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Keeping the plates of a plate heat exchanger clean is one of the important conditions for maintaining a high heat transfer coefficient. Between the plates, the fluid moves along narrow and tortuous flow channels; even the formation of a thin layer of scale can cause changes in these channels, affecting the flow of the fluid, resulting in an increase in pressure drop and a decrease in the heat transfer coefficient. For example, a sugar factory used plate heat exchangers for heating; due to inadequate treatment of the secondary water, the flow channels became clogged after just two months of use, preventing further operation. Below, the editor will provide a detailed introduction to the methods for cleaning plate heat exchangers: 1. Chemical cleaning method – Chemical cleaning involves circulating a chemical cleaning solution through the heat exchanger, where it reacts chemically with the dirt, causing the dirt and other deposits on the surface of the plates to dissolve, fall off, or be removed. This method does not require disassembling the heat exchanger, which not only simplifies the cleaning process but also reduces the physical effort involved in cleaning. Since the corrugations on the plates promote intense turbulence of the cleaning solution, which facilitates the dissolution of scale deposits, chemical cleaning is a relatively ideal method. 1) Common chemical cleaners ● Cleaners that remove dirt through dissolution (including water and organic solvents); ● Surfactant-based cleaners that remove dirt by utilizing surfactant properties (such as cationic, anionic, non-ionic, and amphoteric surfactants); ● Chemical cleaners that remove dirt through chemical reactions (such as acids, bases, salts, oxidizers, etc.). 2) Common methods for chemical cleaning ● Circulation method: A pump is used to force the cleaning solution to circulate, thereby carrying out the cleaning process. ●Impregnation method: Fill the equipment with the cleaning solution and let it sit for a certain period of time. ●Surge method: Fill the device with cleaning solution, then periodically remove a portion of the solution from the bottom and pour it back into the device to achieve thorough mixing and cleaning. 2. Mechanical (physical) cleaning method: Physical cleaning involves using various mechanical forces and energies to remove dirt from the surface of plates or pipes; for example, plates are manually scrubbed with brushes to achieve a cleaning effect. Physical cleaning methods are relatively direct, efficient, non-corrosive, safe, and environmentally friendly. However, thicker and harder layers of scale are difficult to clean thoroughly, and cleaning \"dead zones\" can occur when cleaning the interior of devices with complex structures. 3. Comprehensive cleaning method: In cases where the layer of dirt is hard and thick, it is difficult to clean it thoroughly using just one of the methods mentioned above. The combined method involves first using chemical cleaning to soften the scale layer, and then employing mechanical (physical) cleaning methods to remove it, in order to keep the plates clean. Precautions for cleaning plate heat exchangers: (1) During chemical cleaning, the flow rate of the cleaning solution should be maintained to increase the turbulence level of the solution. (2) Different types of dirt require corresponding chemical cleaners. Cleaning fluids that cause corrosion to the heat exchanger must not be used. (3) Carbon steel brushes must not be used for physical cleaning to avoid oxidative corrosion of the surface of the plates or heat exchange tubes. (4) No scratches shall appear on the metal surface during cleaning. (5) The cleaned plates or heat exchange tubes should be rinsed thoroughly with clean water and dried; they must be stored in a way that prevents deformation.