09-03-30 Topic - Discuss the selection of shell and tube heat exchangers (prizes for participation)

1． Basic principles of design (1) Selection of fluid flow path The selection of fluid flow path refers to which fluid flows on the tube side and shell side. This issue is restricted by many factors. The following takes a fixed tube plate heat exchanger as an example to introduce some selection principles. ①Fluids that are unclean and prone to scaling should be routed through the pipe side because it is easier to clean the pipe side. ②Corrosive fluids should be routed through the pipe side to prevent the pipe and shell from being corroded at the same time, and the pipe side is convenient for maintenance and replacement. ③Fluids with high pressure should be routed through the pipe to avoid pressure on the shell, which can save metal consumption in the shell. ④The cooled fluid should go to the shell side, and the external heat dissipation effect of the shell can be used to enhance the cooling effect. ⑤Saturated steam should be transported to the shell side to facilitate timely removal of condensate, and the steam is relatively clean and generally does not require cleaning. ⑥Toxic and easily polluted fluids should be routed through the pipe to reduce leakage. ⑦Fluids with small flow or high viscosity should go to the shell side, because the fluid flows in the shell side with baffles. Due to the continuous changes in flow speed and flow direction, turbulent flow can be achieved at low Re (Re>100) to improve the heat transfer coefficient. ⑧If the temperature difference between the two fluids is large, it is advisable to let the fluid with a large convective heat transfer coefficient go to the shell side, because the wall surface temperature is close to the fluid with a large α, so as to reduce the temperature difference between the tube wall and the shell wall and reduce the temperature difference stress. The principles discussed above are not absolute and may be contradictory for specific fluids. Therefore, when selecting the flow path of the fluid, it must be determined based on the specific situation and grasping the main contradiction. (2) Selection of fluid flow rate The selection of fluid flow rate involves aspects such as heat transfer coefficient, flow resistance and heat exchanger structure. Increasing the flow rate can increase the convective heat transfer coefficient, reduce the formation of dirt, and increase the overall heat transfer coefficient. ； But at the same time, the flow resistance increases and the power consumption increases. ； Choose a high flow rate to reduce the number of tubes. For a certain heat exchange area, you have to use longer tubes or increase the number of passes. Too long tubes are not conducive to cleaning, and single pass becomes multi-pass, which reduces the average heat transfer temperature difference. Therefore, it is generally necessary to select an appropriate flow rate through multiple trade-offs. Table 4-14 to Table 4-16 list the commonly used flow rate ranges for reference during design. When selecting flow rates, laminar flow should be avoided as much as possible. Table 4-14 Commonly used flow rate ranges in shell and tube heat exchangers Types of fluids General fluids are prone to scaling Liquid gas flow rate, m/s Tube side 0.5 ~3.0 > 1.0 5.0 ~30 Shell side 0.2 ~1.5 > 0.5 3.0 ~15 Table 4-15 Common flow rates for different viscosity liquids in shell and tube heat exchangers Liquid viscosity, mPa·s > 1500 1500 ~500 500 ~100 100 ~35 35 ~ 1 < 1 Maximum flow velocity, m/s 0.6 0.75 1.1 1.5 1.8 2.4 Table 4-16 Safe allowable speed of flammable and explosive liquids in shell and tube heat exchangers Liquid name ether, carbon disulfide, benzyl alcohol, ethanol, gasoline Proper safe allowable speed, m/s < 1 < 2 ~3 < 10 (3) Selection of the final temperature of the cooling medium (or heating medium) In the design of the heat exchanger, the temperatures of the materials entering and exiting the heat exchanger are generally determined by the process, while the inlet temperature of the cooling medium (or heating medium) is generally known, and the outlet temperature is determined by the designer. If cooling water is used to cool a certain thermal fluid, the water inlet temperature can be estimated based on local climate conditions, while the outlet temperature needs to be determined through economic trade-offs. In order to save water, the outlet temperature of the water can be made higher, but the required heat transfer area will