The temperature cross-over problem in heat exchangers
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Temperature crossover phenomenon: the outlet temperature of the cold fluid is higher than that of the hot fluid； When temperature crossover occurs (for example, hot stream: 96°C -> 42℃ ； Cold stream: 34->45℃); it is possible to increase the flow rate of the cold stream or reduce the flow rate of the hot stream ； However, when the process conditions cannot be modified, other methods must be employed: 1. Use a double-pass heat exchanger or two heat exchangers connected in series; 2. Use a single-pass heat exchanger (without using double-pass or multi-pass heat exchangers). If you have any questions regarding these two methods, please help to answer them. Thank you!
Temperature cross-over shouldn’t be what you’re saying, right? In your case, if there’s no phase change, wouldn’t counterflow be achieved easily?
Temperature crossing should refer to the situation where, during a phase change, the intermediate temperatures intersect. Or in another scenario, a similar situation to double-tube layer single-shell layer may also result in a temperature crossover in the middle. What I don’t understand is: if this is the desired outcome, and the process conditions are not to be changed, how can the problem of temperature crossover be avoided through series connection or dual-shell design?
The two questions you replied to are also things that have puzzled me for a long time; I’ve looked up a lot of information, but I still don’t understand them； 1. In this case, if there is backflow, indeed no temperature crossover occurs ； 2. As for using heat exchangers in series or with dual shell circuits to address the issue of temperature cross-over, I’m still not clear about it. I’ve read various materials and posts that state this method can be used, but I remain confused as to why exactly ； I hope you understand as well; please let me know, thank you!
This post was last edited by wanlirn on 2022-8-25 at 10:11. With dual shell processes or shell processes connected in series, it becomes pure counter-current flow – it’s hard to understand why.
:Poster P’s description is accurate, and the expert’s explanation is even better, :)