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Frequently Asked Questions

1.How does microwave heating/drying work?

Microwaves are radio waves operating in a band frequency of 300MHz~300GHz, which is near by the one used by cellular telephones. For industrial microwave, there are two frequencies are most commonly used: 2.45GHz and 915MHz. Microwave cannot be absorbed or conducted by metals, but only be reflected. While it can penetrate glass, ceramic, plastics and other insulation materials. Unlike all other methods of heating which dry from the surface inward, microwaves simultaneously penetrate all parts of the material, so they heat uniformly. It is called volumetric heating.

Microwaves produce heat by vibrating water molecules, almost a billion times per second. The resulting friction converts the radio energy to heat energy and vaporizes the water. Molecules of other substances, such as protein, fat, and fiber, don’t readily absorb microwave energy so they don’t heat up as much. This effect, plus evaporation of surrounding water, keeps the product cool. As a result, almost all the energy applied removes water, unlike conventional dryers where much energy is lost heating air and steel. Microwave dryers typically have 80%+ energy efficiency compared to about 50% for steam dryers and gas-fired rotary drum dryers.

2.How can microwave pasteurize?

Microwave has a biological effect when working on materials. Under the effect of microwave, biological protein in bacteria and worm eggs is inactivated, meanwhile RNA and DNA in the cells are broken avoiding normal metabolism and propagation of bacteria and worms.

3.What’s the advantage of microwave heating compare to conventional heating?

1. As volumetric heating penetrates the materials and transfers heat not by conduction, it is better to use microwave heating for applications where conventional heat transfer is inadequate. One example is fluids containing particulates where the identical heating of solids and liquids is required to minimize over-processing. Another is for obtaining very low final moisture levels for product without over-drying.

2. Microwaves generate higher power densities, enabling increased production speeds and decreased production costs.

3. Microwave systems are more compact, requiring a smaller equipment space or footprint.

4. Microwave energy is precisely controllable and can be turned on and off instantly, eliminating the need for warm-up and cool-down.

5. Lack of high temperature heating surfaces reduces product fouling in cylindrical microwave heaters. This increases production run times and reduces both cleaning times and chemical costs.

6. Microwaves are a non-contact drying technology. IMS planar dryers in the textile industry reduce material finish marring, decrease drying stresses, and improve product quality.

7. Microwave energy is selectively absorbed by areas of greater moisture. This results in more uniform temperature and moisture profiles, improved yields and enhanced product performance.

8. The use of industrial microwave systems avoids combustible gaseous by-products, eliminating the need for environmental permits and improving working conditions.


4. What about safety?

Using  patented applicator design geometries and unique choking mechanisms,  IMS technology reduces microwave leakage from system entry and exit points to  virtually non-detectable levels for both their planar and cylindrical heating  systems. This poses no threat of electromagnetic radiation to the health and  safety of equipment operators. 

IMS heaters and dryers are designed to operate  at a level of electromagnetic emission that is twenty times more stringent than the IEEE/ANSI standard. As a further precaution, all IMS control systems  are supplied with safety interlocks and leakage detectors that shut down power  instantaneously in the event of equipment malfunction or misuse.

5. Frequency of industrail microwave systems.

      ITU (International Telecommunication Union) would assign the available frequencies of radio wave that depends on use. It is finally decided by the laws of each countries.

     Regarding microwave that has frequency of 300MHz to 300GHz (wave length of 1m to 1mm), ITU has allocated frequencies for the purpose of industrial, scientific, medical use, as shown in Table 1.

    433.92MHz has been recognized as ISM frequency in some countries, in the first region (Europe).

    915MHz has been recognized as ISM frequency in the second region (North and South America)

    ISM frequencies that can be used worldwide is the ISM frequency of 2450MHz or higher.


    2450MHz microwave penetration depths is about 12.2 cm and 915MHz microwave is about 36 cm, and WaveLane will give the proper and most effective technique proposal to customer on the frequency selection.


6. Advantage of Microwave System

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       (1) The internal heating                                                                     

As shown in Figure 9, microwave will reach the object to be heated at the same speed of light. Then it enters into the object as a wave, and by getting absorbed, the object generates heat.                                                                                


(2) Rapid heating

As shown in Figure 10, in conventional heating, the object's temperature rises by spreading heat energy from the surface to inside (external heating) On the other hand, by microwave heating, the object will generate heat on their own by the penetration of the microwave. Not necessary to consider about the heat conduction. That is why rapid heating is possible by microwave. Although the object has to be large enough for the microwave to penetrate, the smaller objects will also be heated from inside as the depth of microwave penetration. As shown in Figure11, compare to the conventional heating which is heated from the surface, microwave will still be faster for the small objecs.

                     

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(3) Selected heating

Microwave heating, there is a difference in microwave power absorption depending on the material.

For example , a borosilicate glass is sold as microwavable glass container. When this glass is heated with water in it, only water gets heated. That's because microwave power absorption of the glass is ignored since there is only 3000/1 of water. Therefore, when a good material of container is selected, microwave can only heat the object and heat efficiency improves substantially.


(4) Rapid response and temperature control  

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Microwave penetrates into the object at the speed of light.

And the object to be heated generates heat on their own.

So it allows rapid response. For examle, you can start and

stop the heating instantly. In addition, by the adjustment of

microwave output, you can control the amount of heat

energy generated inside the heated object. Therefore

as shown in Figure 13, you can instantly respond to the

temperature changes of the object to keep the temperature setting.

 

(5) Heating uniformity

Each part of the heated object generates heat, so even for those objects with complicated shape, it can be heated relatively uniform. To keep the heating unifomity, stirrer, turntable, and belt conveyor is used for heating blur related to wave length.

 

(6) Clean energy

Microwave doesn't require a medium, because it propagates only by changes of electric fields and magnetic fields. It can propagate in a vacuum. It reaches the object and penetrates without heating the air. The heated object genarates heat by absorbing microwave energy to convert it to heat energy. Therefore, it can be said as clean energy because it doesn't heat the air during process.

 

(7) Good operation and work environment

Conventional heating requires a heat source, and the temperature rises not only of heated object, but also of heat source and the heating furnace. So the temperature of room equiped heating furnace goes high because of radiant heat. This is a operation and work environment issue. On the other hand, microwave heating only uses electricity to generate heat of the object. The temperature of the object only rises, not the furnace. And there is no radiant heat, so it's possible to keep operational and good working environment.



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