Friday, April 13, 2018

Microwave heating

Microwave processing of materials is a technology that can provide the material processor with a new, powerful, and significantly different tool to process materials that may not be amenable to conventional means of processing or to improve the performance characteristics of existing materials.

Microwaves are electromagnetic waves in the frequency band from 300 MHz to 300 GHz. The commonly used frequency for microwave heating is 2.45 GHz.

The principle of microwave heating is related to the polar characteristic of molecules. During the microwave heating, polar molecules such as water molecules try to orientate with the electric field. When dipolar molecules try to re-orientate with rapid changing alternating electric field, the heat is generated by rotation, friction an collision of molecules.

The main characteristics of microwave heating:
*Penetrating radiation
*Rapid heating
*Controllable field distribution
*Selective heating of materials
*It is self-limiting

Microwave heating for pasteurization and sterilization are preferred for the primary reason that they are rapid (as they do not depend as much on the diffusional limitations) and therefore require less come-up time. They can approach the benefits of high temperature-short tine processes – thermal degradation of the desired components is reduced.

The ability of microwaves to penetrate and heat the material from within provides the possibility of rapid and volumetric heating without overheating the surfaces. This can lead to an increase in product yield since the surface degradation is minimized due to the cooler surface compared to conventional heating methods.
Microwave heating
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