What Is The Heat Transfer Performance Comparation Between Copper Tube And Stainless Steel Heat Exchange Tube?

- Mar 23, 2018-


Stainless steel heat exchange tube: A device made of stainless steel, which is one of the components of the heat exchanger, placed inside the cylinder and used for the exchange of heat between the two media.


Stainless steel  heat exchange tubes have the following advantages:

1. The heat exchange tube uses 0.5-0.8mm thin-walled pipe to improve the overall heat transfer performance. With the same heat transfer area, the overall heat transfer coefficient is 2.121-8.408% higher than that of copper tubes.

2. Because the material is made of SUS304 stainless steel with high quality, it has high hardness, and the degree of rigidity of the pipe is also obviously improved. Therefore, it has strong impact resistance and vibration resistance.

3. Because the inner wall of the tube is smooth, the thickness of the bottom layer of the boundary laminar flow is reduced, which not only enhances the heat exchange but also improves the anti-fouling performance. In order to eliminate the welding stress, heat treatment is performed at a high temperature of 1050°C in the shielding gas. All steel pipes are leak checked with differential pressure, pressure test to 10MPa, no pressure drop for 5 minutes.

Brass tube: Also known as copper tube, a type of non-ferrous metal pipe that is pressed and drawn seamlessly. Copper tubes have strong, corrosion-resistant characteristics, and become the first choice of modern contractors in the installation of water pipes, heating and cooling pipes in all residential commercial housing. Copper tube is the best water supply pipe.


The advantages of copper tube:

1. Lighter weight, good thermal conductivity and low temperature strength. Commonly used in the manufacture of heat exchange equipment (such as condensers, etc.). It is also used to assemble cryogenic piping in oxygen plants. Small diameter copper tubes are commonly used to deliver pressurized fluids (such as lubrication systems, oil pressure systems, etc.) and piezometers used as instruments.

2. Copper pipes have strong, corrosion-resistant characteristics, and become the first choice for modern contractors to install water pipes, heating and cooling pipes in all residential commercial housing.

3. Copper tubes combine many advantages in one: It is strong, with high strength of general metals. At the same time, it is easier to bend than ordinary metals, easy to reverse, hard to crack, hard to break, and has a certain degree of anti-frost and impact resistance. Therefore, the installation of copper pipes in the water supply system in the building is safe and reliable, even without maintenance.

The disadvantages of copper tube: In the case of copper pipes, the high price is its biggest drawback. It is currently the most high-grade water pipe. It is usually installed after the welding process and will not leak water for life. The connection of the copper pipe connection mainly depends on the construction technology level and has a higher requirement on construction quality.


The following will explain the difference between copper and stainless steel heat transfer tubes from the following aspects:

The performance comparison of copper tube and stainless steel heat exchange tube is as follows:

1. Comparison of heat conduction between copper tube and stainless steel heat exchange tube

Since the thermal conductivity of the copper tube is 100 W/m°C, the thermal conductivity of the stainless steel tube is 13 W/m°C, which of course affects the overall heat transfer coefficient. However, the wall thickness of the stainless steel pipe can be reduced by 0.5 to 0.8 mm, and the copper pipe has a wall thickness of not less than 1.2 mm due to strength and erosion wear.

According to the formula: Rc = (1) where: Rc - thermal thermal resistance, m2k/w. Λ—thermal conductivity, W/(m.k).

Δ—wall thickness, m

When the tube is constant and λ is constant, according to formula (1), the smaller the δ is, the smaller the Rc is, and the larger the heat transfer coefficient is. This can reduce the difference in the overall heat transfer coefficient between the stainless steel pipe and the copper pipe.

Because the inner and outer walls of the copper pipe are rougher than stainless steel, it is easy to foul and increase the thermal resistance of the copper pipe, which in turn reduces the overall heat transfer coefficient difference between the copper pipe and the stainless steel pipe.


2. Comparison of Convection and Heat Release Characteristics of Copper Tubes and Stainless Steel Heat Exchange Tubes

Using stainless steel tubes or copper tubes, the flow rate in the tubes is turbulent. The largest contributing factor to the convective heat release is the thickness of the laminar bottom layer because the heat transfer in the laminar bottom layer is thermally conductive and the thermal conductivity of water is very low. In the same flow conditions, the thickness of the laminar bottom layer depends on the roughness of the inner wall of the tube. The inner surface of the copper tube has oxides and its roughness is much larger than that of the stainless steel tube. The thickness of the laminar bottom layer of the copper tube is greater than the thickness of the laminar bottom layer of the stainless steel tube. This causes the convection heat transfer coefficient of the stainless steel tube to be larger than the convective heat release coefficient of the copper tube. 

