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  • 1.
    Hedlund, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Temperature and final moisture content distributions in vacuum driers with different fan configurations1996In: Quality wood drying through process modelling and novel technologies: 5th International IUFRO wood drying conference. pp. 159-168. Quebec City, August 13-17, 1996 / [ed] A. Cloutier; Y. Fortin; R. Gosselin, Sainte-Foy, Québec: Forintek Canada , 1996Conference paper (Refereed)
    Abstract [en]

    In a vacuum kiln working with convective heat transfer the temperature drop across the load is high due to the low density of the superheated steam. It is crucial to maintain a high and uniform steam velocity throughout the drying load in order to achieve a controlled drying process. Later designs of vacuum kilns have focused on an ambition to load large volumes of wood into the kilns or to minimize the installed fan power. The designs have sometimes neglected the need of a controlled steam circulation with an unfavorable steam flow pattern as a result. Measurements of the temperature distributions in vacuum kilns and final moisture content distributions have shown that the fan configuration has a great influence on the kiln performance. An unfavorable steam flow pattern leads to longer drying times as well as larger final moisture spreads in comparison to a more favorable steam flow pattern. A design with fans placed above the wood stack with a well defined pressure and suction side is superior to designs with the fans placed beside the stack and working on a combined pressure and suction side.

  • 2.
    Källander, Björn
    Stora Corporate Research AB.
    Climate control in vacuum dryers for convective heat transfer: Part 1: Demands on climate control2002In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 36, no 6, p. 477-486Article in journal (Refereed)
    Abstract [en]

    The European Drying Group (EDG) proposal on a wood drying quality standard defines demands on final moisture content variation of the dried wood. The final moisture content variation will depend on material parameters as well as the production process and the wood will always show a “natural” moisture content variation after drying. Thus the drying process has to be defined well enough to allow for the natural moisture content variation in order to fulfil the demands of the drying standards. As the average equilibrium moisture content of the wood in a vacuum drying kiln with pure steam atmosphere is determined by the pressure and the temperature, the demands on the climate control system to fulfil the demands of the drying standard can be calculated with regard to the natural moisture content variation of the wood. In the first part of this contribution the demands on climate control in vacuum dryers are calculated based on the EDG-standard and the natural moisture content variation. In the second part of the contribution the demands on climate control are compared with climate and moisture content measurements from industrial production in vacuum kilns. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.

  • 3.
    Källander, Björn
    Stora Corporate Research AB.
    Climate control in vacuum dryers for convective heat transfer: Part 2: Actual climates in industrial kilns and suggestions to improve kiln design2003In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 37, no 1, p. 3-9Article in journal (Refereed)
    Abstract [en]

    The first part of this contribution determined the demands on climate control in vacuum drying kilns that are necessary to achieve the final moisture content variation stipulated in the European Drying Group (EDG) proposal on wood drying quality standards. In this second part of the contribution, these demands are compared with measurements of actual climates and the resulting final moisture content in vacuum kilns during industrial production. The measurements show that none of the studied industrial vacuum kilns are capable of controlling climate with acceptable accuracy. The variations in drying climate lead to large variations in final moisture content and reduced production capacities. Drying quality and drying capacity would be greatly increased with improved kiln design and improved climate control systems. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.

  • 4.
    Källander, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Drying and thermal modification of wood - studies on influence of sample size, batch size, and climate on wood response2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Research on wood drying and wood modification is primarily done in laboratories, using clear wood specimens treated under well-defined conditions in laboratory cabinets. Laboratory tests differ from industrial treatment both regarding the size and homogeneity of the material treated, and the size of the batch and kiln used.Knowledge about how the size of the material treated and the size of the batch or kiln influence the results is limited, which makes it difficult to utilize results from laboratory research in development of industrial processes. A better understanding of the influence of size can also improve the possibilities to design laboratory studies so that the results are easier to implement industrially.The studies presented in this thesis focus on how the size of the batches treated and the size of the individual wood samples treated influence the process and resulting properties of the wood. The aim of the studies, the so called researchquestion in the context of a PhD-thesis, is to help transfer knowledge gained from testing small wooden samples in laboratories to industrial treatment of full size timber.This thesis describes studies on vacuum drying, high temperature (HT) drying, and thermal modification of wood according to the Thermowood© process. Drying and thermal modification of wood have been studied under industrial andlaboratory conditions. Kiln climates and wood response have been determined during vacuum drying, conventional drying, high temperature drying, and thermal modification.The results show that both the size of the material treated and the size of the kiln or batch strongly influence the processes and the resulting wood properties.The results show that the sample size influences different material properties in different ways. Equilibrium moisture content is reduced less during thermal treatment of small clear wood specimens than during treatment of dimensionaltimber. Mass loss on the other hand is higher in small samples. Reduction in impact bending strength, mass loss, and reduction in EMC after thermal treatment of dimensional timber do not seem to be correlated.Laboratory treatment of small clear wood specimens show considerably stronger influence on the wood properties than treatment of similar samples together with industrial production.

