Drying strategies capable of reducing the stress level of a stack of boards as defined by a comprehensive dual scale model

During drying, stresses and deformations develop in a wood board due to shrinkage fields which result from moisture content and temperature field variations. In spite of numerous works done in wood drying modelling in the last decades, wood drying optimisation based on modelling and simulation remains far from initial expectations. Two main reasons can explain this assessment: the huge variability of wood and the variations in drying conditions throughout the board stack in a dryer.To address these two key problems, we used a dual scale numerical tool able to compute simultaneously the stress and deformation of hundreds of boards in the stack during drying. A rigorous one-dimensional mechanical formulation, based on previous works, has been used for calculating stress and deformation during drying. The mechanical model is fitted into a module and then added to a dual scale (boardstack) model. This numerical tool has been used to improve the drying schedules recommended by the Technical Centre for Wood and Furniture in France (CTBA) for spruce. The proposed drying schedules allow the board quality to be improved. Note that the optimisation was limited to medium temperature values, so that the proposed schedule can be applied to conventional kilns

Control of phenotypic diversification based on serial cultivations on different carbon sources leads to improved bacterial xylanase production

peer reviewedThermobacillus xylanilyticus is a thermophilic and hemicellulolytic bacterium of interest for the production of thermostable hemicellulases. Enzymes’ production by this bacterium is challenging, because the proliferation of a cheating subpopulation of cells during exponential growth impairs the production of xylanase after serial cultivations. Accordingly, a strategy of successive cultivations with cells transfers in stationary phase and the use of wheat bran and wheat straw as carbon sources were tested. The ratio between subpopulations and their corresponding metabolic activities were studied by flow cytometry and the resulting hemicellulases production (xylanase, acetyl esterase and β-xylosidase) followed. During serial cultivations, the results pointed out an increase of the enzymatic activities. On xylan, compared to the first cultivation, the xylanase activity increases by 7.15-fold after only four cultivations. On the other hand, the debranching activities were increased by 5.88-fold and 57.2-fold on wheat straw and by 2.77-fold and 3.34-fold on wheat bran for β-xylosidase and acetyl esterase, respectively. The different enzymatic activities then stabilized, reached a plateau and further decreased. Study of the stability and reversibility of the enzyme production revealed cell-to-cell heterogeneities in metabolic activities which could be linked to the reversibility of enzymatic activity changes. Thus, the strategy of successive transfers during the stationary phase of growth, combined with the use of complex lignocellulosic substrates as carbon sources, is an efficient strategy to optimize the hemicellulases production by T. xylanilyticus, by preventing the selection of cheaters. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature

Characterization of sorption behavior and mass transfer properties of four central africa tropical woods: Ayous, Sapele, Frake, Lotofa

This study provides the sorption isotherm, its hysteresis and their mass transfer properties of four Central Africa Tropical woods widely used for building construction: frake (Terminalia Superba), lotofa (Sterculia Rhinopetala), sapele (Entandrophragma Cylindricum) and ayous (Triplochiton Scleroxylon). Characterization of these four species in particular and Central Africa tropical woods in general were necessary to develop conservation and treatment of wood after first transformation using the drying. Also, moisture transport on wooden material used such as wall buildings can be facilitating to found the thermal comfort. Measurements of isotherms were performed using a dynamic vapor sorption apparatus (Surface Measurement Systems) at 20 and 40°C with air relative humidity ranged from 0% to 90%. Mass diffusivity was determined in steady state using a specific vaporimeter. Air permeability was determined using a specialized device developed to measure over a wide range of permeability values. Permeability and mass transfer properties were determined in the tangential direction with a ‘’false’’ quartersawn board (sapele and lotofa) and in the radial direction with a flatsawn board (ayous and frake). Samples of sapele, ayous and frake are heartwood when lotofa contains as well as heartwood than sapwood. Results obtained showed that the temperature effect on sorption behavior was quite low. We observed also a low difference between the sorption behavior of these different species and hysteresis of sorption decreases when temperature increases. Hailwood-Horrobin model’s explains plausibly the experimental sorption isotherms data. Results on characterization of mass transfer properties showed that, in the steady state, mass diffusivity decreases exponentially when basal density increases. Mass diffusivity was higher in desorption than in adsorption phase. The gaseous permeability of these species was between than those of Australian hardwoods and temperate woods. It was difficult to define a relationship between permeability and mass diffusivity

