CN101226021A - Finned tube heat exchanger lined with metal foam - Google Patents

Abstract

The invention relates to a finned tube heat exchanger lined with metal foam in the field of refrigeration technology, which includes metal fins outside the tube, metal tubes and metal foam, and the tube is filled with metal foam to improve the heat transfer performance in the tube of the heat exchanger . There are holes inside the metal foam for the circulation of gas or liquid medium. The metal foam is lined in the metal pipe in the form of one or two or three of the full-section type, the inner ring type, or the top-thin bottom-thickness type. The heat transfer effect of the present invention is obviously better than that of the existing finned tube heat exchanger, thereby reducing the volume of the heat exchanger and saving materials. According to preliminary calculations, both the volume of the heat exchanger and the materials used can be reduced by 20%-40%; and Compared with the finned tube heat exchanger commonly used at present, the cost increase is not much.

Description

Finned tube heat exchanger lined with metal foam

technical field

The invention relates to a heat exchanger in the technical field of refrigeration, in particular to a finned tube heat exchanger lined with foam metal.

Background technique

Finned tube heat exchanger is a form of heat exchanger widely used in refrigeration, air conditioning, chemical and other industrial fields. The finned tube heat exchanger is composed of metal fins and metal tubes. Multiple metal fins with the same shape are distributed in parallel. Multiple metal tubes pass through all the metal sheets. The fluid in the tubes flows in their respective tubes, and the tubes do not interact with each other. Blending, the fluid (usually gas) outside the tube flows in the space formed by the tube and the metal sheet. Taking the application in room air conditioners as an example, finned tube heat exchangers have been widely used as evaporators and condensers. When used as an evaporator, the refrigerant evaporates into gas in the tube, and the way the air flows between the fins outside the tube transfers heat to the refrigerant, thereby reducing the air temperature. When used as a condenser, the refrigerant condenses into a liquid in the tube, and the air flowing between the fins outside the tube takes away the heat released by the refrigerant when it condenses. With the continuous improvement of people's requirements for energy saving and consumption reduction, the requirements for high efficiency, energy saving and miniaturization of heat exchangers are also getting higher and higher. The traditional finned tube heat exchanger structure has low efficiency, small power density, The problem of insufficient compact structure is becoming more and more difficult to meet the needs of the market. Therefore, it is urgent to find a more effective way to enhance heat transfer in the tube to improve the overall efficiency of the finned tube heat exchanger.

In view of the problem that the heat exchange area in the tube of the finned tube heat exchanger cannot be greatly increased, metal foam is a porous material with a large specific surface area (surface area per unit volume) (up to 2000-10000m ² /m ³ ), Its application can provide a new solution. Metal foam is composed of rigid skeleton and internal holes, and it is a new type of material with excellent physical properties and good mechanical properties. The salient feature of metal foam is that it has a large number of pores inside. According to whether the pores are connected or closed, there are open-pore structure and closed-pore structure. A large number of internal pores make the metal foam material have many excellent characteristics, such as small specific gravity, large specific surface area, good energy absorption performance, high heat exchange and heat dissipation capacity (open cell structure), good sound absorption (open cell structure), and excellent permeability. (open cell structure), good electromagnetic wave absorption (open cell structure), heat resistance, heat and fire resistance, thermal shock resistance, regeneration, good processability, etc. Metal foam has a large specific surface area. Taking the open-cell metal foam produced by the PMF method as an example, the specific surface area can reach up to 45cm ² /cm ³ . It can be seen that the metal tube lined with metal foam in the finned tube heat exchanger can effectively increase the heat transfer area in the tube and enhance the heat transfer in the tube. Moreover, due to the complex structure of the metal foam, it is beneficial to use the three-dimensional complex flow under the condition of forced convection to overcome the adverse effects of the boundary layer. In addition, for the fluid boiling phase transfer heat process, filling the tube with metal foam can also increase the bubble point, causing the internal boiling heat exchange of the fluid.

