Heat exchanger (reprint)
Read the number：(3511) Time：2014/3/9 11:34:16
Heat exchanger (English translation: heat exchanger), is part of the heat transfer fluid to heat the cold fluid devices, also known as a heat exchanger. The heat exchanger is chemical, petroleum, power, food and many other common equipment in the industrial sector, plays an important role in production. In chemical production can be used as a heater heat exchangers, coolers, condensers, evaporators and reboilers, more widely. Many different types of heat exchangers, but according to the cold, the principles and methods of thermal fluid heat exchange is basically divided into three categories namely: partitions, hybrid and regenerative. In the three types of heat exchangers, heat exchanger applications up to partitions.
Material heat exchanger can be divided metal and ceramic heat exchanger.
Metal heat exchanger according to the structure can be divided into recuperative heat exchanger and mixed.
Ceramic heat exchanger according to the structure can be divided into single-loop and multi-loop heat exchanger
Metal heat exchanger classification
Recuperative heat exchanger type
This heat exchanger jacket is a jacket made from the container wall installation, simple structure; but it is limited by the heating surface of the container wall, the heat transfer coefficient is not high so as to improve the heat transfer coefficient and the kettle liquid. uniform heating can be installed in the kettle agitator when the jacket cooling water through heating or without phase change agent, may also be provided with helical baffles or other measures to increase the turbulence in the jacket to raise jacket side heat transfer coefficient. to supplement the heat transfer surface, the coil can also be installed inside the autoclave. jacketed heat exchanger is widely used for heating and cooling the reaction process.
Immersive this heat exchanger coil is wound into a metal tube bent container adapted to a variety of shapes and immersed in a container of liquid. Snake tube heat exchanger has the advantage of simple structure, can withstand high pressure, manufacture of corrosion resistant materials available; drawback is the low level of liquid in the container turbulence, heat transfer coefficient small tube in order to improve the heat transfer coefficient can be installed blender container.
This spray heat exchanger tubes in a row is secured to the steel, hot fluid flow in the pipe, the cooling water uniformly poured from above the sprinkler, it is also known as spray cooler . spray heat exchanger tube is a high degree of turbulence layer film, tube heat transfer coefficient increased a lot over the immersive addition, most of this heat exchanger placed in ventilated place, cooling evaporation of water also take some heat, can serve to reduce the cooling water temperature, increasing the role of the heat transfer driving force, therefore, and immersive compared to the effect of spray heat exchanger is greatly improved.
Pipe heat exchanger tube heat exchanger is controlled by the diameter of the different straight into concentric tube, connected together by a U-shaped bend in such a heat exchanger, a fluid tube to go, and the other A fluid annulus walking, both can obtain a higher flow rate, the heat transfer coefficient is large. Further, in the tube heat exchanger, the two fluids may be pure countercurrent on average larger driving force. Tube heat exchanger simple structure that can withstand high pressure, applied also to facilitate (the number of pipe sections can be adjusted according to need), especially due to the heat exchanger tube along with the heat transfer coefficient, heat transfer driving force big and strong to withstand high pressure advantages in the production of high pressure process (e.g., an operating pressure of 3000 atm pressure polyethylene production process) used in almost all of the heat exchanger casing.
Shell and tube heat exchanger shell and tube (also known as the column tube) heat exchanger is the most typical recuperative heat exchanger, it is applied in industry has a long history, but still occupy all of the heat exchanger dominant position.
