CN110763055A - Surface hydrophobic modified composite condensation enhanced heat transfer pipe and preparation method thereof - Google Patents

Abstract

The invention discloses a surface hydrophobically modified composite condensation-enhanced heat transfer tube and a preparation method thereof. The thickness of the liquid is reduced, which reduces the external thermal resistance of the tube, thereby increasing the condensation heat transfer coefficient outside the refrigerant tube, thereby enhancing the effect of condensation heat transfer, and this enhanced effect will change the range of heat flux density in the entire working condition. persistent effect. The heat transfer tube prepared by the present invention can be used in refrigeration, air conditioning and HVAC equipment using shell-and-tube condensers, and the surface hydrophobically modified composite heat transfer tube can conduct heat transfer for condensation in the range of large heat flux density and small heat flux density The heat transfer performance of the device is permanently enhanced. After using the surface hydrophobically modified heat transfer tube, due to the enhanced heat exchange performance of the condensing heat exchanger, the size of the condenser can be reduced, thereby reducing the cost of the system.

Description

A kind of surface hydrophobically modified composite condensation-enhanced heat transfer tube and preparation method thereof

technical field

The invention belongs to the technical field of a surface hydrophobically modified condensation-enhanced heat transfer tube capable of enhancing the condensation phase change heat transfer of a refrigerant outside the tube, and in particular relates to a surface hydrophobically-modified composite condensation-enhanced heat transfer tube and a preparation method thereof .

Background technique

Shell and tube condensers are widely used in refrigeration, air conditioning and waste heat recovery equipment. In the air-conditioning unit, the liquid refrigerant circulating in the system absorbs the indoor heat in the evaporator and gasifies into high temperature and low pressure refrigerant vapor. The refrigerant vapor is then sucked into the compressor and converted into high temperature and high pressure refrigerant vapor. After being discharged, it enters the condenser to cool down and condense, and becomes a low temperature and high pressure refrigerant liquid, and then passes through the throttle valve to become a low temperature and low pressure refrigerant liquid to continue to absorb indoor heat, and so on. The main function of the circulating process condenser is to reduce the temperature of the refrigerant and condense the liquid. If the cooling effect of the condenser cannot reach the expected cooling temperature, the power of the compressor will increase, the energy efficiency of the system will decrease, more electricity will be consumed, and the operating cost of the system will increase. Therefore, improving the cooling efficiency of the shell-and-tube condenser is very important to the performance of the refrigeration system. The general method to improve the heat transfer performance of shell and tube condenser is to optimize the condenser structure. Usually, more measures are taken to adopt heat transfer tubes with better heat exchange performance, optimize the arrangement of tube rows, and use liquid baffles. With the continuous maturity of technology, the optimization of the heat exchange performance of the condenser has gradually approached the bottleneck, and it is more and more difficult to further improve its heat exchange performance, so people have to find other directions and methods to improve the heat exchange of the shell and tube condenser. thermal performance.

At present, after decades of development, it is very difficult to further enhance heat transfer with only machined three-dimensional geometric fins, even 10% is already very difficult. So we need to come up with a new way to strengthen it.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a surface hydrophobically modified composite condensation-enhanced heat transfer tube and a preparation method thereof, which improves the heat transfer coefficient of the heat transfer tube, and the surface hydrophobically modified composite condensation-enhanced heat transfer tube is applied to When the shell and tube condenser is used, the cooling efficiency of the shell and tube condenser is improved.

In order to achieve the above purpose, the surface hydrophobically modified composite condensation-enhanced heat transfer tube according to the present invention includes a tube wall, fins are arranged outside the tube wall, and the fins include fin roots, and the fin roots are The root of the rib is connected to the tube wall, and the end of the rib root extends outward with a first tip and a second tip, the first tip and the second tip meet at the lower part, and the angle at the tip of the first tip and the second tip All are less than 30°; the tube wall and the outer surface of the fin are covered with a hydrophobic layer.

Further, the hydrophobic layer includes a first hydrophobic layer and a second hydrophobic layer covering the first hydrophobic layer, the thickness of the hydrophobic layer is less than 0.1 μm; the thickness of the first hydrophobic layer is greater than the thickness of the second hydrophobic layer.

Further, the material of the hydrophobic layer is a polymer material or plasma.

Further, an internal thread strengthening structure is arranged in the pipe wall.

Further, the angle of the interface between the first tip and the second tip is ≥90°.

Further, the height of the fin root is 2H/3, the height of the first tip is 1H/3, the height of the second tip is 1H/9, and H is the height of the fin.

Further, the rib density of the fins is 38 fpi to 50 fpi, and the rib height is 0.5 mm to 0.9 mm.

