Issue by: Murphy Finned Tubes

Finned tubes and quality fin are usually used in heat exchangers. But you may wonder what these finned tubes are and why are they used over normal tubes in these exchangers. Here’s everything you need to know about fin tubing.

What Are Heat Exchange Finned Tubes?

Heat Exchange Finned tubes are elongated flat tubes that are made of aluminum cladded carbon steel and are provided with brazed aluminum fins. These tubes are used in a series in fin tube radiator. The advantage they offer over ordinary tubes is that the fins offer greater contact with the liquid outside. This quickens the exchange of heat between the liquid inside the tube and the one outside it. With a normal tube, the rate of exchange of heat would be much slower.

Finned tubes are available in different shapes. They are available as oval tubes, round tubes, and flat tubes.

What Are Their Uses?

Finned tubes are particularly useful in the case of air heat exchangers. In an air heat exchanger, the heat transfer is to take place between a liquid and gas. With the heat coefficient of the airside being lower, a finned tube can be exceptionally helpful. A finned tube increases the surface area and thus helps in faster heat transfer between the components.

Example of Finned Tube for Heat Exchangers

Fin tube heat exchangers are used in household appliances and industrial heat exchangers. Fin tube heat exchangers are used in air conditioners and car radiators. The purpose of using a finned tube in an air conditioner is to cool the air passing through it. In a car radiator, it cools the liquid in the tube with the air passing through in crossflow.

Advantages of Using Finned Tubes

Finned tubes offer several advantages:

  • Increase Heat Transfer Rate

The fins in a finned tube increase the surface area of contact. This allows it to quicken the heat transfer rate.

  • Improve Heat Transfer Coefficient

In an ordinary tube, the outer surface area is just about the same or slightly different from the inner surface area. In such a case, the fluid with the lowest heat transfer coefficient will drive the entire heat transfer rate. A finned tube increases the surface area significantly. This is particularly helpful when the heat transfer coefficient of the fluid inside the tube is greater than that of the fluid outside the tube.

  • Reduces Size of the Equipment and Makes Project Cost Efficient

Finned tubes can significantly increase the surface area. The use of a finned tube can cut down the number of tubes used in an application. This results in a considerable reduction in the size of the equipment. In the long run, this can lead to a decrease in the cost of the project.

Finned tubes are a series of tubes which have fins attached on its exteriors. This increases the contact area with the fluid which is outside the tube. This extended outer area augments the heat transfer rate. It also exchanges heat between the outside and inside the tube.

Inside of the tube is for the liquid to flow and the outside has air or some other gas. The main components of heat exchangers in any industry are Finned Tubes. Usually, crossflow happens here and this is due to the radial fins. If you want a counter-flow, use longitudinal fins instead.

In most of the cases, there is an open heat exchanger with the application of finned tubes for air flow. However, internal finned tubes can also be used in a closed heat exchanger.

Finned tubes are made by helically twisting strips on the tubes. They can be longitudinal, transverse, parallel, flat, round, oval, etc. For industrial purposes where the outside flow has to streamline with the tube length, the best finned tube is the one with longitudinal fins. On the other hand, for air coolers, crossflow exchangers, gas flows, shell and tube heat exchangers, or turbulent flows, you can use transverse finned tubes.

High-finned tubes are used to heat and cool down gases in heating, machinery, and plant technologies.

For evaporating and condensing refrigerants or when you have to control the temperature of liquids and gases, you can use low finned tubes. Then there are safety tubes which are also known as double-wall tubes. They have particular leakage paths to separate fluids.

Tubes applicable in oil coolers, condensers, water heaters, etc., are medium-high finned tubes. For specific applications with the best designs, stainless steel finned tubes can be used.

Other Application of Finned Tubes

Finned tubes are used to relay heat in any industry where hot fluid has to be transferred to cold fluid through a proper medium. They expand the exterior of the tube. Finned tubes have the capacity to take the place of bare tubes with reduced volume and cost.

One of the significant feature of finned tubes is to secure the surface area of heat exchanger tubes. Heat transfer is based on the outside area to which the fluid is exposed, temperature difference between the fluids, and the heat transfer between the tube and fluids.

