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Radiofrequency dielectric heating

Identification

Key words radiofrequency, weight, geometry, dielectric, electromagnetism, thermodynamics, loss factor, temperature, surface temperature, speed, heating, heat transfer, calorimetry, cooling, electromagnetic radiation
Latest version 2010/12/20
Completed by IRTA

How does it work?

Primary objective To heat food products.
Working principle Radiofrequency is a form of electromagnetic radiation between 30 kHz and 300 MHz delivered between two electrodes. For the food sector, the following three ISM (industrial, scientific, medical) bands can be used: 13.56 MHz±0.05%, 27.12 MHz±0.05% and 40.68 MHz±0.05%. Like for microwave heating, the production of heat is related with the interaction of the electromagnetic radiation and the material to be processed. In all material, such energy interacts using two main mechanisms: dipole rotation and ionic polarization.

Dipole rotation occurs on polar molecules such as water. Polar molecules are charged and asymmetric molecules which tend to align themselves with the incoming electric field. Ionic polarization occurs in the free ions present in the material. These ions are charged particles and they are accelerated by the electric field. The kinetic energy is released in form of heat when there are collisions. According to literature (Marra et al 2009) for radiofrequency the main heating mechanism is the ionic polarization. Radiofrequency heating involves the use of an electrical generator connected to an electrode configuration where a high frequency directional electrical field is applied. The most common one are the parallel plate electrodes, also called ‘‘through-field” applicators. In contrast to ohmic heating no contact of food/electrode is required.

Images
Additional effects In comparison with microwave, radiofrequency has a higher power penetration in the food matrix, and more uniform field patterns, but a lower power density.
Important process parameters frequency, power, distance between electrodes, application time
Important product parameters geometry of the products, composition of the products, dielectric constants, packaging

What can it be used for?

Products Bread, meat, fish, seafood, vegetables, fruits, herbs (conductive liquid or solid food).
Operations Radiofrequency is an alternative heating technology and all material susceptible to be heated or defrosted can use this technology. The main applications in the food sector are post-baking, drying, thawing of meat or fish blocks, pasteurization, drying and decontamination of whole fruits.
Solutions for short comings Radiofrequency has the possibility to heat faster than conventional technologies with a penetration distance of 20 to 50 cm, depending on the frequency. This ability provides a tool for fast thawing processes or fast continuous drying processes.

What can it NOT be used for?

Products Conductive material, foodstuff with metals.
Operations Radio frequency equipment had to full fit international regulation on electromagnetic leakage. Due to potential electric hazard, electrodes size is restricted, for example for a 27 MHz equipment, they should not be larger than 1,4 m.
Other limitations The radiofrequency technology does not work with highly conductive material (i.e metals) and insulating material (mostly plastic or carton packaging) with a low loss factor. For defrosting the loss factor differences of ice and water are limiting. Whereas for conventional heating, heat recovery can be utilized, for advanced heating based on electric energy the applicability is limited.
Risks or hazards As an electromagnetic device, radiofrequency is submitted to a specific regulation against electromagnetic leakage.

Implementation

Maturity Radiofrequency technology is a mature technology and industrial applications can be found since the eighties, even if there is a lack of information on potential applications.
Modularity /Implementation Radiofrequency technology is based on modules (generators, cavity, applicator, with electrodes) that can be adapted to an existing line. Depending on the application, various radiofrequency modules can be implemented. The technique is available in industrial scale for liquid or solid foodstuff.
Consumer aspects Radiofrequency is a well known technology used especially for medical equipments. As far as we know there are no consumer concerns for the use of radiofrequency in the food sector.
Legal aspects Equipment using radiofrequency source have to comply with the ISM bands and with regulation EN 55011:2009 (Industrial, scientific and medical equipment. Radio-frequency disturbance characteristics. Limits and methods of measurement) and CE marking.
Environmental aspects As far as we know there are no environmental concerns.

Further Information

Institutes IRTA, Wageningen UR - FBR
Companies Petrie Technology, Sairem, Stalam
References 1. Houben, J., Schoenmakers, L., van Putten, E., van Roon, P., Krol, B. (1991). Radio frequency pasteurisation of sausage emulsions as a continuous process. Journal of Microwave Power and Electromagnetic Energy 26 (4), 202–205

2. Luechapattanporn, K., Wang, Y., Al-Holy, M., Kang, D.H., Tang, J., Hallberg, L.M., (2004). Microbial safety in radio-frequency processing of packaged foods. Journal of Food Science 69 (7), M201–M206

3. Manzocco L., Anese M., Cristina Nicoli M (2008). Radiofrequency inactivation of oxidative food enzymes in model systems and apple derivatives. Food Research International, Volume 41 (10), 1044-1049

4. Marra F., Zhang L., Lyng J.G. (2009). Radio frequency treatment of foods: Review of recent advances. Journal of Food Engineering 91, 497–508

5. Piyasena, P., Dussault, C., Koutchma, T., Ramaswamy, H.S., Awuah, G.B., (2003). Radiofrequency heating of foods: principles, applications and related properties. A review. Critical Reviews in Food Science and Nutrition 43 (6), 587–606

6. Richardson P. (2004). Thermal Technologies in food processing edited by Woodhead Publishing Limited ISBN 1 85573 556 3.

7. Zhao, Y., Flugstad, B., Kolbe, E., Park, J.E., Wells, J.H., (2000). Using capacitive (radiofrequency) dielectric heating in food processing and preservation – a review. Journal of Food Process Engineering 23, 25–55



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Created by Hte irta on 9 February 2012, at 10:31