increase ； On the contrary, in order to reduce the heat transfer area, the water volume can be increased and the outlet temperature can be reduced. Generally speaking, the temperature difference of cooling water during design can be 5~10℃. Larger temperature differences can be used in water-scarce areas, and smaller temperature differences can be used in areas with abundant water resources. If a heating medium is used to heat a cold fluid, the outlet temperature of the heating medium can be selected according to the same principle. (4) Pipe specifications and pipe spacing ① Pipe specifications The selection of pipe specifications includes pipe diameter and pipe length. The current trial series of shell and tube heat exchangers only uses heat exchange tubes with two diameter specifications: 25×2.5mm and 19×2mm. For clean fluids, you can choose a small pipe diameter, and for fluids that are prone to scaling or unclean, you can choose a large pipe diameter. The selection of pipe lengths is based on the principles of easy cleaning and rational use of pipe materials. The standard steel pipe length produced in my country is 6m, so there are four types of pipe lengths in the series of standards: 1.5, 2, 3 and 6m. In addition, the ratio of tube length to shell diameter should be appropriate, generally 4 to 6. ②Tube spacing The center distance t of the tubes is called the tube spacing. Small tube spacing is beneficial to improving the heat transfer coefficient and making the equipment compact. However, due to manufacturing limitations, generally, is the outer diameter of the tube. The commonly used comparison relationships between and are shown in Table 4-17. Table 4-17 The relationship between shell and tube heat exchanger and heat exchange tube outer diameter, mm 10 14 19 25 32 38 45 57 heat exchange tube center distance, mm 14 19 25 32 40 48 57 72 (5) Determination of the number of tube passes and shell passes ① Determination of the number of tube passes When the heat exchange area of the heat exchanger is large and the tubes cannot be very long, more tubes must be arranged. In order to increase the flow rate of the fluid in the tubes, the tube bundles need to be divided. However, too many passes will increase the flow resistance on the tube side and increase the power energy consumption. At the same time, multiple passes will reduce the average temperature difference, which should be weighed during design. There are four types of tube passes in the shell and tube heat exchanger series standards: 1, 2, 4, and 6. When using multiple passes, the number of tubes in each pass should usually be equal. The number of tube passes can be calculated according to the following formula, that is (4-114) where──The appropriate velocity of the fluid in the tube pass, m/s ； ──The actual velocity of the fluid within the tube, m/s. ②When determining the shell-side number, the shell-side multi-way should be used when correcting the temperature difference coefficient. Shell multipass can be achieved by installing baffles parallel to the tube bundle. The number of times the fluid flows through the shell is called the shell pass number. However, since the shell side partition is difficult to manufacture, install and maintain, it is generally not suitable to be used. A common method is to use several heat exchangers in series to replace the shell square multi-pass. (6) Selection of baffles The purpose of installing baffles is to increase the speed of the shell-side fluid, intensify the turbulence, and improve the convective heat transfer coefficient of the shell-side fluid. Baffles come in bow-shaped, disc-shaped, shunt-shaped and other forms, among which the bow-shaped baffles are most widely used. The shape and spacing of the baffles have an important impact on the flow and heat transfer of the shell-side fluid. If the arcuate gap of the arcuate baffle is too large or too small, it is not conducive to heat transfer and tends to increase flow resistance. Usually the cut-off bow height is 10~40% of the inner diameter of the shell, with 20% and 25% being commonly used. The baffles should be arranged at equal intervals. The minimum spacing between the baffles should be no less than 1/5 of the inner diameter of the shell and no less than 50mm. ； The maximum spacing should not be greater than the inner diameter of the housing. The plate spacing used in the series of standards is: There are three types of fixed tube plate types: 150, 300 and 600mm. ； Floating head types include 150, 200, 300, 480

