What is a heat exchanger: the principle of operation
In this article we will talk about what a heat exchanger is. The definition of the term will be given, questions about the role of these devices in human life will be considered, the species diversity and some comparative data are given. Also, attention will be paid to the value of the heat exchanger in cars and how to replace it.
What is a heat exchanger? Answering this question, you can define it as a device or technology, within which the phenomenon of heat exchange occurs between 2 environments with different indicators of the temperature state.
In accordance with the principle of operation, heat exchangers can be divided into 2 types:
In a heat exchanger, moving heat carriers are separated by a wall. This includes the predominant number of heat exchangers with the most different types of design. The group of regenerative devices includes heat exchangers, in which coolants in the hot and cold state are alternately in direct contact with one common surface.Heat begins to accumulate in the wall if it is in contact with a hot heat carrier and can be released during contact with a cold one. An example would be a cooper blast furnace.
Answering the question of what a heat exchanger is, it is worth mentioning its scope. First of all, they are important in the technological process of oil refining, as well as in petrochemical, chemical, nuclear, refrigeration, gas, etc., branches of human industrial activity. Energy and utilities are also not without them.
Dependence of conditions and design
Answering the question what a heat exchanger is, it will be important to mention the dependence of its design on the conditions in which it is applied.
There are devices that can include not only the process of heat exchange, but also a number of related phenomena. An example is the phase transformation during which one can observe condensation, evaporation, and mixing. These devices have their own names: condenser, cooling tower, evaporator, mixing condenser.
In accordance with the direction of motion, heat carriers of recuperative type can be divided into straight-flow, in the case of parallel movement in one direction, and countercurrent.In the latter, when following a parallel counter-movement, there is also observed a mutual transverse movement of 2 media that interact with each other.
Types of heat exchangers. Shell and tube heat exchangers
In several points we will consider a brief description of various types of heat exchangers.
Shell-and-tube heat exchangers are characterized by the presence of pipes that are welded to the end. They are fixed bunches of other pipes. Most often, they are fixed by flaring, but the methods are most often dependent on the material. The tube rack is endowed with lockable gaskets, bolts and / or studs. The housing is equipped with fittings, through which one of the coolants makes its way through the space between the tubes. The 2nd heat carrier moves through pipes through the pipe. Multi-pass heat exchangers are equipped with a cover in the case and a number of partitions that increase the speed of movement of the carrier of heat. The increase in heat transfer is improved by the finned tubes for heat exchange.
The elemental heat exchanger includes a number of components, which are presented in the form of the simplest shell-and-tube heat exchangers, but with no partitions. The design itself is rather heavy and bulky.
A submerged coil heat exchanger is characterized by the movement of coolants along a coil, which is immersed in the space of a tank with another heat carrier in liquid form. Most often they are used in small installations, and the device itself is quite cheap and easy to use.
Main designs of heat exchangers
The pipe in the pipe is a heat exchanger in which all the individual components are connected by means of pipes and rolls. As a result, an integral system of the mechanism is formed. Most often they are exploited in the presence of high pressure.
Irrigation heat exchanger - a type of device that is most often used as a condenser in the manufacture of cooling systems. This is a coil formed by horizontal pipes placed in a vertically spaced plane. They form a plurality of sections arranged in parallel with respect to each other.Each row is equipped with a chute, which squeezes out a stream of cooling water to the heat exchange row of pipes. Part of the liquid evaporates, and the other is pumped out by pumps.
Graphite heat exchanger is a type of device used in a chemically aggressive environment. Most often they are made of graphite blocks impregnated with special resins. The unit is equipped with a channel for the carrier of heat. Sealing blocks occurs through the use of gaskets of various materials.
Plate-type heat exchangers are formed by a set of plates that were originally stamped to create a wavy surface. They are endowed with a number of channels through which fluid flows. This heat exchanger is extremely easy to manufacture and / or modify. It is easy to clean and has a high heat transfer coefficient, but it cannot be used under high pressure.
