Tube modelling in a fixed tube heat exchanger 2

[gelsomino]

Hello all.
Is there anyone who can tell me how to model tubes in a FEM 2D axisymm analisys? I have modeled tubesheet and calculated equivalent young's modulus and Poisson'ratio. Now I've to introduce tubes in a axisymm way or not? And how?

Thanks a lot.

 

[jte]

gelsomino-

A paper by Lengsfeld, Bardia, and LaBounty titled "Alternate Method to Determine Fixed Tube Sheet Thickness" would be useful. It was published in an ASME PVP volume sometime around 1997. From the abstract: "... In order to reduce the size of the axisymmetric finite element model, the spring constant of the tubes, based on the method outlined by Hayashi (1977), is modeled as equally spaced concentric cylinders for the FEA. The combined stiffness of the cylinders is the same as the total stifness of the tubes..."

You might be able to get a copy from the ASME.

jt

 

[gelsomino]

Thanks a lot jte

I'm not an old and expert ASME user and i can have access only to 2002 and 2004 (only div VIII and IX). Can you explain me where I can find them. I've to buy it, or can I find it in the standard code?

Thanks a lot again.

 

[bvi]

The Hayashi paper is a good reference, but I would suggest modeling the tube bundle as an axisymmetric solid rather than rings.

The axial stiffness of the solid should be the same as the tube bundle (simply scale the elastic modulus by the area ratio). Radial and hoop modulus would be zero.

Pressure loads need to be scaled based on actual surface areas. Don't forget tube extension or contraction due to the delta P acting on it (Poisson's effect).

Also, you need to use equivalent properties for the tubesheet. Look at the Appendix in Section VIII.

 

[jte]

gelsomino-

bvi provided some good points.

For the paper, I'd suggest you contact the ASME at

Infocentral (at) asme.org
Tel.#: 800-843-2763
Intl.#: 973-882-1167

Ask them to search for the paper. It will be in a PVP conference volume most likely between 1996 and 1999.

jt

 

[gelsomino]

Thanks a lot BVI.

My last questions
I've to study the tube's thickness. So I would take the highest stress value and with TEMA rules (proximity to baffles) and control instability. But how can i consider the stress distribution in a solid? And about termal distribution in the solid? Will it be representative?
Excuse me for my bad English and for my novice condition.

Thanks a lot again

 

[bvi]

Take the axial stress in the solid and scale it by the ratio of the solid area to the tube wall area to get the axial stress in the tube.

For thermal loads, simply include the coefficient of thermal expansion and the temperatures. No adjustment to these is required for the equivalent solid (unless you are incorporating the Poison's effect due to internal pressure in which case you need to make a small adjustment to the input temperature to consider this displacement loading).