Hi Mike
I am a but out of date with tube in tube units so you are probably
better seeing what Alfa Laval offer. From memory, they consisted of tube
in tube U sections with the outer tube coned onto the inner tube just
before each end flange. They could then be bolted together (inner pipe)
and the outer pipes connected by jumper pipes. This largely avoids
differential stressing.
Not familiar with spiral tube units but presumably they are like spiral
plates - big coil in a bucket with close clearances to promote
counterflow.
Years ago I used to make stainless S&T heat exchangers for the meat
industry - used to condense rendering plant steam (100 C) and produce
potable hot water (85 C). Others had problems with stress corrosion
cracking using 316L so we went to 3RE60/SAF2205/2RK65/904L. The steam
went through the tubes and the water over them. 75% baffles were spaced
at about half the shell diameter to approach counterflow conditions and
provide tube support. The tubes were welded into a thin (6mm) tubesheet.
The tubesheets (1.6mm) were welded to the shell, and the shell had a
single large corrugation (fabricated from two "washers" and a band with
corners radiussed) at midspan. The corrugation was sized to accommodate
a 100 deg C temperature differential between tube and shell without
overstressing.
Cant recall any failures.
For liquid food work, mostly plate exchangers are used here now as the
thermal performance (bang per buck) is heaps better.
Cheers
Steve
-----Original Message-----
From: Michael Waugh [mailto:mike@waudesign.com]
Sent: Friday, July 02, 2004 1:18 PM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Shell and tube Heat exchangers
Hi Steve:
Thanks. I am familiar with "spiral tube units", are these the same? With those, I would agree that expansion would be much less of an issue. Dare I ask how these are built?
I want to build a straight shooter, with 3/4" SS316L, polished. Mine is basic or much like a normal HE, but some changes.
I used to work for a large beverage outfit here in Florida, and they had fairly large units, about 6" Dia for each tube. We would experience cracks right at the welded end and we used a florescent green dye to detect them. It's that joint of the tube and the plate weld that has been bugging me. I have been looking at different designs for some ideas.
Appreciate your comments.
Mike Waugh
-----Original Message-----
From: Steve McKenzie <mechproj@xtra.co.nz>
Sent: Jul 1, 2004 6:31 PM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Shell and tube Heat exchangers
Hi Mike
some dairy installations use tube-in tube exchangers for ease of
cleaning. By using a serpentine pattern, expansion can be easily
accommodated. Before designing you may want to see whats currently
available so you can either "borrow" the best ideas or just buy what you
need. APV and Alfa Laval make some good stuff in the dairy industry.
Cheers
Steve
-----Original Message-----
From: mikebw_99 [mailto:mike@waudesign.com]
Sent: Friday, July 02, 2004 3:02 AM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] Shell and tube Heat exchangers
Greetings
Anybody with information on design of heat exchangers? I am starting out on a design, I am seeking some technical information, literature or any other guidance on how to correctly determine the innner shell tube lengths for a sanitary shell and tube heat exchanger(tubes to be built into a bundle). I would like to better understand thermal expansion effects and properties, stress related effects on welded ends, in order to prevent bending of the tubes. These tubes would be welded into end plates and specifying the welds to stop leaks is a concern.
Mike W
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