What are the common methods to enhance heat transfer by heat exchange equipment?
The main methods to enhance heat transfer of heat exchange equipment are: first, to adopt the structure of increasing heat transfer surface:
(1) Using finned tubes, nailhead tubes, threaded tubes, bellows and other spiral tubes.
(2) We machine the surface of the pipe with spiral groove pipe and threaded pipe.
(3) The use of small diameter pipe can increase the number of pipes on the same tube plate area and increase the heat transfer area.
The second is to increase the flow velocity of fluid in the heat exchanger, which can greatly improve its heat transfer coefficient:
(1) Add a spoiler, such as inserting a spiral band in the pipe, setting a baffle plate and a false pipe outside the pipe.
(2) Increase the number of pipe passes or shell sides.
In addition, means of using materials with good thermal conductivity to manufacture heat exchangers, good anti-corrosion and anti-scaling measures for heat exchangers, and timely descaling can all improve the heat transfer effect.
Why does the cooling water heat exchanger produce scale?
Scale is formed by the precipitation of dissolved salt crystals in water and attached to the wall of the heat exchanger tube. It features in compactly hard, firm adhesion which is difficult for removal. A large number of suspended particles in the water can become seed crystals. Other impurity ions, bacteria and rough metal surfaces have a strong catalytic effect on the crystallization process, greatly reducing the supersaturation required for crystallization, so the cooling water heat exchanger is easy to produce scale.
What are the quality standards for the replacement of heat exchange tubes?
(1) The surface of the pipe should be free from defects such as cracks, folds and heavy skin.
(2) When we need to splice the pipes, the same heat exchange tube can only retain one welding port at most (the U-shaped pipe can reserve two welding ports). The shortest pipe length should not be less than 300mm, and the U-shaped pipe bend section must be at least 50mm long. Straight pipe section must not have splicing welds. The amount of misalignment of the counterpart should not exceed 15% of the pipe wall thickness, and not more than 0.5mm.
(3) The hardness of the pipe shall be tested when the pipe and tubesheet adopt expanded tube joint. It requests the hardness of the pipe generally 30HB lower than that of tubesheet. When the hardness of the pipe is higher than or close to the hardness of the pipe plate, we should anneal both ends of the pipe, and the annealed length is 80-100mm longer than the thickness of the pipe plate.
(4) Both ends of the pipe and tube plate holes should be clean, free of grease and other dirt, and there should be no longitudinal or spiral nicks or other defects affecting the tightness of expanded tube joint.
(5) Both ends of the pipe should extend the tube plate, whose length is (4±1)mm.
(6) When we weld the pipe and the tube sheet, the cut surface of the pipe should be flat, free of burrs, bumps, cracks, interlayers, etc., and there should be no slag, iron oxide, grease and other debris that affect the welding quality.