09-04-9 Topic - Design of spiral baffle heat exchanger (prizes for participation)

The determination of the spiral angle depends on the heat transfer characteristics of the entire heat exchanger structure. The relationship between the spiral angle and the pitch, which is what we call the lead, is still somewhat different from the plate spacing between the arcuate baffles. I hope the citation will pay attention. Especially in the process calculations, the intersection of the baffles and the baffles must be considered. 1 The geometry of the spiral baffle The baffles of the spiral baffle heat exchanger are quasi-sector-shaped. It has a certain installation inclination angle α with the cross section of the housing, and its projection on the cross section of the housing is exactly 1/4 of a circle. See Figure 1. According to the baffle spacing required, several spiral baffles are arranged in a continuous spiral shape at a certain angle with the axis of the tube bundle. This arrangement must ensure that the medium advances in a spiral shape from the shell side inlet to the outlet, avoiding the severe pressure drop caused by the violent reentry of the medium in a "Z" shape when arcuate baffles are used. The use of spiral baffles in shell and tube heat exchangers is based on the idea that: By changing the arrangement of the baffles on the shell side, the fluid on the shell side can flow in a continuous spiral. Therefore, the ideal baffle arrangement should be a continuous spiral surface. However, it is difficult to process spiral curved surfaces, and the cooperation between heat exchange tubes and baffles is difficult to achieve. Considering the convenience of processing, a series of quasi-fan-shaped flat plates (called spiral baffles) are used instead of curved surfaces to connect each other, forming an approximate spiral surface on the shell side, so that the fluid on the shell side of the heat exchanger generates a continuous spiral flow. 3. Design of the spiral baffle The shape of the spiral baffle is similar to a fan shape, consisting of an isosceles triangle and an arc with an elliptical curve edge. After installation, the projection on the cross section of the shell is a fan shape composed of an isosceles triangle and an arc, that is, a 1/4 circle. When the installation inclination angle of the spiral baffle is α, the edge of the elliptical curve is part of an ellipse, which is obtained by cutting the cylinder with a plane that makes an angle α with the cross-section of the shell. The size of the spiral baffle can be obtained from the ellipse equation determined by the ellipse. It can be seen from Figure 9 that the size parameters A and R of the spiral baffle are equal to the corresponding size parameters on the projection diagram. The calculation formula [3] of the chord height A is: A=Rcos45° The calculation formula of the major axis of the ellipse is:: P＝Ｒ／ｃcosα The elliptic equation is: Z2/P2+Y2/R2=1 where P—the length of the semi-major axis of the ellipse, mm ； R—Cylinder radius (i.e., the length of the minor semi-axis of the ellipse), mm ； α—the installation inclination angle of the spiral baffle. The numerical value of any point (Z1, Y1) on the edge of the elliptical curve of the spiral baffle can be calculated. When Y1=A, the Z1 value at this time can be obtained: Then the calculation formula of the chord length C of the spiral baffle is:: The calculation formula for the side length S of the spiral baffle is:: The calculation formula of the sector angle β of the spiral baffle is:: β＝2arcsin（Ｃ／2Ｓ）

Today I learned about spiral baffles for the first time from the forum. After reading the explanation on the second floor, I kind of understood it. It would be better to post the pictures on the second floor.

I can't post pictures now. I haven't found out the reason yet. This is all I can do for now, but what we should focus on is the original poster's problem.

