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2018
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06
Introduction to Coolers
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1. Overview: The tube-type cooler is a heat exchange device widely used in various industrial sectors such as metallurgy, chemical engineering, energy, transportation, light industry, and food processing. It is suitable for different operating conditions such as cooling, condensing, heating, evaporating, and waste heat recovery. Due to its robust structure, high elasticity, and strong adaptability, significant improvements have been made in its structure, process, and materials in recent years, making its technical performance more reasonable and advanced. Therefore, among the many types of heat exchangers, coolers and tube heat exchangers still hold an important position. 2. Structure and Working Principle: The tube-type cooler consists of two main parts: the outer shell and the inner cooler body.
1. Overview: The shell-and-tube cooler is a heat exchange device widely used in industries such as metallurgy, chemical engineering, energy, transportation, light industry, and food. It is suitable for various operating conditions such as cooling, condensing, heating, evaporation, and waste heat recovery. Due to its robust structure, high elasticity, and strong adaptability, significant improvements have been made in its structure, process, and materials in recent years, making its technical performance more reasonable and advanced. Therefore, among the many types of heat exchangers, the shell-and-tube cooler still holds an important position.
2. Structure and Working Principle: The shell-and-tube cooler consists of two main parts: the outer shell and the inner cooler body. Depending on the specific structural design, it can be classified into threaded and flanged connections externally; horizontally and vertically installed; floating disc and floating head types; and in terms of tube structure, it can be spiral or finned tubes. Various structural forms of baffle plates include arc baffles, rectangular baffles, double weir baffles, and circular baffles, selected according to specific conditions. The outer shell includes the cylinder, water distribution cover, and return water cover, equipped with inlet and outlet oil pipes and water pipes, as well as drain plugs, air vent plugs, zinc rod installation holes, and thermometer interfaces. The cooler body consists of cooler tubes, fixed hole plates, movable hole plates, and baffle plates. The ends of the cooler tubes connect to the fixed and movable hole plates, while the fixed hole plate connects to the outer flange, and the movable hole plate can freely expand and contract within the outer body to eliminate the impact of temperature changes on the cooler tubes due to thermal expansion and contraction. The baffle plates enhance heat transfer and support the cooler tubes. The heat medium flows from the inlet on the shell to the outlet through various baffle channels in a tortuous path. The cooling medium flows in a double-pipe arrangement, entering half of the cooler tubes from the water inlet through the water distribution cover, then flowing into the other half of the cooler tubes from the return water cover to the other side's water distribution cover and outlet pipe. The cooling medium absorbs the residual heat released by the heat medium and is discharged from the outlet, maintaining the working medium at the rated working temperature.
3. Usage and Operation
1. The foundation of the cooler must be sufficient to prevent sinking. There should be enough space at the end of the fixed hole plate cover to allow for the extraction of the tube bundle from the shell. When positioning the cooler, it should be done according to lifting specifications, and after leveling, the anchor bolts should be tightened, connecting the inlet and outlet pipes of the hot and cold media.
2. Before starting the cooler, the air inside the chamber should be completely released to improve heat transfer efficiency. The steps are as follows:
(1) Loosen the air vent plugs on the hot and cold media ends and close the media discharge valve;
(2) Slowly open the inlet valves for the hot and cold media until the media overflows from the air vent, then tighten the air vent plugs and close the inlet valves.
3. When the water temperature rises by 5 to 10°C, open the inlet valve for the cooling medium (Note: Do not open the inlet valve quickly, as a large flow of water through the cooler can create a poorly conductive 'subcooled layer' on the heat exchanger surface), then open the inlet and outlet valves for the hot medium to allow flow, and adjust the flow rate of the cooling medium to maintain the hot medium at the optimal operating temperature.
4. If electrochemical corrosion occurs on the cooling medium side, zinc rods can be installed at designated locations.
5. A filtration device should be installed before the cooler for relatively dirty media.
6. The pressure of the cooling medium should be greater than that of the cooler medium.
4. Maintenance and Repair
1. After long-term operation, the surface of the cooler tubes may accumulate dirt, increasing thermal resistance and flow resistance, gradually reducing heat exchange performance, which may fail to meet the cooler's requirements. Clearly, the focus of maintenance should be on cleaning the dirt. Here are several cleaning methods:
(1) a. Use an electric cleaning tool. This involves a motor driving a flexible shaft to rotate, with a nylon or steel wire brush attached to the end for scrubbing. Water is injected around the shaft through a watertight cover to wash away loose dirt in a timely manner.
b. Use a round tube with a steel wire brush welded to one end, similar in diameter to the inner tube, rotating while pushing forward. Dirt can accumulate in the inner cavity of the tube without thickening, making it easier to push. This method is commonly used but has a high labor intensity.