What factors need to be considered when selecting a shell and tube heat exchanger and what are the general principles for selection? 1. According to the medium, pressure, and temperature, determine the heat exchanger type, and then determine the fluid in the tube and shell side. 2. Adjust the cylinder diameter, tube length, baffle spacing and number of tube passes to select a suitable heat exchanger.

From the Internet: Shell and tube heat exchanger design and selection steps 1. Process calculation: 1> Calculate the heat that needs to be transferred according to the type of fluid, flow rate of cooling fluid, inlet and outlet temperature, working pressure, etc. 2>Select the materials of the pipe and shell according to the corrosiveness and other characteristics of the fluid. And based on the material processing characteristics, the flow rate, pressure, temperature of the fluid, the temperature of the heat exchange tube and shell, the amount of heat that needs to be transferred, the cost and the convenience of maintenance and cleaning, etc., decide which type of shell and tube heat exchanger to use. 3> Establish the flow space of the fluid, that is, determine what media are in the tube side and shell side. 4> Determine the flow direction of the two fluids participating in the heat exchanger, whether it is co-current, counter-current or cross-flow. And calculate the effective average temperature difference of the fluid. 5> Select the heat transfer coefficient K based on experience, and estimate the required heat transfer area A. 6> Based on the calculated heat transfer area A and referring to the standard series of shell and tube heat exchangers in my country, the basic parameters of the heat exchanger are initially determined (tube diameter, number of tube passes, number of tubes, tube length, tube arrangement, type and arrangement of baffle elements, etc., shell diameter and other structural parameters). 7> According to the determined standard series dimensions, check the heat transfer coefficient and calculate the resistance drop. Finally, select a heat exchanger or perform mechanical design according to standards. 2. Mechanical design calculations Mechanical design calculations include: (1) Calculation of the wall thickness of the shell and tube box (2) Design of the connection structure between the tube and the tube plate (3) Design of the connection structure between the shell and the tube plate (4) Calculation of the thickness of the tube plate (5) Structural design of baffles, support plates and other components (6) Calculation of the stress of the heat exchange tube and shell under the combined action of temperature difference and fluid pressure (7) Tube pull-out force and stability check (8) Determine whether an expansion joint is needed. If so, select the structural form of the expansion joint and perform relevant calculations. (9) Selection of nozzles, nozzle flanges, container flanges, supports, etc. and opening reinforcement design. This post was last edited by laoyier on 2009-3-30 13:03 ]

factor: Temperature difference, medium (cleanliness), pressure, structure, cost, life. General principles: 1. Generally, the fixed tube plate type is always given priority when selecting heat exchangers because of its simple structure and low manufacturing cost. When the temperature difference between the shell side and the tube side is small or slightly large (expansion joints can be installed), the shell side pressure is not high, and the shell side medium is not prone to scaling, fixed tube plate heat exchangers are still preferred. However, its shell side cannot be cleaned mechanically, and the equipment life is relatively short. 2. When the temperature difference between the tube side and the shell side is large, the pressure of the tube side medium is high, the medium in the tube is very clean, and it is not easy to scale, consider using a U-shaped tube heat exchanger. Because it eliminates thermal stress, it also allows the tube bundle to be extracted for cleaning. However, it is difficult to clean the inside of the U-shaped tube. If the heat exchange tube leaks, the tube can only be blocked and cannot be replaced. 3. When the temperature difference between the tube side and the shell side is large, and both the tube side medium and the shell side medium are prone to scaling, a floating head heat exchanger should be considered. It can also eliminate thermal stress and facilitate cleaning of the tube and shell sides. However, its structure is complex and the manufacturing cost is high.

From a process perspective, let’s talk about your own ideas for designing shell and tube heat exchangers. Please correct me if I’m wrong. It is best to consult GB-151 before designing shell and tube heat exchangers. First, the heat load must be calculated based on the process requirements and process conditions, and the inlet and outlet fluid temperatures and inlet and outlet fluid flow rates must be determined. and find the logarithmic mean temperature. Select an appropriate heat exchanger, such as fixed tube plate type, U-shaped tube type, floating head type. Secondly, determine the materials to be transported separately in the tube and shell side. Please refer to the following principles for details:: 1. Fluids that are unclean or easy to scale should go through the pipe side. 2. Corrosive fluids should go through the pipe side. 3. High-pressure fluids should go through the pipe side. 4. Saturated steam should go through the pipe side. 5. Toxic fluids should go through the pipe side. 6. Fluids with higher viscosity or smaller flow rates should go through the shell side, which can improve the convection transmission coefficient. When all the above principles cannot be met, reasonable choices should be made based on the specific process and operating conditions. Select a heat exchange tube with a suitable diameter (usually 25mm), then select the flow rate of the fluid to determine the flow rate of the single tube. For example, in a water-exchange system, the flow rate in a single pipe is often between 0.3 and 3m/s. Calculate the total heat transfer coefficient K. Calculate the heat transfer area. Calculating the length of the heat exchange tube, the common heat exchange tubes in China are 1.5m, 3m, 4.5m, 6m, etc. Select the appropriate pipe diameter ratio, (pipe length/tube bundle diameter). And calculate the required number of heat exchange tubes. Calculate the pressure drop on the shell side and tube side of the heat exchanger. Pipe layout (equilateral triangle or square). According to the fluid temperature and heat transfer temperature difference, the temperature inside and outside the tube is determined. If the fluid temperature is high, temperature compensation (such as adding an expansion joint, etc.) should be considered.

