Shell and tube heat exchangers are among the most common devices. They are used for heat exchange and thermochemical processes between various liquids, vapors and gases - both without changing 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 power plants for heat exchangers with a large surface area, such as condensers and water heaters operating at relatively high pressure. Shell and tube heat exchangers used as condensers, heaters and evaporators. Currently, their design has become much more advanced as a result of special developments taking into account operating experience. In those same years, widespread industrial use began in oil industry. Heavy duty operation required mass 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 when high temperatures and pressures, and therefore had to be designed to be easy to repair and clean.

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 range of design options for various operating conditions, 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 drops on both sides due to the wide variety of options
• meeting thermal stress requirements without significantly increasing the cost of the device
• sizes from small to extremely large (5000 m2)
• possibility of application various materials according to the requirements for cost, corrosion, temperature conditions and pressure
• the use of developed heat exchange surfaces both inside and outside the pipes, various intensifiers, etc.
• possibility of removing the pipe bundle for cleaning and repair

However, such a wide variety of application conditions shell and tube heat exchangers and their designs should in no way exclude the search for others, alternative solutions, such as the use of plate, spiral or compact heat exchangers in cases where their characteristics are acceptable and their use can lead to more cost-effective solutions.

Shell and tube heat exchangers consist of bundles of pipes mounted in tube sheets, casings, covers, chambers, pipes and supports. The pipe and inter-tube spaces in these devices are separated, and each of them can be divided by partitions into several passages. The classic scheme is 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 they consist of 17 thousand pipes with a total heat exchange surface of about 9000 m 2.

Diagrams of shell-and-tube devices of the most common types are presented in the figure:

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

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

The flow area of ​​the interpipe space is 2-3 times larger than the flow area inside the pipes. Therefore, at equal flow rates of coolants with the same phase state, the heat transfer coefficients on the surface of the inter-tube space are low, which reduces the overall heat transfer coefficient in the apparatus. Installation of partitions in the interpipe space shell and tube heat exchanger helps to increase the coolant speed and increase the efficiency of heat transfer.

Pipe boards (grids) are used to secure a bundle of pipes in them using flaring, beading, welding, sealing or gland fastenings. The tube sheets are welded to the casing (Fig. a, c), clamped with bolts 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 board material 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) structures, 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 rigid design. The casing 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 pipe bundle (up to 50 o C). They have low heat transfer coefficients due to the low velocity of the coolant in the interpipe space.

IN shell and tube heat exchangers the flow area of ​​the inter-tube space is 2-3 times larger than the flow area of ​​the tubes. Therefore, at the same flow rates of coolants having the same state of aggregation, the heat transfer coefficients on the surface of the interpipe space are low, which reduces the heat transfer coefficient in the apparatus. The installation of partitions in the inter-tube space helps to increase the coolant velocity and increase the heat transfer coefficient. Figure 1,b shows heat exchanger with transverse partitions in the annular space and semi-rigid membrane compensation of thermal elongations due to some freedom of movement of the upper tube sheet.

In vapor-liquid heat exchangers Steam usually passes in the interpipe space, and liquid through the pipes. The temperature difference between the housing 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 caused by thermal elongation, single-chamber heat exchangers with bent U- and W-shaped pipes. They are suitable for high coolant pressures, since the manufacture of water chambers and fastening of pipes in tube sheets in apparatus high pressure– operations are complex and expensive. However, devices with bent pipes cannot become widespread due to 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 reliable enough in operation (lens, stuffing box). More advanced design heat exchanger with rigid fastening of one tube plate and free movement of the second board together with the inner cover of the pipe system (Fig. e). some increase in the cost of the device due to an increase in the diameter of the body and the manufacture of an additional bottom is justified by the simplicity and reliability of 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 coolants is reduced, however, with a sufficient number of pipe sections, the difference compared to counter flow is small. In some designs such heat exchangers When gas flows in the interpipe space and liquid in pipes, pipes with transverse ribs are used to increase the heat transfer coefficient.

Technical description

Shell and tube heat exchangers produced by Geoclima is a rather complex device, and there are many varieties of it. They belong to the type of recuperative. Heat exchangers are divided into types 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 get their name because the thin tubes through which the coolant moves are located in the middle of the main shell. The speed at which the substance will move depends on how many tubes are in the middle of the casing. The heat transfer coefficient, in turn, will depend on the speed of movement of the substance. Shell-and-tube heat exchangers CROM / GEOCLIMA 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:

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

Peculiarities

The use of advanced developments and technologies in the creation of shell-and-tube heat exchangers ensures maximum heat transfer efficiency with the same dimensions.

