Fin Tubes----Finned tube heat exchanger technology progress
Outline
The heat exchanger is essential to the process of industrial heat transfer equipment, widely used in all areas of industry, especially in technology, metallurgy, power, transportation, aviation, aerospace and other sectors. In recent years, development of new technologies and energy development, improve the heat exchanger performance more and more industry attention. New technologies, new processes in the field of modern industrial production plays an increasingly important role in the more meters. Continuously improve the technological content of products, the pursuit of high efficiency, maximize access to economic benefits, has become the corporate organization of production follows the basic principles. Over the years, widely used in various industrial sectors and tube heat exchanger, with the scientific and technological development, especially the children an industry is developing rapidly, requiring heat set of all compact, lightweight, efficient and compact, while the general Tubular heat exchangers can not meet the above requirements, which encourage people to study efficient heat exchanger. Finned tube heat exchanger which is the most studied one of a heat exchanger. Finned tube heat exchanger core is composed of a variety of components, their quality will directly affect the performance of the heat exchanger.
2, finned tubes developed
2.1, materials, various heat exchanger materials, should be based on the use of the heat exchanger and the choice of different operating conditions. The most commonly used materials are: aluminum, aluminum alloy, copper, brass, nickel, titanium, stainless steel, Inconel, etc.. Among the most widely used aluminum and aluminum alloys. The fin-tube heat exchanger preform basic requirements are: a better soldering properties and formability, 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 at low temperatures, compact heat exchangers, had gained the most widely used:
1), the density of aluminum, by alloying and heat treatment can meet the structural strength of the steel. Aluminum heat exchangers used in various types of transport, especially small cars, will reduce its weight, reducing fuel consumption.
2), good corrosion resistance of aluminum. Aluminum products in harsh conditions resulting oxide non-toxic. Heat exchangers made of aluminum, do not worry too much about a long time after being off the air or other oxidizing fluid tube failure.
3), aluminum having a good thermal conductivity, especially for the heatsink, the heat exchanger with the evaporator and condenser. 4), the yield strength of aluminum, high resistance stamping, molding process more convenient.
2.2, there is a general type finned tubes finned tube and the outer finned tube two kinds, of which the most common application outside of finned tubes. Outer finned tube is generally used method of machining the outer surface of the light pipe of a certain height, certain slice distance, a certain thickness of the fins.
2.2.1, spiral helical fin strip fin is the plane perpendicular to the axis of the pipe, in the form of a spiral wound on the outer surface of the tube. When the formation of the spiral fin, the fins within the recessed panel neutral compressed edge, projecting beyond the neutral panel edges are subject to tension. When m-plane tensile strength of the material stress reaches the limit, the small thickness of the strip to lose stability and formation of wrinkles. Winged helix not thick cold steel used (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 looks like a heat exchanger tubes do, there are many deficiencies: convex part of the increase airflow resistance; concave portion gathering dirt, and cause trouble to clean. Figure 1 hot-dip galvanized steel finned tube wound oval
2.2.2 Set fin fin technology is pre-set with a single punch processing a number of fins, and then use the manual or mechanical means, according to certain fin spacing, interference by the fins on the outer surface of the tube package . It was one of the first processing finned tube method. As set process is simple, less demanding technologies, equipment used inexpensive, and easy to repair, so many factories are still in use. This process is a labor-intensive process scheme, suitable for general small factory or town enterprise funds and technical conditions. We know that the quality requirements of finned tube has three main points: First, the fin spacing: Second fin height; Third, the outer surface of the fins and tubes combined firm level, not fully connected seam as possible, i.e. resistance to be small. In general, the spiral fins and fin suit against former two are relatively easy to maintain, but the third point is often a problem. Fatal shortcoming of these tubes is what makes it. Poor contact between the tubes and the fins, the thermal resistance, affecting heat transfer.