I saw a paper and let’s study together* If you can’t see clearly, you can directly click on the link below http://hexchangers.com/tiring_room/new/hynews/200918142032.htm http://hexchangers.com/images/body-bg1-2.gif Structural design of double-shell spiral baffle heat exchanger Li Jiusheng, Liu Li, Li Zhuo and Wang Bin (Fushun Machinery Equipment Manufacturing Co., Ltd., Fushun, Liaoning 113006) Abstract: The structural type of a double-shell spiral baffle heat exchanger and the structural design method of each component are introduced. This double-shell structure solves the shortcomings of small baffle angle, reduced heat transfer performance and increased pressure drop caused by the single-shell spiral baffle structure in large-diameter heat exchangers, and has good prospects for promotion and application. keywords: Shell and tube heat exchanger; double shell side; spiral baffle; structural design CLC number: TQ051.5; TE965 Document identification code: B Shell-and-tube heat exchangers still account for a large proportion of applications in various industrial fields due to their remarkable features such as simple structure, high reliability, strong adaptability and operational flexibility. Their performance plays an important role in product quality, energy utilization, economy and reliability of system operation, etc. How to improve the performance of shell-and-tube heat exchangers has been a matter of concern to experts and scholars at home and abroad for many years. In particular, a large amount of experimental research has been conducted on improving the shell-side heat transfer coefficient. The new high-efficiency spiral baffle heat exchanger used in the petroleum refining and chemical industry in China in the late 1990s is one of these research results. 1 Introduction to the performance of spiral baffle heat exchangers Domestic research on spiral baffle heat exchangers began in the 1980s. Due to manufacturing difficulties, they have not been deeply studied and widely used. In the 1990s, people began to re-research and develop it. In 1998, the first domestic single-shell spiral baffle heat exchanger was first used in the refining unit of Fushun Petroleum No. 2 Plant and achieved good results. So far, more than 20 domestic refineries and dozens of units have adopted spiral baffle heat exchangers, with good results. Compared with the bow-type baffle heat exchanger, the spiral baffle heat exchanger has the characteristics of high heat transfer coefficient, pressure reduction, good earthquake resistance, anti-fouling and wide application range. It is especially suitable for high viscosity media and low Reynolds number Re situations. Although the single-shell spiral baffle heat exchanger is a new type of heat exchange equipment with high efficiency and energy saving, it also has its own shortcomings, one of which is the restriction of the spiral inclination angle. According to a large number of experimental studies by experts and scholars at home and abroad, the performance of spiral baffle heat exchangers is better than that of bow-type baffle heat exchangers in all aspects when the spiral inclination angle is 25° to 40°. In recent years, the demand for high-temperature and high-pressure heat exchangers in large-scale domestic refining and chemical plants has shown a trend of high quality and large quantity. Therefore, the single-shell spiral baffle structure used in large-diameter heat exchangers will be limited by the spiral inclination angle of 25° to 40°. In the process calculation of the heat exchanger, the main factor that affects the heat transfer coefficient is the Reynolds number Re, and the flow rate of the medium plays a decisive role in Re. The flow velocity in the shell is related to the shell side flow area, that is, to the shell inner diameter and the baffle spacing. A large diameter will inevitably form a larger flow area. When the flow rate is constant, in order to obtain a suitable flow rate, a smaller baffle spacing must be selected to ensure a certain Re value. The small baffle spacing makes the helical inclination angle of the helical baffle structure very small, resulting in less than ideal flow conditions and affecting the heat transfer performance; and the small helical inclination angle increases the pressure drop. In addition, due to reasons such as short circuit of the medium between the baffles, the heat transfer performance is not as good as that of the bow-shaped baffle structure. Only the baffle spacing of smaller shell diameters can be reduced, thereby obtaining a large spiral inclination angle to achieve the ideal flow state. 2 Double-shell spiral baffle heat exchanger This year, our company cooperated with Dalian Haite Refining Technology Co., Ltd. to trial-produce a double-tube, double-shell spiral baffle heat exchanger. The heat exchanger has a nominal diameter of 1400mm and adopts a floating-head structure with a relatively large diameter. According to calculations, when a single shell is used, the baffle spacing is only 370mm to ensure a certain flow speed. After adopting a double shell, it becomes a double helix structure with an inner baffle spacing of 630mm and an outer baffle spacing of 1120mm, as shown in Figure 1. The use of this double shell is equivalent to reducing the shell diameter, which increases the baffle spacing while ensuring a certain flow rate, thereby obtaining a larger spiral inclination angle, which solves the shortcomings of small spiral inclination angle and reduced heat transfer performance of large-diameter spiral baffle heat exchangers. 