Shell and tube heat exchangers, their types and design. Shell and tube heat exchangers

Section content

A shell-and-tube heat exchanger (Fig. 4.9) consists of a casing and a bundle of pipes fixed in tube sheets (boards) to create flow channels. As a rule, less contaminated coolant is supplied to the annular space, and more contaminated coolant is supplied to the pipes. Covers of distributing chambers and casing closing the annulus are equipped with fittings for inlet and outlet of heat carriers.

Fig.4.9. Shell and tube heat exchangers continuous action:

a - single-pass with rigidly fixed gratings; b - with concentric; c - with segmental partitions in the annulus; d - with temperature compensators on the body; e - with a floating lower head; e - with U-shaped pipes; g - with stuffing box seal on the upper floating head; 1 - housing or casing; 2 - tube sheets; 3 - pipes; 4 - bottoms and covers of distribution chambers; 5, 6 - flanges; 7 - supports

Shell and tube heat exchangers are used for heating and cooling liquids and gases, as well as for evaporation and condensation of substances in various technological processes. In particular, they are used as regenerative heaters. feed water, in water treatment systems, as oil coolers.

At given flow coolant G, kg/s, and the selected speed of its movement w, m / s, in pipes their number in one pass of the heat exchanger

n= 4G/(w rp d 2).

Heat exchange surface area

F=p d Wed l nz,

where l- working length of pipes; d cp - their calculated diameter, equal to

d cp = 0.5 ( d n + d in);

z- the number of passages of the pipe space. The length of heat exchange pipes is recommended to be 1000, 1500, 2000, 3000, 4000, 6000 and 9000 mm. In shell-and-tube heat exchangers with a surface area up to 300 m 2 - no more than 4000 mm.

Placement of pipes in tube sheets is carried out along the vertices of equilateral triangles, along concentric circles or along the vertices of squares. The most common way is the first option (Fig. 4.10). The number of pipes in the apparatus, depending on their diameter, the diameter of the body and the number of strokes in the pipe space, is indicated in Table. 4.9 [7, 8].

Fig.4.10. Placement of pipes in the tube sheet:

a - along concentric circles; b - along the vertices of equilateral triangles; c - chess; g - corridor

Table 4.9. The number of pipes in shell-and-tube heat exchangers when they are placed along the vertices of equilateral triangles [7, 8]

Note: In parentheses are the number of pipes for heat exchangers when placed without fenders, when pipes are added on both sides of the large hexagon.

Diameters and pitches of holes in tube sheets and heat exchanger baffles, when pipes are located at the tops equilateral triangle, determined by the outer diameter of the pipes (Table 4.10).

Table 4.10. Hole diameters in tube sheets and baffles of shell-and-tube heat exchangers [8]

When expanding pipes, the step s= (l.3 ¸ 1.6) d n, when welding s= l,25 d n. Minimum Thickness: for steel grating d p min = 5 + 0.125 d n, copper d p min \u003d \u003d 10 + 0.2 d n The thickness of the grid is checked by strength calculation, taking into account its weakening by holes and the way the pipes are placed.

Inner diameter of the shell of a single-pass heat exchanger D in = s (b - 1) + 4d n or D c = l,l s\(\sqrt(n)\) ; multi-way - D c = l,l s \(\sqrt(n/\psi)\), where b is the number of pipes on the diagonal of the large hexagon; \(\psi\)- the filling factor of the tube sheet, equal to 0.6 - 0.8.

The calculated value of the internal diameter of the casing is rounded up to the nearest of the following series: 3600, 3800 and 4000 mm. Cylindrical casings of apparatuses can be made of steel pipes with an outer diameter of 159, 219, 273, 325, 377, 426, 480, 530, 720, 820, 920 and 1020 mm.