For the manufacture of shell-and-tube heat exchangers, alloy 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 these devices are produced:

• with temperature casing compensator;
• with fixed tubes;
• with U-shaped tubes;
• with floating head;
• it's also possible complex application different design solutions, for example, a floating head and a temperature compensator can be used in one design.

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

• Universal heat exchangers;
• Evaporators;
• Capacitors;
• Refrigerators;

According to their location, heat exchangers are:

• Horizontal;
• Vertical

Distinctive properties of the equipment:
The main and most significant advantage is the high resistance of this type of units to water hammer. Most types of heat exchangers produced today do not have this quality.

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

The third significant advantage of shell-and-tube heat exchangers is their high efficiency. In terms of efficiency it can be compared with plate heat exchanger, which is the most effective in most respects.

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

• high productivity
• compactness
• reliability
• versatility in use.

Shell and tube heat exchangers are a heat exchange device between two flows with heating of one medium (liquid, gaseous) due to the cooling agent. During the thermal process, the two media do not mix; they can change their state of aggregation. Hot and cold coolants move in different channels, and heat exchange occurs through the walls of the tube bundles. To increase the heat transfer surface, pipe fins are used, which is done by winding steel tape.

The device received its name from the casing with tubes located inside, through which recovery is carried out. The operating temperature range of the device is from -60°C to +600°C. Depending on its purpose, it can serve as a heat exchanger, refrigerator, condensers or evaporator.

The product is used in heating engineering for equipment DHW systems. The high efficiency of heat exchangers reduces fuel consumption spent on the technological process or heat supply. Shell and tube heat exchangers have always occupied a leading position in demand on the market heating equipment. Over the past 15–20 years, many new analogues with excellent characteristics have appeared. However, heating engineers prefer to use these time-tested, reliable heating units.

What types of heat exchangers are there?

According to GOST 9929–82, shell-and-tube heat exchange products are produced with a diameter from 15.9 cm to 300 cm and can withstand pressure in the range from vacuum to 160 kgf/cm². The length of the device can be from a few centimeters to 8–9 meters.

The heat exchange surface can reach several thousand square meters.

Products are available in the following types:

N – with fixedly built-in tubular grilles;

K – s temperature compensator;

P – with floating head;

U - s U shape tubular elements;

PC – combined, equipped with a floating head with a built-in compensator.

Shell and tube heat exchangers with fixed tube sheets have a rigid component design. They are most common in the oil and gas industry and chemical industry. This type occupies 75% of the total shell-and-tube heat exchanger market. Distinctive feature This type is that the heat exchange pipes are rigidly fastened to tube sheets (flared), which in turn are welded to the inner wall of the housing. In this regard, the possibility of mutual movements of elements in the distribution chamber is excluded.

To supply and remove coolant from pipes and interpipe space, as well as to remove condensate, products are equipped with fittings or other pipeline fittings, exiting the heat exchanger. The intensity of heat transfer during transverse movement of the flow is higher, so it is directed along a zigzag path. To do this, transverse partitions are installed; they are not adjacent to the inner surface of the casing, leaving a gap for flow movement. To concentrate the flow closer to the pipe bundle, the working space of the chamber is narrowed with special plates.

In a shell-and-tube heat exchanger with a compensator on the housing thermal elongation is compensated by longitudinal compression or elongation of flexible inserts and expanders. Such devices are used when excessive deformation of the compensator is within 10–15 mm. In such a semi-rigid structure, lens, stuffing box or bellows expansion joints can be used to compensate for thermal expansion and pipe distortion.

The design of the device is considered more advanced floating head. One of the tube plates is fixed rigidly, the other grid moves freely along with the pipe system. Floating cooking is a movable grate with a lid that it is equipped with. Some increase in the cost of the device due to an increase in the diameter of the body and an additional bottom is justified by greater reliability in operation.

In the product with U-shaped pipes both ends of the tube bundle are fixed to one tube sheet, the tube is bent in a 180° loop with a radius of 4d or more. This allows the pipes to freely extend towards the bend of the tube bundle.

Based on the direction of movement of the medium in the apparatus, there are single/multi-pass heat exchangers. In a one-pass process, the substance moves once along the shortest path from input to output. The most striking representative of this species is the water-water GDP heater, used in heating systems Oh. When is it best to use such a device? It is best where high intensity of the heat exchange process is not required and where there is a small difference between the temperature of the coolant and the environment.