2.1 Structure The double-shell-pass structure of general heat exchangers is mostly used in double-tube heat exchangers, which uses a longitudinal partition to divide the shell side into two passes. There are three types of sealing of the gap between the longitudinal partition and the inner wall of the shell: ① Welded type. ②Plug-in type using guide grooves. ③The most commonly used connection form is a structural type that uses a spring leaf made of corrosion-resistant material to seal the two passes. The difference between the double-shell structure of the spiral baffle heat exchanger is the type of tube bundle. As shown in Figure 1, the tube bundle is composed of a tube plate, a split-pass structure, an inner spiral baffle and an outer spiral baffle. The split-pass structure is composed of a split-pass cylinder and an annular partition plate. The pipe box splitting also uses a splitting cylinder with the same diameter as the shell side. One end of it is welded to the end cover of the pipe box, and the other end is fixed with four support plates, thus dividing the pipe box into two passes. Its working principle is that the tube-side medium first flows from the pipe box nozzle into the split-range cylinder, then flows through the heat exchange tube contained in the cylinder to the tube plate at the other end, then returns to the heat exchange tube outside the cylinder, and then flows to the split-range cylinder outside the pipe box and out from the other nozzle. The shell-side medium also flows in from the shell nozzle first. Due to the barrier of the partition plate, the medium can only enter the split-way cylinder, flow to the tube sheet at the other end, then return to the outside of the cylinder and flow to the front-end partition plate, and flow out from the other nozzle. This completes the heat exchange process of the shell-side medium. 2.2 Structural design of each element of the double-shell tube bundle (1) Arrangement of tubes The type of tube plate of the double-shell spiral baffle heat exchanger is the same as that of the general heat exchanger tube plate, except that the tube holes of the heat exchanger are not arranged according to the conventional triangle or square, but are arranged in a concentric circular tube arrangement. Such tube arrangement is conducive to the opening of circular partition grooves. When dividing, it should be considered that the number of pipes between the two passes should be roughly equal, so that the flow areas of the two passes are basically the same to ensure that the medium between the two passes has the same flow rate. In this way, the diameter of the separate cylinder will be determined after the separation, and then the position of the partition groove will be determined based on the diameter of the cylinder. (2) The split-range structure of the split-range double shell is composed of an annular dividing plate and a split-range cylinder (Figure 2). The thickness of the dividing plate, the thickness of the cylinder and the length of the cylinder can be determined according to the specific situation. The dividing plate has tube holes corresponding to the tube sheets, and the heat exchange tubes outside the cylinder pass through the tube holes. A sealing spring piece is installed on the outer circumference of the partition, and is fixed with a pressure plate and bolts. It is used to seal the annular gap between the inner wall of the housing and the inner wall of the housing to prevent the medium from short-circuiting between the two passes. This structure is the same as the longitudinal partition type, except that the shape of the spring piece and pressure plate is changed from a rectangular lath to an annular plate. The connection between the dividing plate and the split-range cylinder is sealed and welded to form an integral structure, which not only facilitates installation and disassembly, but also prevents leakage. Figure 2 Schematic diagram of shell side split structure (3) Baffles Double-shell spiral baffles can be divided into two types. One is installed in the split-range cylinder, which is called the inner spiral baffle. It has the same shape as the single-shell spiral baffle, which is a 1/4 circle fan-shaped plate (Figure 3). Several plates are staggered up, down, left, and right at a certain inclination angle to form a spiral channel in the barrel. The other is for the outside of the cylinder, called the external spiral baffle, which is also a 1/4-circle annular plate (Figure 4). Several plates are staggered around the outer wall of the divided cylinder at a certain inclination to form a spiral channel outside the cylinder. Both plates are drilled