Shell and tube heat exchangers are mainly housing, tubes, tube plates and top sealing components, housing mostly round, interior fitted with parallel bundles, bundle fixed at both ends of the tube plate. Carried out in the heat exchanger shell and tube heat exchanger of the two fluids, a fluid in the tube, the tube is called its stroke; a flow in the tube, called the shell of its stroke. The wall is the heat transfer surface bundle. To improve the heat transfer coefficient outside the tube to the fluid, generally horizontal baffle mounted a number of baffles within the housing. Not only prevents fluid baffle baffle short circuit, increasing fluid velocity, but also the path many times as required to force fluid through the tube bundle cross-flow, so that greatly increased the degree of turbulence. Lack of common baffle shape and a round disc-shaped two, the former is more widely applied. Fluid in the tube bundle every once called by a tube, called a shell every time through the housing. In order to improve the speed of the fluid within the tube, you can set the appropriate partition in the head at both ends, the average of all the tubes are separated into several groups. Thus, the fluid can be a time through a portion of the tube bundle and the round-trip times, called multi-tube. Similarly, in order to improve the tube velocity, the fluid can be mounted vertical baffles many times through the shell space within the housing, said the multi-shell. In a shell and tube heat exchanger, due to the different fluid temperature inside and outside the tube, shell and tube bundle temperatures are also different. Such as a large temperature difference between the two, the internal heat exchanger will be a big thermal stress, the tube may be bent or broken from the tube panel. Therefore, when the temperature difference exceeds bundle and the housing 50 ℃, the temperature difference between the compensation should take appropriate measures to eliminate or reduce the thermal stress.
Mixed heat exchanger
Hybrid heat exchanger is to rely on cold and hot heat transfer fluid by direct contact, this way avoiding the heat transfer on both sides of the partition and fouling resistance, the contact between the case as long as the fluid is good, there is a greater The heat transfer rate. Where the fluid is mixed with each other to allow the case, can be mixed heat exchanger, such as washing and cooling gas circulating cooling water, steam - water between the mixing and heating, steam condensation and the like. Its applications throughout the chemical and metallurgical enterprises, power engineering, air-conditioning engineering, and many other production sectors.
According to different uses, hybrid heat exchangers can be divided into the following types:
(1) cooling tower (or cooling tower)
In such a device, with natural or mechanical ventilation method, the production has increased water temperatures cool down cycle after use, in order to improve the economic efficiency of the system. Such as thermal power plants or nuclear power plant circulating water, ammonia production in the cooling water, cooling tower water after cooling recycled, this approach works in practice has been widely used.
(2) a gas scrubber (or scrubber)
The device used in industry for various purposes to wash the gas, for example, the liquid absorbing certain components of the gas mixture, the gas Ex dust, or the drying gas is humidified. But it is most widely used to cool the gas, and the cooling water used in the majority of the liquid. Spray chamber is widely used in air conditioning works, it can be considered a special form. Not only can spray chamber as the gas scrubber as the cooling air, but also its heat treatment. However, it also has high requirements for water quality, large area, multi-pump energy, etc. Cons: So, now in the general building, spray chamber has been infrequently used, or only as a humidifying device. However, in order to adjust the humidity for the main purpose of the textile mills, cigarette factory, are still a lot of use!
(3) the injection heat exchanger
In this apparatus, so that the higher pressure fluid discharged from the nozzle, forming a high velocity, low pressure fluid is introduced into the mixing chamber in direct contact with the heat jet, and together into the diffusion tube at the outlet of the diffuser to achieve to give users the same pressure and temperature.
(4) Hybrid condenser
This device is generally the method of direct contact with water and steam condensing the steam.
Regenerative heat exchanger
Regenerative heat exchanger is used for regenerative heat exchanger equipment. The solid filler contents, the storage reservoir for heat. General fire with bricks and other brick lattice (sometimes with a metal wave band, etc.). Heat two stages. The first stage, the hot gases through fire plaid, plaid fire and heat to build up the reservoir. The second stage cooling gas passes through the fire grate, receiving the fire grate is heated by the heat savings. These two stages alternately. Two generally used interchangeably with the accumulator, i.e., when the device enters a hot gas, cold gas into another device. Commonly used in the metallurgical industry, such as open-hearth steelmaking regenerator. Also used in the chemical industry, such as gas furnace or combustion air preheater, artificial petroleum plant regenerative cracking furnace.
Regenerative heat exchangers are generally used for medium mixing requires relatively low occasions.
Ceramic heat exchanger
Ceramic heat exchanger tube is a new high-temperature heat recovery unit, the main ingredients of silicon carbide can be widely used in metallurgy, machinery, building materials, chemical industry, the direct recovery of industrial kilns emissions 850-1400 ℃ high-temperature waste heat in order to get high-temperature combustion air or process gas.