In multi-pass systems, the flow is redirected using a system of longitudinal and transverse partitions in the volume. The use of a heat exchanger in thermal systems with high movement speed or low heat transfer of the agent is considered optimal. According to the method of movement of the agent, they are distinguished direct-flow, counter-flow and cross-flow products.

To operate the heat exchanger in aggressive environments, instead of a steel tube bundle, graphite or glass pipes are used, and the body is sealed with seals of special materials.

On what principle do the units work?

The recovery principle used in the functionality is based on separate heat exchange without mixing the products. Heat transfer from a more heated medium to a less heated one occurs through the walls of the pipes separating the two agents. In this case, the principle of counterflow is observed, as it ensures optimal heat transfer. One coolant (liquid, gas, steam) is supplied under pressure into the space between the pipes, the second circulates through the pipes and may differ in its state of aggregation from the first.

Next, heat exchange processes occur between liquid and gaseous substances in normal mode. To increase heat transfer coefficients, sufficient high speeds products. For steam and gas it should be 8–25 m/s, for liquid agents from 1.5 m/s. To increase heat transfer, the pipes are equipped with special fins.

What does a shell-and-tube apparatus consist of?

The main advantage of the shell-and-tube heat exchanger and the reason for its popularity is its simple but very reliable design. It consists of a distribution chamber equipped with nozzles, a cylindrical casing, tube sheets and a tube bundle. The design is supplemented with end caps and supports for placement on a horizontal base or fastenings for a different orientation in space.

To intensify heat transfer, pipes with external ribs are used, which increase heat transfer. If you need to reduce heat transfer in environment and increase heat-accumulating properties, the casing is covered with a heat-insulating layer. There are also “pipe-in-pipe” designs. The casing is most often made of sheet steel with a thickness of at least 4 mm. The gratings are most often made from the same material and have a thickness of at least 20 mm. The main structural element is the beam metal pipes, on one or both sides it is attached to the tube sheets.

Product marking

The marking of heat exchangers consists of a sequence of alphanumeric code characters. For example, the abbreviation 1400 TKG-1.5-0.5 - M1/40D-6-1-U-I stands for:

diameter 1400 mm;

pressure inside the pipes 1.5 MPa;

the same, only in the space between the pipes 0.5 MPa;

material type M1;

finned pipes with a diameter of 40 mm;

product length 6 m;

one-way design;

used in temperate climate;

There are devices for attaching external thermal insulation.

Advantages and disadvantages of products

Shell and tube heat exchangers have a number of advantages that provide competitive advantages in their segment of heat exchangers in the thermal equipment market:

1. They are highly resistant to water hammer while other analogues do not have this ability.

2. They can work with contaminated products or in aggressive environments, unlike other heat exchangers. For example, plate analogues work exclusively on a pure agent.

3. Easy to maintain (easy to produce mechanical cleaning), technical maintenance and high maintainability.

The disadvantages of products of this type are:

1. Lower coefficient compared to plate products useful action, smaller heat transfer surface area.

2. Large dimensions, which results in increased material consumption and cost of the device.

3. Significant dependence of heat transfer on the speed of the moving agent.

Area of ​​application of the devices

Shell and tube devices are used as basic equipment for heating points and utility networks housing and communal services. Individual heating points(ITP) have significant advantages over centralized heat and water supply. They more efficiently supply energy to facilities and provide thermal regime buildings than heating plants.

Heat exchange equipment this type is indispensable in cases where it is necessary to ensure decoupling of the pressure and temperature of the coolant in the secondary DHW circuit from the supply network water. This is especially true if the heating system is connected to the heat supply network via independent scheme accession. This happens when static pressure, for example, heating systems of connected buildings due to uneven terrain higher than in the network line. Or vice versa, when the pressure in the network “return” is higher than in the servicing heating system.

Heat exchangers of this type are used in the oil, gas, and chemical industries. They can be found in large thermal power plants, where coolants with high parameters are used. The diverse range of applications is not limited to these industries. They are used as evaporators in reboilers, air-cooled condensers, distillation columns. They can also be used to cool raw materials, components or finished products. They are widely used in technological processes dairy, beer and other food industries.

Shell-and-tube heat exchanger (shell-and-tube) horizontal

Tube heat exchanger

NORMIT company has a wide the lineup heat exchangers that can satisfy any requirement various types 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 exchange and thermochemical processes between various liquids, vapors and gases - both without changing and with a change in their state of aggregation. Shell and tube heat exchangers can be used

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

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 a CIP-wash
• Low energy costs
• Safe use for personnel

Shell and tube heat exchangers are one of the most widely used devices in this field, largely due to their reliable design and a variety of design options in accordance with different conditions operation.

