Characterisation of water transfer in a low temperature convective wood drier: influence of the operating parameters on the mass transfer coefficient

Abstract : Different drying cycles were performed in a low temperature convective and homogeneous wood drier in order to evaluate the in¯uence of four operating parameters (wood thickness, air velocity, air temperature and air humidity) on the global mass transfer coef®cient. The wood species used in this study was spruce (Picea abies Karst.). From the synthesis of the results, a general correlation has been obtained permitting to accurately calculate this transfer coef®cient. Moreover, it justi®ed the use of the simple mathematical model chosen to represent the variations of the parameters characterising the wood and air during a drying cycle. Charakterisierung des Wasserflusses in einem Niedrigtemperatur-Trockner: Einfluû der Variablen auf den Koeffizienten fu Èr Massentransport In der Absicht, den Ein¯uû von vier Variablen (Holz-dichte, Luftgeschwindigkeit, Lufttemperatur und Luft-feuchte) auf den Koef®zienten fu Èr Massentransport zu bestimmen, wurden verschiedene Trocknungszyklen in einem homogenen Niedrigtemperatur-Trockner durch-gefu Èhrt. Die hierfu Èr verwendete Holzart war Fichte (Picea abies Karst). Im Anschluû an die Zusammenfassung der Ergebnisse wurde eine allgemeine Korrelation, mit der dieser Koef®zient auf eine bestimmte Weise berechnet werden kann, erzielt. Diese rechtfertigte die Wahl eines einfachen Simulationsmodells, das die Vera Ènderung der charakteristischen Luft-und Holz-parameter wa Èhrend der Trocknung darstellt. List of symbols A Constant a 0 Constant B Constant b 0 Constant c 0 Constant Cp Speci®c heat, J Á kg À1 Á K À1 D Diffusion coef®cient of water in wood, m 2 Á s À1 e Wood thickness, mm G Mass ¯ow rate of dry air, kg Á s À1 h Heat transfer coef®cient, w Á m À2 Á K À1 i Iterative variable k G Partial mass transfer coef®cient in the gas phase, kg Á m À2 Á s À1 k S Partial mass transfer coef®cient in the solid phase, kg Á m À2 Á s À1 k X Global mass transfer coef®cient, kg Á m À2 Á s À1 M Mass of wood, kg m Repartition coef®cient, / m F Final mass of a piece of wood, kg M W Oven dry mass of wood, kg N Number of wood pieces in the drier, / p Constant Rh Air relative humidity, % S Exchange surface between wood and air, m 2 T Air temperature, KY C t Wood temperature, KY C v Air velocity, m Á s À1 w Air moisture content, kg Á kg À1 x F Final moisture content of a piece of wood, kg Á kg À1 x FSP Wood moisture content at the ®bre saturation point, kg Á kg À1 x Wood moisture content, kg Á kg À1 x à Equilibrium moisture content, kg Á kg À1 z Residual air desiccation ratio, / Greek letters a Constant K Latent heat of water in wood at the temperature t, J Á kg À1 K 0 Latent heat of water in air at T ˆ 0 C, J Á kg À1 s Time, s
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Contributor : Laurent Chrusciel <>
Submitted on : Thursday, April 12, 2018 - 3:29:35 PM
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L. Chrusciel, E Mougel, A Zoulalian, T. Meunier. Characterisation of water transfer in a low temperature convective wood drier: influence of the operating parameters on the mass transfer coefficient. Holz als Roh - und Werkstoff, 1999, ⟨10.1007/s001070050070⟩. ⟨hal-01765065⟩

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