A heat transfer element material system developed into new engineering ceramic carbide such apparatus, and which has excellent thermal shock resistance temperature, cooled to room temperature from 1000 ℃, over repeated 50 times without cracks; thermal conductivity and stainless steel equivalent; having good oxidation and corrosion resistance in an acidic medium. In the structure successfully solved thermal compensation and a better solution to the problem of gas seal. The device is a high heat transfer efficiency, energy-saving effect is remarkable to preheat combustion air or heating process gas of certain processes, primary energy savings, fuel savings up to 30% -55%, and strengthen the process, significantly improving production capacity.
Production process and kiln production process is basically the same ceramic heat exchangers, thermal conductivity and oxidation resistance are the main application performance materials. Its principle is to be placed in a ceramic heat exchanger flue outlet close, the temperature is high, no mixed cold and high temperature protection, when the furnace temperature 1250-1450 ℃, the flue outlet temperature should be 1000 - 1300 ℃, ceramic heat recovery heat exchanger can reach 450-750 ℃, the recycling of hot air into the furnace and the combustion gas mixture formation, which directly reduce production costs and increase economic efficiency.
Ceramic heat exchanger limitations in the use of metal heat exchanger has been very good development because it is a better solution to corrosion, high temperature and other topics. Its main advantages are: thermal performance, high temperature strength, oxidation resistance, good thermal shock resistance. Long life, small amount of maintenance, stable and reliable performance, easy operation.
Design requirements
With economic development, a variety of different types and kinds of heat exchangers developed rapidly, new structures, new materials, heat exchangers are emerging. In order to meet the needs of development, China's certain types of heat exchangers has established a standard, forming a series. Perfect heat exchanger meet the following basic requirements in the design or selection should:
(1) reasonably achieve the required process conditions;
(2) the structure is safe and reliable;
(3) ease of manufacture, installation, operation and maintenance;
(4) reasonable economy.
Floating head heat exchanger tube plate and the housing is fixed at one end and the other end of the tube sheet float freely within the housing, the housing and control of the expansion is free, so when large temperature difference between the two media, discipline and no thermal stress between the housing. Floating terminal designed removable structure, the tubes can be easily inserted or withdrawn shell. (Also can be designed to not be demolished). Such as maintenance, cleaning provided for convenience only. However, the heat exchanger structure is more complex, and the floating end cap in the operation of small leaks can not know. So pay special attention to sealing during installation.
Floating Floating part of the structure of the heat exchanger, can be designed according to different requirements of a variety of forms, must be considered in addition bundles can move freely within the apparatus, but also must take into account the part of the floating head maintenance, cleaning and installation convenience.
Must be considered in the design of the outside diameter Do floating head tube sheet. The outer diameter of the housing should be less than the inner diameter Di, the floating head is generally recommended gap between the housing wall of the tube plate and b1 = 3 ~ 5mm. Thus, when the removal of floating head of the hook and loop, the bundle can be withdrawn from the housing. In order to carry out maintenance and cleaning. After the bundle into the floating head cover can be assembled, so that should be considered in the design of the floating head cover during assembly to ensure necessary space.
Hook and loop to ensure the floating head end sealed to prevent leakage between the string media plays an important role. With Fu head heat exchanger design and development of manufacturing technology, as well as in the form of accumulation, hook and loop structures have long experience has also been improved and perfected without segment.
Generally are off the hook and loop type structure, requiring reliable sealing, simple structure, compact, easy to manufacture and easy disassembly.
Floating head heat exchanger for its high reliability and wide adaptability, long-term use of the process has accumulated rich experience. Despite the challenges in recent years by the continuous emergence of new heat exchanger, but in turn also continue to promote their own development. So far in a variety of heat exchangers throw dominate.
Heat transfer surface of the heat exchanger tubes constituting the tube size and shape has a great influence on heat transfer. When using a small diameter tube, the heat exchanger heat transfer area per unit volume of larger, more compact equipment, less consumption per unit of heat transfer area of the metal, the heat transfer coefficient is higher. But trouble, pipes easy to scale, easy to clean. Large diameter pipe for the large fluid or viscous dirty, for a small diameter pipe cleaner fluid.
Select the pipe material shall be determined according to media pressure, temperature and corrosive.