A preparation method of a surface hydrophobically modified composite condensation-enhanced heat transfer tube, comprising the following steps:

Step 1, processing fins outside the pipe wall;

Step 2, remove the lubricating oil remaining on the surface of the heat transfer tube during the process of processing the fins from the heat transfer tube;

Step 3, drying the surface of the heat transfer tube;

Step 4, seal both ends of the heat transfer tube:

Step 5, performing hydrophobic modification coating on the outer surface of the heat transfer tube to form a hydrophobic layer on the outer surface of the heat transfer tube.

Further, in step 1, the surface of the heat transfer tube is washed sequentially with isoacetone, isopropanol and clean water, and then the water droplets on the surface of the heat transfer tube are blown off by a spray gun.

Further, the specific process of step 5 is: vacuumize the vapor deposition system, when the vacuum degree reaches the coating conditions, vapor deposition is performed on the surface of the heat transfer tube, and the outer surface of the heat transfer tube is coated to form a hydrophobic layer; , restore the pressure in the vapor deposition system to atmospheric pressure, and complete the hydrophobic modification of the outer surface of the heat transfer tube when the temperature of the heat transfer tube is cooled to room temperature.

Compared with the prior art, the present invention has at least the following beneficial technical effects:

The characteristic of the surface hydrophobically modified composite condensation-enhanced heat transfer tube is that not only the heat transfer is enhanced by mechanically processed three-dimensional fins, but also the secondary hydrophobic treatment is carried out by the method of surface hydrophobic modification. The main reason why this tube type can strengthen the condensation heat transfer outside the tube is that the surface contact angle developed based on the three-dimensional structure is further increased. Compared to the 3D fins without surface modification and the surface treated only with modification, the heat transfer coefficient is greatly enhanced. Since the refrigerant is generally an organic working medium, the surface tension is very small, generally only about one-tenth of that of water, and only the technology of surface modification treatment has little effect on its condensation heat transfer coefficient. On the other hand, the surface heat transfer tube with a three-dimensional geometric structure coated with a hydrophobic coating can greatly enhance the heat transfer coefficient. The reason why the composite modified surface heat transfer tube can enhance the refrigerant heat transfer is:

Since the fins arranged outside the tube wall are three-dimensional reinforced structures, the peak surfaces formed by the first tip and the second tip can break through the liquid film formed by the refrigerant and promote the discharge of the liquid film; after adding the hydrophobic layer, when the When refrigerant condensate is generated outside the heat transfer tube, the large contact angle on the surface of the composite structure composed of the three-dimensional reinforced structure and the hydrophobic layer can accelerate the discharge of the liquid film on the surface of the reinforced structure, which makes the thickness of the condensate on the outer surface of the tube thin. The external thermal resistance of the tube is reduced, thereby increasing the condensation heat transfer coefficient outside the refrigerant tube, which in turn has the effect of strengthening the condensation heat transfer, and this strengthening effect will continue to work within the change range of the heat flux density of the entire working condition.

Further, the hydrophobic layer includes a first hydrophobic layer and a second hydrophobic layer covering the first hydrophobic layer, the thickness of the hydrophobic layer is less than 0.1 micron; the thickness of the first hydrophobic layer is greater than the thickness of the second hydrophobic layer, the first hydrophobic layer The purpose is to enhance the adhesion strength of the second hydrophobic layer, so that the second hydrophobic layer can more continuously strengthen the condensation heat transfer outside the tube.

Further, the angle of the interface between the first tip and the second tip is greater than or equal to 90°, which can significantly thin the thickness of the refrigerant condensate at the top of the three-dimensional fin.

Further, the height of the rib root is 2H/3, the height of the first tip is 1H/3, the height of the second tip is 1H/9, and H is the height of the rib. This structure can enhance the strength of the rib, increase the heat exchange area and effectively reduce the volume of the liquid film between the fins.

Further, the rib density of the fins is 38 fpi to 50 fpi, and the rib height is 0.5 mm to 0.9 mm. These parameters are optimized rib parameters, and the condensation heat transfer effect of the refrigerant is optimal under these parameters.

The heat transfer tube of the present invention can be used in refrigeration, air conditioning and HVAC equipment using shell-and-tube condensers, and the surface hydrophobically modified composite heat transfer tube can improve the performance of the condensing heat exchanger in the range of large heat flux density and small heat flux density. The heat transfer performance is permanently enhanced. After using the surface hydrophobically modified heat transfer tube, due to the enhanced heat exchange performance of the condensing heat exchanger, the size of the condenser can be reduced, thereby reducing the cost of the refrigeration system.

