Comparison of the 1D and 3D models for the simulation of wood heat treatment process

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Wood heat treatment at high temperatures (in the range of 180–240°C) is an ecological alternative to the chemical treatment of wood for its preservation. Thermal treatment provides dimensional stability and biological durability to wood due its structural changes. The dark color attained also gives the wood an aesthetic appearance. Various mathematical models have been developed for wood heat-treatment furnaces. In this article, two models, 1D and 3D, will be described. They have been used to simulate the furnace behaviour for a number of wood species, and parametric studies have been carried out to determine the impact of various factors. Some of the results of the calculations with the two models will be presented. They will be compared and the applicability and limitations of the 1D approach will be discussed.dc201

Investigation of the refractory bricks used for the flue wall of the horizontal anode baking ring furnace

Anode manufacturing, particularly the baking process, is an important part of the primary aluminium production process. Anode baking is carried out in closed or open top ring furnaces. The anodes are placed in pits and surrounded by packing coke to prevent oxidation by infiltrated air and mechanical support. The anodes are baked through indirect contact with the hot gas flowing in the flues on both sides of the pit. The flue walls are made of commercial refractory bricks, which are subjected to chemical (high temperature corrosion), mechanical (creep, walls, anode loading and unloading) and thermal (high temperature, thermal shock) conditions during the baking process. The resulting stress causes chemical and physical alterations across the width of the wall. This stress generally manifests in the collapsing, cracking and bending of flue walls. The chemical composition and physical properties of refractory bricks taken from degraded flue walls in an industrial plant were investigated, and it was shown that regular redressing and maintenance of flue walls can prevent or reduce additional energy consumption due to pit deformation, consequently reducing the cost of anode production

3D-modelling of conjugate heat and mass transfers: effects of storage conditions and species on wood high temperature treatment

Wood is definitely advantageous for industry because it is a renewable resource environment-friendly produced. However, the biological origin of wood requires some treatments to preserve and stabilise it. Heat treatment of wood at high temperature is one of the new techniques that reduce the hygroscopicity, improve dimensional stability, and increase resistance to biological degradation of wood material without the use of chemical products. In this work, transient heat and mass transfers during heat treatment of wood at high temperature were numerically studied. The averaged energy Reynolds Navier–Stokes equations and concentration equations for the fluid were coupled with the energy and mass conservation equations for the wood. The numerical conjugate problem considered also heat and mass exchange at the fluid-wood interface and was used to study the effects of specie-dependant (specific gravity) and storage-dependant (initial temperature and moisture content) parameters during the heat treatment. Both temperature and moisture content were affected by a low initial temperature during the first hours of the treatment, representing hypothetically a risk for wood quality. A high specific gravity or a high initial moisture content required supplemental heating time to reach the targeted final moisture content that potentially represent a supplemental energy and cost for industry

A novel high temperature heat treatment process for wood

Wood is heated to temperatures in the range of 180–240°C in heat-treatment furnaces. At these temperatures, the wood structure undergoes changes leading to better dimensional stability, better resistance to biological attacks, and a darker attractive color. The high-temperature heat treatment of wood is an alternate and ecologically-sound wood preservation process to chemically treated wood. During heat treatment, wood goes through simultaneous heat and mass transfer. The heat is transferred from the hot gases to the wood boards in the furnace. As the temperature of wood increases, water content of wood vaporizes and diffuses out of the boards. At higher temperatures, a number of irreversible structural changes take place in wood cells. The furnace design is important to carry out the heat treatment process uniformly and effectively. A new heat treatment furnace design has been proposed at UQAC and a prototype furnace has been built and tested. Also, a 3D model of the furnace was developed to complement the experimental work and to gain insight into the heat treatment process taking place in the furnace. In this article, the new furnace design and its advantages are discussed. Results of the measurements and predictions of the mathematical model are presented to show the effectiveness of the new furnace design for heat treating standard wood boards as well as pieces of wood with different geometries

Comparison of the 1D and 3D models for the simulation of wood heat treatment process

