Dry Wood Research Articles

Cutting power and surface quality in sawing kiln-dried, green, and frozen hem-fir wood

The lumber manufacturing industry faces challenges due to the cutting of wood with a high variation in moisture content and temperature. In this study, the cutting power and waviness during the circular sawing process of kiln-dried, green, and frozen hem-fir wood were measured and compared under different feed and rotation speeds. An analysis of variance (ANOVA) was performed to evaluate the impact of cutting parameters and the wood condition (kiln-dried, green and frozen), and a decision tree regression model was developed to predict the cutting power and waviness. The ANOVA highlighted that the feed speed had the most impact on cutting power, followed by the wood condition. Similar results were obtained from the decision tree regression (R2 = 0.89). The developed model failed to accurately predict the waviness from the cutting parameters, which emphasized the need for online wood sawing monitoring systems and a deeper understanding of saw blade’s dynamic behavior. The role of moisture content in the cutting power and waviness was nonlinear. The highest cutting power corresponded to sawing frozen wood, while there was no significant difference between sawing dry and green wood. The largest values of waviness were associated with sawing of dry wood, whereas sawing frozen and green wood yielded similar waviness. Sawing at higher rotation speeds yielded an increase in the cutting power but improved the surface quality by lowering the waviness.

Oak wood drying: precipitation of crystalline ellagic acid leads to discoloration

Oak heartwood usually darkens during and after drying. This darkening can be heterogeneous, leaving noncolored areas in the wood board. These light discolorations have been linked to heterogeneous distribution of tannins, but compelling evidence on the microscale is lacking. In this study Raman and fluorescence microscopy revealed precipitations of crystalline ellagic acid, especially in the ray cells but also in lumina, cell corners and cell walls in the non-colored areas (NCA), which also had higher density. In these denser areas free water is longer present during drying and leads to accumulation of hydrolyzed tannins. When eventually falling dry, these tannins precipitate irreversible as non-colored ellagic acid and are not available for chemical reactions leading to darkening of the wood. Therefore, pronounced density fluctuations in wood boards require adjusting the drying and processing parameters so that water domains and ellagic acid precipitations are avoided during drying.

Identifying Efficient Transport Pathways in Early-Wood Timber: Insights from 3D X-ray CT Imaging of Softwood in the Presence of Flow

Wider use of timber has the potential to greatly reduce the embodied carbon of construction. Improved chemical treatment could help overcome some of the barriers to wider application of timber, by furthering the durability and/or mechanical properties of this natural material. Improving timber treatment by treating the whole volume of a piece of timber, or tailored sections thereof, requires sound understanding and validated modelling of the natural paths for fluid flow through wood. In this study we carry out a robust analysis of three-dimensional X-ray CT measurements on kiln-dried softwood in the presence of flow and identify small portions of early-wood which are uniquely capable of transporting fluids—herein ‘efficient transport pathways’. We successfully model the effects of these pathways on the liquid uptake by timber by introducing a spatial variability in the amount of aspiration of the bordered pits following kiln drying. The model demonstrates that fluid advances along these efficient transport paths between 10 and 30 times faster than in the remainder of the timber. Identifying these efficient transport pathways offers scope to improve and extend the degree to which timber properties are enhanced at an industrial scale through processes to impregnate timber.

Следы от обработки дерева и кости на вулканическом кремне палеовулкана Дунда-Ага: предварительные экспериментальные данные