According to the literature search of the prior art, it is found that there are related patents on the use of foamed metal materials to realize the enhanced heat transfer of heat exchangers, but they are different from the content of this patent application. The previous patents used metal foam to enhance heat transfer outside the tube, or filled metal foam in other forms of heat exchangers to achieve the purpose of enhancing heat exchange, such as the application number 200610105100.6, named "a tube heat exchanger" The patent is to use foam metal instead of traditional aluminum foil to forcefully replace the heat transfer outside the tube, and the patent with the application number 200610104597. In the form of a heater, both the outer tube and the inner tube are filled with metal foam to achieve the purpose of enhancing heat exchange between the fluid in the inner tube and the fluid between the two tubes. However, the heat exchange area in the tube cannot be greatly increased, so that the enhanced heat exchange in the tube encounters a bottleneck.

Contents of the invention

The present invention aims at the above-mentioned deficiencies in the prior art, and provides a finned tube heat exchanger lined with metal foam, which can improve the heat transfer coefficient in the tube by arranging metal foam in the tube, thereby improving the heat transfer rate of the finned tube. The heat exchange efficiency of the fluid inside and outside the tube can be improved to achieve the purpose of reducing the volume of the finned tube heat exchanger and saving materials.

The present invention is achieved through the following technical solutions, the present invention includes: metal fins, metal tubes, metal foam, the metal fins are located outside the metal tube, the metal foam is filled in the metal tube, and the inside of the metal foam has gas or liquid medium holes for circulation.

The metal fins can be made of aluminum, copper or other metals, each fin has the same shape, 10-200cm long and 2-20cm wide, and can be flat fins, corrugated fins, slotted fins, Louvered fins or other fin types to enhance heat transfer across the fin surface.

The metal tube can be a bare tube of aluminum, copper or other metal materials, the inner diameter of the tube is 2.5-30mm, the wall thickness of the tube is 0.2-5mm, and a plurality of metal tubes of the same specification are equidistantly distributed in parallel, and each tube section is made of metal The elbow is in communication with its adjacent pipe, and the other end is connected with the other adjacent pipe by the metal elbow, so that all the pipes are connected into a passage through which the fluid to be exchanged for heat flows.

The foam metal is made by injecting gas foaming agent into liquid metal, electroplating or investment casting, solid powder sintering or injection molding. The foam metal is copper, aluminum, stainless steel or other metals, and the hole diameter is 0.05mm-5mm. Metal foam has three lining forms in the pipe:

(1) Full-section type: metal foam fills the entire metal tube. This form can get the largest heat transfer area and the most complex space structure, and it is expected to get the best heat transfer effect, but its pressure drop may be the largest.

(2) Inner ring type: the inner wall of the metal tube is connected with metal foam with uniform thickness, the center of the metal tube is empty, and the thickness of the metal foam is 1%-45% of the inner diameter of the metal tube. Considering that the full-section type may make the fluid flow resistance coefficient too large, this type of design takes into account the effect of enhancing heat transfer and the size of the flow resistance.

(3) Thin top and thick bottom: more metal foam is distributed at the bottom of the metal tube than at the top, the thickness of the metal foam at the bottom of the metal tube is 1%-45% of the inner diameter of the metal tube, and the thickness of the metal foam at the top is 0% of the inner diameter of the metal tube %-45%. Considering the actual process of phase transformation heat in the tube, taking the evaporation process as an example, the refrigerant has a low dryness at the initial stage of entering the evaporator, and the refrigerant liquid will be distributed near the bottom of the metal tube due to gravity, so the bottom of the metal tube It is more necessary to strengthen the heat exchange measures.

In a finned tube heat exchanger, only one of the above three forms can be used, for example, all metal tubes are lined with inner ring metal foam, or two or three of them can be used, for example, in the heat exchanger Several metal tubes close to the heat exchange fluid inlet are lined with a thin top and a thick bottom, which is more conducive to faster evaporation of low-dryness fluids, and the inner ring lining is used in the subsequent metal tubes.

In the above-mentioned fin-tube heat exchanger, the materials of the metal fins, metal tubes and metal foam can be the same, or can be the same or different from each other.

