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  • 1.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Distribution of preservatives in thermally modified Scots pine and Norway spruce sapwood2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 3, p. 499-513Article in journal (Refereed)
    Abstract [en]

    Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170°C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species.

  • 2.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Evaluation of preservative distribution in thermally modified European aspen and birch boards using computed tomography and scanning electron microscopy2013In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 59, no 1, p. 57-66Article in journal (Refereed)
    Abstract [en]

    The aim of this experiment was to impregnate thermally modified wood using an easy and cost-effective method. Industrially processed thermally modified European aspen (Populus tremula L.) and birch (Betula pubescens Ehrh.) were collected and secondarily treated at the laboratory scale with the preservatives tung oil, pine tar and Elit Träskydd (Beckers) using a simple and effective method. Preservative uptake and distribution in sample boards were evaluated using computed tomography (CT) and scanning electron microscopy (SEM) techniques. Preservative uptake and treatability in terms of void volume filled were found the highest in Beckers and the lowest in tung oil-treated samples. Thermally modified samples had lower treatability than their counterpart control samples. More structural changes after thermal modification, especially in birch, significantly reduced the preservative uptake and distribution. The differences of preservatives uptake near the end grain were high and then decreased near the mid position of the samples length as compared with similar type of wood sample. Non-destructive evaluation by CT scanning provided a very useful method to locate the preservative gradients throughout the sample length. SEM analysis enabled the visualization of the preservative deposits in wood cells at the microstructural level.

  • 3.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Equalization of moisture in pre-dried pinewood using microwave power2010In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 6, no 2, p. 53-59Article in journal (Refereed)
    Abstract [en]

    Commonly, during air-circulation kiln drying moisture gradients within wood cross-sections are developed, i.e. the surfaces become drier than the interior. To minimize these gradients a conditioning step subsequent to the drying is needed. The aim with this study was to investigate the possibility to use microwave power for equalization of moisture within pinewood boards after air-circulation kiln drying to the average moisture content 0,14. Two dimensions of pinewood were tested; thickness 50 and 63 mm, in two different plants, generating 5 and 12 kW microwave power respectively. Results show that microwave energy give rise to a fast and advantageous moisture equalization within the wood. The higher microwave power density the faster heating and moisture redistribution in these wood dimensions. Required time for heating and redistribution of moisture was found to be as short as 3 minutes at the power density 500 kW/m3. In addition, split-tests indicate decreased or elimination of gap after microwave treatment in the investigated specimens.

  • 4.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave treatment of resinous wood2006In: Wood structure and properties '06: [proceedings of the 5th IUFRO Symposium Wood Structure and Properties '06 held on September 3-6, 2006 in Sliač - Sielnica, Slovakia] / [ed] R. Lagana; S. Kurjatko; J. Kudela, Zvolen, Slovakia: Arbora Publishers , 2006, p. 435-437Conference paper (Refereed)
    Abstract [en]

    The output from conventional air-circulation drying of wood is not always satisfying; some individual wood boards often contain somewhat higher moisture content (MC) than the target MC. Higher MC in some pine wood boards after conventional drying could origin from the fact that these contain higher amounts of resin, which may delay or to some extent prevent the moisture flux. It could be the reason to problems in further wood production processes, as for example in gluing processes. The aim of this study was to determine whether or not microwave (MW) heating could be a suitable method to condition these components. Another aim was to investigate if and how migration of resin appears during MW treatment. The study includes experimental tests where determination of both MC and resin content (RC) were carried out before and after MW treatment. Results from the tests show that the RC and the MC are interacting; it means that volumes with high RC also withhold increased amount of moisture; these volumes are often found within boards that origin from the root end of logs. It is possible to dry/condition these planks to reach the target MC within minutes or hours, depending on wood thickness, using MW power. By exposing resinous wood to microwaves, migration of resin takes place from the interior towards the wood surfaces, especially longitudinally through the wood towards the butt ends. It seems to be possible to redistribute RC and MC in wood by exposing only parts of a plank to microwaves.

