Heat exchanger. Types of heat exchangers. Classification of heat exchangers

Each of us faced the simplest heat exchangers. A vivid example of this is the construction of a "pipe in a pipe" or something like that. It would have been difficult to imagine our life if the heat exchanger had not been invented. To date, there is a huge number of heat exchangers. Between them, they differ not only in their technical characteristics, but also in the sphere of application, design, etc. Let's talk in more detail on this topic and understand with interesting moments.

Some general information

A heat exchanger is a device that is used to transfer heat from one environment to another. It should be understood that the heat exchanger itself, without heating equipment, is completely useless, but in the complex it is possible to obtain remarkable results and successfully heat even very large and cold rooms. In addition, scientists have constantly tried to minimize the loss of heat when it is transferred to another environment. For today it is impossible to brag of 100% efficiency, but about efficiency of 90-95% it is possible to speak safely. Operational, as well as technical characteristics of the product are increased due to the use of specially prepared materials, as well as coolant. Of course, all this increases the price of equipment a little, but it's worth it.

When designing, engineers are constantly confronted with contradictory requirements, which need to be combined into one bottle. For example, it is necessary to lower the hydraulic resistance and at the same time to increase the heat transfer coefficient. The heat exchanger must be resistant to corrosion, but not too difficult to maintain. All this led to the fact that many types of heat exchangers appeared. Depending on the situation, the one that is best suited is used.

Classification of heat exchangers

As noted above, currently there is a huge number of heat exchangers. First of all, they need to be divided according to the method of heat transfer to the medium. Here the heat exchangers are divided into the following groups:

• Recuperative;
• Regenerative;
• Mixing;
• With electric heating.

Let's take a closer look at recuperative heat exchangers. The design of the product implies the existence of a single-layer or multilayer wall through which heat is transferred. Usually this happens already in the steady motion. It is interesting that in such apparatuses, heat transfer occurs when forced motion does not change the phase state. But this only applies to permanent heat exchangers. If we talk about aggregates with a periodic mode of operation, then for a certain period of time heating, evaporation, and cooling are carried out, all in a sequential mode. Such apparatuses belong to heat exchangers with unsteady thermal motion. This is due to the fact that the temperature of the coolant at the inlet and outlet is significantly different. Often, such aggregates are found in the form of coils and are lamellar, ribbed and other forms. A little later we will consider several types. But on this classification of heat exchangers does not end.

Regenerative units and electric heating

In this case, just like in the previous one, the heat transfer surface is used to transfer the heat energy . However, this surface is a kind of nozzle. It serves as an intermediate accumulative agent, which accumulates heat. By and large, the whole process can be divided into several stages. At the first stage, the nozzle perceives a certain amount of heat. Then there is a transition to the second stage, and the coolant is transferred over the surface of the nozzle. This happens when changing coolant flows. At this stage, the nozzle gradually cools, and the stored heat is transferred to a heated environment, which can be your room.

Regenerators refer to non-stationary aggregates. The nozzle is often fixed, and the thermal processes are synchronous. Devices of this type are often called scrubbers or cooling towers.

The essence of heat exchangers with electric heating is that electricity is used as the main source of heat. Electric energy is used to convert electricity into heat. They can be either direct or indirect heating. The most common heat exchangers in the industry are induction and resistance heaters. As you can see, heat-exchange equipment can be different, now we will consider in detail each kind, the scope of its application and design features.

Spiral heat exchangers

The device is a pair of spiral channels. Usually they wind around the central partition. For this, they are made of roll material. It is worth noting that spiral heat exchangers are well suited for heating and cooling liquids having a high viscosity coefficient.

By and large, the heating surface is formed by two sheets of metal, which are joined to the core by means of a welded seam. The unit itself consists of only 2 channels, usually a rectangular section, made in the form of a spiral. The end of the spiral (inner) has a dividing wall and is fixed with pins. Heat exchangers can be manufactured both vertically and horizontally. If you can not install one view because of insufficient space or a complex configuration of the room, then the second, more preferable, is used. It is also interesting that the consumer can choose spiral heat exchangers with different spiral widths, from 20 to 150 centimeters. In this case, the heating surface can vary from 3.2 to 100 meters square with a maximum system pressure of 1 MPa.

It should be noted that this heat exchange equipment has a number of significant advantages. Firstly, this is a reduced hydraulic resistance. Secondly, compactness and high efficiency and intensity of heat exchange. But all this contributed to the fact that there were shortcomings in the form of complex construction and repair.

About plate heat exchangers

Currently, dismountable and non-separable plate heat exchangers are manufactured. Naturally, the first species is more preferable for a variety of reasons. Firstly, it's simplicity of service. Such equipment is very quickly dismantled and collected, so any breakdown is eliminated in a short time. Non-dismantled models usually do not repair, and if this is done, then much longer.

Actually, the name says that this equipment consists of a package of prefabricated plates. They can be made of a different material, such as copper, titanium, graphite, etc. Almost always to improve performance, the plates are made of corrugated. In plate heat exchangers, flows of cold and hot coolant pass through layers.

