[TheForge] Chip forge

[Steve Smith]

I could be completely off base here, but why does the surface area 
matter in radiative transfer? If the chips are all pretty much at the 
same temperature, isn't the steel already getting its max radiation, 
regardless of the chip surface area? Isn't the air (whatever) itself 
between chips radiating at the same temp as the chips? I think the steel 
is already getting the max IR since it is completely surrounded by a 
constant temperature environment.

An isolated chip is going to radiate heat away faster if it has larger 
surface area, but that's not what we've got.

Now I do think that chip shape is pretty important. Chip size and shape 
determines how well the flame flows through them and heats them. You 
might want lighter, smaller chips for small pieces of work, but lighter 
chips are probably more fragile too.

I may have to build one of these forges, sounds pretty decent.

Steve

Jerry Frost wrote:

> Yes, radiative heat transfer is what's happening along with a very small 
> percentage of conduction.
> 
> Least first. Conduction is dependant on physical contact, there'll be 
> little actual physical contact between the chips and work so it's not 
> much of a factor.
> 
> I suppose if you used a small gradation of chips, say passing a -20 
> seive, conduction would become the significant transfer. (vehicle?) The 
> problem with using fines as chips is forcing the flame through it 
> without blowing it out of the forge. Not impossible I supppose but I'll 
> bet it'd be really finicky to set up and use. Every time you put a piece 
> of steel in it it'd change the flow patterns and some media would fall 
> out of suspension and some would get blown out of the fire.
> 
> Radiation on the other hand is what's going to do all the serious work 
> and surface area really matters. IR is radiated from the surface only so 
> the higher the ratio of surface area to volume the faster the IR radiates.
> 
> I don't know the mechanics of how the media will pick up heat from the 
> flame but convection doesn't enter into it. The flame is being forced 
> through the media rather than circulating via convection. What I do know 
> is the media picks up heat from contact with the flame or it's radiated 
> IR, so the higher the ratio of surface area to volume the faster heat 
> will transfer.
> 
> I would not use different sizes of chip as they'll fill in gaps and make 
> it less flame flow friendly. My experiments will be with 1/4"-1/2" size 
> chips.
> 
> I got to thinking about chips again this morning over coffee and think 
> if I punch a hole through slightly rounded cubes I'll get much better 
> heat transfer rates. The chips will also be lighter and easier on the work.
> 
> Frosty
> -------------------------------
> If it ain't forged
> it ain't real.
> Wrought iron is.
> The FrostWorks
> 
> Meadow Lakes, AK.
> 
> http://www.artmetalradio.com/
> 
> From: "Steve Smith" <sos at alum.mit.edu>
> 
> 
>>
>>
>>
>> Frosty, I've always heard that at these temps heat transfer was mostly 
>> radiative. Now that may be in relation to convection rather than 
>> conduction, I don't know. If it is radiative, shape and surface area 
>> doesn't matter (to heat transfer). I think maybe some experimentation 
>> is in order (not that I'll actually manage any...).
>>
>> Steve
> 
> 
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