How to choose low finned tube?

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Low finned tube description

Low finned tubes are generally formed by machining on the outer surface of the light tube with a certain height, a certain distance, and a certain thickness of ribs. Finned tubes are mostly used for heat exchange elements of condensers and evaporators of air conditioners, and low-finned tubes are often used in condensers.

It consists of a light pipe and fins “attached” to it. The structural parameters are mainly the inner diameter and outer diameter of the finned tube, the wall thickness of the finned tube, the fin pitch, the fin thickness and the fin height.

The low finned tube mainly relies on the outer rib of the tube (the ribging coefficient is 2 ~ 3) to expand the heat transfer area. Compared with the smooth tube, it has a larger surface area under the same metal material consumption. It is the first heat transfer enhancement from a straight view, but it is actually an increase in the heat transfer area and an increase in the heat transfer coefficient. The fins can make the heat transfer surface peel off the flow layer, and the heat transfer surface disturbance increases and improves The heat transfer effect strengthens the heat transfer twice.

The main factors affecting the enhanced heat transfer of the ribbed surface are the fin height, fin thickness, fin spacing, and thermal conductivity of the fin material. In addition, since one side of the heat transfer wall surface is expanded into a fin surface, the convective heat transfer on the smooth side and the heat conduction of the base wall all have a certain effect on the total heat transfer. The fin pitch size of the low-fin tube needs to be determined according to the surface tension of the liquid and the shear force on the liquid film generated by the flow.

Low finned tube application

The actual application proves that the low finned tube also has excellent anti-fouling performance, because the dirt is often formed along the edge of the wave crest, and the tube will expand and contract with the temperature change during operation. This “accordion” type The effect of expansion and contraction will prevent the formation of dirt. On the light pipe, the dirt will form a layer of cylinder on the wall of the pipe, without any natural mechanism to prevent the generation of dirt. 

Due to the lower fins, the cleaning method and difficulty of the low-fin tubes are exactly the same as for light tubes. In addition, the low-fin tube is made of the ordinary smooth tube as the blank and is processed by simple rolling. Its mechanical strength and corrosion resistance are no less than the original smooth tube blank, which can fully guarantee the long-term reliable operation of the heat exchanger.

Low finned tube performance parameters

There are two important parameters for low-fin tubes to describe their performance, namely the fining ratio β and the fin efficiency η. The fining ratio is expressed by “β”, and its definition can be derived from the formula: β = total external surface area of the finned tube / external surface area of the original smooth tube; the larger the value of β, the more the heat transfer area of the finned tube expands. 

The thermal performance is also enhanced. In the heat exchange process of the finned tube, assuming that the temperature of the fluid in the tube is higher than the temperature of the fluid outside the tube, the heat is transferred from the root of the fin through the tube wall along with the height of the fin through the heat conduction, and the fin also communicates with the surrounding fluid Convective heat transfer occurs, and eventually, the fin temperature gradually decreases along with the fin height.

 

Murphy low finned tube
Murphy low finned tubes

 

Manufacturing process of low finned tube

The low-fin tube is produced by the rolling method (three-roll oblique rolling). Its working principle is: the smooth tube is lined with a mandrel, the tube material is driven by the roller blade to make a spiral linear movement, and is rolled by the roller The hole pattern composed of the groove and the core rod is gradually processed with fins on its outer surface. In order to facilitate the formation of fins. 

The rolling parts adopt three stages of biting, rolling, and shaping during the deformation process, so that the processed fins are complete, smooth, and regular. The finned tube produced by this method is based on the base tube and The outer fin is an organic whole, so there is no problem of contact thermal resistance loss and electrical corrosion. It has good heat transfer efficiency and strong resistance to deformation.

Influencing factors of low finned tube performance

The structural parameters are mainly the inner diameter and outer diameter of the finned tube, the wall thickness of the finned tube, the fin pitch, the fin thickness, and the fin height, etc.

