| 1. |
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| 2. |
- Antti, Lena, et al.
(author)
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Investigation of the heating of wood in an industrial microwave applicator : theory and practice
- 2000
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In: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 18:8, s. 1665-1676
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Journal article (peer-reviewed)abstract
- In this work a comprehensive set of experimental results are used as an excellent means to understand the coupling that exists between the material and the electromagnetic fields in a specific industrial microwave applicator. The analysis of the infrared images allows an accurate map of the power and temperature distributions within the wood sample to be determined. This map, together with the simulation results of a previously developed computational electromagnetic model, can provide a detailed understanding of the design features of the microwave applicator. In particular, it is possible to locate the occurrence of localised hot spots and to examine the uniformity of the heat distribution throughout the sample. The simulation results provide the evolution of the electromagnetic fields inside the entire applicator and the sample. The coupling of theory and practice is the best way to proceed in optimising the design and for proposing new applicator geometry that can heat the material more effectively.
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| 3. |
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| 4. |
- Awoyemi, Lawrence
(author)
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Reversibility of dimensional changes in birch (Betula pubescens) and Scots pine (Pinus sylvestris L.) wood
- 2004
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In: Taiwan Linye Kexue. - 1026-4469. ; 19:2, s. 97-101
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Journal article (peer-reviewed)abstract
- The reversibility of wood shrinkage through swelling of birch (Betula pubescens) and Scots pine (Pinus sylvestris L.) as a measure of their response to changing conditions of adsorption and desorption during service was determined. Virtually all dimensional changes that occurred in the form of shrinkage during drying at both conventional and high temperatures were recovered during swelling in both species. It is suggested that minor changes in the equilibrium moisture content, which commonly occur during the life span of wood, will not result in significant dimensional changes in either species except in the tangential direction of Scots pine. Significant differences between shrinkage and swelling in the tangential direction in Scots pine where swelling was greater than shrinkage implies a higher stability of Scots pine during shrinkage compared to swelling. Hence it is expected that in the tangential direction, this species will be more stable during desorption than adsorption
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| 5. |
- Backman, Anna
(author)
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Interaction and adhesion at the interface between wood and paint, glue, lacquer measured with DMTA and SEM
- 2000
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Licentiate thesis (other academic/artistic)abstract
- The aim of the present thesis was to study the interface between wood (Pinus sylvestis) and synthetic polymers such as glue, lacquer and paint. The weakest part of these interfaces is always the bond. The long-term properties of bonds between wood and an adherend are those which are interesting. If a good bond is achieved, the surface between wood and an adherend would be less susceptible to degradation. To achieve a good bond, the wood polymers and the adhering polymers must be compatible. The contact area between the substrate and an adherend should be as large as possible to give a high quantity of bonds. A large contact area also gives the possibility of adhesion through mechanical interlocking. The interaction between wood and glue and lacquer was studied with Dynamic Mechanical Thermal Analysis. The interaction was correlated with adhesion properties observed with Scanning Electron Microscopy (SEM) fractography. Dynamic mechanical properties of untreated wood in the tangential and radial direction was studied to have a knowledge of the wood polymers behaviour. The properties of the wood polymers was needed for evaluating the change in behaviour when wood was combined with glue and lacquer. It was shown that polymers interacting with the wood polymers experienced a higher free volume in contact with wood, thus decreasing the glass transition temperature of the synthetic polymers. This decrease was considered most probably to be due to the polymers being subjected to tensile forces developed during drying. The high level of interaction was correlated to high adhesion on the wood cell wall level. Two similar commercial polyurethane-alkyd lacquers showed interaction with wood, but a commercial polyvinyl acetate glue showed poor interaction and poor adhesion. The fracture surface between wood and paint in a 50-year-old window was studied with SEM, using backscattered electron image. The method makes it possible to analyse fracture surfaces and determine where the fracture occurrs. It could be used, as an indication of whether the weakest link in different paint/wood systems is the interface.
