Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
circular tubes for heat transfer in boiler
- Thread starter pradeep4u
- Start date
MikeHalloran
Mechanical
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
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
- Thread starter
- #3
MikeHalloran
Mechanical
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
Mike Halloran
Pembroke Pines, FL, USA
Compositepro
Chemical
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.
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
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
- Thread starter
- #7
??
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.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
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.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
- Thread starter
- #10
That information is below my signature line, which means it's on every posting I make
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
- Status
Similar threads
- Question
- Locked
- Question
- Locked
- Question
