Any Experience with Exchanger Tube Inserts

[sshep]

Friends,

Our technology group asked us to identify an excahnger which can be used to test four types of twisted tube type inserts (turbulators). We don't really have a non-critical exchanger to do this, but are willing to make accomidation for them. My previous locations had standards specifically prohibiting the use of inserts, not sure why, but for this reason I have no experience. My current location does not have any standards addressing the use of these devices.

Can anyone with experience give me some feedback on the success and problems associated with these devices. Our cooling water is very very dirty (muddy and biological solids). We we worry about fouling, maintenance (removal) etc. Any feedback could be useful. These are the models we are asked to try and the application description we got:

SPIRELF – suitable for long service time and velocities greater than 1.5 m/s

TURBOTAL – better performance than the one above but limited service time and applicable with velocities below 2 m/s

FIXOTAL – convenient for wall temperature dependent type of fouling (it doubles effectively the fluid velocity)

Hi-Tran of CAL GAVIN (good only for specified range of operating conditions), Scaling is potentially a big problem for these inserts.

best wishes,
sshep

 

[CH5OH]

turbulators are used to reduce installation cost(less tube surface required) over running cost (more erosion/fouling)
or increase capacity at cost of increased running cost
to evaluate different suppliers you could run a dummy air cooler parallel with your critical cooler (in your case existing out of five pipes of which four with turbulator)
Fed with same delta P cooling water and cooled with the same heat sink (air), the outlet temperatures of the tubes gives you a champ (closest to air temp) and a loser (closest to cooling water inlet temperature) in heat exchange rate.Over period of time you get a champ and a loser with regards to fouling.If you're patiently enough you even get a champ and loser with regards to lifetime cycle(take thinnest possible pipes, if you're in a hurry).

 

[CJKruger]

sshep, long time ago we installed one of these devices in crude-vac bot service. Idea was to reduce fouling.

Not sure I really saw a noticeable improvement. Think the benefit (if any) just got lost in the operating "noise".

Down sides I can think of:
- Maintenance. Pulling and inserting them every time you clean the exchanger.
- Breakage. They may break or become lose, and travel downstream to block something else.
- Increase fouling. If they stop working they may create dead zones which may increase fouling.

Cilliers

 

[AggieCHEN04]

Was increased pressure drop ever a problem?

 

[AggieCHEN04]

Years ago, I removed some turbulators from a hot oil air cooler after they had become foulded. This was a much dirtier application than most hot oil operations, so I can't really judge based on my one experience. Actually, I had no idea they were in there until we had to clean the unit out. I do know that they were difficult to remove, and by the time we had removed them, they were too warped to put back in.

I have always been curious to know how they would operate in cleaner services such as a propane condenser or shell & tube heat exchanger in a refrigeration system.

 

[SNORGY]

I used them with success in a 316-SS lube oil air cooler for a 6,000 HP centrifugal compressor. I would not recommend them in anything other than a clean service, and I have unconfirmed doubts - but doubts nonetheless - about their incremental benefit if your Reynolds Numbers are already well in the turbulent flow range.

Regards,

SNORGY.

 

[sshep]

These are really good comments. Thank you very much. Since there are several designs, probably all proprietary enhancements on various twists and shapes, any reference to type could also be useful.

You know that I will give stars, but I am waiting to see if there are any more posts on this topic.

Thanks again,
sshep

 

[speco]

sshep,

I believe that there can be some substantial benefit for using some of these inserts in certain application. I would not consider them for any kind of condenser or application that is normally in turbulent flow.

However, for clean oil services where the viscosities would put the flow at the high end of the laminar region, or in the transition region, you can expect to see an improved inside tube heat transfer coefficient at the cost of some additional pressure drop. Lube oil coolers for light turbine oil are a good example of this.

The most common type that I am familiar with are simple twisted tapes that are about the same length as the tubes, and have a width just a bit under the tube ID. However, there are all kinds of crazy configurations of these. I suspect that some would work much better than others.

Regards,

Speco

 

[rmw]

I don't like their use. Not that they are bad per se, although they have their drawbacks some of which have been brought out above.

If you size your HX for their use and they don't work out for some reason, then you are stuck with an undersized HX.

I think their best use is to help a 'limping' HX get to a point that it can make its duty rather than trying create a new design around them. Or one where you have to change the design conditions, for example, the tubeside flow wasn't what it was designed to be.

BTW, I have seen them used in fire tube boilers too, and after all, isn't that just another form of S&T HX?

And BTW again, turbulators is what I have heard them referred to in mostly cases, inserts are thin wall tubular thingies that are rolled into the first few inches of a tube inlet to repair tube inlet erosion to try to squeeze a little life out of a HX.

rmw