Recipe adaptation and new recipe development for high temperature heat treatment of North American wood species

The thermal treatment of wood at high temperatures is an environment friendly and commercially viable alternative wood modification technology. In this process, wood is heated to temperatures above 200ºC. This modifies the structure of wood and improves its hardness, dimensional stability, and resistance to biological attacks compared to those of the untreated wood. Its color also becomes darker and more attractive. However, this treatment may cause a decrease in wood elasticity. Therefore, optimization of the treatment parameters is necessary for a quality product. In addition, the high temperature heat-treatment processes for wood were first developed in Europe, and the recipes used for the European species were not necessarily applicable to the North American species. Thus, adaptation of the technologies to the latter species was necessary. The industrialists in the Saguenay-Lac-St-Jean region of Quebec brought two heat treatment technologies (Bois Perdure from France and Thermowood from Finland) to Canada. The adaptation of the technology is a very costly procedure at industrial scale. The Research Group on the Thermotransformation of Wood (GRTB – Groupe de recherche sur la thermotransformation du bois) at the University of Quebec at Chicoutimi (UQAC) which works closely with these industries developed a method for adapting the existing recipes to the North American species as well as for developing new ones for other species. UQAC is the first North American university which has such a unique research structure to carry out this type of research. The recipe development starts in a laboratory scale furnace. The high temperature heat-treatment experiments are carried out in a thermogravimetric system under different conditions until a promising set of conditions is identified for the properties sought by the industry. Consequently, the trends are identified for a given species. To determine the properties, various characterization tests (bending, dimensional stability, screw withdrawal, etc.) are done. Then, the heat treatment trials in a prototype furnace are carried out to finalize the recipe. This is followed by trials in an industrial-scale furnace for validation of the results

Modelling of high temperature heat treatment of wood using thermowood technology

Heat treatment of wood at relatively high temperatures (in the range of 180–240°C) is an effective method to improve the dimensional stability and to increase the biological durability of wood. During the heat treatment process, the heat and mass transfer takes place between the solid and the drying medium, and the moisture evaporation occurs within the solid due to the capillarity action and diffusion. In this article, a coupling method is presented for high temperature heat treatment of wood based on ThermoWood technology. A three-dimensional mathematical model considering the simultaneous unsteady heat and moisture transfer between a gas phase and a solid phase during heat treatment has been developed. The conservation equations for the wood part are obtained using the diffusion equation with variable diffusion coefficients, and the 3-dimensional incompressible Reynolds-averaged NavierStokes equations have been solved for the flow field. The coupling between the two parts is achieved by expressing the continuity of the state variables and their respective fluxes through the interface. A detailed discussion of the computational model and the solution algorithm is given

Wood thermodegradation: experimental analysis and modeling of mass loss kinetics

ABSTRACT: In this study, heat treatment was carried out in a relatively low temperature (230˚C). Mass loss kinetics was studied using equipment, specially conceived to measure sample's mass during the thermal treatment. Laboratory experiments were performed for heating rates of 1˚C min-1. Mathematical model for kinetics of pyrolysis process was used and validated. During the pyrolysis of dry wood samples under inert atmosphere, measurements of temperature distribution and dynamic weight loss were performed. Five different wood species Fagus sylvatica (Beech), Populus nigra (Poplar), Fraxinus excelsior (Ash), Pinus sylvestris (Pine) and Abies pectinata (Silver Fir) were investigated. The unsteady-state mathematical model equations were solved numerically using the commercial package Femlab 2.0. A detailed discussion of the computational model and the solution algorithm is given. The validity of different model assumptions was analyzed. Experimental results were compared with those calculated by the model. Acceptable agreement was achieved

Moisture sorption isotherms and heat of sorption of Algerian bay leaves (Laurus nobilis)

