What is a heat exchanger?
A heat exchanger is a system we use to transfer heat between a source and a working fluid. We use heat exchangers in both cooling and heating processes. And we separate the fluids by a solid wall to prevent mixing or they may be in direct contact. We widely use them in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment.
What are the maintenance standards for heat exchangers?
Part 1 (1) In the operation of core-pulling, core-loading, transportation and hoisting of heat exchanger bundle, the exposed wire rope shall not be directly tied. When we move and lift the tube bundle, we should place it on the specific supporting structure to avoid damaging the heat exchange tube. (2) We should clean the structure inside and outside the tube bundle. (3) When the tube box and floating head have partitions, we shall process the gaskets as a whole without any defects affecting the sealing. (4) Tube bundle plugging: in the same pipe, the number of blocked pipes generally does not exceed 10% of its total. The number of blocked pipes can become increased appropriately within the allowable range of the technological index. (5) The parts used should meet the relevant technical requirements and have a material quality certificate.
(6) Change the heat pipe. (7) The overall replacement of the bundle shall be in accordance with GB1511999 (steel tube shell type heat exchanger) or the design drawings. (8) Perform shell repair according to SHS01004-2004 “Rule of Maintenance and Repair of Pressure Vessels”. (9) Select the replacement of sealing gasket according to the design requirements. (10) When it needs to replace the bolts and nuts of heat exchangers, we should select them according to the design requirements and then tighten heat exchanger bolts generally in the order shown in FIG. 2-25 and apply appropriate thread lubricant or anti-bite mixture.
Why we should clean heat exchangers regularly?
After we operate the heat exchanger for a period of time, dirt will often accumulate on the heat transfer wall surface, which will cause additional thermal resistance to the heat transfer and reduce the K value. Generally, the thermal resistance of the dirt is larger than that of the wall surface, so we should consider the influence in the design, and we should regularly clean the heat exchanger in operation.
Cleaning method of heat exchangers
Commonly used cleaning methods are air sweeping, water washing, steam washing, chemical cleaning and mechanical cleaning. How does the surface structure of the heat exchange tube affect the heat exchange result? Use specially designed surface structure of heat exchange tubes, such as finned tubes, nail head tubes, threaded tubes, etc. On the one hand, the heat transfer area becomes increased; on the other hand, the turbulence effect of the special surface greatly increases the degree of turbulence of the fluid outside the tube. Both aspects can improve the overall heat exchange effect of the heat exchanger, so these surface structures are superior to the smooth tube surface. What methods we commonly use for descaling the surface of heat exchange tubes? The common methods of descaling the surface of heat exchange tubes are: manual brazing descaling, mechanical descaling, pressure water descaling, chemical descaling, ultrasonic descaling, etc. What are the methods to prevent scale on the surface of heat exchange tubes? (1) Nickel and phosphorus plating (2) Chemical coating and 847 coating (3) Install ultrasonic scale inhibitor in cold water pipeline.