Specifications may change in accordance with the Client’s technological requirements:

• single-phase flows, boiling and condensation on the hot and cold sides of the heat exchanger with 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 thermal stress requirements without significantly increasing the cost of the device
• sizes from small to extremely large (5000 m2)
• Possibility of using different materials in accordance with the requirements for cost, corrosion, temperature and pressure
• the use of developed heat exchange surfaces both inside and outside the pipes, various intensifiers, etc.
• possibility of removing the pipe bundle for cleaning and repair.

Description

Shell-and-tube heat exchangers consist of tube bundles mounted in tube sheets, casings, covers, chambers, nozzles and supports. The pipe and inter-tube 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. Thus, the condenser of a steam turbine with a power of 150 MW consists of 17 thousand pipes with a total heat exchange surface of about 9000 m 2.

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

The tubular structure 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 interpipe space is 2-3 times larger than the flow area inside the pipes. Therefore, at equal flow rates of coolants with the same phase state, the heat transfer coefficients on the surface of the inter-tube space are low, which reduces the overall heat transfer coefficient in the apparatus. The installation of partitions in the inter-tube space of a shell-and-tube heat exchanger helps to increase the speed of the coolant and improve the efficiency of heat transfer.

Below are diagrams of the most common devices:

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

In a single-pass heat exchanger with straight tubes of rigid construction, 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 pipe bundle (up to 50 o C). They have low heat transfer coefficients due to the low velocity of the coolant in the interpipe space.

In shell-and-tube heat exchangers, the flow area of ​​the inter-tube space is 2-3 times larger than the flow area of ​​the tubes. Therefore, at the same flow rates of coolants having the same state of aggregation, the heat transfer coefficients on the surface of the interpipe space are low, which reduces the heat transfer coefficient in the apparatus. The installation of partitions in the inter-tube space helps to increase the coolant velocity and increase the heat transfer coefficient.

In vapor-liquid heat exchangers, steam usually passes in the inter-tube space, and liquid through the pipes. The temperature difference between the housing wall and the pipes is usually significant. To compensate for the difference in thermal elongation, lens, gland or bellows compensators are installed between the casing and pipes.

To eliminate stresses in the metal caused by thermal elongations, single-chamber heat exchangers with bent U- and W-shaped pipes are also manufactured. They are suitable for high coolant pressures, since the manufacture of water chambers and fastening of pipes in tube sheets in high-pressure apparatuses are complex and expensive operations. However, devices with bent pipes cannot become widespread due to 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 reliable enough in operation (lens, stuffing box). The design of the heat exchanger is more advanced with rigid fastening of one tube sheet and free movement of the second board along with the inner cover of the tube system. some increase in the cost of the device due to an increase in the diameter of the body and the manufacture of an additional bottom is justified by the simplicity and reliability of operation. These devices are called “floating head” heat exchangers. Cross-flow heat exchangers 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 coolants is reduced, however, with a sufficient number of pipe sections, the difference compared to counter flow is small. In some designs of such heat exchangers, when gas flows in the inter-tube space and liquid in 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 surface heat exchangers and “pipe-in-pipe” heat exchangers in cases where their use turns out to be more acceptable from the point of view of technological and economic characteristics.

Technical specifications:

Model	NORMIT Heatex tube 1	NORMIT Heatex tube 2	NORMIT Heatex tube 3	NORMIT Heatex tube 4
Heat exchange area, m2
Material	AISI 304
Number of pipes, pcs
Temperature, °C	Up to 200

Dimensions:

Overall dimensions, mm	A	B	C
NORMIT Heatex tube 1		1500
NORMIT Heatex tube 2		1900
NORMIT Heatex tube 3		2200
NORMIT Heatex tube 4		2600

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 secured by flaring or welding. The device body is closed with lids 5 And 6. Partitions are installed inside the housing 3, creating a certain direction of flow and increasing its speed in the housing (Fig. 8.3.4).

Rice. 8.3.2. Rigid type shell and tube heat exchanger:

1 - casing (housing); 2 - tube; 3 - transverse partition; 4 - tube sheet; 5 - cover; 6 - cover (distribution box); 3.8 - longitudinal partitions in the junction box and in the housing, respectively.

