a. High heat transfer coefficient Because different corrugated plates are inverted with each other, a complicated flow path is formed, so that the fluid flows in a three-dimensional flow in the flow path between the corrugated plates, and can be generated 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.
b. 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 the water can be lower than 1 ° C, and the shell-and-tube heat exchanger is generally 5 ° C. c. The small plate heat exchanger has a compact structure, and the heat exchange area per unit volume is the tube. The shell type is 2~5 times, and it is not like the shell-and-tube type to reserve the inspection place for the tube bundle. Therefore, the same heat exchange amount is realized. The plate heat exchanger covers an area of ​​about 1/0 of the shell-and-tube heat exchanger. 5~1/8.
d. 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.
e. The thickness 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-and-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.
f. The price is low and the same material is used. Under the same heat exchange area, the price of the plate heat exchanger is about 40%~60% lower than that of the shell and tube type.
g. The heat transfer plates for making convenient plate heat exchangers are stamped, highly standardized, and can be mass-produced. Shell-and-tube heat exchangers are generally hand-made.
h. Easy to clean the frame type plate heat exchanger As long as the compression bolt is loosened, the plate bundle can be loosened and the plate can be removed for mechanical cleaning, which is very convenient for the heat exchange process of the equipment to be cleaned frequently. i. Heat Loss Small plate heat exchanger Only the outer plate of the heat transfer plate is exposed 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.
j. The smaller capacity is 10%~20% of the shell-and-tube heat exchanger.
k. The pressure loss per unit length is large due to the small gap between the heat transfer surfaces, and the heat transfer surface has irregularities, so the pressure loss is larger than that of the conventional smooth tube.
l. It is not easy to scale. Because it is fully turbulent inside, it is not easy to scale. The fouling coefficient is only 1/3~1/10 of the shell-and-tube heat exchanger.
m. The working pressure should not be too large, the medium temperature should not be too high, it is possible to leak the plate heat exchanger with a gasket seal, the working pressure should generally not exceed 2.5MPa, the medium temperature should be below 250 °C, otherwise it may leak.
n. Easy to block because the channel between the plates is very narrow, generally only 2~5mm. When the heat exchange medium contains large particles or fibrous substances, it is easy to block the passage between the plates.
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