  • 5.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Redistribution of moisture in pre-dried pinewood using microwave power: a preliminary study2010In: Proceedings, 11th International IUFRO Wood Drying Conference: [... in Skellefteå, Sweden, January 18 - 22, 2010 ... the theme of the conference was "Recent Advances in the Field of Wood Drying"] / [ed] Tom Morén; Lena Antti; Margot Sehlstedt-Persson, Luleå: Luleå tekniska universitet, 2010, p. 234-238Conference paper (Refereed)
    Abstract [en]

    Commonly, during air-circulation kiln drying moisture gradients within wood cross-sections are developed, i.e. thesurfaces become drier than the interior. To minimize these gradients a conditioning step subsequent to the drying isneeded. The aim with this study was to investigate the possibility to use microwave power for redistribution ofmoisture within pinewood planks after air-circulation kiln drying to the average moisture content 0,14. Twodimensions of pinewood were tested; thickness 50 and 63 mm, in two different plants, generating 5 and 12 kWmicrowave power respectively. Results show that microwave energy give rise to a fast and advantageous moistureredistribution i.e. equalization of moisture content within the wood. The higher microwave power density the fasterheating and moisture equalization in these wood dimensions. Required time for heating and redistribution ofmoisture was found to be as short as 3 minutes at the power density 500 kW/m3. In addition, split-tests indicatedecreased or almost no gap in the investigated specimens.

  • 6.
    Cherepanova, Ekaterina
    et al.
    Luleå tekniska universitet.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Determination of wood moisture properties using CT-scanner in a controlled environment2011In: Proceedings of the 7th meeting of the Nordic-Baltic Network in Wood Material Science and Engineering (WSE) / [ed] Erik Larnøy; Gry Alfredsen, Ås: Norsk institutt for skog og landskap , 2011, p. 137-142Conference paper (Refereed)
    Abstract [en]

    The aim of the present work was to examine the existing algorithm for the moisture content calculation and also to use this algorithm to analyze and compare the moisture flow data for high and low temperature drying. The use of the existing algorithm for the dry weight moisture content on density data from the CT-scanning during high and low temperature drying in the climate chamber showed that this method is a powerful tool for analyzing the moisture flow inside the wood piece. Furthermore, the new CT-scanner together with the climate chamber gave unique results, as it has not been possible to study high temperature drying with this method before.

  • 7.
    Couceiro, José
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    In situ CT-scanning for detection of internal checking and cell collapse during drying of hardwood species2016In: The 7th European Conference on Hardwood, Eco-efficient resource wood with special focus on hardwoods / [ed] Teischinger A., Németh R., Rademacher P., Bak M. & Fodor F. (Eds.), Sopron: University of West Hungary , 2016, p. 58-59Conference paper (Refereed)
    Abstract [en]

    During the drying of sawn timber, hydrostatic tension forces within the cell may exceed the compressive strength perpendicular to the grain of the thin cell wall and the cell then collapses. This phenomenon is common in hardwoods such as Sequoia sempervirens, Thuja plicata, Tsuga heterophylla, Juglans nigraand many species of eucalyptus and oak. Usually, this leads to severe surface deformation, and both surface and internal checking(honeycombing) may occur. The quality of the final product is lowered by these cracks and deformations. The aim of this study was to investigate, by CT-scanning samples throughout the drying process, whether it is possible to detect when and how cracking and deformation occurs and develops in specimens of Eucalyptus nitens. Based on this knowledge, better drying schedules can be developed to improve the yield and ensure a higher quality of the sawn timber. Three specimens, one specimen in each drying run, of Eucalyptus nitens were used for the tests. Their cross-sectional dimensions, prior to drying, were 105x23 mm2 and their length was 70 cm. A specially designed laboratory drying kiln that fits within the gantry of a Siemens Somatom Emotion medical CT-scanner was used (Fig. 1). With this equipment, it is possible to scan the inside of the kiln without interrupting the drying process.

