Hi
So we are having a shell and tube heat exchanger where heat is exchanged between 2 fluids. Which fluid shall be on the shell side, and which fluid shall be on the tube side?
This depends on several factors:
1. Which fluid is more fouling? The velocity on the tube side is typically higher than on the shell side. In addition, cleaning the tubes is much easier. So it's better to allocate the fluid in the tube if it is more fouling.
2. Which fluid is more corrosive? A corrosive fluid will need a material of construction that is resistant to corrosion, which is often more expensive. As the shell side needs much more metal weight than the tube side, it will be less costly to allocate the corrosive fluid to the tube side.
3. Is there a great difference in pressure between both sides? Also, if the fluid is operating at high pressure, this means that the exchanger should withstand this pressure and even higher depending on the upset scenarios. Same as in the case of corrosion, this will be more costly if we allocate a fluid with higher design pressure in the shell side. That's why it's will be better to consider the higher pressure on the tube side and apply the 10-13 rule on the shell side.
4. Which allocation shall give better heat transfer? In some cases, we may discover that the fluid flowing in the shell side has a very low heat transfer coefficient. Here we may check if placing this fluid in the tube side would lead to an increase in overall heat transfer coefficient, which shall lead to less area, or in other words, less exchanger dimensions.
So as we can see, there are various factors affecting fluid allocation. These factors may even contradict each other. So we have to evaluate these factors well and determine which factor to be considered and which factor to be sacrificed.
Want to understand exchanger basic design concepts? Check out the below link:
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Regards
Mohamad
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