Factors to consider when selecting a shell and tube heat exchanger: Temperature, pressure, medium, main body material, heat exchange area, number of tube passes, installation method (vertical/horizontal) Design and selection of shell and tube heat exchangers Shell and tube heat exchangers are a traditional standard heat exchange equipment. They have the advantages of easy manufacturing, wide range of material selection, strong adaptability, large processing capacity, easy cleaning, reliable operation, and can withstand high temperatures and high pressures. They are widely used in many industrial sectors, especially among the heat exchangers used in petroleum, chemical, thermal energy, power and other industrial sectors. Shell and tube heat exchangers dominate. To this end, the design and selection of shell and tube heat exchangers will be discussed in this section. (1) Models and series standards of shell and tube heat exchangers. In view of the wide application of shell and tube heat exchangers, in order to facilitate the design, manufacturing, installation and use, the relevant departments have formulated a series of standards for shell and tube heat exchangers. 1． Basic parameters and model representation methods of shell and tube heat exchangers (1) Basic parameters Basic parameters of shell and tube heat exchangers include: ①Nominal heat exchange area ； ②Nominal diameter ； ③Nominal pressure ； ④Heat exchanger tube length ； ⑤Heat exchange tube specifications ； ⑥Number of tubes. (2) Model representation method. The model of shell and tube heat exchanger consists of five parts.: 1──Heat exchanger code 2──Nominal diameter DN, mm ； 3──Number of tubes: ⅠⅡⅣⅥ ； 4──Nominal pressure PN, MPa ； 5──Nominal heat exchange area SN, m2. For example, the model of a fixed tube plate heat exchanger with a single tube pass of 800mm, 0.6MPa and a heat exchange area of ​​110m2 is: G800 I-0.6-110 G──Code name for fixed tube plate heat exchanger. 2. The series of standards for shell and tube heat exchangers and the series of standards for fixed tube plate heat exchangers and floating head heat exchangers are listed in the appendix. For the series of standards for other forms of shell and tube heat exchangers, please refer to the relevant manuals. (2) Design and selection of shell and tube heat exchangers. The design of heat exchangers is based on calculations to determine the economical and reasonable heat transfer area and other relevant dimensions of the heat exchanger to complete the heat transfer tasks required in production. 1． Basic principles of design (1) Selection of fluid flow path The selection of fluid flow path refers to which fluid flows on the tube side and shell side. This issue is restricted by many factors. The following takes a fixed tube plate heat exchanger as an example to introduce some selection principles. ①Fluids that are unclean and prone to scaling should be routed through the pipe side because it is easier to clean the pipe side. ②Corrosive fluids should be routed through the pipe side to prevent the pipe and shell from being corroded at the same time, and the pipe side is convenient for maintenance and replacement. ③Fluids with high pressure should be routed through the pipe to avoid pressure on the shell, which can save metal consumption in the shell. ④The cooled fluid should go to the shell side, and the external heat dissipation effect of the shell can be used to enhance the cooling effect. ⑤Saturated steam should be transported to the shell side to facilitate timely removal of condensate, and the steam is relatively clean and generally does not require cleaning. ⑥Toxic and easily polluted fluids should be routed through the pipe to reduce leakage. ⑦Fluids with small flow or high viscosity should go to the shell side, because the fluid flows in the shell side with baffles. Due to the continuous changes in flow speed and flow direction, turbulent flow can be achieved at low Re (Re>100) to improve the heat transfer coefficient. ⑧If the temperature difference between the two fluids is large, it is advisable to let the fluid with a large convective heat transfer coefficient go to the shell side, because the wall surface temperature is close to the fluid with a large α, so as to reduce the temperature difference between the tube wall and the shell wall and reduce the temperature difference stress. The principles discussed above are not absolute and may be contradictory for specific fluids. Therefore, when selecting the flow path of the fluid, it must be determined based on the specific situation and grasping the main contradiction. (2) Selection of fluid flow rate The selection of fluid flow rate involves aspects such as heat transfer coefficient, flow resistance and heat exchanger structure. Increasing the flow rate can increase the convective heat transfer coefficient, reduce the formation of dirt, and increase the overall heat transfer coefficient. ； But at the same time, the flow resistance increases and the power consumption increases. ； Choose a high flow rate to reduce the number of tubes. For a certain heat exchange area, you have to use longer tubes or increase the number of passes. Too long tubes are not conducive to cleaning, and single pass becomes multi-pass, which reduces the average heat transfer temperature difference. Therefore, it is generally necessary to select an appropriate flow rate through multiple trade-offs. Table 4-14 to Table 4-16 list the commonly used flow rate ranges for reference during design. When selecting flow rates, laminar flow should be avoided as much as possible.

