A relevant and robust vacuum-drying model applied to hardwoods

Redman, Adam; Baillères, Henri; Perré, Patrick; Carr, Elliot J.; Turner, Ian

doi:10.1007/s00226-017-0908-7

Cited by 19 publications

(18 citation statements)

References 21 publications

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“…at the origin of the process [16][17]. More sophisticated modeling approaches taking into account different transport mechanisms for bound water, free water and water vapor have later been developed [18][19][20][21][22], which appear to be able to predict macroscopic trends as soon as a number of parameters are introduced and fitted. However, they are less appropriate to provide a clear appreciation of the dominant physical mechanisms either on a global or on a local scale.…”

Section: Introductionmentioning

confidence: 99%

How Bound Water Regulates Wood Drying

et al. 2020

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For most wood-based product uses it is essential to remove a large part of the water content from wet or green (fresh-cut) wood, to reduce further dimensional variations under varying humidity conditions, improve its mechanical characteristics and protect it from biological attacks. However, the internal mechanisms of drying are not fully described. Here we observe drying at different scales using macroscopic measurements (weighing), NMR (Nuclear Magnetic Resonance) measurements allowing to distinguish bound and free water contents, and XRCT (X-ray computed tomography) images of air-liquid interfaces at the smallest pore scale (wood lumens). We show that during wood drying, even well above the Fiber Saturation Point, bound water diffusion in cell walls (instead of capillary effects) ensures the extraction of liquid water from pores and its transport towards the surface of evaporation, and thus controls the drying rate. The distribution of bound water content (uniform or heterogeneous) along the main sample axis and the drying rate evolution depend on the competition between the external conditions and a characteristic rate of transport due to bound water diffusion. For sufficiently slow drying this distribution remains homogenous until free water is fully extracted. An original physical phenomenon is thus at work which plays a major role of regulation of water extraction, in that it maintains a constant drying rate and a homogeneous distribution of the (mean) water content throughout the material. These results provide sound concepts for modeling and controlling drying properties of wood materials. They open the way to the understanding or control of the properties of many other materials containing two water types in food or civil engineering applications. Our results complete recent observations that bound water diffusion also controls imbibition in hardwood and finally show that transfers between bound and free water play a major role in the interaction of plant-like systems with water.

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Section: Introductionmentioning

confidence: 99%

How Bound Water Regulates Wood Drying

et al. 2020

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“…In the case of sound wood intended for industrial purposes, the applied drying method should ensure the appropriate moisture content with the highest wood quality (lack of defects) in the fastest time whilst being cost-effective. Amongst the most frequently used industrial drying processes are kiln drying and vacuum drying (for hardwood) (Perre and Keey 2006;Redman et al 2016Redman et al , 2017. As for waterlogged archaeological wood, however, although the purpose and general principles of drying are similar to commercial wood, the overarching goal is to remove water whilst keeping the structural integrity and appearance (shape and dimensions) of wooden artefact unaffected.…”

Section: Introductionmentioning

confidence: 99%

The effect of the drying method on the cell wall structure and sorption properties of waterlogged archaeological wood

2021

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Drying is a process affecting various wood properties, including its structure, moisture behaviour and mechanical properties. Since waterlogged wooden artefacts usually constitute priceless objects of cultural heritage, understanding the effect of drying on the complex interactions between the wood ultrastructure and the resulting properties is necessary to ensure their proper conservation. Hence, this was the aim of the present study, with a particular emphasis on the influence of drying conditions on the relations between the cell wall structure, dimensional stability and hygroscopicity of degraded archaeological wood. The choice of the particular drying methods was dictated by their final effect on wood appearance (dimensions). The results obtained clearly show that depending on the drying method applied, the resulting material differs significantly in structure, dimensions and sorption properties, despite the same degree of wood degradation. Air- and oven-drying resulted in the highest wood shrinkage, lower porosity, and a decreased number of free hydroxyls in the wood cell wall. The best wood dimensional stabilisation and the highest porosity were ensured by freeze- and supercritical drying. No correlations were found between wood structure and moisture behaviour. The outcome of the research may be useful for conservators who plan to provide the artefacts with proper storage conditions and effective conservation/reconservation.

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“…A component of the project was to develop a hardwood vacuum drying model (Redman et al 2017) based on previous work conducted for softwood species (Perré 2007b). A two-dimensional, diffusion and permeability based multiphysics heat and mass transfer model was developed by adapting the TransPore model, used to predict the drying behaviour of softwoods, and applying the drying model to Australian hardwood species.…”

Section: Introductionmentioning

confidence: 99%

“…As described by Redman et al (2017), a series of vacuum and conventional drying trials were preformed to generate data to validate the heat and mass transfer model using four Australian hardwood species; mature native forest spotted gum (Corymbia citriodora Hook), blackbutt (Eucalyptus pilularis Sm), jarrah (Eucalyptus marginata D.Don ex Sm. ), and messmate (Eucalyptus obliqua L'Herit.).…”

Section: Introductionmentioning

confidence: 99%

“…Dried quality was quantified by measurements of distribution of average MC and MC gradient, and stress related degrade, including surface checking, end splitting, internal checking and collapse. In the current paper we are only interested in stress-related degrade, and the data produced by Redman et al (2017), expressed as a percentage of degrade existence, from the 100 randomly selected boards, are provided in Table 1. This data highlights that:…”

Section: Introductionmentioning

confidence: 99%

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Finite element analysis of stress-related degrade during drying of Corymbia citriodora and Eucalyptus obliqua

Redman¹,

Baillères²,

Gilbert³

et al. 2017

Wood Sci Technol

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With the use of experimentsl wood properties and input moisture content field data, we developed a predictive 3D stress-strain finite element analysis (FEA) model allowing us to predict the development of stress related end splitting and surface checking degrade during conventional and vacuum wood drying. Simulations were carried out for two Australian hardwood species, messmate (Eucalyptus obliqua) and spotted gum (Corymbia citriodora) as these species contrast, in terms of wood properties, drying rates and stress degrade susceptibility. The simulations were performed using a 1/8 symmetry model where the full board dimensions are 1,900 mm long x 30 mm thick x 100 mm wide. Moisture content field data model simulations were utilised in a three-dimensional FEA model by extruding a 2D moisture content field computed in the T-L plane across the radial direction to create a 3D model. Material mechanical properties and shrinkage were calculated in relation to moisture content, over discrete time intervals, using a quasi-static solver. End split failure was investigated at the board end, and surface check failure at the board surface, using a Tsai-Wu failure criterion. Simulations showed that messmate was more susceptible to end splitting than spotted gum and that conventionally dried messmate was more susceptible to surface checking than vacuum dried messmate. The same results were observed from drying trials.The location of predicted surface check failure also matched drying trials and are compared.

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A relevant and robust vacuum-drying model applied to hardwoods

Cited by 19 publications

References 21 publications

How Bound Water Regulates Wood Drying

How Bound Water Regulates Wood Drying

The effect of the drying method on the cell wall structure and sorption properties of waterlogged archaeological wood

Finite element analysis of stress-related degrade during drying of Corymbia citriodora and Eucalyptus obliqua

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