2.2.3, roll milk finned tubes in recent years, the rapid development of rolling finned tube is an energy efficient heat transfer finned tubes (referred to high-fin tube), cold extruded finned tube is thick-walled tube Continuous extrusion through multiple sets of rollers rolling by extrusion, into a thin-walled tube in the process, the excess metal material of the tube outer surface of the fin. The rolling fin height is generally)-13mm; fin spacing is generally 2-3.5mm, slice thickness generally. .2-0.5 Mm. This same method can also be cold extrusion composite pipe rolling finned tube. Commonly used composite pipe finned its base tube (ie, inner sleeve) is used in carbon steel, stainless steel, titanium wood, copper and so on. The outer tube, which commonly extruded aluminum fins and copper tube jacket. Since rolling fins and fin tube wall as a whole, so there is no contact resistance and the emergence of the phenomenon of galvanic corrosion, which can improve and maintain stable finned tube heat transfer performance and extend the useful life. High fin tube mill rolling finned tube, finned tube tightly with the base, without further brazing, fin spacing, fin height, fin thickness, etc. can be adjusted to be rolling machine working status control, rolling out of the fin surface smooth bellows clear, precise pitch, assembled by a heat exchanger, used by a number of power production enterprises, has good overall economic performance. On the whole, rolling finned tube structure is compact, small flow resistance, thermal conductivity, low thermal resistance, high heat transfer efficiency, small volume, the overall performance is higher. But the need for specialized pipe rolling mill, and end plate finned tubes and easy to leak at the connection. Rolling finned tube composite pipe structure, rolling finned tube coming out of the pipe sleeve, this structure has steel finned tubes and aluminum finned tube double advantage, 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, plate-fin heat exchanger plate-fin structure of many forms, but its structure is basically the same unit body, are made fins, partitions, seals and deflector composition, it is placed on a metal plate fin (the so-called secondary heat transfer area), and then put in a metal plate on both sides to seal the edge seal which consists of a base unit, up and down the two metal plates called the bulkhead. Composed by a number of basic units of plate-fin heat exchanger core. Hot fluid base unit body adjacent the flow path flows through the fin and the spacer integrally with the fin for heat exchange. For each channel are stacked and arranged in different ways, brazing into a whole, you can get the most commonly used counterflow, crossflow, wrong countercurrent plate-fin heat exchanger plate beam. In addition to the heat transfer fins bear the main task, but also plays a role in strengthening between the two partitions. So, although fins and separator material is very thin, but its intensity is high, it can withstand high pressures. For a like heat exchangers, plate-fin heat exchanger has the following advantages: high heat transfer efficiency; Compact; lightweight and strong adaptability to large c; economy is good. However, this heat exchanger fin spacing is small, easy to plug and plug and difficult to clean, making the resistance increased significantly, if not its cleaning, it will affect the system safe and stable operation. Plate-fin heat exchanger is mainly used in the compressor oil cooler and air cooler, there is air-cooled and water-cooled two forms. Either air or water cooler, high temperature 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, and the resulting heat exchange efficiency decline in air conditioning plate-fin heat exchanger there is a similar situation. Although aluminum and its alloys have good corrosion resistance, long-term retention of the aluminum surface the air to absorb the condensed water oxygen, sulfur and nitrogen, etc., formed on the surface of the aluminum corrosion cell, accelerate corrosion. Corrosion products on the surface of aluminum fins aggregation, will reduce the heat exchange rate. For the water cooler, in the presence of corrosive water side of the same problem, will also reduce the long-running aluminum plate-fin heat exchanger life. Work under high pressure plate-fin heat exchanger loop due to pressure changes can cause fatigue cracks leaving the separator, causing leak, therefore must be considered in the structural design of fatigue damage.
2.3, the development direction of the analysis by the upper surface of the comparison can be seen, the future development of finned tube heat transfer surface greatly enhanced towards fin tube fused with the base direction. Also, a significant reduction in the cost of production, production is also increasingly large scale.
3, finned tubes and specially designed for special applications
3.1, the design of cooler air cooling and water cooling methods discussed has lasted quite a long time, to the still ongoing between the analysis and discussion of the economy, but the superiority of cooler more and more people attention to air cooling instead of water cooling trend continues to grow. Air-cooled cooler is implemented in the air, the gas cooling medium is led, can be used for cooling and condensing the various fluids. Specific heat of the air (about 1.005kJ/kg "-C), only one quarter of the specific heat of water, so if the same heat transfer, the same cooling medium temperature, the required amount of air will water four times. leggings considered far less than the density of the air in water, the relative water cooler, the volume of air is great. Further, steam-side heat transfer coefficient of air is very low, about 50 - 60W / (m '· ℃), led light tube cooler overall heat transfer coefficient is very low, compared to water-cooled heat transfer coefficient of about 10 - 30 times, in order to offset the air-side heat transfer coefficient is low impact, so cooler generally used expansion finned tube surface, the wings of the ratio is roughly 10-24. finned tube is air-cooled heat exchanger core and key components, its performance will directly affect the performance and development of air coolers in fact , precisely because of the emergence of finned tubes, air coolers to develop it so that in addition to the cooling medium can be used dry longitudinal fin tube, all air coolers are used in the tube transverse fins.