Abstract: The article is a description of an experiment on planing the raw and dry wood, as well as boiled bone, which was carried out by flakes from volcanic flint from the raw material source of the Dunda-Aga paleovolcano, located in the Aginsky Buryat district of the Transbaikal region. In its course, changes in the working edge of the tools were monitored using binocular and metallographic microscopes, as well as photographic recording of these results using digital cameras and Helicon Focus v. 5.3. During the experiment, it was possible to identify a tendency for the formation of macro and micro wear of the surface of the working edge of objects, depending on the material processed by planing. It was found that on volcanic flint, in places of the most intense contact with a hard surface to be treated, micropolishing in individual microsections is formed already within the first 30 minutes of operation. Then these areas expand and close along the length of the working edge. Over time, tools that work dry wood show a fine micro-polish line, while wet wood forms a more discontinuous line of different widths. Bone processing showed the strongest modification of the tool. After an hour of work, it became dull due to intense rounding, and after two hours it almost completely lost its effectiveness. The results of this experiment clarify the dynamics of the formation of macro and micro wear on tools made of volcanic flint when processing dry and damp wood, as well as bone. Keywords: microwear analysis, petroarcheology, the sources of raw materials, Stone Age, Transbaikalia, Dunda-Aga paleovolcano, volcanic flint Acknowledgements: The work was supported by a grant from the Transbaikal State University No. 292‑ГР.

The Use of Cellular Automata in the Study of Heat and Mass Transfer Processes in Particular During Wood Drying

This paper demonstrates the use of cellular automata in the study of heat and mass transfer processes, in particular during wood drying. For study, we developed a three-dimensional mathematical model. This model is described by a system of interconnected differential equations. These equations are described in partial time derivatives and coordinates in space. The peculiarity of this work is the possibility of combining a three-dimensional mathematical model and the theory of cellular automata in solving the problem. Usage of the theory of cellular automata requires the presence of a certain number of identical elements of the system. In this case, we propose to present the studied CAD model in the form of cubes of the same size. The paper also describes the relationships between the created cubes. In addition, we give the algorithm of calculations. Based on the described algorithm, we carried out the number of experiments, which prove the possibility of using the theory of cellular automata in solving the problem.

Multiple-criteria location selection for wood kiln operations using AHP/TOPSIS

This study attempted to determine a suitable combination of multiple-criteria selection techniques for the best location for wood drying kiln operations in Iran. Utilising field studies across the wood-drying industry, limitations of existing selection-method criteria were identified, and a hierarchy of decision-making factors and weights was designed utilising AHP to overcome those limitations. The alternatives were then prioritised using fuzzy TOPSIS. Results indicate that a location in the province of Mazandaran is the best solution. In validation, the results from fuzzy TOPSIS were compared with the results from interview questionnaires in relation to priority alternatives. This validation demonstrates that the results of the fuzzy TOPSIS were confirmed in the resultant order with an acceptable rate of error. Moreover, the Spearman rank correlation coefficient of the results of alternative priorities with two methods of fuzzy TOPSIS and the interview questionnaires (99.23%) indicated that there was a strong positive correlation between the results.

Effects of Drying Temperatures on the Occurrence of Sticker Stain in Japanese Cedar (Cryptomeria japonica D. Don)

Abstract Sticker stain is a material defect that results from moisture migration during wood drying, often spoiling the appearance of the surface of wood products. The effect of drying temperatures on the occurrence of surface sticker stain was investigated using Japanese cedar (Cryptomeria japonica D. Don) and three types of stickers (air-dried Japanese cedar, aluminum, and stainless steel) under four drying temperatures (20°C, 50°C, 75°C, and 100°C). At lower drying temperatures, the air-dried wood sticker tended to suppress the occurrence of surface sticker stains, whereas higher temperature or metal stickers produced sticker stains with deep color. However, no definitive relation was shown between the initial moisture content and the extent of sticker stain with deep color regardless of drying temperatures. It was considered that the partial delay of drying happened around the contact area with stickers, especially in cases of metal stickers. It was also found that the use of metal stickers at higher drying temperatures induced depressions in Fourier transform infrared spectra related to the occurrence of hygrothermal conditions.

