History of shell and tube heat exchangers

Devices of this kind were first developed at the very beginning of the twentieth century, when thermal power plants needed heat exchangers with a large heat exchange surface and capable of operating at sufficiently high temperatures. high blood pressure.

Today, shell-and-tube heat exchangers are used as preheaters, condensers and evaporators. The experience of many years of operation and numerous design developments have led to significant improvements in their design.

Then, at the beginning of the last century, shell-and-tube heat exchangers began to be widely used in oil industry. The harsh conditions of oil refining required oil mass heaters and coolers, condensers and evaporators for certain fractions of crude oil and organic liquids.

The high temperatures and pressures at which the equipment operated, the properties of the oil itself and its fractions led to rapid contamination individual parts devices. In this regard, heat exchangers had to have such design features, which would ensure ease of cleaning and, if necessary, repair.

Execution options

Over time, shell-and-tube heat exchangers have become widely used. This was determined by the simplicity and reliability of the design, as well as the large number possible options executions suitable for various conditions operation, including:

vertical or horizontal design of the heat exchanger, boiling or condensation, single-phase coolant flows on the hot or cold side of the apparatus;

possible operating pressure range from vacuum to fairly high values;

the ability to change pressure drops over a wide range on both sides of the heat exchange surface as a consequence of a large number of design options.

the ability to meet thermal stress requirements without significantly increasing the cost of the device;

device sizes - from small to largest, up to 6000 m²;

materials can be selected depending on corrosion, pressure and temperature conditions, taking into account their respective costs;

heat transfer surfaces can be used both inside and outside pipes;

the ability to access a bundle of pipes for repair or cleaning.

However, the wide range of applications of shell-and-tube heat exchangers when selecting the most suitable options for each specific case should not exclude the search for alternative options.

Components

Components of shell-and-tube heat exchangers: tube bundles mounted in tube sheets, covers, casings, pipes, chambers and supports. The pipe and inter-tube spaces in them are most often separated by partitions.

Circuit diagrams and types

Schematic diagrams of the most widely used types of shell-and-tube heat exchangers are presented in the figure:

The heat exchanger casing is a pipe welded from steel sheets. The difference between the casings lies mainly in the way the casing is connected to the tube sheet and to the covers. The thickness of the casing wall is selected depending on the operating pressure of the medium and its diameter, but is generally taken to be at least 4 mm. Covers or bottoms are welded to the edges of the casing using flanges. The apparatus supports are attached to the outside of the casing.

In shell-and-tube heat exchangers, the total effective cross-section of the inter-tube space is usually 2-3 times larger than the corresponding cross-section of the pipes. Therefore, regardless of the temperature difference between the coolants and their phase state, the overall heat transfer coefficient is limited by the surface of the interpipe space and remains low. In order to increase it, partitions are installed, which increases the speed of the coolant and increases the efficiency of heat transfer.

The tube bundle is secured in tube sheets using various methods: using beading, flaring, sealing, welding or gland fastenings. Tubesheets are welded to the casing (Types 1 and 3), or bolted between the cover and casing flanges (Types 2 and 4), or bolted to the flange only (Types 5 and 6). The material for the grating is usually sheet steel, the thickness of which must be at least 20 mm.

These heat exchangers differ in design: rigid (Type 1 and 10), semi-rigid (Type 2, 3 and 7) and non-rigid (Type 4, 5, 6, 8 and 9), according to the method of coolant movement - multi-pass and single-pass, direct-flow, cross-flow and countercurrent, and according to the method of arrangement - vertical, horizontal and inclined.

Figure 1 shows a single-pass, rigid design heat exchanger with straight tubes. The casing is rigidly connected to the tubes by grids; there is no possibility of compensating for thermal elongations. The design of such devices is simple, but they can only be used when the temperature difference between the pipe bundle and the body is not very large (up to 50°C). In addition, the heat transfer coefficient in devices of this type is low, because the speed of the coolant in the interpipe space is low.

