Air Flow Analysis in Pharmaceutical Clean Rooms

1
Air Flow Analysis in Pharmaceutical Clean Rooms

• Patrick Phelps
• ( Flowsolve )
• and
• Richard Rowe
• ( Clean Room Construction Ltd )

IPUC 8 - Luxembourg - May 2000
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Air Flow Analysis in Pharmaceutical Clean Rooms

• Industrial Context
• Health and Safety Issues
• Application to an Existing Room
• Application to New Ventilation Designs
• Conclusions
• Experimental Verification

3
Clean Rooms

• Areas concerned with the
• preparation, processing and packaging
• of pharmaceutical products
• Strict codes of practice employed to eradicate
  risk of product contamination

4
Clean Rooms

• Personnel access controlled
• 2-layer sterile over-clothing
• Equipment sterilised before entry
• Strict cleansing procedures
• Particular attention to ventilation

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Ventilation of Clean Rooms

• Design and performance of air supply, filtration,
  and extraction arrangements must meet exacting
  standards
• Positive pressure areas
• Use of Laminar Flow Units (LFUs)

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Laminar Flow Units

• Devices which deliver a controlled
• down-draught of re-filtered air
• over sensitive regions
• preparation areas
• processing areas
• packaging areas
• storage areas

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Air Flow Analysis in Pharmaceutical Clean Rooms
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CFD Application to Air Flow Analysis in Clean
Rooms

• Context
• Upgrade of ventilation system in
• a suite of clean rooms at a
• UK pharmaceutical company

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CFD Application to Air Flow Analysis in Clean
Rooms

• Objective
• Use CFD to ensure exacting requirements
• can be met , following installation of a
• number of LFUs .

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CFD Application to Air Flow Analysis in Clean
Rooms

• Workscope
• 3 rooms selected as representative
• examples of areas being upgraded
• Room 30
• Room 23
• Room 42

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Modelling Considerations - 1

• Irregular shaped domains
• Internal Obstructions to flow
• Cartesian grid employed
• K-e (Chen) turbulence model used
• Buoyancy important in transient
• (otherwise assume isothermal)

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Modelling Considerations - 2

• Dependent variables solved
• pressure, p
• lateral velocity component, U
• vertical velocity component, V
• Longitudinal velocity component, W
• Turbulence kinetic energy, k
• Turbulence energy dissipation rate, e
• residence time parameter, tres
• (temperature, T (for transient)

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Modelling Considerations - 3

• Boundary Conditions
• Air supply ducts
• prescribed sources of mass, momentum, turbulence
  and residence time
• Air Extract ducts
• specified fixed-pressure outlet sinks
• LFUs
• inlets and outlets specified as above

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Representation of LFUs

• Air flow in individual units not solved
• treated as internal blockages in domain
• air discharged from base at prescribed rate
• matching intake from front face
• interactive updating of discharge residence time
• constant internal residence time assumed

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Room 30

• Small room - 4.94 x 5.94 x 2.92 m.
• Used for processing, filling and packaging of
  products
• Contains central plinth with filling-machine
  enclosure above
• Conveyor-linked trays outboard of enclosure, for
  containers finished goods

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Room 30 - Before
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Room 30 Simulations

• Steady flow patterns before
• LFUs in enclosure only
• Steady flow patterns after
• following fitment of 10 new LFUs
• 75,000 node 3-D model
• Distribution 50 x 30 x 50

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Room 30 - After
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Room 30 Simulations

• Objectives
• Check for dead zones
• ensure ventilation criteria met
• Criteria
• 25 Air changes per hour
• (residence time 144 seconds)

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Room 30 - Sectional Planes
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
30
Room 30 - After
31
Room 30 - Before
32
Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 - Before
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Room 30 - After
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Room 30 Ventilation Summary(after refurbishment)

• Complex flow paths between inlet and outlet
• Pattern complicated by LFU intake extraction
  flows
• air has to pass around central plinth and
  filling-machine enclosure
• air in near-side passage has to run gauntlet of
  LFUs

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Room 30 Ventilation Summary(after refurbishment)

• Outflow-weighted residence time of 121 seconds
  meets client criterion
• near extract air considerably older than
  far extract air
• some dead zones still apparent
• evidence of entrainment into more than one unit

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Dead Zones - before
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Dead Zones - after
45
LFU intake times - 1
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LFU Unit intake times - 2
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LFU Unit intake times - 3

• Units D1, D2, B2, C2, A1 receive considerably
  fresher air than their neighbours A2-A4, B2 and
  C1
• Air entering A4 is 2.2 times older than that
  entering D1
• Air leaving A4 exceeds air-change criterion en
  route to outlet

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Conclusions

• Residence time analysis concept adds
  considerable value to vector and contour plots in
  assessment of complex ventilation flows.