Heat exchangers can be complex structures. With Heat exchangers, we see different loads on nearly every part resulting from different pressure loads on tube side and shell side, temperature loads due to thermal expansion and nozzle loads from the attached pipes. In addition, external loads like wind or earthquake loads might affect the apparatus.
Up to now, the stress and stability in these exchangers were calculated by formula using different codes like ASME or if the task is more complicated by FEM. The disadvantage of FEM in this case is, that we need a very fine mesh on the tube sheet to solve the problems on this highly perforated part. On the other hand, the tube sheet might get very large in diameter, which causes a very high number of elements, and subsequently a very long calculation time.
Take for example the following heat exchanger. This complex assembly consists of 566 separate parts including 112 nuts and bolts.
Figure 1 – Transparent view of heat exchanger showing internal pipe details
Figure 2 – Detailed view of internal pipes with external shell hidden
Altair SimSolid allows not only to calculate the tube sheet displacements and stresses using a fraction of time spent for meshing the FEM calculation, but also allows to overlay the loads resulting from the additional effects. Moreover, we are now for the first time able to optimize these material consuming tube sheets, due to the quick answers. Typical run times for this project is under 10 minutes.
Figure 3 – v. Mises stress during critical start-up conditions with floating head cover hidden
Figure 4 – Critical areas with a safety factor near or less than 1.5
We find Altair SimSolid to be a very valuable tool analyzing complex structures. We look forward to using in more and more in our business. For more information on this project please see our website http://www.lv-soft.com
Dietmar Fischer, Dipl. Ing.
Lauterbach Verfahrenstechnik GmbH