For heat exchangers without baffles, the free cross-sectional area of ​​the annulus (nd))_(n)^(2)z\right)\text(.)\)

If a f mt > f, where f- the calculated value of the open section of the annular space, then the annular space is divided by partitions into the number of passages i = f mt / f. The number of passes in the annular space is recommended to be taken from the range 1, 2, 3, 4, 6. For a heat exchanger, in which the annulus is divided into i passages by transverse segmental partitions, the reduced section, according to the area of ​​\u200b\u200bwhich the coolant velocity in the annular space is calculated (specified),

\((f)_(\text(pr))=(f)_(\text(mt))(l)_(c)\phi /(L)_(\text(eq)),\)

where l c is the distance between the segment partitions; j - coefficient taking into account the narrowing of the open section of the annulus ())^(2));\]

L eq = l c+ D at 4 b /3 – equivalent path length of the coolant; b- distance from the edge of the segmental partition to the body of the device, b= (0.2 ¸ 0.4) D in.

Shell and tube heat exchangers general purpose made from carbon or of stainless steel with a heat exchange surface area from 1 to 2000 m 2 for nominal pressure up to 6.4 MPa. Structurally, they are divided into types shown in Fig. 4.9. The main parameters and dimensions of shell-and-tube heat exchangers are given in Table. 4.11 - 4.16.

Shell-and-tube heat exchangers of the TN type (with fixed grates) and TK (with lens compensators on the casing) are made horizontal and vertical from carbon steel (Fig. 4.11). TH type heat exchangers are used for heating and cooling liquid and gaseous media with temperatures from – 30°С to + 350°С for conditional pressure from 0.6 to 6.4 MPa.

Fig.4.11. Block of two shell-and-tube heat exchangers

If the temperature difference between the heat carriers exceeds 50°C, it is recommended to use collector-type heat exchangers designed for a working pressure of not more than 2.5 MPa.

Heat exchangers of the TN, TK, and TP types made of carbon steel and designed for an explosive or toxic environment, depending on the temperature, must be allowed to operate at reduced pressure according to [8]. At coolant temperatures above 400 ° C, it is necessary to use heat exchangers made of alloyed steel.

The main parameters of welded heat exchangers are given in Table. 4.13 and 4.14.

Pipes for heat exchangers are selected from the operating conditions and the aggressiveness of the environment. For standard heat exchangers, pipes made of carbon steel 10 or 20, corrosion-resistant steel OX18N10T and brass LOMsh 70-1-0.06 are used. Placement of pipes in lattices is carried out along the vertices of equilateral triangles.

Table 4.11. Specifications water-water heaters, GOST 27590-88 and OST 34-588-68

Table 4.12. Technical characteristics of horizontal steam-water

heaters, GOST 28679-90, OST 34-351-68, OST 34-352-68,

OST 34-376-68 and OST 34-577-68

Tube sheets of heat exchangers with a shell diameter from 600 to 1200 mm, designed for aggressive environments, are made of two layers of steel: VMStZsp together with Kh18N10T or from 16GS together with Kh18N10T.

Heat exchangers of the TN and TK types can be assembled into blocks consisting of several horizontal units. The number of devices in the block and dimensions taken according to the total area of ​​the heat exchange surface [8].

Floating head heat exchangers (Fig. 4.3 and 4.12) are used to heat or cool liquid and gaseous media within operating temperatures from – 30 to +450 °С and conditional pressure from 1.6 to 6.4 MPa in the pipe or annular space. The main parameters of vertical and horizontal heat exchangers are given in Table. 4.12, 4.13 and 4.15. The casing, distribution chamber and covers are made of VMStZsp steel or 16GS steel. Depending on the purpose of the apparatus, pipes made of steel 20 or AMg2M alloy are used. For capacitors, pipes made of brass LOMsh 70-1-0.06 or LAMsh 77-2-0.06 are used. For heating or cooling aggressive media, pipes made of X5M steel or OX18N10T corrosion-resistant steel are used. In this case, tube sheets are made of steel 16GS or two layers of steels 16GS and X18X10T.

