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 Home Brew Forums > Microwave RIM system

01-11-2007, 01:55 PM   #21
zoebisch01
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Quote:
 Originally Posted by david_42 Second point: Is the oven you are thinking of using variable power or does it just cycle on-off? There are very few ovens out there that actually vary power levels, as it is an expensive process.

I think all of them are pretty much duty cycle 'variable' power, at least for the home consumer.
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01-11-2007, 03:55 PM   #22
brewman !
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"It would have to be food-grade, high temperature AND not absorb microwaves itself."

How about a plastic similar to a bowl you would heat soup up in... in a microwave ? Lets not make this more complicated than it is.

"So ... there is a difference between nuclear radiation and microwave radiation, and that does not mean that microwave radiation is safe! Sure the debate is out there regarding cell phones, but don't forget that cell phone only transmit a few watts of power versus the 1300W of power in your oven!"

Lets put some numbers to things. Lets say the power radiated out of the two holes is proportional to the hole surface area divided by the total surface area of the inside of the oven. Reasonable assumption ? Actually it will probably be less than that, because the water coils will absorb a most of the energy, but lets neglect that.

I just measured a microwave and it is 13.5" x 14" x 7.5". So the interior surface area is 2 x 13.5x14 + 2 x 7.5 x 14 + 2 x 7.5 x 13.5 = 790 in^2.

The area of our 2 holes is 2 x 0.375^2 pi/4 = 0.221in^2

So estimated radiated power would be 1300 watts x 0.221/790 = 0.3632 watts.

Now that assumes that the water doesn't absorb any of the microwave power leaving those holes.

"Also, water is a dielectric and not a 'perfect conductor' the way the mesh is in the faraday cage."

I never said that water was a perfect conductor ! Here is an absorption curve for water for various wavelengths. A household microwave runs at about 2.5 GHz. Its wavelength is about 300x10^6 / 2.5x10^9 = 8 cm

http://omlc.ogi.edu/spectra/water/gif/segelstein81.gif

"If you poke a couple of holes in your microwave oven, and 'fill' the holes with water, you attenuate the leakage, sure, but you are still going to have lots of leakage, and at that power level there can be health impacts over a period of time."

Do you have any math to prove this or is it just a wild guess ? Did you read all of the post and see that my approach would be to measure a few things as we went along ?

"And even if someone wants to debate the health impacts, the faraday cage is also there to keep the emissions below FCC requirements, so if you increase the emmisions you are actually breaking government regulations (the requirement is international...)"

Yeah, the FCC police are going to shut me down for radiating less power than a cell phone !

"If you put a metal coil inside the microwave oven, you will get some REALLY high potential (voltage) differences at various points around your setup, and you will have a REALLY cool light show due to all the breakdown and arcing. Remember what your mom always told you - don't put anything metal in the microwave!"

First of all, if you watch Mythbusters, you would find that not all metal objects arc. Secondly, if you looked at my illustration, it clearly labels the coil as PLASTIC !

"I do honestly enjoy and respect the ingenuity homebrewers show, but sometimes creativity can be dangerous. This is a really clever setup, but it is not worth the risk."

And you have made that determination how ? Did you do some math or experimentation ? Are you an expert in microwave radiation ?

"You'd be better off running a coil through a pot of hot/boiling water on a hot plate and controlling the heat that way."

Otherwise known as HERMS and if you look at my sig, you will see that I have a HERMS setup now. Or one could inject steam in the mash and if you look at my other posts you will see that I am working on that too.

"I think all of them are pretty much duty cycle 'variable' power, at least for the home consumer."

Did you follow the link I provided for the microwave ? The Panasonic models are called inverter microwaves and they modulate the power level of the microwave unit, not simply turn it on and off.

Are people out to constructively contribute to this idea or shoot it down outright ? Lets keep an open mind about things and quantify the risks before we get our panties in a knot.

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Last edited by brewman !; 01-11-2007 at 04:01 PM.

