Wavet, a Custom Device Able to Measure Viscoelastic Properties of Wood Under Water-Saturated Conditions Up to 140 deg C (WAVET : Environmental Vibration Analyser for Wood)

This work presents an innovative experimental device conceived to characterize the time-dependent behavior of hygroscopic materials, as wood, at controlled moisture content and temperature. This device, the WAVET, permits the determination of the viscoelastic properties of samples, using harmonic tests at frequencies varying from 5.10-3 Hz to 10 Hz. Conceived to work up to 5 bar, it allows tests in dry or water-saturated conditions to be performed over the temperature range 0\degree C to 140\degree C. In spite of these severe working conditions, the careful device design, together with a rigorous data analysis, allows a rigorous determination of the storage and loss modulus and the loss factor. The results collected for several species of wood emphasize the ability of the WAVET to underline the influence of numerous parameters, namely specie, material direction, anatomical and macromolecular structure, on the rheological properties and notably on the softening temperature. The WAVET also establishes a efficient tool to follow the modifications of the constitutive amorphous polymers of materials submitted to hydrothermal treatments, in relation to the evolution of their viscoelastic properties.Comment: 3

Viscoelastic properties of wood across the grain measured under water-saturated conditions up to 135\degree C: evidence of thermal degradation

In this paper, the viscoelastic properties of wood under water-saturated conditions are investigated from 10\degree C to 135\degree C using the WAVET* apparatus. Experiments were performed via harmonic tests at two frequencies (0.1 Hz and 1 Hz) for several hours. Four species of wood were tested in the radial and tangential material directions: oak (Quercus sessiliflora), beech (Fagus sylvatica), spruce (Picea abies) and fir (Abies pectinata). When the treatment is applied for several hours, a reduction of the wood rigidity is significant from temperature values as low as 80-90\degree C, and increases rapidly with the temperature level. The storage modulus of oak wood is divided by a factor two after three hours of exposure at 135\degree C. This marked reduction in rigidity is attributed to the hydrolysis of hemicelluloses. The softening temperature of wood is also noticeably affected by hygrothermal treatment. After three short successive treatments up to 135\degree C, the softening temperature of oak shifted from 79\degree C to 103\degree C, at a frequency of 1 Hz. This reduction in mobility of wood polymers is consistent with the condensation of lignins observed by many authors at this temperature level. In the same conditions, fir exhibited a softening temperature decreasing of about 4\degree C. In any case, the internal friction clearly raises

Enumeration method and medium design for a mixed culture of saccharomyces cerevisiae and chlorella vulgaris

The scientific literature shows a rising interest in studies on symbiotic mixed cultures as an innovative bioprocess to increase biomass and lipid productivity. The main issue with mixed cultures appears to be the dominance of one organism over the other during cultivation. In the current work, a methodology is proposed to develop a co-dominant mixed culture of Saccharomyces cerevisiae GFP and Chlorella vulgaris, in which their growth would be based on mutual symbiosis through recycling O2 and CO2. The first challenge was to develop a rapid and accurate method to distinguish and enumerate each population. Please click on the link below for full content

Shrinkage of cane (Arundo donax L.) II Effect of drying condition on the intensity of cell collapse

To improve the drying method in the manufacture of woodwind reeds, green canes (Arundo donax L.) were dried under various humidity-temperature conditions and the intensity of cell collapse was evaluated from the swelling due to steaming involving the recovery of collapse. At 30 C, the intensity of collapse was increased by slower drying. It was considered that: 1) slower drying resulted in higher sample temperature in the early stage of drying to increase the collapse; 2) rapid drying stiffened the surface of sample and such "shell" prohibited the following collapse; 3) slower drying i.e. longer loading of liquid tension caused more remarkable and/or frequent viscoelastic yields of cells. Consequently the intensity of collapse increased when the cane was dried from its waxy outer surface or in the presence of node: both of them retarded the drying. On the other hand, higher drying temperature caused greater intensity of collapse in spite of faster drying. It was suggested that the thermal softening of cane cells leads to easier yield of the cell wall, at the same time the rapid drying does not allow the recovery of collapse after the disappearance of free water. These results indicated that faster drying at lower temperature is preferable for drying cane with less collapse.Comment: Will be published in J. Wood Sci. (Japanese wood research society) - follows part I: J. Wood Sci. 50 : 295-30

8th International IUFRO wood drying conference Brasov-Romania, August 24-29, 2003

