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FLUID MECHANICS IN HEADBOXES
M. Shariati, E. Bibeau, M.Salcudean and I. GartshoreMarch 12th, 2001Cincinnati, OH
PRESENTATIONMathematical modelling in the pulp and paper industryWhy we model headboxesHow we model headboxesExamplesflow in the header, tubes and sliceConclusions and future
PROCESS MODELLING GROUP
Dr. Martha Salcudean, Principal Investigator
Dr. Ian Gartshore, Co-Investigator
Bian Zhengbing
Feng Xioasi
Mohammad Shariati
Dr. Eric Bibeau
Dr. Pingfan He
Dr. David Stropky
Chris Chiu
Lu Hua
Zhu Zhi Xiao
Suqin Dong
Dr. Emil Statie
Dr. Jerry Yuan
Michael Georgallis
Dr. Paul Nowak
Kegang and Xun Zhang
Note: UBC and PSL Personnel (Pulp & Paper Section)
UBC-PSL TECHNOLOGY APPLICATIONOther InstitutionsGovernmentIndustry License agreementServiceagreementsConsultingagreementsCustomagreementsLicenseagreements
PROCESS MODELLING
PROCESS
IN PROGRESS
INDUSTRIAL APPLICATION
SIMULATOR & TRAINER
WOOD KILNS
(
LIME KILNS
(
DIGESTERS
(
HEADBOXES
(
HYDROCYCLONES
(
PRECIPITATORS/HEATERS
(
BARK & UTILITY BOILERS
(
RECOVERY BOILERS
(
STAGES OF ANALYSISIN PROGRESSINDUSTRIALAPPLICATIONPROCESSSIMULATORS
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 transferINITIALSTAGE
MODELLING EXAMPLESComputerJet enginesWeatherAutomotiveHarrier jet
HEADBOXESPaper quality depends on the flow and fluid/fiber interaction in the headboxFlow at the exit of the slice needs to be uniformgoal can be achieved only by knowing and controlling the flow upstreamDesirable paper properties impose certain requirements of fiber orientation which depends on the flow and turbulence characteristicsWHY MODEL HEADBOXES
HOW WE MODEL HEADBOXESDeveloped a model for the flow through the headbox including the header, individual tubes and sliceDeveloped a fiber motion model, which allows to compute the motion of the fiber in the fluidCouple the fiber motion model with the fluid dynamics modelCompute the fiber motion in the fluid for a large number of fibers and obtain information on fiber orientation through the sliceWater model experiments to validate the above
NUMERICAL CFD CODECode developed at the University of British ColumbiaGeneralized curvilinear systemFinite volume methodBlock structuredSecond order accurate for cross derivative termsSteady and transientPartial multigrid capability
HEADBOX WISH LISTSelect sheet properties Improve control of fiber distributionControl MD/CD ratiosPrevent non-uniformities (basis weight, fibre orientation)Control fiber distributionFlow Field (velocity, stresses, vorticity)Fluid-fibre interaction
HEADBOX REQUIREMENTSSupply to sheet forming sectionWell dispersed stockConstant percentage of fibersPrevent formation of flocsRemove flow non-uniformitiesCreate high-intensity turbulence
MODEL DELIVERABLESManufacturers and Pulp MillsEvaluate new headbox designsCompare headbox designsTrouble-shoot existing headboxesPredict influence of control devicesEvaluate proposed retrofits and design changesHelp correlate sheet properties to headbox behavior
GENERIC HEADBOX MODELLED
EFFECT OF FLOW RECIRCULATION
VELOCITY IN CD DIRECTION
TYPICAL TUBEVelocity VectorsPressure contours
TUBE FLOW ENTRANCE EFFECTGreenFlow turns before entering tubesRedFlow enters straightAffects Flow profile into sliceFibre distribution and orientation
CONVERGINGSECTIONVelocity vectors3 slices in CD direction
CONVERGING SECTIONVelocity vectorsContours in machine Direction (MD)
VELOCITY IN CD DIRECTION
VELOCITY IN MD DIRECTION
KINETIC ENERGY IN CONVERGING SECTION
LENGTH SCALE
EXPERIMENTAL METHOD
MD VELOCITY
CD VELOCITY
Velocity at the exit plane V, W/Uinlet and Uinlet= 1.22 m/s
CD VELOCITY (m/s)K-eRSM
Symmetry Plane Velocity Fluctuations (RMS/RMS at inlet)
TURBULENCE INTENSITY (RMS/MD VELOCITY) SYMMETRY PLANE
TURBULENCE KINETIC ENERGY
EFFECT OF SHAPE
KINETIC ENERGY
SIMULATION OF CONVERGING SECTION WITH TUBE BANKS
FIBER MOTIONFiber is modeled as chains of spheroids
Model can deal with the wall automatically for different geometry23N-11NBall and Socket Joints
EXPERIMENTAL SETUP
FIBER MOTION RESULTSFiber orientation mid channel at x = 12.2 cmEdge viewSide view
FIBER MOTION RESULTSFiber orientation mid channel at x = 19.2 cm
Edge viewSide view
FIBER MOTION RESULTSFiber orientation mid channel at x = 26.2 cm
Edge viewSide view
RESULTS HIGHLIGHTSThere exists obvious difference between the results from the experiments and simulationsCause for this phenomenon maybe the fact that in our fiber simulation, only the effects of the mean flow properties are consideredAs a result, the turbulence effect on the fiber orientation should not be neglected
RESULTS OVERVIEWSimulation results from the mean flow field show fiber orientation has little relation withthe mean flow velocitythe channel lengththe fiber aspect ratio in the interested rangeFiber orientation increases with the increment of the contraction ratio of the channel
CONCLUSIONSDesigning of the header is critical to obtain flow uniformity in the sliceLevel of turbulence induced by the tubes is very important for the exit flow characteristicsSecondary flows induced by turbulence anisotropy are negligibleMain flow is well predicted by the standard K-e equationsTurbulence characteristics are not well predicted by the standard K-e modelThe fiber is significantly aligned by the contraction in the slice. However the turbulence induced fiber randomness is very essential
FUTURE WORKTurbulence modeling needs to be improved. Large eddy simulation is currently under developmentFiber/ fiber interaction will have to be introduced in the fiber model and will be introduced in the model in the futureTurbulence 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 improvementsCurrent model allows for assessing headboxes and can be used as a design assessment and optimization toolDevelopment currently under way will allow for realistic assessment of fiber orientation at the exit of the slice