Shell and tube heat exchanger- This is a device for exchanging heat between two different flows. One medium is heated due to the cooling agent of the other. Two different media can change their state of aggregation, but mixing does not occur during the transfer of energy. Heat exchange occurs through the walls of the device. Pipes are often ribbed to increase the heat transfer surface area.
Types of heat exchangers
There are heat exchangers various types. Their diameter can range from 159 to 3000 mm. Maximum pressure - 160 kg/cm2. The length can vary from several tens to 10,000 mm. Types of units:
- With built-in grilles made in the form of a pipe.
- The design of a shell-and-tube heat exchanger may include a temperature compensator.
- A device equipped with a floating head.
- With U-shaped device.
- Combined. It has a compensator and a built-in floating head.
In this video you will learn how heat exchangers are classified:
The design of the shell-and-tube heat exchanger, which contains tube sheets, has a rigid coupling of all elements. Such devices are most often used in the oil or chemical industries. This type of device accounts for approximately three-quarters of the total market. In this type, tube sheets are welded from the inside to the walls of the body, and attached to them with a rigid coupling heat exchange pipes. This avoids any shifts of all constituent elements inside the case.
A shell-and-tube heat exchanger compensates for elongation due to heat by longitudinal compression or with the help of special flexible inserts in expanders. This is a semi-rigid structure.
A device with a floating head is considered much more advanced. The floating head is a special movable grille. It moves throughout the pipe system along with the cover. Such a device is more expensive, but also much more reliable.
There are single-pass and multi-pass heat exchangers For a device with a U-shaped pipe system, two ends are welded to one grid. The rotation angle is 180°, and the radius is from 4 pipe diameters. Thanks to this design, the pipes inside the housing can be freely extended.
There are single-pass and multi-pass heat exchangers. The choice depends on the direction of movement of the coolant inside the apparatus. In a single pass, the filler moves along the shortest path. Most shining example this type of device - This is a GDP water heater, which is used in heating systems. Such a device is best used in places where a high heat transfer rate is not needed (the difference between the temperature environment and the heat carrier is minimal).
Multi-pass devices have special transverse partitions. They provide redirection of coolant flow. Used where high heat transfer rates are required. Tubular devices are also divided into single-flow, cross-flow and counter-flow.
So that the heat exchanger can be operated in extreme conditions, instead of the usual steel pipes use glass or graphite. The housing is sealed using seals.
Operating principle
The device has a fairly simple principle of operation. A shell and tube heat exchanger separates the media. There is no mixing of products inside the structure. Heat transfer occurs along the walls of the tubular elements, which separate coolants. One carrier is located inside the pipes, and the other is supplied under pressure into the interpipe space. Aggregate states both energy carriers may differ. It can be gas, steam or liquid.
Operating principle shell and tube heat exchanger consists in the normal processes of energy transfer between liquids and various gases. To increase the coefficient of thermal energy transfer, rather high speeds of movement of products inside the structure are used. For steam or gas, they generate from 8 to 25 m/s. For liquid coolants the minimum speed is 1.5 m per second.
Heat passes through the walls of this unit Design of a shell-and-tube apparatus
The main advantage of a shell-and-tube heat exchanger and main reason its popularity lies in high reliability designs. It includes distribution chambers, which are equipped with tubes. A cylindrical casing, a bundle of pipes and a certain number of gratings are also provided. The entire structure is complemented by covers that are located at the ends. The kit includes supports that allow you to place the device in a horizontal plane. There is also a mount for mounting the device anywhere in space.
To increase heat exchange between the coolant, pipes that are covered with special ribs are used. If the task is to reduce heat transfer, then the body is covered with some kind of heat-insulating layer. This way you can significantly increase the accumulating properties of the product. Special designs are used in which one pipe is located in the second.
Thick sheet steel (from 4 mm) is used to make the casing. To produce gratings, most often the same material is taken, but its thickness is much greater (from 2 cm). The main element is a bundle of pipes made of a material that has high thermal conductivity. This bundle is fixed on one or both sides on tube sheets.
Advantages and Disadvantages
These devices have several advantages, which ensures sufficient competitiveness in the market heat exchange systems. Main advantages of the equipment:
- The design provides excellent resistance to hydraulic shocks. Similar systems do not have this characteristic.
- Shell and tube heat exchangers are capable of operating in extreme conditions or with products that are quite heavily contaminated.
- They are very easy to use. Easy to carry out mechanical cleaning equipment, its planned maintenance. The equipment has high maintainability.
This heat exchanger has both pros and cons Despite all the advantages, this device also has disadvantages. These should be considered before purchasing. Depending on the intended use, other similar systems may be required. Disadvantages of the device:
- The efficiency is lower than that of plate products. This is because shell-and-tube exchangers have less surface area to transfer heat.
- Has large sizes. It boosts it final cost, as well as operating costs.
- The heat transfer coefficient strongly depends on how fast the agent moves.
Despite all their shortcomings, shell-and-tube devices have found their niche in the heat exchanger market. They remain popular and are used in many industries.
Scope of application
Shell and tube products are used as part of utility networks Housing and communal services. They are also used in heating stations to provide hot water residential buildings. Individual heating points have certain advantages over central heat and water supply: they provide heat to buildings and other objects much more efficiently than a centralized heating network.
Heat exchangers of this type are also used in the oil, chemical and gas industries. They are used in the field of thermal power engineering, where coolants have high temperature transfer rates. And this is not all the industries where such equipment is used. It can be found in reboiler evaporators or in air heat exchange condenser coolers, distillation columns. It has found application in beer production and the food industry.