It is generally used in applications where the heat supply coefficient inside the tube is more than double the heat supply coefficient outside the tube. The most typical application is an oil heat exchanger. For condensation and boiling outside the tube, due to the effect of surface tension, it also has a good effect on strengthening heat transfer. Its processing has been industrialized and has been verified by many refineries.

(1) As far as the heat transfer effect is concerned, the primary and secondary relationship between the structural parameters of the low-fin tube is wing pitch → wing height → wing thickness, and the fin pitch is within 1 ~ 2 mm. The thermal performance increases with the increase of the wing pitch. When the wing pitch exceeds 2mm, the heat transfer performance decreases with the increase; the heat transfer performance decreases with the increase of the wing thickness and increases with the increase of the wing height.

(2) The pressure drop outside the finned tube is significantly affected by the height of the wing. The pressure drop increases geometrically with the increase of the wing height. The influence of the wing distance on the pressure drop is also obvious. The pressure drop increases with the wing distance. As it becomes larger, the pressure drop is hardly affected by the thickness of the wings.

(3) When the fluid flow rate inside and outside the tube increases, the heat transfer volume and pressure drop of the finned tube also increase. When the fluid flow rate outside the tube increases, the increase in pressure drop is significantly greater than the increase in heat transfer volume. When the flow rate increases, the pressure drop outside the tube remains unchanged, and the pressure drop inside the tube increases less

For more information about low finned tube get in touch with us.

High-frequency welding finned tube

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How does high-frequency welding finned tube work?

The high-frequency welding finned tube use the skin effect and proximity effect of the high-frequency current to heat the outer surface of the steel strip and the steel tube while the steel strip is wound around the steel pipe, until the plastic state or melting, a certain pressure on the wound steel strip Complete welding next.

This high-frequency welding is actually solid-phase welding. Compared with inlaying, brazing (or integral hot-dip galvanizing) and other methods, it is excellent in terms of product quality (high welding rate of fins, up to 95%), productivity, and degree of automation.

High-frequency welding uses solid resistance heat as an energy source. The resistance heat generated by the high-frequency current in the workpiece during welding heats the surface of the welding zone of the workpiece to a molten or near plastic state, and then applies (or does not apply) upsetting force to achieve metal bonding.

Therefore, it is a solid phase resistance welding method. High-frequency welding can be divided into contact high-frequency welding and induction high-frequency welding according to the way that high-frequency current generates heat in the workpiece.

When contacting high-frequency welding, high-frequency current is introduced into the workpiece through mechanical contact with the workpiece. During induction high-frequency welding, the high-frequency current generates an induction current in the workpiece through the coupling effect of the induction coil outside the workpiece.

High-frequency welding is a highly specialized welding method, and special equipment should be equipped according to the product. High productivity, welding speed up to 30m / min. Mainly used for welding longitudinal or spiral seams when making pipes.

The contents of the two major effects of high-frequency current in high-frequency welding are:

Skin effect: When a conductor is fed with alternating current, the current distribution on the conductor cross-section is uneven, the current density gradually increases from the center of the conductor to the surface, and most of the current only flows along the surface of the conductor.

The lower the resistivity of the conductor, the greater the magnetic permeability, and the higher the frequency of the current, the more significant the skin effect.

Proximity effect: When high-frequency currents flow in opposite directions in two conductors or in a reciprocating conductor, the current will concentrate on a special physical phenomenon that flows on the adjacent side of the conductor.

High-frequency welding usually uses a current frequency range of 300 to 450kHz, and sometimes a frequency as low as 10kHz

 

Murphy high frequency finned tube scaled

 

High-frequency welding fin characteristics

  1. Due to the fast welding speed and the strong self-cooling effect of the weldment, not only is the heat-affected zone small, but it is also not easy to oxidize, so the structure and performance of the weld is very good.
  2. Anti-corrosion performance, wear resistance, low contact thermal resistance, high stability, anti-ashing ability.
  3. Large heat exchange area.

High-frequency welding type

There are two types of high-frequency welding: high-frequency resistance welding and high-frequency induction welding.

