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Old   November 8, 2005, 13:37
Default Flame thickness
  #1
John.
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Hi all,

I am wondering how I can calculate the laminar flame thickness of a flame. The equation is as follows:

delta= (Heat diffusion coefficient)/ (density*Cp*Laminar burning velocity).

Now, how do I get the values of the heat diffusion coefficient and Cp for a given mixture, say methane/air premixed?

Any other equations/correlations which can help would also be of use.

Any help would be appreciated.

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Old   November 8, 2005, 15:38
Default Re: Flame thickness
  #2
Guillaume
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You have to use the kinetic theory of complex mixture for that.

However, the formula you give is an order of magnitude. It may be different by a factor of 3 or even 5 (see Zeld'ovitch / Frank-Kamenetskii --ZFK -- theory). Hence, you can consider that premixed CH4 / Air has the same properties than Air, since CH4 is diluted. Any Handbook can give what you want for Air.
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Old   November 8, 2005, 16:45
Default Re: Flame thickness
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martin
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you can use the properties of air for cp and K however for the density, it is the density of the unburned fuel, this density should be evaluated at the average temperature ( Tb + Tu ) / 2

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Old   November 9, 2005, 08:09
Default Re: Flame thickness
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John.
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Hi Martin,

I thought the density was the density of the unbrnt mixture rather than the unburnt fuel (CH4)? Also, why at the average temperature? Is this related to the idea of using the gradient of the temperature to give the flame thickness?

Thanks.

John.
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