How to write the introduction for a graduation project on heat exchangers

1 Introduction This graduation project concerns the first and second heat exchangers of ******** Factory. 1.1 Heat exchangers are devices used in industrial production to facilitate the transfer of heat between materials; hence, they are also known as heat exchangers. It is a general-purpose device widely used in the chemical, petroleum refining, power, nuclear energy, and many other industrial sectors; it is the main equipment used to maintain the required process conditions and to recover waste heat and save energy by utilizing secondary energy sources. In chemical plants, heat exchangers account for approximately 10–20% of the total investment ； Due to different process flows, heating, cooling, evaporation, or condensation are often carried out during production. Through the heat exchanger, heat is transferred from the fluid at a higher temperature to the fluid at a lower temperature to meet the process requirements. 1.2 Fixed-tube-sheet heat exchangers There are a wide variety of heat exchange devices, and each structural type has its own characteristics and operating properties. Some structural types are suitable for use in certain situations, but they may not be appropriate, or even unusable, in other circumstances. Based on the structural characteristics of shell-and-tube heat exchangers, they can be classified into five types: fixed-head type, floating-head type, U-tube type, stuffing box type, and kettle-type reboilers. Among them, the fixed tube sheet type is the most commonly used. The typical structure of a fixed-tube-sheet heat exchanger is shown in Figure 1; the tube bundle is connected to the tube sheet, which is welded to the shell. Its advantages include a simple and compact structure, a large number of tubes; it has a larger surface area for the same nominal diameter of the heat exchanger, is easy to manufacture, allows for convenient cleaning of the shell side, and makes it easy to block or replace the tubes in case of damage. The disadvantage is that when there is a large difference in the temperature difference between the tube bundle and the shell wall, or in the linear expansion coefficients of the materials, significant thermal stresses will be generated in both the shell and the tube bundle. This type of heat exchanger is suitable for applications where the fluid on the shell side is clean and not prone to scaling, as well as in situations where the temperature difference between the tube side and the shell side is small, or where the temperature difference is large but the pressure on the shell side is not high. Figure 1.1 Typical structure of a fixed-tube-sheet heat exchanger 1.3 Heat exchanger selection When selecting a heat exchanger, many factors need to be considered, primarily the properties of the fluids ； Range of pressure, temperature, and allowable pressure drop ； Requirements for cleaning and maintenance ； Material prices ； Service life, etc. Physical properties of fluids such as type, thermal conductivity, and viscosity, as well as chemical properties like corrosivity and heat sensitivity, have a significant impact on the selection of heat exchangers. In this design, heat exchange takes place between the reformate gas and water gas; since the reformate gas coming from the reformer has a high temperature, it involves a large volume of flow and is prone to scaling. After comprehensive consideration, a fixed tube sheet heat exchanger is selected for this design. 1.3 Heat transfer coefficient The heat transfer coefficient is a metric that reflects the intensity of the heat transfer process; its value depends on factors such as the structural design of the heat transfer equipment, the properties of the fluid, the flow conditions, the thermal conductivity of the materials, and the properties of the materials themselves. Generally speaking, the higher the heat transfer coefficients at each stage of the heat transfer process, the greater the overall heat transfer coefficient will be. The total thermal resistance of 1/K for the heat transfer process is the sum of the thermal resistances of each series-connected element; in principle, reducing the thermal resistance of any of these elements can increase the heat transfer coefficient and thus speed up the heat transfer process. However, when the thermal resistances of various components are in different orders of magnitude, the value of the total thermal resistance will be primarily determined by the largest among them. At the same time, there may be a certain control step during the series connection process; if such a control step indeed exists in the heat transfer process, then when considering ways to enhance heat transfer, efforts must be made to reduce the thermal resistance of this control step. If the thermal resistance of the control step is not reduced while efforts are made to address the thermal resistance of the non-control step, it will be difficult to achieve enhanced heat transfer. Similarly, during design calculations, the step thermal resistance or α value should be controlled as accurately as possible, and a sufficient safety factor should be applied. In heat transfer calculations, using the inner surface or the outer surface as the heat transfer area yields the same results; however, in engineering practice, the outer surface is commonly used as the heat transfer area for