  • 5.
    Källander, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Influence of sample size during thermal modification on resulting equilibrium moisture content of Scots pine2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736XArticle in journal (Refereed)
  • 6.
    Källander, Björn
    Stora Enso Timber AB.
    Kiln Climate and Internal Wood Climate during Drying and Heat Treatment of Logs, Planks and Clearwood Samples2010In: Recent Advances in the Field of Wood Drying: 11th International IUFRO Wood Drying Conference. pp. 194-199. Skellefteå, Sweden, January 12-22, 2010 / [ed] Tom Morén; Lena Antti; M. Sehlstedt-Persson, Skellefteå, 2010, p. 194-199Conference paper (Refereed)
    Abstract [en]

    Effects of elevated temperatures on wood properties have been reported in numerous studies. Altered properties on microscopic level as well as plank level have been reported. The altered properties are related to physical as well as chemical phenomena. Changes in chemical properties can be expected to be greatly influenced by the internal wood climate. The internal climate will influence speed of chemical reactions and possibly also lead to different processes for a dry specimen as compared to a moist, and for specimens at high temperature as compared to lower temperature. The internal wood climate during drying and heat treatment will be determined by factors like drying climate, moisture content of the wood, material properties, and size of the specimen studied. Evaporation of moisture and moisture flux will influence kiln climate as well as internal wood temperature level and temperature distribution. A small specimen will adapt faster to the surrounding climate than a large specimen. A specific kiln climate will lead to different moisture gradient and internal stresses in a small sample as compared to a full size plank. When resultsfrom small samples are to be compared to results from planks or logs, the correlation between internal climate in small and large samples needs to be considered. The present paper reports results from temperature measurements during drying and heat treatment of logs, planks and small clearwood specimens. The results illustrate the great difference in internal climate between small and large specimens treated in the same external climate. The paper includes principal suggestions on strategies for how to adapt laboratory tests on small samples to industrial treatment of sawn lumber.

  • 7.
    Källander, Björn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bengtsson, Charlotte
    SP Swedish National Testing and Research Institute.
    Dahlberg, Jonas
    Wood Technology an Engineering, Luleå University of Technology, Forskargatan 1, SE-931 87 Skellefteå, Sweden.
    Influence of drying in temperatures between 70 °C and 125 °C on selected wood properties of Norway spruce2001In: Moisture control in environment-friendly housing and wood drying technology in new century: July 9-13, 2001 Tsukuba, Japan / [ed] K. Hayashi, Forestry and Forest Products Research Institute , 2001, p. 306-311Conference paper (Refereed)
    Abstract [en]

    The present study deals with the influence of drying schedule on the strength and the stiffness of Norway Spruce timber. A previous study gave 11.5 % lower bending strength of timber dried at 115°C compared to timber dried under conventionally (70°C) low temperatures. No influence of high temperature drying on the stiffness was found. These results are in the present paper further evaluated. Special attention is made to the influence of the drying process on the strength and stiffness of structural timber. A comparative study with the mechanical properties of old timber from buildings more than 50 years old is planned.A total number of 634 logs from two regions in Sweden were sawn into planks of dimension 50 mm x 150 mm. The planks were pre sorted in terms of raw stiffness by a stress grading machine. This resulted in eight groups of 156 planks with equal stiffness in the raw condition. Six different drying schedules in maximum dry temperatures ranging from 70 °C to 125 °C were applied to different groups of planks, including a test made to study the effects on the wood during the heating phase to 125 °C.After non destructive evaluation of the dried material by machine stress grading and optical scanning, the mechanical properties of the dried wood was determined. Both bending- and tension strength were evaluated. Failure modes with special concern to failure close to knots are being analysed. Fracture energy is determined for samples from each drying schedule.The results from the present study will give new information on the influence of high temperature drying on strength and stiffness of structural timber. As a wide range of drying schedules are studied valuable information for the optimisation of drying schedules as well as stress grading will be available.