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| 6. |
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| 7. |
- Bengtsson, Peter, 1974-
(author)
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The release of Hydrocarbons from softwood drying : Measurement and modeling
- 2004
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In: MADERAS. - : SciELO Agencia Nacional de Investigacion y Desarrollo (ANID). - 0717-3644 .- 0718-221X. ; 6:2, s. 109-122
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Journal article (peer-reviewed)abstract
- The release of volatile organic compounds (VOC) during the drying of Norway spruce and Scots pine was experimentally studied. Heartwood and sapwood were separately dried at 60 ºC. The Flame Ion Detector (FID) was used to measure the total amount of hydrocarbons (THC) released during the drying process. A large difference of the emissions course between heartwood and sapwood were found. For heartwood, a release maximum of hydrocarbons followed by a typical negative exponential course was found. When drying sapwood, the released amount of hydrocarbons was evidently more fluctuating before reducing to zero. A model describing the release of hydrocarbons during the drying with only diffusion as transport mechanism was applied. The aim was to obtain a suitable explanation of the characteristic release behavior from sapwood and develop a model describing the process.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Danvind, Jonas
(author)
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Methods for collecting and analysing simultaneous strain and moisture data during wood drying
- 2002
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Licentiate thesis (other academic/artistic)abstract
- Improved understanding of moisture and mechanical behaviour is an international objective for wood drying research. The main objective of this licentiate thesis work was to develop an experimental method suitable for collecting valuable response data related to the moisture and mechanical behaviour of drying wood. Another objective was to provide an example on how multivariate methods can be used to analyse response data. A method for simultaneous non contact measuring of two dimensional surface deformations and interior densities have been developed. This was done using Digital Speckle Photography, DSP, and X-ray Computerised Tomography (CT). Displacements and densities were used for calculation of strains and moisture contents using a custom software developed in Matlab. Experimental tests of the measuring method were made on cross sections of Scots pine. The following accuracy was stated for different properties: - Displacements measured with DSP could be measured with a random error down to 0.01 pixels. A more typical calculated displacement error of approximately 10 micrometres, was found in paper I. - Strains derived from the displacements had a maximal error of 1.11 mstrain in an experimental test in paper II. - Accuracy in density measurements was expected to be less than +-6 kg/m3 for wet wood with moisture contents ranging from 6-100% and less than +-2 kg/m3 in dry wood, at a significance level of 0.05. This was estimated for a 2x2x1.5 mm3 measuring volume. - Moisture content measuring accuracy was estimated by simulations in paper II, which resulted in a measuring accuracy of +-1.8% moisture content at a significance level of 0.05 in a measuring volume with the approximate size of 2x2x1.5 mm3. A multivariate analysing method has been used to present an example on multivariate modelling of shrinkage behaviour in Radiata pine. The method was found to be an easy-to-use tool and useful for valid prediction of radial, tangential, longitudinal and volume shrinkage in the moisture range between 0% and 22% moisture content of the studied wood. The method also proved to be effective for untangling relationships between variables and generating information out of data. Finally, it can be stated that the developed measuring technique and the tested multivariate analysing method will be of use to improve the understanding of the behaviour of drying wood, focusing on moisture and mechanical properties.
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| 13. |
- Danvind, Jonas
(author)
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PLS prediction as a tool for modeling wood properties
- 2002
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In: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 60:2, s. 130-140
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Journal article (peer-reviewed)abstract
- During an earlier study, material responses of shrinkage and deformation during air-drying were measured on small wood specimens cut from the cross section of a Pinus radiata log. In this paper the analysis of the collected data and the modeling of studied responses were done using multivariate methods. A first model with all variables and all 104 observations was created. In this model there were observations that deviated from the rest and some of them were therefore excluded from further modeling. Also, weak variables and undesired variables were excluded from further modeling. After these exclusions, 77 observations of wood responses below fiber saturation point remained. The results showed good modeling of radial, tangential and volumetric shrinkage between 0-22% MC, with explained variance (R2) and predicted variance (Q2) at approximately 0.9, and moderate modeling of longitudinal shrinkage, R2 = 0.67 and Q2 = 0.65. It was also shown that longitudinal shrinkage has weak correlation to density-related variables in the studied wood. No model with good predictability of deformation was found. This study showed that PLS prediction modeling of shrinkage and deformation in studied wood samples was found to be an effective and easy-to-use tool for untangling relationships between variables and generating information from data.
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| 14. |
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| 15. |
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| 16. |
- Elustondo, Diego, et al.
(author)
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Drying with superheated steam : Maximum drying rate as a linear function of pressure
- 2002
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In: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 86:1-2, s. 69-74
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Journal article (peer-reviewed)abstract
- Drying with superheated steam (SS) as heating agent is controlled through three operative variables, the steam temperature, the recycle velocity, and the system pressure. Once the other conditions are fixed, there is an optimum pressure at which drying rate reaches its maximum value. The exact optimum conditions can be found through a differential mass and energy balance over the heat exchange area, resulting in two equations. The first one to calculate the drying rate as function of the operating conditions and the second one to find the values of those conditions which make the operation optimum. Then, using these equations, this paper shows that the relationship between maximum drying rate and pressure can be rewritten in a unique linear equation. Experiments were performed in a model system to obtain a family of drying rates versus pressure curves, and in accordance with the predicted behaviour, it was observed that all maximum drying rates lay on a straight line
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| 17. |
- Elustondo, Diego, et al.