Measure method of effective diffusion in gas oscillating in channels of variable radius or porous medium

The paper discusses a new technique for measuring the diffusion coefficient of vapor of a volatile fluid in air in long straight channels or porous media. The proposed experimental technique is universal and allows a) determining the coefficient of molecular diffusion of vapor of a volatile liquid in air; b) calculating the coefficient of effective diffusion of vapor in oscillating air. The proposed technique was tested in the study of the diffusion of 2-propanol vapor in air at rest and oscillating air in a channel of variable radius and a porous medium consisting of randomly packed hard spheres of equal diameter and was found to be relevant. Initial experiments with a porous medium show that the proposed experimental technique can also be used to estimate the diffusive tortuosity of porous media. The results of studies, finished and planned, are useful for understanding the physical processes taking place in various technical operations including wood and food drying, drug delivery, etc.•The new experimental technique provides accurate measurement of the molecular diffusion coefficient of vapor of a volatile fluid in air.•The experimental setup allows measuring the enhanced mass transfer of vapor of a volatile fluid in oscillating air in a straight channel of constant/variable radius and a porous medium.•The additional advantage of the present technique is that it enables the estimation of the diffusive tortuosity of a porous medium.

Остатки производственных сооружений на севере Верхнего Приобья (Ташара-3): к проблеме древнего смолокурения

This article analyzes Medieval production ground structures at the Tashara 3 site located on the right bank of the Ob River (on the border of Tomsk and Novosibirsk Regions). These archaeological objects were excavated by E.M. Evteeva and V.A. Sumin in 1994 (270 sq. m). In terms of morphological, stratigraphic, and planigraphic features, the archaeological structures represent funnel-shape pits partly covered by redeposited soil. Calcined spots and remains of charred wooden structural elements were found in the upper part of pits’ filling. The main component of filling was ashy layer. The sizes of the structures were 3.14-3.4 x 2.94 x 1.1—1.8 m. Additional small pits remaining from a canopy-like structure were found near the larger pits. Finds in the pits are rare. However, pottery fragments have made it possible to attribute structures 1 and 2 to the Middle—Late Upper Ob culture (6th — 9th centuries AD). General description of dry wood pyrolysis and earliest methods of tar production in pits, which are known from historical and technological literature, as well as comparative archaeological evidence on structures 1 and 2 at the Tashara-3 site are provided. The hypothesis on the use of these structures as pits for producing tar of coniferous wood species is suggested. The resulting products could have been in demand among the local Medieval population of the Upper Ob culture for veterinary and medicinal purposes, exchange, and for ensuring land and river communications which, according to various sources, ran in the northern part of the Upper Ob River basin.