Tube heat exchanger tubes are arranged in the board to consider not only the compact equipment, but also taking into account the nature of the fluids, structural design and manufacturing aspects. Tubes arranged in the standard form of the tube plate there are four: the corner of an equilateral triangle and triangle arranged for the media and the shell clean, and does not require mechanical cleaning of the occasion. Square and corner squares arranged, enabling the bridge between the tubes form a straight line path, easy to use mechanical cleaning, generally used for cleaning tube bundle can be drawn between the occasion.
In addition to the multi-tube heat exchanger, often using a combination of permutation method, each process is generally triangular arrangement, but the process is often used between a square arrangement, it is easy to arrange bulkhead position.
When the heat exchanger larger diameter pipe is large, must try to configure the tubes in a bundle around the arched space. This can not only increase the effective heat transfer area can be prevented from short-circuiting in the shell side fluid in the arcuate region to adversely affect heat transfer.
Select tubes tube plate center distance is necessary to consider the compact, heat transfer structure, but also consider the strength of the tube plate and the outer surface of the tube cleaning space required. In addition, consider the tubes in the tube plate fixation. If the spacing is too small, when using welded connections, weld two pipes adjacent too, easily affected by heat weld quality is assured; If using Expansion, extrusion pressure may cause large deformation tube plate happened, lose binding force between the tube and the tube sheet. Centre tubes are generally used at not less than 1.25 times the pipe diameter.
When the heat exchanger required more than the larger, but do not be too long when the tube, you have to increase the diameter of the shell, to arrange more tubes. At this point the tube in order to improve the flow rate, increasing the heat transfer effect, shall bundle of processes, so that the fluid flows through the tubes of each process.
In order to make multi-tube heat exchangers, respectively, a number of spacers arranged in one or both ends of the tube in the tank.
Advantages and disadvantages of floating head heat exchanger
Advantages:
(1) bundle can be withdrawn in order to facilitate cleaning tube, shell;
Room (2) medium temperature difference unrestricted;
(3) can be operated at high temperature, generally a temperature less than or equal to 450 degrees, pressure is 6.4 MPa or less;
(4) can be used to scale the more serious occasions;
(5) can be used for tube corrosive applications.
Disadvantages:
(1) Small Floating prone to leakage;
(2) Metal material consumption, high cost of 20%;
(3) complex
Manufacturing process
Select the material and heat exchange equipment for the manufacture grades tested for the chemical composition of the material, the mechanical properties of the passing of the orthopedic plate, comprising orthopedic manual, mechanical and flame orthopedic orthopedic.
Preparation - dash - cutting - edge processing (testing) - Forming - set on - Welding - Welding Quality Inspection - assembly and welding - Pressure test
Quality Inspection
Not only in the manufacture of chemical equipment prior to inspection of raw materials, but also in the manufacturing process should always be checked.
Quality Content
Equipment manufacturing process inspection, including inspection, testing and stress testing processes between raw materials, as follows:
(1) Raw materials and testing equipment part size and geometry;
(2) materials and weld chemical composition analysis, mechanical property test analysis, microstructure examination, referred destructive testing;
(3) Raw materials and weld defects in internal testing, the test method is non-destructive testing, which includes:-ray inspection, ultrasonic testing, magnetic particle testing, penetration testing;
(4) pressure test equipment, including: pressure test, test medium, air tightness testing.
Pressure test and leak test:
Manufacture of finished heat exchanger tube plate to deal with connectors, tube and shell pressure test or increased air tightness test, hydrostatic pressure test, including test and pressure test. Heat exchanger pressure test generally, but due to structural or support reasons, not filling liquid or liquid residue test conditions were not running, can be pressure tested.
If the media is extremely toxic, highly hazardous or tubes, have allowed to trace the leak between the shell, you must increase the air tightness test.
Quality control methods
Heat exchanger pressure test sequence is as follows:
Fixed tube sheet heat exchanger shell first pressure test conducted while checking tubes and tube plate connectors, and then pressure test tube;
U-tube heat exchanger, kettle reboiler (U-shaped tubes) and packing function first with a test pressure of the heat exchanger shell ring pressure test, check the connectors at the same time, and then pressure test tube;
Floating head heat exchanger, kettle reboiler (floating head bundles) first with a test pressure ring and special tools for tube head floating head pressure test, for kettle reboiler tube head shall also be equipped with a special casing pressure test, then pressure test tube, and finally the shell pressure test;
Overlapping joints exchanger pressure test may be single, when inter-process communication with heat exchangers, the tube and shell pressure test should be carried out after the overlap assembly.