Application of Finned Tubed in Industries

  • Petroleum Industry
  • Chemical industry
  • Wood industry
  • Food industry
  • Steel Industry
  • Plastic molding industry
  • Glycol dehydration units
  • Coils for hybrid cooling towers
  • Printing Machines
  • Production of surface coatings
  • Solvent recovery
  • Cooling of turbine air intakes
  • Textile production
  • Greenhouse heaters and breeding
  • Tanneries
  • Anti-freeze coils for process air
  • Paper works

Finned tubes heat exchangers can be applied in various household as well as industrial machineries. Car radiator also used finned tube heat exchangers which cools the hot water in the tubes when air passes through it. This is a crossflow process.

For industrial purposes, finned tube heat exchangers are generally used to heat or cool the air and other gases. Finned tubes have fins attached to its exterior areas. Hence, with the increase in the outside area, the heat transfer rate also increases. Moreover, in the long run, it abbreviates the overall equipment size.

Advantage of Fin Tube Heat Exchanger

A finned tube adds a lot of heat transfer surface area for the fluid outside the tube, which is usually air or some other gas for a fin tube exchanger.

Use of a fin tube exchanger works especially well for an air heat exchanger.

Introduction

For a liquid-liquid heat exchanger, the use of a finned tube isn’t normally needed, because the heat transfer coefficient for both sides of the heat transfer surface is relatively high. For an air heat exchanger, however, where one of the fluids is air or some other gas, the air side heat transfer coefficient will be much lower, so additional heat transfer surface area, as in a fin tube exchanger is very helpful. The overall flow pattern for a finned tube exchanger is often crossflow, but it can also be counterflow or parallel flow.

General Configuration of a Fin Tube Exchanger

A finned tube heat exchanger will typically have tubes with fins attached to the outside of them. There will usually be a liquid flowing through the inside of the tubes and air or some other gas flowing outside of the tubes, where the additional heat transfer surface area due to the finned tube, increases the heat transfer rate. For a crossflow fin tube exchanger, the fins will typically be radial fins either circular or square, as shown in the pictures in this section.

Most finned tube heat exchangers are crossflow, using finned tubes somewhat like the upper pictures. For a counterflow or parallel flow fin tube exchanger, the fins should be longitudinal instead of radial, as shown in the lower diagram at the left. Finned tubes may be used as internal tubes in an enclosed heat exchanger, but in many cases with an air heat exchanger, the air flows through an open heat exchanger as shown in the next section, where some typical applications of finned tube heat exchangers are shown and discussed.

Examples of Fin Tube Heat Exchangers

Finned tube heat exchangers are used in a variety of household applications and as industrial heat exchangers. An air heat exchanger like the evaporator coil for an air conditioning unit is typically a fin tube heat exchanger. Another common fin tube air heat exchanger is the car radiator. The purpose of the car radiator is to cool the hot water in the tubes with the air passing through in crossflow. The air conditioner evaporator coil has the purpose of cooling the air passing through it.

A fin tube heat exchanger can be used as an industrial heat exchanger also. An application that has seen widespread expansion recently is ‘dry cooling’ for steam power plants. This consists of using an air cooled condenser instead of a water cooled condenser. Interest in dry cooling for steam power plants has increased because of concern about the amount of water use and thermal effects on water bodies from the traditional cooling systems, ‘once through cooling’ and ‘closed system – cooling tower cooling.

The heat exchange principle of finned tube and the application of finned tube

The characteristics of finned tube 

In order to improve the heat exchange efficiency, fins are usually added on the surface of the heat exchange tube to increase the heat exchange.

The outer surface area (or inner surface area) of the tube, so as to achieve the purpose of improving the heat exchange efficiency, so

The heat exchange tubes are called finned tubes.

The finned tube is used as a heat exchange element and works under high temperature flue gas conditions for a long time, such as a pot

The finned tubes for furnace heat exchangers are used in harsh environments, high temperature and pressure, and corrosive atmosphere.

The finned tube should have a high performance index.

1) Anti-corrosion

2) Wear resistance (Anti-wear)

3) Low contact resistance (lower contact resistance)

4) High stability (Higher Stability)

5) Anti-fouling ability

High-frequency welding spiral finned tube is one of the most widely used spiral finned tubes.

It is widely used in power, metallurgy, cement industry preheat recovery and petrochemical industries. High

The frequency welding spiral fin tube uses the skin effect of high frequency current while the steel strip is wound around the steel tube.

