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Common malfunctions of plate heat exchangers

Common malfunctions of plate heat exchangers

Leakage Mainly manifested as seepage (small amount, discontinuous water droplets) and leakage (large amount, continuous water droplets). The main parts where leakage occurs are the seals between plates, the secondary sealing leakage grooves of the plates, and the inner side of the end plates and the pressure plates. Liquid Leakage The main characteristic is that the medium on the side with higher pressure enters the medium on the side with lower pressure, and the system will show abnormal pressure and temperature. If the medium is corrosive, it may also cause corrosion of the sealing gasket of the plate heat exchanger. Liquid leakage usually occurs in the flow guiding area or the secondary sealing area. Large Pressure Drop The pressure drop at the inlet and outlet of the medium exceeds the design requirements, or even many times higher than the design value, seriously affecting the system's requirements for flow rate and temperature. In the heating system, if the pressure drop on the hot side is too large, the flow rate on the primary side will be seriously insufficient, that is, the heat source is insufficient, resulting in the secondary side outlet temperature not meeting the requirements. Heating Temperature Cannot Meet Requirements The main characteristic is that the outlet temperature is too low and does not meet the design requirements.

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2022-09

Cooling characteristics of shell and tube heat exchangers

Cooling characteristics of shell and tube heat exchangers

1. The heat transfer tube adopts a copper tube with externally rolled fins, which has high thermal conductivity and a large heat transfer area. 2. The baffle plates guide the shell-side fluid to flow continuously in a zigzag shape within the heat exchanger. The spacing between the baffle plates can be adjusted according to the optimal flow rate. The structure is robust and can meet the heat exchange requirements of large or even ultra-large flow rates and high pulsation frequency shell-side fluids. 3. When the shell-side fluid is oil, it is suitable for heat exchange of low-viscosity and relatively clean oil.

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2022-09

Component functions of plate heat exchangers

Component functions of plate heat exchangers

The reasonable selection of heat exchange area is the key to procurement. When selecting a heat exchanger, the required flow rate should be determined first based on process requirements, material viscosity, heat exchange temperature difference, etc. Excessive flow rate leads to waste and easy blockage of the flow channel. Too small a flow rate affects usage, increases non-fermentation time, and can cause adverse phenomena such as damage to the baffle plate due to excessive pressure. Therefore, scientific selection should be made based on operating conditions. Plate heat exchangers have a plate thickness of only 0.6~0.8mm, while tube-shell heat exchangers have a heat exchange tube thickness of 2.0~2.5mm; the shell of a tube-shell heat exchanger is much heavier than that of a plate heat exchanger. Under the same heat exchange mission, the heat exchange area required by a plate heat exchanger is smaller than that of a tube-shell heat exchanger. From a strength perspective, the structure of a tube-shell heat exchanger is excellent, but from a heat exchange perspective, it is not ideal, because when the fluid flows in the shell side, there are bypasses between the baffle plate-shell, baffle plate-heat exchange tube, and tube-shell. The fluid passing through these bypasses does not fully participate in the heat exchange. In a plate heat exchanger, there is no bypass, and the corrugation of the plates allows the fluid to become turbulent at a lower flow rate. Therefore, plate heat exchangers have a higher heat transfer coefficient, usually 3~5 times that of tube-shell heat exchangers.

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2022-09

Assembly and disassembly of plate heat exchangers

Assembly and disassembly of plate heat exchangers

The newly purchased heat exchanger has been assembled into a whole unit and can be installed as a whole. It should not be disassembled unless necessary. Disassembly and reinstallation of plate heat exchangers is a delicate task that requires experienced personnel to follow certain rules to ensure good sealing and normal operation after installation. Incorrect assembly and installation can cause poor sealing and even plate deformation and damage, which is difficult to restore. Before disassembling the heat exchanger, use a steel ruler to measure the original thickness of the plate pack. Measurements should be taken at the four corners (top, bottom, left, and right) of the equipment and recorded. During reinstallation, this thickness should be restored as much as possible. If the number of plates is increased or decreased, the correct total thickness should be calculated first. For example, with 80 BR50 plates, the nominal thickness is: 80 × (3.8 + 0.6) = 352 mm The difference between the thickness after installation and tightening and the nominal value should be less than 1%; in the above example, the thickness should be between 347 and 357 mm. Plate heat exchangers are usually tightened into a whole unit using 6-12 bolts. When assembling or disassembling, these bolts should be tightened or loosened evenly and balanced; they should never be tightened or loosened unevenly. When disassembling and loosening the bolts, the center bolts should be loosened first, followed by the corner bolts. Initially, loosen 1-2 turns at a time, then more, repeating several times until completely loosened. During the loosening process, the total thickness of the plates should be measured at the four corners, with a left-right deviation of no more than 10 mm and an up-down deviation of no more than 25 mm.

