Overview As we all know , the heat exchanger is essential to the process of industrial heat transfer equipment , widely used in all industries , especially technology , metallurgy , power , transportation, aviation , aerospace and other sectors. In recent years , due to the development of new technologies and energy development to improve the performance of the heat exchanger industry, more and more attention . New technologies, new processes play a more and more important role in meters of modern industrial production areas. Constantly improve the technological content of products , the pursuit of energy efficient, maximize access to economic benefits, has become the basic principle followed by the organization of production . For many years, tube heat exchanger is widely used in various industrial sectors, with the development of science and technology, especially the rapid development of these children industries requiring heat set each compact , lightweight , efficient and compact , and general tube heat exchanger can not meet the above requirements, which encourage people to study efficient heat exchanger. Finned tube heat exchanger which is one of the most studied heat exchanger . Finned tube is a core element composed of a variety of its quality directly affects the performance of the heat exchanger .
2.1 , the heat exchanger materials of various materials according to the different uses of the heat exchanger and operating conditions selected .The commonly used materials: aluminum , aluminum , copper, brass , nickel , Chin , stainless steel, Inconel , etc. .
Among the most widely used aluminum and aluminum alloys . The basic requirement for finned tube heat exchanger of the base material are: a better soldering properties and moldability , high mechanical strength, good corrosion resistance and thermal conductivity. Aluminum and aluminum alloy not only meets these requirements , but also has the ductility and tensile strength with decreasing temperature and improved features, so in the world of compact heat exchangers , especially in low temperature compact heat exchangers , had access to the most widely used :
1 ) , the density of aluminum is small, by alloying and heat treatment to achieve strength structural steel. Aluminum heat exchangers used in various types of transport , especially small cars , will lighten its weight , lower fuel consumption.
2 ) , good corrosion resistance of aluminum . Aluminum products in harsh conditions generated oxide non-toxic. Heat exchangers made of aluminum , do not worry too much time lapsed after being long tube of air or liquid Hugh peroxide .
3 ) , having a good thermal conductivity of aluminum , especially for heat sink, a heat exchanger with a condenser and an evaporator .
4 ) , high yield strength aluminum tolerance stamping , molding process more convenient.
2.2 , type finned tubes are generally two types of inner tubes finned tube and the outer fins , which finned tube outside the most common. Outer finned tube is generally used method of machining the outer surface of the light pipe of a certain height, a certain pieces from the fin of a certain thickness .
2.2.1 finned steel spiral fin is a plane perpendicular to the axis of the tube to form a spiral wound around the outer surface of the tube . In forming the spiral fin , the concave edge of the fin panels are compressed within the neutral line , the panel edges projecting beyond the neutral wire is stretched . Ultimate strength of the material when the m -plane tensile stress is reached, a small thickness of the strip will lose stability, and the formation of wrinkles . Winged helix cold steel is not used thick ( typically 6 = os-2.smm), instability phenomenon often occurs . It can be said fin root spiral finned tube wrinkling is a common problem . Fin fin root root causes wrinkling plane becomes uneven . If this way of doing the tube heat exchanger , there are many deficiencies : convex part of the increased airflow resistance ; concave portion gathering dirt and cleaned to bring trouble. Figure 1 hot-dip galvanized steel finned tube winding Oval
2.2.2 , holiday packages fin fin punch process is pre- processed by a number of individual fins , and then use manual or mechanical methods , according to Certain fin spacing , fin suit against interference in the outer surface of the pipe . It is the first method of processing a finned tube . Since the suit process is simple, less demanding technologies , equipment used inexpensive , and easy to maintain , so there are still many factories in adoption. This process is a labor-intensive process solutions , suitable for general small factory or town corporate financial and technical conditions . We know that the quality requirements of finned tubes are mainly three points: First, the fin spacing : Second fin height ; Third degree fins and firmly bound to the surface of light tube , sewing is not fully connected , the better , that is Thermal resistance is smaller . In general, the spiral fins and fin packages for the first two are relatively easy to guarantee , but the third point is often a problem. The fatal flaw of these tubes is what this is . Bad contact between the tubes and fins , large thermal resistance , impact heat .
