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

CFD Modelling Group Department of Mechanical Engineering University of British Columbia. Process Simulations Limited. FLUID MECHANICS IN HEADBOXES M. Shariati, E. Bibeau, M.Salcudean and I. Gartshore. March 12th, 2001 Cincinnati, OH. PRESENTATION.

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

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  1. CFD Modelling Group Department of Mechanical EngineeringUniversity of British Columbia Process Simulations Limited FLUID MECHANICS IN HEADBOXESM. Shariati, E. Bibeau, M.Salcudean and I. Gartshore March 12th, 2001 Cincinnati, OH

  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

  4. UBC-PSL TECHNOLOGY APPLICATION License agreement Custom agreements Service agreements Consulting agreements License agreements Government Industry Other Institutions

  5. PROCESS MODELLING

  6. STAGES OF ANALYSIS INITIAL STAGE IN PROGRESS INDUSTRIAL APPLICATION PROCESS SIMULATORS Literature review Mill interaction Industrial innovators Process knowledge Commitment of industry Physical model Numerical model Model development Model validation Industrial testing Industrial application Parametric studies Solve problems Model proposed retrofits Improve operations Reduce costs Envelope calculations Interpolation Operational simulator Training& safety Interacts with control system Technology transfer

  7. MODELLING EXAMPLES Jet engines Weather Computer Harrier jet Automotive

  8. HEADBOXES WHY MODEL 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 • Flow Field (velocity, stresses, vorticity) • Fluid-fibre interaction

  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

  16. VELOCITY IN CDDIRECTION

  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. CONVERGINGSECTION • Velocityvectors • 3 slices in CD direction

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

  21. VELOCITY IN CD DIRECTION

  22. VELOCITY IN MD DIRECTION

  23. KINETIC ENERGY IN CONVERGING SECTION

  24. LENGTH SCALE

  25. EXPERIMENTAL METHOD

  26. U MD VELOCITY

  27. CD VELOCITY

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

  29. CD VELOCITY (m/s) K-e RSM

  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

  34. KINETIC ENERGY

  35. SIMULATION OF CONVERGING SECTION WITH TUBE BANKS

  36. FIBER MOTION • Fiber is modeled as chains of spheroids • Model can deal with the wall automatically for different geometry 1 N-1 N 3 2 Ball and Socket Joints

  37. EXPERIMENTAL SETUP

  38. FIBER MOTION RESULTS • Fiber orientation mid channel at x = 12.2 cm Side view Edge view

  39. FIBER MOTION RESULTS • Fiber orientation mid channel at x = 19.2 cm Side view Edge view

  40. FIBER MOTION RESULTS • Fiber orientation mid channel at x = 26.2 cm Side view Edge view

  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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