Is it possible that all three of these results are correct?
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I used the TASC+ software to calculate three shell-and-tube heat exchangers, and the resulting overall heat transfer coefficients are as follows: 1. Heat transfer rate: Normal condition – 18.3; Dirty condition – 32.1; Clean condition – 34.3 W/(m2*K). 2. Heat transfer rate: Normal condition – 42.7; Dirty condition – 38.3; Clean condition – 40.1 W/(m2*K). 3. Heat transfer rate: Normal condition – 42.1; Dirty condition – 42.3; Clean condition – 44.6 W/(m2*K). Why are the values of the overall heat transfer coefficient so strangely different for normal, dirty, and clean conditions?
I don’t quite understand it; I’m waiting for someone more knowledgeable to explain it. I’m still learning.
There’s nothing strange about this; naturally, the performance of heat exchangers varies depending on the operating conditions. The transfer rate for Service 42.1 is not a normal value; it is the heat transfer rate calculated as heat transferred / (temperature difference for heat transfer * heat transfer area), that is, the heat transfer rate required under those operating conditions ； Dirty 42.3 is the actual heat transfer rate obtained by calculating the convective heat transfer coefficient based on the heat exchanger geometry and fluid conditions, taking the fouling factor into account ； Clean 44.6 is the actual heat transfer rate obtained by calculating the convective heat transfer coefficient based on the heat exchanger geometry and fluid conditions, without considering the fouling factor. Generally, Dirty/Service represents the design margin, while Clean/Service represents the design margin for the new heat exchanger.
Thank you very much for the answer from above. Now there is a question: based on the data above, is there an issue with the definition of \"design margin\"?
May I ask, when providing the overall heat transfer coefficient to the design institute, should the value of the heat transfer coefficient for service conditions, dirty conditions, or clean conditions be used? I’m very confused; which one is better to choose?