  • 8.
    Couceiro, José
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    The use of X-ray computed tomography in timber construction research2016In: New Horizons for the Forest Products Industry: 70th Forest Products Society International Convention, June 26-29, Portland, Oregon, USA, Madison: Forest Products Society, 2016Conference paper (Other academic)
    Abstract [en]

    powerful tool for the non-destructive measurement of dynamic processes in wood. For more than 20 years, CT has been used in wood research at Luleå University of Technology. The uniqueness of the CT equipment means that processes such as drying, modification, water absorption, internal and external cracking and material deformation can be studied in temperature- and humidity-controlled environments. The data recorded by the CT during the process is converted into two- or three-dimensional images that for instance can show dynamic moisture behavior in wood drying.This paper gives an overview of the possibilities of using CT in timber construction research, and shows examples of applications and results which can be particularly difficult to achieve using other methods. A specific focus is on studies on wood products for construction, and how to deal with different material combinations such as wood and metal.The practical application of the result is that CT-scanning, combined with image processing, can be used for non-destructive and non-contact 3-D studies of exterior constructions elements during water sorption and desorption, to study swelling and shrinking behaviour, delamination phenomena, crack development, etc.

  • 9.
    Couceiro, José
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Norwegian University of Science and Technology (NTNU), Department of ICT and Natural Sciences, Norway.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    CT scanning of capillary phenomena in bio-based materials2017In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 13, no 4, p. 181-187Article in journal (Refereed)
    Abstract [en]

    X-ray computed tomography (CT) is a powerful tool for the non-destructive study of dynamic moisture processes in wood and other bio-based materials. In the CT facilities at Luleå University of Technology, it is possible to study wood-moisture relations such as water absorption, drying and related material deformation under a temperature- and humidity-controlled environment.An increase in the use of bio-based materials in building construction has led to an increased interest in capillary phenomena in these materials, because of an increasing number of moisture-related damage in timber and hybrid-timber buildings. This article shows some examples of how different bio-materials used in construction interact with liquid water over time. The overall purpose has been to develop the CT technique as a powerful tool for the determination and visualization of capillary flow that can be a base for modelling and an increased understanding of moisture flow in new bio-based building materials.Early-stage observation of the behaviour of different traditional and new bio-based building materials shows that CT scanning, combined with image processing, has a high potential to be used in performing non-destructive and non-contact tests that can help to increase the knowledge of water-material interactions and develop building materials with an optimized performance.

  • 10.
    Couceiro, José
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Vikberg, Tommy
    SP Technical Research Institute of Sweden .
    Hansson, Lars
    Natural Sciences and Preliminary Courses, NTNU Ålesund, Norway .
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    In Situ CT-Scanning of Checking and Collapse Behaviour of Eucalyptus nitens During Drying2016In: Proceedings of the 59th International Convention of Society of Wood Science and Technology March 6-10, 2016 – Curitiba, Brazil, 2016Conference paper (Other academic)
    Abstract [en]

    Eucalyptus nitens has become a commercially important species in Chile and it isrepresenting one of the fastest growing wood-stock in the country. Today, it is widelyused for pulp and paper production, but the interest in using the solid wood has increasedin recent years. Before the sawn timber can be utilized, its moisture content must bereduced. Often during drying, hydrostatic tension forces within the cell exceed thecompressive strength of the thin cell wall of Eucalyptus nitens and the cell collapses. Thisphenomenon usually leads to severe surface deformation and both surface and internalcracks (honeycombing). Yield and quality of the final product, and thereby sawmills’profitability, are decreased by these cracks and deformations. The aim of this study wasto investigate, by CT-scanning samples throughout the drying process, if it is possible todetect when and how cracking and deformation occurs and develops in specimens ofEucalyptus nitens from Chile. Based on this knowledge, better drying schedules canhopefully be developed to improve the yield and provide a higher end-quality of the sawntimber.