Wood heat treatment at high temperatures (in the range of 180–240°C) is an ecological alternative to the chemical treatment of wood for its preservation. Thermal treatment provides dimensional stability and biological durability to wood due its structural changes. The dark color attained also gives the wood an aesthetic appearance. Various mathematical models have been developed for wood heat-treatment furnaces. In this article, two models, 1D and 3D, will be described. They have been used to simulate the furnace behaviour for a number of wood species, and parametric studies have been carried out to determine the impact of various factors. Some of the results of the calculations with the two models will be presented. They will be compared and the applicability and limitations of the 1D approach will be discussed

Effect of thermal modification on mechanical properties of Canadian White Birch (Betula papyrifera)

Wood is a renewable material widely used in the construction industry. However, it is susceptible to fungal degradation. Several chemical products have been developed to improve its durability, but the toxicity of some of these products limits their use. One alternative to chemical treatment is thermal modification of wood. This method improves the dimensional stability of wood and reduces its susceptibility to decay. The impact of different parameters (maximum temperature, heating rate, holding time and gas moisture content) of thermal modification on the mechanical properties of Betula papyrifera was studied in a prototype furnace. The results show a marked decrease in the modulus of rupture with increasing temperature while the modulus of elasticity does not seem to be affected. The hardness increases with maximum modification temperature, and in the absence of moisture in gas, and there is an improvement in the dimensional stability after thermal modification

A dynamic process model for simulating horizontal anode baking furnaces

Anode manufacturing is an important step during the production of primary aluminum, and baking is the costliest stage of the anode manufacturing process. The industrial challenge resides in obtaining a good anode quality while keeping the energy consumption, environmental emissions, and cost to minimum. A dynamic process model of a horizontal anode baking furnace has been developed. It covers all important parameters such as fuel combustion, generation and combustion of volatiles (tar, methane, and hydrogen), air infiltration, and heat losses to the atmosphere and the foundation. The model was built using two coupled sub-models of the flue and the pit and was validated using plant data. It simulates the dynamic behavior of the furnace and gives a prediction of its operation and performance. In this article, the modelling approach will be described, and the results showing some of the industrial applications will be presented

Different mathematical modelling approaches to predict the horizontal anode baking furnace performance

The quality of carbon anodes has a considerable impact on the cell stability, energy consumption, environmental emissions, and the cost. The anode quality is influenced by many factors ranging from raw material properties to various process parameters. The anodes are baked in large furnaces and the final properties are fixed during this stage of production. For the past number of years, mathematical modelling has become a powerful tool to study and analyze industrial processes. The field of anode baking was no exception. Various models have been developed and reported for the baking furnace analysis. Experimental studies of such complex systems are quite costly. The mathematical models provide an insight into the core of the operation. A process model and a 3D model (both dynamic) have been developed for horizontal anode baking furnaces, and they were validated using experimental data. All the important phenomena have been taken into consideration in the models. The two models are being used to predict the performance of horizontal anode baking furnaces. In this article, the models will be described, the use of each model will be discussed, and the results of a number of practical applications for both models will be presented

Use of mathematical modelling to study the behavior of a horizontal anode baking furnace

Large numbers of carbon anodes are used in aluminum industry. The manufacture of carbon anodes involves the preparation of a paste (a mixture of coke, pitch, and recycled material), the production of green anodes via mixing and compaction of this paste, followed by cooling and baking of the green anodes. Anode baking is carried out in large furnaces. Any modification to design or operation would require a careful study of its impact on anode quality. In recent years, mathematical models have been used effectively to complement the experimental work in order to improve furnace operation and design. A design model and a process model are being developed to study the behavior of a horizontal anode baking furnace and to determine the necessary improvements. In this article, these models and their use for the study of a furnace will be described, and the results of the numerical simulations will be presented

La caractérisation mécanique de systèmes film-substrat par indentation instrumentée (nanoindentation) en géométrie sphère-plan