The preparation method of the heat transfer tube includes two steps, namely, the processing of the strengthening tube and the double-layer and multi-layer coating process. The coating material is a polymer material or plasma, and the cost of use is low. Due to the long running time and high energy consumption of the central air-conditioning water-cooling unit, compared with the increase in the coating cost, the increase in heat exchange efficiency and the increase in energy efficiency will return the benefits. More. The formation of the double-layer coating can also significantly improve the corrosion resistance of the heat transfer tube and increase the average service life of the heat transfer device.

Description of drawings

Fig. 1 Schematic diagram of hydrophobic modification on the surface of light pipe;

Figure 2. Double-sided three-dimensional enhanced heat transfer tube;

Figure 3 Schematic diagram of three-dimensional fin outer coating;

Figure 4a is a schematic diagram of the static contact angle before the coating of the light pipe;

Figure 4b is a schematic diagram of the static contact angle after coating of the light pipe;

Figure 4c is a schematic diagram of the static contact angle after the light pipe coating experiment;

Figure 4d is a schematic diagram of the static contact angle of the three-dimensional reinforced tube before coating;

Figure 4e is a schematic diagram of the static contact angle of the three-dimensional reinforced tube after coating;

Figure 4f is a schematic diagram of the static contact angle after the three-dimensional reinforced tube coating experiment;

Figure 4g is a schematic diagram of advancing angle-dynamic contact angle before three-dimensional strengthening tube coating;

Figure 4h is a schematic diagram of the advancing angle-dynamic contact angle of the three-dimensional reinforced tube after coating;

Figure 4i is a schematic diagram of the advancing angle-dynamic contact angle after the three-dimensional strengthening tube coating experiment;

Figure 4j is a schematic diagram of the back-advance angle - the dynamic contact angle of the three-dimensional reinforced tube before coating;

Figure 4k is a schematic diagram of the back-advance angle - the dynamic contact angle of the three-dimensional reinforced tube after coating;

Fig. 4l is a schematic diagram of the dynamic contact angle after the back-advance angle-three-dimensional strengthening tube coating experiment;

Figure 5a is a 100x-3D reinforced tube uncoated electron microscope image;

Figure 5b is a 500x-3D reinforced tube uncoated electron microscope image;

Figure 5c is a 5000x-uncoated electron microscope image of a three-dimensional reinforced tube;

Fig. 5d is the electron microscope image of 100x-3D reinforced tube after coating;

Figure 5e is the electron microscope image of the 500x-3D reinforced tube after coating;

Figure 5f is the electron microscope image of the 5000x-3D reinforced tube after coating;

Figure 5g is the electron microscope image after the 100x-3D reinforced tube coating experiment;

Figure 5h is the electron microscope image after the 500x-3D reinforced tube coating experiment;

Figure 5i is the electron microscope image after the 5000 times-three-dimensional strengthening tube coating experiment;

Figure 6a shows the comparison of the condensation heat transfer coefficient of the refrigerant R134a before and after the coating of the light pipe when the saturation temperature is 40 °C;

Figure 6b shows the comparison of the condensation heat transfer coefficient of the refrigerant R134a before and after the coating of the light pipe when the saturation temperature is 30 °C;

Figure 7a shows the comparison of the condensation heat transfer coefficient of the refrigerant R1234ze(E) before and after the light pipe coating when the saturation temperature is 40 °C;

Figure 7b shows the comparison of the condensation heat transfer coefficient of the refrigerant R1234ze(E) before and after the coating of the light pipe when the saturation temperature is 30 °C;

Figure 8a shows the comparison of the condensation heat transfer coefficient of the refrigerant R290 before and after the coating of the light pipe when the saturation temperature is 40 °C;

Figure 8b shows the comparison of the condensation heat transfer coefficient of the refrigerant R290 before and after the coating of the light pipe when the saturation temperature is 30 °C;

Figure 9a shows the comparison of the condensation heat transfer coefficient of R134a before and after machining the three-dimensional fin surface coating when the saturation temperature is 40 °C;

Figure 9b shows the comparison of the condensation heat transfer coefficient of R134a before and after machining the three-dimensional fin surface coating when the saturation temperature is 30 °C;

Figure 10a shows the comparison of the condensation heat transfer coefficient of R1234ze(E) before and after machining the three-dimensional fin surface coating when the saturation temperature is 40 °C;

Figure 10b shows the comparison of the condensation heat transfer coefficient of R1234ze(E) before and after machining the three-dimensional fin surface coating when the saturation temperature is 30 °C;

Figure 11a shows the comparison of the condensation heat transfer coefficient of R290 before and after machining the three-dimensional fin surface coating when the saturation temperature is 40 °C;

Figure 11b shows the comparison of the condensation heat transfer coefficient of R290 before and after machining the three-dimensional fin surface coating when the saturation temperature is 30 °C.

