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Old   November 3, 2005, 13:20
Default Furnace wall heat exchange
  #1
Andrea
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I have to simulate a burner in a furnace. How I must set the boundary conditions on the furnace wall. In the reality, I have a wall of about 30mm in ceramic fiber. When I simulate, the furnace temperature is about 2500K, but in the reality I have 1250C.

Shell coduction? Temperature? Heat transfer? Help please!

Andrea
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Old   November 3, 2005, 13:45
Default Re: Furnace wall heat exchange
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Allan Walsh
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Many factors will influence the predicted temperature including fuel specification, way in which combustion is calculated, gas specific heat specification, etc.

But for the wall boundary condition, why don't you use a thin wall where you specify the outer wall temperature (i.e. side away from flame), the wall (ceramic fiber)thickness, and the wall thermal conductivity. I am assuming you are including radiation so you also need to specify the wall emissivity - you should be able to find something reasonable by Googling it.

Good luck.
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Old   November 4, 2005, 03:12
Default Re: Furnace wall heat exchange
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Andrea
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I don't use radiation. If it's wrong, how can I set the radiation?

Thx
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Old   November 4, 2005, 09:45
Default Re: Furnace wall heat exchange
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Mary
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??? Radiation is the most important mechanism of heat transfer in a furnace
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Old   November 4, 2005, 09:55
Default Re: Furnace wall heat exchange
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Andrea
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Please give me some advise
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Old   November 4, 2005, 14:57
Default Re: Furnace wall heat exchange
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Allan Walsh
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A good start would be to use the P1 radiation model. It is quite simple but robust. For your gas mixture, use the WSGGM-cell based approach for calculating the absorption coefficient. (This is quite easy in Fluent).

Try a wall emissivity of about 0.5, using the BC set-up I suggested earlier, and see what you get.
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Old   November 5, 2005, 04:00
Default Re: Furnace wall heat exchange
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Andrea
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You are very kind, I tried in your ways and it's ok! Another question: in the wall I used in the thermal conditions the mixed ones. Now, where I can find a good value of heat transfert coefficient and heat generation rate? And then, do I have to use shell conductions? What's the difference by using it or not?

Thx very much Andrea
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Old   November 7, 2005, 12:49
Default Re: Furnace wall heat exchange
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Allan Walsh
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You should be able to find the thermal conductivity quite easily for your insulation material from a text book, by googling it, or using an estimated value for a similar material.

There should not be any heat generation (or sink) in the wall - the heat release is in the furnace cavity.

Don't use the shell wall boundary condtion - this is for a heat exchanger. Just specify the outer (cooler) wall temperature, wall thickness, wall thermal conductivity, and let Fluent do the 1-dimensional calculation for wall temperature at the furnace side.
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Old   November 11, 2005, 04:37
Default Re: Furnace wall heat exchange
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Andrea
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In species transport (methane air 2 steps)if I define the mixture thermal conductivity & viscosity as "ideal-gas mixing-law", what must I set in the thermal cond. & viscosity of each fluid (CO,CO2,AIR...)

Thx Andrea

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