, which breaks up the sheet at rbu,sh into a fragment having characteristic length bu,sh/2. Approach Dimensionless Wave Growth Rate Viscous Inviscid Fastest Growing Wave Most Unstable Wavelength Gas p- p- p- U p+ p+ Sinusoidal Waves Wave Growth (Sterling and Sleicher, 1975; Weber, 1931) Viscous r The most unstable wave is determined, which breaks up the sheet at rbu,lig into a fragment having characteristic length bu,lig. r Vjet z p+ p-

  17. Results Sheet Formation Governing Equations , b Dimensionless Solution • The thickness and velocity of the sheet is reduced by viscous effects depending on the nozzle geometry (not yet accounting for spaces).

  18. Results Sheet Formation • Two distinct streams are formed: the jet is deflected radially outward along the tines and the jet is forced downward through the spaces • The flow split between these streams governs the sheet thickness and the resulting drop size.

  19. Results Sheet Breakup Standard Nozzle, Do= 6.35 mm, p = 2 bar • Sheet breakup locations occur several jet diameters away from the sprinkler. • Data collapses well with appropriate theory

  20. Results Drop Formation p = 2 bar Dimensionless Drop Size, dv50/Do • Drop size in the space stream are siginificantly smaller than tine stream, but follow Rosin-Rammler • Testing scaling law for drop size

  21. Results Dispersion The radial coordinate has been normalized with the maximum theoretical radial value for each condition. Spatial Drop Size Distributions Spatial Volume Flux Distributions K = 7.2 (0.5) K = 25.9 (1.8) K = 54.7 (3.4)

  22. Summary • Viscous effects along the deflector can be important (for small K-factors). • Two well characterized sheets (radially expanding and orthogonal fan) are formed through the tines and the spaces. • SAM successfully models the tine stream. Space stream submodel in SAM currently under development. • Sheet breakup locations are predicted well by SAM with We-1/3. • ‘Ligament’ break-up (high We) modes and ‘rim’ break-up modes (low We) are observed. The We transition depends on nozzle geometry. • Drop size predicted well by SAM when nozzle operates in ‘ligament’ breakup mode with We-1/3.

  23. Experimental Plans BREAKUP IMAGING Tine Stream Space Stream QUANTITATIVE SHADOWGRAPH / PTV DROP SIZE / VELOCITY

  24. Experimental Plans

  25. SAM Modeling Plans Device Characterization Space Stream Submodel Fundamental Models To Outer Splitter To Inner Expanding Validated Parameter Space CFD Integration Standard Nozzle(Tyco D3 Nozzle) Basis Nozzle

  26. Questions?

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