A microwave applicator for on line wood drying: Temperature and moisture distribution in wood |
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| Authors: | A L Antti P Perré |
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| Institution: | Lule? University of Technology, Division of Wood Physics, S-931 87 Skellefte?, Sweden e-mail: lena.antti@tt.luth.se, SE
ENGREF – Laboratory of Forest Sciences, Forest Products Team, F-54042 Nancy Cedex, France e-mail: perre@engref.fr, FR
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| Abstract: | Summary An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea
was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard
magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using
an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in
the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and
moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate
determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal
direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was
not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying
rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy,
meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the
position of each applicator in a larger scale microwave pilot plant.
Received 25 February 1997 |
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