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Microwave heating

  1. Feb 9, 2005 #1
    I'm currently sitting in a very cold room, it's cold because heating costs too much darn money (we haven't got central heating:(). Well, this got me thinking over cheap ways to heat a room. The idea of heating air with microwaves struck me being really cheap and effiecient. But it's so obvious, I thought, that it should be common place. Why isn't it? Is there a reason why the technology of microwave ovens can't be turned to heating nitrogen in air, or water in central heating pipes, immersion heaters, or a kettle even? (and yes, I know about the superheating problem, but this seems easy enough to overcome)

    The only applications I've seen on the net are industrial, but how easy would it be to scale these processes down? I'm left thinking that it's possible, but maybe copyrights are getting in the way of it being used.
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  3. Feb 9, 2005 #2


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    So you feel a blast of hot air coming out of the microwave every time you open it? No?? Microwaves are tuned to heat up water, not air.
  4. Feb 9, 2005 #3
    Yes, but as I understand it, it is the frequency of the microwave that is tuned to h2o in ovens. Industrial microwave heaters can be set up to heat other materials by changing the frequency to it's resonant freq. [afaik:)]

    Why not tune to nitrogen or oxygen or co2 if that's the case?

    Also, even if it can only do water, then why not water in central heating or powershowers? Why can't I take the prehistoric 3kw electric element out of the immersion heater and replace it with an 0.5kw immersable microwave generator that's twice as fast?
    Last edited: Feb 9, 2005
  5. Feb 9, 2005 #4
    the effiecency of a heater is 100% already...... what is the point of microwave heating air????
  6. Feb 9, 2005 #5


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    Micro waves heat water by inducing molecular level vibrations, this energy is transfered to Kinetic energy during collisions with other water molecules. So one thought would be that in a gas this type of mechanism would not be as efficient due to the lower frequency of molecule to molecule collisions.

    You need to know the bond length of O2 and N2 to find the frequency needed to induce intra molecular vibrations. Is this frequency in the microwave range?

    I don't know the answers off the top of my head. If you can answer those questions you may be able to discover if your concept is viable.
  7. Feb 9, 2005 #6
    Not entirely true I'd say, heaters lose energy to light in some cases. Those that are fairly efficient (electric oil filled radiators) spend a good deal of energy heating the oil first, microwaves are direct. Probably only IR heaters approach 100% efficient, and they are expensive (and overkill for domestic use).

    Central heating though, is at best (ie condensing boilers) only 85% efficient, surely direct microwave heating would be better in this case?
    Last edited: Feb 9, 2005
  8. Feb 9, 2005 #7
    This would not be a good idea. Exposure to microwaves tend to cause sterility and cataracts. Probably not something you want to be pervasive in your home.
  9. Feb 10, 2005 #8
  10. Feb 10, 2005 #9


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    I'm getting images of those old ladies who put their pet cat into their microwave oven to warm them up...
  11. Feb 10, 2005 #10


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    Light is just high frequency heat. And as long as it stays in the room, the heat stays there as well (the light gets absorbed by the walls, turning it to heat). Yes, all forms of electric heat are about (at least - heat pumps are more) 100% efficient.
    Well, boilers use gas or oil - they have hot exhaust, which is hot air being blown out the top. That's where the 85% efficiency comes from. 100% efficiency applies to electric only. The reason they are cheaper is simply a matter of the economics of the fuel.

    Now infrared and microwave heating would have an advantage over other forms: they do not require heating the air. This is why at some restaraunts and driving ranges, they use infrared (also, its actually illegal to use conventional heat outside) - you can heat people directly, reasonably inexpensively. But I wouldn't want to risk using microwaves.
  12. Feb 10, 2005 #11
    Ok, well, some of you got the impression that I meant to open the door of a microwave, break the safety latch and switch on... That's not quite what I meant. Obviously the microwave generator would have to be inside a metal box, with diffraction gratings top and bottom to allow air to convect up and out (drawing more air in as it does).

    However, looking into it more, I found that what Integral said was true, that microwaves only heat water, or hydrogen bonded molecules(fats etc) from what I can tell.
    So thanks for the info guys, I'll put this idea to bed.