In shell-and-tube heat exchangers, the cross-section of the inter-tube space is usually 2-3 times larger than the corresponding cross-section of the pipes. Therefore, the overall heat transfer coefficient is affected not so much by the temperature difference of the coolants or their phase state; on the contrary, it is limited by the surface of the interpipe space and remains low. In order to increase it, partitions are made in the inter-tube space, which slightly increases the speed of the coolant and thereby increases the efficiency of heat transfer.

Partitions installed in the interpipe space, increasing the speed of the coolant, increase the heat transfer coefficient.

In vapor-liquid heat exchangers, steam is usually passed between the tubes, and the liquid flows through the pipes. In this case, the temperature difference between the pipes and the housing wall is usually very large, which requires installation various types compensators. In these cases, lens (Type 3), bellows (Type 7), stuffing box (Type 8 and 9), and compensators are used.

Single-chamber heat exchangers with W- or more commonly U-shaped tubes also effectively eliminate thermal stress in the metal. It is advisable to use them at high coolant pressures, since in high-pressure apparatuses, fastening pipes in grates is an expensive and technologically complex operation. However, bent tube heat exchangers are also not widely used due to the difficulty of obtaining tubes with different bending radii, the difficulty of replacing bent tubes, and problems encountered when cleaning them.

The design of the heat exchanger, which provides for rigid fastening of one tube sheet and free movement of the second, is more advanced. In this case, an additional internal cover is installed, which relates directly to the pipe system (Type 6). The slight increase in the cost of the device, associated with an increase in the diameter of the body and the manufacture of a second, additional bottom, is justified by reliability in operation and simplicity of design. Such devices are called “floating head” heat exchangers.

Cross-flow heat exchangers (Type 10) are distinguished by an increased heat transfer coefficient, since the coolant in the inter-tube space moves across the tube bundle. In some types of such heat exchangers, when gas is used in the annulus and liquid is used in pipes, the heat transfer coefficient is further increased by using pipes with transverse ribs.

Operating principle of shell-and-tube heat exchangers:

Types of shell and tube heat exchangers:

water-water heaters;
water and oil coolers for compressors and diesel engines;
steam-water heaters;
oil coolers of various types of turbines, hydraulic presses, pumping and compressor systems, power transformers;
air coolers and heaters;
coolers and heaters of food media;
coolers and heaters used in petrochemicals;
water heaters in swimming pools;
evaporators and condensers of refrigeration units.

Scope and scope

Shell and tube heat exchangers are used in industrial freezing plants, in the petrochemical, chemical and food industries, for heat pumps in water treatment and sewerage systems.

Shell-and-tube heat exchangers are used in the chemical and thermal industries for heat exchange between liquid, gas and vapor coolants in thermochemical processes, and today they are the most widely used devices.

Advantages:

Reliability of shell-and-tube heat exchangers in operation:

Shell and tube heat exchangers easily withstand sudden changes in temperature and pressure. Pipe bundles are not destroyed by vibration and hydraulic shocks.

Low contamination of devices

Pipes of this type of heat exchangers are little contaminated and can be quite easily cleaned using the cavitation-impact method, chemical, or - for collapsible devices - mechanical ways.

Long service life

The service life is quite long - up to 30 years.

Adaptability to different environments

Shell-and-tube heat exchangers used today in industry are adapted to a wide variety of technological environments, including sanitary, sea and river water, petroleum products, oils, chemically active environments, and even the most aggressive environments practically do not reduce the reliability of heat exchangers.

The easiest way to understand how a shell-and-tube heat exchanger works is by studying its circuit diagram:

Picture 1. The operating principle of a shell-and-tube heat exchanger. However, this diagram illustrates only what has already been said: two separate, non-miscible heat exchange flows passing inside the casing and through the tube bundle. It will be much clearer if the diagram is animated.

Figure 2. Animation of the operation of a shell-and-tube heat exchanger. This illustration demonstrates not only the operating principle and design of the heat exchanger, but also what the heat exchanger looks like outside and inside. It consists of a cylindrical casing with two fittings, and two distribution chambers on both sides of the casing.

The pipes are assembled together and held inside the casing by two tube sheets - all-metal disks with holes drilled in them; tube sheets separate the distribution chambers from the heat exchanger body. Pipes on the tube sheet can be secured by welding, flaring, or a combination of these two methods.