Operating the device
The tubular heat exchanger has a high service life. In order for it to perform its role efficiently and serve for a long time, it is necessary to carry out scheduled maintenance in a timely manner. Most often, the unit is filled with liquid that has not gone through the filtration stages. This leads to gradual clogging of the tubes, which prevents the coolant fluid from moving freely throughout the system. It is necessary to carry out timely and systematically mechanical cleaning all elements of the shell and tube product. It is also necessary to wash the components under high pressure.
If there is a need to repair a tubular apparatus, the first step is to carry out diagnostic measures. This allows you to discover the main problems. The most vulnerable part is the tubes, which are most often damaged. Diagnostics is carried out using hydraulic tests.
All thermal energy exchange equipment is quite capricious. This includes shell-and-tube devices. When making any interventions in the structure for repairs, it must be taken into account that this may affect the coefficient of thermal conductivity and, accordingly, heat exchange between media. Many businesses and individuals buy several installations at once so that you can quickly connect to another device.
It is important to remember that certain difficulties may arise when regulating equipment based on condensate. Absolutely any changes entail an increase or decrease in heat transfer. It should also be taken into account that the change in area occurs nonlinearly.
Drawings of heat exchangers in Compass
On this page you can download drawings in the Compass program various heat exchangers for a symbolic amount or
You can send your drawing. It will be posted on our website. By doing so, you will provide an invaluable service to the next generation of students.
Only high-quality drawings are published. Preference is given to 3D drawings.
Download a set of 3D drawings of a plate heat exchanger with details for only 100 rubles.
Download a set of drawings of a horizontal heat exchanger in 3d.
The 3D model is sent with a construction history, which allows you to independently change the dimensions of the 3D assembly.
Download a set of drawings of a horizontal cooler heat exchanger with details.
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Download the drawing of the heat exchanger and heater.
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Download the drawing of the heat exchanger and secondary steam heater.
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Download the drawing of the heat exchanger evaporator in the production of secondary steam.
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Download the drawing of the heat exchanger and boiler of the stripping column.
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Download the drawing of the heat exchanger and network water heater.
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Download the drawing of the recuperator with details.
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Download a drawing of a recuperator in the production of higher aliphatic amines with details.
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Download the drawing of a heat exchanger for a liquid ammonia cooler.
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Download a drawing of a heat exchanger and amine cooler in the production of higher aliphatic amines.
Depending on the method of heat transfer, there are two main groups of heat exchangers:
- - Surface heat exchangers, in which heat transfer between heat-exchanging media occurs through the heat exchange surface separating them - a blank wall;
- - Mixing heat exchangers, in which heat is transferred from one medium to another when they are in direct contact.
Regenerative heat exchangers are used much less frequently, in which liquid media are heated due to their contact with previously heated media. solids- a nozzle that fills the apparatus, periodically heated by another coolant.
The design of heat exchangers should be simple, easy to install and repair. In some cases, the design of the heat exchanger must ensure the least possible contamination of the heat exchange surface and be easily accessible for inspection and cleaning.
Transfer of energy in the form of heat that occurs between bodies having different temperatures, is called heat transfer.
The driving force of any heat exchange process is the temperature difference between a more heated and a less heated body, in the presence of which heat spontaneously, in accordance with the second law of thermodynamics, moves from a more heated to a less heated body.
The bodies involved in heat exchange are called coolants.
Where to download heat exchanger drawings
- Search query: drawing of a heat exchanger in Perm - will allow you to download it in Perm and the Perm region, for example, for the Perm National Research Polytechnic University.
- Search query: drawing of a heat exchanger in Kazan - will allow you to download it in Kazan, say, for technical specialties of the Kazan National Research University.
- Search query: drawing of a heat exchanger in Omsk - will allow you to download it from Omsk State Technical University.
Shell and tube heat exchangers
These heat exchangers are among the most commonly used surface heat exchangers. shell-and-tube heat exchanger of a rigid structure, which consists of a housing, or casing 1, and tube sheets 2 welded to it. A bundle of tubes 3 is fixed in the tube sheets. Covers 4 are attached to the tube sheets (with gaskets and bolts).
In a shell-and-tube heat exchanger, one of the heat-exchanging media moves inside the pipes (in the pipe space), and the other moves in the inter-tube space.
The media are usually directed countercurrent to each other. In this case, the heated medium is directed from bottom to top, and the medium giving off heat is directed in the opposite direction. This direction of movement of each medium coincides with the direction in which this medium tends to move under the influence of changes in its density when heated or cooled.
In addition, with the indicated directions of media movement, more uniform distribution speeds and identical heat transfer conditions over the cross-sectional area of the apparatus. Otherwise, for example, when a colder (heated) medium is supplied from above the heat exchanger, the more heated part of the liquid, being lighter, can accumulate in the upper part of the apparatus, forming “stagnant” zones.
At relatively low fluid flow rates, the speed of its movement in the pipes is low, and, consequently, the heat transfer coefficients are low. To increase the latter for a given heat exchange surface, the diameter of the pipes can be reduced, correspondingly increasing their height (length). However, heat exchangers of small diameter and considerable height are inconvenient for installation, require high premises and increased metal consumption for the manufacture of parts not directly involved in heat exchange (device casing). Therefore, it is more rational to increase the heat transfer rate by using multi-pass heat exchangers.
In a multi-pass heat exchanger, the housing 1, tube sheets 2, pipes 3 and covers 4 secured in them are the same as in a single-pass heat exchanger. Using transverse partitions 5 installed in the heat exchanger covers, the pipes are divided into sections, or passages, through which the liquid moves sequentially flowing in the tube space of the heat exchanger. Typically, the division into passages is carried out in such a way that all sections contain approximately the same number of pipes.