3.2, auto air conditioning thus far only, people have more buildings air conditioning technology research and exploration, comparison, for automobiles, trains, ships and work in high temperature environments and other special engineering vehicles and vehicular mobility means less air-conditioning technology. Cars, trains, ships and high-temperature environments such as engineering vehicles and driving a sense, can be considered as a special motion "of the building." Therefore, the installation in the class "building" special air and land within the existing buildings the same point, has its particularity. Simply put, auto air conditioning requirements of heat exchangers, 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, the only efficient finned tubes to meet its requirements.
3.3, in the small piston refrigeration compressor refrigeration compressor, finned tube most previous to and around the chip chip set used in the form of tubes, which is mainly used for various types of finned tube condenser and Yan hair. Finned tube heat exchangers mainly by changing the geometry of the surface or surface condition to enhance heat transfer tube that can effectively enhance the condensation heat transfer and improve the overall heat transfer coefficient of the heat exchanger.
3.4, the condenser to the condenser, the land generally use copper finned condenser tube or aluminum composite finned tube. The marine condenser cooled with seawater because, although its structure is the same with the land, but taking into account the impact of seawater corrosion, at the site of contact with seawater, generally made of copper or aluminum, brass finned tubes; while most of the evaporator brass sleeve is aluminum forms.
3.5, diesel intercooler some large transport type diesel engine, in consideration of the needs of traveling speed and size by space constraints, are generally fitted the high specific power of turbocharged and intercooled diesel. Selecting and designing appropriate intercooler can be largely improved fighting engine economy and reliability.
4, finned tube from the upper surface of the development of analysis we can see, the development of energy-efficient finned tube is imperative and requires economic performance and the performance has improved. Now study the overall aluminum finned tube (AIF tube) as described above kinds of finned tubes, has the following advantages:
(1), either the tube or pipe, finned tube heat exchanger area is greatly increased;
(2), fins and medium flow pipeline as one structure, combined rate of 100%, the gap resistance is zero, which greatly improves the heat transfer effect, and there is no hot corrosion problems;
(3), on the medium flow cross-sectional shape is optimized piping design, shape and number of lumen change. Dielectric constant mass flow at the inlet in the case (compressor outlet flow), the equivalent diameter of the cross section or lumen reduction, resulting in increased heat transfer coefficient.
(4), finned tube, high strength, thermal shock and mechanical vibration, thermal expansion properties, structural reliability, long life.
(5), smooth ** fin spines, wrinkles, 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 is made of aluminum, very light weight. Small density of aluminum materials, good heat transfer performance and high corrosion resistance, easily processed into complex shapes tubes. <
7), the fin thickness is small, a higher altitude, the fin pitch is small, the wall thickness is relatively small. But also to the different needs of the workpiece to change the size of each parameter.
(8), fins and tubing for the integration of the flow medium, machining process is very simple, requiring only a process, that is, the base material - the tubular-shaped aluminum tubes with a special processing on the planer.
(9), less investment in equipment, just a simple main processing equipment and welding equipment and pipe equipment; production yield, less leakage points. Summing up the above, AIF pipe is a new and efficient heat exchange, and its development prospects are very optimistic.
5, the overall conclusion aluminum aluminum finned tube (AT tube) processing technology, is a national initiative, is an international leader. After analysis, AIF pipe applications market is very broad, you can use it to replace the heat transfer performance of today's well-plate-fin-tube heat exchanger and rolling, and the thermal and economic performance have been further improved. Not difficult to guess, AIF tube heat exchanger sector will be the new darling, it will auto air conditioning, all kinds of air coolers and oil intercooler heat exchanger, etc.
Key Words: Finned Tube, Fin Tubes, Extruded Fin Tubes, Embedded Fin Tube, L Fin tube, Tubos Aletados