Hybrid drying with HF heating and hot-air under atmospheric pressure, 3: Relation between pressure and water movement in Cryptomeria japonica square lumber
2002
Kawai, Y. (Akita Prefectural Univ., Noshiro (Japan)) | Kobayashi, Y. | Norimoto, M.
Relationships among internal temperature, internal pressure and water movement in sugi (Cryptomeria japonica D. Don) square lumber during high frequency (HF) heating under atmospheric pressure were investigated. The results obtained are as follows: 1) The internal temperature and pressure reached 140degC and 360 kPa, respectively. Increases in internal temperatures occurred, in order, in the core, the intermediate zones, and the surface zones of the lumber. Internal pressure gradients also varied following the changes in the temperature gradients. 2) Liquid water flowed out of the surfaces and cross sections above 60degC when internal pressure increased to 160-200 kPa. 3) While the internal pressure and temperature at the core were higher than at the intermediate zone of the lumber initially, pressure inversion occurred at the same time as temperature inversion. Moisture content gradients varied following the behavior of the internal pressure. 4) The location of highest temperature and pressure in the lumber moved with time from the core to the surface zone during HF heating. From these results, it can be concluded that the internal pressure is the driving force for water movement in lumber during HF heating.
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