Flow induced vibration problem in a cross flow tube bundle heat exchanger.

The picture is a bit blurred.

Your proposed solution, putting in the wiggly strips in from the side looks reasonable.

If you put 'em in alternately from side, then above, e.g. an X Y grid this should restrain the movement in 2 axes. Is this too obvious?

Maybe I'm missing something?

Del,

Thats correct, and that is that obvious. which your comment is what I was looking for.

Considering that the exchager itself is larger than the illustration depicts. and the expense the company already put into correcting it without a lasting improvement.

When it was tried and with limited success (i.e. eventual failure), I am pushing that they were on the right track. and avoid going in another direction that may not help.

I apoligize for the burred illustrations, should have uploaded them individually.

don't think I can ammend this post. I can email a pdf.

Sorry, the figures are not very clear, so it is hard to comment. What exactly is the problem? Are tubes breaking due to vibration? If so where?

These problems are usually due to an excitation of the tube natural frequency that results in tube cracking typically at supports or at the tube sheet. Increasing the natural frequency of the tube by reducing the unsupported span often solves the problem.

If you are certain that it is due to vortex shedding, then geometry changes that eliminate the votex would be effective as well, this is often done on smoke stacks with vortex shedding issues.

Steve,

I can email you a clearer picture. The problem first is the issue of noise. (rattling and such from the tubes. Which can fatigue the tubes and tube weld joints.

With the company putting in cross tubes to firm up the tubes. I believe this helped, it only did it in 1 axis. Considering the limited information and the ability for a visual inspection (it is very difficult). That is why I am formulating a plan with the information I have and deduce a possible solution. The reason of course is there is only a limited window for a down time. (none) But since it has to be correct. we try to avoid a second downtime (may happen anyways) for a inspection then another downtime to fix.

Considering That I can't be certain that its due to vortex shedding, I'm am only going on information that was given to me in the last 24 hour. I am only speculating with the information from the previous repairs. I start working here less than a month ago.

I read a thread about about the smoke stacks, what do you mean be geometry changes? On the tubes??

Thanks

I'd also suggest building a test rig so that you can induce resonance and try different positioning of the strips, as their position will be critcal.

Ideally you could induce resonance and view the assembly under a strobe light and then position your strips at anti-nodes. (obviously this is much easier to say than to do ).

Hope the ideas are of some help.

Yes they are helpfull. and yes it is much easier to say than to do. kinda like reading a map on how far is it from detroit to chicago..... about 6 inches.

thanks

You say the tubes are welded or swaged to the tube sheet?

What high side and low side temps are you working with?

How thick are the end tube sheets? What is ID and wall thickness of tubes?

A guess would be to try and reinforce the tubes near the tube sheet. If you or the heat exchanger supplier have the ability to swag the tube ends, my first suggestion would be to insert short under diameter tubes (About 2 or 3 times the tube sheet thickness) in the tubes and swage them in to reinforce the tubes internally. Second suggestion is to try to install the additional tube supports closer to the end tube sheets, maybe 3 to 5 times the tube diameter.

Good luck!

PS, could I get a clean picture? This looks similar to a heat recovery HX for a fume incinerator that I worked on a number of years ago. Is this a similar application; 100F air from process preheated with 1400F incinerator exhaust?

sure, ......... how? I don't see anyway to put a attachment to the messages here

The PDF is great. I assume the tube side is cold air flow? Could a vibration monitor be install in one of the tube to determine frequency and displacement of vibration? The intermediate tube support concept looks good, but fabrication is more expensive than simple tube insertion as done by the HX company. I would install the additional supports at a spacing that would be different from 1/2, 1/3, or 1/4 that may have an additional harmonic to current vibration. (Like a plucked guitar string) Based on the use of SS materials, my suggestion of swaging a reinforcment is no good. Don't worry about CR4 difficulties, I also have occasional trouble.

I guess my thought was "is it vortex shedding from the tubes that is the problem? Or is there something in the flow stream upstream of the tubes that is generating vortices? If it is the first row of tubes, fins may help to break up the vortex generation. If there is a flow splitter, or a nozzle or a dead leg side branch upstream that is generating vortices, then you might focus you effort on geometry changes to that thing or things, rather that mess with the tubes.

In any vibration problem, you can try to effect the force, or effect the response. Often, reducing the force is the most effective approach. Do you really under stand the flow issues that are causing the vibration of the tubes?

Understanding the flow issues. No, I don't at least not as an expert. Thank you for questioning.

I like to approach this in a systemical way. Also to express that there may be information that has not come out yet.

I am attempting to start with by drilling down to a reference point, which is difficult. by doing this, information, or questions/statements such as yours helps.

I suspect that there may be more to this that just the vibration problem.

Thanks

Steve,

"Or is there something in the flow stream upstream of the tubes that is generating vortices?"

After your comments, I started pressing and more information just came through, It is something upstream. It was working fine, until they installed a (5th) valve just prior to the HX, when they did that. the vibrations started.

(flow is 4000 CFM)

I'll email you a clearer picture, which figure 2 may be effective. you can ignore it or not.

Thanks for the tip.

From private emails I understand this issue is being resolved.

Yes it is, once we received all the information from the customer. (we have 10 of these units in the field and there are 6 left to deleiver). So we will be doing a test on the one we are experiencing problems with, and this fix would be an option for the customer if they do the same with the existing and remainder units.

Thanks,

phoenix911