Installation
Basic installation of the heat exchanger must be met in order to make the heat sink does not occur, or to excessive deformation of the pipe to spread the heat's over. Base is generally divided into two types: one for the brick foundation saddle, saddle no bearing on the heat directly on the saddle on the basis of the heat exchanger and without a fixed base, may be needed as the thermal expansion move freely. Another concrete foundation, through the heat exchanger by a bolt saddle supports it firmly connected with the foundation.
Before installing the heat exchanger should be the basis of strict quality inspection and acceptance of work, the main items as follows: base surface profiles; basic level, flat position, shape and size, and set aside the main hole meets the practical requirements; bolt position is correct, whether good screw, nuts and washers are complete; whether the underlying surface of the horn is placed flat and so on.
After basic inspection is completed, before installing the heat exchanger placed on the foundation horn, horn placed at the base surface must be leveled, so that the two can be a good touch. Horn thickness can be adjusted so that the height of the heat exchanger to reach the level of the design. After placing the horn to increase the stability of the heat exchanger on the basis of the weight and uniformly transmitted through the horn to the base up. Horn can be divided into flat horn, horn and oblique opening horn. Among them, the oblique horn must be used in pairs. Both sides of the bolt should have horns, horn installation should not interfere with the thermal expansion of the heat exchanger.
After the heat exchanger in place a level of heat required leveling, so that each can take over the case could not force the connection pipe. After leveling, oblique horn with Chi seat weld, but not with the following welded flat horn or skateboard. When two or more overlapping heat exchanger is installed, you should look for are completed in the lower heat exchanger, and the bolt fully fixed, and then install the upper heat exchanger. Can be pumped heat exchanger tube bundles should be installed before pumping core inspection, cleaning, should draw attention to the protection tubes and baffles the sealing surface. When lifting and moving the bundle of tubes is placed on a dedicated support structure to avoid damage to the heat transfer tubes.
According to the form of heat, sufficient space should be left at both ends of the heat exchanger to satisfy the conditions (operating) cleaning and maintenance needs. Fixed Floating bonnet side heat exchanger should be sufficient space to pull out from the casing tubes, outer bonnet client must also set aside more than a meter in position to dismantle the outer bonnet and floating cover.
Fixed at both ends of the tube plate heat exchanger should leave enough space in order to extract and replace the pipe. Also, when using mechanical methods to clean the pipe. Both ends of the tube can scrub operation. U-tube heat exchanger fixed bonnet should leave enough space to pull out tubes, but also leave enough space at its opposite end in order to disassemble the casing.
Heat exchanger shall be run under specified conditions over the plate. Should always be on the tube, shell medium temperature and pressure drop supervise, analyze tubes leaks and fouling. Shell and tube heat exchanger tubes is to use it outside the heat exchange materials, cooling, condensation and evaporation processes such as heating, compared with other devices, the surface area in contact with the rest of the corrosive medium, it is very large, corrosion perforation junction relaxation at high risk of leakage, so the heat exchanger corrosion and leak prevention methods are also considered to be more than any other device, when heated by steam or heat exchangers used to cool the water, the solutes in the water after heating, Most are increased solubility, and the type of material the calcium sulphate is almost no change. Circulating cooling water is often used due to the evaporation of water, so that salt concentration, or the deposition of dirt. Because the water contains dissolved gases and corrosive chlorine ions cause equipment corrosion, corrosion and fouling alternately, intensified the corrosion of steel. Must be cleaned to improve the performance of the heat exchanger. Due to the difficulty of cleaning the dirt layer thickness increases or deposit increases rapidly, so the cleaning interval time not too long, you should regularly according to the characteristics of the production unit, the nature of heat transfer medium, the corrosion rate and operating cycle, etc. inspect, repair and cleaning.
Heat exchangers are widely used in daily life with the heating fins heating, steam turbine condenser unit and the oil cooler on space rockets are heat exchangers. It is also widely used in chemical, petroleum, power and nuclear industries. Its main function is to ensure that a specific process temperature required for the media, but also one of the main equipment to improve energy efficiency.