Modifications of heat exchangers
Plate-type heat exchangers have a number of common parameters with plate-type apparatus, but their separation plate system includes a set of ribbed surfaces — nozzles that are attached to the plate itself by applying the method of soldering in vacuum space.On the sides are the limiting bars designed to support the plate. In other words, this matrix is based on a matrix that is integrally welded, as well as extremely strong and rigid. It is built in the similarity of the cellular principle, and its performance can be maintained in conditions of up to hundreds of atm. and even higher. A variety of nozzles have been developed for such devices, allowing to select the channel geometry for any flows and needs. The main advantage of such devices is their compactness.
The finned-plate heat exchanger is formed of thin-walled finned panels, which are created using high-frequency welding, and they are connected alternately with a turn of ninety degrees. Most often they are used in the course of heat recovery from the exhaust gas.
The spiral heat exchanger includes 2 spiral tubules that wind around the partition located in the center. To create the coils using roll material. The main purpose is to cool and heat liquids with a high viscosity index.
Some comparative data
When choosing to use a plate or shell-and-tube heat exchanger, more often people choose the first ones, since their heat transfer coefficient is much higher than that of a traditional shell-and-tube apparatus. In addition, plate devices have a smaller area.
Plate-type heat exchangers, manufactured abroad, are equipped with a number of tools that allow them to work in automatic mode through initial adjustment and regulation, and they are also equipped with robust fittings. In such devices decreases the amount of coolant that is consumed to heat water. Consequently, this allows you to reduce the load on the network set of pumps, as well as reduce the amount of energy that they consume.
Currently, with increasing popularity are beginning to produce and use helicoid heat exchangers. Their feature is the profiling of the tubes. It is done in order to increase the resistance of the hydraulic nature could exceed the increase in heat transfer in the case of the use of turbulence in the flow. This device is quite cheap compared to foreign models.and its quality is very high. To protect the mechanism from corrosion, gas-thermal spraying is used for each tube plate.
The three heat exchangers mentioned in this paragraph are made, as a rule, through the use of steel with a high rate of corrosion resistance and heat resistance. However, despite the operation of such materials, the structural components of heat exchangers can still be subject to pitting-type corrosion.
The cooling system, which is responsible for the process of heat exchange in the car, is a multifunctional means of temperature control. In a machine, there may be several such systems, but in general they are all responsible for controlling the same phenomenon, only in different areas of transport. An example is the heating of air in a heating or ventilation system, the cooling of oils inside the system, which is responsible for lubrication, the engine heat exchanger is engaged in its cooling. There is also a system responsible for reducing the temperature in a turbocharger, etc.
Automotive heat exchangers principle of operation may differ among themselves, which is caused by the characteristics of the system itself. On the car most often used liquid cooling devices.Their advantage lies in the fact that they allow to evenly reduce the temperature of the motor and have low noise performance. If we talk about the cooling system of the engine as a whole, it includes a huge number of parts, including: an oil-type radiator, a heating heat exchanger, a centrifugal pump, a thermostat, a radiator for reducing the temperature of liquids, and an expansion tank.
Flushing the heat exchanger is an important process that should be performed regularly, otherwise untimely cleaning it can lead to problems in the operation of the engine. However, this, in particular, is applicable to a specific fragment of the overall system of thermoregulation of the machine, namely to the radiator.
The normal operation of the cooling system designed to cool the engine cannot last forever. To ensure the health it is necessary to regularly carry out preventive manipulations. A radiator is a device that is subjected to frequent and heavy exposure to dirt and dust. Therefore, it is necessary to perform periodic flushing of the heat exchanger.
The cause of frequent overheating of the car may be the presence of failures in the radiator. Depending on whether it has become broken or polluted, this problem can be solved in two appropriate ways:
- Purchase a new device in the store.
- Rinse the heat exchanger and clean it.
To clean the radiator from the inside, you must first remove the antifreeze from it by draining. It is important to remember that if the substance is pure, then this process is not necessary. If the liquid is contaminated, then water without impurities should be poured into the cooling system. Next, you need to start the car and allow it to work for 15-25 minutes, and then the water should be drained. The operation is carried out repeatedly until the liquid is clear.