Due to the smaller total cross-sectional area of the pipes placed in one section compared to the cross-section of the entire bundle of pipes, the fluid speed in the pipe space of a multi-pass heat exchanger increases (relative to the speed in a single-pass heat exchanger) by a factor of equal to the number moves. Thus, in a four-pass heat exchanger, the speed in the pipes, all other things being equal, is four times greater than in a single-pass one. To increase the speed and lengthen the path of movement of the medium in the inter-tube space, segment partitions 6 are used. In horizontal heat exchangers, these partitions are also intermediate supports for the tube bundle.
An increase in heat exchange intensity in multi-pass heat exchangers is accompanied by an increase in hydraulic resistance and a more complex design of the heat exchanger. This dictates the choice of an economically feasible speed, determined by the number of heat exchanger strokes, which usually does not exceed 5-6. Multi-pass heat exchangers operate on the mixed current principle, which is known to lead to some reduction driving force heat transfer compared to purely countercurrent movement of the media involved in heat transfer.
In single-pass and especially multi-pass heat exchangers, heat transfer can deteriorate due to the release of air and other non-condensable gases dissolved in the liquid (or steam). For their periodic removal, purge taps are installed in the upper part of the heat exchanger casing.
Single-pass and multi-pass heat exchangers can be vertical or horizontal. Vertical heat exchangers are easier to operate and occupy a smaller production area. Horizontal heat exchangers are usually made multi-pass and operate at high speeds of the media involved in heat exchange in order to minimize the stratification of liquids due to the difference in their temperatures and densities, as well as to eliminate the formation of stagnant zones.
If the average temperature difference between the pipes and the casing in heat exchangers of a rigid structure, i.e. with fixed tube sheets welded to the body becomes significant, then the pipes and casing are lengthened unequally. This causes significant stress in the tube sheets, can disrupt the tightness of the connection between the pipes and the sheets, and lead to destruction welds, unacceptable mixing of heat-exchanging media. Therefore, when the temperature difference between the casing and pipes is greater than 500C, or when the pipes are of a significant length, shell-and-tube heat exchangers of a non-rigid design are used, allowing some movement of the pipes relative to the body of the apparatus.
To reduce temperature deformations caused by the large temperature difference between the pipes and the casing, the significant length of the pipes, as well as the difference in the material of the pipes and the casing, shell-and-tube heat exchangers with a lens compensator are used, which have a lens compensator 1 on the body that is subject to elastic deformation. This design is simple, but is applicable at low excess pressures in the annulus (6 atm).
Download drawing Shell and tube heat exchangers with compensating devices:
a - with a lens compensator; b - with a floating head; c - with U-shaped pipes; 1 - compensator; 2 - movable tube sheet; 3 - U-shaped pipes.
If it is necessary to ensure large movements of pipes and casing, a heat exchanger with a floating head is used (Fig. 1.2b). The lower tube sheet is movable, which allows the entire tube bundle to move freely regardless of the apparatus body. This prevents dangerous temperature deformation pipes and violation of the tightness of their connection with the tube sheets. However, compensation temperature extensions achieved in in this case due to the complexity and weight of the heat exchanger design.
In a shell-and-tube heat exchanger with U-shaped tubes, the tubes themselves act as compensating devices. At the same time, the design of the apparatus, which has only one fixed tube sheet, is simplified and simplified. The outer surface of the pipes can be easily cleaned by removing the entire tube from the apparatus body. In addition, in heat exchangers of this design, which are two- or multi-pass, fairly intense heat exchange is achieved. Disadvantages of U-tube heat exchangers: Difficult to clean inner surface pipes, the difficulty of placing a large number of pipes in a tube sheet.
In the chemical industry, heat exchangers with double pipes are also used. On one side of the apparatus there are two tube grids, and in one grid there is a bundle of pipes of smaller diameter, open at both ends, and in the other grid there are pipes larger diameter with closed left ends, installed concentrically relative to the pipes. The medium moves through the annular spaces between the pipes and is removed from the interpipe space through the pipes. Another medium moves from top to bottom along the inter-tube space of the heat exchanger housing, washing the pipes from the outside. In heat exchangers of this design, the pipes can elongate under the influence of temperature, regardless of the heat exchanger body.
Shell and tube heat exchanger with double pipes:
Elemental heat exchangers. To increase the speed of movement of the medium in the annulus without the use of partitions that make cleaning the apparatus difficult, elemental heat exchangers are used. Each element of such a heat exchanger is a simple shell-and-tube heat exchanger. The heated and cooled media successively pass through individual elements, consisting of a bundle of pipes in a casing of small diameter. A heat exchanger consisting of such elements (passes) allows significant excess pressure in the inter-tube space; it can be considered as a modification of a multi-pass shell-and-tube heat exchanger.
In elemental heat exchangers, the mutual movement of media approaches an effective scheme of pure counterflow. However, due to the division of the total heat exchange surface into individual elements, the design becomes more cumbersome and the cost of the heat exchanger increases.
Double tube heat exchangers
Heat exchangers of this design, also called pipe-in-pipe heat exchangers, consist of several tubular elements connected in series, formed by two concentrically arranged pipes. One coolant moves through the inner pipes, and the other through the annular gap between the inner pipes and the outer pipes. Internal pipes(usually with a diameter of 57-108 mm) are connected by rolls, and external pipes having a diameter of 76-159 mm are connected by pipes.
Thanks to the small cross-section of the difficult and inter-tube space in two-tube heat exchangers, even at low flow rates, quite high speeds liquids, usually equal to 1-1.5 m/sec. This makes it possible to obtain higher heat transfer coefficients and achieve higher thermal loads per unit mass of the apparatus than in shell-and-tube heat exchangers. In addition, with increasing coolant velocities, the possibility of contaminant deposition on the heat exchange surface decreases.
