Heat Transfer Across Simple Block

[amoncur]

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

 

[imcjoek]

I think this should help you.

http://web.mit.edu/16.unified/

http://www/SPRING/propulsion/notes/node118.html

 

[IRstuff]

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

FAQ731-376

 

[amoncur]

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.

 

[IRstuff]

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

 

[imcjoek]

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.

 

[amoncur]

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