2.2.3 , roll milk finned tube in recent years , the rapid development of rolling finned tube is an energy efficient heat transfer fin tube ( referred to as high- fin tube ) , cold extruded finned tube is thick-walled tube continuous extrusion through multiple roller rolling extruded , thin-walled tube in the process becomes , the excess metal material is formed on the outer surface of the tube fins . The fin height is rolled )-13mm; sheet is generally from 2-3.5mm, film thickness is generally 0.2-0.5mm. This same method can also be cold extrusion composite pipe rolling finned tube . Commonly used composite pipe finned its base tube ( that is, within the casing ) is used in carbon steel, stainless steel , Chin wood, copper and so on. The outer tube , an outer sleeve that is commonly extruded aluminum fins and copper tubing. Since rolling fins and fin tube wall as a whole , so there is no electrical contact resistance and corrosion phenomena occur , which can improve and maintain the stability of the heat transfer performance and extend the useful life of finned tubes . High fin tube rolling machine rolling finned tube, finned tube tightly with the base , do not need to be subject to rolling machine by adjusting working condition brazing, fin spacing, fin height, fin thickness, etc. control , rolling out of the fin surface smooth, bellows clear, precise pitch , assembled by the heat , electricity production by a number of enterprises to use , has good overall economic performance. Overall, the structure is relatively compact rolling finned tube , flow resistance, small thermal resistance , high heat transfer efficiency, small volume, higher overall performance. But require specialized rolling machine , and the connection of the end plate of the fin tube easy leakage. Rolling finned tube composite pipe structure , is about rolling out steel finned tube sets , this structure has the dual advantages of steel and aluminum finned tubes finned tubes , currently has been successfully developed, but complex process . Therefore, also to be studied more advanced technology . Figure 2 pairs of rolled sheet metal pipe
2.2.4 , in the form of structural plate-fin plate-fin heat exchanger lot, but its structure is basically the same unit body , fins are made , partitions, seals and baffle composition, it is placed on a flat metal plate fins ( i.e. the so-called secondary heat transfer area ) , and then placed on a metal plate , both sides of the edge seal to form a seal and the base unit , the two upper and lower metal plate called a separator. Many basic units of plate-fin heat exchanger core . Hot and cold fluids in the flow channel adjacent to the body of the basic unit of flow through the fin and the spacer integrally with the fin for heat exchange. Superimposed on each channel and arranged in different ways , brazed into a whole , you can get the most commonly used counterflow , crossflow , wrong counterflow plate-fin heat exchanger plate beam . In addition to the heat transfer fins bear the main task , but also plays a role in strengthening the bulkhead between the two . So, although fins and separator material is very thin, but its high intensity , it can withstand high pressure. For the average heat exchangers, plate-fin heat exchanger has the following advantages : high heat transfer efficiency ; compact ; lightweight and strong adaptability to large c ; economic good. However, this heat exchanger fin spacing is small, easy to plug , and difficult to clean the plug, so that the resistance increased significantly, if not its cleaning, security will affect the stability of the system operation. Plate-fin heat exchangers are mainly used in the compressor oil cooler and air cooler , there is air-cooled and water-cooled two forms. Air-cooled or water-cooled intercooler either high temperature compressed air in the cooling process , there will be precipitated condensate and gather on the fins to form a " water bridge " , preventing the flow of air , so that the air pressure is increased , and the guideTo decrease the heat exchange efficiency of the air conditioning in the plate -fin heat exchanger there is a similar situation. Although aluminum and its alloys have good corrosion resistance , but the long-term retention of the aluminum surface to absorb condensed water in the air of oxygen, sulfur and nitrogen , aluminum surface corrosion cell , accelerate corrosion. Corrosion products on the surface of aluminum fins aggregation, to reduce the heat exchange rate . For the water cooler , in the presence of corrosive water side of the same problem , it will shorten the long-running aluminum plate -fin heat exchanger life. Working under high pressure plate-fin heat exchanger due to changes in pressure will cause the cycle fatigue cracks leaving the separator , causing leaks, therefore must be considered in the structural design of fatigue damage.
2.3 , the development direction of the comparison can be seen from the above analysis, the future development of the finned tube heat exchanger surface is greatly strengthened toward the direction of the fins integral with the base of the tube . Furthermore, a significant reduction in production costs , but also the production of increasingly large scale.
3 , finned tubes for special applications and special design
3.1 , the design of air coolers and air cooling method of cooling water has been discussed for a long time continue to present ongoing economic analysis and discussion between the two, but the superiority of air coolers more and more people Note to air cooling instead of water cooling trend continues to grow . Air cooling is achieved in the air cooler , a cooling medium gas is led , can be used for cooling and condensing the various fluids . Due to the small air specific heat ( about 1.005kJ/kg "-C) fourth , only the specific heat of water , so if the same heat transfer , the same as the cooling medium temperature, the amount of air is needed for . considering leggings water four times the density of air is much less than in water, relative to the water cooler , the air cooler is a great volume of the other , empty the steam side heat transfer coefficient is very low , about 50 -. 60W / (m '• ℃), air-cooled tubes leading to the total heat transfer coefficient is very low, compared to the low heat transfer coefficient of water coolers about 10 - 30 times lower to offset the impact of the air-side heat transfer coefficient , so the air cooler Usually the surface of the fin are made of the expansion tube, fin ratio of approximately 10-24 . finned air-cooled heat exchanger tube is the core and the key member , the air cooling performance directly affect the performance and development. fact , precisely as a result of finned tubes , air coolers to develop it so that in addition to the cooling medium can be used dry longitudinally finned tube outside air coolers were all outside the tube using a lateral fins.