Rw=(2)

Among them: Rw—Thermal and thermal resistance to exile, m2k/w. Αw—convection heat release coefficient, w/m2.k. According to formula (2), the larger αw, the smaller Rw.


3. Condensation heat transfer coefficient comparison of copper tube and stainless steel heat exchange tube

There are two types of condensation heat release coefficient: film condensation and bead condensation, and the bead condensation heat release coefficient is much larger than the film condensation heat release coefficient. However, it is unclear which type of bead-like condensation occurs on the outer wall of the stainless steel pipe and the outer wall of the copper pipe, but it can be said that most of the outer wall of the two types of pipe are film-like condensation. The size of the exothermic coefficient of the film-like condensation has a great relationship with the thinness of the film because the inside of the film is thermally conductive. The thermal conductivity of the water film is particularly low and the thickness of the film depends on the roughness of the outer wall of the tube. The outer wall of the copper tube is much rougher than the stainless steel tube due to the oxide layer. Therefore, the condensation heat coefficient of the outer wall of the stainless steel pipe is larger than the condensation heat coefficient of the outer wall of the copper pipe.

Rm=(3)

Among them: Rm—condensation heat resistance of the outer wall of the pipe, m2k/wαm—condensation heat coefficient of the outer wall of the pipe, w/m2.k. According to formula (3), the larger αm, the smaller Rm.


4. Comparison of Heat Transfer Coefficients of Copper and Stainless Steel Tubes

K=(4)

Among them: R - total thermal resistance, m2k/w. K - overall heat transfer coefficient, w/m2.k.

From (4), it can be seen that the convection thermal resistance, the thermal conductivity and the condensing thermal resistance all decrease, and the total thermal resistance decreases: the total thermal resistance decreases, and the overall heat transfer coefficient increases.

With the same wall thickness, the overall heat transfer coefficient of the stainless steel pipe is 6% lower than that of the copper pipe. Due to the use of stainless steel tubes that are thinner than copper tubes, the overall heat transfer coefficient and the condensation heat release coefficient of the stainless steel tubes are larger than those of the copper tubes, so that the overall heat transfer coefficient of the stainless steel tubes is improved. 


Copper tube and stainless steel tube heat transfer performance   comparison table

Name

Specificationmm)

Material

Overall heat transfer coefficientW/m².k

Copper tube

1

HSn70-IA

3682.423869

Stainless steel tube

1

AI304

3460.327347

Stainless steel tube

0.7

AI304

3760.628476

Stainless steel tube

0.8

AI304

3872.686729


5. Long-term Economical Comparison of Copper Tubes and Stainless Steel Heat Exchange Tubes

As the running time increases, the copper oxide layer will become thicker and the heat transfer effect will become worse and worse. Stainless steel does not oxidize or it oxidizes very slowly. Therefore, if the heat exchangers of stainless steel tubes and copper tubes are put into operation at the same time, the longer the running time is, the more economical the heat exchangers of stainless steel tubes will be than the copper tube heat exchangers. At the same time, the capacity of the copper tubes to absorb impurities in cooling water is much stronger than that of stainless steel tubes, which greatly reduces the economical efficiency of the equipment.


6. Comparison of safety performance between copper tube and stainless steel heat exchange tube


Copper tube and stainless steel tube heat   transfer engineering characteristics table

Tube Material

Copper tube

Nickel copper tube

304/316 stainless steel tube

Density(t/m³)

8.4

&8.9

8

Yield Strength (Mpa)

120

140

280-350

Tensile Strength (Mpa)

330

390

550-659

Elongation rate (%)

60

43

30-60

Elastic Modulus (Mpa)

13.3

15.4

20

Thermal expansion coefficient (10-6)

16

16

17

Thermal conductivity (w/mk)

100

30

13


From the above table, it can be seen that the yield strength and tensile strength of stainless steel tubes are higher than those of copper tubes. The service life of stainless steel tubes is necessarily longer than that of copper tubes. The coefficient of thermal expansion is lower than that of copper tubes and is closer to that of tube tubes. Therefore, It is not easy to damage the pipe or affect the expansion due to the thermal expansion and contraction.

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