High-frequency resistance welding: use rollers or contactors as electrodes to introduce high-frequency current into the workpiece, suitable for continuous longitudinal seam butt welding and spiral lap seam welding of tubes, welding of boiler finned tubes and spiral fins of heat exchangers.The outer diameter of the weldable pipe is 1200 mm, the wall thickness is 16 mm, and the thickness of the ventral pole of the I-beam can be welded 9.5 mm. The productivity is very high.

High-frequency induction welding: the induction coil is used to heat the workpiece, which can weld small-diameter tubes with an outer diameter of 9 mm and thin-wall tubes with a wall thickness of 1 mm. Commonly used for longitudinal seam welding of small and medium diameter steel pipes and brass tubes, but also for girth welding, but the power loss is greater than high-frequency resistance welding.

The main parameters that affect the quality of high-frequency welding are the frequency, power, forming an angle of the workpiece, extrusion force, the distance between the electrode (or induction coil), and the extrusion roller, and the welding speed.

The main equipment includes high-frequency power supply, workpiece forming equipment, and extrusion machinery. High-frequency welding has stable quality, high productivity, and low cost. It is suitable for high-efficiency automatic production lines and is an advanced method for producing seamed pipes.

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What should you know for laser welding finned tube

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Laser welding finned tube manufacturing

Laser welding finned tube is processed by laser welding machine. Laser welding is a welding method that irradiates a high-intensity laser beam onto the metal surface. Through the interaction of the laser and the metal, the metal absorbs the laser light and converts it into heat, melting the metal to form a cooling crystal. 

Laser welding machine is the most advanced laser welding equipment for finned tubes. Because the welding process is fully automatic and mechanical, the scientific and technological content and quality of laser welding finned tubes are superior to traditional cooling tubes.

The laser welding finned tube has a fully automatic welding process, saving manpower costs; secondly, the laser welding fin is firm, strong, and the test with high tensile strength is qualified. Laser welding is more efficient.

Advantages of laser welding finned tube

1. The laser welding finned tube (finned tube) fin machine has a high degree of automation, and the welding of the fin to the tube and the winding of the tube are synchronized

2. 100% welding rate, laser welding finned tube and fins are strong, the welding strength exceeds 600MPa.

3. The precision of laser welding tube finishing machine is up to 0.05mm

4. 0 contact resistance, achieve high efficiency of heat transfer of spiral finned tube by laser welding.

5. Save production costs. The laser welding finned tube (finned tube) has a smaller fin spacing, less than 2.5mm. Compared with the high frequency welded spiral (spiral) finned tube, the heat transfer area is increased by about 50%, which makes the material cost Reduced, volume reduced heat exchanger.

6. The advantages over conventional MAG / HF welding are of decisive importance. The complete connection between the fin and the base tube brings excellent heat transfer, and the thermal performance of the fin tube is increased by 2.5 times. Continuous welding prevents the notch effect, thereby avoiding the formation of v-corrosion and cracks under the condition that the finned tube may swing. 

The heating of base metals during welding is low and the travel speed is up to 20m / min. Minimize the heat affected zone in the base tube. Therefore, it does not include the complete melting of the tube and the related metallurgical transformation of the parent metal.

Specifically:

· Thin and continuous ideal seams

· Small heat affected area

· Slightly discolored welding parts

· The tubes and fins have only slight microstructure changes

· High heat forms seams

· Since the high welding integrity between the tube and the fins is avoided, the crevice corrosion is avoided, thereby improving safety

· Laser welding is carried out in a protective atmosphere, so the weld is free of impurities.

 
Murphy laser welded finned tube

Application

 Power Plants

· Cooling towers or cooling water recooling plants with dry, dry / wet or wet operation

·  Flue gas cooling and heating in flue gas desulfurisation scrubbers (FGD) and nitrogen removing plants (DENOX)

 Chemical Industry

· Heat exchangers of all kinds for cooling and heating of liquids and gases

· Heat exchangers tor nitric acid (HNO3) plants, e.g. for the fertilizer industry

 Heat Recovery Plants

·  Flue gas coolers

 Heating Industry

·  Primary heat exchangers in gas heating boilers

·  Secondary heat exchangers for domestic water heating in condensing boilers

 General Engineering

·  Heat exchangers for gas cooling of industrial furnaces

·  Heat exchangers for tank heating

·  Oil coolers for vacuum plants, ship plants, pumps etc.

