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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.

30

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.

30

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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2022-09

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