  • 11.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Controlling microwave heating and its effect on the properties of wood2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Drying wood with microwave energy is not so common, but could be a complement to conventional air circulation drying due to the possibility of drying wood faster than with conventional drying methods with preserved quality. An industrial-scale, on-line microwave drier for wood components is under development at the Division of Wood Physics. This drier will be mainly used for demonstrations, product testing and for students? laboratory work. The purpose of the present work was to study the drying of wood by microwave heating and to investigate whether the method affects the properties of wood. The aim was also to ascertain how to adjust the design of a microwave construction for industrial use. Testing of the mechanical properties of the wood showed no difference in bending strength in comparison with the conventional air-circulation method. Nor did testing of wood hardness (Janka) show any significant difference between the drying methods and the temperature level during microwave drying. Furthermore, when using the microwave drying method, the infrared (IR) images showed that it is very important to control microwave heating and to move the components during the drying process in order to achieve more uniform heating and avoid thermal runaway at the end of the process. This runaway effect can negatively affect the mechanical properties of the wood.

  • 12.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave treatment of wood2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Drying wood using microwave energy is not very common, but could be a complement to conventional air-circulation drying due to the possibility to dry wood faster than the conventional drying methods with preserved quality. Furthermore, this technique could be used to condition boards with too high moisture content gradient. In this study, an industrial-scale, online microwave drier for wood components has been used and adapted to wood treatment. The aim of the present work was to investigate if the microwave drying method itself affects such wood properties as bending strength, hardness and colour change. Another aim was to explain, with finite element model simulations, the interaction between microwaves and wood during heating and drying and to a lesser extent also during microwave scanning of wood. Tests of the mechanical properties of wood showed no difference in bending strength in comparison with the conventional air circulation method. Nor was there any significant difference in wood hardness (Janka) perpendicular to the grain between the drying methods or between different temperature levels during the microwave drying. However, the results showed that there is a significant difference in wood hardness parallel to the grain between the methods when drying progressed to relatively lower levels of moisture content; i.e. wood hardness becomes higher during microwave drying. The developed multiphysics finite element model is a powerful evaluation tool for understanding the interaction between wood and microwaves during heating and drying as well as scanning. The model can be used for simulation of different microwave treatments of wood.

  • 13.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Styrprogram för temperaturhållning av last i mikrovågsugn2002Report (Other academic)
    Abstract [sv]

    För att kunna studera hur trä påverkas om det torkas med hjälp av mikrovågor vid olika temperaturer, har avdelning för träfysik Institutionen i Skellefteå använt sig av bl a en vanlig hushållsmikrovågsugn. Mätningen av temperaturen har skett med en fiberoptisk termometer. Torkningarna kan vara relativt tidsödande, och eftersom termometern och mikrovågsugnen inte har varit sammankopplade så har det hitintills varit så att den som utfört torkningen alltid fått närvara vid denna process. Syftet med detta projekt var att göra en styrning som fungerar som en automatisk temperaturstyrning av processen och inte som tidigare en manuell temperatur övervakning. Resultatet visar att med detta nya styrprogram så reduceras behovet av den manuella övervakningen till att endast se till så att träbitarna uppnår önskad fuktkvot

  • 14.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    Design and performance of an industrial microwave drier for on-line drying of wood components2003In: Proceedings of the 8th IUFRO International Wood Drying Conference: Improvement and innovation in wood drying : a major issue for a renewable material : 24-29 August 2003, Brasov, Romania / [ed] Mihai Ispas; Sergiu T Chiriacescu, Brasov: Transilvania University of Brasov, Faculty of Wood Industry , 2003, p. 156-158Conference paper (Other academic)
    Abstract [en]

    The most common industrial method for drying wood is by air circulation. However, an alternative method - microwave drying-has been investigated at the Division of Wood Physics, Luleå University of Technology in Skellefteå, Sweden. The use of microwave energy to dry wood is not very common, but it could be advantageous due to the possibility of heating and drying wood much faster than conventional methods and with preserved quality. The objective of the investigation is to install an on-line microwave drier for wood components and, furthermore, to integrate this drying process into the total production. The purpose of this paper is to briefly describe the design and performance of this on-line microwave drier, its advantages and its limitations.

