How is the equivalent of pressure-induced instability of heat exchange tubes determined?
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Dear teachers, when calculating fixed tube sheets, one encounters the equivalent value Lcr for pressure-induced instability of the heat exchange tubes (page 42 of GB151); this value is to be determined by referring to Figure 32 (page 59 of GB151). But there are five ways shown in the diagram; I’m not sure how to choose, please advise.
Select the appropriate diagram and formulas based on the number of baffles; use those for 5 baffles or more.
Note: 1. Figure 1 shows the case without a support plate, using half of the length between the tube sheets. 2. Figures 2, 3, 4, and 5 show the maximum dimension that is either the length between the two support plates, or (1/)^0.5 times the distance from the tube sheet to the support plates. It’s just a simple calculation; you’ll understand it by comparing it with your diagram.
I remember having answered this question; actually, if the original poster searches for “instability equivalent,” they will find relevant discussions there: http://bbs.hcbbs.com/viewthread.php?tid=363719&highlight=%CA%A7%CE%C8%B5%B1%C1%BF
Simply put, it is the largest distance between the two partitions on a tube.
First, several length dimensions need to be identified, and then the values on the right side of the diagram are calculated; the longest length is taken as the instability length. This length may be the most dangerous one, but it represents the safest value for the calculations related to the entire heat exchanger.