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Heat Transfer Across Simple Block

Heat Transfer Across Simple Block

Heat Transfer Across Simple Block

(OP)
Hi,

It has been far too long since my heat transfer class in college and I am struggling to do a simple (I think?) problem.  Basically I have 3 materials sandwiched together:

1. A heated material (probably stainless at 450F)
2. An insulating material (maybe PTFE...still looking into it)
3. A material I want to keep below 185F

I am trying to figure out what T2 will be in the attached diagram.  I know the thermal conductivity constant (k), the length, and T1.  What equation can I use (or what additional info do I need) to solve for T2?

Thanks!

Aaron

RE: Heat Transfer Across Simple Block

You need to know all the thicknesses, and the temperature on the right side of your protected material.  Heat is flowing from left to right, so you need a heat sink on the right.

TTFN

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RE: Heat Transfer Across Simple Block

(OP)
imcjoek, thanks so much for the link.  Their example assumes that multiple temperatures are known in the system.  I only know one temperature and am trying to predict my final temperature.  Is there a way to do this without knowing q dot?

I can use my desired temperature for T2, and calculate q dot, but then I'd need to verify in my system that q dot is equal to or less than what I've calculated, and I want to do the opposite: verify with a calculation that T2 will be less than or equal to my material's melting temperature.  Any ideas?

Thanks, again.

RE: Heat Transfer Across Simple Block

Q dot is essentially calculated once you know the temperature at the other end.  

Q dot = (T1-T3)/(Ri+Rp)

T2 = (T1-T3)*Rp/(Ri+Rp)

something like that...

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Heat Transfer Across Simple Block

As IRstuff mentions, you need to make an assumption (or better, know!) about the ambient(?) temperature on the right side.  Alternately knowing q-dot would work.  For instance if the heated material has a 1000W heater inside...  

Also be aware there will be contact resistances at the interfaces between your materials that could be important to you.

 

RE: Heat Transfer Across Simple Block

(OP)
Thanks so much for the help.  I used an ambient temperature for my third and was able to get the answer I was looking for.  Thanks, again.

Aaron

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