A lot has been said above. I also said that for selection, I think the first step should be based on temperature and pressure. For high temperatures and high pressures, heat exchangers with some structures are not suitable. For some high or low temperatures, heat exchangers with special structures will be better. Secondly, the physical properties of the fluid. For those with high viscosity and corrosiveness, the structure and materials of the heat exchanger should be considered. There are also space constraints. For example, if there is no room horizontally or the space is small, vertical or some reinforced heat exchangers should be considered to make the floor area smaller. Some reinforced heat exchangers have particularly obvious advantages in the working conditions they are being used for. They should also be taken into consideration when selecting.

http://bbs.hcbbs.com/archiver/tid-179060.html There is a lot of knowledge about this in previous posts, so I won’t go into details here.

The problem is huge and there are many selection criteria. The most basic involve the type of fluid to be treated, operating pressure and temperature, heat load and cost, etc. Comprehensive consideration of the characteristics of the heat transfer fluid: Pressure, temperature, phase state, physical properties, toxicity, corrosiveness, scaling. The operating conditions of various heat exchangers are different, and their design and performance requirements are also different. Therefore, for the selection of heat exchanger with a certain heat load, the following points should be considered: 1. Material of heat exchanger ； 2. Operating pressure and temperature, temperature changes, and temperature difference driving force 3. Flow rate 4. Flow mode 5. Performance parameters - thermal efficiency and pressure drop 6. Fouling 7. Fluid type and phase state 8. Maintenance, overhaul, cleaning, expansion, and repair possibilities 9. Overall economy 10. Processing and manufacturing technology 11. Other uses. During the selection, aspects such as structural strength, material sources, processing conditions, sealing, and safety should also be considered and solved through design optimization. In addition, each industry has its own preferences and usage * You are used to it, so you should pay more attention when selecting a model! I hope experts can correct me by offering advice.

It is important to correctly select the type of shell and tube heat exchanger for the specific situation. There are many factors that need to be considered when selecting a shell and tube heat exchanger, the main ones are: 1) Heat load and flow rate 2) Properties of the fluid 3) Temperature, pressure and allowable pressure drop range 4) Requirements for cleaning and maintenance 5) Equipment structure, material, size, weight 6) Price, safety and lifespan 7) Structural strength 8) Source of materials 9) Processing conditions 10) The above factors such as sealing and safety often restrict and influence each other and can be solved through design optimization.

Well, this problem is a bit big! ! But I agree with the design principles of the first floor!

The main basis is still GB151-1999 "Shell and Tube Heat Exchanger". Anyone who has read it carefully will know that it contains all the questions you want to know.

