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X-ray computed tomography to study moisture distribution in wood
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.ORCID-id: 0000-0001-7270-1920
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

X-ray computed tomography (CT) has been used as an analysing tool for different features in wood research since the beginning of the1980s, but it can also be used to study wood-water interactions in different ways, such as by determining wood moisture content (MC). The determination of wood MC with CT requires two CT images: one at the unknown moisture distribution and a second one at a known reference MC level, usually at oven-dry condition. The two scans are then compared, and the MC is calculated based on the differences between the images. If the goal is to determine the MC in local regions within the wood volume, e.g. when studying moisture gradients in wood drying, wood shrinkage must be taken into account during the data processing of the images. The anisotropy of wood shrinkage creates an obstacle, however, since the shrinkage is not uniform throughout the wood specimen. The technique is thus limited in two ways: it cannot measure MC in local regions and it cannot do it in real time.

The objective of this thesis was to study methods to overcome these two limitations. The work explores up to three different methods to estimate local MC from CT images in real time. The first method determines shrinkage for each pixel using digital image correlation (DIC) and is embedded in a broader method to estimate the MC, which verified against a reference. It involves several steps in different pieces of software, making it time-consuming and creating many sources of possible experimental errors. The determination of shrinkage within this method is further explored to enable the implementation of all steps in a unique piece of software. It is shown that it is possible to calculate MC through this method with a root mean square error of prediction of 1.4 percentage points for MC between 6 and 25%.

The second method studied succeeds in determining the MC distribution in research applied to wood drying, but the calculation of shrinkage differs from the previous method: instead of calculating shrinkage in the radial and tangential directions, it does so by using the displacement information generated from the spatial alignment of the CT images. Results show that the algorithm can provide consistent data of internal MC distribution of wood at the pixel level that entail continuing researching wood drying processes with an improvement in the accuracy of the MC determination. It represents an improvement regarding the first method because the calculation is fast and highly automatized in a single piece of software.

The third method studied is the application of dual energy CT (DECT) to moisture. DECT would provide means for MC calculation at the pixel level and, potentially, in real time, which would mean an important breakthrough in wood drying research. Previous research shows promising results, but its implementation in medical CT, the tool used throughout this work, has shown poor predicting ability. Nevertheless, further research is encouraged.

The work done in this thesis proves that it is possible to measure local distribution of MC in wood using CT with accuracy and precision. It also shows that further research could potentially provide a means for MC estimation in real time.

Ort, förlag, år, upplaga, sidor
Luleå tekniska universitet, 2019.
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nationell ämneskategori
Trävetenskap
Forskningsämne
Träteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-73860ISBN: 978-91-7790-382-6 (tryckt)ISBN: 978-91-7790-383-3 (digital)OAI: oai:DiVA.org:ltu-73860DiVA, id: diva2:1313940
Disputation
2019-09-12, Hörsal A (A193), Skellefteå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-05-07 Skapad: 2019-05-07 Senast uppdaterad: 2019-08-21Bibliografiskt granskad
Delarbeten
1. Implementation of Computer Aided Tool for Non-Destructive X-Ray Measurement of Moisture Content Distribution in Wood
Öppna denna publikation i ny flik eller fönster >>Implementation of Computer Aided Tool for Non-Destructive X-Ray Measurement of Moisture Content Distribution in Wood
2015 (Engelska)Ingår i: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, nr 4, s. 330-336Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper reports recent attempts for implementing non-destructive measuring of moisture contentin wood based on computed tomography technology. The study focus onan image analysis method that has been already proposed and validated in the literature, but ithas not been tested for measuring low moisture content variations below fibre saturation point.The computed tomography method was tested against the oven-dry method.The results show thatit is possible to apply this technology to measure low levels of moisture content based on a regression model, where therootmean square error of the modelwas 1,4percentage points of moisture content. The method can still be improved because the density differences between samples are relatively small in relation to the experimental error and the computed tomography precision.

Nationell ämneskategori
Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
urn:nbn:se:ltu:diva-9800 (URN)87b757a9-bc3f-414d-a29f-1eba479e9c58 (Lokalt ID)87b757a9-bc3f-414d-a29f-1eba479e9c58 (Arkivnummer)87b757a9-bc3f-414d-a29f-1eba479e9c58 (OAI)
Anmärkning

Validerad; 2016; Nivå 1; 20151221 (andbra)

Tillgänglig från: 2016-09-29 Skapad: 2016-09-29 Senast uppdaterad: 2019-05-07Bibliografiskt granskad
2. Estimation of shrinkage coefficients in radial and tangential directions from CT images
Öppna denna publikation i ny flik eller fönster >>Estimation of shrinkage coefficients in radial and tangential directions from CT images
2017 (Engelska)Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, nr 4, s. 251-256Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The aim of the present work was to use the displacement information generated from the spatial alignment in order to compute wood shrinkage in the radial and tangential directions in computed tomography (CT) images, and to compare the results with those obtained with computer-aided design software on the same images. To estimate the shrinkage coefficients from tomography images, wood specimens in the green state, equilibrium moisture content 15% and 8% state and oven dry condition were scanned. Specimens were taken from Norway spruce and Scots pine logs. The root-mean-square-error calculations showed acceptable small differences between the two measuring methods, which means that the algorithm is a useful tool for estimating the shrinkage coefficients in radial and tangential direction from CT images. This provides an image processing tool to monitor the dimensional changes during the drying and heat treatment process. 

