Physics Help Forum Help needed for thermodynamics questions

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

 Feb 6th 2019, 11:58 AM #1 Junior Member   Join Date: Feb 2019 Posts: 2 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 Attached Thumbnails   Last edited by Kalle123; Feb 8th 2019 at 11:07 AM. Reason: Decided to ask a specific question.
 Feb 8th 2019, 12:31 PM #2 Junior Member   Join Date: Feb 2019 Posts: 2 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     Last edited by Kalle123; Feb 8th 2019 at 04:36 PM.

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