The principle of operation and design of shell-and-tube heat exchangers. Shell-and-tube heat exchanger (shell-and-tube)

Shell and tube heat exchangers are the most common design of heat exchange equipment. According to GOST 9929, steel shell-and-tube heat exchangers are manufactured in the following types: HP - with fixed tube sheets; TK - with a temperature compensator on the casing; TP - with a floating head; TU - with U-shaped pipes; TPK - with a floating head and a compensator on it (Fig. 2.19).

Depending on the purpose, shell-and-tube devices can be heat exchangers, refrigerators, condensers and evaporators; they are made single- and multi-pass.

A shell-and-tube apparatus with a fixed tube sheet (TN type) is shown in fig. 2.20. Such devices have a cylindrical casing 1 , in which the tube bundle is located 2 ; tube sheets 3 with flared tubes are attached to the body of the apparatus. Both ends of the heat exchanger are closed with lids 4 . The device is equipped with fittings 5 for heat exchange media; one medium goes through the tubes, the other passes through the annulus.

Heat exchangers of this group are manufactured for a nominal pressure of 0.6 ... 4.0 MPa, with a diameter of 159 ... 1200 mm, with a heat exchange surface of up to 960 m2; their length is up to 10 m, weight is up to 20 tons. Heat exchangers of this type are used up to a temperature of 350 °C.

There are various options for the material design of the structural elements of heat exchangers. The body of the apparatus is made of steel VStZsp, 16GS or bimetallic with protective layer from steels 08X13, 12X18H10T, 10X17H13M2T. For the tube bundle, pipes are used from steels 10, 20 and X8 with dimensions of 25 × 2, 25 × 2.5 and 20 × 2 mm, from high-alloy steels 08X13, 08X22H6T, 08X18H10T, 08X17H13M2T with dimensions of 25 x 1.8 and 20 x 1 .6 mm, as well as pipes made of aluminum alloys and brass. Tube sheets are made of steels 16GS, 15Kh5M, 12Kh18N10T, as well as bimetallic with hardfacing of a high-alloy chromium-nickel alloy or a layer of brass up to 10 mm thick.

Rice. 2.20. Scheme of a single-pass heat exchanger of the TN type (vertical version):

1 - casing; 2 - tubes; 3 - tube sheet; 4 - covers; 5 - fitting

Figure 2.19. Main types of shell-and-tube heat exchangers:

a) - with fixed gratings (TN) or with a compensator on the casing (TK); b) - with a floating head; c) - with U-tubes

A feature of the TN type devices is that the pipes are rigidly connected to the tube sheets, and the lattices to the body. In this regard, the possibility of mutual movements of pipes and casing is excluded; so the devices of this

type are also called rigid heat exchangers. Some options for fastening tube sheets to a casing in steel are shown in fig. 2.21.

Pipes in shell-and-tube heat exchangers are placed so that the gap between the inner wall of the shell and the surface that envelops the tube bundle is minimal; otherwise, a significant part of the coolant may bypass the main heat exchange surface. To reduce the amount of coolant passing between the tube bundle and the casing, special fillers are installed in this space, for example, longitudinal strips welded to the casing (Fig. 2.22 a) or blind pipes that do not pass through the tube sheets and can be located directly at the inner surface of the casing (Fig. 2.22 b).

Rice. 2.21. Some options for attaching tube sheets to the casing of the apparatus

In shell-and-tube heat exchangers, to achieve high heat transfer coefficients, sufficiently high heat carrier velocities are required: for gases 8 ... 30 m/s, for liquids at least 1.5 m/s. The speed of heat carriers is provided during design by appropriate selection of the cross-sectional area of ​​the pipe and annulus space.

If the sectional area of ​​the pipe space (the number and diameter of pipes) is selected, then as a result thermal calculation determine the heat transfer coefficient and the heat exchange surface, which calculate the length of the tube bundle. The latter may be longer than the length of commercially available pipes. In this regard, multi-pass (through the pipe space) apparatuses with longitudinal partitions in the distribution chamber are used. The industry produces two-, four- and six-way heat exchangers of a rigid design.

A two-way horizontal heat exchanger of the TN type (Fig. 2.23) consists of a cylindrical welded casing 5 , distribution chamber 11 and two covers 4 . The tube bundle is formed by tubes 7 fixed in two tube sheets 3 . The tube sheets are welded to the casing. Covers, distribution chamber and casing are connected by flanges. In the casing and the distribution chamber there are fittings for input and output of heat carriers from the pipe (fitting 1 ,12 ) and annulus (fitting 2 ,10 ) spaces. Partition 13 in the distribution chamber forms coolant passages through the pipes. A gasket was used to seal the junction of the longitudinal partition with the tube sheet. 14 , laid in the groove of the lattice 3 .