The present invention has significant advantages and positive effects. The heat transfer effect can be significantly better than the existing finned tube heat exchanger, thereby reducing the volume of the heat exchanger and saving materials. According to preliminary calculations, the volume and materials of the heat exchanger can be reduced by 20%-40%; and with Compared with the commonly used finned tube heat exchanger at present, the cost increase is not much.

Description of drawings

Figure 1 shows three distribution modes of metal foam in the pipe, among which: Figure 1a is the full-section type, Figure 1b is the inner ring type, and Figure 1c is the top-thin bottom-thick type.

Fig. 2 is a schematic structural view of a fin-tube heat exchanger, wherein: Fig. 2a is a front view of the heat exchanger, and Fig. 2b is a side view of the heat exchanger.

In the figure, 1 is a metal pipe, 2 is metal foam in the metal pipe, 3 is a metal fin, and 4 is a metal elbow.

Detailed ways

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

The traditional finned tube heat exchanger consists of metal fins 3 and metal tubes 1, in which the metal tube 1 can be a plain tube or a strengthened tube, such as a threaded grooved tube, a horizontal grooved tube, a corrugated tube, etc. They all enhance the heat transfer effect in the tube.

As shown in Figure 1-2, the finned tube heat exchanger of the present invention includes metal fins 3 outside the tube, metal tube 1 and metal foam 2 inside the metal tube 1, and metal foam 2 inside the tube to increase the heat exchange area inside the tube , to enhance the turbulence, the metal foam 2 has a through hole for the gas or liquid medium to circulate.

Due to the unique structure and performance of the metal foam 2, the heat exchange efficiency in the heat exchanger tube is greatly improved, so that the heat exchange efficiency between the fluid inside and outside the heat exchanger tube is greatly improved.

The above-mentioned metal foam 2 in the tube can be any one of three lining forms, so as to meet different heat exchange requirements. The hole diameter of the metal foam 2 is 0.05mm-5mm. The metal foam 2 is covered on the inner surface of the tube by methods such as metal powder sintering, electroplating or investment casting (seepage).

Taking the full-section foam metal 2 lining form as an example, the specific implementation method of making the finned tube heat exchanger shown in Figure 2 is introduced:

Cut the cylindrical metal foam 2 whose length is the same as that of the metal pipe 1 and whose diameter is slightly larger than the inner diameter of the metal pipe 1 (the axial section is shown in Figure 1a). Fix the metal tube 1, push the cylindrical metal foam 2 into the metal tube 1 along the axial direction of the tube, and at the same time use a wire to connect with the end of the columnar metal foam 2 entering the metal tube 1, and help overcome the problem by pulling the metal wire. The frictional resistance between the metal foam 2 and the pipe wall until the metal foam 2 is completely embedded in the metal pipe 1. Since the diameter of the columnar metal foam 2 is slightly larger than the inner diameter of the metal tube 1, the edge of the metal foam 2 will be squeezed and deformed, so as to be more tightly combined with the inner wall of the metal tube 1. Of course, other methods can also be used to fill the metal foam 2 In the metal tube 1, as long as the two are closely combined to achieve the purpose of increasing the heat exchange effect.

Drill circular holes on each metal fin 3, the aperture is slightly smaller than the outer diameter of the metal tube 1, the number of holes is the same as the number of the metal tube 1, and the positions of the holes on each metal fin 3 are the same (the metal fins 3 are drilled The location is shown in Figure 2b). All the metal fins 3 are placed in parallel, and each metal tube 1 lined with metal foam 2 passes through the hole at the same position of each fin. Since the aperture on the metal fin 3 is slightly smaller than the outer diameter of the metal tube 1, when the metal tube 1 passes through the metal fin 3, extrusion deformation will occur around the round hole of the metal fin 3, so that it is tightly connected to the outer wall of the metal tube 1. touch.

The metal pipes 1 are connected by metal elbows 4. The connection between the pipes is shown in Figure 2. The two uppermost metal pipes 1 that are not connected to the metal elbows 4 are used as the heat exchange fluid in the heat exchanger. The import and export of (as shown in Figure 2a).

