dielectric heating.pptx

Dielectric heating

1. DIELECTRIC HEATING Submitted By Unnimaya K 22412MFT007

2. DIELECTRIC A dielectric (dielectric material) is an electrical insulator that can be polarized by an applied electric field When a dielectric material is placed in a electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field

3. This creates an internal electric field that reduces the overall field within the dielectric itself If a dielectric is composed of weakly bonded molecules , those molecules not only become polarized, but also reorient

4. DIELECTRIC PROPERTIES Permeability of the material Ability of the food to interact with the magnetic field of the microwave Measured in Henrys per meter or H/m Relative complex permittivity of the medium Composed of two different properties – dielectric constant & dielectric loss factor

5. DIELCTRIC CONSTANT & DIELCTRIC LOSS FACTOR Both the dielectric constant and dielectric loss factor measure the ability of the material to interact with the electric field of the microwave Dielectric constant is a measure of the food material’s ability to store electromagnetic energy Dielectric loss is the material’s ability to dissipate electromagnetic energy (which results in heating) Loss tangent is defined as the ratio of dielectric loss factor to the dielectric constant

6. DIELCTRIC HEATING Electronic heating , radio frequency heating , high- frequency heating The process in which a radio frequency(RF) alternating electric field or radio wave or microwave electromagnetic radiation heats a dielectric material At higher frequencies , this heating is caused by molecular dipole rotation within the dielectric Dielectric heating uses electromagnetic radiation in the frequency range of 300 kHz to 300 GHz

7. RF wave has lower frequency but longer wavelength than microwave The radio frequency(RF) ranges is from 300kHZ 300 MHz Microwave range is from 300 MHz to 300GHz

8. MECHANISM The majority of foods contain a substantial proportion of water The molecular structure of water consist of a negatively charged oxygen and positively charged hydrogen and this forms an electric dipole When a microwave or radio frequency electric field is applied to a food, dipoles in the water and in some ionic compounds(salt) attempt to orient themselves to the field

9. Since the rapidly oscillating electric field changes from positive to negative and back again several million times per second, the dipole attempt to follow and these rapid reversal creates frictional heat The increase in temperature of water molecules heats surrounding components of the food by conduction and /or convection The depth of penetration of both microwaves and radio frequency energy is determined by the dielectric constant and the loss factor of the food

10. Lower the loss factor and lower the frequency, the greater the penetration depth Microwave penetration increase when water changes phase to ice ( ice has lower loss factor than water) Radio frequency energy is mostly used to heat or evaporate moisture from a product Higher frequency microwaves are used for defrosting and low pressure drying

11. MICROWAVE HEATING

12. MICROWAVE GENERATION Microwave equipment consists of a microwave generator (magnetron ) , aluminium tube ( wave guides), metal chamber for batch operation or tunnel fitted with a conveyor belt for continuous operation Magnetron is a cylindrical diode which consists of a sealed copper tube with a vacuum inside The copper tube pointing towards the centre- anode and a spiral wire filament at the centre

13. When a high voltage(4000 v) is applied , the cathode produces free electron, which give up their energy to produce rapidly oscillating microwave, which are directed to the waveguide by electromagnets The wave guide reflects the electric field internally and transfer it to the heating chamber In batch equipment a rotating antenna or fan is used to distribute the energy or the food may be rotated on a turntable

14. In continuous tunnels different design of antennae is used to direct a beam of energy over the food as it passes on a conveyer Common frequencies used in microwave oven are 2450 MHz and 915 MHz

15. Microwave oven

16. RADIO FREQUENCY HEATING Similar to microwave heating but at lower frequencies Food is passed between electrodes and a radio frequency voltage is applied across the electrodes

17. This changes the orientation of water dipoles and results in very rapid heating Radio frequency heating allows selectivity in the location of heating and accuracy in control of the duration of heating Limitation -The thickness of the food is restricted by the distance between the capacitor plates

18. RADIO FREQUENCY HEATING SYSTEM

19. A P P L I C A T I O N S

20. A P P L I C A T I O N S

21. Heating is rapid and uniform High heating efficiency Minimum surface damage and no surface browning Equipment is small, compact & perfect geometry for CIP There is no contamination of food by products of combustion Suitable for heat sensitive , high viscous and multiphase fluid ADVANTAGES

22. DISADVANTAGES Food cooked in microwave oven will not be brown , so no crust formation or browning in bread or meat Short cooking time does not allow flavours to develop and this makes food unacceptable High initial cost

23. CONCLUSION Dielectric materials always have poor electrical conduction properties these are associated with poor thermal conduction properties Conventional heating take relatively long time to heat dielectric materials The process of heating in which radio waves or microwave electromagnetic radiation are used to heat the dielectric materials is known as dielectric heating Most food products are dielectric material which indicates the huge application potential for dielectric heating in the food processing industry

24. REFERENCES Food processing technology ,Principles and practices ( second edition ) P . Fellows, 2000 Radio-Frequency Heating in Food Processing , principles and applications ,George B . Awuah, Hosahalli S. Ramaswamy , Juming Tang https://www.Ift.org/news-and-publications/food-technology-magazine/issue/2016/ august/columns/processing-radio frequency – processing-of-food https://www.tutorialspoint.com/applications-of-dielectric-heating https://foodtechnotes.com/2020/07/21/non-thermal-preservation-of-food-dielectric-heating http://ecourseonline.iasri.res.in

25. THANK YOU