重度火烧迹地兴安落叶松(Larix gmelinii)根际土壤真菌群落研究

为探究内蒙古根河大兴安岭林区重度火烧迹地不同生长状态的兴安落叶松根际土壤真菌群落特征，选取火烧枯立木（BDW）、火烧存活木（BSW）、未火烧对照木（CK），通过磷脂脂肪酸方法分析根际土壤真菌群落生物量变化，利用高通量测序技术对根际土壤真菌群落组成与功能进行分析，探讨影响根际土壤真菌群落的主要环境因子。结果表明：（1）相较于未火烧对照木，火烧枯立木与火烧存活木根际土壤真菌群落磷脂脂肪酸含量显著降低，真菌群落α多样性显著降低。β多样性分析与群落相似性分析结果显示，火烧枯立木、火烧存活木、未火烧对照木根际土壤真菌群落组成存在显著差异。（2）相较于未火烧对照木，火烧枯立木与火烧存活木根际土壤中担子菌门（Basidiomycota）真菌相对丰度显著下降，子囊菌门（Ascomycota）真菌相对丰度显著升高。子囊菌门（Ascomycota）内，火烧枯立木根际土壤中内生真菌相对丰度显著高于火烧存活木与未火烧对照木，而火烧存活木根际土壤中腐生-外生菌根复合型真菌相对丰度显著高于火烧枯立木与未火烧对照木。（3）根际土壤总磷、总钾含量是影响重度火烧迹地兴安落叶松根际土壤真菌群落优势菌门由担子菌门（Basidiomycota）转变为子囊菌门（Ascomycota）的主要环境因子，而根际土壤总碳、总氮、总磷含量则是造成火烧枯立木与火烧存活木根际土壤真菌群落组成与功能差异的主要环境因子。本研究有助于了解大兴安岭林区土壤真菌群落结构，对真菌群落多样性的维持与管理具有参考价值。;Fire is an important disturbance factor in forest. The severe fire will significantly change the structure and succession process of forest ecosystem. As an important component of soil microorganisms, fungi respond quickly to fire disturbance and are very sensitive to changes in soil physicochemical properties. The composition and function of fungal communities are important biological indicators for restoration after severe fire. When plants are disturbed by fire, the fungal community are also affected. In the case of severe fire, such a correlation will persist for a long time. The Great Xing'an Mountain forest ecosystem is of great strategic significance to China, and is also the area of frequent forest fires. L. gmelinii is the main zonal vegetation in this area. The restoration of L. gmelinii is of great importance to the restoration of forest ecosystem after fire. The relationship between the growth status of L. gmelinii and rhizosphere soil fungal community after severe fire has not been studied.The purpose of this study was to investigate the characteristics of the rhizosphere soil fungal community of L. gmelinii in different growth status in the severe burned area of Great Xing'an Mountain, Genhe, the Inner Mongolia Autonomous Region. We investigated the growth status of L. gmelinii, selected the burned dry wood (BDW), burned survival wood (BSW) and unburned control wood (CK). We measured the physicochemical properties of rhizosphere soil. The phospholipid fatty acid of rhizosphere soil was sampled and analyzed to understand the change of fungal community biomass, and the composition and function differences of the fungal community were analyzed by high-throughput sequencing. We also discussed the key environmental factors affecting the rhizosphere soil fungal community. Results show that:(1) compared with CK, the content of phospholipid fatty acid and alpha diversity of fungal community in the rhizosphere soil of BDW and BSW were significantly reduced. Beta diversity and community similarity analysis showed that there were significant differences in the rhizosphere soil fungal community between BDW, BSW and CK. (2) The relative content of Basidiomycota decreased significantly and the relative content of Ascomycetes increased significantly in the rhizosphere soil of BDW and BSW compared with those of CK. In Ascomycota, the relative content of endophyte fungi in the rhizosphere soil of BDW was significantly higher than that of BSW and CK, the relative content of saprophytic-ectomycorrhizal compound fungi in the rhizosphere soil of BSW was significantly higher than that of BDW and CK. (3) The contents of total phosphorus and total potassium in rhizosphere soil were the main environmental factors affecting the transformation of the dominant fungi phylum from Basidiomycota to Ascomycota in the rhizosphere soil of L. gmelinii after severe burned. The contents of total carbon, total nitrogen, total phosphorus were the main environmental factors that caused the differences in the composition and function of fungi in the rhizosphere soil between BDW and BSW. The study is helpful to understand the structure of soil fungal community in the Great Xing'an Mountain forest ecosystem and has reference value for the maintenance and management of fungal community diversity.

Indigenous Navigatory Devices used during the High Floods in North Bihar

This paper takes into account the methods of adaptations to the extreme situations of floods in the rainy season of 2020 in the rural and urban areas of Darbhanga district in northern Bihar, India. Boats made of different types of woods are the first choice of people. The region has a sprawling boat industry that provides a basis of livelihood to the wood smith community. Boats are generally made available to the needy people by the agencies of Government. However, those deprived of the boat facility adapt to the situation by carving makeshift devices made from banana pseudo stems, water hyacinth fronds, dry wood pieces, pitcher floats, bamboo rafts, cement bowls for feeding the livestock etc. High floods of 2020 witnessed people using boats of thermocol and rubber tubes on a large scale. All these devices, whether natural or man-made, work on the principle of Archimedes. The paper reports an innovative practice of using the hollow gas cylinders intricately strung in the fashion of an open boat that was used for about 15-20 days till the high floods receded in the village Harichanda of Hanuman Nagar C.D. Block of Darbhanga district India. The system was devised by local young men to tide over the crisis of ferrying people to local orchards for defecation and also for maintaining the supply chain of drinking water, cooking gas and other essential services. The plant items achieve buoyancy due to their density lower than water. Those made of flattened wood or tin plates achieve floatability on account of large volume of water that they displace. The weight of people carried on these boats is lighter than the weight of the volume of water displaced in the process.