  • 15.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    Modeling microwave heating and moisture redistribution in wood2008In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 26, no 5, p. 552-559Article in journal (Refereed)
    Abstract [en]

    A finite element model was developed to describe and explain microwave heating of wood and the following moisture redistribution in wood. Dielectric and thermal properties are of great importance, since they are continuously affected during the process by moisture content, density, grain direction, temperature, and more. Computer tomography was used to detect wood density and moisture content. Heat distribution was verified by fiber-optic temperature sensors. The tests were performed in a designed microwave dryer based on 1-kW generators, 2.45GHz. The results show that finite element modeling is a powerful tool to simulate heat and mass transfer in wood, providing the material is well described.

  • 16.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    The effect of drying method and temperature level on the hardness of wood2006In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 171, no 3, p. 467-470Article in journal (Refereed)
    Abstract [en]

    The purpose of the present work was to investigate whether wood hardness is affected by temperature level during microwave (MW) drying and whether the response is different from that of conventionally dried wood. Matched samples of Norway spruce (Picea abies) were therefore dried from green state to different moisture content (mc) at different temperature levels, both conventionally by air circulation and by MW. The results show that specimens dried by any of the two methods at a temperature level of 100 or 60°C there is a significant difference in wood hardness parallel to the grain between the methods when drying progresses to relatively lower level of moisture content, i.e. wood hardness becomes higher during MW drying. Temperature level in the range 60-110°C during MW drying has no significant influence on wood hardness. Variables such as density and mc have a greater influence on wood hardness than does the drying method or the drying temperature. Since wood is a biological material, its strength varies within the specimens as well as between different samples. For this reason it is important to use matched samples when performing this type of comparative investigation.

  • 17.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    The effect of microwave drying on Norway spruce woods strength: a comparison with conventional drying2003In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 141, no 1, p. 41-50Article in journal (Refereed)
    Abstract [en]

    The purpose of the present work was to investigate whether the drying method itself affects strength of wood apart from fibre direction, density, temperature in the wood, moisture content and with which angle the microfibril is placed in the middle layer at the secondary cell wall S2. The drying methods compared were microwave drying and conventional air-circulation drying, and the species tested was Norway spruce. The result shows that it is not possible to demonstrate any difference between the two drying methods with respect to the strength of the wood. What affects wood strength are such variables as moisture content, number of annual rings and the density properties weight, width and thickness

  • 18.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    Lundgren, Nils
    Hagman, Olle
    Finite element modeling (FEM) simulation of interactions between wood and microwaves2006In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 52, no 5, p. 406-410Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to use finite element modeling (FEM) as a tool to analyze microwave scattering in wood and to verify the model by measurements with a microwave scanner. A medical computed tomography scanner was used to measure distribution of density and moisture content in a piece of Scots pine (Pinus sylvestris). Dielectric properties were calculated from measured values for cross sections from the piece and used in the model. Images describing the distribution of the electric field and phase shift were obtained from the FEM simulation. The model was verified by measurements with a scanner based on a microwave sensor. The results show that simulated values correspond well to measured values. Furthermore, discontinuities in the material caused scattering in both the measured and the simulated values. The greater the discontinuity in the material, the greater was the need for computational power in the simulation.