Figure 3. Tube grid with flared bundle tubes. The first coolant enters the casing directly through the inlet fitting and leaves it through the outlet fitting. The second coolant is first supplied to the distribution chamber, from where it is directed to the tube bundle. Once in the second distribution chamber, the flow “turns around” and again passes through the pipes to the first distribution chamber, from where it exits through its own outlet fitting. In this case, the reverse flow is directed through another part of the tube bundle so as not to interfere with the passage of the “forward” flow.

Technical nuances

1. It should be emphasized that diagrams 1 and 2 show the operation of a two-pass heat exchanger (the coolant passes through the pipe bundle in two passes - forward and reverse flow). Thus, improved heat transfer is achieved with the same length of pipes and exchanger body; however, its diameter increases due to an increase in the number of pipes in the tube bundle. There are simpler models in which the coolant passes through the tube bundle in only one direction:

Figure 4. Schematic diagram single pass heat exchanger. In addition to one- and two-pass heat exchangers, there are also four-, six- and eight-pass heat exchangers, which are used depending on the specifics of specific tasks.

2. Animated diagram 2 shows the operation of a heat exchanger with partitions installed inside the casing that direct the coolant flow along a zigzag path. Thus, a cross flow of coolants is ensured, in which the “external” coolant washes the tubes of the bundle perpendicular to their direction, which also increases heat transfer. There are models with a simpler design, in which the coolant passes in the casing parallel to the pipes (see diagrams 1 and 4).

3. Since the heat transfer coefficient depends not only on the trajectory of the working fluid flows, but also on the area of ​​their interaction (in in this case– from the total area of ​​all pipes of the tube bundle), as well as from the velocities of the coolants, it is possible to increase heat transfer through the use of pipes with special devices - turbulators.

Figure 5. Pipes for shell-and-tube heat exchanger with wave-like knurling. The use of such pipes with turbulators in comparison with traditional cylindrical pipes makes it possible to increase thermal power unit by 15 - 25 percent; In addition, due to the occurrence of vortex processes in them, self-cleaning of the inner surface of the pipes from mineral deposits occurs.

It should be noted that the heat transfer characteristics largely depend on the pipe material, which must have good thermal conductivity and the ability to withstand high pressure working environment and be corrosion resistant. Based on the totality of these requirements for fresh water, steam and oils best choice are modern brands of high quality of stainless steel; for sea or chlorinated water - brass, copper, cupronickel, etc.

Manufactures standard and upgraded shell-and-tube heat exchangers according to modern technologies for new installed lines, and also produces units designed to replace heat exchangers that have exhausted their service life. and its production is carried out according to individual orders, taking into account all the parameters and requirements of a specific technological situation.

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

Shell and tube (or) heat exchangers were invented at the beginning of the last century in order to be actively used in the operation of thermal power plants, where a large number of heated water was distilled at high blood pressure. Subsequently, 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 been improved, the design has become less cumbersome, and it is now designed so that individual elements can be cleaned. Similar systems have begun to be used more often in the oil refining industry and production household chemicals, since the products of these industries contain a lot of impurities. It is their sediment that requires periodic cleaning of the internal walls of the heat exchanger.

As we can see in the diagram presented, shell and tube heat exchanger consists of a bundle of tubes, which are located in their own chamber and mounted on a board or grid. The casing is, 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 small tubes and a board are located. Sheet steel is usually used as the material for the board. The tubes are connected to each other by pipes; there is also an entrance and exit 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 power 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 with a 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 greater than their cross-section. Due to this, 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 in 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 for, otherwise the device would have significant heat losses. For this purpose, so-called compensators of three types are used: lenses, oil seals 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 voltage in steel caused by thermal elongation. Their production is quite expensive, and pipes are difficult to replace in case of repair. Therefore, such heat exchangers are in less demand on the market.