  • 8.
    Källander, Björn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Influence of sample size during industrial and laboratory thermal modification on mass loss and impact bending strength of Scots pine2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736XArticle in journal (Refereed)
  • 9.
    Källander, Björn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Landel, Pierre
    ENSAM, Centre d'Enseignement et de Recherche de Cluny, Fristad Bygg AB.
    Effects of heat treatment of small clearwood samples on equilibrium moisture content and deformation2007In: Quality Control for Wood and Wood Products: COST E53 The First Conference, COST, European Cooperation in Science and Technology , 2007, p. 63-68Conference paper (Refereed)
    Abstract [en]

    High Temperature drying has by numerous studies been shown to affect strength properties as well as moisture properties of the wood treated. The present study aims at determining the effects of different heat treatments of small clearwood samples on material properties. Samples were treated in dry and moist air, saturated steam and water. Temperatures varied from 20 °C to 150 °C. Treatment periods varied from 6 h to 96 h. The results of the study indicate that the effects of treatment are dependent not only on the method of treatment and time, but also on the pre treatment of the samples such as ingoing moisture content.

  • 10.
    Källander, Björn
    et al.
    Stora Enso Building and Living.
    Ormarsson, Sigurdur
    Linnéuniversitetet, Institutionen för byggteknik.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fuktförändringar, klimat och mögelpåväxt vid lagring av granvirke: Kalibrering av Finit Elementmodell för fuktförändringar2016Report (Other academic)
    Abstract [en]

    A diffusion based Finite Element- model designed to calculate changes in moisture content distribution in packages of wood during storage has been calibrated by means of combined measurements of climate and moisture content in a test package. Moisture content distribution before and after storage has been determined by dry mass measurements and X- ray Computer Tomography (CT- scanning). CT- scanning was done on individual planks to reduce interference from surrounding material. As a complement to the measurements of climate and moisture content, the test material was inspected visually after storage to determine if mould growth had occurred.The results from the study show that the moisture flux within a package of wood is slower than the moisture flux theoretically estimated based on published diffusion coefficients of wood. The moisture flux from the interior of a plank to the surface is slower than the removal of moisture from the surface, also when the plank is within a closed package covered with plastic on five surfaces.The calibration of the Finite Element model makes it ready for calculations of changes in moisture content in wood with high accuracy.

  • 11.
    Källander, Björn
    et al.
    Luleå tekniska universitet (student).
    Ormarsson, Sigurdur
    Danmarks tekniska universitet.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fuktförändringar, klimat och mögelpåväxt vid lagring av granvirke: Laboratoriestudie och modellering av industriellt torkat virke2014Report (Other academic)
    Abstract [sv]

    Studien avsåg att bestämma hur fuktkvoten i virke förändras under lagring i paket och vid vilka klimat och fuktkvoter mögelpåväxt uppkommer. Fyra satser virke med medelfuktkvoter mellan 18 % och 24 % skulle studeras för att säkerställa att studien omfattade virke både över och under fuktnivåer där mögel kan uppkomma. En Finit Element- modell som kan beräkna förändringar i fuktkvot i virke under lagring utvecklas och kalibreras mot mätdata för att resultaten ska kunna tillämpas på industriell produktion.Studien avsåg komplettera den tidigare studien i industrimiljö genom att dels oförstörande mäta förändringar i fuktkvotens fördelning under lagringen, dels bestämma fuktens fördelning med större noggrannhet än torrviktsmätningar för att ge underlag till kalibrering av FE-modellen.

1 - 11 of 11
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