At the same time, these heat exchanger drawings are more cumbersome than shell-and-tube drawings, and require more metal consumption per unit of heat exchange surface, which in devices of this type is formed only by internal pipes.
Download drawing double-tube heat exchangers can operate efficiently at low coolant flow rates, as well as at high pressures. If a large heat exchange surface is required, then these devices are made of several parallel sections.
Coil heat exchangers
Submersible heat exchangers download. In a submersible coil heat exchanger, dropping liquid, gas or steam moves along a spiral coil made of pipes with a diameter of 15-75 mm, which is immersed in a liquid located in the body of the device. Due to the large volume of the housing in which the coil is located, the fluid velocity in the housing is insignificant, which causes low values of the heat transfer coefficient outside the coil. To increase it, the fluid velocity in the housing is increased by installing an internal glass in it, but at the same time the usable volume of the apparatus body is significantly reduced. At the same time, in some cases, a large volume of liquid filling the housing also has a positive value, since it ensures more stable operation of the heat exchanger during regime fluctuations. The coil pipes are attached to the structure.
In heat exchangers of this type, the coils are often also made of straight pipes connected by rolls. At high flow rates of the medium moving along a coil of straight pipes, it is first directed to a common collector, from which it enters parallel sections of pipes and is also removed through a common collector. With this parallel connection sections, the speed decreases and the length of the flow path decreases, which leads to a decrease in the hydraulic resistance of the apparatus.
Heat transfer in the inter-tube space of submersible heat exchangers is low-intensity, since heat is transferred almost by free convection. Therefore, heat exchangers of this type operate at low thermal loads. Despite this, immersion heat exchangers are found to be quite wide application due to the simplicity of the device, low cost, accessibility for cleaning and repair, as well as ease of operation at high pressures and in chemically active environments. They are used for heating surfaces up to 10-15 m2. Download the drawing of the submersible heat exchanger.
If saturated water vapor is used as a heating agent in a submersible heat exchanger, then the ratio of the length of the coil to its diameter should not exceed a certain limit; for example, at a steam pressure of 2 105-5 105 N/m2 (2-5 atm), this ratio should not be more than 200-275. Otherwise, the accumulation of steam condensate in the lower part of the coil will cause a significant decrease in the heat exchange rate with a significant increase in hydraulic resistance.
Irrigation heat exchangers
Such a heat exchanger consists of coils made of straight pipes placed one above the other, which are connected to each other by rolls. The pipes are usually arranged in parallel vertical sections with common manifolds for supplying and discharging the cooled medium. From above, the coils are irrigated with water, evenly distributed in the form of drops and streams using a gutter with jagged edges. Waste water is discharged from a pan installed under the coil. Sprinkler heat exchangers are used primarily as refrigerators and condensers, with about half of the heat being removed by evaporation of the cooling water. As a result, water consumption is sharply reduced compared to its consumption in other types of refrigerators. Relatively low water consumption - important dignity irrigation heat exchangers, which, in addition, are also distinguished by their simplicity of design and ease of cleaning the outer surface of the pipes.
Despite the fact that the heat transfer coefficients in irrigation heat exchangers operating on the cross-flow principle are somewhat higher than those of submersible ones, their significant disadvantages are: bulkiness, uneven wetting of the outer surface of the pipes, the lower ends of which, with a decrease in irrigation water flow rate, are very poorly wetted and practically do not participate in heat exchange. In addition, the disadvantages of these heat exchangers include: corrosion of pipes by air oxygen, the presence of drops and splashes entering the surrounding space.
Due to the evaporation of water, which increases with insufficient irrigation, heat exchangers of this type are most often installed on outdoors; they are fenced off wooden gratings(blinds), mainly to minimize the entrainment of splashing water.
Irrigation heat exchangers operate at low heat loads and their heat transfer coefficients are not high. They are often made from chemically resistant materials.
Description of capacitor design
The advantage of shell-and-tube condensers is the possibility of creating high and even identical velocities of both coolants and, consequently, high heat transfer coefficients. Their disadvantages include high hydraulic resistance and significant metal consumption.
The most widely used are shell-and-tube condensers used for heat exchange between flows in various states of aggregation (vapor-liquid, liquid-liquid, gas-gas, gas-liquid). The device consists of a bundle of pipes placed inside a cylindrical body (shell), welded from sheet steel, less often cast. The tubes are rolled into two tube sheets or welded to them, depending on the properties of the structural materials. Most often, pipes with diameters are used: 25x2; 38X2; 57X2.5 mm; their length usually reaches 6 m. The tubes are placed in a bundle in a checkerboard pattern, along the vertices of an equilateral triangle, with a step t = (1.25-1.30) dн, where dн - O.D. pipes The device is equipped with two removable covers with fittings for the inlet and outlet of the coolant moving inside the pipes. The pipe and inter-pipe spaces are separated. The second coolant moves in the interpipe space, equipped with inlet and outlet fittings. As a rule, the flow that moves through the pipes contains suspended solid particles (for ease of cleaning), is under high pressure (so as not to weigh down the body) or has aggressive properties (to protect the body from corrosion) .
Design of a shell-and-tube refrigerator from:
- housings;
- pipes;
- tube sheet;
- covers;
- fittings for entry and exit from the pipe space;
- fittings for entry and exit from the interpipe space;
- transverse partitions of the interpipe space;
- support legs, respectively, for vertical and horizontal positions of the apparatus.
