Issues related to the arrangement of heat exchange tubes in shell-and-tube heat exchangers
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I’m a beginner and have a question that’s bothering me: GB151 specifies that for fixed-tube-sheet heat exchangers, the diameter of the circular boundary within which the heat exchange tubes must be arranged is given by DL = Di – 2b3, where b3 = 0.25d. Generally, b3 should not be less than 8 mm. So if b3 = 0.25d is to be at least 8 mm, that means 0.25d ≥ 8, or d ≥ 8/0.25 = 32 mm. This implies that the diameter of the heat exchange tubes must be at least 32 mm. However, in practice, the diameter of such tubes is often less than 32 mm; for example, tubes with a diameter of 12.7 mm. Using the formula, b3 = 0.25d = 0.25*12.7 = 3.175, which is less than 8 mm. What should I do in this case? I’m not sure if my understanding of this formula is correct I hope kind brothers and sisters who understand this can help me out by explaining this formula. Thank you! ! !
:hug: I think what it means is that if 0.25d is less than 8, then set b3 to 8; if 0.25d is greater than 8, then set b3 to 0.25d :hug: And then, you just need to ensure that the gap between the piping constraint circle and the inner wall of the shell is larger than b3, because too small a gap could cause difficulties in manufacturing. As for what size the piping constraint circle should be, that’s up to you
Reply to 2# yuri714: I find it quite awkward to understand! You see, in GB151 it is stated that b3 should generally be no less than 8 mm; this statement confuses me – does it mean that the value calculated using the formula must be no less than 8? Or does it mean that no matter what the calculation yields, b3 cannot be less than 8 when taking its value? How do you understand it?
It should be: regardless of the calculation result, it must be less than or equal to 8 mm; for example, if the calculated value is 7.0 mm, then the limiting circle of 8 mm should be used. If the calculation result is greater than 8 mm, then that result is taken… In fact, what was explained on the second floor was already very clear.
Reply to 3# bianjia: lol, understand it based on the text before the second question mark
Reply to 5# yuri714: Thank you, haha
Reply to 4# 6mkl: Thank you, haha
Reply to 2# yuri714: I still need your advice, teacher. The rule states that b3 must not be less than 8. However, on page 89 of “Principles and Design of Heat Exchangers,” there is a calculation table in which steel tubes with a diameter of φ25*2.5 are used. When using the formula b3=0.25d to calculate b3, the value obtained is 12.5; but based on the diameter, it should be 6.25, right? According to the rules, if the value is less than 8, it should be counted as 8. So how does 12.5 come about? The main question is: how is this 12.5 determined? ? Please give me some guidance! Thank you first
The standard specifies that it should generally be no less than 8, but it does not set an upper limit. In my opinion, it’s fine to use a higher value, but it shouldn’t be too high to prevent short circuits caused by materials on the periphery; the standard needs to be interpreted flexibly.
Those less than 8 are considered as 8! Those greater than 8 are classified as such!