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Antti Hukka, Olli Oksanen
Convective Mass Transfer Coefficient at Wooden Surface in Jet Drying of Veneer
The relationship between heat and mass transfer at wooden surface is investigated experimentally by drying 1.6 mm thick birch veneers in constant conditions in a laboratory-scale roller dryer. By intermediate weighing of the samples a drying curve is established for each specimen. The drying curves are formulated in a functional form to produce the drying rate as a function of wood moisture content. Based on that and the measured heat-transfer coefficient a correction factor is calculated for the mass transfer coefficient predicted by the boundary layer theory.
The results show that the convective mass transfer coefficient for wooden surfaces substantially deviates from that given by the analogy between heat and mass transfer. The correction factor describing the internal resistance for evaporation is strongly dependent on wood temperature within the range 50–90°C, but for practical purposes not dependent on the average moisture content of the veneer (range 40–70%). The numerical value of the correction coefficient established is somewhat lower than published earlier by other researchers.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 53, 03/1999
Pages: 204 - 208