The heat exchanger can be a single device, such as heaters, coolers and condenser, etc.; also be a part of the process equipment, such as ammonia synthesis tower heat exchanger.
Due to limitations of the manufacturing process and the scientific level, the early heat only a simple structure, and a small heat transfer area, bulky and heavy, like a snake-tube heat exchanger. With the development of the manufacturing process, and gradually form a shell and tube heat exchanger, which not only has a larger unit volume heat transfer area and heat transfer effects are good, long time to become a typical change in industrial production heat.
Development History
1920s appear plate heat exchanger and used in the food industry. With plate heat exchanger made of escrow, compact structure, good heat transfer, thus gradually developed into various forms. The early 1930s, Sweden for the first time into a spiral plate heat exchanger. Then the British legal system create a brazing copper and its alloys made by the plate-fin heat exchanger for cooling aircraft engines. The late 1930s, Sweden has created the first shell heat exchanger for pulp mills. In the meantime, in order to solve the heat problem of corrosive media, people new material began to pay attention to the heat exchanger.
About 60 years, due to the rapid development of space technology and cutting-edge science, the urgent need of various high-performance compact heat exchangers, plus the development of stamping, brazing and sealing technology, heat exchanger manufacturing process has been further improved, thus promoting the compact plate heat exchanger surface vigorous development and wide application. In addition, since the 1960s, heat and energy in order to meet the high temperature and high pressure conditions requires typical shell and tube heat exchanger has been further developed. Mid-1970s, in order to enhance heat transfer, on the basis of research and development has created a heat pipe heat pipe heat exchanger out.
Heat exchanger according to different methods can be divided into hybrid, regenerative and recuperative categories.
Hybrid heat exchanger is cooled by direct contact with hot fluids, for mixing the heat exchange heat, also known as contact heat exchanger. As the two fluids must be promptly separated mixed heat, such heat exchangers suitable for gas, liquid heat exchange between the two fluids. For example, chemical plants and power plants used in the cooling tower, spray water from the top-down, bottom-up and cold air inhalation, surface water film or droplets on the surface of the filler and water drops, hot and cold heat exchange contact with each other, the hot water is cooled by the cold air is heated and then the two can be separated in time relies on the difference in density of the fluid itself.
Regenerative heat exchanger is the use of cold and hot fluid alternately (filler) surface flows in the regenerator regenerator, heat exchanger and thus be exchanged, such as coke oven preheated air below the regenerator. Such heat is mainly used for high-temperature exhaust gas heat recovery and utilization of. For the purpose to recover the cold accumulating unit, said similar device, used for the air separation unit.
Recuperative heat exchanger cold and hot fluids are separated by a solid partition, and the heat exchanger through the exchange partition, also known as surface heat exchanger, such heat exchangers most widely used.
Recuperative heat exchanger according to the different surface structure can be divided into a tube, board type and other types. Tube heat exchanger with a heat transfer surface of the tube surface, including snakes and tube heat exchangers, tube type heat exchangers and shell and tube heat exchangers, etc.; plate surface heat exchanger to the board as a heat transfer surface, including Plate heat exchanger, spiral plate heat exchangers, plate-fin heat exchangers, shell heat exchanger plate heat exchanger and an umbrella, etc.; other types of heat exchanger is designed to meet the special requirements of certain heat exchanger such as scraped surface heat exchanger, rotary heat exchangers and air coolers.
Heat exchangers are generally relatively fluid flow downstream and upstream two. When the downstream entrance to the maximum temperature difference of the two fluids, and gradually decreases along the heat transfer surface to the outlet of the temperature difference is minimized. When reflux, along the heat transfer surface temperature difference between the two fluids distribution is more uniform. In the cold, import and export of certain conditions, the temperature of the hot fluid, when the two fluids are no phase change, the average temperature difference between the maximum downstream countercurrent minimum.
In the same heat transfer completion condition countercurrent mean temperature can increase the heat transfer area is decreased; if the heat transfer area of the same, can heat or cool the fluid consumption during countercurrent reduced. The former can save equipment costs, which can save operating costs, so in the design or production use should be adopted in countercurrent heat exchanger.