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

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

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

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

Wide range of shell-and-tube heat exchanger capabilities

1. The pressure in the tubes can reach different values, from vacuum to the highest;
2. Can be achieved necessary condition according to thermal stresses, while the price of the device will not change significantly;
3. The dimensions of the system can also be different: from a domestic heat exchanger for a bathroom to an industrial one with an area of ​​5000 square meters. m.;
4. There is no need to pre-clean the work environment;
5. To create the core use 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 any disadvantages? Not without them: shell and tube heat exchanger very cumbersome. 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 purchased, despite the high cost. On the other side, self-production such a system will cause great difficulties, and most likely lead to significant heat losses during operation.

When operating the heat exchanger, special attention should be paid to the condition of the pipes, as well as the settings depending on the condensate. Any intervention in the system leads to a change in the heat exchange area, so repairs and commissioning must be carried out by trained specialists.

You may be interested in:

An industrial pump is necessary in almost any production. Unlike household pumps, they must withstand high loads, be wear-resistant and have maximum performance. In addition, pumps of this type must be cost-effective for the enterprise in which they are used. In order to buy a suitable industrial pump, you need to study its main characteristics and take into account...

Heating and cooling liquids is a necessary step in a number of technological processes. Heat exchangers are used for this. The principle of operation of the equipment is based on the transfer of heat from a coolant, the functions of which are performed by water, steam, organic and inorganic media. Choosing which heat exchanger is best for a particular production process, you need to be based on the design and material features...

A vertical sump has the shape of a cylindrical tank made of metal (sometimes it is made square). The bottom shape is conical or pyramidal. Sedimentation tanks can be classified based on the design of the inlet device - central and peripheral. The most commonly used type is with a central inlet. The water in the sump moves in a downward-ascending motion. The working principle of vertical...

The Ministry of Energy has developed a plan for the development of green electricity by 2020. Share of electricity from alternative sources electricity should reach 4.5% of the total energy generated in the country. However, according to experts, the country simply does not need such an amount of electricity from renewable sources. The general opinion in this area is to develop electricity generation through...

Shell and tube heat exchangers emerged in the early 20th century in response to the needs of thermal power plants for large surface area heat exchangers such as condensers and water heaters operating at relatively high pressures. Shell and tube heat exchangers are 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 of shell-and-tube heat exchangers began in the 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 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 application various materials according to cost, corrosion, temperature and pressure requirements;

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.

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

Shell-and-tube heat exchangers can be single-pass, where both coolants move without changing direction throughout the entire cross-section (one along the pipe, the other along the inter-tube), and multi-pass, in which the flows successively change direction with the help of additional partitions, thereby increasing the heat transfer coefficient and flow rate.

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

To increase the speed of movement of coolants in order to intensify heat transfer, partitions are often installed, both in the pipe and in the inter-pipe spaces.

Shell and tube heat exchangers can be vertical, horizontal or inclined to suit process requirements or ease of installation. Depending on the magnitude of the thermal elongation of the tubes and housing, shell-and-tube heat exchangers of 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 (housing) of a 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 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.

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.

The designs of modern surface-type recuperative heat exchangers of continuous action are very diverse. Let's look at the most typical ones.

Shell and tube heat exchangers are devices made of bundles of pipes, fastened with tube sheets (boards) and limited by casings and covers with branch pipes. The pipe and inter-tube spaces in the apparatus are separated, and each of them can be divided by partitions into several passages. The partitions are designed to increase the speed and, therefore, the heat transfer coefficient of the coolants. Heat exchangers of this type are intended for heat exchange between various liquids, between liquids and steam, between liquids and gases. Typical designs Shell and tube heat exchangers are used in cases where a large heat exchange surface is required.

When heating a liquid with steam, in most cases, steam is introduced into the inter-tube space, and the heated liquid flows through the tubes. In shell-and-tube heat exchangers, the flow area of ​​the inter-tube space is 2... 3 times larger than the flow area inside the pipes. Therefore, at the same flow rates of coolants having the same state of aggregation, the coolant velocities in the annulus are lower and the heat transfer coefficients on the surface of the annulus are low, which reduces the heat transfer coefficient in the apparatus. In Fig. 4.5 shown Various types shell and tube heat exchangers.

