The article presents the impact of drying process and selected parameters on the color changes on the surface of pine wood (Pinus sylvestris L.). Three predetermined process conditions (modes), mild, ...normal, and intensive, were investigated. The experiments were conducted using a semi-industrial scale dryer designed at the Gdańsk University of Technology with a loading capacity of 0.55 m3. The drying process was applied to pine wood grown in the northern part of Pomeranian region in Poland. The specimens were selected taking into consideration the radial angle of the growth rings. During each drying mode, 25 pieces of wood with dimensions (thickness, width, length) of 0.03 m, 0.2 m, and 1.5 m, respectively, were dried. The total color change (ΔE) after drying process and color saturation (h*) before and after drying processes of the wood surface was determined using the normalized CIELAB methods. The obtained results indicated that the color change of the pine wood surface increased simultaneously with the intensification of the drying process. However, the normalized wood quality after drying under intensive drying process conditions remained within the standard limits. The application of intensive drying process conditions remarkably changes the surface color of the obtained material, while remarkably reducing the drying process duration.
•Drying poplar wood with buds and without cover is best natural drying method.•Poplar and willow wood have different course of the drying process.•Buds presence on willow wood has no effect on the ...rate of moisture decrease.
This study deals with the use of evapotranspiration and covering as a means of drying wood. The principle is based on the fact that tree species with outstanding sprouting capacities are able to leaf after being felled and are physiologically active as long as they have enough water. The course of wood drying (the stems) was examined in relation to their subsequent foliage creation and ongoing evapotranspiration, and how those factors related to other factors (climatic factors, storage). The experiment was realized with two fast-growing tree species (special clones): Hybrid poplar (Populus maximowiczii A. Henry × Populus nigra L. ‘Max 4-5’) and Salix × smithiana Willd. (Salix caprea L. and Salix viminalis L.). In the case of poplar wood samples, the presence of roof cover significantly affects the rate of moisture content decrease in wood samples. Wood samples dried slower under the roof. The buds left on the stems probably accelerate the drying process in case of poplar samples. Willow wood samples were in terms of rate of moisture content decrease in four experimental variants indifferent. Presence of roof or buds had no significant effect on the rate of sample moisture content decrease. These findings may help achieve more efficient handling of the timber from fast-growing species in relation to their processing and storage.
This paper succinctly presents new developments, preliminary statements and a number of energy results in the area of high-temperature heat pump technology for wood drying in a Canadian economic ...environment. A hybrid (electricity/fossil), high-temperature technology has been investigated and then field tested over the last two years. Several technical developments were achieved at the level of fluid selection, refrigerant flow control and system stability, variable dehumidifying capacity and appropriate drying schedules. The present study demonstrates that the thermodynamic efficiency and specific energy performance of the developed high-temperature drying heat pumps have generally reached the initial designed targets. Refinements of the integrated control methods involving variable speed and electronic devices are currently being undertaken in order to avoid undesired operating conditions that could cause mechanical failures or inefficient dehumidifying processes. The current research program aims at diversifying the applicable thermodynamic cycles, testing new environmentally friendly refrigerants and advanced components, and developing more advanced drying control strategies.
This study examined the changes in the properties of beech wood (Fagus sylvatica L.) after intense drying. Beech wood with false red heartwood was selected as the test specimen. The test samples had ...dimensions of 50 mm thickness, 180 mm width, and 350 mm length. The specimens were divided into two groups, false red heartwood and sapwood. These specimens were selected with different angles of the growth rings (radial and tangential). The results showed that samples with red heartwood, in comparison to samples with sapwood content, had a remarkable effect in covering. Observation of specimens with false red heartwood and sapwood before and after drying process revealed significant differences in color changes and measured values during the covering-slicing test, but not between samples with different growth ring angles.
Drying is the most energy consuming process in the industrial transformation of wood. The current energy and climate crisis makes it imperative to adapt the process to energy availability, in terms ...of quantity, cost and temperature level. Wood drying schedules are historically based on practice. In the present work, a mechanistic drying model is used as a predictive tool to adapt conditions to specific situations. A multiscale computational model, Multi_Wood_DryS, has been combined with a probabilistic optimization code to propose tailor-made drying schedules that meet operators' expectations in terms of energy consumption, quality, drying time and cost. Optimizations of drying schedules of a stack of boards are proposed. The cost-optimized schedule is advantageous for all criteria with a 48% reduction in drying time. The resulting metamodel is a first step toward an intelligent controller for wood drying.
Wood is widely considered to be a green and renewable building material. However, many of the challenges to using wood as an engineering material arise from the shrinkage and swelling behaviors ...during moisture content (MC) loss or gain. In this study, the shrinkage behavior of Queensland peppermint (Eucalyptus exserta F. V. Muell) wood was investigated at the macroscopic and cellular levels, and the interdependence between the two levels was explored. Results revealed that the tangential shrinkage of 2% and radial shrinkage of 1% was observed as MC decreased from about 60% to 32% in the macroscopic level. The most obvious anisotropic shrinkage was presented at the MC region of 32-22%, and the ratio of T/R was ranged from 1.6 to 1.75 below the fiber saturation point. At the cellular level, a considerable shrinkage was observed at MC of 42%. The cell wall was shrunk, but the lumen in radial (TR plane) was expanded with MC loss. The shrinkage of the total wood cell showed a linear relationship with MC. The shrinkage ratio of T/R was maintained around 1.5 below the fiber saturation point, indicating that the MC states have little effect on the anisotropic shrinkage. Besides, the shrinkage value at the macroscopic level was slightly smaller than the cellular level, but the anisotropic shrinkage showed an opposite trend.
The drying process was examined relative to parameters’ influence on the deformation and surface layer color changes of beech wood (Fagus sylvatica L.) and oak wood (Quercus robur L.). The goal was ...to analyze the impact of drying process conditions, wood and growth rings types, and load on the deformation and surface color changes of drying thin wooden elements. A further aim was to reduce the time of the lamella drying and minimize wood products defects. During each drying, 40 pieces of wood were dried, divided into two groups. For the first group, 30 pieces were dried under a uniformly distributed load of approximately 50 kg, while for the second group, 10 samples were dried without weight. The lamellas dried under load exhibited fewer cup, bow, and twist deformations than the lamellas dried without load. Cracks in the dried lamellas occurred comparably in those dried under and without load. Color changes in the specimens before and after drying were observed and measured. The differences in colorimetric parameters (a, b, and L) between wood without defects and with defects were less marked after drying than before drying. The color changes were only noticed in the surface layers of the specimens.
PDF