The IUFRO 5.04.06 Wood Drying Conference was organised by the "Transilvania" University of Brasov - Faculty of Wood Industry and hosted by the Aro Palace Complex in Brasov (Romania). Over 100 scientists from 28 countries attended the meeting. Two Keynote Addresses: " The Role of Wood Anatomy in the Drying of Wood: "Great Oaks from Little Acorns Grow " by the Wood Drying Working Party Leader, Patrick PerrC (France) and " High-Frequency Heating Combined With Vacuum Drying Of Wood by Helmut Resch (Austria) was an excellent start of the technical program of over 80 oral presentations and 28 poster presentations. The topics of the 10 oral presentation sessions and the poster session covered modelling, stress and strain behaviour of wood, properties ofwood related to drying, fast drying procedures, applied drying, heat and mass transfer, kiln control, drying quality, colorations and general

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

8th International IUFRO wood drying conference Brasov-Romania, August 24-29, 2003

The IUFRO 5.04.06 Wood Drying Conference was organised by the "Transilvania" University of Brasov - Faculty of Wood Industry and hosted by the Aro Palace Complex in Brasov (Romania). Over 100 scientists from 28 countries attended the meeting. Two Keynote Addresses: " The Role of Wood Anatomy in the Drying of Wood: "Great Oaks from Little Acorns Grow " by the Wood Drying Working Party Leader, Patrick PerrC (France) and " High-Frequency Heating Combined With Vacuum Drying Of Wood by Helmut Resch (Austria) was an excellent start of the technical program of over 80 oral presentations and 28 poster presentations. The topics of the 10 oral presentation sessions and the poster session covered modelling, stress and strain behaviour of wood, properties ofwood related to drying, fast drying procedures, applied drying, heat and mass transfer, kiln control, drying quality, colorations and general

Use of Heating Configuration to Control Marangoni Circulation during Droplet Evaporation

The present work presents a numerical study of the evaporation of a sessile liquid droplet deposited on a substrate and subjected to different heating configurations. The physical formulation accounts for evaporation, the Marangoni effect, conductive transfer in the support, radiative heating, and diffusion-convection in the droplet itself. The moving interface is solved using the Arbitrary Lagrangian-Eulerian (ALE) method. Simulations were performed using COMSOL Multiphysics. Different configurations were performed to investigate the effect of the heating conditions on the shape and intensity of the Marangoni circulations. A droplet can be heated by the substrate (different natures and thicknesses were tested) and/or by a heat flux supplied at the top of the droplet. The results show that the Marangoni flow can be controlled by the heating configuration. An upward Marangoni flow was obtained for a heated substrate and a downward Marangoni flow for a flux imposed at the top of the droplet. Using both heat sources generated two vortices with an upward flow from the bottom and a downward flow from the top. The position of the stagnation zone depended on the respective intensities of the heating fluxes. Controlling the circulation in the droplet might have interesting applications, such as the control of the deposition of microparticles in suspension in the liquid, the deposition of the solved constituent, and the enhancement of the evaporation rate

Technical Note: Equilibrium Moisture Content of Norway Spruce at Low Pressure

The EMC of Norway spruce (Picea abies) was determined at various levels of temperature and RH under low pressures. EMC corresponded to temperature and RH and was strongly related to vapor pressure inside the chamber. The amount of air present in the vacuum chamber did not significantly affect the EMC. The Hailwood-Horrobin model can be used to estimate the EMC of wood under vacuum, although it is about 2-3% MC less than the actual EMC of wood during initial desorption

A mesoscopic drying model applied to the growth rings of softwood: Mesh generation and simulation results

A mesoscopic drying model that enables the drying simulation of quartersawn and flatsawn wood sections consisting of several growth rings is presented. The procedure to generate the virtual board description directly from real sample images is also described. This virtual structure accommodates the prominent sample features, including its geometrical and physical properties, together with the density and structural variation across the growth rings. We give a synopsis of the sophisticated techniques developed specifically to generate this virtual description and exhibit the final computational meshes produced by the software for quartersawn and flatsawn sections. Low temperature drying simulations are then performed for both heterogenous and homogeneous model variants using these virtual descriptions and comparisons are made of the resulting MC field evolution. A highlight of these comparisons is that the heterogeneous model captures realistic drying effects, including the fast drying of earlywood and the late removal of liquid water in latewood. In comparing the drying of quartersawn and flatsawn boards we conclude that the effect of the heterogeneous nature of the MC fields is diminished somewhat when considering the flatsawn section over the quartersawn section