1,721,309 research outputs found
The Use of Implicit Flux Limiting Schemes in the Simulation of the Drying Process: A New Maximum Flow Sensor Applied to Phase Mobilities
No full textA heterogeneous wood drying computational model that accounts for material property variation across growth rings
No full textIn this work, a comprehensive two-dimensional drying model, known as TransPore, is extended so that the effect of material heterogeneity and local material directions on the heat and mass transport processes evolving within the medium can be investigated. The underlying mathematical theory enables the property variations as well as the spatial changes of local material directions to be taken into consideration throughout the computation. The model, which enables the behaviour of the moisture content, internal temperature and pressure fields to be monitored during the drying process, uses a control-volume finite-element (CV-FE) formulation, together with a suite of sophisticated numerical techniques to ensure both accurate and efficient simulation results.\ud
A board section of softwood is used to depict the possibilities offered by this model. In this case, the material directions vary along the section according to the pith position that defines the radial and tangential directions. In addition, the material properties change significantly from earlywood to latewood. A comparison of the overall drying kinetics generated by both the heterogeneous and the classical homogeneous models will provide a clear understanding of the impact and importance of treating the local wood properties when drying softwood
A dual-scale model for describing drier and porous medium interactions
No full textA dual-scale modeling approach is proposed to describe the coupling of the drier\ud
(large-scale) and the porous medium (macroscale) throughout drying. This model is used\ud
to investigate the vacuum drying of a softwood board placed in an experimental vacuum\ud
chamber that is heated by two infrared (IR) emitters. The large-scale model provides\ud
important information for the drying engineer to assess and tune the performance of the\ud
drier. This model allows simulation of the chamber wall and IR emitter temperature\ud
evolution, together with changes in the chamber vapor, air, and water mass balances. The\ud
comprehensive two-dimensional drying model known as TransPore is used to determine\ud
the heat and mass transfer occurring at the macroscale of the board. Finally, four case\ud
studies are presented to elucidate the intricate coupling that exists between the chamber\ud
technical specifications and the drying behavior of the porous medium. A highlight of the\ud
dual-scale model is its ability to predict the condensation on the walls of a poorly\ud
insulated vacuum chamber for the case of a weak pump
Vacuum Drying of Wood with Radiative Heating: II. Comparison between Theory and Experiment
No full textInternational audienceIn part I of this work extensive experimental data sets for the vacuum drying of wood with radiative heating were presented for sapwood and heartwood of different species (Picea abies, Abies alba, and Fagus silvatica). These data sets are used here to validate two previously developed drying models. The first drying model, which is known as TransPore, is a comprehensive model able to capture the intricately coupled heat- and mass-transfer mechanisms that evolve throughout the drying process. The second model, which is known as Front_2D, uses a number of simplifying assumptions to reduce the complexity of the comprehensive model to a system that enables a semianalytical approach to be exploited for its solution. Although the first model provides a more accurate description of the entire process, the second model is able to produce representative solutions very efficiently in terms of overall computational times, making it a viable option for on-line control purposes. The comparison with experimental data highlights that both models are able to capture all of the observed trends, allowing them to be used with confidence for investigating the vacuum drying process at a fundamental level. The new contribution of this work lies in the fact that both models are used here for the first time to simulate drying at a reduced external pressur
The use of fractional-in-space diffusion equations for describing microscale diffusion in porous media
No full text
Determination of the material property variations across the growth ring of softwood for use in a heterogeneous drying model. Part 2 use of homogenisation to predict bound liquid diffusivity and thermal conductivity
No full textIn this work, the extensive knowledge of wood gained at the Ecole Nationale du Genie Rural des Eaux et Forets by using a combination of microscopic observation and experimental work is being used to postulate material property correlations for a macroscopic heterogeneous "Cerne" growth ring model of softwood. In this second part, the method of homogenisation is used to capture the contrast of property between the gaseous phase and the solid phase. \ud
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Homogenisation problems are computed using a Control Volume formulation. The tracheid model developed in Part 1 has been used to define several elementary representative volumes. Consequently, bound water diffusivity and thermal conductivity can be predicted for each material direction as a function of local wood density. For practical applications, analytical models fitted from the computed values allow these property variations to be easily and accurately determined
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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