with tube holes corresponding to the tube plate and with a certain inclination (processed on a special mold). The calculation of the dimensions of the plates can be found in relevant literature. Figure 3 Schematic diagram of the inner spiral baffle Figure 4 Schematic diagram of the outer spiral baffle 3 Conclusion The double-shell spiral baffle heat exchanger is a new type of high-efficiency and energy-saving heat exchanger. In addition to having all the advantages of the single-shell spiral baffle heat exchanger, it has a wider range of applications. This structure can be used in large-diameter heat exchangers and heat exchangers with small spiral spacing due to small shell-side medium flow. Another biggest feature is that it can realize pure countercurrent heat transfer. The average temperature difference of countercurrent heat transfer is larger than that of parallel flow. Under the condition of transferring the same heat, the heat transfer area required for countercurrent flow is small, making the structure more compact. The main disadvantage of the double-shell spiral baffle heat exchanger is that the manufacturing process is relatively complex and the one-time investment in tooling costs is large, so it is suitable for mass production. References: Zhang Kezheng, Chen Shixing, Zhang Qiang. Development and research of spiral baffle heat exchanger. Journal of Fushun Petroleum Institute, 1998, 18(3): 31 38. Xu Bin, Zhang Maigui. Application of spiral baffle heat exchanger in atmospheric and vacuum devices. Petrochemical Equipment, 2003, 32(5): 53 54. Wang Suhua, Wang Shuli, Zhao Zhiyong. Research on flow characteristics of spiral baffle heat exchanger. Journal of Petroleum and Chemical Engineering College, 2001, 14(1): 64 67. Wang Liang. Experimental study on heat transfer and resistance performance of spiral baffle heat exchanger. Xi'an: Xi'an Jiaotong University, 2001. Zhang Shaowei, Sang Zhifu. Influence of structural and operating parameters on the performance of spiral baffle heat exchangers. Petrochemical Equipment, 2004, 33(3):17 20. GB151—1999, Shell and Tube Heat Exchangers. (Editor Xu) This post was last edited by prt0683 on 2009-4-9 22:17 ]

Spiral baffle heat exchanger can also be referred to as spiral heat exchanger (Helixchanger). Its basic structure is still a shell-and-tube heat exchanger, which complies with GB151-1999 or TEMA standards. It only improves the design of the shell-side baffles and designs a new type of baffles to form a spiral channel on the shell side, thereby forcing the fluid to flow through the shell-side channel in a spiral shape, resulting in a relatively high heat transfer coefficient without causing too much pressure loss. The idealized spiral baffle has a natural spiral curved surface, and its geometric rules are the same as those of a spiral. The spiral baffle uses a spiral surface to fix the tube bundle, forcing the shell-side fluid to flow through the shell in a spiral shape. In the spiral baffle structure, existing research shows that different helix angles have different heat transfer and resistance properties, but in general, the pressure drop of the spiral baffle is much smaller than that of the arcuate baffle structure, the heat transfer performance is equivalent to or slightly lower than that of the arcuate baffle, and the overall heat transfer performance is better than the arcuate baffle. In ordinary shell and tube heat exchangers, the aspect ratio of the shell is generally 6 to 10. Use a helix angle of 40. The spiral baffles can only arrange three half-pitch spiral baffles, while in ordinary single arcuate baffle heat exchangers, the number of baffles is generally much more than this. In this way, in the spiral baffle structure, on the one hand, because the flow channel is too short, it is not guaranteed that the fluid will flow out when it has fully developed into a spiral flow. On the other hand, the pressure drop of this structure is very small and cannot fully utilize the pressure head provided by the user [6]. In order to further improve the performance of the spiral baffle and provide a wider range of possible uses, it is necessary to further improve the structure of the spiral baffle. On the one hand, a smaller helix angle can be used. Although this will reduce the overall performance of heat transfer, it can increase the heat transfer effect under the condition of making full use of the pressure drop allowed by the user, so that it can not only meet the use requirements but also obtain better heat transfer performance as much as possible. On the other hand, consider using a double helix structure to arrange more baffles within the same length. 