CN101329146A - Porous surface U-shaped heat exchange tube - Google Patents

Abstract

The invention relates to a U-shaped heat exchange tube with a multi-aperture surface, which comprises a parent tube and a multi-aperture layer that is adhered on the surface of the parent tube; the outer diameter of the heat exchange tube is Phi 10mm to Phi 57mm, the thickness of the multi-aperture layer on the surface of the heat exchange tube is 0.1 to 0.5mm, the porosity of the heat exchange tube is 30 to 60 percent, and the smallest bending radius Rmin of a first bending pipe section of the U-shaped heat exchange tube is not less than two times of the outer diameter of the heat exchange tube; the two end parts of the heat exchange tube have smooth surfaces with the length that is less than or equal to 300mm. The U-shaped heat exchange tube is used in U-shaped tube-typed and shell-and-tube heat exchangers, and has freely stretching tube bank, good thermal compensation performance, longer flow path, higher flow speed, and better heat conductivity and strong bearing capacity.

Description

Porous surface U-shaped heat exchange tube

technical field

The invention relates to a heat exchange tube in a shell-and-tube heat exchanger used in the industrial fields of petroleum, chemical industry, metallurgy, etc., in particular to a heat exchange tube in a U-shaped tube heat exchanger.

Background technique:

Heat exchangers are widely used in chemical industry, chemical fertilizer, oil refining, power, construction, food and other industrial sectors. The tubes used in traditional shell-and-tube heat exchangers usually use smooth tubes, which have low heat transfer efficiency. Since the porous tube artificially provides a large number of capillary holes on the porous surface, it provides a large number of vaporization cores for boiling heat transfer. Compared with the smooth surface, the bubble emission frequency on the porous surface is higher, the number of activated pores is larger, and the bubble jumping diameter is larger. . Therefore, the surface porous tube has good boiling heat transfer ability, its heat transfer coefficient can reach 5 to 15 times that of the same smooth tube, maintain boiling under a small temperature difference, and has good anti-fouling performance. The main advantage of the heat exchanger made of U-shaped tubes is that the tube bundle can be freely expanded and contracted, no thermal stress will be generated due to the temperature difference between the tube shells, and the thermal compensation performance is good; The thermal performance is good, the pressure bearing capacity is strong, the tube bundle can be pulled out from the shell, which is convenient for maintenance and cleaning, and the structure is simple and the cost is cheap. Porous tube for heat exchange and its manufacturing method (200610139226.5), a low-temperature sintering method for a surface porous tube (03116481.1), a porous tube (02291429.3), a porous tube for a heat exchanger, and a tube expansion method for a porous tube for a heat exchanger (200480033028. Patents such as X), flat porous tube and heat exchanger (200580029119.0) have proposed several styles and forming methods of porous tubes, but these patents do not involve the forming method of U-shaped tubes with porous surfaces. Heat exchange tubes in a U-tube heat exchanger.

Contents of the invention

The purpose of the present invention is to overcome the disadvantage of low heat transfer efficiency of traditional heat exchange tubes, and to invent a heat exchange tube that enhances boiling heat transfer, so as to improve the heat transfer efficiency of the heat exchanger and reduce the operating energy consumption of the existing heat exchanger and equipment investment.

The present invention is achieved through the following technical solutions:

A U-shaped heat exchange tube with a porous surface, characterized in that the heat exchange tube 1 is U-shaped, including a base tube 2 and a porous layer 3 attached to the surface of the base tube 2; the outer diameter of the heat exchange tube 1 is Φ10mm～ Φ57mm, the thickness of the porous layer 3 on the surface of the heat exchange tube is 0.1-0.5mm, the porosity is 30%-60%, and the minimum bending radius R _min of the U-shaped heat exchange tube 1 elbow section is not less than twice the outer diameter of the heat exchange tube ; The two ends of the heat exchange tube 1 are smooth surfaces, and the length L of the smooth surfaces is ≤300mm.

The material of the base pipe can be one of carbon steel, alloy steel, stainless steel and copper alloy.

The porous surface of the heat exchange tube can be formed by direct machining on the outer surface of the heat exchange tube matrix by a machine tool, or can be formed by high-temperature sintering or high-temperature spraying of a layer of metal powder on the outer surface of the heat exchange tube matrix. The metal powder can be iron-based powder and copper-based powders.

During production, surface porous U-shaped heat exchange tubes with different bending radii can be produced on the tube bender according to the actual tube layout requirements, and the size of L can be determined according to the thickness of the heat exchanger tube sheet. During production, the thickness of the porous layer 3 on the surface of the heat exchange tube is 0.1-0.5 mm, and the thickness of the base tube varies from 0.5-10 mm according to different specifications of the tube.

Beneficial effect

1. The efficiency of boiling heat transfer depends on the number of vaporization cores on the heat exchange surface. Porous surface heat exchange tubes are more likely to generate bubble cores on the heat exchange surface than smooth surface heat exchange tubes. Porous surface heat exchange tubes can effectively enhance boiling heat transfer. Compared with the smooth surface heat exchange tube, the boiling heat transfer coefficient outside the tube is increased by 5 to 15 times.