ABSTRACT: The moisture sorption isotherms of Algerian bay leaves (Laurus nobilis) were determined experimentally in this work. The equilibrium moisture contents of the leaves were measured at 40, 50, and 60 °C using static gravimetric method. Six mathematical models were tested to fit the experimental data of sorption isotherms and predict the hygroscopic behavior during storage or drying. Peleg model was found to be the best fitting model for describing the sorption curves. The net isosteric heat of sorption was computed from the equilibrium data at different temperatures by applying the integrated form of the Clausius-Clapeyron equation. The net isosteric heat of sorption is inversely proportional to the equilibrium moisture content and is found to be an exponential function of moisture content

Computational analysis of MHD flow, heat and mass transfer in trapezoidal porous cavity

Numerical simulations are conducted for two-dimensional steady-state double diffusive flow in a trapezoidal porous cavity, submitted to axial magnetic field. The Darcy equation, including Brinkmamn and Forchheimer terms account for viscous and inertia effects, respectively is used for the momentum equation, and a SIMPLER algorithm, based on finite volume approach is used to solve the pressure-velocity coupling. An extensive series of numerical simulations is conducted in the range: 103 ≤ Ra ≤ 106,1 ≤ Ha ≤ 102, Da =10-5, N = 1, and Le = 10. It is shown that the application of a transverse magnetic field normal to the flow direction decreases the Nusselt number and Sherwood number. Illustrative graphs are presented

SIMULATION NUMERIQUE DU TRANSFERT<br />DE CHALEUR ET DE MASSE EN MILIEUX<br />FLUIDES ET POREUX

In this thesis, heat and mass transfer by natural convection in confined fluid and porousmedia has been studied numerically. Two of its parallel walls are maintained at constantand different temperature and concentrations. The other two walls are impermeable andwell insulated. The thermosolutal convective phenomena inside the enclosure is describedby Navier-Stokes equations, the energy and species conservation equations. The porousmedia is modeled according to the Darcy-Brinkman and Forchheimer model. Theconvective flow is governed by the Rayleigh number (Ra), the buoyancy ratio (N), thePrandtl number (Pr), the Lewis number (Le), the Darcy number and the porosity ε. Thecontrol volume approach is employed to solve the governing equations. Concerning thevalidation of the numerical algorithm, The results are found to be in excellent agreementwith those of previous work. The influence of the physical and geometrical parameters isexamined. Results shows that increasing of porous layer thickness reduces the global heatand mass transfer for low values of permeability. The decrease in heat transfer withincreasing buoyancy ratio at high Lewis numbers is analyzed. Furthermore, in order to puta the disposal of the engineer a tool allowing him to evaluate the thermal and solutaltransfer taking place in the considered type configuration, a correlations are proposed.Dans cette thèse, les transferts de chaleur et de masse par convection naturelle enmilieux fluides et poreux ont été étudiés numériquement. Les parois verticales sontsoumises à des températures et concentrations constantes, tandis que les paroishorizontales sont adiabatiques et imperméables. Le phénomène de la convectionthermosolutale est régi par les équations de conservation de la masse, de la quantité demouvement, de l'énergie et de la concentration. le milieu poreux est modélisé suivant lemodèle général de Darcy – Brinkman – Forchheimer. L'écoulement convectif est régi pardifférents paramètres de contrôle, à savoir le nombre de Rayleigh (Ra), le rapport desforces de volume (N), le nombre de Prandtl(Pr), le nombre de Lewis (Le), le nombre deDarcy (Da) et la porosité ε de la matrice poreuse. La méthode des volumes de contrôle aété employée pour résoudre les équations de base en milieux fluide et poreux. Concernantla validation du code de calcul, l'accord obtenu entre nos résultats et ceux disponiblesdans la littérature s'est avéré excellent. L'influence des paramètres physiques etgéométriques est examinée. L'augmentation de l'épaisseur de la couche poreuse de faibleperméabilité réduit considérablement les transferts thermique et massique. Ladécroissance du transfert de chaleur avec l'accroissement du rapport des forces de volumeà nombre de Lewis élevé est mise en évidence. Par ailleurs, dans un souci de mettre à ladisposition de l'ingénieur un outil lui permettant d'évaluer les transferts thermiques etmassiques ayant lieu dans une configuration de type considérée, des corrélations sontproposées