MPM modelling of the cellular collapse of bio-products due to capillary forces

The Material Point Method (MPM) was implemented to predict the mechanical behavior of the cellular arrangement of biological tissues. The choice of this method was motivated by its ability to easily account for the actual and complex morphology of bioproducts at the cellular level and to deal with large deformations. The vectorial image processing facilities provided by the custom software MeshPore allow such a procedure to be easily applied to microscopic images. In this work, the morphology of the cellular structure is observed using an Environmental Scanning Electron Microscope (ESEM). Our MPM model has been adapted to model the collapse of the cellular structure due to a negative water pressure inside the cell lumens. The simulations illustrate how the cellular morphology, resulting from the formation of radial lines of cells, induced a collapse mainly in the tangential direction of wood. The computed deformation in the tangential direction is roughly five fold the radial one. Finally, we discuss how the same modeling chain of tools, from image to computed results, could be applied to other bio-products, namely the cellular structure of fruits or vegetable

MPM modelling of the wood/water relations at the cellular level : shrinkage and collapse

MPM modelling of the wood/water relations at the cellular level : shrinkage and collapse. 3. International Conference on Porous Medi

Spreading and penetration of a water droplet on native and heat treated wood

A custom device was conceived to place a water droplet (diameter c.a. 0.5mm) at the surface of wood and follow its evolution. The device comprises a minute needle, micrometric displacement stages, a backward light, a telecentric magnifying lens and a fast camera.Before each test, the wood surface was carefully prepared using a sledge microtome. Due to the difficulty to cut heat-treated wood, the surface was always prepared before heat treatment (220°C, 1 hour). Earlywood and latewood samples of fir, before and after heat-treatment, were tested with the droplet placed on a transverse section (imbibition along the longitudinal direction). Image processing allows the evolution of droplet height, droplet diameter and apparent contact angle to be obtained.Based on the Washburn’s law, a theoretical model was developed to predict the evolution of the droplet height, using the evolution of the droplet diameter as input parameter. Simulated and experimental curves were matched by tuning one single parameter, the true contact angle.This theoretical model allowed the competition between spreading and penetration depicted by the experimental data to be analyzed in detail:- the porosity promotes penetration and weakens spreading,- the contact angle is reduced by heat-treatment,- the identified values of the true contact angle are always very close to 90°

Multiscale analysis of water vapor diffusion in low density fiberboard: implications as a building material

International audienceThis work is devoted to diffusion mechanisms in low-density fiberboard (255 kg.m −3). Experiments were performed under unsteady state conditions (relative humidity step from 37% to 71%) with different thicknesses (half thickness ranging from 1 mm to 20 mm). The mass diffusivity was determined by inverse analysis from the experimental moisture content evolution, using a comprehensive macroscopic model of coupled heat and mass transfer. A clear failure of Fickian's law becomes evident regarding the effect of thickness. A dual-scale model, based on the concept of distributed microstructure models with coupled heat and mass transfer at both scales, was used to simulate the experiments. The large number of dual-scale simulations proposed in this work were also analyzed by the inverse method. These dual-scale simulation results were successfully confronted to the experiment. The good fit with the experimental data is obtained for a diffusivity of the microscopic phase (the storage phase) equal to 1.10 −13 m 2 .s −1 for a fiber radius of 20 µm. As the main recommendation, we advise that the dual scale effect can be neglected for this kind of fiberboard for a total thickness larger than some centimeters, depending on the panel density. This also means that this effect must be considered in material characterization or when capturing the buffering effect of the surface layers of the envelope

TORREFACTION OF CELLULOSE: VALIDITY AND LIMITATION OF THE TEMPERATURE/DURATION EQUIVALENCE

During torrefaction of biomass, equivalence between temperature and residence time is often reported, either in terms of the loss of mass or the alternation of properties. The present work proposes a rigorous investigation of this equivalence. Cellulose, as the main lignocellulosic biomass component, was treated under mild pyrolysis for 48 hours. Several couples of T-D (temperature-duration) points were selected from TGA curves to obtain mass losses of 11.6%, 25%, 50%, 74.4%, and 86.7%. The corresponding residues were subjected to Fourier transform infrared spectroscopy for analysis. According to the FTIR results, a suitably accurate match to global T-D equivalence is exhibited up to 50% mass loss: in this domain, mass loss is well correlated to the treatment intensity (molecular composition of the residue) except for slight differences in the production of C=C and C=O. For mass loss levels of 74.4% and 86.7%, distinct degradation mechanisms take place at different combinations of temperature and duration, and the correlation fails. Compared to the mass loss at 220°C and 250°C, the equivalent molecular composition can be achieved through treatment at 280°C with shorter treatment time and less depolymerization and oxidation. The main conclusion drawn is that mass loss can be used as a synthetic indicator of the treatment intensity in the temperature range of 220°C to 280°C up to a mass loss of 50%

Imbibition capillaire du bois : simulation Lattice Boltzmann à partir d'une anatomie réelle

Le bois est un milieu poreux hydrophile, il est donc crucial de tenir compte de ses interactions avec l’eau. Nous nous intéresserons plus particulièrement à la dynamique d’imbibition capillaire d’un échantillon de bois. Celle-ci est étudiée numériquement par une approche Lattice Boltzmann diphasique. L’anatomie 3D de l’échantillon est reconstituée par interpolation au moyen du logiciel Meshpore à partir d’une série d’images en microscopie optique de coupes 2D réalisées au microtome

Torrefaction Of Cellulose: Validity And Limitation Of The Temperature/Duration Equivalence

During torrefaction of biomass, equivalence between temperature and residence time is often reported, either in terms of the loss of mass or the alternation of properties. The present work proposes a rigorous investigation of this equivalence. Cellulose, as the main lignocellulosic biomass component, was treated under mild pyrolysis for 48 hours. Several couples of T-D (temperature-duration) points were selected from TGA curves to obtain mass losses of 11.6%, 25%, 50%, 74.4%, and 86.7%. The corresponding residues were subjected to Fourier transform infrared spectroscopy for analysis. According to the FTIR results, a suitably accurate match to global T-D equivalence is exhibited up to 50% mass loss: in this domain, mass loss is well correlated to the treatment intensity (molecular composition of the residue) except for slight differences in the production of C=C and C=O. For mass loss levels of 74.4% and 86.7%, distinct degradation mechanisms take place at different combinations of temperature and duration, and the correlation fails. Compared to the mass loss at 220 degrees C and 250 degrees C, the equivalent molecular composition can be achieved through treatment at 280 degrees C with shorter treatment time and less depolymerization and oxidation. The main conclusion drawn is that mass loss can be used as a synthetic indicator of the treatment intensity in the temperature range of 220 degrees C to 280 degrees C up to a mass loss of 50%