(author)
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Evaluation of three semi-empirical models for superheated steam vacuum drying of timbers
- 2003
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In: Drying Technology. - 0737-3937 .- 1532-2300. ; 21:5, s. 875-893
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Journal article (peer-reviewed)abstract
- Superheated steam drying at sub-atmospheric pressure (SSV) has been successfully employed in Europe and Asia for drying some types of timbers, showing that drying time could be reduced by 50% with respect to conventional drying without significant losses in the quality of the final product. This reduction is the consequence of a different heat and mass transfer control mechanism. Since SSV drying is carried out in absence of gaseous air, diffusion of the generated vapor is not a limiting factor and drying rate becomes more dependent on heat transference. Therefore, classical interpretation of timber drying as a process based on moisture migration control is not applicable to SSV. This work is targeting the development and validation of a simplified semi-empirical model for SSV drying of timbers. Mathematical representation of the proposed model is uncomplicated and straightforward to apply, and the comparison between model predicted and experimental data showed a high degree of agreement under variable drying conditions.
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| 18. |
- Elustondo, Diego, et al.
(author)
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Mathematical modeling of moisture evaporation from foodstuffs exposed to subatmospheric pressure superheated steam
- 2001
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In: Journal of Food Engineering. - 0260-8774 .- 1873-5770. ; 49:1, s. 15-24
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Journal article (peer-reviewed)abstract
- In this work, a reduced expression to calculate the drying rate of foodstuffs being dried with low pressure superheated steam is developed. It is based on a theoretical drying mechanism which assumes that water removal is carried out by evaporation in a moving boundary making the vapor to flow through the dry layer built as drying proceeds. The theoretical model can be applied to any form and features dimensionless parameters to allow for the influence of form, shrinking effect and boiling point rise. To make the application easier, a simplified expression was derived, which has only two experimentally determined parameters and allows the calculation of the drying rate of a given product. Different foodstuffs were dried with this technique and the empirical parameters were calculated from the experimental data fitting equation. Interestingly, those parameters can be considered constant within the 10000-20000 Pa pressure range and the 60-90°C temperature range
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| 19. |
- Elustondo, Diego, et al.
(author)
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Modeling a timber "dry/sort/re-dry" strategy using combined conventional and dielectric technologies
- 2002
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Conference paper (peer-reviewed)abstract
- In this work, a numerical stochastic model is presented and utilized to study the dry/sort/re-dry (DSRD) strategy for 116-mm square ,timbers ,by using ,combined conventional,and ,radio frequency ,vacuum ,(RFV) drying ,technologies. The model parameters are calibrated with experimental timber drying data of mixed western hemlock and amabilis fir, and the total percentages of on-grade, over-dried and under-dried timbers are simulated for different conventional and RFV target moisture content situations. The results of the simulated percentages of timbers are presented in 2-D level curves, and the ranges of target that should be used ,in order ,to obtain ,maximum ,on-grade timbers are analyzed.
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| 20. |
- Elustondo, Diego, et al.
(author)
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New thermal conductivity probe design based on the analysis of error sources
- 2001
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In: Journal of Food Engineering. - 0260-8774 .- 1873-5770. ; 48:4, s. 325-333
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Journal article (peer-reviewed)abstract
- The thermal conductivity determination by means of the thermal probe is a classical non-stationary method, suitable for foodstuffs because of the relatively short period of time and the small temperature rise required during experimental measurements. Even though its simplicity, this method has theoretical and practical implicit errors, their main sources being evaluated in this paper. The theoretical analysis shows that experimental errors can be kept within acceptable values, if the testing time period is within certain limits, out of which the errors grow quite rapidly. The error arising from the calculation of the thermal conductivity by means of an approximate equation is studied and a new way to express it is presented. Also, testing times were calculated for different probe dimensions. Finally, on the basis of two former probe which exhibits some advantages upon each other, a new probe design is proposed which recoveries those features.
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| 21. |
- Elustondo, Diego, et al.
(author)
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Non-deterministic description of wood radio frequency vacuum drying
- 2003
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In: Holzforschung. - 0018-3830 .- 1437-434X. ; 57:1, s. 88-94
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Journal article (peer-reviewed)abstract
- A numerical method is proposed to predict the stochastic dispersion of data that unavoidably occurs in a real drying process. The method is based on the use of discrete frequency distribution curves to predict a random variation on some parameters of the process and is applied to the case of radio frequency vacuum (RFV) drying of wood. Experimental data of RFV drying of western hemlock timbers were used to obtain the numeric values of the stochastic parameters and their standard deviation. A mathematical model was designed to simulate the final moisture content dispersion on hypothetical examples. Results were quantified using three indices: average, range and standard deviation.