1. Factors to be considered when selecting the heat exchanger. The selection of the heat exchanger is to select a relatively reasonable heat exchanger form based on comprehensive factors such as the structural characteristics, usage conditions, investment and operating costs of the heat exchanger. Before selecting a model, you must be familiar with the structural characteristics and working characteristics of various heat exchangers, make plans based on specific conditions, and compare various plans to make the optimal choice. 1． Factors to consider when selecting include:: Materials, media, pressure, temperature, temperature difference, pressure drop, scaling conditions, maintenance and cleaning methods and other factors. 2. Safety factor - is the most important factor when selecting a heat exchanger. Including sufficient strength and rigidity, reliable structure, meeting sealing requirements, and compatibility of materials and media. (For example, consideration of temperature difference stress, sealing, etc.) 3. It can meet the process requirements - there is sufficient heat transfer area, the medium has a good flow state that is conducive to heat transfer, and it is economically reasonable. (For example, whether U-shaped tubes can be used, cleaning of the tube and shell side, whether the stages are separated, the impact of the viscosity of the medium on the flow, whether the structure must be detachable, etc.) 4. Convenient for manufacturing, installation and maintenance - relatively simple manufacturing, good operating performance, low operating costs, etc. 2. General principles for selection: When the temperature difference is not large, the fouling of the shell-side medium is not serious, and the shell-side can be chemically cleaned, a fixed tube plate heat exchanger should be selected. When the temperature difference is large, floating head heat exchangers, U-shaped tube heat exchangers, stuffing box heat exchangers and sliding tube plate heat exchangers can be used. When mechanical cleaning of the shell side is required, a structure with extractable tube bundles can be used. At high temperatures and high pressures, U-shaped tube heat exchangers can be used. When the shell-side medium is flammable, explosive, toxic or volatile, or when the operating pressure and temperature are high, it is not appropriate to use a packed function heat exchanger. When the tube-side medium and the shell-side medium are not allowed to mix, a heat exchanger with a double tube sheet structure can be used.

Basic steps for shell and tube heat exchanger selection and design 1. Preliminary size specifications of the heat exchanger 1.1. Preliminary selection of the flow mode of the heat exchanger. Calculate the temperature difference correction coefficient FT based on the inlet and outlet temperatures of the hot and cold fluids. If FT

