RFTrocknung

RFTrocknung, commonly referred to as RF-Trocknung in German, describes drying processes that use radio frequency electromagnetic energy to heat materials. It relies on dielectric heating to raise the temperature inside moist products, enabling volumetric drying rather than heating primarily at the surface.

The technique operates by exposing materials to an alternating electric field in the radio frequency range. Polar molecules such as water rotate and ions move under the field, generating heat throughout the material. Industrial RF drying typically functions in the low to high frequency RF bands, roughly 1 to 100 MHz. Common commercial frequencies are 13.56, 27.12, and 40.68 MHz, chosen to balance penetration depth and heating rate.

RF drying systems use electrodes or coaxial applicators to create the field, with the product placed between two conductive surfaces or inside a dielectric chamber. The process can be batch or continuous and may be combined with forced hot air, vacuum, or pressure to move moisture to the surface for removal. In many installations, RF drying is preceded or followed by conventional drying to optimize moisture gradients and product quality.

Advantages include shorter drying times, higher energy efficiency for moist products, and more uniform heating with reduced case hardening, which helps preserve quality. Limitations include uneven heating for heterogeneous materials, dependence on dielectric properties and moisture content, higher equipment costs, and stringent safety requirements to shield RF fields and protect operators.

Applications span wood drying, fruits and vegetables, grains, and other hygroscopic materials, as well as ceramic and polymer composites where rapid internal heating aids moisture removal without excessive surface temperatures.