Discussion on the operations for putting heat exchangers into use and taking them out of use
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In the operation of heat exchangers, many factory operation manuals state that cold material should be introduced first, followed by hot material; the reverse order is applied when shutting them down. Some manufacturers suggest doing this in order to prevent the heat exchanger from being heated in only one flow path, that is, with no flow on the cold side while the hot side is heated alone. Other reasons given are to avoid damage to the heat exchanger caused by deformation under extreme cold or heat conditions, among other things. Logically speaking, for heat exchangers used in waste heat recovery, steam heaters, coolers, etc., it is generally fine to start by introducing cold fluid first. However, for heat exchangers whose maximum temperature is equal to the ambient temperature, it is usually necessary to introduce the hot fluid first. Could you explain how you understand the process of starting up and shutting down heat exchangers? What is the typical sequence of operation for your heat exchangers?
In addition to the reasons mentioned by the original poster, another issue is that feeding the hot material first and then the cold material may cause the cold material to vaporize rapidly, thereby damaging the heat exchanger
For heat exchangers with a large temperature difference, it is generally advisable to first put into use those with a smaller temperature difference between the fluid and the ambient temperature, and then introduce the other type of fluid. When the temperature difference between the two and the difference from the ambient temperature is not large, the order of operation doesn’t matter much. For heat exchangers that undergo cooling, it is possible to first use a hot medium at normal temperature and then introduce the cold medium. Just my personal opinion