Modeling heat and moisture flow through a wood fiber network during calendering of paper sheets

• Unité de recherche: COST
• Numéro de projet: C11.0130
• Titre du projet anglais: Modeling heat and moisture flow through a wood fiber network during calendering of paper sheets

Mots-clé (Anglais)

Numerical modeling; heat and mass transfer; paper; cardboard; calender; MDF; hot-press

Programme de recherche (Anglais)

COST-Action FP1005 - Fibre suspension flow modelling - a key for innovation and competitiveness in the pulp & paper industry

Description succincte (Anglais)

Numerical models of the physical mechanisms taking place during calendering of paper or cardboard sheets have become important tools for optimizing thermal heat consumption, which is one of today's main concerns of the paper industry, and to further improve the surface quality without reducing paper or board thickness. Corresponding models are also used in the medium density fiberboard (MDF) industry. While the actual technological challenges may be different in MDF production, the physical mechanisms taking place inside the wood fiber network during hot-pressing of MDF and calendering of paper sheets, respectively, show remarkable similarities. Interestingly, hot-pressing models typically include physical mechanisms such as phase change of water, convective heat transfer inside the web, in-plane gas (and possibly heat) transfer, and the development of cross-sectional differences in material density, but calendering models do not. The objective of this project is to use an existing hot-pressing model as a starting point for modeling crosssectional and within-plane heat and moisture transfer during calendering of paper sheets. Similarities and differences of the two processes will be critically evaluated before adapting the existing hot-pressing model to the calendering process. Permeability data needed as model input will be measured, and measurements of the cross-sectional temperature distribution inside paper sheets will be done to validate the model.

Partenaires et organisations internationales (Anglais)

AT; DK; FI; FR; DE; IL; IT; NL; NO; PL; PT; RO; SL; ES; SE; UK; CA; BR; US

Résumé des résultats (Abstract) (Anglais)

Calendering is a finishing process carried out on paper in order to obtain certain features or surface characteristics regarding its further use, e.g. printing. Depending on different paper grades, the main properties to look at are gloss, smoothness/roughness, density, blackening, brightness and opacity. ln general, the challenge of calendering is to obtain good surface quality with low thickness reduction of the web. The present project pretends to adapt the existing Hot Pressing Model of MDF panels to the Paper Calendering Process. A first step was a deep literature review to define/adapt boundary conditions, modify mass and heat transfer equations, and propose physical properties measurements. ln a second stage, the model was adapted and the main differences with the MDF panel process were clarified. ln a third step, the relevant flow properties (thermal conductivity and permeability) were measured for several types of paper. ln a fourth step, temperature development measurements through the thickness of stacks of selected paper types were performed in order to validate the adapted model. Finally, a sensibility analysis to evaluate the effect of the material properties and the process parameters will be incorporated.

Références bases de données (Anglais)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C11.0130