Since the intensity of heat transfer with a transverse flow around the pipes with a heat carrier is higher than with a longitudinal one, fixed by ties are installed in the annular space of the heat exchanger. 5 transverse partitions 6 , providing a zigzag movement of the coolant along the length of the apparatus in the annular space. A baffle is provided at the inlet of the heat exchange medium into the annulus 9 - a round or rectangular plate that protects pipes from local erosion wear.

The advantage of devices of this type is the simplicity of design and, consequently, lower cost.

However, they have two major drawbacks. Firstly, cleaning the annular space of such devices is difficult, therefore, heat exchangers of this type are used in cases where the medium passing through the annulus is clean, not aggressive, i.e. when there is no need for cleaning.

Secondly, a significant difference between the temperatures of the tubes and the casing in these devices leads to a greater elongation of the tubes compared to the casing, which causes the occurrence of thermal stresses in the tube sheet. 5 , violates the tightness of the tubes in the lattice and leads to the ingress of one heat-exchanging medium into another. Therefore, heat exchangers of this type are used when the temperature difference of the heat exchange media passing through the tubes and the annular space is not more than 50 ° C and with a relatively short length of the apparatus.

Heat exchangers with a temperature compensator of the TK type (Fig. 2.24) have fixed tube sheets and are equipped with special flexible elements to compensate for the difference in the elongation of the casing and pipes resulting from the difference in their temperatures.

Vertical shell and tube heat exchanger type TK differs from heat exchanger type TH by the presence of a shell welded between the two parts 1 lens compensator 2 and fairing 3 (Fig. 2.25). The fairing reduces the hydraulic resistance of the annular space of such an apparatus; the fairing is welded to the casing from the side of the coolant inlet into the annulus.

Most often, in apparatuses of the TK type, single- and multi-element lens compensators are used, which are made by running from short cylindrical shells. The lens element shown in Figure 2.25 b, welded from two half-lenses obtained from a sheet by stamping. The compensating ability of a lens compensator is approximately proportional to the number of lens elements in it, however, it is not recommended to use compensators with more than four lenses, since the resistance of the casing to bending is sharply reduced. To increase the compensating ability of the lens compensator, it can be pre-compressed (if it is designed to work in tension) or stretched (when working in compression) when assembling the casing.

When installing a lens compensator on horizontal devices, drainage holes are drilled in the lower part of each lens with plugs to drain water after hydraulic testing of the device.

Rice. 2.24. Vertical shell and tube heat exchanger type TK

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 can see in the diagram, 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 work 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: the shell-and-tube heat exchanger is 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 exchanger (shell-and-tube) horizontal

tube heat exchanger

NORMIT has a wide the lineup heat exchangers that can meet any requirement various kinds industry. We are ready to provide our Clients with European quality equipment at reasonable prices.

Purpose

Shell and tube heat exchangers 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 can be used

as condensers, heaters and evaporators. At present, the design of the heat exchanger as a result of special developments, taking into account operating experience, has become much more advanced.

Advantages shell and tube heat exchangers:

• Reliability
• High efficiency
• compactness
• Wide range of applications
• Large heat exchange area
• Does not damage the structure of the product
• Easy cleaning and maintenance
• No "dead zones"
• Can be equipped with CIP-sink
• Low energy costs
• Safe use for personnel

Shell and tube heat exchangers are one of the most widely used devices in this area, largely due to their robust design and many options for execution in accordance with various conditions operation.

Specifications may change in accordance with the technological requirements of the Client:

• 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 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.

Description

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.

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

The shell of a shell-and-tube heat exchanger is a tube welded from one or more steel sheets. Casings differ from each other mainly in the way they are connected to the covers and the tube sheet. 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.

The tubing of shell-and-tube heat exchangers is 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 shell and tube heat exchangers 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 arrangement of baffles in the annular space of a shell-and-tube heat exchanger helps to increase the coolant velocity and increase the efficiency of heat transfer.

Below are diagrams of the most common devices:

Shell and tube heat exchangers can be rigid, non-rigid and semi-rigid, single-pass and multi-pass, direct-flow, counter-flow and cross-flow, horizontal, inclined and vertical.

In a single-pass straight tube heat exchanger of a rigid design, the shell and tubes are connected by tube sheets and therefore there is no possibility of compensating for thermal expansion. 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.

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.