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2017
Nationell ämneskategori
Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
urn:nbn:se:ltu:diva-60142 (URN)10.1080/17480272.2016.1249405 (DOI)000402709800009 ()2-s2.0-84997272329 (Scopus ID)
Anmärkning

Validerad;2017;Nivå 2;2017-06-07(andbra)

Tillgänglig från: 2016-11-03 Skapad: 2016-11-03 Senast uppdaterad: 2019-05-07Bibliografiskt granskad
3. CT-scanning of the drying process of Eucalyptus nitens.
Öppna denna publikation i ny flik eller fönster >>CT-scanning of the drying process of Eucalyptus nitens.
2018 (Engelska)Ingår i: Proceedings of 21st International Drying Symposium. / [ed] Cárcel JA, Polo GC, García-Pérez JV, Mulet A, Rosselló C.,, Valencia: Editorial Universitat Politècnica de València , 2018, s. 1269-1276Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

The drying of Eucalyptus nitens is a troublesome process as the species is extremely prone to drying defects. This paper reports ongoing research toimprove the understanding of surface checking and cell collapse in Chilean grown Eucalyptus nitens during drying. Computed tomography (CT) scanning was used as a powerful tool for studying the internal changes in the wood-material during the drying process. Different levels of temperatures have been tested with the same equilibrium moisture content (EMC) conditions and low air velocity. The results confirm that a low drying temperature and a low air velocity, which results in a slow rate of drying, reduce internal cell collapse and surface checking .

Ort, förlag, år, upplaga, sidor
Valencia: Editorial Universitat Politècnica de València, 2018
Nyckelord
Cell collapse, computed tomography, surface checks, wood drying, internal checks
Nationell ämneskategori
Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
urn:nbn:se:ltu:diva-71201 (URN)10.4995/ids2018.2018.7380 (DOI)000477977800160 ()978-84-9048-688-7 (ISBN)
Konferens
21st International Drying Symposium, Valencia, Spain, Sep 11-14, 2018
Tillgänglig från: 2018-10-13 Skapad: 2018-10-13 Senast uppdaterad: 2020-01-28Bibliografiskt granskad
4. Real-time wood moisture-content determination using dual-energy X-ray computed tomography scanning
Öppna denna publikation i ny flik eller fönster >>Real-time wood moisture-content determination using dual-energy X-ray computed tomography scanning
Visa övriga...
2019 (Engelska)Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, nr 6, s. 437-444Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The estimation of the pixel-wise distribution of the moisture content (MC) in wood using X-ray computed tomography (CT) requires two scans of the same wood specimen at different MCs, one of which is known. Image-processing algorithms are needed to compensate for the anisotropic distortion that wood undergoes as it dries. An alternative technique based on dual-energy CT (DECT) to determine MC in wood has been suggested by several authors. The purpose of the present study was to evaluate the hypothesis that DECT can be used for the determination of MC in real time. A method based on the use of the quotient between the linear attenuation coefficients (μ) at different acceleration voltages (the so-called quotient method) was used. A statistical model was created to estimate the MC in solid sapwood of Scots pine, Norway spruce and brittle willow. The results show a regression model with R2 > 0.97 that can predict the MC in these species with a RMSE of prediction of 0.07, 0.04 and 0.11 (MC in decimal format) respectively and at MC levels ranging from the green to the totally dry condition. Individual measurements of MC show an uncertainty of up to ±0.4. It is concluded that under the conditions prevailing in this study, and in studies referred to in this paper, it is not possible to measure MC with DECT.

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2019
Nyckelord
CT-scanning, dual-energy X-ray absorptiometry, wood drying, attenuation coefficient
Nationell ämneskategori
Trävetenskap Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
urn:nbn:se:ltu:diva-75497 (URN)10.1080/17480272.2019.1650828 (DOI)000480865200001 ()
Anmärkning

Validerad;2019;Nivå 2;2019-10-24 (johcin)

Tillgänglig från: 2019-08-13 Skapad: 2019-08-13 Senast uppdaterad: 2020-01-28Bibliografiskt granskad

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