Each heat exchange tube of the U-tube heat exchanger is bent into a U shape, and the inlet and outlet are respectively installed on both sides of the same tube sheet, and the head is divided into two chambers by a partition. Each tube is free to expand and contract, independent of the housing. Thereby eliminating thermal stress, the structure is simpler than the floating head heat exchanger. However, the tube process is not easy to clean, and the use has great limitations only for clean fluids.
The plate heat exchanger is composed of a set of rectangular thin metal heat transfer plates, and the plate is clamped and assembled on the bracket by a frame. The edge linings of two adjacent sheets are pressed by gaskets (made of various rubber or compressed asbestos, etc.), and the corners of the sheets have round holes to form a fluid passage.
The difference between plate heat exchanger and shell-and-tube heat exchanger:
a. High heat transfer coefficient
Since the 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 turbulence can be generated at a low Reynolds number (generally Re=50-200), so heat transfer The coefficient is high, which is generally considered to be 3 to 5 times that of the shell-and-tube type.
b. The logarithmic mean temperature difference is large, and the end temperature difference is small.
In the shell-and-tube heat exchanger, the two fluids flow in the tube and shell, respectively, which are generally cross-flow, with a small logarithmic mean temperature difference correction coefficient, while the plate heat exchangers are mostly cocurrent or countercurrent flow. The correction coefficient is usually about 0.95. In addition, the flow of cold and hot fluid in the plate heat exchanger is parallel to the heat exchange surface and there is no bypass flow, so that the temperature difference at the end of the plate heat exchanger is small, and the heat exchange with water can be Below 1 ° C, and shell-and-tube heat exchangers are generally 5 ° C.
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