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Comparison between plate heat exchanger and shell-and-tube heat exchanger
1. High heat transfer coefficient Because different corrugated plates are inverted with each other, a complicated flow path is formed, so that the fluid flows three-dimensionally in the flow path between the corrugated plates, and can be produced at a low Reynolds number (generally Re=50-200). Turbulent flow, so the heat transfer coefficient is high, generally considered to be 3 to 5 times the shell-and-tube type.
2. The logarithmic mean temperature difference is large, and the terminal temperature difference is small. In the shell-and-tube heat exchanger, the two fluids flow in the tube and shell processes respectively, which is generally a cross-flow flow, and the logarithmic mean temperature difference correction coefficient is small, and the plate type The heat exchangers are mostly cocurrent or countercurrent flow modes, and the correction coefficient is usually about 0.95. In addition, the flow of cold and hot fluids in the plate heat exchanger is parallel to the heat exchange surface and there is no bypass flow, thus making the plate heat exchanger The temperature difference at the end of the device is small, the heat transfer to water can be lower than 1 ° C, and the shell-and-tube heat exchanger is generally 5 ° C.
3. The small-plate heat exchanger covers a compact structure, and the heat exchange area per unit volume is 2~5 times that of the shell-and-tube type. It is not the same as the shell-and-tube type, and the maintenance site for the extracted tube bundle is reserved. The heat exchange capacity of the plate heat exchanger is about 1/5~1/8 of the shell-and-tube heat exchanger.
4. It is easy to change the heat exchange area or process combination. As long as several plates are added or reduced, the purpose of increasing or decreasing the heat exchange area can be achieved. By changing the plate arrangement or replacing several plates, the required process combination can be achieved. To adapt to the new heat exchange conditions, the heat transfer area of the shell-and-tube heat exchanger is almost impossible to increase.
5. The thickness of the plate of the light weight plate heat exchanger is only 0.4~0.8mm, while the thickness of the heat exchange tube of the shell-and-tube heat exchanger is 2.0~2.5mm, and the shell-shell type is more than the plate heat exchanger. The frame is much heavier, and the plate heat exchanger is generally only about 1/5 of the shell-shell weight.
6. Low price With the same material, the plate heat exchanger is about 40% to 60% lower than the shell-and-tube type under the same heat exchange area.
7. Convenient production The heat transfer plate of the plate heat exchanger is stamped, highly standardized, and can be mass-produced. The shell-and-tube heat exchanger is generally hand-made.
8. Easy to clean The frame type plate heat exchanger can loosen the plate bundle and loosen the plate for mechanical cleaning as long as the compression bolt is loosened, which is very convenient for the heat exchange process of the equipment to be cleaned frequently.
9. Small heat loss The plate heat exchanger only exposes the outer plate of the heat transfer plate to the atmosphere, so the heat loss is negligible and no heat preservation measures are required. The shell-and-tube heat exchanger has a large heat loss and requires a heat insulating layer.
10. Smaller capacity is 10%~20% of shell-and-tube heat exchangers.
11. Large pressure loss per unit length Since the gap between the heat transfer surfaces is small, the heat transfer surface has irregularities, so the pressure loss is larger than that of the conventional smooth tube.
12. Not easy to scale Because the inside is fully turbulent, it is not easy to scale, and its fouling coefficient is only 1/3~1/10 of the shell-and-tube heat exchanger.
13. The working pressure should not be too large, the medium temperature should not be too high, and it may leak. The plate heat exchanger is sealed with a gasket. The working pressure should not exceed 2.5 MPa, and the medium temperature should be below 250 °C, otherwise it may leak.
14. Easy to block Because the passage between the plates is very narrow, generally only 2~5mm. When the heat exchange medium contains larger particles or fibrous substances, it is easy to block the passage between the plates.