Hot liquid enters a pipe space consisting of pipes. The cold coolant enters the annulus; as a result of the contact of two coolants with different heat flows, heat exchange occurs and heat flows are leveled, thereby determining the set inlet temperature for hot or cold coolant. Coolants enter the pipe space using fitting 6, and into the inter-tube space - a fitting. The apparatus has elliptical covers and a bottom; the apparatus is fastened using support legs 8. The pipes are attached to the tube sheet 8 by flaring.
The flow area of the interpipe space is significantly larger (sometimes 2 times) than the total open cross-section of the pipes, therefore, at the same volumetric flow rates of coolants, the heat transfer coefficient from the side of the interpipe space turns out to be lower. To eliminate this phenomenon, they resort to increasing the coolant velocity by placing various partitions in the interpipe space. Shell-and-tube devices are located vertically or horizontally according to local conditions; if it is necessary to lengthen the coolant path, they can be connected in series, and if it is impossible to place the required number of pipes in one housing, they are connected in parallel. To lengthen the path of coolants in order to increase their speed and intensify heat transfer, multi-pass devices are used. Thus, in a two-pass apparatus, thanks to the partition 1 in the top cover 2, the coolant first passes through the pipes only through half of the bundle and in the opposite direction through the second half of the bundle.
Ease of manufacture, maintainability, good performance characteristics and reliability of the design make the recuperative or shell-and-tube apparatus one of the most common types heating equipment. The following working media can be used: gas, water, steam, air, oil, etc. The higher their popularity, the more often specialists are faced with the need to make calculations for their selection. Fortunately, progress does not stand still. A program was developed for selecting recuperators. Let's tell you more about it.
Rice. 1 Shell and tube diagramheat exchanger
What does the calculation of a shell-and-tube heat exchanger come down to? Towards the determination of the heat exchange surface and the final temperatures of the coolant. What is it based on? In preparation heat balance recuperator according to a given scheme (see Fig. 1) and determination of the heat transfer coefficient.
Initial data:
- initial temperatures of both media (heating and heated), their pressure and mass flow.
- physical characteristics of coolants (viscosity, density, thermal conductivity, etc.).
- the final temperature of one of the temperature media.
Surface calculation.
The program determines thermal power recuperator from the heat balance equation.
Heat Balance Equation
- Q = Av* Ϭt.
- G - mass flow rate of the medium, kg/s.
- Ϭt - change in ambient temperature, °C.
We substitute the resulting power into the heat transfer coefficient equation and find from it the heating (heat exchange) surface, m2.
- F = Q / k ∆t.
- Q - thermal power, already determined from the heat balance equation, W.
- k is the heat transfer coefficient through the dividing wall, W/m2K, determined by a rather complex calculation.
- ∆t – average temperature difference, which determines the pattern of movement of the heating and heated media (countercurrent, forward flow), °C.
Having determined the heating surface of the heat exchanger from the last equation, an option with similar characteristics is selected from the database of standard recuperators.
Rice. 2The calculation described above was preliminary. After this, the most difficult and lengthy stage begins - the verification calculation of the shell-and-tube heat exchanger. The flow sections for the heating and heated medium are calculated, the strength of the heat exchanger is calculated, the flow pattern of the media is changed and everything is recalculated anew. Ultimately, the program determines the safety factor for the heating surface.
This reserve is necessary in case the load on the heat exchanger suddenly changes (poor operation of the feed pumps, sludge formation in the pipes, part of the tube bundle had to be plugged for repairs). Finally, the program will calculate the mass of the recuperator. This is convenient - there is immediately work for the builders (a task for foundations is issued).
The program uses the method of numerous iterations to find optimal options and displays it as a list. Even if no option for a typical capacitor circuit suits you, you will have a calculation in your hands, which contains all the data for developing a working project.
Previously, this work was done manually, you can do it now, but it takes a long time to choose optimal scheme no one will - they will choose the first one that passes by temperature. So why bother for several days if the program will provide you with a calculation of a shell-and-tube heat exchanger in just minutes?
Shell and tube heat exchanger. Design and operating principle
Let's consider a shell-and-tube heat exchanger, the drawing of which we see in Figure 2. Let's describe its design, observing the sequence of its assembly.
Rice. 3- Pipes with spacer grids pre-installed on them are welded between the tube grids. The latter not only distance the tubes of the bundle, they also make the heat exchanger multi-pass, increasing the thermal efficiency of its circuit. This design forms pipe system recuperator.
- Two fittings are welded to the casing - medium inlet and outlet. Flanges are welded to the ends of the casing.
- Connections for the supply and outlet of the medium are welded into the bottom of the recuperator. The flanges corresponding to the casing flanges are welded.
- The pipe system is inserted into the casing. Tube sheets are clamped between the flanges of the bottom and casing, sealed with gaskets, and connected with bolts or studs (see Fig. 3). This makes it possible to easily repair shell-and-tube heat exchangers: loosen the flange connection and remove the tube bundle.
The heating medium can circulate in the interpipe space, or it can go through the pipe system. Both variants of the scheme are equally probable. It all depends on physical characteristics environment and ease of installation of supply pipelines. The shell-and-tube heat exchanger diagram is included in the program calculation.
Compensation for thermal expansion
A shell-and-tube heat exchanger, the operating principle of which is always based on the transfer of heat from the heating medium to the heated medium through a dividing wall, has one point that greatly affects its design. In the event that the temperatures of the heating and heated medium differ greatly, the design must provide for compensation for temperature extensions. If this is not done, the housing will expand faster than the tube bundle (or vice versa). This will lead to deformation of the pipes, which means repairs are inevitable. Possible options solutions are shown in Fig. 4
Rice. 4I and II - heating and heated medium.