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

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

Rice. 8.3.4. Types of transverse partitions:

I – with a sector cutout ensuring fluid flow along a helical line;

II – with a slotted cutout providing wave-like movement;

III – with a segmented cutout;

IV – circular, providing movement from the periphery to the center, and vice versa.

The transverse partitions are fixed to one another by means of spacer pipes pressed against them by common rods (usually four). Except technological purposes transverse partitions also serve as intermediate supports for the tube bundle, preventing it from bending during horizontal position apparatus.

One of the heat exchange media moves through the tubes, and the other moves inside the housing between the tubes. A more contaminated medium, as well as a medium with a lower heat transfer coefficient, is allowed into the tubes, since cleaning the outer surface of the tubes is difficult, and the speed of movement of the medium in the inter-tube space 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 housing, disruption of flaring density, etc. That's why Hard type heat exchangers are used when the temperature difference between the heat exchanged media is no more than 50°C.

Heat exchangers with lens compensator on the housing (Fig. 8.3.3) are used to reduce temperature stress in rigid type devices. Such heat exchangers have a lens compensator on the body, due to the deformation of which the thermal forces in the body and tubes are reduced.

This reduction is greater, the greater the number of lenses in the compensator. Floating head heat exchangers(Fig. 8.3.5)

found the most widespread use. In these devices, one end of the tube bundle is fixed in a tube sheet connected to the body (in the figure on the left), and the second can move freely relative to the body when temperature changes in the length of the tubes. This eliminates temperature stresses in the structure and allows you to work with large temperature differences in heat-exchange media. In addition, it is possible to clean the tube bundle and the apparatus body, making it easier to replace the bundle tubes. However, the design of heat exchangers with a floating head is more complex, and the floating head is not accessible for inspection during operation of the device.

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

1 – casing; 2.3 – inlet and outlet chambers (covers); 4 – tube bundle; 5 – tube sheets; 6 – floating head cover; 7 – partitions; 8 – clamps for securing the cover; 9 – supports; 10 – foundation; 11 – inter-tube guide partitions; 12 – sliding support of the tube bundle; I, II – input and output of heating fluid; III, IV – input and output of the heated flow.

The inter-tube space of devices with a floating head is usually made one-pass. With two strokes, a longitudinal partition is installed in the body. However, in this case a special seal is required between the partition and the housing. The heat exchange surface of shell-and-tube heat exchangers can be 1200 m2 with pipe 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 u, 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 for high blood pressure. The medium sent into the tubes must be sufficiently clean, since cleaning the inner surface 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 partitions in the housing and distribution boxes, shell-and-tube heat exchangers are divided into one-, two- and multi-pass, both in the pipe and in the inter-tube space. So, in Fig. 8.3.2 the heat exchanger is two-pass both in the pipe and in the inter-tube space, which is achieved by installing longitudinal partitions 7 And 8.

heat exchangers of the "pipe-in-pipe" type.

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

“Pipe-in-pipe” devices are made non-separable and collapsible. The first of them are used for media that do not produce deposits in the interpipe space, the outer pipes of which are connected by welding pipes. The connections of the internal pipes of such devices can be rigid (transition twins 3 welded to the tubes) and detachable (twins on flanges, as shown in the figure). In a rigid system, the heat exchanger can be used for environments in which the temperature difference between the outer and inner pipes should be no more than 50°C.

Rice. 8.3.7. Section of a four-pass non-separable pipe-in-pipe heat exchanger:

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

Rice. 8.3.8. Section of a single-flow gasketed 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 contaminated flow; B – input and output of a less polluted stream

Collapsible “pipe-in-pipe” devices (Fig. 8.3.8) are made from sections where the outer pipes 4 united by a common cover 3, serving to turn the flow of coolant from one external pipe to another, and the internal pipes are connected using rotary twins on the flanges inside this cover. The battery of a multi-flow apparatus can be assembled from such sections if the coolant flow is high (10–200 t/h in the pipe and up to 300 t/h in the interpipe space). The advantage of dismountable “pipe-in-pipe” devices is that they can be regularly (like shell-and-tube) cleaned of deposits and the internal or external pipes can be replaced in case of damage or corrosion.

Typically, in “pipe-in-pipe” devices, a more contaminated coolant flow is allowed through the internal tubes, and a less contaminated one is directed through the interpipe space.

In heat exchangers of a collapsible design, the internal pipes on the outside may have fins to increase the heat exchange area and thereby increase the efficiency of heat transfer. Collapsible heat exchangers allow cleaning the external and internal surfaces of pipes, as well as the use of finned internal pipes. 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.