Fig.4.12. Shell and tube heat exchanger with floating head:

1 - distribution chamber cover; 2 - distribution chamber; 3 - casing; 4 - pipes; 5 - casing cover; 6 - floating head cover; 7 - support

Fig.4.13. Shell and tube heat exchanger with U-tubes:

1 - distribution chamber cover; 2 - casing; 3 - U-shaped pipes; 4 - support

Heat exchangers with U-shaped pipes (Fig. 4.13) are used in heat exchange conditions at operating temperatures of the medium from -30 to +450 ° С. Standard heat exchangers are manufactured with a shell diameter from 325 to 1400 mm and the characteristic parameters indicated in Table. 4.16. The use of heat exchangers with U-shaped pipes is regulated by the nominal pressure, which for neutral and non-explosive media ranges from 1.6 to 6.4 MPa. In heat exchangers with a medium temperature of 100 to 450°C, the working pressure decreases within the limits specified in [8]. The casing and distribution chamber are usually made of VMStZps or 16GS steel. Heat exchange tubes are made of steel 20, and in condensers - from AMg2M alloy.

Strength calculations structural elements heat exchangers made of carbon or alloy steel are made in accordance with the requirements of [9].

Heat exchangers "pipe in pipe" (Fig. 4.14) are used for heating and cooling liquids at pressures up to 2.5 MPa and temperatures up to + 450 ° C. By design, devices are distinguished with a rigid welded structure (type TT), with stuffing boxes at one or both ends of the pipes (type TT-C), with finned tubes (type TT-R). The main parameters and dimensions of the heat exchangers are given in Table. 4.17. They are made from solid-rolled pipes. Pipe material - carbon steel or stainless steel.

Fig.4.14. Heat exchanger type "pipe in pipe":

1 – inner tube; 2 - outer pipe; 3 - kalach

Serial and parallel connection of individual devices "pipe in pipe" allows you to create heat exchangers with a surface area of ​​1 to 250 m 2 . The simplicity of the design of devices of this type allows them to be manufactured in repair shops of enterprises.

Table 4.13. Welded shell-and-tube heat exchangers with fixed tube sheets and shell-and-tube heat exchangers with a temperature compensator on the shell [8]

Table 4.14. Shell and tube heat exchangers [ 8 ]

Table 4.15. Floating head shell and tube heat exchangers [ 8 ]

Table 4.16. Shell and tube heat exchangers with U-shaped

pipes [ 8]

Table 4.17. Heat exchangers of the "pipe in pipe" type [ 8 ]

Technical description

Shell and tube heat exchangers manufactured by Geoclima- a rather complex device, and there are many varieties of it. They belong to the type of recuperative. The division of heat exchangers into types is made depending on the direction of movement of the coolant.

Types of shell-and-tube heat exchangers:

• cross-flow;
• countercurrent;
• direct-flow.

Shell-and-tube heat exchangers got their name because the thin tubes through which the coolant moves are located in the middle of the main casing. The number of tubes in the middle of the casing determines how fast the substance will move. In turn, the heat transfer coefficient will depend on the speed of the movement of the substance. CROM / GEOCLIMA shell-and-tube heat exchangers are used for heating/cooling, condensation/evaporation of various liquid and vapor media in various production processes.

The production of shell-and-tube heat exchangers in Russia makes the following types of devices:

• Shell-and-tube heat exchangers Geoclima for compressed gases
• Shell-and-tube heat exchangers Geoclima for exhaust gas heat recovery
• Shell-and-tube heat exchangers Geoclima for biogas cooling
• Shell-and-tube heat exchangers Geoclima – steam/water
• Shell and tube heat exchangers Geoclima for CO 2
• Shell-and-tube heat exchangers Geoclima made of special materials (inox 304, 316, 316L, 316Ti, 321, 90Cu10NiFe, 70Cu30NiFe, carbon steel, titanium)
• Shell-and-tube heat exchangers Geoclima with coaxial tubes. (used for heating cooling of gases, oils, aggressive media, waste heat recovery flue gases. Working conditions of shell-and-tube heat exchangers with CROM coaxial tubes; pressure -300ATM, temperature +600*С.
• Shell-and-tube heat exchangers Geoklima of the flooded type (refrigerant circulation occurs in the annular space, and water circulation occurs through pipes).