The heat transfer surface of the devices can range from several hundred square centimeters to several thousand square meters. Thus, the condenser of a modern steam turbine with a power of 300 MW has more than 20 thousand pipes with a total heat exchange surface of about 15 thousand m 2.

The body (casing) of a shell-and-tube heat exchanger is a cylinder welded from one or more steel sheets. The casings differ mainly in the way they are connected to the tube sheet and covers. The thickness of the casing wall is determined by the maximum pressure of the working medium and the diameter of the apparatus, but not less than 4 mm. Flanges are welded to the cylindrical edges of the casing for connection with covers or bottoms. The pipes and supports of the apparatus are welded on the outer surface of the casing.

The tubes of shell-and-tube devices are made straight or curved (U-shaped) with a diameter of 12 to 57 mm.

The tube material is selected depending on the environment washing its surface. Tubes made of steel, brass and special alloys are used.

Tube sheets are used to secure pipes in them using flaring, welding, sealing or gland connections. Tube sheets are bolted between the casing and cover flanges or welded to the casing, or bolted only to the free chamber flanges (see Fig. 4.5).

Rice. 4.5. Types of shell and tube heat exchangers:

a - single-pass; b - multi-pass; c - film; g - with a lens compensator; d - with floating head closed type; e - with an open floating head; g - with stuffing box compensator; h - with U-shaped tubes; 1 - casing; 2 - exit chamber; 3 - tube sheet; 4 - pipes; 5 - entrance chamber; 6 - longitudinal partition; 7 - camera; 8 - partitions in the chamber; 9 - lens compensator; 10 - floating head; 11 – oil seal; 12 - U-shaped pipes; I, II - coolants

The covers of shell-and-tube devices have the shape of flat plates, cones, spheres, and most often convex or concave ellipses.

Sectional heat exchangers(Fig. 4.6) are a type of tubular apparatus and consist of several sections connected in series, each of which is a shell-and-tube heat exchanger with a small number of pipes and a casing of small diameter.

In sectional heat exchangers, at the same fluid flow rates, the speeds of coolant movement in the pipes and inter-tube space are almost equal, which provides increased heat transfer coefficients compared to conventional tubular heat exchangers. The simplest of this type is a “pipe-in-pipe” heat exchanger (a smaller diameter pipe is inserted into the outer pipe). All elements of the device are connected by welding.

Rice. 4.6. Sectional heat exchangers:

a - water heater of the heating network; b - “pipe in pipe” type; 1 - lens compensator; 2 - tubes; 3 - tube sheet with a flange connection to the casing; 4 - “kalach”; 5 - connecting pipes

The disadvantages of sectional heat exchangers are: high cost per unit of heating surface, since dividing it into sections causes an increase in the number of the most expensive elements of the apparatus - tube sheets, flange connections, transition chambers, compensators, etc.; significant hydraulic resistance due to various turns and transitions cause increased energy consumption to drive the pump pumping the coolant.

The casings of serial sectional heat exchangers are made from pipes up to 4 m long, with an internal diameter from 50 to 305 mm. The number of pipes in a section ranges from 4 to 151, heating surface from 0.75 to 26 m2, brass pipes with a diameter of 16/14 mm. The ratio of the heating surface to the volume of the heat exchanger reaches 80 m 2 /m 3, and the specific structural weight is 50...80 kg/m 2 of the heating surface.

Spiral heat exchangers(Fig. 4.7) consist of two spiral channels of rectangular cross-section through which coolants I and II move. The channels are formed by metal sheets that serve as a heat exchange surface. The inner ends of the spirals are connected by a dividing partition. To ensure structural rigidity and fix the distance between the spirals, bosses are welded. The ends of the spirals are closed with lids and tightened with bolts.

Horizontal spiral heat exchangers are used to exchange heat between two fluids. Vertical spiral heat exchangers are used for heat exchange between condensing steam and liquid. Such heat exchangers are used as condensers and steam heaters for liquids.