The equipment itself is good in that it has a competent layout. This allowed to increase the area of the heat exchange surface and all this to accommodate in a relatively small size. In any case, before the purchase, the calculation of heat exchangers is carried out, which allows you to obtain data on how much power the device needs in a particular case. It should be understood that all the plates that are strapped into the bag, due to the same shape form channels among themselves. Through them, the liquid flows. Well, now we'll look at some interesting details that relate to this equipment.

Use of gaskets

As already noted above, plates serve as the main element of heat transfer. They are made by cold stamping. For this, corrosion-resistant alloys are used, which significantly increases the durability and efficiency of the unit. The thickness of the plates can vary from 0.4 to 1.0 mm depending on the model. In the working position, the plates are firmly pressed against each other. In this case, small slit channels are formed. On the front side there is a special groove, there is installed a rubber gasket (sealant). In addition, the gaskets have holes that are necessary for the supply and discharge of liquid. In the case of a breakthrough of one of the holes, a system of drainage grooves is provided, which eliminates the mixing of cold and hot media.

By creating a countercurrent between the two media, it was possible to achieve not only an improvement in the temperature set, but also a faster heat transfer with relatively small hydraulic resistances. It will not be superfluous to say that the basic principle of operation is based on countercurrent, that is, the movement of the heating and heating liquid in different directions. To avoid mixing, a double rubber seal or a metal plate is installed. The number of plates and channels may differ depending on the operational requirements for the equipment. Before the creation, the thermal calculation of heat exchangers is carried out, which allows to determine the optimum operating mode. Sometimes expensive alloys are used, which are not afraid of prolonged use in an aggressive environment.

Plate-fin heat exchangers

PRTs are used to transfer heat in non-corrosive and gas environments over a wide range of temperatures, from -270 to +200 degrees Celsius. The pressure in the system can reach 100 atmospheres and start with a vacuum. In the design is the idea of applying a ribbed surface on both sides of the plates. The product itself consists of several ribs, due to which the heat transfer between media is realized. It is worth noting that it is the ribbed-plate heat exchanger that has a wide variety of rib shapes. This allows several to change the operational and technical characteristics. Most often you can see continuous and undulating ribs. But besides these, there are also more exotic, such as perforated and scaly ones. As a material, thin-sheet metals are usually used. Their thickness is adjustable depending on the pressure in the system and the fluid used.

Often such types of heat exchangers are manufactured with different types of flow motion . The counter-current is most often used, but there are both direct-flow and cross-flow schemes. If we briefly talk about the strengths of such equipment, there are a lot of them. First, these are operational properties, such as fast and intensive heat exchange. Secondly, this is a small size. Today, many people say that it is the finned heat exchangers that are the most perfect. Most often, PRTs are used in such industries as energy, oil refining, chemical and aviation industries. All this is due to a large number of advantages, as well as a wide range of used liquids and pressures in the system.

Shell-and-tube heat exchanger: design and features

Heat exchanging equipment of surface type, which we have already considered, is not as popular as shell and tube units. This is precisely the apparatus, which was said at the very beginning, in the simplest version - the "pipe in the pipe" system. A heat exchanger of this type is a system (bundle) of tubes that are placed in a casing. Tubes are rolled and welded to the body of the article. In some cases, they are additionally scalded. This is done to ensure 100% tightness. The body is supplied with additional nozzles. Some are needed for steam supply, others for condensate drain. In addition, the body has transverse grilles, which are used to support heat exchange tubes along the entire length of the unit. Interestingly, shell-and-tube heat exchangers are used at temperatures of 190 degrees Celsius or saturated steam pressures of more than 15 bar.

Any system that implies fluid movement may be subject to water hammering. This phenomenon can partially or completely remove the equipment from the working state. To prevent this from happening, different kinds of storage elements are used, so-called expansion tanks. But in our case this is not necessary, because the shell-and-tube heat exchangers are very stable to them. In addition, there are no stringent requirements for cleanliness of the environment. A significant disadvantage of such equipment is that all types of heat exchangers of this type are very metal consuming, which affects the final cost and dimensions.

Heat exchangers for gas equipment

It's no secret that any solid fuel or gas boiler has a heat exchanger in its design, they are also called calorifiers. The main species we have already considered. As you probably noticed, these or other types are used in various industries. Some devices have found wider application, others are used in certain industries and do not fit into others. In our case, tubular and plate heat exchangers are used. In the first case we are dealing with a system of tubes, in the second - plates. In principle, regardless of the type, the heat exchanger for the gas column must meet a number of requirements. First, to have a high coefficient of heat transfer, and second, to be durable and resistant to high temperatures. The most popular materials are copper, aluminum and steel. The latter option is less preferable, since such a metal has a large weight, which lowers the efficiency. In any case, the heat exchanger for the gas column should serve no less than 5 years.

Conclusion

So we looked at the main types of heat exchangers with you. Without attention there were such species as shell-and-plate. In principle, they differ slightly from the classical lamellar or ribbed. But it is not uncommon to find stoves for a bath with a heat exchanger having a casing. However, the key feature is that the equipment is resistant to high temperatures and operating pressures. The body can be made of materials such as titanium, stainless steel or carbon steel. Interestingly, the furnaces for a bath with a shell-plate heat exchanger are well regulated by steam or condensate, which is undoubtedly a weighty advantage. In principle, this can end the story, since now you know about the heat exchangers all you need.