Microwave Drying Device 2

[Subcooled]

I've been asked to develop a microwave drying device that is rolled over a large surface of material. Is this feaseable or will stray microwaves cause problems?

 

[Comcokid]

Your post reminded me of a recent article that appeared in the Microwave Journal October 2005, "An Improved Microwave Weed Killer". Your short post sounds like you're looking for something just like the contraption these researchers built. They used some metal plates and carefully placed chokes to supress the TE/TM in unwanted directions.

This article shows them keeping a distance of about 6 meters from the device which rides over the ground at about 10 cm.

I remember this article because it made me laugh and think of a recent episode of the show "Myth Busters" where they tried to wire several magnetrons together to get more power. I just hope no teenagers come across this article. I remember the crazy things I tried when I was that age!

 

[Subcooled]

Thank you Comcokid. I've been asked to investigate the feaseability of a concept, before proceeding to budgetary costs of a prototype. Any further information from others is still appreciated.

 

[biff44]

Some microwave heaters and dryers are developed already. Don't know how practical. Patent 5085527, 4347016 etc. Outdoor uses, like paving roads, etc.

 

[zeitghost]

I worked very briefly for a chap who had the idea of a microwave clothes dryer / clothes press.

Don't know if he ever got anywhere with it.

 

[Subcooled]

Comcokid; The article was very informative. This is basically what we have in mind. Power requirements should be less, approximately 1.5 to 2.5kW. Safety of the device is of concern, so those are the issues I'm working through. Could an inner shell house and transmit the microwave energy and an outer shell serve as a dummy load for stray energy?

 

[Comcokid]

I'm not a high power microwave or waveguide person. Everything I do is at 20 dBm (100 milliwatts) or less. I just know that there are companies that make industrial microwave conveyor-type ovens and dryers (a goolge search you might also try). The article was a recent one I just happened to remember seeing.

 

[Higgler]

A friend of mine did similar at a paper mill. They needed to dry ?3 foot wide x 80 feet long paper going into rolls. He made a high power Colpitts oscillator source and created a metal waveguide around the paper having two slits on either end. I believe it's a standard item.

I've also seen Microwave termite exterminators in my area (Santa Barbara). I believe he uses 2 microwave oven sources and has two waveguide horns that he places against the wood to overheat those pesky termites.


You will have FCC problems if you don't contain the RF. Also, any operator getting a headache can sue you for illegal emissions. If you can put your material inside a metal box similar to the paper drying mechanism, that would help alot. Use a microwave oven (taken apart) as a source, attach it to the box. Microwave ovens come with probes that could couple into the box easily.

kch

 

[Subcooled]

Higgler; We will probably enlist the services of an expert to insure that the device is safe and effective. There are several companies online that provide design and testing of industrial microwave heating systems. If you are familiar with someone through your work, we would appreciate the information. Just let me know, yes or no. If it is yes, post their URL.

 

[Higgler]

My friend was just an engineer. This is not a firm I referred to.

I read the article, that must have huge leakage when used in the photo showing the guy controlling the unit. I don't suggest doing similar unless you make your own sealed RF chamber.

I suggest something like using a microwave oven, most have rf coming out of the side wall vertically polarized. Cut a thin vertical slit in the wall opposite the source power. Have the paper feed thru this slit into the oven Have it wrap around a vertically oriented low loss dielectric tube (you'd have to install that), then back out the same slit opening. The RF will dry it as it moves towards and away from the source. To reduce leakage out this slit (from crosspole energy), add an extension to the slit (essentially a piece of flat waveguide, say 5-20 inches long (the longer the better for leakage suppression), as wide as your vertical slit, and narrow enough to fit some Magnetically resonant absorber inside and have the paper come thru.

I've done a similar thing winside a microwave oven whereby I had a waveguide to coax transition inside sitting atop a water filled tupperware. A coax attached to the waveguide transtion funnelled rf out the modified door (I added a bulkhead N-f to N-f adapter to the door to get the rf out). We didn't have any arcing problems and now had a cheap variable power RF source.


kch