DEPENDENCE OF STRENGTH OF FIBERBOARDS FROM TERMS OF PREPARATION OF WOOD FIBER SEMI-FINISHED PRODUCTS

Despite the reduced demand for fiber boards, research related to their manufacture is relevant, since the production of wood-based materials significantly contributes to solving the problem of the integrated use of wood raw materials.
 The paper presents the results of experimental studies reflecting the dependence of the strength characteristics of dry and wet wood fiber boards on the structural and technological parameters of grinding plants of various modifications. The experiments were carried out in laboratory facilities and in the production environment on existing industrial equipment. Based on the results of processing multifactor experiments implemented in a second-order B plan, a mathematical description was obtained of the dependence of the tensile strength during static bending of solid wood fiber boards of the dry and wet production method on the gap between the grinding disks, wear of the segments and the concentration of wood fiber mass. The obtained regression models are adequate to the process and can be applied in practice to predict the strength characteristics of fiberboards depending on the parameters of the grinding process.
 As a result of the analysis of the calculated and graphical dependences obtained on the basis of studies in the production environment on the existing equipment, it is possible to determine what parameters on the grinding equipment must be set in order to obtain the necessary physical and mechanical properties of the fiberboard.

CT more accurately detects foreign bodies within the equine foot than MRI or digital radiography.

Identification and characterization of foreign bodies in the distal limb of horses poses a diagnostic challenge. The aims of this prospective experimental cadaver study were to describe the appearance of five foreign body materials within the equine hoof using CT, MRI, and digital radiography (DR) and to compare interrater agreement among three reviewers. Fifty foreign bodies consisting of five materials were implanted at a solar location or a coronary location in 25 equine cadaver feet. The images were reviewed by three equine veterinarians experienced in advanced imaging interpretation, who were blinded to the material of the foreign body. Foreign bodies were graded on visibility and appearance. Sensitivity and specificity were calculated for accurate identification of the different materials. Interrater agreement was assessed using Fleiss' kappa. Computed tomography had higher visibility score, sensitivity/specificity, and interrater agreement for detection of all materials; particularly slate, glass, and dry wood, compared to the other imaging modalities. Soaked wood and plastic had lower sensitivity (31-33%) on CT with a similar attenuation of the two materials. Foreign bodies were often visible on MRI, although with similar appearance and unclear details. On DR, only slate and glass were visible. The interrater agreement for identifying the correct material was almost perfect for slate, glass, and dry wood (κ = 0.92-1.00) and poor for plastic and soaked wood (κ<0.20) on CT. Interrater agreement was poor for all materials on MRI and DR (κ<0.20), with the except for fair (κ = 0.28) for slate on DR and moderate (κ = 0.28) for soaked wood on MRI.

PENGERINGAN KAYU KARET (Hevea brasiliensis) DENGAN METODE RADIASI MATAHARI (GREEN HOUSE)

The aim of this study is to analyze the optimal drying time of rubber wood (Hevea brasiliensis) in direct drying in the sun and by a solar kiln (green house). This research is expected to provide information on optimal drying time on natural drying directly under sunlight (solar radiation) and with kiln (Green House) to prolong the utilization of wood and reduce the costs. The parameters tested in this study are water content, density, drying rate, shrinkage, and color change. The results on optimal drying of rubber wood at 6 weeks drying time either in drying under direct sunlight or solar kiln in the green house.