- 1 - recuperator casing.
- 2 - pipe system.
- 3 - compensator.
- 4 - head of the pipe system.
a) Heat exchanger with a lens compensator, to which two independent parts of the housing are welded. This design (circuit) is only suitable for recuperators with low temperatures and pressure. If you supply coolants with high parameters to it, then stopping for repairs cannot be avoided (the operation of a thin compensator in such conditions is impossible). Shell and tube heat exchanger, the drawing of which is shown in Fig. 2 specifically applies to lens heat exchangers.
b) Recuperator with floating head. The pipe system is sandwiched on one side only between the flanges of the body and the cover (bottom). On the other hand, the ends of the pipes are welded into a separate chamber (head), which is not rigidly connected to the body. In this way, the tube bundle and the body can be extended independently of each other. Repair in this case will not be a problem - the pipe system is pulled out along with the head.
c) Heat exchanger with tubes U shape. The lid, where the heating medium enters, is divided by a partition into two chambers. The principle on which heat exchange is based: medium I enters one chamber and along half of the U-shaped pipes, passing through the entire shell-and-tube heat exchanger, returns to the second chamber of the inlet cover. Medium II enters one nozzle of the casing, circulates in the interpipe space and exits through the second nozzle. The housing and pipe system expand independently of each other.
The calculation program for a shell-and-tube heat exchanger requires clearly formulated initial data. In order for the recuperator to operate flawlessly and stops for repairs to be rare, a correctly defined circuit is needed.
There are several features that are very important for the calculation. This:
- Coolant speed. So, for liquid coolants ω = 0.6...6 m/s, for gaseous coolants ω = 3-30 m/s. The higher the speed, the higher the thermal output of the heat exchanger. But at the same time, the energy consumption (load) on the feed pump, which needs to “push” the medium through the system, also increases. Most often, speeds are deliberately underestimated.
- When choosing the diameter and material of the tube bundle, you need to consider:
- water (steam) quality. Slag and scale will reduce heat transfer and heat output of the recuperator.
- how worse conditions, in which the heat exchanger will operate, the better the steel from which it will be made should be. If you have to do acid washing, then you can’t do it without stainless steel. Better time spend money on manufacturing rather than constantly stopping the recuperator for repairs.
- Size restrictions. Its dimensions should not exceed the maximum possible transportation dimensions.
- Maintainability. After installation, there must be enough space in front of the recuperator so that the shell-and-tube heat exchangers can be repaired (remove the pipe system from the casing). The work of welders also requires room to maneuver. If this is not possible, then the design (circuit) shown in Fig. 5.
- Ease of use. Its design should provide for free access to valves, control devices, and flanges.
- Manufacturing technology. The work itself (technology) and the range of materials impose certain restrictions. So, for example, it will be very difficult to find a sheet with a thickness of 9 mm, while 10 mm can be bought from any company. It's expensive to turn out a lot of parts. It is advisable to change such design elements immediately. Etc., etc.
Rice. 5Initially, incorrect calculation of the recuperator and the choice of an inappropriate scheme are the main reasons why the heat exchanger is repaired. Calculation program heat exchangers will significantly speed up the calculation process and reduce the error rate to zero. The simple interface of the program will be understandable even to a novice calculator.
Plate heat exchangers used in hot water supply, air conditioning, heating systems of private homes and businesses, in heating points and networks as heaters, refrigerators or condensers. Heat exchangers carry out heat transfer between different media, for example, steam-liquid, steam-gas-liquid, liquid-liquid, gas-gas. Heat is transferred from a hot medium (coolant) to a cold one.
Structurally, the heat exchangers are a recuperative heat exchanger with a system of corrugated stamped plates, closely pressed against each other.
The standard sizes of heat exchangers are described in GOST 15518-87 "Plate heat exchangers. Types, parameters and main dimensions."
Technical parameters for using plate heat exchangers:
- heat exchange area 1-800 m 2
- working pressure- not lower than 0.002 MPa
- temperature of working media - -70°С...+200°С
Operating principle and design of plate heat exchangers
The coolant and the heated medium move towards each other along plates pulled together into a package. The plates in the package have same sizes. The plates are located to each other rotated by 180°C. Slit channels are formed between the machined packages with plates located on the frame. Liquids move through these channels. Thus, there is an alternation of channels through which the coolant moves in one direction and the heated medium in the other. The tightness of the channels is ensured by a rubber contour gasket on each plate. The gasket is installed in four groove holes: through two grooves, liquids are supplied/discharged; the other two holes provide mixing of two liquids of different temperatures. In the event of a possible breakthrough of the grooves, the leaking liquid exits through the drainage grooves.
The tortuous movement of fluids creates turbulence in flows. The intensity of heat exchange increases due to the temperature difference from the counterflow of two different liquids. Hydraulic resistance at the same time quite low. The formation of scale during heat transfer is minimized through the use of corrosion-resistant materials (galvanized steel, titanium, aluminum) processed by cold stamping. Gaskets are traditionally made from rubber-based polymers (natural or synthetic).
Plate heat exchanger drawing
1-fixed plate, 2-top guide, 3-movable plate, 4-stand, 5, 6-plate packs, 7-bottom guide, 8-tie bolts
Types of plate heat exchangers
Structurally, plate heat exchangers come in two main types:
- gasketed plate heat exchangers
- non-separable plate heat exchangers (brazed, welded)
The most commonly used are gasketed plate heat exchangers, the design of which is described above.
Plate heat exchangers can be manufactured in several designs: single-pass, double-pass, three-pass.