When cold, the hot fluid in one or both of the phase change has (boiling or condensing), since only the emission or absorption of the latent heat of phase change, the temperature of the fluid itself does not change, and therefore is equal to the fluid outlet temperature, which When the temperature difference between the two fluids flowing fluid on the choice irrelevant. In addition to these two flows downstream and upstream, there are cross-flow and flow baffles, etc..
In the transfer process, the recuperative heat exchanger to reduce the thermal resistance in order to improve the heat transfer coefficient is an important issue. Thermal main viscous fluid from both sides of the thin-wall heat transfer surface (called the boundary layer), and a heat exchanger fouling layer used in the formation of the side walls, the thermal resistance of the metal wall is relatively small.
Increased velocity and disturbance of the fluid, the boundary layer can be thinned to reduce the thermal resistance to heat transfer coefficient improved. However, the fluid flow rate will increase energy consumption increases, so should be designed to reduce the thermal resistance between the rational and reduce energy consumption for coordination. In order to reduce the thermal resistance of the dirt, you can try to delay the formation of dirt, and regular cleaning of heat transfer surfaces.
Heat exchangers are generally made of metallic material, which mostly carbon steel and low alloy steel for the manufacture of medium and low pressure heat exchanger; stainless steel mainly used in addition to the different corrosion conditions, but also as resistant austenitic stainless steel high and low temperature materials; copper, aluminum and its alloys are used for manufacture of cryogenic heat exchangers; nickel alloy is used in high temperature conditions; non-metallic materials in addition to the production of parts washer, but some have begun for the production of non-metallic materials resistant heat losses, the heat exchanger such as graphite, glass and fluorine plastic heat exchanger and the like.
The operation of the heat exchanger
Unit structure
Heat exchanger unit is a direct bridge between the user network and heat from a heat network to get heat, automatically and continuously converted into domestic water and heating water users need for air conditioning (heating and cooling), heating, domestic water ( bathing) or other heat exchange circuit (e.g., a floor heating, process water cooling). Heat exchanger unit by a plate heat exchanger, circulation pump, water supply pump, filters, valves, crew base, heat meter, distribution box, electronic instrumentation and automation systems and other components. Steam heat or hot water into the primary side of the plate heat exchanger from the water inlet of the unit, the secondary side of the low-temperature return water passes through the filter decontamination, enters the pump through the loop filter plate, at two different temperatures through heat exchange with water , the heat supplied to the secondary heat users.
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Common problems and treatment
In the production process, the corrosion of the heat exchanger tube sheet moisture, erosion, cavitation and trace chemical medium tubesheet welds often leak, leading to water and mixing chemical material occurs, the temperature is difficult to control the production process, resulting in generation Other products seriously affect product quality, reduce product level. After the condenser tube plate weld leakage, companies often use traditional welding methods to repair the internal tube plate is easy to produce stress, and difficult to eliminate, causing other heat leakage, the enterprise through pressure, test equipment repair case , repeated welding, experiment, people need 2-4 days to complete the repair, use a few months after the tube plate weld corrosion again, to bring a waste of manpower, material and financial resources, increasing production costs. By Salvo blue polymer composites corrosion and erosion resistance, through advance the protection of the new heat exchanger, so that not only the weld and trachoma effective governance problems exist in the new heat exchanger, but also to avoid the use of chemical substances corrosion of metal surfaces and welded heat exchangers point in the future when the regular maintenance can also be applied Salvo blue polymer composites to protect the bare metal; leak even after the emergence of the phenomenon of the use of, or by Salvo Blue timely repair technology, Avoid lengthy welding repairs affect production. It is because of this fine management, which makes the probability of heat leakage is greatly reduced, not only reduces the cost of the heat exchanger equipment purchases, but also to ensure the product quality, production time and improve product competitiveness.
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New heat exchanger
Pneumatic Spray finned tube heat exchanger
Proposed a sophisticated method of Russia, i.e. pneumatic spraying, to improve the performance of the fin surface. Its essence is the use of high-speed fluid containing particles of cold or slightly warm to the fin surface spray powder particles. This method not only can be sprayed with the metal alloy and the ceramic coating can (metal ceramic composites) to obtain various surface properties. In practice, typically the bottom surface of the contact resistance of the fin is one factor limiting the fin tube installation. To assess the finned tube heat exchanger elements studied. Test was adopted in ac-fin surface coating of aluminum, and alumina added 24a white electric stove. The obtained experimental data collated, you can evaluate the underside of the fin contact resistance. The study of the fin efficiency and calculation data for comparison, the conclusion is: no substantial impact efficiency contact resistance pneumatic spray the underside of the fins. To confirm this, but also on the base (tube) and surface (fin) transition zone were metallurgical structure analysis.
