Download

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






Advertisement
/ 44 []
Download Presentation
Comments
meryl
From:
|  
(932) |   (0) |   (0)
Views: 78 | Added: 21-04-2012
Rate Presentation: 0 0
Description:
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.
FLUID MECHANICS IN HEADBOXES M. Shariati, E. Bibeau, M.Salcudean and I. Gartshore

An Image/Link below is provided (as is) to

Download Policy: Content on the Website is provided to you AS IS for your information and personal use only and may not be sold or licensed nor shared on other sites. SlideServe reserves the right to change this policy at anytime. While downloading, If for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.











- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -




Slide 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

Slide 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

Slide 3

PROCESS MODELLING GROUP

Slide 4

UBC-PSL TECHNOLOGY APPLICATION

License

agreement

Custom

agreements

Service

agreements

Consulting

agreements

License

agreements

Government

Industry

Other Institutions

Slide 5

PROCESS MODELLING

Slide 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

Slide 7

MODELLING EXAMPLES

Jet engines

Weather

Computer

Harrier jet

Automotive

Slide 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

Slide 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

Slide 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

Slide 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

Slide 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

Slide 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

Slide 14

GENERIC HEADBOX MODELLED

Slide 15

EFFECT OF FLOW RECIRCULATION

Slide 16

VELOCITY IN CDDIRECTION

Slide 17

TYPICAL TUBE

  • Velocity Vectors

  • Pressure contours

Slide 18

TUBE FLOW ENTRANCE EFFECT

  • Green

    • Flow turns before entering tubes

  • Red

    • Flow enters straight

  • Affects

    • Flow profile into slice

    • Fibre distribution and orientation

Slide 19

CONVERGINGSECTION

  • Velocityvectors

  • 3 slices in CD direction

Slide 20

CONVERGING SECTION

  • Velocity vectors

  • Contours in machine Direction (MD)

Slide 21

VELOCITY IN CD DIRECTION

Slide 22

VELOCITY IN MD DIRECTION

Slide 23

KINETIC ENERGY IN CONVERGING SECTION

Slide 24

LENGTH SCALE

Slide 25

EXPERIMENTAL METHOD

Slide 26

U

MD VELOCITY

Slide 27

CD VELOCITY

Slide 28

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

Slide 29

CD VELOCITY (m/s)

K-e

RSM

Slide 30

Symmetry Plane Velocity Fluctuations (RMS/RMS at inlet)

Slide 31

TURBULENCE INTENSITY (RMS/MD VELOCITY) SYMMETRY PLANE

Slide 32

TURBULENCE KINETIC ENERGY

Slide 33

EFFECT OF SHAPE

Slide 34

KINETIC ENERGY

Slide 35

SIMULATION OF CONVERGING SECTION WITH TUBE BANKS

Slide 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

Slide 37

EXPERIMENTAL SETUP

Slide 38

FIBER MOTION RESULTS

  • Fiber orientation mid channel at x = 12.2 cm

Side view

Edge view

Slide 39

FIBER MOTION RESULTS

  • Fiber orientation mid channel at x = 19.2 cm

Side view

Edge view

Slide 40

FIBER MOTION RESULTS

  • Fiber orientation mid channel at x = 26.2 cm

Side view

Edge view

Slide 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

Slide 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

Slide 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

Slide 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


Copyright © 2014 SlideServe. All rights reserved | Powered By DigitalOfficePro