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CT-studies during the Conditioning phase of the Wood Drying Process
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. (Träteknik)ORCID iD: 0000-0001-7270-1920
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Norwegian University of Science and Technology (NTNU), Ålesund, Norway.ORCID iD: 0000-0002-5869-2236
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0002-3544-8716
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0002-4526-9391
2018 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Computed tomography (CT) during drying of sawn timber is an excellent non-destructivetechnique to study the moisture flux as a function of drying time. In this study, a climatechamber combined with a medical CT- scanner has been used for non-destructive studies ofdensity changes in sawn timber during drying and conditioning.Green sawn timber contains large amounts of water and has to be dried before it can befurther processed and used in various building applications. The most common dryingmethod is convective air-circulation drying in large industrial kilns, where the relativehumidity (RH) of the hot circulating air is gradually reduced until the timber reaches thetarget moisture content (MC).Drying of sawn timber is driven by the existence of a difference in MC between the coreand the surface, so that moisture moves from the wet inner region towards the drier outerregion. During the early capillary stages of drying, the drying rate is high while, at the laterstages when all liquid water has evaporated, the drying rate is slow and diffusioncontrolled.At the end of the drying process, the timber surface is always drier than its core.In addition to this moisture gradient, internal stresses develop within the cross section withcompression stresses in the timber surface and tension in the inner regions. To avoidunwanted distortions, both these stresses and the moisture gradient, need to be eliminatedbefore the timber is further processed. This is achieved in a final conditioning stage withinthe drying process by moistening the circulating air through steaming or water spraying.The aim of the present work was to optimize the conditioning stage by developing amethod for studying of moisture gradients, deformations and internal and externaldimensional changes in sawn timber during the conditioning phase by using a CT-scannercombined with a drying unit for in-situ measurements of moisture flow.The results show that it is possible to detect the moisture gradient between the surface andcore of the timber with satisfactory reliability, but not the internal and external dimensionalchanges. However, this method creates a potential for increasing the knowledge andunderstanding of the conditioning phase and makes it possible to optimize and develop thisstep in the drying process to improve the yield and ensure a higher quality of the sawntimber.

Place, publisher, year, edition, pages
2018.
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-71117OAI: oai:DiVA.org:ltu-71117DiVA, id: diva2:1253559
Conference
21st International Drying Symposium (IDS), Valencia, Spain, Sep 11-14, 2018
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2019-01-15Bibliographically approved

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Hansson, LarsSehlstedt-Persson, MargotSandberg, Dick

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