    However, heating the water in central heating pipes or immersion heaters still seems feasible. Industrial units that do similar jobs can raise the temperate of liquids from 30c to 200+c in a high flow rate system, with only a few feet of exposure, ie in a matter of seconds. These are 100Kw systems tho, but I would still think that, when scaled down, this method would be more effecient that electric heater coils which require direct contact with water and can only heat the water they touch. It requires convection to take the heat away from the coil, where as microwave can heat it a)quicker and b) evenly.
    Last edited: Feb 10, 2005
  13. Feb 10, 2005 #12


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    Actually he might be on to something.

    The only problem is, as Integral stated, you will need to know the frequency of O2-N2 oscillation, and plus this is extremely inefficient for gases. Your best bet is to heat water in a large pipe which lays on the bottom of a floor, with microwaving equipment at 2 ends, shielded and outside of the domestic area preferrably.

    Another thing is - will it be efficient at all?? Your idea seems viable but the engineering aspect of such an enclosed container with all the microwaves propagating at water under pressure is hard to accomplish safely.

    Edit: you edited it! :grumpy:
  14. Feb 10, 2005 #13
    (the edit was only for typos:))

    Safety is quite easy to accomplish. The industrial system uses a teflon pipe, which is transparent to MW, and pumps the water through a focused microwave beam.
    It's a powerful system (and heavily copyright by the look) and it says somewhere on that site it is slightly less efficent that trandition heating, but benefits from smooth heating gradients. But that system is constantly on, ie its constantly heating cold liquid. Whereas a domestic system is sealed (more-or-less), and the benefit would be that microwave heating would be faster, so cost less in way of kwh that traditional heating, maybe:confused:

    Edit: I said the site says it's less effecient, but that not quite the case.
    I understand tho, that it's a corporate site, so is purposely vague and defence about mw heating.
    Last edited: Feb 10, 2005
  15. Feb 10, 2005 #14


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    A reasonable question to ask is how efficient is the process of creating Microwaves? This is a fair amount of heat generated behind a working microwave, this is all wasted energy. You may want to reseach the effeciancy of a microwave magnetron.
  16. Feb 10, 2005 #15
    Haha, yet again, spot on with your advice, thanks Integral. This from wikipedia.
    That incredibly ineficiant if you ask me, they should design a better one. :devil:
  17. Jul 27, 2005 #16
    Hi, I would be very interested in using microwaves to heat the water for my central heating system. I wou think that the energy consumption should be less because the heating time would be reduced. Even if a part transmitted directly as heat and not as microwave energy would not be a big problem as we could also use this heat to haet up the water for my centrel heating system. I popped a question for information at the webadress I found above. waiting for the answer. Will keep you posted.

  18. Jul 27, 2005 #17
    Hmm, heating up the air seems terribly ineffecient... I think I'll design a microwave heater tuned to h2o frequency that skips the middle man and heats up the people in the room directly. :biggrin: :biggrin:
  19. Jul 27, 2005 #18


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    Microwaves are bad for our bodies. They are so bad, they are being developed as weapons by the US military. It was a secret for a long time and soon to go into the field for the first time.
  20. Jul 27, 2005 #19
    As far as I know, microwaves don't ionize human tissue, only heat it up, so the most damage you can sustain is being cooked.
  21. Jul 28, 2005 #20


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    They're also so bad for our bodies that they're being used for mobile telecommunications all around the world. :tongue:
  22. Jul 28, 2005 #21


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    I have heard from my colleagues who served in the Navy, that sailors who stood watch on ships at sea would stand in front of the radar units because it would keep them warm during the night watch. It gets quite cool on the ocean at night.

    As far as I know, there have been no reports of ill effects from being warmed by microwaves, but perhaps no one has bothered to investigate.

    That may depend on energy density. Certainly if one heats a body (particularly brain) above 104°F (40°C), which is considered a high fever, some organ (cell) damage will occur. Much hotter and significant cell death occurs.
    Last edited: Jul 28, 2005
  23. Jul 28, 2005 #22


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    You are probably talking about the not-very-well known "Active Denial" project, sometimes nicknamed the "pain ray"

    see for instance

    http://www.afrlhorizons.com/Briefs/Sept01/DE0101.html [Broken]

    The effect is due entirely to heating of the skin, due to what is known as the "skin effect".

    The nerve endings present in people's skin make them feel like they are being burned alive, but the beam does not have any known adverse effects.

