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


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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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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


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


PROCESS MODELLING GROUP


UBC-PSL TECHNOLOGY APPLICATION

License

agreement

Custom

agreements

Service

agreements

Consulting

agreements

License

agreements

Government

Industry

Other Institutions


PROCESS MODELLING


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


MODELLING EXAMPLES

Jet engines

Weather

Computer

Harrier jet

Automotive


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


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


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


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


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


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


GENERIC HEADBOX MODELLED


EFFECT OF FLOW RECIRCULATION


VELOCITY IN CDDIRECTION


TYPICAL TUBE

  • Velocity Vectors

  • Pressure contours


TUBE FLOW ENTRANCE EFFECT

  • Green

    • Flow turns before entering tubes

  • Red

    • Flow enters straight

  • Affects

    • Flow profile into slice

    • Fibre distribution and orientation


CONVERGINGSECTION

  • Velocityvectors

  • 3 slices in CD direction


CONVERGING SECTION

  • Velocity vectors

  • Contours in machine Direction (MD)


VELOCITY IN CD DIRECTION


VELOCITY IN MD DIRECTION


KINETIC ENERGY IN CONVERGING SECTION


LENGTH SCALE


EXPERIMENTAL METHOD


U

MD VELOCITY


CD VELOCITY


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


CD VELOCITY (m/s)

K-e

RSM


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 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


EXPERIMENTAL SETUP


FIBER MOTION RESULTS

  • Fiber orientation mid channel at x = 12.2 cm

Side view

Edge view


FIBER MOTION RESULTS

  • Fiber orientation mid channel at x = 19.2 cm

Side view

Edge view


FIBER MOTION RESULTS

  • Fiber orientation mid channel at x = 26.2 cm

Side view

Edge view


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


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


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


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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