Rinse the heat exchanger thoroughly. Enhancing the effect can be achieved by using a liquid with the addition of special cleaning agents. However, you should not resort to abuse of them, because a couple of grams is enough. The use of an excessive amount of cleaning agents can damage the cooling system.
After the automobile heat exchanger has been washed, water is again drained from it with an admixture of detergent and it is poured clean and the procedure is repeated at least five times. Poor removal of residual detergent components may adversely affect the radiator and lead to the formation of corrosion. To avoid scaling, a variety of additives are poured into the antifreeze fluid, which are endowed with anti-corrosion and lubricating properties. They prevent the formation of rust, as well as other types of deposits inside the radiator.
One should not forget that driving outside the radiator, for example, with down, wool or dust, can also lead to overheating of the automobile engine. To solve this problem, a method of blowing through a heat exchanger is usually used. First, it is separated from the car, and then through the use of conventional mini-sinks or a simple water jet under pressure, washed and rinsed. Do not forget that the use of excessive pressure force can damage the radiator. Try to dispense with the use of chemicals that include corrosive acid constituents.
At the final stage of cleaning, it is necessary to change the liquid for cooling and extract excess air from the system space. Air may form during the pouring of antifreeze. This process can be done by opening the radiator cap, and then you just need to start the engine for a while (about a couple of minutes). After the plugs formed by air leave the internal system of the device, add antifreeze and put the cover back in place, securing it tightly.
The difficulty of replacing parts inside the car
The purpose of the automotive heat exchanger is also in the overall air conditioning system of the machine. In this case, he is responsible for the process of thermoregulation of air in the cabin space. This is mainly a passive part without any subtleties; it is already more difficult to change it than to remove a radiator. Its location is between the panel with the instruments and the partition, and outwardly it resembles a radiator, but with a missing neck. There are various forms of this part, but replacing a heat exchanger is usually not particularly difficult.It is important to be careful in this case, since water circulates in the system of such a device to which antifreeze can be added - a rather toxic substance.
Find a new heat exchanger on the "Opel-Astra" or on any other car is quite simple: the network has a huge number of online stores that provide services for the sale of spare parts. They can choose the required model and type of device, and then just place an order.
To find, for example, a used Astra heat exchanger, you can also contact the disassembly points of the corresponding machine model. Here, a person is given the independent right to choose the required model, directly live. You can buy it immediately or order it. Since heat exchangers and other parts are used for such disassembly, this will save you money in case of an acute shortage of capital. Do not neglect this service, as you can often find the original spare part, not inferior to the new one.
Currently, auto dismantling points are simultaneously engaged in a large number of services for various brands of vehicles, so here you can always find a heat exchanger on Chevrolet, Lada, Peugeot, etc.Most often, these points can be found in the location of a private workshop, garages, a number of warehouses and hangars. Buying such a device in the company store will cost more, but also eliminates the chance of buying low-quality products. However, regardless of your choice of place of purchase, it is better to provide a replacement for specialists. Especially if you are not confident in your own strength and sufficient skill development. Regardless of whether you need to put or change the heat exchanger on an Opel or Ford, in specialized workshops you will help solve this problem quickly and efficiently.
A couple of words about laying
Replacing the heat exchanger on your own car can sometimes not be done. It depends on what exactly the problem.
If the car has an unpleasant smell after driving on roads, and especially on wet asphalt or covered with reagents, then you should pay attention to the possible leakage of the internal gasket located on the side of the catcollector. There you can find a large layer of dirt and oils. If there is no emulsion under the valve cover, this indicates the flow of oil into the antifreeze, and only in one direction.This is an equivalent phenomenon for most brands of cars, starting with Daewoo and ending with Opel. Heat exchanger gaskets must also be replaced. It is not always necessary to resort to extreme measures to remove it and install a new one, because sometimes it will be enough just to change the gasket itself.