Hello all,

I hope someone can advise on the requirement for the use of a bellow in a heat exchanger. I've come across on several occasion on a fixed tubesheet heat exchanger design but not sure what is the governing factor or when is it required to use a bellow.
I notice towards the end of the tubesheet analysis there's a 'Max axial differential thermal expansion' result whereby it states the movement/growth, but at what point does it really need a bellow? Also there's an 'Allowable load on the Tube/Tubesheet Joint' & 'Actual loading' calculation, does this have any correlation with the movement/growth result?
Appreciate all reply.

Thanks.

Hello Azman

Section UHX of ASME VIII, Division 1 is quite complicated. There are many equations, and many load cases to be considered. Therefore there is no convenient 'rule of thumb' to determine whether or not bellows are to be encorporated into the design. It is really a matter of trial and error and perhaps a little experience. Designing a heat exchanger takes patience. Perhaps several designs should be tried until an economical design is achieved.

Your question about growth:

Growth is determined by mainly two factors: The temperature and the coefficient of thermal expansion. In the case of a fixed tubesheet configuration, the shell is a different temperature from the temperature of the tubes, so the growth of one is fighting with the growth of the other. The calculations to determine the final growth are complicated.

Hi Ray,

Yes, I agree and thank you for the explanation.