  • 19.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    IR- och HFV-teknik för virkestorkning2002Report (Other academic)
    Abstract [sv]

    Syftet med föreliggande arbete är att presentera några relativt nya virkestorkningsmetoder. Tanken är att visa på metodernas möjligheter och begränsningar för den svenska träbranschen. De metoder som valts ut är torkning med hjälp av infraröd strålning och högfrekvens/vakuum-torkning. Studien baseras på fysikaliska förutsättningar, litteraturinventering, intervjuer med metodutvecklare och i IR-fallet på medverkan vid praktiska kvalitetsmätningar av det torkade virket. Resultatet visar att teknologin som bygger på infraröd teknik möjligen kan minska torkningstiden, men detta antagande bygger endast på den grundläggande fysiken bakom teknologin. De som har investerat i denna teknologi vill ej ge ut information kring tekniken innan den grundligt har testats. Därför finns en del obesvarade frågeställningar, såsom hur mycket tid som kan tjänas vid torkningen, energiåtgångens storlek samt vilken torkningskvalitet som erhålls med denna torkningsmetod. Det sistnämnda undersöks för närvarande av Trätek. Högfrekvens/vakuumtekniken som beskrivs här är utvecklad i Kanada och används industriellt där, än så länge dock i liten skala. Träslag som på senare tid undersökts och torkas med denna metod är företrädesvis nordamerikanskt barrvirke. Metoden lämpar sig ur ekonomiskt perspektiv (i Kanada) framför allt för torkning av grövre dimensioner, men också för att fuktutjämna konventionellt torkat virke. Fördelarna med metoden jämfört med konventionell teknik är kortare torkningstid, mindre förekomst av ytsprickor, inre spänningar och fläckvis missfärgning förekommer inte alls och dessutom uppnås en jämn slutfuktkvot i hela lasten. Virket behöver inte ströläggas då den huvudsakliga fukttransporten sker i fiberriktningen. Svårigheter med torkstyrningen i form av övertorkning och kollaps har numera minimerats genom den senaste generationen högfrekvens-/vakuumtorkar. Metoden kräver tillgång till elenergi och energiförbrukningen uppges till 1.2 kWh per kg bortfört vatten.

  • 20.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cherepanova, Ekaterina
    Determination of wood moisture properties using a CT-scanner in a controlled high-temperature environment2012In: Journal of Civil Engineering and Architecture, ISSN 1934-7359, E-ISSN 1934-7367, Vol. 6, no 3, p. 372-378Article in journal (Refereed)
    Abstract [en]

    The aim of the present work was to analyze moisture flow and moisture content data for high-temperature drying by using an advanced image- processing algorithm.Since wood starts to shrink below the fibre saturation point during drying, the size and shape of wood will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight moisture content. The use of the image- processing algorithm for the dry weight moisture content on density data from the CT-scanning during drying in a controlled high-temperature environment showed that this method is a powerful tool for analyzing the moisture flow inside the wood piece. Furthermore, the new CT-scanner together with the climate chamber gave unique results, as it has not been possible to study high-temperature drying with this method before.

  • 21.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cherepanova, Ekaterina
    Luleå University of Technology.
    Determination of wood moisture properties using a CT-scanner in a controlled low-temperature environment2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 2, p. 87-92Article in journal (Refereed)
    Abstract [en]

    The aim of the present work was to examine an advanced image-processing algorithm for moisture content (mc) calculation and also to use this algorithm to analyse moisture loss data for low temperature drying. Since wood starts to shrink below the fibre saturation point during drying, the geometrical shape of the wood piece will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight mc. The results show that the algorithm for the dry weight mc on density data from the CT-scanning during low-temperature drying in the climate chamber is a powerful tool for analysing the moisture loss inside the wood piece. This method can make it possible to get a higher quality on the product

  • 22.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cherepanova, Ekaterina
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    CT-scanning during heat treatment of wood2011In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 7, no 4, p. 11-17Article in journal (Refereed)
    Abstract [en]