Peculiarities

The use of advanced developments and technologies in the creation of shell-and-tube heat exchangers provide the ultimate heat transfer efficiency with the same size.

For the manufacture of shell-and-tube heat exchangers, alloyed and high-strength steels are used. These types of steels are used because these devices, as a rule, operate in an extremely aggressive environment that can cause corrosion.

Heat exchangers are also divided into types. The following types of device data are produced:

• with temperature casing compensator;
• with fixed tubes;
• with U-tubes;
• with floating head;
• maybe also complex application various design solutions, for example, a floating head and a thermal compensator can be used in one design.

Shell-and-tube devices are classified according to their functions:

• Heat exchangers are universal;
• Evaporators;
• Capacitors;
• Refrigerators;

By location, heat exchangers are:

• Horizontal;
• vertical

Distinctive properties of the equipment:
The main and most significant advantage is high durability of this type units for hydraulic shocks. Most types of heat exchangers produced today do not have this quality.

The second advantage is that shell and tube units do not need a clean environment. Most devices in aggressive environments are unstable. For example, plate heat exchangers do not have this property, and are able to work exclusively in clean environments.

Third significant advantage shell and tube heat exchangers is their high efficiency. In terms of efficiency, it can be compared with plate heat exchanger, which by most parameters is the most effective.

Thus, we can say with confidence that shell-and-tube heat exchangers are among the most reliable, durable and highly efficient units:

• great performance
• compactness
• reliability
• versatility in use.

Shell and tube heat exchangers are among the most common devices. They are used for heat transfer and thermochemical processes between various liquids, vapors and gases - both without change, and with a change in their state of aggregation.

Shell and tube heat exchangers appeared at the beginning of the twentieth century in connection with the needs of thermal stations in heat exchangers with large surface, such as condensers and water heaters operating at relatively high pressure. Shell and tube heat exchangers used as condensers, heaters and evaporators. At present, their design, as a result of special developments, taking into account operating experience, has become much more advanced. In the same years, wide industrial use began in oil industry. For operation in difficult conditions heaters and mass coolers, evaporators and condensers were required for various fractions of crude oil and associated organic liquids. Heat exchangers often had to work with contaminated liquids during high temperatures and pressures, and so they had to be designed to be easy to repair and clean.

Over the years shell and tube heat exchangers became the most widely used type of apparatus. This is primarily due to the reliability of the design, a large set of options for various conditions operation, in particular:

• single-phase flows, boiling and condensation on hot and cold sides heat exchanger with vertical or horizontal design
• pressure range from vacuum to high values
• widely varying pressure differences on both sides due to the wide variety of options
• meeting the requirements for thermal stresses without a significant increase in the cost of the device
• sizes from small to extremely large (5000 m2)
• possibility of application various materials according to cost, corrosion, temperature regime and pressure
• the use of developed heat exchange surfaces both inside and outside the pipes, various intensifiers, etc.
• the possibility of extracting the tube bundle for cleaning and repair

However, such a wide variety of application conditions shell and tube heat exchangers and their design should in no way preclude the search for other, alternative solutions, such as the use of plate, spiral or compact heat exchangers, where their characteristics are acceptable and their use can lead to more economical solutions.

Shell and tube heat exchangers consist of tube bundles fixed in tube sheets, casings, covers, chambers, nozzles and supports. The tube and annulus spaces in these devices are separated, and each of them can be divided by partitions into several passages. Classic scheme shown in the figure:

The heat transfer surface of the devices can range from several hundred square centimeters to several thousand. square meters. So, capacitor steam turbine with a capacity of 150 MW consist of 17 thousand pipes with a total heat exchange surface of about 9000 m 2 .