·  Heat exchangers for oil preheating

Dimensions

· Tube outside diameter 8.0–50.0 mm

·  Fin outside diameter 17.0 –80.0 mm

·  Fin pitch 5 –13 fin/inch

·  Fin height 5.0 –17 mm

·  Fin thickness 0.4 – 1.0 mm

·  Maximum tube lengths 12.0 m

Murphy manufactures various types of heat exchanger elments like finned tubes, fin tube coils, stainless pipes, 

heat exchangers, customized according to your need.

For more details about laser welding finned tube and other finned tube please contact us.

 

How to maintain your fin tube in a optimal operation

Murphy factory finnedtubes 1

What is fin tube?

A fin tube is a tube that has small fins around the outside surface. These fins act as a filter and a mechanism to transfer heat from the material inside the tube to the outside space or vice versa. Fin tubes are used in applications that require a transfer of heat from a hot fluid to a colder fluid through the tube’s wall. The rate at which such heat transfer occurs depends on three factors:

The temperature difference between the two fluids.

The heat transfer coefficient between each of the fluids and the tube wall.

The surface area to which the fluid is exposed.

In the case of a bare (unfinned) tubes, where the outside surface area is not significantly greater than the inside surface area, the fluid with the lowest heat transfer coefficient will dictate the overall heat transfer rate. 

When the heat transfer coefficient of the fluid inside the tube is several times larger than that of fluid outside the tube (for example steam inside and oil outside), the overall heat transfer rate can be greatly improved by increasing the outside surface of the tube. In mathematical terms, the product of the heat transfer coefficient for the outside fluid multiplied by the outside surface area is made to more closely match the product of the inside fluid heat transfer coefficient multiplied by the inside surface area.

So the whole concept of finned tubes is to increase the outside surface area of the tube. As an example, a finned tube configuration of 2” (nominal, 2.375” actual) pipe with a ¾” high welded helical solid fin of 12 gauge thickness with 6 fins per inch has an outside surface area of 8.23 sq. ft. per linear foot; whereas the same bare pipe has an outside surface area of only .62 sq. ft. per linear foot. That is a 13X increase in the outside surface area. See Design Information for extensive tables of surface areas and fin weights.

Why is fin tube important?

Finned tubes are the heart of any gas–gas or gas-liquid type of heat exchanger. Finned tube banks are compact units of robust and corrosion-resistant construction. The type of finned tube is chosen (ie, the fin type and combination of materials) depending on the specific requirements of each process equipment unit. Commonly, tubes currently have circular cross-section fins. Convective heating surfaces with circular, square, or helical fins represent tube bundles or tube banks with staggered or in-line arrangement of tubes in cross-flow.

 

Stainless steel finned tube murphy

 

Fin tube types

Fin tube manufacturers produce a wide range of fin tubes. They are used in heat exchangers (air, water and chemically cooled) for various industries such as petroleum, petrochemical, steel, power generation and many more.

Corrosion protection processes are performed during fin tube manufacturing and the material used is corrosion-resistant. Some fin tube types are:

“L” fin tubes:

  • Max working temperature – 150 °C (302 °F)
  • Atmospheric corrosion resistance – acceptable
  • Mechanical resistance – poor
  • Fin material – aluminum, copper

“LL” fin tubes

  • Max working temperature – 180 °C (356 °F)
  • Atmospheric corrosion resistance – acceptable
  • Mechanical resistance – poor
  • Fin material – aluminum, copper

“KL” fin tubes

  • Max working temperature – 260 °C (500 °F)
  • Atmospheric corrosion resistance – acceptable
  • Mechanical resistance – acceptable
  • Fin material – aluminum, copper

“G” fin tubes

  • Max working temperature – 400 °C (752 °F)
  • Atmospheric corrosion resistance – poor
  • Mechanical resistance – acceptable
  • Fin material – aluminum, copper, carbon steel

Extruded fin tubes

  • Max working temperature – 285 °C (545 °F)
  • Atmospheric corrosion resistance – excellent
  • Mechanical resistance – excellent
  • Fin material – aluminum

Why we use fin tube?