The transition zone specimen analysis showed that all the rigor of micro-cracks on the entire length of the border connections. Therefore, promoting the formation of branched pneumatic spray boundary surface interacting with the base, to facilitate penetration of the powder particles to the substrate, which shows a high adhesion strength, and physical contact is formed of metal chains. Thus not only can be used for pneumatic spraying molding, can also be used for manufacturing the conventional method will be fixed on the surface of the fin tube heat exchanger, can also be used to supplement the ordinary reinforcement of the bottom surface of the fin. It can be expected in a compact and efficient pneumatic spraying production of heat exchangers, will be widely used.
Helical baffle heat exchanger
In shell and tube heat exchangers, shell is usually a weak link. Usually normal segmental baffles can cause tortuous flow channel system (z-shaped flow channel), this will result in a larger dead and a relatively high backmixing. These dead shell can cause increased fouling of heat transfer efficiency disadvantage. Backmixing also make the average temperature distortion and out. As a consequence, compared with piston flow, segmental baffles will reduce net heat. Superior segmental baffle shell and tube heat exchanger efficiency is difficult to meet the requirements, it is often replaced by other types of heat exchangers (such as compact plate heat exchanger). Ordinary baffle geometry improvements, is the first step in the development of the shell. Although the introduction of such seals and additional partial transition flow plate and take other measures to improve the performance of the heat exchanger, but the main drawback of the ordinary baffle design still exists.
To this end, the United States proposed a new plan, which proposes using a spiral baffle. This design has been confirmed by the advanced nature of fluid dynamics and heat transfer research results, this design has been patented. The main disadvantage of this structure to overcome the ordinary baffle. Helical baffle design principle is simple: the special panel mounted circular cross-section, "intends helical baffle system", each baffle heat exchanger shell accounts for a quarter of the cross section, its inclination toward the axis of the heat exchanger, which maintained a tilt axis of the heat exchanger. Surrounding the adjacent baffle phase, with a continuous spiral outer office. Axially overlapping baffles, support tubes To narrow span, double spiral design can be obtained. Helical baffle structure to meet the relatively wide process conditions. This design has a great deal of flexibility for different operating conditions, select the best helix angle; may overlap each case selected baffle or baffles double helix structure.
The new twist tube heat exchangers
Swedish alares developed a flat tube heat exchanger, often referred to twist tube heat exchanger. Houston Brown company made improvements. Flat spiral pipe manufacturing process includes a "flattening" and "hot twist" the two processes. The improved twist tube heat exchangers with traditional shell and tube heat exchangers as simple, but there are a lot of exciting progress, it gained economic techniques are as follows: the improved heat transfer, reduced fouling, true countercurrent reduce the cost, no vibration, saves space, no baffle element.
Due to the unique structure makes the tube and the tube shell in a spiral motion while promoting the degree of turbulence. The overall heat transfer coefficient of 40% compared to conventional heat exchangers, and pressure drop is almost equal. Flat spiral tube may also be mixed with the light pipe heat exchanger when assembling manner. The heat exchanger manufactured in strict accordance with asme standards. Any use of the shell and tube heat exchangers and can be used to replace traditional devices such heat exchangers. It can get the best value of the ordinary shell and tube heat exchangers and plate and frame heat transfer equipment acquired. Estimates have broad application prospects in the chemical, petrochemical industry.
Non-soldering wire around the spiral rib tube heat exchanger
Wire wound on the tube as the ribs (fins) of the spiral heat exchanger (ta), usually by welding the wire fixed on the tube. However, this method has a number of effects on the quality of the entire apparatus, as will brazing heat from the "net" a large part of the surface of the tube and the wire. More importantly, because the solder can cause rapid aging and broken machinery and equipment clogging, followed earlier reported loss