    Earlier experiences from industrial heat treatment of wood with the ThermoWood® process show that more or less extensive internal cracking may occur for thicker dimensions. This type of timber damage is particularly troublesome because these cracks do not reach the surface and are thus not visible on unprocessed timber. After resawing or planing the boards, cracks can appear, resulting in costly downgrading of the material. The ThermoWood® heat treatment process can be divided into six periods. The first period, the heating period, is when saturated steam is injected into the kiln, the second period is the drying step, which can be either high or low temperature drying, the third period is when the final heating and drying take place, the fourth period is when the temperature is kept constant for about 2–4 hours, the fifth period is the cooling regime, the sixth period is the conditioning regime for remoistening the material, and the last period is the cooling one. At the Division of Wood Physics at Luleå University of Technology in Skellefteå a climate chamber has recently been installed. This climate chamber together with a CTscanner makes it possible to study wood density changes in different climates. As the maximum temperature that can be reached in the climate chamber is 220 °C, it is also possible to study the heat treatment process, besides conventional air circulation drying. The aim of this study was to use the CT-scanning (CT) technique during heat treatment of wood in order to investigate whether it is possible to detect internal checking in situ during the treatment.

  • 23.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Faculty of Engineering and Natural Sciences, Norwegian University of Science and Technology (NTNU), Ålesund.
    Couceiro, José
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fjellner, Bengt-Arne
    Luleå University of Technology, Professional Support, IT-Service.
    Estimation of shrinkage coefficients in radial and tangential directions from CT images2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 4, p. 251-256Article in journal (Refereed)
    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. 

  • 24.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fjellner, Bengt-Arne
    Luleå University of Technology, Professional Support, VSS Support.
    Wood shrinkage coefficient and dry weight moisture content estimations from CT-images2013In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 9, no 4, p. 557-561Article in journal (Refereed)
  • 25.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lundgren, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    Hagman, Olle
    FEM simulation of heating wood in an industrial microwave applicator2005In: 10th International Conference on Microwave and High Frequency Heating : Modena, Italy, September 12 - 15, 2005 / [ed] Cristina Leonelli, 2005Conference paper (Refereed)
  • 26.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lundgren, Nils
    Antti, Lena
    Hagman, Olle
    Microwave penetration in wood using imaging sensor2005In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 38, no 1, p. 15-20Article in journal (Refereed)
    Abstract [en]

    It is possible to determine properties of wood using microwave scanning techniques. The purpose of this study was to verify the measured values from a microwave imaging sensor. Attenuation and phase shift of an electromagnetic wave transmitted through birch wood were measured and compared with theoretical calculated values. A test piece with varying thickness was measured with a scanner based on a microwave sensor (Satimo 9.375GHz) at different temperatures and moisture contents. The density distribution of the test piece was determined by computer tomography scanning. The result showed good correspondence between measured and theoretical values. The proportion of noise was higher at low moisture content due to lower attenuation. There is more noise in attenuation measurement than in measurement of phase shift. A reason for this could be that wood is an inhomogeneous material in which reflections and scattering affect attenuation more than phase shift. The microwave scanner has to be calibrated to a known dielectric to quantify the error in the measurement

  • 27.
    Lundgren, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    PLS models for predicting wood properties from microwave measurements based on three dimensional FEM simulations2007In: Proceedings from the Nordic Workshop in Wood Engineering / [ed] Helena Johnsson, Luleå: Luleå tekniska universitet, 2007Conference paper (Other academic)
    Abstract [en]

    When electromagnetic waves propagate through wood they will be affected by variations in the dielectric properties. These variations are related to different properties within the wood. Dielectric properties of wood depend on moisture content, density, temperature, grain angle and frequency of the electromagnetic wave. The aim with this study was to use threedimensional finite element modelling (FEM) in combination with multivariate statistics and projection to latent structures (PLS) to develop a prediction model for moisture content and dry basis density in wood. An X-ray computed tomography (CT) scanner was used to detect density and, with that, moisture content in wood. Dielectric properties were calculated within a wood volume and used in the simulation. Different frequencies and directions of the electric field were simulated. Previous studies have shown that this method gives a good description of the interactions between wood and microwaves in two dimensions. The results show that 3D finite element modelling can be used to generate a prediction model for moisture content from microwave scanning. Other properties of wood such as density and grain angle have less influence on the microwaves but might be predicted by further processing of the signal.

