Regarding the reboiler

Based on the unit following \"clean\", it can be determined that its meaning is: the heat transfer coefficient at the cold material side of the pipe train. As for service, it’s indeed not easy to understand. Could you provide a more complete version of this data table? I hope the original poster will upload the entire data table, so that the problem can be solved more effectively! ! ! This post was last edited by bolinuser on 2008-1-11 10:15]

That’s right; it should be the overall heat transfer coefficient. \"Clean\" refers to the value when there is no scaling, \"service\" refers to the value under operating conditions (taking scaling into account), and \"minimum\" refers to the lowest value under extreme conditions (with design margins taken into consideration).

230 is the minimum heat transfer rate required by the design specifications; \"service\" refers to the heat transfer rate under actual operating conditions, taking scale formation into account, while \"clean\" denotes the heat transfer rate in the clean state at the time of initial use.

In other words, the transfer rate is the overall heat transfer coefficient, which exists in three forms: the value when the surface is clean, the value taking into account the thermal resistance caused by dirt during operation, and the minimum value when no design margin is considered! ! ! Haha, I totally get it now! ! !

The data format used by the original poster comes from line 30 of the heat exchanger data sheet in the TEMA standard (8th edition), with slight differences. In the standard, it should be written as follows: transfer rate: service XXX clean XXX Kcal/hr-M2_℃. Some heat exchanger calculation software may generate a format similar to that used by the original poster: transfer rate: service 260 dirty 260 clean 405 Kcal/hr-M2_℃. The meanings of these terms are as follows: transfer rate refers to the overall heat transfer coefficient; service refers to Q/A*LMTD, that is, the overall heat transfer coefficient required under design conditions; dirty (which corresponds to the “minimum” value mentioned by the original poster) refers to the overall heat transfer coefficient taking into account the fouling factors on both the hot and cold sides under design conditions; clean refers to the overall heat transfer coefficient after the first startup or cleaning, when the fouling factors on both sides are zero. The values of dirty/service represent the design margin under the most adverse conditions, and this value is generally greater than 1. Otherwise, there isn’t enough margin at the end of operation under severe conditions. Once the meanings of these terms are understood, it’s easier to answer the original poster’s question, and it’s also possible to identify the issues in their data: specifically, the value of service should be less than that of dirty; otherwise, when fouling occurs and dirty becomes smaller than service, the heat exchanger will not meet the requirements. Were the data provided by the original poster from foreign design sources? It would be great if foreigners could be shown wrong! Hehe!

I don’t quite agree with what was said on floor 6: Since min. represents the overall heat transfer coefficient taken into account of the fouling coefficients on the hot and cold sides under design conditions, and service refers to the overall heat transfer coefficient required under those same design conditions, then the value of service should not be less than that of min.