2 Spiral baffle double helix structure In order to make the spiral baffle can be used in actual production, the spiral baffle can generally be realized by splicing flat boards. That is, the spiral baffle within one pitch is usually composed of four flat plates connected end to end, and each plate is an elliptical fan-shaped plate with an outer circumference (Figure 1). In order to arrange more baffles, an overlapping structure is usually used. The so-called overlap structure means that the contact points of two adjacent baffles overlap each other by a certain height, and the flow cross-sectional area is reduced accordingly, so that more baffles can be arranged in a shell of the same length. The overlap distance can be determined based on actual usage conditions. The larger the overlap distance, the better the heat transfer effect on the shell side and the higher the pressure drop will be. In the overlapping structure, the overlapping distance is further increased. When the overlapping distance is half of the pitch, the two adjacent baffles are placed opposite each other, and the original alternate baffles are continuous together, forming a so-called double helix structure. For the purpose of distinction, the ordinary continuous structure is now called a single helix knot. For spiral baffles, the use of a double helix structure can improve the heat transfer performance per unit pressure drop. At the same time, in the processing of the test pieces, the two test pieces adopt the same processing technology and assembly method. Compared with the weight of the heat exchanger, the increase in the weight of the test piece is negligible, and the increase in assembly time is also very small. The double helix structure can better fix the heat exchange tube bundle and prevent the vibration of the tube bundle. Therefore, the use of a double helix structure can improve the heat transfer performance per unit pressure drop with a small increase in production costs. 5 Conclusion (1) In the spiral baffle, two different structural forms, single helix and double helix, can be used. Using the double helix structure, more baffles can be arranged on the shell side. (2) The use of spiral baffles with a double helix structure can reduce leakage between the baffles, allow the fluid to flow better in a flat push flow, and improve the performance of the spiral baffles. (3) Experimental research shows that using a double helix structure, compared with a single helix structure, the pressure drop and heat transfer performance at the same shell side JRe are increased, and the heat transfer performance per unit pressure drop is improved.

This kind of problem should be treated with a rigorous attitude. Some people have overplayed the spiral baffle heat exchanger. I think Xi'an Jiaotong University has done a very good job. Their research results are very objective. The spiral baffle is mainly used to control the resistance drop, not to enhance heat transfer. With the same equipment and the same operating conditions, the heat transfer efficiency will decrease if the single-arch plate is replaced by a spiral baffle. It means that the spiral baffle not only reduces the resistance but also reduces the heat transfer coefficient. However, the heat transfer coefficient on the shell side per unit pressure drop is higher than that of a single bow plate. This means that the equipment can be made smaller than the single bow plate equipment. This also depends on the situation on the tube side. As for the appropriate spiral angle, it depends on the allowable pressure drop of the equipment. It is determined by process calculations. If the allowable pressure drop is large, there is no need to choose a spiral baffle.

I want to know how to process the inclination angle of the distance tube

This post was last posted by michaelzh on 2013-11-12 14:17 The editor agrees with the point of view on the 7th floor. The spiral baffles are indeed overblown, but it is not objective to say that "the heat transfer efficiency of single-arch plates is reduced when replaced by spiral baffles." Most of the patents based on domestic research or applications are based on published articles by Lummus. Some have been modified, and some are even copied directly without any more in-depth research (I personally feel that some of these public documents have been tampered with, and some key points are not mentioned at all). Judging from the projects I have experienced, some of them have indeed increased the pressure drop and reduced the heat transfer coefficient after replacing them with spiral baffles (the size of the heat exchanger remains unchanged). But for the most part, with the same heat exchanger size, the heat transfer coefficient has increased, but it is only slightly better than the arcuate plate. It is not as exaggerated as the manufacturer said! As for "spiral baffles are mainly used to control resistance drop, not to enhance heat transfer", I have a different view on this point. In some systems, with the same heat exchanger size and baffle spacing, the pressure drop of spiral baffles is much larger than that of ordinary arcuate plates, and the heat transfer coefficient is only slightly increased. When choosing between spiral baffles and ordinary arcuate plates when designing, don’t listen to the manufacturer’s lies, and don’t beat the spiral baffles to death with a stick. It’s better to compare them through calculations! For now, there are still many issues worth discussing in the calculations of domestic manufacturers. The above is just my personal opinion!