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

2. 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. Areas concerned with the preparation, processing and packaging of pharmaceutical products Strict codes of practice employed to eradicate risk of product contamination “Clean Rooms”

4. “Clean Rooms” • Personnel access controlled • 2-layer sterile over-clothing • Equipment sterilised before entry • Strict cleansing procedures • Particular attention to ventilation

5. 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 (LFU’s)

6. “ 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

7. Air Flow Analysis in Pharmaceutical “Clean Rooms”

8. 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

9. 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 LFU’s .

10. 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

11. 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)

12. 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)

13. 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 • LFU’s • inlets and outlets specified as above

14. Representation of LFU’s • 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

15. 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

16. Room 30 - “ Before ”

17. Room 30 Simulations • Steady flow patterns “ before ” • LFU’s in enclosure only • Steady flow patterns “ after ” • following fitment of 10 new LFU’s • 75,000 node 3-D model • Distribution : 50 x 30 x 50

18. Room 30 - “ After ”

19. Room 30 Simulations Objectives • Check for “dead zones” • ensure ventilation criteria met Criteria • 25 Air changes per hour • (residence time 144 seconds)

20. Room 30 - Sectional Planes

21. Room 30 - “ Before ”

22. Room 30 - “ After ”

23. Room 30 - “ Before ”

24. Room 30 - “ After ”

25. Room 30 - “ Before ”

26. Room 30 - “ After ”

27. Room 30 - “ Before ”

28. Room 30 - “ After ”

29. Room 30 - “ Before ”

30. Room 30 - “ After ”

31. Room 30 - “ Before ”

32. Room 30 - “ After ”

33. Room 30 - “ Before ”

34. Room 30 - “ After ”

35. Room 30 - “ Before ”

36. Room 30 - “ After ”

37. Room 30 - “ Before ”

38. Room 30 - “ After ”

39. Room 30 - “ Before ”

40. Room 30 - “ After ”

41. 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 LFU’s

42. 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

43. “ Dead Zones ” - before

44. “ Dead Zones ” - after

45. LFU intake times - 1

46. LFU Unit intake times - 2

47. 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

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