01-11-2007, 05:02 PM   #23
zoebisch01
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>>"I think all of them are pretty much duty cycle 'variable' power, at least for the home consumer."

Did you follow the link I provided for the microwave ? The Panasonic models are called inverter microwaves and they modulate the power level of the microwave unit, not simply turn it on and off. <<

No I didn't follow the link (well I did after reading this). I wasn't aware that companies had actually invested the time and money into producing a better microwave, I guess there are folks who actually cook food in them rather than reheating stuff (The only real reason to have a true variable power output vs. a duty cycle (label that ripoff))...Interesting.

>>Lets keep an open mind about things and quantify the risks before we get our panties in a knot.<<

I still say just stand far enough away

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01-11-2007, 05:07 PM   #24
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Would you still be able to pop corn in it?

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01-11-2007, 05:20 PM   #25
Tom Smith
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Brewman,
I appologize if I came off sounding confrontational. I certainly didn't mean to offend. It is an interesting idea, I wanted to highlight some things that some people may not be aware of.
You ask if I'm a microwave expert, and I have to say, humbly, yes. I design high power components for satellite systems, and have hardware on a large number of satellites ... I'm willing to bet that the episode of mythbusters that you were watching was actually streaming through my filters...
You would actually radiate more power than you think. Your formula for surface area would be true if the microwave were lined with a microwave absorber material, which it's not. A microwave oven is a resonant cavity, and poking a hole in it couples energy out in an inductive manner - you can go to http://www.microwaves101.com/ if your interested in learning more about it, but basically, if you have the microwave - iris - freespace system 'tuned' properly, you can actually get the 'full' 1300 W coming out (ignoring the wort/water/coils that we have inside). If you don't agree, think of the openning to get the power in - the surface area of the openning is much less than the microwave oven.
No, I didn't watch the mythbusters episode, but I'm sure they probably mentioned something about the shape of the object. But what they hopefully mentioned was that depending on the shape of the object, you would get standing waves on the surface which could set up some rather large potential differences from one surface to another.

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01-11-2007, 08:34 PM   #26
brewman !
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I'm busy with work things right now. I think I disagree with some of the points you make, but I'll have to check a few things before I say that.

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01-11-2007, 08:38 PM   #27
zoebisch01
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Quote:
 Originally Posted by Brewpastor Would you still be able to pop corn in it?

Shore! As long as you stand far away enough from it :P

In all seriousness, I admire brewman for always thinking of new ways of doing things. Engineers tend to immediately point out what is wrong with something and what the problems could be or are.
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Last edited by zoebisch01; 01-11-2007 at 08:46 PM.

01-11-2007, 09:13 PM   #28
Orfy
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There are three engineers in a car; an electrical engineer, a chemical engineer and a Microsoft engineer carpooling together on their way to work one Monday morning. Suddenly the car just stops. They pull over to the side of the road, and the three engineers look at each other wondering what could be wrong. The electrical engineer suggests stripping down the electronics of the car and trying to trace where a fault might have occurred. The chemical engineer, not knowing much about cars, suggests that maybe the fuel is becoming emulsified and getting blocked somewhere.
Then, the Microsoft engineer, not knowing much about anything, comes up with a suggestion, "Why don't we close all the windows, get out, get back in, open the windows again, and maybe then it'll work!?"
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01-11-2007, 09:25 PM   #29
Scalliwag
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I'm just hoping whoever tries this makes a video. Some guys on the hookah forum I frequent said they started natural coals in a microwave with great success. Others popped in and said that they tried it as well and it worked.
For giggles I decided to video tape it. Hopefully you guys get better results... no one or nothing gets hurt... and if it goes bad that at least it is funny

http://www.scalliwag.com/hookah/mwave/mwave01.wmv

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01-12-2007, 05:37 AM   #30
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*laughs. The coal video is funny. Was it actually arcing or was the coal wet and the microwave boiled the water in it and that split the coal apart ?

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