2. The present invention is used for heat exchange tubes in U-shaped tube shell-and-tube heat exchangers. The main advantage of U-shaped tube heat exchangers is that the tube bundles can be freely expanded and contracted, and no heat will be generated due to the temperature difference between the tubes and shells. Stress and heat compensation performance is good; the tubes are double tubes, the process is longer, the flow rate is higher, the heat transfer performance is better, the pressure bearing capacity is strong, the tube bundle can be drawn out from the shell, easy to repair and clean, and the structure is simple and the cost is cheap.

Description of drawings

Figure 1 Schematic diagram of U-shaped heat exchange tube on porous surface, in which: 1-U-shaped heat exchange tube, 2-substrate tube, 3-porous layer, I-2,3 enlarged view in Figure 2, R _min - heat exchange tube The minimum bending radius, L- the length of the smooth surface of the end.

Fig. 2 is a partial enlarged view (sectional view) of the porous surface heat exchange tube at I in Fig. 1 . Among them: 2-base tube, 3-porous layer, the thickness of the base tube and porous layer in this figure is not scaled up.

Detailed ways

The present invention will be further elaborated below in conjunction with the accompanying drawings and specific embodiments.

Example:

(1) Preparation of U-shaped heat exchange tubes with porous surface

1. Sintering method

(1) material preparation

Choose metal heat exchange tubes, the tube length is not limited, the tubes are first polished, then sand blasted to increase the surface roughness and the bonding strength of the powder and the matrix, and then degreasing. Choose metal powder with a mesh number of 100 to 300.

(2) Sintered porous tube

Evenly coat a layer of binder solution on the surface of the base metal, and then cover it with a certain mesh of bronze powder. When the binder solution is air-dried, place it in a sintering furnace and heat it to the metal powder under the protection of nitrogen gas. The surface tends to melt, keep the temperature for about 20 minutes to decompose and volatilize the binder, and the metal powder is sintered into one body and sintered on the substrate, thus forming a layer of porous metal covering layer on the surface of the metal substrate.

The resulting porous layer 3 on the surface of the heat exchange tube (as shown in Figure 2) has a thickness of 0.2-0.3 mm and a porosity of 50%-60%. The length L of the smooth surfaces at both ends is 150mm.

(3) Elbow

The sintered porous pipe is bent. The equipment used for bending is a common pipe bending machine. The minimum radius R _min of the bend is 50mm. If the radius of the bend is too small, it will cause the detachment of the porous layer on the surface of the bend and the destruction of the basic structure of the bend.

2. Spraying method

A special flame spray gun is used to spray metal powders of different particle sizes (such as aluminum powder, etc.) and organic polymer material powder or low melting point metal powder mixture as an auxiliary pore-forming agent to the outside of the treated and preheated metal tube at high speed. On the surface of the substrate, it produces a certain chemical metallurgical bond. Compared with the powder sintering method, the processing cost of the flame spraying method is reduced. However, this method cannot produce a metal porous layer on the inner surface of the pipe, and the thickness and aperture of the porous layer are not uniform. The resulting porous layer 3 on the surface of the heat exchange tube (as shown in Figure 2) has a thickness of 0.1-0.2mm and a porosity of 40%-50%. The length L of the smooth surfaces at both ends is 150mm. The porous pipe is subjected to pipe bending treatment. The equipment used for the pipe bending is a common pipe bending machine, and the minimum radius R _min of the pipe bending is 50mm.

3. Machining method

Machining surface porous tubes is to use special tools to open holes of different shapes on the metal tube wall by machining. The resulting porous layer 3 on the surface of the heat exchange tube (as shown in Figure 2) has a thickness of 0.3-0.4mm and a porosity of 45%-55%. The length L of the smooth surfaces at both ends is 150mm. The porous pipe is subjected to pipe bending treatment. The equipment used for the pipe bending is a common pipe bending machine, and the minimum radius R _min of the pipe bending is 50mm.

(2) U-shaped heat transfer tube with porous surface of the present invention compares with smooth tube heat transfer performance

The comparison experiment with the smooth tube of the same material and size shows that the boiling heat transfer coefficient of the U-shaped heat exchange tube with a porous surface can reach about 5 to 15 times that of the smooth tube, the strengthening effect is very significant, and the boiling temperature difference can be reduced to 1 ~3°C, the critical heat load is 2 to 5 times that of the smooth tube.

Claims (2)

1, a kind of porous surface U shape heat exchanger tube is characterized in that, described heat exchanger tube 1 is a U-shaped, comprises parent tube 2 and attached to the porous layer 3 on parent tube 2 surfaces; Heat exchanger tube 1 external diameter is Φ 10mm～Φ 57mm, and heat exchanger tube porous surface layer 3 thickness are 0.1～0.5mm, and porosity is 30%～60%, the minimum bending radius R of U-shaped heat exchanger tube 1 bend loss _MinBe not less than 2 times of heat exchanger tube external diameter; Two ends of heat exchanger tube 1 are smooth surface, the length L≤300mm of smooth surface.

2, porous surface U shape heat exchanger tube as claimed in claim 1 is characterized in that, the material of parent tube is to be selected from a kind of in carbon steel, steel alloy, stainless steel or the copper alloy.

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