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Old Feb 6th 2019, 11:58 AM   #1
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Finding the correct 'Length' of a pipe?

Hello again, i've been struggling with question a) for a few days now and I have now reached a cross-road. The problem in itself lays in the framing of the question. So if you would take a look at the question in the attached document you will see that my professor is asking for the required 'Length' in order to heat the water from 20(C) to 80(C) degrees Celcius.

However, he also includes in the question,
"Heat transfer coefficient and pressure loss can be calculated by correlative equations in the above table."

Why would I need pressure loss? I found a formula to get the length, and it's
Q=k*A*ΔT(lm)

k = heat transfer coefficient
A = heat transfer area (of pipe) = L * [pi*(d(outer)^2-d(inner)^2)]/4
ΔT(lm) = Log mean temperature difference

I assumed this 'Length (L)' would be the one in question to find. Since it actually has a temperature included. But I looked up the formula for 'pressure loss' and apparently I can get a Length (L) that way as well. Is that what my professor is asking for? Are they the same lengths? Why do I need the pressure loss to solve this question? Did he mean to include it in question b) perhaps?

Thank you in advance.
/Kalle
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Help needed for thermodynamics questions-screenshot-2019-02-09-04.04.16.png  

Last edited by Kalle123; Feb 8th 2019 at 11:07 AM. Reason: Decided to ask a specific question.
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Old Feb 8th 2019, 12:31 PM   #2
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This is as far as i've made it.

This is as far as I've made it. If someone could take a look it would be extremely appreciated. I've attached a picture of how the double tubed pipe would look like. And a picture of my current calculations. However, as I mentioned in my previous post, I can't tell if first of all, i've chosen the L correctly.

If you see a problem, please feel free to correct it.


PS. Is the λ in the table correct? λ = mW/(m*K)? I thought it was supposed to be λ = W/(m*K)
Attached Thumbnails
Help needed for thermodynamics questions-termodynamik-uppgift_1.jpg   Help needed for thermodynamics questions-termodynamik-uppgift_2.jpg  

Last edited by Kalle123; Feb 8th 2019 at 04:36 PM.
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