The Academy Lecture

Helmuth Resch

Trying to Dry Using High-Frequency Electric Current

Among the many interesting topics in the field of Wood Science and Technology is a fascinating story about research and development on drying wood products with high-frequency electric current. Historically, it can be traced back over decades. Heat transfer to and evaporation of moisture from wood may be accomplished with high frequency current depending on its dielectric properties. Because wood is generally heterogeneous, these properties vary not only with the frequency of the current and the field orientation, but also with the moisture content, temperature, and density of wood.

Research on this technology has covered many products from paper and veneer to lumber and heavy timbers. Much emphasis, however, has been placed on wood species and/or products with larger dimensions that are difficult or impossible to dry when using conventional drying methods. The advantages were found to be rapid and fairly uniform heat transfer often to solidly stacked timbers, very high drying rates, and avoidance of significant case-hardening and oxidative discoloration of the wood.

During the last two decades, the development focused mainly on drying lumber in vacuum kilns using dielectric heating, often termed high-frequency/vacuum drying. It has been justified economically on the basis of increased throughput and higher quality. Existing industrial installations provide a positive picture for higher value products. The economics should improve with advances in available equipment, better basic understanding and more practical experience with operating industrial units. The combination of high-frequency/vacuum drying with other systems, such as moisture leveling after primary drying or pre-heating prior to the high-frequency/vacuum step, hold promise for further technical improvement.

The Lecturer

Helmuth Resch is professor emeritus at the University for Natural Resources, Vienna, Austria, and Chair of Sector Group Wood Technology, Cooperation in Science and Technology (European Science Foundation) European Union. His education includes Diploma Engineer, Forest Engineering, University of Natural Resources, Vienna; MS at Utah State University, and returning to Vienna for the doctorate. Following this, he was as a faculty member in Wood Science at University of California, Berkeley. He was then appointed Professor and Head, Department of Forest Products, Oregon State University, followed by Dean of Research at State University of New York, College of Environmental Science and Forestry, Syracuse. Helmuth then returned to Vienna as Professor and Head of the Institute of Wood Science and Technology, University Natural Resources, and Director of the Austrian Forest Products Research Laboratory. Helmuth is a member of the Forest Products Society and the Society of Wood Science and Technology; Fellow of the Indian Academy of Wood Science; Honorary Professor at Transilvania University, Brasov, Romania; and Honorary Doctor at University of Western Hungary, Sopron. His fields of interest include physical properties of wood and wood products, drying and impregnation of wood, production of plywood and other composite boards, and research management. He was elected a Fellow in IAWS in 1983.

Presented at the 59th International Convention of the Forest Products Society at Quebec City, Quebec, Canada, 20 June 2005.