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Re: Heat Flow Rate Across/Through Steel

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Mcsherrygp(--nospam--at)aol.com wrote:
> 
> Does anyone know what the heat flow rate across/through steel is?
> 
> We are applying a small amount of fillet weld to a grade A36 steel plate and
> we are concerned about the temperature of the opposite face of the plate.  All
> of the variables for conduction are known to determine the opposite wall face
> temperature.  We need to know the heat flow rate through steel (if there is a
> constant value for a particular grade).
> 
> Thank you.
> 
> John Carroll
> Structural Engineer
> The McSherry Group, Inc.
> 


The conductivity of steel is about 25 Btu/hr/ft./F at 572 Deg. F.  It 
veries slightly with temperature and alloy but could be considered 
constant for your purposes.

Which leads me to explain that you can't get the answer you want from 
just this value.  First of all this is really a transient problem (not 
steady state) because it takes time for temperature to travel to the 
surface in question and the time it takes is a function of the heat 
applied to the metal, the temperature at which the heat is applied, the 
mass of the metal, the distance through the metal the temperature 
gradient will occur and the boundary conditions of the metal.  ie the 
amount of heat that can be carried away to other sources such as exposed 
surface to air.  You could try to solve this using a steady state 
solution technique (assume the heat is applied until the model reaches 
steady state) which won't give you a very good answer.  Transient heat 
transfer problems of this type are difficult to solve, require a computer 
model, and would yeild results that would reflect more on the model than 
on your situation.  

You might take a good look at what you are trying to do and if the path 
length between applied heat and surface that should remain cool is short 
and the weld time long then you might be in trouble.  You could try a 
test in the shop.

David Carpenter