The working principle of heat exchanger is that heat is transferred from high temperature end to low temperature end.

Each tube in the tube side of the U-tube heat exchanger is bent into a U-shape, both ends of the tube are installed on both sides of the same fixed tube plate, and the head is divided into two chambers by a partition plate, and each tube can automatically shrink, regardless of other tubes and shells.

Even when the temperature difference between the shell and the pipe is a, the U-tube heat exchanger is usually used to cool high-temperature gas with circulating water in actual production. After the tubes of the heat exchanger are corroded or leaked, only the core can be replaced, but it is not suitable for cleaning.

U-tube manometer is the oldest pressure measuring instrument. It belongs to absolute vacuum gauge in vacuum measurement and can be used as vacuum measurement standard. Its typical principle structure is shown in the right figure. It consists of two measuring tubes. By measuring the height difference H of the working liquid column in the pipe, the value of the pressure P to be measured can be calculated. One side of the liquid column needs to be evacuated, so that the pressure P0 on it can be compared with the pressure P to be measured.

Ignoring, the accuracy and lower limit of this pressure gauge mainly depend on how to measure the height difference H of the liquid cylinder and the accuracy of measuring H, as well as the density of the working liquid. There are many methods to measure H, such as direct measurement with scale, altimeter, point contact micrometer and optical interferometry. Among them, interferometry has the highest accuracy.

Mercury was first used as working liquid, but in order to extend to low pressure range in vacuum measurement, oil with low saturated vapor pressure, low density and low viscosity is also commonly used. This manometer can measure low vacuum and medium vacuum.

What is the working principle of tube heat exchanger?

Tubular heat exchanger is also called shell-and-tube heat exchanger and tubular heat exchanger. The working principle of tubular heat exchanger is as follows:

Shell-and-tube heat exchanger is composed of multiple layers of materials with good thermal conductivity, and its working principle is similar to that of water heater.

The water heater generates heat through gas, and the heat exchanger generates heat through media other than naked flame. There are two pipeline loops in the heat exchanger, one is the heat source and the other is the heated source, just like the flame of hot water or steam when the water heater burns.

A heat source is like hot water in a water heater. There is also a regulating valve in front of the heat source inlet of the heat exchanger in the heat source loop, and the temperature of the heated source can be adjusted by changing the opening of this valve.

Tubular heat exchanger is the most typical baffle heat exchanger, which has a long history of industrial application and still occupies a dominant position in all heat exchangers. Tubular heat exchanger is mainly composed of shell, tube bundle, tube sheet and head. The shell is mostly round, with parallel tube bundles inside, and both ends of the tube bundles are fixed on the tube sheet.

References:

Baidu encyclopedia? Introduction of tubular heat exchanger

Working principle of heat exchanger

Principle: The compressor compresses the refrigerant into high-pressure saturated gas, which is condensed by the condenser.

After being throttled by the throttling device, it enters the evaporator for cooling and exchanges heat with the cooled medium. For example, if the evaporator is connected to all rooms in the building, the serpentine tube in the evaporator exchanges heat with the air, and then the cold air is blown into the air in the room by blowing air.

The refrigerant in the serpentine tube of the evaporator changes into low-pressure steam after heat exchange and returns to the compressor, and then is compressed by the compressor, thus completing the refrigeration system in a reciprocating manner.

The principle of heating and refrigeration is the same, both of which are reverse Carnot cycle, but different from refrigeration principle is the exchange of condenser and evaporator, that is, compressor-evaporator-throttle device-condenser.

Extended data:

Characteristics of heat-sensitive sensing heat exchanger unit

1, heat transfer is fast and efficient, and the heat transfer efficiency can reach 100%.

2. All condensed water is recycled, and the whole system is self-cleaning and anti-scaling. The heat exchanger, radiator and heat exchange system of the invention can maintain long-term, stable and efficient heat exchange performance, minimize the scaling phenomenon of the system, and will not reduce the heat exchange efficiency of the system due to insurmountable scaling disadvantages.

3. The heat exchanger is made of all stainless steel, with scientific product structure design, excellent technology and long service life, which can reach more than 20 years.

4. The key components are processed by German advanced technology and order, and the main engine is not affected by steam pressure and system pressure, effectively eliminating noise and steam hammer, and the whole machine runs smoothly.

5. The condensed water is completely absorbed and utilized, and there is no special reason for the system, so there is no need to set up a water replenishing device, which greatly saves the water consumption and operating cost of the system.

6. The whole unit is compact in structure and occupies a small area, which greatly saves the civil engineering investment. At the same time, due to the high heat exchange efficiency, there is no need to make up water when the system is running, and the whole unit is a trinity of steam, electricity and water saving, creating considerable energy-saving benefits for users.

