Radio Frequency Technology
Radio Frequency (RF) is a drying and thermal processing technology based on the dissipation of electromagnetic energy within the product. Unlike conventional techniques, where heat is transferred to the product through its surface from an external heat source by conduction, convection or irradiation, a Radio Frequency field generates heat directly inside the entire product mass – that is why the related mechanism is called “endogenous” or “volumetric”. The heat generation is instantaneous and allows a rapid, uniform and perfectly controlled process, thus delivering outstanding results in terms of product quality, operational flexibility and energy savings.
The RF heating mechanism, excluding the materials (like metals) which are good conductors of electric current, is related to the so called “dielectric losses”. Dielectric losses are caused by the vibration and rotation of polar or polarised molecules, and by the polarisation and translation movement of ionic particles inside the material, induced by the quick (several million times per second) polarity reversal of the RF field. This can be interpreted as if the electromagnetic field is absorbed and converted into thermal energy by the effect of the rapid movement of polar(ised) molecules and ions. Water molecules are highly polar, more than all substrates in which water can normally be found, and many ionic species are usually dissolved in water. Therefore, RF electromagnetic fields can heat up very quickly wet materials. In particular, RF has the ability to evaporate water rapidly, efficiently and selectively from many substrates (textiles, agricultural commodities, bakery products, etc.).
Broadly speaking, all RF heating and drying equipment consist of two main distinct parts:
- the generator
- the applicator (or electrodes)
The generator converts the normal electricity from the mains supply into radio frequency electromagnetic energy. It is composed of a suitably designed combination of capacitors and inductances (the oscillating LC circuit) connected to a vacuum valve (the triode), complete with the high voltage DC supply unit.
The applicator receives the electromagnetic energy from the generator through simple conductive metal connectors and applies it to the product to be processed.