Schemes of shell-and-tube devices of the most common types are shown in the figure:

Casing (body) shell and tube heat exchanger is a pipe welded from one or more steel sheets. Shells differ mainly in the way they are connected to the tube sheet and covers. The wall thickness of the casing is determined by the pressure of the working medium and the diameter of the casing, but is assumed to be at least 4 mm. Flanges are welded to the cylindrical edges of the casing for connection with covers or bottoms. Apparatus supports are attached to the outer surface of the casing.

tubular shell and tube heat exchangers made of straight or curved (U-shaped or W-shaped) pipes with a diameter of 12 to 57 mm. Seamless steel pipes are preferred.

In the flow area of ​​the annular space is 2-3 times greater than the flow area inside the pipes. Therefore, at equal flow rates of heat carriers with the same phase state, the heat transfer coefficients on the surface of the annular space are low, which reduces the overall heat transfer coefficient in the apparatus. The device of partitions in the annular space shell and tube heat exchanger contributes to an increase in the speed of the coolant and an increase in the efficiency of heat transfer.

Tube boards (grids) are used to fix a bundle of pipes in them by means of flaring, disassembly, welding, sealing or stuffing boxes. The tube plates are welded to the casing (Fig. a, c), bolted between the flanges of the casing and the cover (Fig. b, d) or bolted only to the flange of the free chamber (Fig. e, f). the material of the boards is usually sheet steel with a thickness of at least 20 mm.

Shell and tube heat exchangers can be rigid (Fig. a, j), non-rigid (Fig. d, e, f, h, i) and semi-rigid (Fig. b, c, g) design, single-pass and multi-pass, direct-flow, counter-flow and cross-flow, horizontal, inclined and vertical.

Figure a) shows a one-way heat exchanger with straight tubes of a rigid design. The casing and tubes are connected by tube sheets and therefore there is no possibility of compensating for thermal elongations. Such devices are simple in design, but can only be used at relatively small temperature differences between the body and the tube bundle (up to 50 ° C). They have low heat transfer coefficients due to the low velocity of the coolant in the annulus.

AT shell and tube heat exchangers the flow area of ​​the annular space is 2-3 times greater than the flow area of ​​the tubes. Therefore, at the same flow rates of heat carriers having the same state of aggregation, the heat transfer coefficients on the surface of the annular space are low, which reduces the heat transfer coefficient in the apparatus. The arrangement of baffles in the annular space contributes to an increase in the coolant velocity and an increase in the heat transfer coefficient. Figure 1b shows heat exchanger with transverse baffles in the annular space and semi-rigid membrane compensation for thermal elongations due to some freedom of movement of the upper tube plate.

In vapour-liquid heat exchangers steam usually passes in the annular space, and the liquid - through the pipes. The temperature difference between the shell wall and the pipes is usually significant. To compensate for the difference in thermal elongation between the casing and the pipes, lens (Fig. c), stuffing box (Fig. h, i) or bellows (Fig. g) compensators are installed.

To eliminate stresses in the metal due to thermal elongation, single-chamber heat exchangers with bent U- and W-shaped pipes. They are expedient at high pressures of coolants, since the manufacture of water chambers and the fastening of pipes in tube sheets in high-pressure apparatuses are complex and expensive operations. However, apparatuses with bent pipes cannot be widely used because of the difficulty of manufacturing pipes with different bending radii, the difficulty of replacing pipes, and the inconvenience of cleaning bent pipes.

Compensation devices are difficult to manufacture (membrane, bellows, with bent pipes) or not sufficiently reliable in operation (lens, gland). More perfect design heat exchanger with rigid fastening of one tube plate and free movement of the second board together with the inner cover of the tube system (Fig. e). some increase in the cost of the apparatus due to an increase in the diameter of the body and the manufacture of an additional bottom is justified by simplicity and reliability in operation. These devices are called heat exchangers"floating head". Heat exchangers with transverse current (Fig. j) are characterized by an increased heat transfer coefficient on the outer surface due to the fact that the coolant moves across the tube bundle. With cross flow, the temperature difference between the heat carriers decreases, however, with a sufficient number of pipe sections, the difference in comparison with counterflow is small. In some designs such heat exchangers when gas flows in the annular space and liquid in pipes, pipes with transverse ribs are used to increase the heat transfer coefficient.