By increasing the outside surface area of the tube, the overall heat transfer rate is increased, thereby reducing the total number of tubes required for a given application. This reduces the overall equipment size and the cost of the project. In many cases, one finned tube replaces six or more bare tubes at less than 1/3 the cost and ¼ the volume.

How to maintain fin tube

Generally, when water is used for circulation at the beginning of the operation, there may be slight leakage. When the temperature rises to the sterilization temperature, the leakage will disappear by itself. If the leakage does not stop, the finned tube must be compressed a little more. If it is still ineffective, it is necessary to open and check the rubber gasket. It is also possible that the finned tubes are arranged in the order of numbers on the fins, which should be corrected.

Regularly check whether the finned tubes are complete, whether there are deposits, coking, rust layer, and other scaling adhesion, and clean them immediately. At the same time, it is also necessary to check whether the adhesion between each fin tube and the rubber washer is tight and whether the rubber washer itself is in good condition, so as to avoid leakage caused by rubber washer degumming and damage.

When the rubber gasket needs to be replaced or the degummed part needs to be repaired, the finned tube shall be removed and placed on the table, and the old gasket shall be removed, or the glue traces in the groove of the finned tube shall be wiped out with fine sandpaper at the degumming position, and then the oil traces in the groove shall be wiped out with carbon tetrachloride or trichloroethylene, and then the back of the new rubber gasket shall be wiped out with fine sandpaper, similarly with carbon tetrachloride or trichloroethylene, the alkene solvent wiped out the oil. 

Then, apply a thin layer of glue on the back of the groove and rubber washer. Let it dry a little, but it still sticks. That is to say, the rubber washer is embedded in the groove, flattened around, and coated with a layer of talcum powder. Then install the fin tube and clamp it gently. According to the glue instructions, it can be used after a period of time.

When replacing the rubber gasket of the finned tube, it is necessary to update all the segments so as to avoid uneven clearance between the fins and affect the heat transfer effect.

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Brass tube basic instruction

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Brass is an alloy of copper and zinc. If it is only composed of copper and zinc, it is called ordinary brass. Brass is often used to make valves, water pipes, connecting pipes of air conditioners and radiators.

Brass tubes are generally used to make heating coil tubes for condensers and coolers and tubes for general purposes. Brass 68 and 70 for condensers and 62 for general purpose cold drawn tubes from 3 to 100 cm OD. Its length is 1-6 meters.

Tubes for condensing cooler and other heat exchange equipment shall be subject to water pressure test with pressure up to 50 kg / cm2, and the test time shall not be less than 10 seconds.

Compared with the shell and tube heat exchanger, the brass tube has the following advantages:

1. High heat transfer coefficient, which is due to high velocity, turbulence and complete countercurrent;

2. The weight of equipment required for unit heat transfer is small;

3. The compensation of temperature deformation is good.

 

brass tubes murphy 1

 

What are the characteristics and uses of brass tubes:

Brass tubes has many advantages in one body. It has high strength of general metal, and it is easy to bend, twist, crack and break compared with general metal. It also has certain frost resistance and impact resistance. Therefore, once installed, the copper tubes in the water supply system in the building can be used safely and reliably, even without maintenance.

Brass tubes also have the characteristics of hard texture, corrosion resistance, high-temperature resistance and high-pressure resistance, which can be used in various environments. Compared with this, the disadvantages of many other pipes are obvious. For example, in the past, the galvanized steel pipes used in residential buildings were easy to rust.