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2022-09

What are the characteristics of gas flow in a heat exchanger?

What are the characteristics of gas flow in a heat exchanger?

Different gas flow patterns within a heat exchanger result in different thermal characteristics. Under the same inlet waste gas temperature, countercurrent flow can preheat air to a higher temperature than cocurrent flow. Under the same conditions, countercurrent flow achieves greater heat transfer and a more compact structure compared to cocurrent flow. From the perspective of heat exchanger wall operating conditions, cocurrent flow is more advantageous. This is because the temperature of the heat exchanger wall is nearly equal at both ends for cocurrent flow, with a lower maximum temperature than countercurrent flow. This makes the heat exchanger less prone to deformation and damage, and less demanding on material properties. In countercurrent flow heat exchangers, the temperature of the wall at the high-temperature end is close to the waste gas inlet temperature, resulting in a large temperature difference between the two ends. This places higher demands on the wall material and, due to the large temperature difference between the two ends, makes it more susceptible to deformation and damage. In practical applications, countercurrent flow is more commonly used in heat exchangers.

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2022-09

Plate heat exchangers use corrosion inhibitors to achieve corrosion protection and maintenance effects

Plate heat exchangers use corrosion inhibitors to achieve corrosion protection and maintenance effects

How should plate heat exchangers be maintained and protected against corrosion during use? After understanding the various causes of heat exchanger corrosion, how to choose suitable corrosion prevention measures can achieve the goal of efficient equipment utilization. The following corrosion prevention methods are proposed based on the relevant corrosion situations: This mainly introduces corrosion inhibitors. Corrosion prevention using corrosion inhibitors. When corrosion inhibitors are combined with cathodic inhibitors, they can achieve satisfactory and economical corrosion prevention effects. Chromate-zinc-polyphosphate: The use of polyphosphate is due to its ability to clean metal surfaces and has corrosion inhibition capabilities. Polyphosphate can be partially converted into orthophosphate, which, when combined with calcium, forms colloidal cations, inhibiting the formation of impurities in the plate heat exchanger. Chromate-zinc-phosphonate: This method is similar to the above method, except that sodium phosphonate replaces polyphosphate. The almost formed scale is effectively inhibited by aminomethylenephosphonate, and calcium salt precipitation can be controlled even at a pH of 9. Chromate-zinc-hydrolyzed polyacrylamide: Due to the dispersing effect of the cationic copolymer hydrolyzed polyacrylamide, it can prevent the scale in the plate heat exchanger from turning into fouling.

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2022-09

How to improve the heat transfer efficiency of plate heat exchangers

How to improve the heat transfer efficiency of plate heat exchangers

Plate heat exchangers are wall-type heat exchangers. The cold fluid transfers heat through the heat exchanger plates, and the fluid is in direct contact with the plates. The heat transfer method is heat conduction and convection. The key to improving the heat transfer efficiency of a plate heat exchanger is to increase the heat transfer coefficient and the logarithmic mean temperature difference. 1. To improve the heat transfer coefficient of the heat exchanger, it is necessary to simultaneously increase the surface heat transfer coefficients on both the cold and hot sides of the plate, reduce the fouling resistance, select plates with high thermal conductivity, and reduce the thickness of the plates to effectively improve the heat transfer coefficient of the heat exchanger. (1) Improve the surface heat transfer coefficient of the plate Because the corrugations of the plate heat exchanger can cause the fluid to become turbulent at a lower flow rate, a higher surface heat transfer coefficient can be obtained. The surface heat transfer coefficient is related to the geometric structure of the plate corrugations and the flow state of the medium. The plate corrugations include chevron, straight, and spherical shapes. After years of research and experiments, it has been found that chevron plates with a triangular corrugated cross-section have a higher surface heat transfer coefficient, and the larger the corrugation angle, the higher the flow rate of the medium in the inter-plate flow channel, and the greater the surface heat transfer coefficient. (2) Reduce fouling resistance The key to reducing the fouling resistance of the heat exchanger is to prevent plate scaling. When the plate structure thickness is 1 mm, the heat transfer coefficient is reduced by about 10%. Therefore, it is necessary to monitor the water quality at both ends of the heat exchanger to prevent plate scaling and prevent impurities in the water from adhering to the plates. Some heating units add chemicals to the heating medium to prevent water theft and steel corrosion. Therefore, attention must be paid to the water quality and the fouling of the heat exchanger plates caused by viscous chemicals. If there are viscous impurities in the water, a special filter should be used for treatment. When selecting chemicals, non-viscous chemicals should be selected.

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