Heat exchanger gasket, U-tube heat exchanger each tube is bent into a U-shape, both ends of the tube are fixed on the same tube sheet, Shandong heat exchanger gasket 6 (2) U-tube heat exchanger. Each tube of the U-tube heat exchanger is bent into a U-shape, and both ends of the tube are fixed on the same tube sheet, so each tube can stretch freely to solve the compensation problem. This type of heat exchanger has simple structure and light weight, and is suitable for high temperature and high pressure. Its main disadvantage is that it is difficult to clean the tube side; Because the tube needs a certain bending radius, the tubesheet utilization rate is poor（ 3) Floating head heat exchanger. One end of the tubesheet at both ends of the floating head heat exchanger is not fixedly connected with the shell, which is called floating head. In this way, when the thermal expansion of the tube bundle and the shell is different due to the large temperature difference, the tube bundle and the floating head can expand and contract freely in the shell, independent of the shell, so as to solve the problem of thermal compensation. In addition, because the tubesheet at the fixed end is connected with the shell by flange, the tube bundle can be extracted from the gasket body of the shell heat exchanger, which is convenient for cleaning and maintenance. So floating head heat exchanger is widely used, but the structure is more complex. The metal consumption is large and the cost is high. The heat exchanger needed in this design is cooled by circulating cooling water. Considering this factor, it is estimated that the temperature difference between the tube wall and the shell wall of the heat exchanger is large. When the temperature difference between the two fluids is large, the fixed tube sheet can be selected. And it has the advantages of simple structure and low cost. Therefore, the fixed tube sheet is preliminarily selected in this design. Generally, heat exchangers are made of metal materials, and carbon steel and low alloy steel are mostly used to manufacture medium and low pressure heat exchangers; In addition to the different corrosion resistance conditions, austenitic stainless steel can also be used as high and low temperature resistant material; Copper, aluminum and their alloys are mostly used to manufacture low temperature heat exchangers; Nickel alloy is used at high temperature; In addition to making gasket parts, some non-metallic materials have been used to make corrosion-resistant heat exchangers of non-metallic materials, such as graphite heat exchanger, fluoroplastic heat exchanger and glass heat exchanger. 2. Structure design process 2.1 selection steps of tubular heat exchanger: which fluid flows through the tube side and which fluid flows through the shell side of the heat exchanger, the following points are available for reference (taking fixed tube sheet heat exchanger as an example)（ 1) The unclean and easy scaling fluid should go through the pipe to clean the pipe（ 2) Corrosive fluid should go through the pipe to prevent the shell and pipe from being corroded at the same time, and the pipe is also easy to clean and repair（ 3) The fluid with high pressure should go through the pipe to avoid pressure on the shell. In addition, multiple tube passes can be used to increase the flow rate（ 4) The fluid with high viscosity or low flow rate in the seal gasket of Shandong heat exchanger should go between the tubes, because when the fluid flows in the shell side with baffles, due to the constant change of flow velocity and direction, turbulence can be achieved at low Re (re > 100), so as to improve the convective heat transfer coefficient. When selecting the flow path, the pressure, anti-corrosion and cleaning requirements of the fluid are considered first, and then the convective heat transfer coefficient and pressure drop are checked（ 2) U-tube heat exchanger. Each tube of the U-tube heat exchanger is bent into a U-shape, and both ends of the tube are fixed on the same tube sheet, so each tube can stretch freely to solve the compensation problem. This type of heat exchanger has simple structure and light weight, and is suitable for high temperature and high pressure. Its main disadvantage is that it is difficult to clean the tube side; Because the tube needs a certain bending radius, the tubesheet utilization rate is poor（ 3) Floating head heat exchanger. One end of the tubesheet at both ends of the floating head heat exchanger is not fixedly connected with the shell, which is called the floating head. When the thermal expansion of the tube bundle and the sealing gasket body of the shell heat exchanger is different due to the large temperature difference, the tube bundle and the floating head can expand and contract freely in the shell, independent of the shell, so as to solve the problem of thermal compensation. In addition, because the tubesheet at the fixed end is connected with the shell by flange, the tube bundle can be pulled out from the shell for easy cleaning and maintenance. So floating head heat exchanger is widely used, but the structure is more complex. The metal consumption is large and the cost is high. The heat exchanger needed in this design is cooled by circulating cooling water. Considering this factor, it is estimated that the temperature difference between the tube wall and the shell wall of the heat exchanger is large. When the temperature difference between the two fluids is large, the fixed tube sheet can be selected. And it has the advantages of simple structure and low cost. Therefore, the fixed tube sheet is preliminarily selected in this design. Generally, heat exchangers are made of metal materials, and carbon steel and low alloy steel are mostly used to manufacture medium and low pressure heat exchangers; Stainless steel is mainly used in different corrosion resistant conditions, and austenitic stainless steel can also be used as high and low temperature resistant material; Copper, aluminum and their alloys are mostly used to manufacture low temperature heat exchangers; Nickel alloy is used at high temperature; In addition to making gasket parts, some non-metallic materials have been used to make corrosion-resistant heat exchangers of non-metallic materials, such as graphite heat exchanger, fluoroplastic heat exchanger and glass heat exchanger.