Enhancing Heat Transfer in Heat Exchange Equipment: Common Methods
What methods can be employed to enhance heat transfer in heat exchanger equipment?
One primary method is to increase the heat transfer surface area through various structural modifications:
(1) Utilizing finned tubes, nailhead tubes, threaded tubes, spiral tubes, or bellows.
(2) Machining the surface of the pipe with spiral grooves or threads.
(3) Employing smaller diameter pipes to increase the number of pipes within the same tube plate area, thereby augmenting the heat transfer area.
Another approach involves raising the fluid flow velocity within the heat exchanger, significantly improving the heat transfer coefficient:
(1) Incorporating spoilers, such as inserting spiral bands in the pipe or using baffle plates and false pipes.
(2) Increasing the number of pipe passes or shell sides.
Additionally, utilizing materials with high thermal conductivity, implementing effective anti-corrosion and anti-scaling measures, and conducting timely descaling can all contribute to improving heat transfer efficiency.
Why does scale form in cooling water heat exchangers?
Scale is created by the precipitation of dissolved salt crystals in water, adhering to the heat exchanger tube walls. It is characterized by compact, hard, and firmly attached deposits that are challenging to remove. Suspended particles in the water can act as seed crystals, and impurity ions, bacteria, and rough metal surfaces catalyze the crystallization process, reducing the required supersaturation for crystallization. As a result, cooling water heat exchangers are prone to scale formation.
What are the quality standards for heat exchange tube replacement?
(1) The pipe surface should be free from defects like cracks, folds, and heavy skin.
(2) When pipes need to be spliced, only one welding port can be retained at most for the same heat exchange tube (U-shaped pipes can retain 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 sections must not have splicing welds. The misalignment of the counterpart should not exceed 15% of the pipe wall thickness, and not more than 0.5mm.
(3) Hardness testing is required when using expanded tube joints between the pipe and tubesheet. The pipe's hardness should be 30HB lower than that of the tubesheet. If the pipe's hardness is higher or close to the tubesheet's hardness, both ends of the pipe should be annealed, with an annealed length 80-100mm longer than the thickness of the pipe plate.
(4) Both ends of the pipe and tubesheet holes should be clean, free of grease and other dirt, with no defects affecting the tightness of the expanded tube joint.
(5) Both ends of the pipe should extend into the tubesheet, with a length of (4±1)mm.
(6) When welding the pipe and tubesheet, the cut surface of the pipe should be flat, free of burrs, bumps, cracks, interlayers, etc. There should be no debris, such as slag, iron oxide, or grease, that affects welding quality.
One primary method is to increase the heat transfer surface area through various structural modifications:
(1) Utilizing finned tubes, nailhead tubes, threaded tubes, spiral tubes, or bellows.
(2) Machining the surface of the pipe with spiral grooves or threads.
(3) Employing smaller diameter pipes to increase the number of pipes within the same tube plate area, thereby augmenting the heat transfer area.
Another approach involves raising the fluid flow velocity within the heat exchanger, significantly improving the heat transfer coefficient:
(1) Incorporating spoilers, such as inserting spiral bands in the pipe or using baffle plates and false pipes.
(2) Increasing the number of pipe passes or shell sides.
Additionally, utilizing materials with high thermal conductivity, implementing effective anti-corrosion and anti-scaling measures, and conducting timely descaling can all contribute to improving heat transfer efficiency.
Why does scale form in cooling water heat exchangers?
Scale is created by the precipitation of dissolved salt crystals in water, adhering to the heat exchanger tube walls. It is characterized by compact, hard, and firmly attached deposits that are challenging to remove. Suspended particles in the water can act as seed crystals, and impurity ions, bacteria, and rough metal surfaces catalyze the crystallization process, reducing the required supersaturation for crystallization. As a result, cooling water heat exchangers are prone to scale formation.
What are the quality standards for heat exchange tube replacement?
(1) The pipe surface should be free from defects like cracks, folds, and heavy skin.
(2) When pipes need to be spliced, only one welding port can be retained at most for the same heat exchange tube (U-shaped pipes can retain 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 sections must not have splicing welds. The misalignment of the counterpart should not exceed 15% of the pipe wall thickness, and not more than 0.5mm.
(3) Hardness testing is required when using expanded tube joints between the pipe and tubesheet. The pipe's hardness should be 30HB lower than that of the tubesheet. If the pipe's hardness is higher or close to the tubesheet's hardness, both ends of the pipe should be annealed, with an annealed length 80-100mm longer than the thickness of the pipe plate.
(4) Both ends of the pipe and tubesheet holes should be clean, free of grease and other dirt, with no defects affecting the tightness of the expanded tube joint.
(5) Both ends of the pipe should extend into the tubesheet, with a length of (4±1)mm.
(6) When welding the pipe and tubesheet, the cut surface of the pipe should be flat, free of burrs, bumps, cracks, interlayers, etc. There should be no debris, such as slag, iron oxide, or grease, that affects welding quality.