calculations. Therefore, the heat transfer coefficient K mentioned in this design refers to the outer surface of the tube. 1.4 Tube Sheet Design The tube sheet is one of the main components of shell-and-tube heat exchangers; especially in high-parameter and large-scale applications, the material supply, processing techniques, and production cycle of the tube sheet often become decisive factors in the manufacturing of the entire equipment. Since the tube sheet is connected to the heat exchange tubes, shell, tube box, flanges, etc., forming a complex elastic system, this poses certain difficulties for accurate strength analysis. However, a proper design of the tube sheet is of great significance for improving the safety of heat exchangers, saving materials, and reducing manufacturing costs. The main task in tube sheet design is to determine the thickness of the tube sheet. Due to the complex structure and stress conditions of the tube sheet, there are many factors that affect its strength and stiffness, making accurate strength analysis difficult. The calculation methods specified in the design codes for pressure vessels and heat exchangers around the world are all approximate formulas obtained by simplifying the tube sheet to some extent, and they are generally based on the following assumptions: The first assumption is that the tube sheet is considered a regularly perforated circular plate subjected to a uniform load on an elastic foundation; the maximum bending moment in the tube sheet depends on factors such as the magnitude of the load, geometric dimensions, edge support conditions, and foundation stiffness. The second method is based on the formula for a circular plate subjected to a uniformly distributed load, with appropriate correction factors added to take into account the characteristics of the tube sheet; this calculation approach is empirical in nature. The third approach uses the heat exchange tubes to provide a certain degree of stiffness as a fixed support for the tube sheet, with the tube sheet itself being a flat plate supported by this fixed structure; the thickness of the tube sheet depends on the area on it that is not occupied by tubes, and its strength is calculated based on that of a flat plate. The formula for the tube sheet included in domestic standards is based on the basic consideration of simplifying the actual tube sheet into an equivalent circular plate that is subjected to a uniformly distributed load, placed on an elastic foundation, and weakened uniformly by the tube holes. The heat exchanger is decomposed into an elastic system composed of elements such as end caps, shells, flanges, tube sheets, bolts, and gaskets; the interactions between these elements are represented by internal forces. The tube sheet is simplified to an equivalent homogeneous circular plate resting on an elastic foundation, taking into account both the pressure on the shell side and the pressure on the tube side. If it cannot be ensured that the shell-side pressure and the tube-side pressure act simultaneously under all conditions, it is not permissible to design the tube sheet using the difference between these two pressures. If either of and is at negative pressure, then the four dangerous combinations of pressure differences must be considered: (1) only the shell-side pressure, with the tube-side pressure = 0, ignoring the difference in thermal expansion ； (2) Only the shell-side pressure, with the tube-side pressure = 0, while taking into account the difference in thermal expansion ； (3) Only the tube side pressure, while the shell side pressure = 0; the difference due to thermal expansion is not considered ； (4) Only the tube side pressure, with the shell side pressure = 0, while considering the difference in thermal expansion.

There are graduation project materials on this topic in the forum; you can look for them by yourself!

Generally, access to the China National Knowledge Infrastructure can be obtained at schools; it is recommended to browse it more often, as one will discover that there are many valuable resources available there once starting work.

The original poster should clarify whether it is the process design of the heat exchanger or its equipment design I thought to myself: These days, the graduation project involves heat exchangers. Sigh. :L

There are too many college students; there aren’t that many questions to do. :lol

Any type of heat exchanger can be used; fixed-tube-sheet type, floating-head type, U-tube type, stuffing-box type, and kettle-type reboilers – these are all well described in textbooks, with detailed analyses provided. The heat exchangers I’ve seen in factories are of the fixed-tube-sheet type, as they are inexpensive

There’s a lot of information available; check it online, and if that doesn’t work, look at the graduation theses of seniors.

Choose the appropriate one based on the fluid used for heat exchange! Of course, for the factory, cost and maintenance are the most important!

In the introduction, I think it is necessary to explain the uses and significance of heat exchangers, as well as their development history and various types. Finally, I will focus on highlighting the advantages of the type of heat exchanger you have designed.

My graduation project was also on heat exchangers, similar to the one on the second floor.

Doing a graduation project on heat exchangers is very useful for one’s work