The change of inlet and outlet water temperature and pressure before and after heat exchanger cleaning can show the cleaning effect. The following is an example of dismantling and cleaning the plate heat exchanger for heating in the office building of Henan water conservancy department in October 2007. 51 1 chemical cleaning process control (see Table 1) table 1 chemical cleaning process control cleaning time cleaning agent molar concentration / (mol? L - 1) pH cleaning measures 8 ∶ 0001 0211 5 cycle dosing 9 ∶ 0001 1211 0 continue cycle 10 ∶ 0001 0511 5 cycle dosing 11 ∶ 0001 1311 0 continue cycle 12 ∶ 0001 0811 0 add soaking 14 ∶ 0001 0611 5 cycle dosing 15 ∶ 0001 1311 0 continue Cycle 16 ∶ 0001 1211 0 continue cycle 17 ∶ 0001 1111 0 continue cycle 18 ∶ 0001 1111 0 stop cycle? 24? Clean the world phase 1 © 1994-2010 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net In the cleaning process, a combination of cycle cleaning and immersion cleaning was used, and the cleaning process took 10 hours. The cleaning end point is judged by the change of cleaning agent concentration with time and the reaction degree of scale on the heat transfer plate. When the cleaning agent concentration does not change or the change is very small within 2 hours, it can be regarded as the cleaning end point. Dirt.