Rice. 4.7. Types of spiral heat exchangers:

a - horizontal; b - vertical; 1, 3 - sheets; 2 - dividing partition; 4 - covers; I, II - coolants

The advantages of spiral heat exchangers include compactness (larger heat exchange surface per unit volume than multi-pass tubular heat exchangers) with the same heat transfer coefficients and lower hydraulic resistance for the passage of coolants. The disadvantages are the complexity of manufacturing and repair and the suitability of working under an excess pressure of no more than 1.0 MPa.

Plate heat exchangers have flat heat transfer surfaces. Typically, such heat exchangers are used for coolants whose heat transfer coefficients are the same.

The disadvantages of plate heat exchangers manufactured until recently were low tightness and insignificant pressure drops between coolants.

Recently, compact collapsible plate heat exchangers have been manufactured, consisting of stamped metal sheets with external protrusions located in a corridor or checkerboard pattern. Such designs are used for heat exchange between liquids and gases and operate at pressure drops of up to 12 MPa. In Fig. 4.8 shows several designs of heat exchangers of this type. Due to the small distance between the plates (6...8 mm), such heat exchangers are very compact. The specific heating surface F/V is 200...300 m 2 /m 3. Therefore, plate heat exchangers in some cases are replacing tubular and spiral ones.

But this design has the following disadvantages: the difficulty of cleaning inside the channels, repairs, partial replacement of the heat exchange surface, as well as the impossibility of manufacturing plate heat exchangers from cast iron and brittle materials and long-term operation.

Currently, in the heat supply systems of housing and communal services and a number of industrial enterprises, plate heat exchangers are installed as hot water supply (DHW) and heating heaters (Fig. 4.8) instead of the traditional sectional shell-and-tube heaters previously used for these purposes. This is due to a number of circumstances and advantages:

1. The heat transfer coefficient in plate heat exchangers is 3...4 times higher than in shell-and-tube heat exchangers, thanks to the special corrugated profile of the flow part of the plate, which ensures a high degree of turbulization of coolant flows. Accordingly, the surface of plate heat exchangers is 3...4 times smaller than shell-and-tube heat exchangers.

Rice. 4.8. Plate water-to-water heat exchanger "Teplotex":

A - general form; b - flow diagram of coolants

2. Plate heat exchangers have low metal consumption, are very compact, and can be installed in a small room.

3. Unlike shell-and-tube ones, they are easy to disassemble and quickly clean. This does not require dismantling the supply pipelines.

4. In a plate heat exchanger, the plate or gasket can be easily and quickly replaced, and the surface area can be increased if the heat load increases over time.

Sectional shell-and-tube heat exchangers are difficult to accurately calculate for the required thermal performance and permissible pressure losses, since the surface of one section is large and reaches 28 m2 (at D y = 300 mm).

Plate heat exchangers are assembled from individual plates, the heating surface of which, as a rule, does not exceed one meter. This circumstance, combined with the optimally selected type of plate, allows you to accurately select the heat transfer surface of the heat exchanger without excess margin.

According to their own technical specifications Teplotex heat exchangers are collapsible and single-pass; plate material - ALSL 316 steel; plate thickness - 0.5 ...0.6 mm; matte gaskets - EPDM rubber; maximum operating coolant temperature - 150 °C; working pressure - 1... 2.5 MPa; water consumption depending on the type of heat exchanger from 2 to 100 kg/s; surface - from 1.5 to 373 m2.

Finned heat exchangers are used in cases where the heat transfer coefficient for one of the coolants is significantly lower than for the second. The heat exchange surface on the side of the coolant with a low α value is increased compared to the heat exchange surface on the side of the other coolant. In such devices, the heat exchange surface has ribs of various shapes on one side (Fig. 4.9). As can be seen from the figure, finned heat exchangers are manufactured in a wide variety of designs. In this case, I make the ribs transverse, longitudinal, in the form of needles, spirals, twisted wire, etc.

Rice. 4.9. Types of finned heat exchangers:

a - lamellar; b - cast iron pipe with round ribs; c - tube with spiral fins; g - cast iron pipe with internal fins; d - fin fins of tubes; e - cast iron pipe with double-sided needle fins; g - wire (bispiral) finning of the tubes; h - longitudinal fins of pipes; and - multi-fin tube