Wood Drying: What is Dielectric Heating? (Serial 1)

Introduction

Dielectric heating (also known as electronic heating, RF heating, high-frequency heating) is the phenomenon in which radiowave or microwave electromagnetic radiation heats a dielectric material, especially as caused by dipole rotation (Wikipedia: Dielectric Drying).

Dielectric heating is the use of either microwave or radio frequency (RF) technologies to heat materials. Microwave and RF interact with individual molecules to quickly generate heat within a product. This is in contrast to conventional heating where heat is applied externally.

When a dielectric material is brought into a rapidly altering electrical field, heat is generated inside the material. This is known as heating by dielectric hysteresis or, in short, dielectric heating. Radio frequency and microwave heating are both applications of this principle. In technological terms, however, there is a clear distinction between the two techniques.

The essential advantage of dielectric heating resides in the generation of heat within the material to be heated. In comparison with more conventional heating techniques (hot air, infrared) in which the material is heated via the outer surface, dielectric heating is much more rapid. This is because electrically insulating materials are mostly also poor conductors of heat.

Advantages of Dielectric Heating

• Shorter processing times for heating or drying
• More uniform, volumetric heating
• Less energy required
• Greater controllability
• Shorter production line lengths

References:

Roussy, G., Pearce, J. A. (1995). Foundations and Industrial Applications of Microwaves and Radio Frequency Fields. Physical and Chemical Processes, John Wiley & Sons, Chichester.

Riande, E., Diaz-Calleja, R. (2004). Electrical Properties of Polymers. Marcel Dekker, New York.

M. Willert-Porada (ed.). (2006). Advances in Microwave and Radio Frequency Processing, 8th International Conference on Microwave and High-Frequency Heating, Springer Verlag, Berlin.

Van Reusel, K., Belmans, R. (2006). Technology Bound and Context Bound Motives for the Industrial Use of Dielectric Heating, Proceedings of the 40th Annual International Microwave Symposium.

Von Starck, A., Mühlbauer, A., Kramer, C. (2005). Handbook of Thermoprocessing Technologies. Vulkan Verlag, Essen.