Bern University of Applied Sciences Architecture , Wood and Civil Engineering
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Transcript of Bern University of Applied Sciences Architecture , Wood and Civil Engineering
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Bern University of Applied SciencesArchitecture, Wood and Civil Engineering
COST Action FP1005Working Group Meeting (WG 3)Nancy, 13/10/2011
Two sectors, same questions: Flow simulations as tools in paper and wood-based panel manufacture
Heiko Thoemen
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2Heiko ThoemenCOST Action FP1005, 13/10/2011
Bern University of Applied SciencesArchitecture, Wood and Civil Engineering
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3Heiko ThoemenCOST Action FP1005, 13/10/2011
Bern University of Applied SciencesArchitecture, Wood and Civil Engineering
Education
• Higher Technical Schools• Bachelor Programs• Master Programs• Postgraduate Courses
Research and development
• About 100 full-time equivalent employees• One field of research: Wood-based composites
process technology, process modelling
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4Heiko ThoemenCOST Action FP1005, 13/10/2011
Background of COST project proposal
• Considerable similarities between hot-pressing process and calendering of paper sheets
– Wood fibers as raw material – Micro-structure of material– Material compression at elevated temperatures– Inhomogeneous cross-sectional density distribution– Moisture content below fiber saturation
• Advanced models available in the wood-based composite sector
• Important features are missing in today's calendering models– Phase change of water– Convective heat transfer inside the web– Material compaction– Development of cross-sectional density profile
Great potential for facilitating synergies and scientific exchange
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5Heiko ThoemenCOST Action FP1005, 13/10/2011
Motivation for modelling the calendering process
• Understand fundamentals of paper calendering• Further improve surface quality without reducing paper or board
thickness• Develop strategies to reduce energy consumption
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6Heiko ThoemenCOST Action FP1005, 13/10/2011
Objective of COST Action FP1005
"Promote and disseminate validated computer modeling and simulation techniques in papermaking industry. These modern numerical tools, allowing for deep insight into the physics of the momentum, mass and heat transfer processes, provide new possibilities for design engineers resulting in innovative solutions unavailable with already utilized methodologies"
Memorandum of Understanding, COST Action FP1005
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7Heiko ThoemenCOST Action FP1005, 13/10/2011
Content
1. Process comparison
2. Modelling hot pressing of MDF*
3. Model adaptation to calendering
* MDF = Medium Density Fiberboard
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9Heiko ThoemenCOST Action FP1005, 13/10/2011
Calenders (long nip) Process comparison
Shoe calender Belt calender
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10Heiko ThoemenCOST Action FP1005, 13/10/2011
MDF hot press Process comparison
Forming line Hot press
Pressure
Temperature in heating circuits
p
T
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12Heiko ThoemenCOST Action FP1005, 13/10/2011
Material structure Process comparison
Cross-sectional position (mm)0 5 10 15 20
Den
sity
(kg/
m³)
400
600
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1000
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MDF Newsprint Paper
Source: Christine Antoine et al. (2002). 3D images of paper obtained by phase-contrast X-ray microtomography: image quality and binarisation
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13Heiko ThoemenCOST Action FP1005, 13/10/2011
Challenging differences Process comparison
• Thickness of material• Duration of temperature and pressure exposure• Pre-treatment of paper sheet / fibres before calendering
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14Heiko ThoemenCOST Action FP1005, 13/10/2011
Content
1. Process comparison
2. Modelling hot pressing of MDF
3. Model adaptation to calendering
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19Heiko ThoemenCOST Action FP1005, 13/10/2011
Heat and moisture transfer
Basic transfer mechanisms
heatconduction
> 200°CHeating platenor steel belt
Fibre mat
MDF modelling
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20Heiko ThoemenCOST Action FP1005, 13/10/2011
Heat and moisture transfer
Basic transfer mechanisms
heatconduction
> 200°C
evaporationof water
MDF modelling
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21Heiko ThoemenCOST Action FP1005, 13/10/2011
Heat and moisture transfer
Basic transfer mechanisms
heatconduction
> 200°C
evaporationof water
convection
MDF modelling
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22Heiko ThoemenCOST Action FP1005, 13/10/2011
Heat and moisture transfer
Basic transfer mechanisms
heatconduction
> 200°C
evaporationof water
condensationof water vapor
gas and heatconvection
MDF modelling
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25Heiko ThoemenCOST Action FP1005, 13/10/2011
Density profile
Density profile
Rheology MDF modelling
Cross-sectional position
Den
sity
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29Heiko ThoemenCOST Action FP1005, 13/10/2011
Numerical solution & implementation MDF modelling
• Modified finite volume approach (constitutive flux equations are coupled by local energy and mass balances)
• 3D flow computations, 1D densification model• Implicit approach for cross-sectional flow computations to avoid
numerical instabilities• In-house programming code is
written in ANSI C• Commercialized as simulation
platform Virtual Hot Press
Copyright© 2000 - 2003 Heiko ThoemenUniversity of Hamburg
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Copyright© 2000 - 2003 Heiko ThoemenUniversity of Hamburg
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Copyright© 2000 - 2003 Heiko ThoemenUniversity of Hamburg
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33Heiko ThoemenCOST Action FP1005, 13/10/2011
Content
1. Process comparison
2. Modelling hot pressing of MDF
3. Model adaptation to calendering
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34Heiko ThoemenCOST Action FP1005, 13/10/2011
Selected key assumptions of hot-pressing model
Assumption 1: The material is macroscopically homogeneous
• Daryc's and Fourier's law, macroscopic flow coefficients• Approach is valid for MDF and even oriented strandboard (OSB),
probably also for thick paper and cardboard
Assumption will be maintained
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40Heiko ThoemenCOST Action FP1005, 13/10/2011
Tasks / Working packages
1. Model adaptation
2. Measurement of flow properties• Thermal conductivity• Gas permeability (only in z-direction)
3. Model validation: Measurement of cross-sectional temperature development in thick paper• Will be done at laboratory of Voith Paper (Ravensburg, Germany)• Different paper types
4. Sensitivity analysisEffects of a) material property data and b) process parameters on the heating pattern during paper calendering will be evaluated
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42Heiko ThoemenCOST Action FP1005, 13/10/2011
Thank You