Among all types of heat exchangers, this type is the most common. It is used when working with any liquids, gaseous and vaporous media, including if the state of the medium changes during the distillation process.

History of appearance and implementation

Invented shell-and-tube (or) heat exchangers at the beginning of the last century, in order to actively use during the operation of thermal power plants, where a large number of heated water was distilled at elevated pressure. In the future, the invention began to be used in the creation of evaporators and heating structures. Over the years, the design of the shell-and-tube heat exchanger has improved, the design has become less cumbersome, it is now being developed so that it is accessible to clean individual elements. More often, such systems began to be used in the oil refining industry and production household chemicals, since the products of these industries carry a lot of impurities. Their sediment just requires periodic cleaning of the inner walls of the heat exchanger.

As we see in the presented diagram, a shell-and-tube heat exchanger consists of a bundle of tubes that are located in their chamber and fixed on a board or grate. Casing - in fact, the name of the entire chamber, welded from a sheet of at least 4 mm (or more, depending on the properties of the working environment), in which there are small tubes and a board. Sheet steel is usually used as the material for the board. Between themselves, the tubes are connected by branch pipes, there is also an inlet and outlet to the chamber, a condensate drain, and partitions.

Depending on the number of pipes and their diameter, the power of the heat exchanger varies. So, if the heat transfer surface is about 9,000 sq. m., the heat exchanger capacity will be 150 MW, this is an example of the operation of a steam turbine.

The design of a shell-and-tube heat exchanger involves the connection of welded pipes to the board and covers, which can be different, as well as the bending of the casing (in the form of the letter U or W). Below are the types of devices most commonly encountered in practice.

Another feature of the device is the distance between the pipes, which should be 2-3 times their cross section. As a result, the heat transfer coefficient is small, and this contributes to the efficiency of the entire heat exchanger.

Based on the name, a heat exchanger is a device created to transfer the generated heat to a heated object. The coolant in this case is the design described above. The operation of a shell-and-tube heat exchanger is that cold and hot working media move through different shells, and heat exchange occurs in the space between them.

The working medium inside the pipes is liquid, while hot steam passes through the distance between the pipes, forming condensate. Since the walls of the pipes heat up more than the board to which they are attached, this difference must be compensated, otherwise the device would have significant heat losses. Three types of so-called compensators are used for this: lenses, glands or bellows.

Also, when working with liquid under high pressure, single-chamber heat exchangers are used. They have a U, W-type bend, necessary to avoid high stresses in the steel caused by thermal expansion. Their production is quite expensive, pipes in case of repair are difficult to replace. Therefore, such heat exchangers are less in demand in the market.

Depending on the method of attaching pipes to a board or grate, there are:

• Welded pipes;
• Fixed in flared niches;
• Bolted to flange;
• sealed;
• Having oil seals in the fastener design.

According to the type of construction, shell-and-tube heat exchangers are (see the diagram above):

• Rigid (letters in fig. a, j), non-rigid (d, e, f, h, i) and semi-rigid (letters in fig. b, c and g);
• By the number of moves - single or multi-way;
• In the direction of the flow of the technical fluid - direct, transverse or against the directed current;
• By location, the boards are horizontal, vertical and located in an inclined plane.

The wide range of shell-and-tube heat exchangers

1. The pressure in the pipes can reach different values, from vacuum to the highest;
2. Can be reached necessary condition by thermal stresses, while the price of the device will not change significantly;
3. The dimensions of the system can also be different: from a household heat exchanger in a bathroom to an industrial area of ​​​​5000 square meters. m.;
4. There is no need to pre-clean the working environment;
5. Use to create the core different materials, depending on production costs. However, they all meet the requirements of temperature, pressure and corrosion resistance;
6. A separate section of pipes can be removed for cleaning or repair.

Does the design have flaws? Not without them: shell and tube heat exchanger very bulky. Due to its size, it often requires a separate technical room. Due to the high metal consumption, the cost of manufacturing such a device is also high.