MONITORING THE TOXICITY OF DRY WOOD TERMITES USING THREE PLANT POWDERS IN LABORATORY CULTURE

In order to model a suitable control alternative for subterranean termites and termites infesting wooden furniture and cabinets where consumables are likely stored, this present study monitored the efficacy of three plant powders at different doses (0.50-1.50g) against the dry wood termite,Cryptotermes cavifrons Banks (Blattodea). Plant materials were locally prepared into powders and assigned to 20 wood termites in 5g substrates of sand and stick. The culture was set up in triplicates and lethal concentrations were determined by Probit analysis. The plant powder could not exerted 100% mortality, but the highest mortality was recorded in Dennettia tripetala (1.50g) on stick (mean= 8.33±0.80). All concentration of D. tripetala on sand and stick caused mortality within 0 to 48 hours after exposure and compared favorably with Permethrin which recorded the highest mean time mortality on sand at 0-24 hrs after exposure. The lowest LC50value (0.75 and 0.79g/g) corresponded to Permethrin and D. tripetala on sand and stick respectively. This results suggest that best concentrations of pepper fruit powder can be adopted as potential alternative to chemical powders.

Effects of Environmental Traits and Landscape Management on the Biodiversity of Saproxylic Beetles in Mediterranean Oak Forests

This study assesses the effects of environmental traits and landscape management on the biodiversity of saproxylic beetles from “dehesas” located in Sierra Morena Mountains (Córdoba, Southern Iberian Peninsula). The dehesa is an open savanna-like landscape with mature/old trees scattered on a pasture cover where both living and dead wood are of great importance for the maintenance of macroinvertebrate fauna. The study was carried out in five plots, with different environmental features and management. A total of 137 branches belonging to the four main tree species present in the area were collected, classified, and kept under four different thermal conditions. From January to June 2019, the adult emergences were followed. A total of 466 saproxylic specimens of 31 species were obtained, 5 of them included in red lists of protected fauna. Two Bostrichidae species (Lichenophanes numida Lesne and Scobicia pustulata Fab.) and two Cerambycidae (Chlorophorus ruficornis Oliv. and Trichoferus fasciculatus Faldermann) are included in the “European Red List of Saproxylic Beetles”; and the Clerid Tillus ibericus Bahillo de la Puebla, López–Colón and García–Paris, is included in the “Red Book of Invertebrate of Andalucía”. Differences were observed regarding the diversity and abundance among the plots and among the tree species from which the beetles emerged. Simple regression analyses revealed negative relationships between tree density/Buprestidae, livestock/Bostrichidae, and land use/Cerambycidae. Multivariant logistic regression analysis did not find significant relationships among environmental traits and saproxylic diversity. Results confirmed that dry wood was a main resource for the maintenance dehesas’ biodiversity because it constitutes an ecological niche exploited by a significant set of saproxylic beetles belonging to the Bostrichidae, Buprestidae, and Cerambycidae families, in addition to other guilds of species, mainly Carabidae and Cleridae, which feed on the above-mentioned groups. Our results also support that increasing environmental temperature accelerates the development of Buprestidae, but this effect was not evident for the Bostrichidae species.

The effect of silver and copper nanoparticles as resin fillers on less-studied properties of UF-based particleboards

ABSTRACT The aim of this study was to investigate the effect of using silver and copper nano-suspensions in mixture with resin, upon screw withdrawal capacity (in face and edge directions) and hardness (at different depths of penetration) of particleboards. An aqueous-suspension of 200 ppm silver and copper was mixed with urea-formaldehyde resin at two levels of 100 and 150 mL/kg dry weight wood particles. The size range of at least 70% of nano-particles was 20–90 nm. The results revealed a significant increase in screw withdrawal capacity and hardness by adding the nanometals to composite mats. The increased properties were partially attributed to an improvement in heat transfer in mats that facilitated the curing of resin. Moreover, theoretical simulations based on density functional theory (DFT) clearly demonstrated high adsorption energy of silver and copper atoms on cellulose and hemicellulose polymers; this contributed to a formation of additional bonds throughout the composite matrix, which in turns improved the board properties.