If they were used for a short time, the tap water would turn yellow and the water flow would become smaller. The strength of some other materials will decrease rapidly under high temperatures, which will cause unsafe risks when used in hot water pipes. The melting point of copper is as high as 1083 ℃, and the temperature of the hot water system is negligible for copper pipes. Now it is generally used as a copper pipe for electrical appliances, refrigeration, high-pressure, corrosion-resistant, connection, water channel, electric heating, and industrial purposes.

In addition, because Murphy Thermal brass tubes have the characteristics of firmness and corrosion resistance, it has become the first choice of modern contractors in the installation of water pipes, heating, and cooling pipes in all residential commercial houses. At the same time, it has the characteristics of lightweight, good thermal conductivity, and high low-temperature strength.

It is often used to manufacture heat exchange equipment (such as condenser) and also used to assemble low-temperature pipeline in oxygen production equipment. Small diameter copper pipe is often used to transport pressure liquid (such as lubrication system, oil pressure system, etc.) and pressure pipe used as an instrument.

Get in touch with us for more information about brass tubes.

How does finned tube enhance heat transfer?

high fin tube MURPHY

As flat fin heat exchanger is simple and convenient in structure and manufacture, durable in use and good in applicability, so far, the heat exchanger widely used in Refrigeration Engineering (such as evaporator of ammonia cooling fan, surface air cooler, etc.) still widely uses rectangular flat fin as expansion surface. 

Heat transfer characteristics of fins

Rectangular flat fin has the advantages of simple and compact structure, convenient defrosting, easy manufacturing and so on. At the same time, because it only depends on increasing the heat transfer area to enhance the heat transfer, the effect is poor, especially in the heat exchanger with phase change heat transfer of fluid in the tube and forced flow heat transfer of air outside the tube, the heat resistance of the air side is still the main heat resistance in the whole process despite the addition of fins.

Corrugated fins are widely used in air conditioning and refrigeration because they can increase the length of air passage and mix the air flow sufficiently. Corrugated fins can change the direction of air flow, greatly increase the area of air heat transfer and enhance the fluid disturbance. 

Because of the formation and separation of vortices, the continuous development of the heat boundary layer is reduced or damaged, the characteristics are effectively strengthened, and at the same time, a large loss of resistance is brought, but the increase of heat transfer is greater than the increase of resistance. 

Under the wet condition, the resistance of the slotted fins increases more, and the air volume of the system decreases. At this time, the corrugated fin heat exchanger can be considered, and the fin spacing should not be too small.

 

Murphy finned tubes heat exchanger

 

Heat transfer enhancement solutions

In the research of heat transfer enhancement on the surface of stainless steel fin tube by laser welding, Murphy experts put forward various methods of enhancement, mainly including the following: first, to enhance the turbulence intensity on the air side, the purpose of heat transfer enhancement can be achieved by constantly changing the flow direction of the air flow, mainly by stamping the fins into corrugations, resulting in the type of corrugation fins. 

The second is to use the discontinuous fin surface to gradually disconnect the fin surface along the air flow direction, so as to prevent the development of the air laminar boundary layer on the fin surface, make the boundary layer continuously damaged on each surface, and form a new boundary layer on the next punching strip, and constantly use the leading edge effect of the punching strip to achieve the purpose of strengthening heat exchange. 

There are slat fins, louver fins, etc. belonging to this kind of finsCorrugated fins are widely used in air conditioning and refrigeration because they can increase the length of air passage and mix the air flow sufficiently. Corrugated fins can change the direction of air flow, greatly increase the area of air heat transfer and enhance the fluid disturbance. 

Because of the formation and separation of vortices, the continuous development of the heat boundary layer is reduced or damaged, the heat transfer characteristics are effectively strengthened, and at the same time, a large loss of resistance is brought, but the increase of heat transfer is greater than the increase of resistance. Under the wet condition, the resistance of the slotted fins increases more, and the air volume of the system decreases. At this time, the corrugated fin heat exchanger can be considered, and the fin spacing should not be too small.

For more details about heat transfer please contact us. We can provide customized products according to your individual needs.