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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

March 12th, 2001

Cincinnati, OH

- 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

UBC-PSL TECHNOLOGY APPLICATION

License

agreement

Custom

agreements

Service

agreements

Consulting

agreements

License

agreements

Government

Industry

Other Institutions

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

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

- 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

- 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

- 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

- Supply to sheet forming section
- Well dispersed stock
- Constant percentage of fibers

- Prevent formation of flocs
- Remove flow non-uniformities
- Create high-intensity turbulence

- 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

VELOCITY IN CDDIRECTION

- Velocity Vectors
- Pressure contours

- Green
- Flow turns before entering tubes

- Red
- Flow enters straight

- Affects
- Flow profile into slice
- Fibre distribution and orientation

- Velocityvectors
- 3 slices in CD direction

- Velocity vectors
- Contours in machine Direction (MD)

VELOCITY IN CD DIRECTION

VELOCITY IN MD DIRECTION

KINETIC ENERGY IN CONVERGING SECTION

LENGTH SCALE

U

CD VELOCITY

K-e

RSM

KINETIC ENERGY

SIMULATION OF CONVERGING SECTION WITH TUBE BANKS

- 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

- Fiber orientation mid channel at x = 12.2 cm

Side view

Edge view

- Fiber orientation mid channel at x = 19.2 cm

Side view

Edge view

- Fiber orientation mid channel at x = 26.2 cm

Side view

Edge view

- 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

- 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

- 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

- 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