Depth sensing Indentation (nanoindentation) is an experimental technique increasing retained for the assessment of the mechanical properties of materials (hardness H, Young's modulus E) for which common homogeneous mechanical tests can not be performed or are extremely difficult to perform. The mechanical parameters are obtained from the indentation curve (the plot of the load vs penetration depth during both load and unload). Usually, some methodology reported in the literature (Oliver and pharr, Field and Swain, Doener and Nix, Loubet and al.) are used in order to assess E and H. We have performed a number of experiments on homogeneous materials (stainless steel AISI304, AISI316, AISI430; high-speed steel HSS652; glass SiO2) as well as a film-substrate system (TiN/AISI430, TiN/HSS652, TiO2/HSS652). Applying the Oliver and Pharr methodology, E end H vary with the applied load as well as the percentage of used unload curve retained for the analysis, as reported in the literature. Besides, in the case of the film-substrate system, only composite parameters are obtained instead of the in-situ films properties. In order to establish a simple strategy for the determination of the elastic modulus of a hard coating, we have carried out many simulations using a boundary element based numerical tool. Then a number of useful results have been identified. The well known elastic relation [delta]=a2/R between the relative approach [delta], the projected contact radius a and the punch radius R, remain valid in the plastic range for homogeneous as well as film-substrate specimens. This allows data indentation to be represented in term of mean pressure F/[pi]a2 vs indentation strain a/R . The initial slope of the loading part of the latter curve is proportional to the elastic modulus of the film, while the slope of the initial part of the unloading curve is proportional to the substrate elastic modulus. Our indentation procedure anlysis has been validated experimentally on a number of samples (TiN/AISI430, TiN/HSS652, TiO2/HSS652) after having established a relation between the punch displacement and the relative approach [delta]L'indentation instrumentée (nanoindentation) est une technique d'analyse des données expérimentales utilisées pour atteindre les propriétés mécaniques de matériaux (dureté H, module de Young E) pour lesquels les techniques classiques sont difficilement applicables voire non envisageables. Ces paramètres mécaniques sont issus de l'exploitation de la seule courbe expérimentale charge-décharge. L'analyse de cette dernière repose sur des nombreux modèles reportés dans la littérature (Oliver et pharr, Field et Swain, Doener et Nix, Loubet et al.) qui considèrent la décharge purement élastique. De nombreuses expériences que nous avons menées, sur divers types de matériaux massifs (aciers inoxydables AISI304, AISI316, AISI430; aciers rapides HSS652; verre de silice SiO2) et revêtus de films minces de TiN et TiO2 ont montré que les propriétés mécaniques (E et H), déduites de la méthode de Oliver et Pharr, dépendent du pourcentage de la courbe de décharge considéré, de la charge appliquée et du rayon de la pointe. De plus, pour un système film-substrat, la technique est en général utilisée pour atteindre les propriétés in-situ du film ou du substrat, alors que la méthode de dépouillement fournit des paramètres composites qu'il faut ensuite déconvoluer. Dans la recherche d'une stratégie simple, permettant d'accéder au module élastique d'un film « dur » pour les applications mécaniques, nous avons fait appel à la simulation numérique. Le code de simulation numérique utilisé, est basé sur la méthode des éléments de frontière. Nos investigations numériques utilisant l'indentation sphérique nous ont permis de mettre en évidence un certain nombre de résultats utiles pour l'analyse des données expérimentales. Nous avons commencé par montrer que aussi bien pour un matériau massif homogène élastoplastique que pour un système film dur substrat élastoplastique, la relation [delta]=a2/R demeure valable (R étant le rayon de l'indenteur, a le rayon de l'aire projetée de contact). Cela permet de représenter les résultats de l'essai d'indentation sphérique par la courbe pression moyenne F/[pi]a2- déformation a/R . Au début du chargement, la pente cette courbe est proportionnelle au module de Young du film tandis que la pente initiale de la courbe de décharge est proportionnelle au module d'élasticité du substrat. Une relation entre le déplacement de l'indenteur et [delta] , puis une méthode d'analyse d'indentation ont été établies. Enfin, la procédure a été validée numériquement et expérimentalement sur les données issues de l'indentation de divers combinaisons film-substrat (TiN/AISI430, TiN/HSS652 et TiO2/HSS652) avec succè