Skin Effect and Electroplating in Resistance Heating

Discussion in 'The Projects Forum' started by amspurge, Sep 9, 2016.

  1. amspurge

    Thread Starter Member

    Jan 15, 2016
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    Hello All,

    I have a resistance heating project where I'm using steel as the heating element and I'd like to find different ways of boosting the efficiency. I only need to have heat for a short amount of time (300F for 1.5s).

    Does anyone know if I would benefit from the skin effect by electroplating chrome or nickel on the surface of the steel? Would there be a greater flow of current at the surface (and more efficient heat generation) by using one of these platings? My goal is to generate as much heat as possible in the shortest amount of time with the least amount of current.

    Any advice would be great!
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    No, the skin effect won't help you. Plating is done with DC current.
     
  3. amspurge

    Thread Starter Member

    Jan 15, 2016
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    I'd like to know if the difference in the resistance of the skin (Nickel or Chrome) would improve efficiency. It doesn't have much to do with the plating process. My question concerns the resistance heating process.

    Edit: I want to know how the skin would effect the heating process. Basically, would a bare steel resistance heater perform better or worse than that same heater plated with a Nickel or Chrome skin?
     
  4. DickCappels

    Moderator

    Aug 21, 2008
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    Just to be clear, the term "skin effect" refers to the phenomenon in which high frequency currents to flow near the surface of conductors to a greater extent than through the center.

    Plating a highly conductive "skin" onto a low conductivity core could give you a higher resistance heater with improved heatsinking.

    Given optimised drive in both cases it would not affect efficiency much it at all because a watt is a watt no matter how you dissipate it.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Apparently your concept is employed in cookware for induction stoves. This patent seems right on point: https://www.google.ch/patents/US5770837 The "skin" is chosen to produce heat efficiently. The purpose of the middle layer (zinc and similar) is not described in great detail. It seems to be necessary to get the outer layer (e.g, steel) to adhere well to the aluminum inner layer.

    However, that begs your question. For just 300°F, it could be that a steel alloy is your best surface material because of its magnetic properties. This table from Wikipedia suggests that a 400 series stainless might work well:
    upload_2016-9-10_3-54-22.png

    I suspect a more thorough search might find a more common, but still highly desirable alloy.

    John

    Edit: You might consider plating with nickel instead of chrome,
     
    Last edited: Sep 10, 2016
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I agree with DickCappels. You end up with a different heater, but still need about the same input power for a given output power. Bear in mind that the higher the drive frequency the greater the likelihood of power losses due to parasitics and of generation of EM interference (which would need suppression). Because of those losses I suspect the overall system efficiency would actually decrease as frequency is increased.
     
  7. amspurge

    Thread Starter Member

    Jan 15, 2016
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    I think the difference in my heater is that it needs to get as hot as possible in the shortest amount of time (or the same amount of time with less current). If I could get to 300F in one second with a skin (Nickel or Chrome) as opposed to 1.5 seconds without a skin (steel only), that would be a big gain for me. If it were running continuously then I understand there would be little improvement.
     
  8. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    How much heat is produced depends only on the input power - element material, power frequency including DC, makes no matter.
    How quickly a particular temperature is reached depends only on input power, thermal mass, and any heat lossed while heating. Once again materials and frequency make no difference.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    @AlbertHall
    I don't think anyone here disagrees with that. However, efficiency can mean a lot of things other than its purely thermodynamic one. I assumed the TS had limited current from the oscillator, but the voltage could be increased. Therefore, increasing the skin resistance would allow more heat to be produced at the same current.

    Another approach is to confine the production of heat to a small area and let it spread to a much larger area by simple conduction. That approach is practiced for heating large pipelines were inductively heating the entire pipe is simply impractical.

    Perhaps the TS can clarify the former and give a little more insight as to why he needs such a relatively low temperature.

    John
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    As Albert says. So for a given input power, reducing the thermal mass of the heating element would reduce the heat-up time. Adding a layer to the element will increase the thermal mass; which isn't what you want.
     
  11. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Seems you are overlooking a fundamental physical property called thermal mass.

    The only way to get a mass to heat up faster with a fixed energy input is to reduce its mass. No change in surface coatings or frequency will change that fundamental value.

    Also.

    How are you generating as much heat as possible with a 300 F thermal limit? o_O

    Whats your method of heat transfer ( radiant, convection, conduction, other) and to what medium is it going into (gas , liquid, solid, other)? o_O
     
    Last edited: Sep 11, 2016
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