Chemical industry heat exchangers: [Weekly Topic] The impact of heat exchange tube length on process design and equipment manufacturing (2011.7.12-17)
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This post was last edited by penryn on 2011-7-12 at 17:45. I have a shell-and-tube heat exchanger whose tube length is 9 meters, but the diameter of the heat exchanger shell is only 400 mm, making it quite slender; it’s made of carbon steel, and a 0Cr19Ni10 double-wave expansion joint is installed in the middle. There are two saddles, each with a span of 7 meters. The two tube sections at the ends of that expansion joint bent downward significantly when the vehicle was lifted last time. Moreover, the spacing between the baffle plates is 110 mm, with a total of 73 baffle plates. There are over 80 heat exchange tubes, made of stainless steel. There are 2 tubeside passes and 1 shellside pass. Now let’s discuss the mistakes in this design. Then, a detailed discussion is carried out on the impact of the length of the heat exchange tubes on process design, strength design, equipment manufacturing, and equipment operation.
:It’s way too long and thin; as a result, a large number of baffle plates will be needed, which is likely to cause a significant pressure drop. Working with pipes in this situation is quite troublesome, and so is maintenance and cleaning. During lifting, it cannot be lifted around the workshop like an ordinary container. I’m afraid there are problems with the manufacturing process alone for this thing.
This post was last edited and replied to by penryn on 2011-7-12 at 19:02. Reply to 2# Wen Bing: I also think this device has tons of problems! When I first saw the condition diagram proposed by the process team, I found it really awkward!
The length-diameter ratio is severely mismatched; either the cylinder diameter must be increased, a series arrangement must be used, or heat transfer equipment must be enhanced.
Could LZ send us the process conditions so we can take a look? I think if the process calculations are correct, shell-and-tube heat exchangers are not suitable.
With such a high height-to-diameter ratio, it’s obviously too distorted; two units in series should have been considered during the design.
Reply to 5# Final Fantasy Pig: I don’t have the process parameters; I’m not in charge of developing those processes.
Reply 6# emirateyi: Yeah, but it’s due to cost considerations – after all, it’s about money! !
Just ask about your own manufacturing process.
Reply to 9# wangzhongtj: If he knew a little about heat exchangers, he wouldn’t have set such conditions! This is my weekly topic post, not a request for help!
The length-to-diameter ratio of the shell should be 3:1 ≤ L/D ≤ 15:1; in other words, this is the ratio of the length of the heat exchange tubes to the diameter of the shell. This is because L/D＜3 ； At 1, the shell side is shorter; due to the effects at the inlet and outlet, the fluid flow distribution is poor, resulting in inadequate heat transfer. The pressure drop across the inlet and outlet accounts for a large proportion, and the cost is higher compared to those with a larger L/D ratio for the same area, especially when the pressure on the shell side is high. When L/D > 15:1, machining is difficult, and more space is required for manufacturing, assembly, and maintenance; however, it offers better heat exchange and higher thermal efficiency. Development in this direction may occur in the future, provided that requirements regarding pressure drop and stiffness are met. The optimal L/D should be between 6:1 and 8:1.