Compared to U, W-tube and fixed tube heat exchangers, shell and tube heat exchangers have more advantages and are more efficient. Therefore, they are more often bought, despite high cost. On the other side, independent production such a system will cause great difficulties, and most likely will lead to significant heat losses during operation.

Particular attention during the operation of the heat exchanger should be paid to the condition of the pipes, as well as the adjustment depending on the condensate. Any intervention in the system leads to a change in the heat exchange area, therefore, repairs and commissioning must be carried out by trained specialists.

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Shell and tube heat exchangers appeared at the beginning of the 20th century due to the need of thermal plants for large surface heat exchangers, such as condensers and water heaters, operating at relatively high pressure. Shell and tube heat exchangers are used as condensers, heaters and evaporators. At present, their design, as a result of special developments, taking into account operating experience, has become much more advanced. In the same years, the widespread industrial use of shell-and-tube heat exchangers in the oil industry began. Heavy-duty operation required stock heaters and coolers, evaporators and condensers for various fractions of crude oil and associated organic liquids. Heat exchangers often had to work with contaminated liquids at high temperatures and pressures, and therefore they had to be designed so that they could be easily repaired and cleaned.

Over the years, shell and tube heat exchangers have become the most widely used type of apparatus. This is primarily due to the reliability of the design, a large set of options for various operating conditions, in particular:

single-phase flows, boiling and condensation on the hot and cold sides of the heat exchanger with a vertical or horizontal design;

pressure range from vacuum to high values;

widely varying pressure drops on both sides due to the wide variety of options;

meeting the requirements for thermal stresses without a significant increase in the cost of the device;

sizes from small to extremely large (5000 m 2);

the possibility of using various materials in accordance with the requirements for cost, corrosion, temperature and pressure;

the use of developed heat exchange surfaces both inside the pipes and outside, various intensifiers, etc.;

the possibility of extracting the tube bundle for cleaning and repair.

In a shell-and-tube heat exchanger, one of the heat carriers flows through the pipes, the other - through the annulus. Heat from one coolant to another is transferred through the surface by a wall of pipes.

Shell-and-tube heat exchangers are single-pass, here both heat carriers move without changing direction over the entire section (one along the pipe, the other along the annulus), and multi-pass, in which flows sequentially change direction with the help of additional partitions, thereby increasing the heat transfer coefficient and flow velocity.

The main elements of shell-and-tube heat exchangers are tube bundles, tube sheets, housing, covers, branch pipes. The ends of the pipes are fastened in the tube sheets by flaring, welding and soldering.

To increase the speed of movement of heat carriers in order to intensify heat transfer, partitions are often installed, both in the pipe and in the annulus.

Shell and tube heat exchangers can be vertical, horizontal and inclined according to process requirements or ease of installation. Depending on the size of the temperature elongation of the tubes and the body, shell-and-tube heat exchangers of a rigid, semi-rigid and non-rigid design are used. One of the options for such a heat exchanger is shown in Figure 1.2.1.

Rice. 1.2 - Shell and tube heat exchanger

The heat transfer surface of the devices can range from several hundred square centimeters to several thousand square meters.

The casing (body) of a shell-and-tube heat exchanger is a pipe welded from one or more steel sheets. Shells differ mainly in the way they are connected to the tube sheet and covers. The wall thickness of the casing is determined by the pressure of the working medium and the diameter of the casing, but is assumed to be at least 4 mm. Flanges are welded to the cylindrical edges of the casing for connection with covers or bottoms. Apparatus supports are attached to the outer surface of the casing.

In shell-and-tube heat exchangers, the flow area of ​​the annular space is 2-3 times larger than the flow area of ​​the tubes. Therefore, at the same flow rates of heat carriers having the same state of aggregation, the heat transfer coefficients on the surface of the annular space are low, which reduces the heat transfer coefficient in the apparatus. The arrangement of baffles in the annular space contributes to an increase in the coolant velocity and an increase in the heat transfer coefficient.