How Bound Water Regulates Wood Drying

For most wood-based product uses it is essential to remove a large part of the water content from wet or green (fresh-cut) wood, to reduce further dimensional variations under varying humidity conditions, improve its mechanical characteristics, and protect it from biological attacks. However, the internal mechanisms of drying are not fully described. Here we observe drying at different scales using macroscopic measurements (weighing), nuclear magnetic resonance measurements allowing to distinguish bound- and free-water contents, and x-ray computed tomography images of air-liquid interfaces at the smallest pore scale (wood lumens). We show that during wood drying, even well above the fiber saturation point, bound-water diffusion in cell walls (instead of capillary effects) ensures the extraction of liquid water from pores and its transport towards the surface of evaporation, and thus controls the drying rate. The distribution of bound-water content (uniform or heterogeneous) along the main sample axis and the drying-rate evolution depend on the competition between the external conditions and a characteristic rate of transport due to bound-water diffusion. For sufficiently slow drying this distribution remains homogenous until free water is fully extracted. An original physical phenomenon is thus at work, which plays a major role in regulating water extraction, in that it maintains a constant drying rate and a homogeneous distribution of the (mean) water content throughout the material. These results provide sound concepts for modeling and controlling drying properties of wood materials. They open the way to the understanding or control of the properties of many other materials containing two water types in food or civil-engineering applications. Our results complete recent observations that bound-water diffusion also controls imbibition in hardwood and finally show that transfers between bound and free water play a major role in the interaction of plantlike systems with water.

Acoustical Extinction of Flame on Moving Firebrand for the Fire Protection in Wildland–Urban Interface

Firebrands are a widely observed phenomenon in wildland fires, which can transport for a long distance, cause spot ignition in the wildland–urban interface (WUI) and increase the rate of wildfire spread. The flame attached to a moving firebrand behaves as a potential pilot source for ignition, so extinguishing such a flame in the process of moving can effectively minimize its fire hazard. In this work, firebrands were represented by a dry wood ball with a diameter of 20 mm and a weight of 2.9 g, which carried a flame with the heat release rate of 250 W. The firebrand was held by a pendulum system to adjust the velocity. Results showed that there is a minimum sound pressure to extinguish the firebrand flame, which increases slightly with the sound frequency. As the firebrand velocity increases from 0 m/s to 4.2 m/s, the minimum sound pressure for extinction decreases significantly from 114 dB to 90 dB. The cumulative effect of firebrand motion and acoustic oscillation was found to facilitate flame extinction. A characteristic Damkohler number (~ 1), with the ratio of the fuel residence time to the flame chemical time, is used to quantify the extinction limit of the flaming firebrand. This work provides a potential technical solution to mitigate the hazard of firebrand flame and spotting ignition in WUI and helps understand the influence of acoustic waves on the flame stability on the solid fuel.

Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas.

Conventional kiln drying of wood operates by the evaporation of water at elevated temperature. In the initial stage of drying, mobile water in the wood cell lumen evaporates. More slowly, water bound in the wood cell walls evaporates, requiring the breaking of hydrogen bonds between water molecules and cellulose and hemicellulose polymers in the cell wall. An alternative for wood kiln drying is a patented process for green wood dewatering through the molecular interaction of supercritical carbon dioxide with water of wood cell sap. When the system pressure is reduced to below the critical point, phase change from supercritical fluid to gas occurs with a consequent large change in CO2 volume. This results in the efficient, rapid, mechanical expulsion of liquid sap from wood. The end-point of this cyclical phase-change process is wood dewatered to the cell wall fibre saturation point. This paper describes dewatering over a range of green wood specimen sizes, from laboratory physical chemistry studies to pilot-plant trials. Magnetic resonance imaging and nuclear magnetic resonance spectroscopy were applied to study the fundamental mechanisms of the process, which were contrasted with similar studies of conventional thermal wood drying. In conclusion, opportunities and impediments towards the commercialisation of the green wood dewatering process are discussed.