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nichrome wire insulation

Discussion in 'Electronic Design' started by [email protected], Feb 16, 2008.

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  1. Guest

    I am building a compact air heater as a hobby project where the air is
    blown between fine fins of several aluminum heat sinks. The
    temperature needs to be raised from ~0C to ~37C and needs to handle
    air flows of up to ~100 L/min. I did an envelope calculation taking
    into account heat capacity of dry air, and it appears that I would
    need ~100W, 300W to be safe, for that.

    So I want to run a nichrome wire in a spiral pattern along the surface
    of the aluminum heat sinks. But wouldn't that cause a short? Can I get
    insulated nichrome which would conduct heat, but not conduct
    electricity? Any suggestions?
     
  2. JeffM

    JeffM Guest

  3. Guest

  4. JeffM

    JeffM Guest

  5. John Larkin

    John Larkin Guest


    Why use a heat sink? The nichrome will heat air all by itself.

    John
     
  6. Guest

    It will, but I wanted to increase the surface contact area.
     
  7. Phil Allison

    Phil Allison Guest


    ** No good reason exists to do that.

    You are totally clueless.




    ........ Phil
     
  8. Phil Allison

    Phil Allison Guest


    ** Yep - buy a few of these:

    http://au.farnell.com/jsp/Passive+C...splayProduct.jsp?sku=9508317&_requestid=94795

    A totally stupid WOFTAM just to heat some air.



    ........ Phil
     
  9. Guest

    You might look for "water glass". It's a silicon compound (???) that's
    water soluble. Evidently, it is used as an electrical insulator at hi
    temperatures.

    Hul
     
  10. Guest

    Perhaps. But this is how we learn.

    The resistor idea by itself - would not work. The more surface there
    is in contact with air of unit volume per unit time, the faster the
    heat transfer, isn't it? Yes, I can run the heat wire in a complex 3D
    spiral pattern to get the same contact surface. But running a wire in
    a spiral on the base of a heat sink and have the fins take care of the
    3D makes more sense. Just some clueless thoughts.
     
  11. John Larkin

    John Larkin Guest

    No. Adding the thermal mass of the heat sinks would substantially slow
    things down.

    Using a heatsink might make sense if you need non-stratified heating
    (not guaranteed *with* a heatsink, and do-able other ways anyhow) or
    if you want to avoid scorching dust particles in the air.

    What are you trying to do?

    John
     
  12. Tom Bruhns

    Tom Bruhns Guest

    For very little cash outlay, you can go buy a hair dryer that has the
    fan and a (presumably) safe heating element, all in one compact case.
    I'd guess the fans in those are capable of providing your desired 100
    L/min airflow.

    If you INSIST on using a heatsink, why not just mount two or three
    cheap power semiconductors to it and use them to generate the heat?
    This is done in some crystal ovens. Or get some of the power
    resistors designed to mount to heat spreaders. Caddock and others
    make them in cases similar to power semiconductors, or you can find
    ones in aluminum cases with a flat side and mounting holes that bolt
    easily to a heatsink. Another alternative would be something like a
    hot water tank heater of the sort that's a metal tube bent in a tight
    "U" shape with terminals at one end. The tube is already insulated
    from the heating element. They are typically rated a couple kilowatts
    or more, but that's in water for cooling; if you control the power so
    the case doesn't get too hot you should be OK. You're still left with
    the problem of getting it to make good thermal contact with the heat
    sink. -- But as others have pointed out, you can make nichrome wire
    hot enough that it will have no trouble getting rid of the heat you
    want just into the forced airstream, as is done in a hair dryer (or,
    alternatively, a heat gun; Harbor Freight has one on sale at the
    moment for under $10).

    Or, go get one or two tubular ceramic-core 200W resistors and arrange
    a fan to blow through their open centers. Since they are designed to
    dissipate 200 watts in free air, you should be able to use just one to
    get the effect you want, keeping it a bit cooler by blowing air
    through it.

    In short, don't mess with trying to use nichrome wire directly; use a
    heating source someone else has already done for you. It will be
    cheaper and much safer in the long run. (Though there are still
    plenty of ways you can make it un-safe, of course.)

    Cheers,
    Tom
     
  13. Guest

    I am blowing cold air with an air pump through a tube of ~ 2 inch
    cross section. The air needs to come out of the tube heated. The tube
    needs to be as short as possible. The simplest design is to run a wire
    around the tube's wall and make the tube heat conducting (e.g. Al).
    But I figured I could heat the air more efficiently if there are fine
    metal fins across the tube's cross-section to expose as much surface
    of the heating element to the air as possible inside the tube. This is
    where the "heat sink" came from - it works not as a "sink" per se, but
    as a heat exchanger. Heat sinks happen to be easily accessible and
    have a large surface which I can use experiments
     
  14. Phil Allison

    Phil Allison Guest


    ** One learns by thinking and asking the right questions.

    But that don't work for arrogant fuckwits with no brain like YOU.


    ** You are one dumbfuck, oversnipping ASSHOLE !!

    The 50 watt metal clad resistors are DESIGNED to be bolted to a heatsink! !!

    http://au.farnell.com/jsp/Passive+C...splayProduct.jsp?sku=9508317&_requestid=94795



    ** Run the wire hot enough and heat transfers to the air fantastically
    well.

    How all fan driven room heaters work.



    ....... Phil
     
  15. Guest

    Thank you, Tom,

    What I have described probably indeed looks like a hairdrier. However,
    hairdriers quickly heat air in a small package because of heating the
    wire to a very hot temperature (don't know how hot, but the wire glows
    with infrared). In my case, I want to avoid using high localized
    temperatures due to safety concerns. So the idea was to re-distribute
    the heat over a large surface, and thus being able to use lower
    temperatures.
     
  16. Guest

    ** Run the wire hot enough and heat transfers to the air
    fantastically

    I just have explained why I do not want that.
     
  17. Guest

    ..
     
  18. Phil Allison

    Phil Allison Guest



    ** I have already described how to do that ( with a link to the needed
    power resistors) with complete safety.

    LEARN to READ - you

    FUCKING

    OVERSNIPPING

    GOOGLE GROPING

    PITA !!!




    ......... Phil
     
  19. D from BC

    D from BC Guest

    Ohhhh ...I get it. It's hair dryer design.. :p


    D from BC
    British Columbia
    Canada.
     
  20. Guest

    ..
     
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