  • 28. Lundgren, Nils
    et al.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Antti, Lena
    FEM simulation of interactions between microwaves and wood during thawing2006In: Mathematical modeling of wave phenomena: conference on mathematical modeling of wave phenomea, Växjö, Sweden, 14 - 19 August 2005 / [ed] Börje Nilsson; Louis Fishman, Melville, NY: American Institute of Physics (AIP), 2006, p. 260-267Conference paper (Refereed)
    Abstract [en]

    Dipole polarization of water molecules is an important factor when microwaves interact with moist wood. Hence there will be a considerable change in dielectric properties when the wood changes from frozen to nonfrozen condition. The aim of this study was to develop a model that simulates measurements with a microwave scanner based on a sensor working at 9.4 GHz. Two-dimensional finite element modelling (FEM) was implemented to analyze interactions between microwaves and green wood during thawing of frozen wood at room temperature. A medical computed tomography scanner was used to measure the internal structure of density in a piece of wood in green and dry condition. From these density images the distribution of dry weight moisture content was calculated for a cross section of the piece and used in the model. Images describing the distribution of the electric field and phase shift at different temperatures where obtained from the FEM simulation. The results show that simulated values correspond well to measured values. This confirms that the model presented in this study is a useful tool to describe the interaction between microwaves and wood during microwave scanning at varying conditions.

  • 29.
    Vikberg, Tommy
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Schajer, Gary S.
    University of British Columbia.
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Effects on microwave measurements and simulations when collecting data close to edges of wooden boards2012In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 45, no 3, p. 525-528Article in journal (Refereed)
    Abstract [en]

    Parameters like strength, moisture content, density and grain direction are important when sorting wood according to their individual properties. All those parameters can be correlated to microwave measurements of phase shift and attenuation. Measurements of phase shift and attenuation are, however, affected by the vicinity of a board edge. In this article a simulation of the measurement system is used to create a compensation function for the measurements taken close to edges as if those were taken where no effects of the board edge could be noticed. It is shown, by comparison with real measurements, that by doing this the deviation between the values measured close to the board edges and those measured in the middle of the board is decreased, meaning a higher accuracy can be achieved by using the compensating function.

  • 30.
    Vikberg, Tommy
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sterley, Magdalena
    SP Technical Research Institute of Sweden, Wood Technology.
    Moisture movements during drying of green glued glulam beams from Norway spruce sideboards2012Conference paper (Refereed)
    Abstract [en]

    Form defects such as cup, crook, twist and bow, often causes low volumetric and economical yield in dried sideboards of Norway spruce. The high stiffness and density of sideboards, however, make them attractive to use as structural timber. The green gluing process i.e. gluing of unseasoned timber (with the subsequent drying) can make gluing of side boards efficient and can overcome the difficulties in utilization of side boards for structural applications.In present work, a study where computed tomography was used to monitor the drying process of a green glued glulam beam is presented. The beam had a dimension in cross-section of approximately 105×235 mm2 and consisted of eleven sideboards, planed and flat wise glued together with a 1-component polyurethane adhesive. After curing, and prior to drying, the beam was split into two halves, of approximate size of 50×235 mm2.The drying took place in a small drying kiln and computed tomography scanning was done every second hour throughout the drying process to get the density distribution in the beam. When the drying was finished the temperature in the kiln was increased to 103°C and kept for 24 hours, as to get a dry density reference. By use of an algorithm for subtracting the dry density, the moisture evaporation throughout the drying process could be estimated. Despite the harsh drying conditions, with a wet bulb depression of 10°C already from the start of the drying process, no formation of cracks or other quality problems could be seen in the process. Neither could any moisture gradient from the outer to the inner boards be detected.

1 - 30 of 30
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