    One might think of this technology as somewhat Orwellian, but it does not demonstrate any unknown effect of non-ionizing radiation on humans or animals.

    Last I heard, other than heating, there was some concern that pulsed microwave/radio energy could affect the calcium ion reflex. These are the only two known and replicable biological effects of non-ionizing radio/microwaves on animals or humans.
    Last edited by a moderator: May 2, 2017
  24. Jul 28, 2005 #23
    1) There is always a suggestion in these microwave threads that cooking microwaves are tuned to a specific frequency water atoms have a mode at. This is not really the case. Home microwaves are tuned closely to a rotational mode (not vibrational, as someone might misinterpret integrals post as suggesting), but this has little affect on liquid water. Heat generated by your microwave is largely due to the resistance encountered by electrical currents that travel in the materials inside. You could alter the frequency greatly and still get a very similar result.

    This is an interesting issue because it is almost always physicists who make the above claim about microwaves being tuned to a mode, but it has been well documented in chemistry that this is just not the case.

    2) Light is not "high energy heat." That just makes no sense at all.

    3) The word "microwaves" is generally used to specify a very wide range of frequencies. Government programs that use "microwaves" are in the very top of the frequency you might call that. In fact, I wouldn't even call them "micro"waves. There is a great deal of argument over how safe these are in crowd control, and you can expect problems to arise from their use.

    The lower frequency regimes of microwave light are very bad for the human body. They tend to heat soft tissue deep in the body; the brain, eyes and genitals are often affected. What frequency navy radar is at I don't know, but we are very careful with our 915mhz generator (generally operated between 3kw and 9kw) due to safety concerns.
  25. Jul 29, 2005 #24


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    For a realistic view of the hazzards, take a look at the FCC publication


    which also includes current regulatory standards.

    Microwaves are not in general "very bad", and are even used in medical treatments to help patients suffering from exposure and low body temperature (diathermy) by heating them up.

    Heating effects *can* cause problems if too much heat is delivered, the eyes and genitals are particularly suspectible. The effects on the genitals are temporary, however - sperm do not like warm temperatures, but new sperm are constantly being produced.

    *very* high levels of microwaves can cause problems with cataracts. Most of the body is well-cooled by it's blood supply, the lens of the eye is an exception.

    What is *very bad* is ionizing radiation. Ionizing radiation should not be confused with non-ionizing radiation like microwaves.
    Last edited by a moderator: Apr 21, 2017
  26. Sep 24, 2005 #25
    Does Anyone Know Anything About This Product ?

    This is an article from 2003 and I was wondering if anyone had any experience with this type of equipment?

    Web Exclusive--Electro Silica Announces New Water Heating Systems

    Electro Silica has developed a new technology for heating and purifying water.
    Electro Silica has announced that it has developed a new way for heating and purifying water. The company applies a new technology to water treatment, offering an

    efficient water heater powered by a clean and renewable energy. It offers the ability to save water and energy using microwave technology.

    How Do Microwave Water Heating Systems Work?

    Mains water enters into the Electro Silica boiler as the user requires. The heating system will be controlled by taps, heating timing devices, or the demands of an industrial process. As a demand for water is made, the magnetron fires up and bombards it with microwaves. These microwaves excite the water molecules, providing heat to the required temperature. Water exits the unit into either the heating system or the hot water pipes.

    The Chamber Design Is the Difference
    The microwave continuous flow and linear water heater consists of a closed chamber into which microwaves at a frequency of 2,450 mhz are introduced via magnetrons. The water heater is characterized by a chamber of the truncated conical section with a concave base of stainless steel, wherein no adjacent sections are at right angles, thus preventing generation of refraction and diffraction waves.The base of the chamber serves as a reflecting dish to direct energy towards the silica-based flexible coil disposed against the chamber wall. The coil is a spiral led inside the chamber and is terminated to inlet and outlet glands. These allow for a continuous flow of water to pass through the coil in any direction, depending upon the application and/or the plumbing arrangements in which it is being used.

    How Safe Is Electro Silica?
    The water heater produces fewer emissions than a microwave oven or even a mobile phone, with no risks of explosions or carbon monoxide. It is equipped with a heating automatic control system, water temperature and level display, and temperature automatic control.

    http://www.pmengineer.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2732,96706,00.html [Broken]
    Last edited by a moderator: May 2, 2017
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