Can someone help me with the following?

I'm designing a heat exchanger with both tubesheets fixed integral to the shell.

I'need to know if there is a criteria in order to consider the worst load case. TEMA indicates that the worst case is the loss of fluid in one side (tube or shell), but this criteria is extreme and obligates to use and expansion joint almost under all operation or design condition due to the great diferencial thermal expansion.

Paulo Luman

Hello Paulo

If the code of manufacture is ASME Section VIII, Division 1 or 2, and you are considering new construction, you should design to section UHX of the code.

There is no simple ‘rule of thumb’ for designing heat exchangers. If you are using PVElite or CodeCalc, it is simple to consider a number of different cases fairly quickly. Fixed tubesheets (for example integral both sides) are subject the thermal loads as well as pressure loads, and the outcome is not predictable in advance.

Ok Ray, but with PVelite you can set and analyze a lot of load cases (as many as you want). So that is my real problem. I need to eliminate some load cases before the analysis using a prestablished criteria (a code criteria would be ideal). If I consider all the possibilities (including the most extreme) I'll be obligated to use an expansion joint in my specific design.

Paulo Luman

Hi Paulo,

In ASME Part UHX, there are 7 basic load cases that must be run, in both the new and corroded conditions. These cases will automatically be analyzed no matter what you do. The program allows you print out results of individual cases if you wish to view those results. However, that printout could get rather lengthy if you check all of the boxes.

It is empirically difficult to know which case will govern the exchanger design. This is why UHX runs each case. TEMA sorts the complexity out of what case should govern and that is what is analyzed.

PVElite does allow up to 8 different exchanger operating scenarios. This facility is handy if you have an upset condition or two to run.

I hope this helps to clarify what is going on for you.

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