Metal foam 2 is mainly produced by liquid metal injection gas or foaming agent method, investment casting method, solid powder sintering method and injection molding. There are holes in the metal foam 2 for the circulation of gas or liquid medium, and the diameter of the holes ranges from tens of microns to several millimeters.

The material of the foamed metal 2 can be the same material as the commonly used heat exchange tube, or a metal different from the heat exchange tube, such as aluminum, copper or other metal materials. The remarkable advantages of using metal foam 2 are that it has the characteristics of high heat transfer efficiency, large specific surface area, low density, light weight, compact structure, and excellent noise reduction function, and any metal material can be processed, so in the design High-efficiency and compact fin-tube heat exchangers have shown great application value.

For the preparation of the metal pipe 1 of the metal foam 2 inner ring type lining mode, a kind of specific implementation method is provided below:

Cut a piece of metal foam 2 for lining in the metal pipe 1, its length is equal to the length of the metal pipe 1, its width is equal to the circumference of the inner wall of the metal pipe 1, and its thickness is equal to the thickness of the metal foam 2 that needs to be lined in the design. The metal foam 2 pieces are curled into a cylindrical shape with the length direction as the axial direction, and the metal foam 2 is built into the metal tube 1. For the specific method, please refer to the full-section placement method. Of course, other methods can also be used to prepare the metal pipe 1 of the inner ring of the metal foam 2 or the inner lining mode with a thin top and a thick bottom, as long as the metal foam 2 can form the distribution form required by the design in the metal pipe 1, and the metal foam 2 and the It is sufficient that the inner walls of the metal pipe 1 can be closely connected.

Claims (10)

1. A finned tube heat exchanger lined with metal foam, comprising metal fins, metal tubes, metal foam, metal fins located outside the metal tube, characterized in that the metal tube is filled with metal foam, the foam metal There are holes in the metal for the flow of gas or liquid medium. 2. The finned tube heat exchanger lined with metal foam according to claim 1, characterized in that, the metal foam is lined in the metal tube in the form of a full-section type, an inner ring type or an upper thinner lower One or two or three in thick style. 3. The finned tube heat exchanger lined with metal foam according to claim 2, wherein the full-section lining means that the metal foam fills the entire metal tube. 4. The finned tube heat exchanger lined with metal foam according to claim 2, characterized in that, the inner ring type lining means that the inner wall of the metal tube is connected with the metal foam with uniform thickness, and the metal The center of the tube is empty. 5. The finned tube heat exchanger lined with metal foam according to claim 2 or 4, characterized in that, in the form of the inner ring lining, the thickness of the metal foam is 1% of the inner diameter of the metal tube -45%. 6. The finned tube heat exchanger lined with metal foam according to claim 2, characterized in that, the upper thinner and lower thick lining means that the bottom of the metal tube is more distributed than the top metal foam. 7. The finned tube heat exchanger lined with metal foam according to claim 2 or 6, characterized in that, in the form of the upper thinner and lower thick inner lining, the thickness of the metal foam at the bottom of the metal tube is 1%-45% of the inner diameter of the tube, and the thickness of the metal foam at the top is 0%-45% of the inner diameter of the metal tube. 8. The finned tube heat exchanger lined with metal foam according to claim 1 or 2 or 3 or 4 or 6, characterized in that the metal foam has a pore diameter of 0.05mm-5mm. 9. The finned tube heat exchanger lined with metal foam according to claim 1, characterized in that, the metal fins have the same shape of each fin, with a length of 10cm-200cm and a width of 2cm-200cm. 20cm. 10. The metal foam-lined finned tube heat exchanger according to claim 1 or 2 or 3 or 4 or 6, characterized in that the metal tube has an inner diameter ranging from 2.5 mm to 30 mm, The wall thickness of the tube is 0.2mm-5mm, and a plurality of metal tubes of the same specification are equidistantly distributed in parallel. One section of each tube is connected by a metal elbow and its adjacent tube, and the other end is connected by a metal elbow and its adjacent one. One tube is connected, so all the tubes are connected to form a passage through which the fluid requiring heat exchange flows.

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