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A.A. Goryaev, V.I. Melekhov, N.B. Balantseva, O.A. Kalinicheva Complete text of the article:Download article (pdf, 0.5MB )UDС674.047.38DOI:10.17238/issn0536-1036.2016.5.132AbstractThe paper considers the convective drying of softwood lumber at the continuous circulation of a drying agent under low pressure. A noticeable rate reduction of the drying agent circu-lation takes place in the kiln at a pressure of 50 kPa and less. The water-vapor saturation pressure in the drying medium is uniquely and logarithmically dependent on a temperature. That is why the steam point reduces with decrease of a medium pressure. Moreover the dif-fusion and self-diffusion coefficients of water vapor and the moisture content of the drying medium increase. In connection with these phenomena, heat- and mass transfer under re-duced medium pressure is determined. The diffusion coefficients under reduced pressure increase. The intensity of the vacuum drying process depends on the internal diffusion of moisture to the wood surface. The moisture content of the drying agent determined by the partial pressure of water vapor in a vacuum kiln increases with decreasing pressure. The temperature of wood should be equal to the boiling temperature or higher to intensify the evaporation of moisture from wood. The evaporating moisture cools the wood surface, and the internal diffusion of moisture to the wood surface increases. An overpressure occurs inside the wood, which relaxes depending on the hydraulic resistance of wood. After the relaxation of pressure in wood the saturation temperature is below of the moisture tempera-ture, and moisture boils throughout the wood volume. A drying process is carried out in a vacuum drying kiln – an autoclave. The autoclave casing is doubled for water-cooling for condensation of water vapor from the drying agent. The condensed moisture is collected in a graduated container with a water meter. In the initial lumber moisture we can determine the current moisture content of wood by a condensate volume. The autoclave single occupancy is up to 22 m3 of sawn timber. Three autoclaves work at the same time. The use of a medium low-pressure in the process of convective drying of softwood lumber reduces its duration by 13...26 hours. The drying process is controlled by the remote control using the wood tem-perature and medium condition in a vacuum drying kiln.AuthorsA.A. Goryaev, Candidate of Engineering Sciences, Associate Professor V.I. Melekhov, Doctor of Engineering Sciences, Professor N.B. Balantseva, Candidate of Engineering Sciences, Associate Professor O.A. Kalinicheva, Candidate of Engineering Sciences, Associate ProfessorAffiliationNorthern (Arctic) Federal University named after M.V. Lomonosov, Naberezhnaya Severnoy Dviny, 17, Arkhangelsk, 163002, Russian Federation; е-mail: ark16111936@gmail.comKeywordsdrying, timber, vacuum, degree of saturation, drying agent, superheated steam, equilibrium moisture content, diffusion, heat conduction, circulation, pressure.References1. Adriano D. Osobennosti ispareniya vody so svobodnoy poverkhnosti i s poverkh-nosti drevesiny v usloviyakh vakuumnoy sushki [Features of Water Evaporation from a Free Surface and a Wood Surface in a Vacuum Drying]. Revista padurilor – industria lemnului celuloza si hartie – RSR, 1980, vol. 31, no. 3. 2. Lamb F.M., Wengert E.M. Hardwood Drying Test Evaluates New Methods. For-est Industries, 1982, vol. 109(13), pp. 21–22. 3. Herman G. Vacuum Drying – State of the Art and Future Projections. HOB, 1980, no. 4. 4. Goryaev A.A. Sovremennye vakuumnye lesosushil'nye kamery: obzor [Modern Vacuum Wood-Drying Kilns: a Review]. Moscow, 1985. 32 p. 5. Goryaev A.A., Melekhov V.I. Ustanovka dlya sushki drevesiny [Apparatus for Wood Drying]. Certificate of Authorship, 1983. Bulletin no. 45, p. 164. 6. Goryaev A.A., Popov N.Yu. Opredelenie parametrov vozdukha po Id-diagramme pri ponizhennom davlenii [Defining of Air Parameters by the ID-Diagram under Reduced Pressure]. Sushka i zashchita drevesiny [Drying and Wood Protection]. Arkhangelsk, 1985, pp. 59–68. 7. Krechetov I.V. Sushka drevesiny [Wood Drying]. Moscow, 1980. 432 p. 8. Lee A.W.C., Harris R.A. Properties of Red Oak Lumber Dried by Radio-Frequency / Vacuum Process and Dehumidification Process. Forest Products J., 1984, no. 34(5), pp. 56–58. 9. Panotstsi M. Vacuum Drying of Wood. Woodworking and furniture industry, 1984, no. 1. 10. Petukhov S.V., Balantseva N.B., Goryaev A.A. Konvektivno-vakuumnaya su-shka khvoynykh pilomaterialov [Convective and Vacuum Softwood Lumber Drying]. “Razvitie Severo-Arkticheskogo regiona: problemy i resheniya”: materialy nauch. konf. SAFU [“Development of the Northern Arctic Region: Problems and Solutions”: Proc. Conf. NArFU]. Arkhangelsk, 2015, pp. 129–131. 11. Popov N.Yu. Ob osobennostyakh kombinirovannoy konvektivno-dielektricheskoy sushki drevesiny pri ponizhennom davlenii sredy [On the Specifics of the Combined Convective and Dielectric Timber Drying under Medium Reduced Pressure]. Sushka i zashchita drevesiny [Drying and Wood Protection]. Arkhangelsk, 1985, pp. 69–71. 12. Rivkin S.L., Aleksandrov A.A. Teplofizicheskie svoystva vody i vodyanogo para [Thermal Properties of Water and Steam]. Moscow, 1980. 424 p. 13. Rukovodyashchie tekhnicheskie materialy po tekhnologii kamernoy sushki pilo-materialov [Reference Specification for Chamber Lumber Drying Technology]. Arkhan-gelsk, 2000. 125 p. 14. Sergovskiy P.S. Gidrotermicheskaya obrabotka drevesiny [Hydrothermal Treat-ment of Wood]. Moscow; Leningrad, 1975. 400 p. 15. Harris R.A., Taras M.A. Comparison of Moisture Content Distribution, Stress Distribution, and Shrinkage of Red Oak Lumber Dried by a Radio-Frequency / Vacuum Drying Process and a Conventional Kiln. Forest Products J., 1984, no. 34(1), pp. 44–54. Received on May 26, 2016 Features of Softwood Lumber Drying Under Reduced Medium Pressure |
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