FLUID MECHANICS IN HEADBOXES M. Shariati, E. Bibeau, M.Salcudean and I. Gartshore

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PRESENTATION. Mathematical modelling in the pulp and paper industryWhy we model headboxesHow we model headboxesExamplesflow in the header, tubes and sliceConclusions and future. . PROCESS MODELLING GROUP. UBC-PSL TECHNOLOGY APPLICATION. . Other Institutions. Government. . Industry. . . . . . License agreement.
FLUID MECHANICS IN HEADBOXES M. Shariati, E. Bibeau, M.Salc...

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1. FLUID MECHANICS IN HEADBOXES M. Shariati, E. Bibeau, M.Salcudean and I. Gartshore

2. PRESENTATION Mathematical modelling in the pulp and paper industry Why we model headboxes How we model headboxes Examples flow in the header, tubes and slice Conclusions and future

3. PROCESS MODELLING GROUP

5. PROCESS MODELLING

6. STAGES OF ANALYSIS

8. HEADBOXES Paper quality depends on the flow and fluid/fiber interaction in the headbox Flow at the exit of the slice needs to be uniform goal can be achieved only by knowing and controlling the flow upstream Desirable paper properties impose certain requirements of fiber orientation which depends on the flow and turbulence characteristics

9. HOW WE MODEL HEADBOXES Developed a model for the flow through the headbox including the header, individual tubes and slice Developed a fiber motion model, which allows to compute the motion of the fiber in the fluid Couple the fiber motion model with the fluid dynamics model Compute the fiber motion in the fluid for a large number of fibers and obtain information on fiber orientation through the slice Water model experiments to validate the above

10. NUMERICAL CFD CODE Code developed at the University of British Columbia Generalized curvilinear system Finite volume method Block structured Second order accurate for cross derivative terms Steady and transient Partial multigrid capability

11. HEADBOX WISH LIST Select sheet properties Improve control of fiber distribution Control MD/CD ratios Prevent non-uniformities (basis weight, fibre orientation) Control fiber distribution

12. HEADBOX REQUIREMENTS Supply to sheet forming section Well dispersed stock Constant percentage of fibers Prevent formation of flocs Remove flow non-uniformities Create high-intensity turbulence

13. MODEL DELIVERABLES Manufacturers and Pulp Mills Evaluate new headbox designs Compare headbox designs Trouble-shoot existing headboxes Predict influence of control devices Evaluate proposed retrofits and design changes Help correlate sheet properties to headbox behavior

14. GENERIC HEADBOX MODELLED

15. EFFECT OF FLOW RECIRCULATION

17. TYPICAL TUBE Velocity Vectors Pressure contours

18. TUBE FLOW ENTRANCE EFFECT Green Flow turns before entering tubes Red Flow enters straight Affects Flow profile into slice Fibre distribution and orientation

19. CONVERGING SECTION Velocity vectors 3 slices in CD direction

20. CONVERGING SECTION Velocity vectors Contours in machine Direction (MD)

25. EXPERIMENTAL METHOD

26. MD VELOCITY

28. Velocity at the exit plane V, W/Uinlet and Uinlet= 1.22 m/s

29. CD VELOCITY (m/s)

30. Symmetry Plane Velocity Fluctuations (RMS/RMS at inlet)

31. TURBULENCE INTENSITY (RMS/MD VELOCITY) SYMMETRY PLANE

32. TURBULENCE KINETIC ENERGY

33. EFFECT OF SHAPE

36. FIBER MOTION Fiber is modeled as chains of spheroids Model can deal with the wall automatically for different geometry

37. EXPERIMENTAL SETUP

38. FIBER MOTION RESULTS Fiber orientation mid channel at x = 12.2 cm

39. FIBER MOTION RESULTS Fiber orientation mid channel at x = 19.2 cm

40. FIBER MOTION RESULTS Fiber orientation mid channel at x = 26.2 cm

41. RESULTS HIGHLIGHTS There exists obvious difference between the results from the experiments and simulations Cause for this phenomenon maybe the fact that in our fiber simulation, only the effects of the mean flow properties are considered As a result, the turbulence effect on the fiber orientation should not be neglected

42. RESULTS OVERVIEW Simulation results from the mean flow field show fiber orientation has little relation with the mean flow velocity the channel length the fiber aspect ratio in the interested range Fiber orientation increases with the increment of the contraction ratio of the channel

43. CONCLUSIONS Designing of the header is critical to obtain flow uniformity in the slice Level of turbulence induced by the tubes is very important for the exit flow characteristics Secondary flows induced by turbulence anisotropy are negligible Main flow is well predicted by the standard K-e equations Turbulence characteristics are not well predicted by the standard K-e model The fiber is significantly aligned by the contraction in the slice. However the turbulence induced fiber randomness is very essential

44. FUTURE WORK Turbulence modeling needs to be improved. Large eddy simulation is currently under development Fiber/ fiber interaction will have to be introduced in the fiber model and will be introduced in the model in the future Turbulence effect on the fiber has to be accounted for. The model is being currently developed. The fiber orientation in the slice has to be modelled again with the above mentioned improvements Current model allows for assessing headboxes and can be used as a design assessment and optimization tool Development currently under way will allow for realistic assessment of fiber orientation at the exit of the slice


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