7. The unit has highly intelligent automatic control function, which can realize overpressure and overtemperature protection, automatically cut off steam in case of power failure, automatically compensate outdoor temperature, and realize remote monitoring, providing users with a safe and secure operation platform.

8. It has a wide range of applications, and can be widely used for heating, hot water bathing and other purposes in the fields of thermoelectric, factories and mines, food and medical care, mechanical light industry, civil buildings and so on.

9. Wide application conditions, which can be used for heat exchange in a large pressure and temperature range.

References:

Baidu encyclopedia-heat exchanger

Schematic diagram and classification of tubular heat exchanger

With the deepening of people's understanding of heat energy, the demand is increasing, and many people often hear and see such a thing-heat exchanger in their work or life. Heat exchanger refers to a device that transfers heat energy from hot fluid to cold fluid to meet the specified process requirements. It is an industrial application of heat transfer and heat conduction. Simply put, it is a relatively sealed container with a large internal contact surface. Household heat exchangers are more common, so let's talk about tube heat exchangers widely used in industrial fields today.

basic concept

Two fluids that exchange heat in a tube heat exchanger, one flows in the tube, and its stroke is called tube side; A kind of flow outside the tube, its stroke is called shell side. The wall surface of the tube bundle is the heat transfer surface. In order to improve the heat transfer coefficient of the fluid outside the tube, a certain number of transverse baffles are usually installed in the shell. Baffles can not only prevent the fluid from short circuit and improve the fluid velocity, but also force the fluid to pass through the tube bundle many times according to the specified path, which greatly increases the turbulence. There are two kinds of baffles commonly used: circular notch and disk, and the former is more widely used.

Every time the fluid passes through the tube bundle in the tube, it is called tube side, and every time it passes through the shell, it is called shell side. In order to improve the flow velocity of the fluid in the pipe, appropriate baffles can be set in the heads at both ends to divide all the pipes into several groups equally. In this way, the fluid can only pass through some tubes and return to the tube bundle many times at a time, which is called multi-tube pass. Similarly, in order to improve the flow velocity outside the tube, longitudinal baffles can be installed in the shell to make the fluid pass through the shell space many times, which is called multi-shell pass. In tube heat exchanger, the temperature of shell and tube bundle is different because of the different fluid temperatures inside and outside the tube.

Basic classification

fixed tube sheet

The fixed tubesheet heat exchanger is to weld the tubesheets at both ends directly with the shell. It is mainly composed of shell, tubesheet, tube bundle, head and other main components. A tube bundle is arranged in the shell, both ends of the tube bundle are fixed on the tube sheet by welding, expansion joint or expansion joint, and the periphery of the tube sheet is fastened with the flange of the head by bolts. The fixed tube-plate heat exchanger has the advantages of simple structure, low cost, easy manufacture and convenient cleaning and maintenance of tube side, but it is difficult to clean the shell side, and there is temperature difference stress after the tube bundle is manufactured. When the temperature difference between the heat exchange tube and the shell is large, the shell should also be provided with an expansion joint.

Floating head type

The tubesheet at one end of the floating head heat exchanger is fixed between the shell and the tube box, and the tubesheet at the other end can move freely in the shell, that is, the thermal expansion of the shell and the tube bundle is free. So there is no temperature difference stress between the tube bundle and the shell. Generally, the floating head is detachable, and the tube bundle can be freely drawn out and loaded. This floating head heat exchanger structure can be used in the case of large temperature difference between tube bundle and shell. The cleaning and maintenance of tube bundle and shell are convenient, but their structures are relatively complex and require high sealing.

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U-tube heat exchanger is a U-tube with two ends fixed on the same tube plate. Because the shell and the heat exchange tube are separated, the heat exchange tube bundle can expand and contract freely, and there will be no temperature difference stress due to the temperature difference of the medium. The U-tube heat exchanger has only one tube plate and no floating head, and its structure is relatively simple. The tube bundle can be pulled out and put in freely, which is convenient for cleaning. It has the advantages of floating head heat exchanger. However, because the heat exchange tubes are made into U-bends with different radii, the outermost heat exchange tubes can be replaced after being damaged, and other tubes can only be blocked after being damaged. At the same time, compared with the fixed tube-plate heat exchanger, because the heat exchange tube is limited by the bending radius, there is a gap in the center of the tube bundle, and the fluid is easy to short circuit, which affects the heat transfer effect.

The above is the structural schematic diagram of tube heat exchangers commonly used in industry under classification and subdivision. The principle is simple, the design is complex, and the requirements of technology and materials are also high. The purpose is to improve the heat exchange efficiency of the heat exchanger. However, due to its special tubular structure, the fluid used in the process of use must contain some impurities, so it is difficult to clean it thoroughly. This has also caused a waste of resources, time and manpower for enterprises, and cleaning will be the main development direction in the future.