Induction Cooking, skin effect, hysteresis losses

Discussion in 'Physics' started by yoamocuy, Nov 21, 2011.

  1. yoamocuy

    Thread Starter Active Member

    Oct 7, 2009
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    I've been looking into the induction heating a bit lately and have come up with a few questions.

    One is in regards to hysteresis losses. I know what hysteresis is and how it contributes to the heat generation, but how much of an effect does it actually have? Some articles I've read have said that it is the main source of heat generation while others have said it accounts for less than 10% of the heat used in the induction cooking process.

    My second question is in regards to skin effect. I understand that skin effect relates to the heat produced by eddy currents, and that you want a small skin effect Also, skin effect is a function of permeability, frequency, and conductivity. Aluminum has a lower permeability than ferromagnetic materials, so if one were to increase the operating frequency to account for the lower permeability of aluminum, would it be possible to generate a large amount of heat in aluminum cookware?
     
  2. SPQR

    Member

    Nov 4, 2011
    379
    48
    HERE's a nice Wiki on induction heating which describes the two mechanisms:
    1 - Joule heating
    2 - hysteresis loses

    I'll leave your second question to our metallurgists.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,429
    3,360
    I cannot answer your questions but we do have a new induction cooking stove.
    AFAIK, you cannot use aluminum cookware. We had to replace all of our previous pots and pans. We have found the induction cooking elements to be very effective and fast heating. It takes some getting use to since you can easily burn what you are cooking if you do not turn down the power level.

    The oven is a convection oven and we (the cook in the family) are extremely happy with both stove top and oven.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    First of all, you will probably get better answers in a dedicated physics forum.

    You are right, informations on the internet are incoherent.
    AFAIK all metals/conductive materials can be heated by this method. Depending on the metals characteristics different mechanism take place.

    For ferromagnetic materials friction caused by reorientation of the magnetic domains seems to be a major contributor to heating. This works for temperatures lower than the Curie temperature.

    For other metals it's eddy currents. The lower the electrical resistance of the metal the more difficult it will be to heat it up with a given power. I would guess you are right about a frequency increase to cause more heat, but the higher the frequency the more the heating will take place near the surface, as penetration depth will decrease due to the skin effect. There is probably for every workpiece a certain frequency that works best...

    Induction oven frequency and power for cooking was chosen as to work best with a thin layer of a ferromagnetic material, the cookware.

    Multilayer cookware has aluminium inside for better heat transfer.

    There are several DIY project sites/physics forums that will give you more in depth information about the physical principals.

    Since you are talking about induction heating of a non-ferromagnetic material you could also google for publications about non-destructive technologies measurement methods, they employ eddy currents too and I suppose heating of the object to be examined is not desirable.
     
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