Shandong heat exchanger cleaning (4) the spacing of tubes on the tube sheet (refers to the center distance of two adjacent tubes) varies with the different connection methods between tubes and tube sheet. In general, t = (1.3 ~ 1.5) do is used for tube expansion method, and the outer wall spacing between two adjacent tubes should not be less than 6 mm, that is, t ≥ (D + 6). In this design, the welding method is used to connect, so the arrangement spacing is t = 32mm (pipe spacing)（ 5) The number of tube side and shell side is determined. When the flow rate of fluid is small or the heat transfer area is large and the number of tubes is large, sometimes the velocity in the tube is low, so the convective heat transfer coefficient is small. In order to increase the flow rate in the tube, multi tube pass can be used. However, too many passes will increase the fluid resistance and increase the power cost; At the same time, multi pass will reduce the cleaning degree difference of the average temperature heat exchanger; In addition, the area available on the tubesheet is reduced by the multi pass diaphragm, which should be considered in the design. In the series standards of tubular heat exchanger, there are four kinds of tube pass number: 1, 2, 4 and 6. When using multiple passes, the number of tubes in each pass should be approximately equal. Considering the small diameter of the selected pipe, in order not to affect the heat exchange requirements, this design selects 4 passes. 2.5 determination of shell diameter the inner diameter of shell of heat exchanger should be equal to or slightly larger than the diameter of tube sheet (for floating head heat exchanger and Shandong heat exchanger). According to the actual pipe number, pipe diameter, pipe center distance and pipe arrangement method calculated, generally in the preliminary design, the flow velocity of two fluids can be selected respectively, and then the required cross-sectional area of pipe side and shell side can be calculated, and the diameter of shell can be found out in a series of standards. After all the designs are completed, the drawing method is still used to draw the pipe arrangement diagram. 2.6 the material selection of tube and tube heat exchanger shall be based on the operating pressure, temperature and corrosive property of fluid. At high temperature, the mechanical properties and corrosion resistance of general materials are decreased. There are few materials with heat resistance, high strength and corrosion resistance. The commonly used metal materials are carbon steel, stainless steel, low alloy steel, copper and aluminum; Non metallic materials include graphite, polytetrafluoroethylene and glass. Although stainless steel and nonferrous metals have good corrosion resistance, they are expensive and scarce, so they should be used as little as possible. The shell is made of carbon steel and the tube side is made of stainless steel. In this design, the allowable pressure drop is not more than 10, and the outer wall spacing between two adjacent pipes should not be less than 6 mm, that is, t ≥ (D + 6). In this design, the welding method is used to connect, so the arrangement spacing is t = 32mm (pipe spacing)（ 5) The number of tube side and shell side is determined. When the flow rate of fluid is small or the heat transfer area is large and the number of tubes is large, sometimes the flow rate in the tube is low, so the cleaning number of convective heat exchanger is small. In order to increase the flow rate in the tube, multi tube pass can be used. However, too many passes will increase the fluid resistance and increase the power cost; At the same time, the average temperature difference will decrease due to multi pass; In addition, the area available on the tubesheet is reduced by the multi pass diaphragm, which should be considered in the design. In the series standards of tubular heat exchanger, there are four kinds of tube pass number: 1, 2, 4 and 6. When using multiple passes, the number of tubes in each pass should be approximately equal. Considering the small diameter of the selected pipe, in order not to affect the heat exchange requirements, this design selects 4 passes. 2.5 determination of shell diameter the inner diameter of heat exchanger shell shall be equal to or slightly larger than (for floating head heat exchanger) the diameter of tube sheet. According to the actual pipe number, pipe diameter, pipe center distance and pipe arrangement method, generally in the preliminary design, the flow rate of two fluids can be selected according to the heat exchanger cleaning, and then the required flow cross-sectional area of tube side and shell side can be calculated, and the diameter of outer shell can be found out in a series of standards. After all the designs are completed, the drawing method is still used to draw the pipe arrangement diagram.