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| 22. |
- Elustondo, Diego, et al.
(author)
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Optimum operating conditions in drying foodstuffs with superheated steam
- 2002
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In: Drying Technology. - 0737-3937 .- 1532-2300. ; 20:2, s. 381-402
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Journal article (peer-reviewed)abstract
- It is inferred from experimental data that in drying foodstuffs with superheated steam, the initial drying rate has a direct effect on the rate at which the overall drying takes place. That is, the faster the initial drying rate, the shorter the overall drying time. This criterion is very convenient because at the beginning, water moistens the sample external surface so evaporation does not depend on internal sample characteristics, but only on external convective heat and mass transfer rates. Mass and energy balance equations are solved and the result converted into a general initial drying rate equation, in which all dryer characteristics are grouped into one dimensionless parameter. The initial drying rate equation is mathematically maximized and the optimum working conditions determined. The result shows that initial drying rate always increase with increases of either the superheated steam temperature or velocity, but once these two variables are fixed, there exists at least one "optimum" pressure at which the initial drying rate is a maximum. Finally, the initial drying rate and optimum condition equations are applied to three model dryers, a dryer for a flat sheet, a fixed bed dryer and a rotary dryer. In each case, numeric values are computed and plotted as drying rate versus pressure curves, in which the optimum drying rate is also included. Also presented is a chart to compare the optimum pressures as functions of temperature and steam velocity for the three dryers.
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| 23. |
- Elustondo, Diego, et al.
(author)
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Predicting thermal efficiency in timber radio frequency vacuum drying
- 2004
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In: Drying Technology. - 0737-3937 .- 1532-2300. ; 22:4, s. 795-807
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Journal article (peer-reviewed)abstract
- In this work, the efficiency of transforming dielectric energy into evaporated water is analyzed for the case of timber radio frequency vacuum drying. Based on well-known heat and mass transfer equations, a simplified mathematical model is proposed that estimates the drying efficacy in regards to the thermo-physical properties of wood. Although not exact, the theoretical results are close to the experimental observations and elucidate some phenomena like the tendency of the timber to dry from inside to outside, and the drying rate increase with the rise of the timber gas permeability. The theoretical efficiency model also predicts a range of wood permeability values for which the drying efficiency changes from 100 to 0%, thus providing a quantitative scale for classifying the spectrum of "difficult-to-dry" all the way to "easy-to-dry" wood species when using radio frequency vacuum technology
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| 24. |
- Elustondo, Diego, et al.
(author)
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Simulated comparative analysis of sorting strategies for RFV drying
- 2003
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In: Wood and Fiber Science. - 0735-6161. ; 35:1, s. 49-55
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Journal article (peer-reviewed)abstract
- In this work, a numerical stochastic model is used to compare three possible sorting strategies in radio frequency vacuum (RFV) drying of thick timbers, namely, moisture content based pre-sorting (MCPS), batch dry/sort/redrying (b-DSRD) and continuous or retro-feed dry/sort/redry (c-DSRD). The model parameters were calibrated with experimental data of western hemlock dried in a commercial RFV dryer, and the results of the simulations were compared to a single pass base case (SPBC). The numerical results clearly demonstrated the differences among these strategies. The MCPS showed no significant improvement in final timber quality as defined by average timber moisture content, but there is an evident improvement in both b-DSRD and c-DSRD. The comparison was based on the increment of the percent of the on-grade wood (within moisture content range) and the reduction of overdried and underdried (wets) percentages. Furthermore, it was also shown that the effective drying time is roughly independent of the drying strategy
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| 25. |
- Elustondo, Diego, et al.
(author)
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Stochastic numerical model for conventional kiln drying of timbers
- 2003
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In: Journal of Wood Science. - : Springer Science and Business Media LLC. - 1435-0211 .- 1611-4663. ; 49:6, s. 485-491
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Journal article (peer-reviewed)abstract
- A numerical model that predicts the stochastic dispersion associated with industrial kiln drying of timber was adapted to conventional drying and evaluated with experimental data. The theoretical aspects of the model are briefly explained, a selection of the calibration parameters was carried out, and a new empirical dispersion factor is proposed to account for all unknown sources of random behavior. The model was calibrated with six experimental runs of western hemlock and amabilis fir (116 mm2 timbers) to an average moisture content (target) of 14%-20%. It was found that with implementation of the dispersion factor, the number of required simulations is considerably reduced, the calibration results are consistent for all the experimental runs, and the target moisture content along with its standard deviation can be well reproduced using the all-run average parameters.
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