And proximity effect, heating the steel strip and the outer surface of the steel pipe until the plastic state or melting, in the winding

The welding is completed under a certain pressure around the steel belt. This kind of high frequency welding is actually a solid phase welding.

Compared with inlaying, brazing (or overall hot-dip galvanizing) and other methods, whether it is in product quality (fin’s

The welding rate is high, up to 95%), and the productivity and the degree of automation are more advanced.

Second, the principle of finned tube heat transfer

Below we discuss the heat transfer of the lower fin tube through an example of a specific heat transfer device thermal principle.

There is a heat exchanger that uses hot water to heat the air. The hot water flows in the tube and the air is outside the tube.

flow. For example, the hot air curtain for heating or the radiator on the car belong to this

A type of heat transfer, that is, the heat of the hot water is transferred through the tube wall to the cold fluid outside the tube—air.

It can be seen that the heat transfer process is closely related to the two convective heat transfer processes on both sides of the partition wall.

For the above example: the convective heat transfer coefficient on the water side of the tube is about 5000, while the

convective heat transfer coefficient on the air side is about 50, and the difference between the two is 100 times. Due to the heat exchange on the air side the “capacity” is much lower than the water side, which limits the performance of the heat exchange “capacity” of the water side and makes the air the side becomes the “bottleneck” of the heat transfer process, limiting the increase in heat transfer. 

To overcome the air side for the bottleneck effect, adding fins on the outer surface of the air side will be the most sensible choice.

After installing the fins, the original heat transfer area on the air side has been greatly expanded to make up for overcome the shortcomings of low heat transfer coefficient on the air side, the heat transfer is greatly improved.

The effect of adding fins can also be illustrated by the following more vivid example:

The immigration department at the border port assumes that Party A’s port has ten inspection ports and can be released every hour

5000 people, but there is only one ticket gate at Party B’s port, and it is very slow. It can only be released every hour.

Line 50 people. In this way, Party B’s side becomes a bottleneck for passenger clearance, making Party A’s “ability”

Can’t play. In order to increase the flow of customs clearance, the most effective way is to open a few more on the side of Party B.

Inspection port. This is the same as the principle of installing fins.

When should finned tubes be used for heat exchange?

After understanding the principle and function of finned tubes, where to choose finned tubes, there are the following principles:

(1) If the heat transfer coefficients on both sides of the tube are very different, the heat transfer coefficient should be small

Fins are installed on one side.

Example 1: The boiler economizer has water in the tube and flue gas out of the tube, and fins should be used on the flue gas side.

Example 2: Air cooler, liquid is in the tube, air flows out of the tube, fins should be added to the air

side.

Example 3: In the steam generator, water is boiled inside the tube, and flue gas flows outside the tube. Fins should be added to the

Smoke side. It should be noted that in the design, the side with the smaller heat transfer coefficient should be placed outside the tube as much as possible to facilitate the installation of fins.

(2) If the heat transfer coefficients on both sides of the tube are very small, in order to enhance heat transfer, the same

When installing fins, if there are structural difficulties, no fins can be added on both sides. under these circumstances,

If only fins are added to one side, there will be no obvious effect on the increase in heat transfer.

Example 1: The traditional tubular air preheater uses air inside the tube and flue gas outside the tube. because

It is the heat transfer of gas to gas, the heat transfer coefficients on both sides are very low, and it is difficult to add fins in the tube, so I had to use a bare tube.

Example 2: Heat pipe air preheater, although the flue gas still heats the air, but due to the flue gas and

The air flows outside the tube, so finned tubes can be conveniently used on both the flue gas side and the air side, so that

the heat transfer is greatly increased.

(3) If the heat transfer coefficients on both sides of the tube are large, there is no need to use finned tubes.

Example 1: Water/water heat exchanger, when hot water is used to heat cold water, the heat transfer coefficients on both sides are sufficiently high, there is no need to use finned tubes. But in order to further enhance heat transfer, threaded pipe or

the corrugated tube replaces the light tube.

Example 2: In the condenser of a power plant, water vapor is condensed outside the tube, and water flows inside the tube. On both sides.

The heat transfer coefficient is very high, under normal circumstances, no need to use finned tubes.

Are you looking for idea and suitable solution for your heat exchange work.

Murphy Finned Tubes might be the one for your inquiry.

info@murphyfinnedtubes.com

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