source_dispersion_fillin - Agenda Safety topic Source...

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Agenda Safety topic Source Models Toxic Release and Dispersion Models
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Source Models Chapter 4 An Equal Opportunity University
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Source Models Source models are part of consequence modeling Particularly important for evaluating effects of explosions, relieving scenarios, how large to make secondary containment, etc. A source model describes how material is discharges from the process. Rate of discharge Total quantity or time State (i.e. liquid or vapor)
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Source Models Source models are for design purposes Should provide conservation 保护 estimates (i.e. maximize release rate and quantity) Two types of release mechanisms Wide aperture 空穴 Large hole, releasing substantial amount of material in a short time Example: overpressuring and explosion of storage tank
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Source Models Limited aperture Slow enough rate that upstream conditions are not immediately affected Often can assume constant upstream pressure
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Physical State of Release Affects release mechanism Leak in gas/vapor storage tank results in jet release Leaks below liquid level stream release Liquids stored under pressure may flash to vapor upon leak
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Basic Source Models Flow of liquid through a hole Flow of liquid through a hole in a tank Flow of liquids through pipes Flow of gases or vapor through holes Flow of gases or vapor through pipes Flashing liquids Liquid pool evaporation or boiling
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Flow of Liquid Through Hole Starts with a Mechanical energy balance P = Pressure ρ = density ū = average inst. Velocity gc = gravitational constant α = velocity profile correction factor (goes to 1 for turbulent) g = gravitational acceleration z = height F = frictional loss term Ws = shaft work Incompressible fluid dP   u 2 2 g c g g c z F   W s m P
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Flow of Liquid Through Hole Assumptions Incompressible fluid Constant gauge pressure Shaft work = zero Velocity of fluid in process unit is negligible Change in elevation of fluid during discharge is negligible Friction losses are approximated by a constant coefficient, C 1 P P g z 0 P F C 1 2 P
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Flow of Liquid Through Hole Plug into mechanical energy balance Define a new coefficient, C o Find mass flow rate, Q m , resulting from hole of area, A u C 1 2 g c P g C o C 1 Q m uA AC o 2 g c P g
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Choice of Discharge Coefficient
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