Exchanger Tube Thickness and HTC
Exchanger Tube Thickness and HTC
(OP)
Hi All,
I'm replacing a tube bundle in shell and tube exchanger which has cracked with a new, slightly thicker one. The old tubes were 1.2mm thick, new 1.6mm. I'm wondering (and can't seem to find anywhere) how much this will affect heat transfer. Looking at Fourier's Law for conductive heat transfer it says that the relationship is linear between different thicknesses (i.e. it will be 33% harder for heat to travel through this extra 0.4mm which does make sense), however saying that the HTC will be 33% reduced just doesn't feel right to me. It feels like there's something big I'm missing, but just can't put my finger on it. If anyone has any advice it'd be much appreciated.
Thanks,
Rob
I'm replacing a tube bundle in shell and tube exchanger which has cracked with a new, slightly thicker one. The old tubes were 1.2mm thick, new 1.6mm. I'm wondering (and can't seem to find anywhere) how much this will affect heat transfer. Looking at Fourier's Law for conductive heat transfer it says that the relationship is linear between different thicknesses (i.e. it will be 33% harder for heat to travel through this extra 0.4mm which does make sense), however saying that the HTC will be 33% reduced just doesn't feel right to me. It feels like there's something big I'm missing, but just can't put my finger on it. If anyone has any advice it'd be much appreciated.
Thanks,
Rob





RE: Exchanger Tube Thickness and HTC
RE: Exchanger Tube Thickness and HTC
RE: Exchanger Tube Thickness and HTC
RE: Exchanger Tube Thickness and HTC
Investigate the "overall heat transfer coefficient" for shell and tube heat exchangers.
You will find that the increased wall thickness will only be a small part of the coeffiecient.
Chapter 11... Perry's handbook..... and
http://web2.clarkson.edu/projects/subramanian/ch30...
RE: Exchanger Tube Thickness and HTC
RE: Exchanger Tube Thickness and HTC
Be careful not to exceed the allowable tube velocities for whatever tube metallurgy you have.
Why pray tell are you increasing the tube wall thickness?
rmw
RE: Exchanger Tube Thickness and HTC
RE: Exchanger Tube Thickness and HTC
Since you are suspect of the original design of your HX, I suggest you consider getting a quote for a new replacement HX from a fabricator.
I would use the original TEMA data sheets, if still avaialble from your records.
Compare the recommended tube thicknesses (and many other design details) of a replacement unit with your existing one.
Suggest that you also compare performance results in an "off original design" condition........ This is simple to do in most modern HX design programs.
Best regards
RE: Exchanger Tube Thickness and HTC
I have the quote from a fabricator to replace the entire unit, which is what we'll end up doing. I was just trying to find how much the resizing will affect our operation, but from everything I've done (and other engineers) all seems fine.
Thanks everyone for your help,
Rob
RE: Exchanger Tube Thickness and HTC
For example, if, say, SA-178 had been specified before, could one now specify SA-179?
Might save you a new unit...
RE: Exchanger Tube Thickness and HTC
RE: Exchanger Tube Thickness and HTC
If tube cracking was the prevalent concern, you might have had the option to review seamless tubes in lieu of welded tubes.
RE: Exchanger Tube Thickness and HTC
Did your vendor take the increase in tube thickness into account in the new design or is it a replacement in kind with thicker tubes? If the former, then you are probably OK, except that the Hx is larger somewhere - longer, larger diameter, etc. If the latter, then your performance is going to be affected as per my previous post.
And to my colleague Snorgy, that would have been the last thing I would have suggested - changing from welded tubing to seamless assuming that is the direction change would occur. When I use welded tubing, I expect the strongest part of the tube to be the weld. Seamless Hx tubing hasn't been a friend of mine.
rmw
RE: Exchanger Tube Thickness and HTC
Fair comment. Without knowing more about what was meant by "cracking", and not knowing the mechanism at play, perhaps it was premature to suggest that maybe it might be a seam problem. Would you think it would be worthwhile to see where the cracking is occurring, as well as whether they are transverse, longitudinal or random?
RE: Exchanger Tube Thickness and HTC
-Christine