(2) Use a high-pressure pump (pressure 10-20 Mpa) to spray high-pressure water for flushing, which is effective, mainly for cleaning between tubes.
(3) Use sponge balls for automatic cleaning inside the heat exchange tubes. Different hardness sponge balls are used according to the type of scale. For special hard scales, a 'strip' type of diamond sand sponge ball can be used. The sponge ball, being soft and elastic, enters the heat exchange tube, compressing against the inner wall, creating relative motion with the wall to continuously rub against it and remove deposits.
(4) Chemical cleaning method: a. For oil-side cleaning, trichloroethylene solution can be used for reverse circulation cleaning, with the solution pressure not exceeding the rated working pressure. The cleaning time depends on the dirt condition, followed by flushing with clean water until the outflowing water is clean. b. Soak in carbon tetrachloride. Fill the cooler with the solution and observe the color after 15-20 minutes. If heavily contaminated, replace with new liquid and soak again until the outflowing solution is similar in color to clean water, then rinse repeatedly with clean water. This cleaning should be done in a well-ventilated environment to avoid poisoning. This method is suitable for oil cleaning.
2. Most failures of the cooler are caused by the cooler tubes. Due to corrosion, cavitation, and wear, the tube walls may thin and perforate, and due to thermal expansion and contraction, vibrations during fluid movement can cause damage at connections and other areas. When the cooler tubes are damaged, the two media will intermix, and timely repairs should be made. The methods include:
(1) Identify the damaged cooling tubes and seal both ends with tube plugs. The taper of the tube plug should be between 3 to 5 degrees, and the hardness of the tube plug material should be less than or equal to that of the tube. The total number of sealed tubes must not exceed 10% of the total number.
(2) Remove the damaged tube and replace it with a new one, then re-expand it.
(3) If there is leakage at the connection between the tube end and the tube sheet, it should be re-expanded. If corrosion is severe, the tube bundle should be replaced.
3. For coolers that are not in use during winter, drain the medium inside to prevent freezing and cracking of the cooler. 4. The disassembly and reassembly of the cooler should follow the steps below:
(1) Close the oil and water valves, drain the retained medium, and then disassemble the cooler from the system.
(2) Remove the return water cover and the water distribution cover, and check the sealing ring, damage to the cooling tubes, and accumulation of dirt. If only tube plugging or replacement of cooling tubes is needed, it can be done immediately. If the tube bundle needs to be pulled out, it must be removed from the fixed tube sheet direction (for large coolers, it can be done vertically with the fixed tube sheet facing down, and then use lifting equipment to lift the shell to expose the tube bundle).
(3) During assembly, follow the reverse process of disassembly, and the sealing rings should generally be replaced with new ones.
(4) After installation, perform air-tightness tests on the oil side first and then the water side, with the test pressure being greater than 1.2 times the actual working pressure.
Five, Faults and Troubleshooting: Decreased heat exchange performance
1. Faults and Causes
(1) Insufficient water flow in the cooler; (2) Accumulation of gas in the chamber; (3) Accumulation of dirt on the heat exchange tube wall increasing flow resistance and thermal resistance; (4) Oil floating in the machine oil or a mixture of oil and water in the cooler; (5) Leakage at the flange connection between the return water cover and the water distribution cover; (6) Corrosion at the connection between the dynamic and static hole plates and the heat exchange tubes leading to loss of sealing.
2. Troubleshooting Methods
(1) Faults and Causes: ① Open the inlet valve wider; ② Clear blocked pipes, valves, filters, or heat exchange tubes;
(2) Unscrew the plug to release air;
(3) Use appropriate methods to clean the dirt on the inner and outer surfaces of the heat exchange tubes;
(4) ① Replace the heat exchange tubes; ② Use tube plugs to seal damaged tubes (not exceeding 10);
(5) ① Tighten the screws on both end covers; ② Replace the sealing gasket;
(6) Replace the tube bundle.
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Chongqing Southwest Saiwei Heat Exchange Equipment Co., Ltd. is committed to providing customers with excellent heat exchange equipment solutions. With the rapid development of the industrial field, the demand and application of heat exchange equipment are becoming more and more extensive. The company deeply knows that each customer's needs are unique, so customized solutions have become our core competitiveness.
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Chongqing Southwest Saiwell Heat Exchange Equipment Co., Ltd.
Specializing in the research, development, production and sales, equipment consulting, maintenance, and accessory services of heat exchange technology, equipment, and systems, and undertaking the design and installation of thermal system engineering, energy conservation and emission reduction, and energy conservation and emission reduction system engineering.
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