Shell and tube heat exchanger is also called tube and tube heat exchanger. It is a partition type heat exchanger that uses the wall surface of the tube bundle enclosed in the shell as the heat transfer surface. This type of heat exchanger has a simple structure and reliable operation. It can be made of various structural materials (mainly metal materials) and can be used under high temperature and high pressure. It is currently the most widely used type. 　　The structure consists of shell, heat transfer tube bundle, tube plate, baffle (baffle) and tube box. The shell is mostly cylindrical, with a tube bundle installed inside, and both ends of the tube bundle are fixed on the tube plate. There are two fluids, hot and cold, for heat exchange. One flows inside the tube, which is called the tube-side fluid. ； The other flows outside the tube and is called shell-side fluid. In order to improve the heat transfer coefficient of the fluid outside the tube, several baffles are usually installed in the shell. The baffle can increase the velocity of the fluid on the shell side, forcing the fluid to pass through the tube bundle multiple times along the specified path, thereby enhancing the degree of fluid turbulence. The heat exchange tubes can be arranged in an equilateral triangle or square on the tube sheet. The equilateral triangle arrangement is relatively compact, the fluid outside the tube is highly turbulent, and the heat transfer coefficient is large. ； The square arrangement makes it easy to clean the outside of the tube and is suitable for fluids that are prone to scaling. 　　Each time the fluid passes through the tube bundle, it is called a tube pass. ； Each pass through the shell is called a shell pass. The picture shows the simplest single-shell and single-tube heat exchanger, referred to as the 1-1 type heat exchanger. In order to increase the fluid velocity in the pipe, partitions can be installed in the pipe boxes at both ends to divide all the pipes into several groups. In this way, the fluid only passes through part of the tubes at a time and therefore travels back and forth in the tube bundle multiple times. This is called multi-tube pass. Similarly, in order to increase the flow rate outside the tube, longitudinal baffles can also be installed in the shell to force the fluid to pass through the shell space multiple times, which is called multi-shell pass. Multi-tube and multi-shell processes can be used together. 　　Due to the different temperatures of the fluid inside and outside the tube, the temperatures of the heat exchanger shell and the tube bundle are also different. If there is a large difference between the two temperatures, great thermal stress will be generated in the heat exchanger, causing the tubes to bend, break, or pull off the tube sheet. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50°C, appropriate compensation measures must be taken to eliminate or reduce thermal stress. Depending on the compensation measures adopted, shell and tube heat exchangers can be divided into the following main types:: 　　① The tube plates at both ends of the tube bundle of the fixed tube plate heat exchanger are integrated with the shell. The structure is simple, but it is only suitable for heat exchange operations when the temperature difference between hot and cold fluids is not large, and the shell side does not require mechanical cleaning. When the temperature difference is slightly larger and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce thermal stress. 　　② The tube plate at one end of the tube bundle of the floating head heat exchanger can float freely, completely eliminating thermal stress; and the entire tube bundle can be extracted from the shell, making it easy for mechanical cleaning and maintenance. Floating head heat exchangers are widely used, but their structures are complex and their costs are high. 　　③ Each heat exchange tube of the U-tube heat exchanger is bent into a U shape, with both ends fixed on the same tube plate and the upper and lower areas respectively. It is divided into two chambers, the inlet and outlet, with the help of partitions in the tube box. This type of heat exchanger completely eliminates thermal stress and has a simpler structure than the floating head type, but the tube side is not easy to clean. 　　Non-metallic material heat exchangers For heat exchange of highly corrosive fluids in chemical production, non-metallic materials such as ceramics, glass, polytetrafluoroethylene, graphite and other non-metallic materials must be used to make shell and tube heat exchangers. This type of heat exchanger has poor heat transfer performance and is only used in situations with low pressure, small vibration, and low temperature. 　　Selection of flow channels For hot and cold fluids to be used for heat exchange, the flow channels should be selected according to the following principles.: ①Fluids that are unclean and prone to scaling should be routed through the pipe because it is easier to clean inside the pipe. ； ②Corrosive fluids should be routed along the pipe side to prevent the pipe bundle and shell from being corroded at the same time. ； ③Fluids with high pressure should be routed through the pipe to prevent the shell from bearing pressure. ； ④Saturated steam should be transported to the shell side because the steam condensation heat transfer coefficient has nothing to do with the flow rate and the condensate is easily discharged. ； ⑤If the temperature difference between the two fluids is large, when a fixed tube plate heat exchanger is selected, the fluid with a large heat transfer coefficient should be moved through the shell to reduce thermal stress. 　　Operation enhancement When the heat transfer coefficients on both sides of the tube wall are very different (such as heat exchange between a liquid and a gas with a low viscosity), efforts should be made to reduce the thermal resistance on the side with a low heat transfer coefficient. If the heat transfer coefficient outside the tube is small, an externally threaded tube (low-fin tube) can be used to increase the heat transfer area and fluid turbulence on the outside side of the tube and reduce thermal resistance. If the heat transfer coefficient in the tube is small, twist iron, spiral coils and other additives can be installed in the tube to enhance the disturbance in the tube and enhance heat transfer. Of course, the flow resistance of the fluid will also increase at this time.

Heat source properties； The temperature of the inlet and outlet of the heat source, the amount of heat exchanged, the temperature of the inlet and outlet water of the heat exchanger, and the pressure drop

Model selection in the chemical industry is also a small project.

After reading so much, I summarized a few points for easy memory: 1. Process requirements 2. Safety requirements 3. Economic requirements 4. Maintenance requirements

I would like to know what you need to pay attention to when using HTRI software to select products, or to communicate with everyone who uses HTRI software to select products. Although I have been using this software for half a year, the company's product range is very small. I would like to know how experts use it and how to calculate it in strong electrolyte solutions (NaCl, CaCl solutions).