high flux tubES

[liberoSimulation]

Hi All
I would like to know your opinion in the use of high flux tubES in heat exchangers to reduce surface area required to get the duty.
does any one have an experience or background in this regard and the applications of such tubes and the vendors of these special tubes?

Any help is appreciated.

Regards
LiberoSimulation

 

[Longinthetooth]

Hi-flux tubes are marketed by UOP. They have had extensive use in the petrochemical industry, especialy ethylene. For instance they can cut the size of an ehane/ethylene splitter reboiler by over 1/3. We have used them for many years. They are very reliable and have never had a leak. They are no fouling concerns over and above regular tubes, however, they are being overtaken (in clean services) by plate-fin units which can half the area yet again.

 

[sshep]

A few years back I made a study to use hi-flux tubes in our ethylene fractionator condensers (i.e. boiling propylene). This also would have reduced our area requirement by 1/3 as cited by geordie87 above. During this period I made some phone surveys to see what other UOP customers thought of the performance. Of particular concern was whether the performance would deteriorate over time (fouling, etc). It was reported that the very process of nucleate boiling also kept the surface in good shape. No problems were reported by anyone I talked to, however, we did not actually purchase high flux tubes so I cannot give you firsthand feedback.

best wishes, sshep

 

[liberoSimulation]

Thank you for the valuable information,
I would like to know more about this interesting area;
Who other than UOP has good experience in the marketing of these tubes?
What the significant differences between these tubes and the conventional tubes?

Regards to all

 

[StoneCold]

liberosimulation
the high flux tubes have little scores on them. When they are on the inside they look like they are made for a splined shaft to fit in. Although they are probably only about 1/16" of an inch deep. You can also get them on the outside of the tubes. Very rarely would you get them on both sides. Usually one side of the exchanger is the controlling coefficient side and that is where you put the "high flux" modifications. They work by increasing the surface area of the tube.

Regards
StoneCold

 

[Longinthetooth]

The High flux tubing that we have has a coating that looks like powder that has been sintered on to the tube. The surface is very rough and porous. It is placed on the boiling side, since it is an enhancement to boiling. you can get then on shell or tube sides according to service. The other side can have longidudinal fins as Stonecold decribes. These flutes promote condensation or just cooling by enhanced area.
The high flux works by providing numerous stable bubble nucleation sites. this is because it has a combination of good matrix thermal conducivity, high microsurface area, and many contact points within the porous layer.
Another advantage ie that you can get good boiling at temperature differences of only 1-2 Deg C.
If the coating is on the outside it is thin enough so that the tubes can be installed through the tubesheet in the normal way.
As to cost, my recollection is that the bare SS tubes and the shell accounted for only 1/4 of the exchanger cost. The rest was the UOP cost of coating the tubes. This cost may have come down since there are more enhancement technologies available now.
UOP will do the sizing for you, but they used to have a program that they might give you to play with. I used it for rating existing units, and I found the way that best represented actual plant operation was to use the program to calculate the boiling coeficient and transfer that number manualy into a TASC or HTFS simulation.

Hope this helps,

 

[sshep]

While UOP doubly enhanced tubes do use extended area to gain heat transfer advantage, the high flux enhancement really targets boiling by assisting in bubble formation. I think I had a brochure once, but couldn't find it in my files or on the UOP website. This extract is from a UOP paper available on their website which describes the high flux enhancement.

====from UOP Paper on an ethylene fractionator revamp====
HIGH FLUX tubing utilizes a porous metal matrix that is metallurgically bonded to either the inside or outside surface of a bare tube. The manufacturing process ensures a mechanically strong surface that is highly resistant to abrasion and erosion. The HIGH FLUX surface works by providing a large number of cavities or pores that function as ideal nucleation sites for the generation of vapor bubbles. With a highly extended mircosurface area and good matrix thermal conductivity, this surface produces boiling coefficients that are 10-30 times greater than bare tubes, while extending the nucleate boiling range to very low temperature differences. High performance is maintained because of the high internal circulation rates that occur as liquid continually replaces the escaping vapor within the porous structure. The high boiling coefficients achieved with the porous surface usually shift the controlling heat transfer resistance to the condensing/sensible side, and create substantial incentive to enhance those sides for full exploitation of the boiling technology.