Sorption behavior of four tropical woods using a dynamic vapor sorption standard analysis system

Sorption behavior of four tropical woods coming from Cameroon is studied using a Dynamic Vapor Sorption-Intrinsic apparatus. Sorption isotherms at 20°C and 40°C of Triplochiton scleroxylon (obeche), Entandrophragma cylindricum (sapele), Sterculia rhinopetala (lotofa) and Terminalia superba (frake also called limba) are compared to those in the literature with methods using saturated salts for lotofa and frake with satisfactory results. Experimental values are fitted using two sorption isotherm models. Sorption hysteresis is greatest in sapele and least in frake. When temperature increases, differences in the hysteresis of sorption among the woods decreases. Hystereses of all studied woods ranged from 0,5 to 3%. Our studied woods have lower equilibrium moisture content probably caused by the higher values of extractives content. The water sorbed molecules on multilayer during both adsorption and desorption at 20°C and 40°C is greater in the case of frake and lower in the case of lotofa. The water sorbed molecules on multilayer of sapele is greater than those of obeche. The predominance of multilayer over monolayer of our woods is from 0,2 to 0,4 relative humidity in adsorption phase, and from 0,3 to 0,4 relative humidity in desorption phase

Drying strategies capable of reducing the stress level of a stack of boards as defined by a comprehensive dual scale model

During drying, stresses and deformations develop in a wood board due to shrinkage fields which result from moisture content and temperature field variations. In spite of numerous works done in wood drying modelling in the last decades, wood drying optimisation based on modelling and simulation remains far from initial expectations. Two main reasons can explain this assessment: the huge variability of wood and the variations in drying conditions throughout the board stack in a dryer.To address these two key problems, we used a dual scale numerical tool able to compute simultaneously the stress and deformation of hundreds of boards in the stack during drying. A rigorous one-dimensional mechanical formulation, based on previous works, has been used for calculating stress and deformation during drying. The mechanical model is fitted into a module and then added to a dual scale (boardstack) model. This numerical tool has been used to improve the drying schedules recommended by the Technical Centre for Wood and Furniture in France (CTBA) for spruce. The proposed drying schedules allow the board quality to be improved. Note that the optimisation was limited to medium temperature values, so that the proposed schedule can be applied to conventional kilns

DRYING STRATEGIES CAPABLE OF REDUCING THE STRESS LEVEL OF A STACK OF BOARDS AS DEFINED BY A COMPREHENSIVE DUAL SCALE MODEL

During drying, stresses and deformations develop in a wood board due to shrinkage fields which result from moisture content and temperature field variations. In spite of numerous works done in wood drying modelling in the last decades, wood drying optimisation based on modelling and simulation remains far from initial expectations. Two main reasons can explain this assessment: the huge variability of wood and the variations in drying conditions throughout the board stack in a dryer. To address these two key problems, we used a dual scale numerical tool able to compute simultaneously the stress and deformation of hundreds of boards in the stack during drying. A rigorous one-dimensional mechanical formulation, based on previous works, has been used for calculating stress and deformation during drying. The mechanical model is fitted into a module and then added to a dual scale (board-stack) model. This numerical tool has been used to improve the drying schedules recommended by the Technical Centre for Wood and Furniture in France (CTBA) for spruce. The proposed drying schedules allow the board quality to be improved. Note that the optimisation was limited to medium temperature values, so that the proposed schedule can be applied to conventional kiln

Numerical investigation of wood drying with intermittent energy source at low exergy content

International audienceThe possibility to dry heat-sensitive timber with solar energy or residual energy from industrial processes with low exergy content, may be of double interest: the use of energy sources with very low price and the reduction of thermal pollution. The important issue when using such energies is to adapt the process control to the availability of the energy. Additionally, there is a major concern that this energy saving could be done at the detriment of drying quality or drying time. This paper proposes a numerical investigation of the possibility to use intermittent energy source to dry wood drying by comparing different strategies

Drying strategies capable of reducing the stress level of a stack of boards as defined by a comprehensive dual scale model. Maderas. Ciencia y tecnología 10(1

