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