The U-tube heat exchanger bends the heat exchange tubes into a U-shape, with both ends fixed on the same tube plate. As the shell and heat exchange tubes are separate, the tube bundle can expand and contract freely without generating differential stress due to temperature differences in the medium. The U-tube heat exchanger has only one tube plate and no floating head, making its structure relatively simple. The tube bundle can be easily removed and installed, facilitating cleaning, and possesses the advantages of a floating head heat exchanger. However, since the heat exchange tubes are bent into U-shapes with unequal radii, only the outer tube can be replaced if damaged, while other tubes can only be plugged if they are damaged. Additionally, compared to the fixed tube plate heat exchanger, the tube bundle has gaps in the middle due to the limitation of the bending radius of the heat exchange tubes, allowing fluid to take short-cuts easily, which affects the heat transfer efficiency.