In vapor-liquid heat exchangers, the vapor usually passes in the annular space, and the liquid passes 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 pipes, lens, stuffing box or bellows compensators are installed.

To eliminate stresses in the metal due to thermal elongation, single-chamber heat exchangers with bent U- and W-shaped pipes are also manufactured. They are expedient at high pressures of coolants, since the manufacture of water chambers and the fastening of pipes in tube sheets in apparatuses high pressure operations are complex and expensive. 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). Improved design of the heat exchanger with rigid fastening of one tube plate and free movement of the second plate together with the inner cover pipe system. 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 "floating head" heat exchangers. Heat exchangers with transverse current 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 of such heat exchangers, when gas flows in the annular space and liquid in the pipes, pipes with transverse ribs are used to increase the heat transfer coefficient.

The widespread use of shell-and-tube heat exchangers and their designs should not exclude the use of scraped-off heat exchangers and tube-in-pipe heat exchangers in cases where their use is more acceptable from the point of view of technological and economic characteristics.

Technical specifications:

Dimensions:

Now we will consider the technical characteristics and principle of operation of shell-and-tube heat exchangers, as well as the calculation of their parameters and the features of the choice when buying.

Heat exchangers provide the process of heat exchange between liquids, each of which has different temperature. At present, the shell-and-tube heat exchanger has found its application with great success in various industries: chemical, oil, gas. There are no difficulties in their manufacture, they are reliable and have the ability to develop large surface heat exchange in one device.

Received this name due to the presence of a casing that hides internal pipes.

Device and principle of operation

Structure: a structure of tube bundles fixed in tube sheets (grids) of covers, casings and supports.

The principle by which the shell-and-tube heat exchanger operates is quite simple. It consists in the movement of cold and hot coolants through different channels. Heat transfer occurs precisely between the walls of these channels.

Working principle of shell and tube heat exchanger

Advantages and disadvantages

Today, shell-and-tube heat exchangers are in demand among consumers and do not lose their positions in the market. This is due to a considerable number of advantages that these devices have:

1. High resistance to . This helps them to easily endure pressure drops and withstand severe loads.
2. They don't need a clean environment. This means that they can work with low-quality liquid that has not been pre-treated, unlike many other types of heat exchangers that can only work in unpolluted environments.
3. High efficiency.
4. Wear resistance.
5. Durability. With proper care, shell and tube units will work for many years.
6. Safety of use.
7. Maintainability.
8. Work in an aggressive environment.

Given the above advantages, we can argue about their reliability, high efficiency and durability.

Shell and tube heat exchangers in industry

Despite the large number of noted advantages of shell-and-tube heat exchangers, these devices also have a number of disadvantages:

• overall size and significant weight: for their placement, a room of considerable size is required, which is not always possible;
• high metal content: this is the main reason for their high price.

Types and types of shell-and-tube heat exchangers

Shell and tube heat exchangers are classified depending on the direction in which the coolant moves.

Allocate the following types according to this criterion:

• straight-through;
• countercurrent;
• cross.

The number of tubes located in the heart of the casing directly affects the speed at which the substance will move, and the speed has direct influence by coefficient heat transfer.

Given these characteristics, shell-and-tube heat exchangers are of the following types:

• with temperature casing compensator;
• with fixed tubes;
• with floating head;
• with U-tubes.

The U-tube model consists of a single tube sheet into which these elements are welded. This allows the rounded part of the tube to rest freely on the swivel shields in the housing, while they have the ability to expand linearly, which allows them to be used in large temperature ranges. To clean the U-tubes, you need to remove the entire section with them and use special chemicals.

Calculation of parameters

For a long time, shell-and-tube heat exchangers were considered the most compact in existence. However, they appeared, which are three times more compact than shell-and-tube ones. In addition, the design features of such a heat exchanger lead to thermal stresses due to the temperature difference between the pipes and the casing. Therefore, when choosing such a unit, it is very important to make its competent calculation.

Formula for calculating the area of ​​a shell-and-tube heat exchanger

F is the area of ​​the heat exchange surface;
t cf - the average temperature difference between coolants;
K is the heat transfer coefficient;
Q is the amount of heat.

To carry out the thermal calculation of a shell-and-tube heat exchanger, the following indicators are required:

• maximum consumption of heating water;
• physical characteristics of the coolant: viscosity, density, thermal conductivity, final temperature, heat capacity of water at an average temperature.

When ordering a shell and tube heat exchanger, it is important to know which technical specifications he has:

• pressure in pipes and casing;
• casing diameter;
• execution (horizontal\vertical);
• type of tube sheets (movable\fixed);
• Climatic performance.

