circular tubes for heat transfer in boiler

[pradeep4u]

Dear Sir
I have question in mind that why circular tubes used and not square or rectangular tubes for heat tranfer in boilers? Instead of no of circular tubes why no no of square or rectangular tubes for this purpose/
Regards
Pradeep

 

[MikeHalloran]

Square or rectangular tubes have problems with fatigue in the corners when subjected to pressure cycles.

Still, they might give better heat transfer in some configurations, i.e., if they can induce some extra turbulence on the shell side.

But the most likely answer is that there's no simple way to terminate the ends of square/rectangular tubes to a tubesheet.

You could use square tubes that are formed with round ends and terminate them in the usual way, but that leaves no way to replace individual tubes, e.g., pulling a square tube through a round hole.

Note that obround tubes are used extensively in automobile radiators, but they are never individually replaced, and are assembled with external fins, for which the flattened sides are a great advantage in conducting heat from the tube wall to the fin material.



Mike Halloran
Pembroke Pines, FL, USA

 

[pradeep4u]

What if tube sheets will of rectangular or square shape?
Regards

 

[MikeHalloran]

It's not super hard to make a tube sheet with square holes, but how do you 'roller swage' the square tube into it? ... and seal the joint? AFAIK, no tooling exists to do that, and I can't conjecture a way to do it successfully.





Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

There is no real advantage to square tubes for heat transfer. Square tubes must be much thicker walled to withstand pressure and the inside corners would be more prone to fouling. One of the basic practical principles of engineering is that there are almost always good reasons for everyone doing something the same way. Everyone is not stupid.

 

[davefitz]

The required thickness of a square tube is much thicker than that needed for a round tube, to restrain the fluid pressure. Power boilers have design pressures in the range of 3000-4000 psig ( 200-300 atm) and minimizing the wall thickness is important.

Oblong tubes are used in air cooled condensers installed in freezing climates, since they can survive several ice freezing events without cracking. Their design pressure is only +- 1 atm, so wall thickness is not an issue.

Oblong tubes also have minimal frictional pressure drop for the outside flowing flue gas if the major axis is parallel to the fluegas direction ( eg Joukowski airfoil) but this also means low convective heat transfer coefficient- to offset that penalty, extended fins are added.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[pradeep4u]

@Compositepro (Chemical)
I am not talking about advantage or disadvantage of using square or other non circular shape. I am just asking for curiosity that any specific reason for circular tubes

Regards
Pradeep

 

[IRstuff]

??

Your question was answered several times. If there's no benefit, then there is no engineering reason for choosing them, particularly since they are hard to make and harder to form.

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[chicopee]

It is also more practical and easier to make a circular coil using a mandrel with a spherical head on a hydraulic tube bender.

 

[pradeep4u]

@IRstuff (Aerospace)
Why u sent Yutube video and Forum policies? I also know that my question answered but with every new answer new information I came to know. Is'nt good that every one get to know new information.

 

[IRstuff]

That information is below my signature line, which means it's on every posting I make

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