RF Dielectric Heater circuit design

[arunachalam]

I am interested in RF Dielectric Heater circuit design with following specifications:
6 MHz to 15 MHz
10KW.
The application is to dry farm products.
Though I am microcontroller programmer, I am not Power / RF Signal designer.
I searched on internet but I am not able to verify if the resources fit to my requirement.
Any lead?

 

[dick_freebird]

Such a heater would depend on the dielectric loss
@ frequency of the material. Milk or cheese may or
may not have an absorption peak in the stated
frequency band, and the exact frequency center
of that peak (if any) is important.

I'd begin with chasing down references on that
(RF absorption properties of dairy products) and
then worry about getting the correct frequency
and power out of some black box or other. If there
is no strong peak then another heating method
may be a better bet.

I imagine there will be other interests such as
sample agitation, etc. - like in a microwave oven
(which works on water's absorption peak in the
2GHz range), absorption occurs preferentially at
the outer surfaces and attenuates the energy
available to the interior. 10kW might just give you
a crispy shell around cold glop (or something).
Maybe applying power offset from frequency peak
could produce a more uniform heating, but that
too wants some checking of present art.

 

[arunachalam]

Such a heater would depend on the dielectric loss
@ frequency of the material. Milk or cheese may or
may not have an absorption peak in the stated
frequency band, and the exact frequency center
of that peak (if any) is important.

I'd begin with chasing down references on that
(RF absorption properties of dairy products) and
then worry about getting the correct frequency
and power out of some black box or other. If there
is no strong peak then another heating method
may be a better bet.

I imagine there will be other interests such as
sample agitation, etc. - like in a microwave oven
(which works on water's absorption peak in the
2GHz range), absorption occurs preferentially at
the outer surfaces and attenuates the energy
available to the interior. 10kW might just give you
a crispy shell around cold glop (or something).
Maybe applying power offset from frequency peak
could produce a more uniform heating, but that
too wants some checking of present art.

Thank you !
Target material are mostly herbs grown in our area used mainly for Indian traditional medicinal purposes like Ayrveda and Siddha medicines.
Trial material would be broken coconut with shell to be dried to become copra. Coconut has more than 40% moisture. Copra normally has a residual moisture of around 7%.

Hope this clarifies concerns about the material to be heated or more precisely, dried.

Other heating methods may lead to loss of nutrients in the herbs when compared to RF method. Other advantages could be like higher power efficiency.

What I learn from internet is dielectric heater is made of two plates and does not require any movement of material like agitation or rotation as in microwave oven because RF gives uniform heating - microwave heating pattern follows the waveform.

More than 20KW should be a concern as it would increase investment and cost of production.
Government / local body restriction is key issue about the frequency. I read that 10MHz to 100MHz is ideal for heating and below 6-15MHz is not restricted. I am open about a particular frequency unless using it is restricted.

Here is a video that used triode valve:

 

[KlausST]

Other heating methods may lead to loss of nutrients in the herbs when compared to RF method.

Why? Both use heat. Heat is heat. Temperature is temperature.

In opposite some say that microwave ovens "harm" nutritients. I can't say whether one of the statements is true or not.

I'm no specialist in this area ... but in my opinion the lower the temperature the less harmful.
So vacuum drying at room temperature or freeze drying should be rather optimal.
But I'm curious to learn..

Klaus

 

[arunachalam]

If there
is no strong peak then another heating method
may be a better bet.

I tried to say RF Dielectric Heating is what I am interested in for various reasons.

but in my opinion the lower the temperature the less harmful.

Agree.

I am going to try one by one like RF Dielectric, Vacuum & Freeze drying methods for efficiency, investments and cost.

So I hope we would continue with RF Dielectric now.

 

[KlausST]

I am going to try one by one like RF Dielectric...

use perforated metal plates for the capacitors ... for the humidity to pass..
air flow should support drying process.

Klaus

 

[ZASto]

The best method for preserving nutrients is freeze drying, but it is less economical method, very energy demanding.
Freeze drying method is known as lyophilisation.

 

[arunachalam]

Thank you all for the leads.

These could be interesting reads: NXP has RF Modules and Goji has RF Oven:

http://www.nxp.com/products/rf/rf-power/rf-cooking:RF-COOKING

RF cooking with Goji

Make food better with Goji technology. Our pioneering RF solid-state cooking technology enables healthier, tastier, faster and simpler food preparation.

www.gojifoodsolutions.com

If I try NXP solution, I would post the results here.