It is quite difficult to make a competent calculation on your own. This requires knowledge and deep understanding the whole essence of the process of its work, therefore the best way will turn to specialists.

Operation of the tubular heat exchanger

The shell and tube heat exchanger is a device that is characterized by a long service life and good parameters operation. However, like any other device, for high-quality and long-term work, it needs scheduled maintenance. Since in most cases shell and tube heat exchangers work with a liquid that has not been pre-treated, sooner or later the tubes of the unit become clogged and sediment forms on them and an obstacle is created for the free flow of the working fluid.

To ensure that the efficiency of the equipment does not decrease and that the shell-and-tube unit does not break down, it should be systematically cleaned and flushed.

Thanks to this, he will be able to carry out high-quality work for a long time. When the device expires, it is recommended to replace it with a new one.

If there is a need to repair a tubular heat exchanger, then it is first necessary to diagnose the device. This will identify the main problems and determine the scope future work. The weakest part of it is the tubes, and, most often, damage to the tube is the main reason for repair.

To diagnose a shell-and-tube heat exchanger, a hydraulic test method is used.

In this situation, it is necessary to replace the tubes, and this is a laborious process. It is necessary to muffle the failed elements, in turn, this reduces the area of ​​the heat exchange surface. By implementing repair work, it is necessary to take into account the fact that any, even the slightest intervention, can cause a decrease in heat transfer.

Now you know how a shell-and-tube heat exchanger works, what varieties and features it has.

SHELL AND TUBE HEAT EXCHANGERS.

Rigid type heat exchangers (Fig. 8.3.2) have a cylindrical body 1 , in which the tube bundle is installed 2, fixed in tube sheets 4, in which the tubes are fixed by flaring or welding. The body of the device is covered 5 and 6. Partitions are installed inside the body 3, creating a certain direction of flow and increasing its speed in the body (Fig. 8.3.4).

Rice. 8.3.2. Rigid shell and tube heat exchanger:

1 - casing (case); 2 - tube; 3 - transverse partition; 4 - tube sheet; 5 - cover; 6 - cover (junction box); 3,8 - longitudinal partitions, respectively, in the junction box and in the housing.

Rice. 8.3.3. Shell and tube heat exchanger with a lens compensator on the body.

To lengthen the path of the liquid in the body, the tube bundles are provided with transverse partitions. from sheet steel with a thickness of 5 mm or more. The distance between the partitions is taken from 0.2 m to 50 D N – outside diameter heat exchange pipe. The geometric shape of the partitions and their mutual arrangement determine the nature of the flow movement through the heat exchanger housing.

Rice. 8.3.4. Types of cross partitions:

I - with a sector cutout providing fluid flow along a helical line;

II - with a slit cut, providing a wave-like movement;

III - with a segment cutout;

IV - ring, providing movement from the periphery to the center, and vice versa.

The transverse partitions are fixed one in relation to the other by means of spacer pipes pressed against them by common rods (usually four). In addition to the technological purpose, the transverse partitions also serve as intermediate supports for the tube bundle, preventing it from bending when horizontal arrangement device.

One of the heat exchange media moves through the tubes, and the other - inside the body between the tubes. A more polluted medium is allowed into the tubes, as well as a medium with a lower heat transfer coefficient, since cleaning the outer surface of the tubes is difficult, and the velocity of the medium in the annulus is less than in the tubes.

Since the temperatures of the heat exchange media differ, the body and tubes receive different elongations, which leads to additional stresses in the heat exchanger elements. With a large temperature difference, this can lead to deformation and even destruction of the tubes and the body, violation of the density of the flaring, etc. So hard-type heat exchangers are used when the temperature difference of the heat-exchanging media is not more than 50°C.

Heat exchangers with a lens compensator on the body (Fig. 8.3.3) are used to reduce thermal stresses in rigid-type apparatuses. Such heat exchangers have a lens compensator on the body, due to the deformation of which the temperature forces in the body and tubes are reduced. This decrease is greater than more number lenses at the compensator.

Floating head heat exchangers (Fig. 8.3.5) found the widest application. In these devices, one end of the tube bundle is fixed in a tube sheet connected to the body (on the left in the figure), and the other end can move freely relative to the body with temperature changes in the length of the tubes. This eliminates thermal stresses in the structure and makes it possible to work with large temperature differences of heat exchange media. In addition, cleaning of the tube bundle and the body of the apparatus is possible, and the replacement of bundle tubes is facilitated. However, the design of floating head heat exchangers is more complex, and the floating head is not accessible for inspection during operation of the apparatus.