ABSTRACT During drying, stresses and deformations develop in a wood board due to shrinkage fi elds which result from moisture content and temperature fi eld variations. In spite of numerous works done in wood drying modelling in the last decades, wood drying optimisation based on modelling and simulation remains far from initial expectations. Two main reasons can explain this assessment: the huge variability of wood and the variations in drying conditions throughout the board stack in a dryer. To address these two key problems, we used a dual scale numerical tool able to compute simultaneously the stress and deformation of hundreds of boards in the stack during drying. A rigorous one-dimensional mechanical formulation, based on previous works, has been used for calculating stress and deformation during drying. The mechanical model is fi tted into a module and then added to a dual scale (boardstack) model. This numerical tool has been used to improve the drying schedules recommended by the Technical Centre for Wood and Furniture in France (CTBA) for spruce. The proposed drying schedules allow the board quality to be improved. Note that the optimisation was limited to medium temperature values, so that the proposed schedule can be applied to conventional kilns

Aplicación de espectrometría de rayos X para el estudio de la madera: Algunos resultados iniciales

El objetivo de este artículo es mostrar la posibilidad de utilizar fuentes policromáticas de rayos X en experimentos relacionados con la madera en que normalmente se requiere de fuentes monocromáticas. Se presentan diferentes aplicaciones de espectrometría de rayos X en base a fuentes policromáticas conformadas por tubos sin dispositivos de monocromatización, pero usando detectores espectrométricos de alta resolución energética. En primer lugar se describe una aplicación de transmisión o atenuación de rayos X destinada a obtener la variación espacio-temporal del contenido de humedad al interior de una tabla en proceso de secado a 70ºC y 50ºC en bulbo seco y bulbo húmedo respectivamente. Esta aplicación permitió realizar una cartografía digital del interior de la tabla y se reveló útil para caracterizar el proceso de evacuación de la humedad desde el interior de la madera. Luego se presenta un equipamiento innovador diseñado y fabricado por los autores para registrar la intensidad de dispersión coherente de rayos X. Los resultados demuestran la posibilidad de acceder al contenido de humedad y el ángulo microfibrilar, cuantificando las señales espectrales registradas tanto para el agua como para el plano cristalino (002) de la celulosa. La existencia de una señal de fondo originada por la fase amorfa de la madera impidió realizar estimaciones cuantitativas de contenido de humedad cuando la densidad anhidra de la madera es desconocida. AbstractWe investigated the possibilities to use polychromatic X-rays sources to study wood properties that usually require of monochromatic radiation. Three applications using X-ray tubes without monochromator together with high-resolution energy-sensitive X-rays detectors are presented. In a first experiment, a standard X-ray source and a spectrometric detector were placed on both sides of a wood dryer which operates at 70ºC and 50ºC for dry-bulb and wet-bulb respectively. Digital cartography obtained can offer the possibility to identify some phenomenological parameters of fluid migration in wood. In a second part, an innovative device designed and made by the authors to record X-ray scatter intensities is presented. The feasibility to use the ratio of diffraction to attenuation for moisture content determination is discussed. This device has been also used for microfibril angle determination by recording and analyzing the X-ray scattered intensities of cellulose (002) lattice. The microfibril angle determination was successful; however, a background of X-rays scattering from amorphous component of wood prevented the determination of moisture content

APLICACIÓN DE ESPECTROMETRÍA DE RAYOS X PARA EL ESTUDIO DE LA MADERA: ALGUNOS RESULTADOS INICIALES

El objetivo de este artículo es mostrar la posibilidad de utilizar fuentes policromáticas de rayos X en experimentos relacionados con la madera en que normalmente se requiere de fuentes monocromáticas. Se presentan diferentes aplicaciones de espectrometría de rayos X en base a fuentes policromáticas conformadas por tubos sin dispositivos de monocromatización, pero usando detectores espectrométricos de alta resolución energética. En primer lugar se describe una aplicación de transmisión o atenuación de rayos X destinada a obtener la variación espacio-temporal del contenido de humedad al interior de una tabla en proceso de secado a 70°C y 50°C en bulbo seco y bulbo húmedo respectivamente. Esta aplicación permitió realizar una cartografía digital del interior de la tabla y se reveló útil para caracterizar el proceso de evacuación de la humedad desde el interior de la madera. Luego se presenta un equipamiento innovador diseñado y fabricado por los autores para registrar la intensidad de dispersión coherente de rayos X. Los resultados demuestran la posibilidad de acceder al contenido de humedad y el ángulo microfibrilar, cuantificando las señales espectrales registradas tanto para el agua como para el plano cristalino (002) de la celulosa. La existencia de una señal de fondo originada por la fase amorfa de la madera impidió realizar estimaciones cuantitativas de contenido de humedad cuando la densidad anhidra de la madera es desconocid