3.2 , auto air conditioning so far , people have more buildings air conditioning technology research and exploration , comparison, cars, trains, ships and construction vehicles and driving to work in high-temperature environments , such as the movement of the device special less air conditioning technology research . Cars, trains, ships and construction vehicles and high-temperature environments , such as driving to work a sense, can be regarded as a special sport " building ." Therefore , both the similarities and the land of special air conditioning installed in such buildings , " building" , has its particularity. In simple terms, the car air conditioner requires heat exchanger small size, light weight , so you can save space and energy consumption. Moreover , taking into account the working conditions of automotive air conditioning must be required to have a certain degree of seismic capacity . Thus, only efficient finned tubes meet its requirements.
3.3 , in small and medium sized piston refrigeration compressor refrigeration compressor, finned tubes in the past, most of the sets of films and film around the tube form , which is mainly used for all kinds of fin tube condenser and swallow hair . Relies mainly on the use of finned tube geometry or surface conditions change heat transfer surfaces to enhance heat transfer , so can effectively enhance the condensation heat transfer tube to improve the overall heat transfer coefficient of heat exchangers.
3.4 , the condenser on the condenser , the condenser generally use land use copper or aluminum composite finned tubes finned tubes . And due to the use of marine sea water cooling condenser , although its form and structure with the same land , but taking into account the effects of seawater corrosion of parts in contact with the water , generally use copper or aluminum finned tube brass material ; while most of the evaporator is a form of aluminum brass sleeve .
3.5 , in the cold of some diesel vehicles on large diesel engines , due to consider the needs of the traveling speed and the size of the affected space constraints , are generally higher than the power of each loaded turbocharged and intercooled diesel engine . Select and design appropriate intercooler diesel engine can fight largely improve the economics and reliability.
4 , the development of finned tubes from the above analysis we can see that the development of energy-efficient finned tubes is imperative , and the requirements of economic performance and job performance has improved . Now study the overall aluminum finned tubes (AIF tube ) all kinds of fin tube described above compared to the following advantages:
( 1 ) , either the inner tube or tubes , finned tube heat exchanger area are greatly increased ;
( 2 ) , fin and medium flow pipe into one structure, combined rate of 100% , the gap is zero thermal resistance , which greatly improves the heat transfer effect, and hot corrosion problem does not exist ;
( 3 ) , cross-sectional shape of the medium flow line optimized design, shape and number of lumen changes . Dielectric constant mass flow rate at the inlet of the case ( compressor outlet flow ) , or by reducing the cross sectional area equivalent diameter of the lumen , resulting in increased heat transfer coefficient .
( 4 ) , high- finned tube strength, thermal shock and mechanical vibration , thermal expansion properties , reliable structure, long life.
( 5) , fin spines smooth , wrinkle-free , easy to knot dust , fouling , easy to clean and remove surface water , fluid resistance , long-term to maintain good heat transfer properties.
( 6 ) , the base material made of aluminum , very light weight . Density of the material of aluminum , good heat transfer performance, and high corrosion resistance , easily processed into complex shapes tubes .
( 7 ) , the fin thickness is small , the higher height , the fin pitch is small , the wall thickness is relatively small. According to the different needs of the workpiece and to change the size of each parameter.
( 8 ) , and the medium flowing fins pipeline for the integration process , process is very simple , just a process, that is, the base material - processed tubular -shaped aluminum tubes with a special planer .
( 9 ) , less investment in equipment , just a simple main processing equipment and welding equipment and bending equipment ; production yield, less leakage points . In
Summary , AIF tube is a new and efficient heat transfer tubes , and its prospects are very optimistic.
5 , the overall conclusion aluminum aluminum finned tubes (AT tube ) processing technology , is a national initiative , is an international leader . After analysis, the application of a very broad market AIF managed , can use it to replace the heat transfer performance of today's well- plate-fin -tube heat exchanger and rolling , and thermal performance and economic performance have been further improved. Difficult to speculate , AIF will be the new darling of the heat exchanger tube sector, it will accomplish much in the automotive air-conditioning , all kinds of air coolers and oil intercooler heat exchanger , etc.
Key Words: fin tube, finned tube,tubos aletados, extruded finned tube,finned tube heat exchanger, fin tube condenser, aluminum aluminum finned tubes