Flow movement in single-pass, double-pass and three-pass heat exchangers
Advantages of plate heat exchangers
- the heat transfer surface is 99-99.8% of the total surface area of the heat exchanger
- high heat transfer coefficient
- reusable
- easy installation, because fastening elements are located on one side of the heat exchanger
- possibility of changing the width and number of channels to reduce hydraulic losses
- the possibility of increasing the heat exchange surface to increase heat transfer by installing additional plates
Depending on the method of heat transfer, there are two main groups of heat exchangers:
1) surface heat exchangers, in which heat transfer between heat-exchanging media occurs through the heat exchange surface separating them - a blank wall;
2) mixing heat exchangers, in which heat is transferred from one medium to another when they are in direct contact.
Regenerative heat exchangers are used much less frequently in the chemical industry, in which heating of liquid media occurs due to their contact with previously heated solids - a nozzle that fills the apparatus, periodically heated by another coolant.
Surface heat exchangers are the most common, and their designs are very diverse. Below are considered typical, mostly normalized, designs of surface heat exchangers and common mixing condensers.
Chemical technology uses heat exchangers made from the most various metals(carbon and alloy steels, copper, titanium, tantalum, etc.), as well as from non-metallic materials, such as graphite, Teflon, etc. The choice of material is dictated mainly by its corrosion resistance and thermal conductivity, and the design of the heat exchanger significantly depends on the properties of the selected material .
The designs of heat exchangers should be simple, easy to install and repair. In some cases, the design of the heat exchanger must ensure the least possible contamination of the heat exchange surface and be easily accessible for inspection and cleaning.
Tubular heat exchangers
Shell and tube heat exchangers. These heat exchangers are among the most commonly used surface heat exchangers. In Fig. VSH-11 A shows a shell-and-tube heat exchanger of rigid construction, which consists of a housing, or casing 1, and tube sheets welded to it 2. A bundle of tubes is fixed in the tube sheets 3. Covers are attached to the tube sheets (on gaskets and bolts) 4.
In a shell-and-tube heat exchanger, one of the heat-exchanging media I moves inside the pipes (in the pipe space), and the other II- in the interpipe space.
The media are usually directed countercurrent to each other. In this case, the heated medium is directed from bottom to top, and the medium giving off heat is directed in the opposite direction. This direction of movement of each medium coincides with the direction in which this medium tends to move under the influence of changes in its density when heated or cooled.In addition, with the indicated directions of media movement, a more uniform distribution of velocities and identical heat transfer conditions over the cross-sectional area of the apparatus are achieved. Otherwise, for example, when a colder (heated) medium is supplied from above the heat exchanger, the more heated part of the liquid, being lighter, can accumulate in the upper part of the apparatus, forming “stagnant” zones.
Pipes in lattices are usually evenly placed along the perimeters of regular hexagons, i.e., along the vertices of equilateral triangles (Fig. VIII-12, a), less often they are placed in concentric circles (Fig. VIII-12, b).
In some cases, when it is necessary to ensure convenient cleaning of the outer surface of the pipes, they are placed along the perimeter of the rectangles (Fig. VIII-12, c). All these methods pipe placements pursue one goal - to ensure the most compact placement of the required heat exchange surface inside the apparatus. In most cases, the greatest compactness is achieved by placing the tubes along the perimeters of regular hexagons.
Rice. VIII -12. Methods for placing pipes in heat exchangers:
a - along the perimeters of regular hexagons; b - along concentric circles;
V- along the perimeters of rectangles (corridor arrangement)
The heat exchanger shown in Fig. VIII-11, A, is one-way. At relatively low fluid flow rates, the speed of its movement in the pipes of such heat exchangers is low and, therefore, the heat transfer coefficients are low. To increase the latter for a given heat exchange surface, the diameter of the pipes can be reduced, correspondingly increasing their height (length). However, heat exchangers of small diameter and considerable height are inconvenient for installation, require high premises and increased metal consumption for the manufacture of parts not directly involved in heat exchange (device casing). Therefore, it is more rational to increase the heat transfer rate by using multi-pass heat exchangers.
In a multi-pass heat exchanger (Fig. VIII-11, b) housing 1, tube sheets 2, pipes reinforced in them 3 and lids 4 identical to those shown in Fig. VIII-11, A. With the help of transverse partitions 5 installed in the heat exchanger covers, the pipes are divided into sections, or passages, along which the liquid flowing in the pipe space of the heat exchanger sequentially moves. Typically, the division into passages is carried out in such a way that all sections contain approximately the same number of pipes.
Due to the smaller total cross-sectional area of the pipes placed in one section compared to the cross-section of the entire tube bundle, the fluid speed in the pipe space of a multi-pass heat exchanger increases (relative to the speed in a single-pass heat exchanger) by a number of times equal to the number of passes. Thus, in a four-pass heat exchanger (Fig. VIII-11, b), the speed in the pipes, all other things being equal, is four times greater than in a single-pass one. To increase the speed and lengthen the path of movement of the medium in the annulus (Fig. VIII-11, b) serve as segmental partitions 6. In horizontal heat exchangers, these partitions are also intermediate supports for the tube bundle.
An increase in heat exchange intensity in multi-pass heat exchangers is accompanied by an increase in hydraulic resistance and a more complex design of the heat exchanger. This dictates the choice of an economically feasible speed, determined by the number of heat exchanger strokes, which usually does not exceed 5-6. Multi-pass heat exchangers operate on the principle of mixed current, which, as is known, leads to a slight decrease in the driving force of heat transfer compared to the purely countercurrent movement of the media involved in heat exchange. In single-pass and especially multi-pass heat exchangers, heat transfer can deteriorate due to the release of air and other non-condensable gases dissolved in the liquid (or steam). For their periodic removal, purge taps are installed in the upper part of the heat exchanger casing.