Rice. 8.3.5. Shell and tube heat exchanger with floating head:

1 - casing; 2,3 - inlet and outlet chambers (lids); 4 - tube bundle; 5 - tube sheets; 6 - floating head cover; 7 - partitions; 8 - clamps for fastening the cover; 9 - supports; 10 - foundation; 11 - annular guide baffles; 12 - sliding support tube bundle; I, II - inlet and outlet of the heating coolant; III, IV - inlet and outlet of the heated flow.

Baffles installed in the distribution chamber and in the floating head increase the number of passes in the tube bundle. This allows you to increase the flow rate and the heat transfer coefficient to the inner wall of the pipes.

The annular space of devices with a floating head is usually performed as a single-pass. With two moves, a longitudinal partition is installed in the body. However, in this case, a special seal between the baffle and the housing is required. The heat exchange surface of shell-and-tube heat exchangers can be 1200 m 2 with tube lengths from 3 to 9 m; conditional pressure reaches 6.4 MPa.

U-tube heat exchangers (Fig. 8.3.6) have a tube bundle, the tubes of which are bent in the form of the Latin letter and, and both ends are fixed in the tube sheet, which ensures free extension of the tubes, regardless of the body. Such heat exchangers are used at elevated pressures. The medium sent to the tubes must be sufficiently clean, since cleaning the inside of the tubes is difficult.

Rice. 8.3.5. Shell and tube heat exchanger with floating head.

Fig.8.3.6. Shell and tube heat exchanger with U-tubes

Depending on the number of longitudinal baffles in the housing and distribution boxes, shell-and-tube heat exchangers are divided into one-, two- and multi-pass both in the tube and in the annulus. So, in fig. 8.3.2 the heat exchanger is two-pass both in the tube and in the annular space, which is achieved by installing longitudinal baffles 7 and 8.

tube-in-pipe type heat exchangers.

Unlike shell-and-tube devices, where a bundle of several hundred tubes is placed in the casing, in devices of this type each tube has its own individual casing (Fig. 8.3.7). heat exchanger is recruited from several such sections connected by collectors at the inlet and outlet of the heating coolant. Such devices are used for heating viscous and high-viscosity petroleum products (oil, diesel fuel, fuel oil, tars).

Devices "pipe in pipe" are made non-separable and collapsible. The first of them is used for media that do not give deposits in the annular space, the outer pipes of which are connected by welding nozzles. The connections of the inner pipes of such devices can be rigid (transitional twins 3 welded to the tubes) and detachable (twins on the flanges, as shown in the figure). With a rigid system, the heat exchanger can be used for such media, when using which the temperature difference between the outer and inner pipes should not exceed 50 ° C.

Rice. 8.3.7. Section of a four-way non-separable heat exchanger of the "pipe in pipe" type:

1, 2 - outer and inner pipes; 3 - rotary twin; I, II - inlet and outlet of the heating coolant; III, IV - inlet and outlet of the heated flow.

Rice. 8.3.8. Section of a single-flow collapsible heat exchanger of the "pipe in pipe" type:

1 - external pipes; 2 - internal pipes; 3 - cover; 4 - rotary twins; 5 - partition; 6 - tube sheet; A - inlet and outlet of a more polluted stream; B - inlet and outlet of a less polluted stream

Collapsible devices "pipe in pipe" (Fig. 8.3.8) are made from sections where the outer pipes 4 united by a common lid 3, which serves to turn the flow of the coolant from one outer pipe to another, and the inner pipes are connected using swivel twins on the flanges inside this cover. From such sections, a battery of a multi-flow apparatus can be recruited if the coolant flow rate is high (10–200 t/h in the pipe and up to 300 t/h in the annulus). The advantage of collapsible tube-in-pipe apparatus is that they can be regularly (like shell and tube) cleaned of deposits and replaced internal or external pipes in case of damage or corrosion.

Usually, in "pipe-in-pipe" devices, a more polluted coolant flow is allowed through the inner tubes, and a less polluted one - through the annulus.

In heat exchangers of a collapsible design, the inner pipes on the outside may have fins to increase the heat exchange area and thereby increase the heat transfer efficiency. Collapsible heat exchangers allow cleaning of external and internal surfaces pipes, as well as use finned inner tubes. This makes it possible to significantly increase the amount of heat transferred.. Figure 8.3.9 shows finned tubes.

Rice. 8.3.9. Finned tubes:

a - trough-shaped welded ribs; b - rolled ribs; c - extruded ribs; g - welded spike-shaped ribs; d - knurled ribs.