Single-pass and multi-pass heat exchangers can be vertical or horizontal. Vertical heat exchangers are easier to operate and occupy a smaller production area. Horizontal heat exchangers are usually made multi-pass and operate at high speeds of the media involved in heat exchange in order to minimize the stratification of liquids due to the difference in their temperatures and densities, as well as to eliminate the formation of stagnant zones.
If the average temperature difference between the pipes and the casing in heat exchangers of a rigid structure, i.e. with fixed tube sheets welded to the body, becomes significant (approximately equal to or greater than 50 ° C), then the pipes and casing elongate unequally. This causes significant stress in the pipes
Rice. VIII-14. Shell and tube heat exchangers with compensating
devices:
A - with lens compensator; b - with a floating head; c - with U-shaped pipes;
1 - compensator; 2 - movable tube sheet; 3 - U-shaped pipes.
gratings, can disrupt the tightness of the connection of pipes with gratings, lead to the destruction of welds, and unacceptable mixing of heat-exchanging media. Therefore, when the temperature difference between the pipes and the casing is greater than 50°C, or when the pipes are of a significant length, shell-and-tube heat exchangers of a non-rigid design are used, allowing some movement of the pipes relative to the casing of the apparatus.
To reduce temperature deformations caused by the large temperature difference between the pipes and the casing, the significant length of the pipes, as well as the difference in the material of the pipes and casing, shell-and-tube heat exchangers with an all-in-one compensator are used (Fig. VIII-14, a), which have a lens compensator 1, subject to elastic deformation. This design is simple, but is applicable for small excess pressures in the annulus, usually not exceeding 6 10 6 N/m 2 (6 at).
If it is necessary to ensure large movements of pipes and casing, a heat exchanger with a floating head is used (Fig. VIII-14, b). Bottom tube sheet 2 is movable, which allows the entire bundle of pipes to move freely regardless of the body of the device. This prevents dangerous temperature deformation of the pipes and disruption of the tightness of their connection with the tube sheets. However, compensation for temperature expansion is achieved in this case by making the heat exchanger design more complex and heavier.
In a shell-and-tube heat exchanger with U-shaped pipes (Fig. VIII-14, c), the pipes themselves 3 perform the function of compensating devices. At the same time, the design of the apparatus, which has only one fixed tube sheet, is simplified and simplified. The outer surface of the pipes can be easily cleaned by removing the entire tube from the apparatus body. In addition, in heat exchangers of this design, which are two- or multi-pass, fairly intense heat exchange is achieved. Disadvantages of heat exchangers with U-shaped tubes: difficulty in cleaning the inner surface of the tubes, difficulty in placing a large number of tubes in the tube sheet.
Steel shell-and-tube heat exchangers are standardized according to GOST 9929-67.
IN
In the chemical industry, heat exchangers with double pipes are also used (Fig. VIII-15). On one side of the apparatus there are two tube grids, and a bundle of tubes is fixed in grid 1 2
smaller diameter, open at both ends, and in the lattice 3
- pipes 4
larger diameter with closed left ends, installed concentrically relative to the pipes 2.
Wednesday I moves along the annular spaces between the pipes 2
And 4
and is removed from the inter-tube space of the heat exchanger through pipes 2.
Other environment II moves from top to bottom along the inter-tube space of the heat exchanger housing, washing the pipes 4
outside. In heat exchangers of this design, the pipes can elongate under the influence of temperature, regardless of the heat exchanger body. Elemental heat exchangers. To increase the speed of movement of the medium in the annulus without the use of partitions that make cleaning the apparatus difficult, elemental heat exchangers are used. Each element of such a heat exchanger is a simple shell-and-tube heat exchanger. The heated and cooled media sequentially pass through separate elements consisting of a bundle of pipes in a casing of small diameter. A heat exchanger consisting of such elements (passes) allows significant excess pressure in the inter-tube space; it can be considered as a modification of a multi-pass shell-and-tube heat exchanger.
In elemental heat exchangers, the mutual movement of media approaches an effective scheme of pure counterflow. However, due to the division of the total heat exchange surface into individual elements, the design becomes more cumbersome and the cost of the heat exchanger increases.
Double-tube heat exchangers. Heat exchangers of this design, also called pipe-in-pipe heat exchangers, consist of several tubular elements connected in series, formed by two concentrically arranged pipes (Fig. VIII-16). One coolant moves through the internal pipes 1 , and the other - along the annular gap between the internal 1 and external 2 pipes. Internal pipes (usually 57-108 in diameter mm) are connected by rolls 3, and outer pipes having a diameter of 76-159 mm,- pipes 4.
Rice. VIII-16. Two-pipe heat exchanger: 1 - internal pipes;
2 - external pipes; 3 - kalach; 4 - pipe branch.
Due to the small cross-sections of the pipe and inter-tube space in two-tube heat exchangers, even at low flow rates, fairly high fluid velocities are achieved, usually equal to 1-1.5 m/sec. This makes it possible to obtain higher heat transfer coefficients and achieve higher thermal loads per unit mass of the apparatus than in shell-and-tube heat exchangers. In addition, with increasing coolant velocities, the possibility of contaminant deposition on the heat exchange surface decreases.
At the same time, these heat exchangers are more bulky than shell-and-tube heat exchangers and require a greater consumption of metal per unit of heat exchange surface, which in devices of this type is formed only by internal pipes.
Double-tube heat exchangers can operate efficiently at low coolant flow rates, as well as at high pressures.
If a large heat exchange surface is required, then these devices are made of several parallel sections.