In the drawings: 1-pipe wall, 2-fins, 3-inner thread reinforcement structure, 4-hydrophobic layer, 41-first hydrophobic layer, 42-second hydrophobic layer, 5-light pipe, three-dimensional strengthening pipe finger, A heat transfer tube with three-dimensional strengthening fins is arranged outside the tube wall.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

In the description of the present invention, it should be understood that the terms "center", "portrait", "horizontal", "top", "bottom", "front", "rear", "left", "right", " The orientation or positional relationship indicated by vertical, horizontal, top, bottom, inner, outer, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and The description is simplified rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as limiting the invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, unless otherwise specified, "plurality" means two or more. In the description of the present invention, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense, unless otherwise expressly specified and limited, for example, it may be a fixed connection or a detachable connection Connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

A surface hydrophobically modified composite condensation-enhanced heat transfer tube is characterized by not only using mechanically processed three-dimensional fins to enhance its heat transfer, but also using a surface hydrophobic modification method to perform hydrophobic treatment. The surface contact angle developed based on the 3D fins is further increased, and the heat transfer coefficient is greatly enhanced compared to the 3D fins without surface modification and the surface only treated with modification.

Referring to Figure 2, a surface hydrophobically modified composite condensation-enhanced heat transfer tube includes a tube wall 1, an inner thread strengthening structure 3 inside the tube wall 1, a three-dimensional strengthening fin 2 outside the tube wall 1, and the roots of the fin roots are connected on the pipe wall 1. The rib density of the fin 2 is 38fpi-50fpi (fins per inch, the number of teeth per inch), the rib height is 0.5mm-0.9mm, the fin 2 is Y-shaped, and the fin 2 includes a fin root 21 and a first tip 22 and the second tip 23. The end of the rib root 21 extends outward with a first tip 22 and a second tip 23, the first tip 22 and the second tip 23 are in contact with the lower part, and the angle of the interface between the first tip 22 and the second tip 23 is ≥90°, The tops of the first tip 22 and the second tip 23 are both inverted V-shaped, and the included angle between the tops is less than 30°. The height of the rib root 21 is 2H/3, the height of the first tip 22 is 1H/3, the height of the second tip 23 is 1H/9, and H is the height of the rib 2 .

The outer surface of the heat transfer tube is covered with a hydrophobic layer 4, and the hydrophobic layer 4 can adopt double-layer coating, or can adopt single-layer or multi-layer coating, and the total thickness of the two layers is less than 0.1 micron.

When the hydrophobic layer 4 is two layers, the hydrophobic layer 4 includes a first hydrophobic layer 41 and a second hydrophobic layer 42 covering the first hydrophobic layer 41; the material of the first hydrophobic layer 41 is a polymer material, such as polytetrafluoroethylene Ethylene, parylene, the thickness of the first hydrophobic layer 41 is greater than 0.05 micron; the material of the second hydrophobic layer 42 is a polymer material or plasma, which can be the same or different from that of the first hydrophobic layer.

The used coating material of the hydrophobic layer 4 can be a polymer material or plasma, or a chemical etching method can be used to form the hydrophobic layer.

Next, the surface hydrophobic modification treatment method will be described. The preparation method is suitable for the light pipe and the reinforced pipe. The schematic diagram of the preparation is shown in Figure 1.

Step 1, surface cleaning. Use isoacetone to wash the surface of the machined three-dimensional condensing heat transfer tube, the main purpose is to remove the lubricating oil left on the surface of the heat transfer tube during processing, and then use isopropyl alcohol to wash the surface of the heat transfer tube to remove the surface The residual isoacetone liquid is used, and finally the surface of the heat transfer tube is rinsed with clean water. And use the spray gun to blow off the water droplets on the surface.

Step 2, drying the surface of the heat transfer tube. Since the equipment for modifying the hydrophobic surface must ensure that the surface is dry, use a heating table to dry the surface of the heat transfer tube with the surface hydrophobic modification, adjust the temperature of the heating table to 110 °C and place the heat transfer tube on the heating table. , when the temperature of the heating table reaches 110 ℃, it can be used to heat the heat transfer tube for 15 to 20 minutes to stop heating.

Step 3, sealing both ends of the heat transfer tube. Since only the outer surface of the heat transfer tube is hydrophobically modified, in order to prevent the inner surface of the heat transfer tube from being hydrophobically modified during the preparation process and affecting subsequent experimental measurements, both ends of the heat transfer tube should be sealed. The sealing method used is to use a rubber stopper slightly larger than the inner diameter of the heat transfer tube to seal both ends of the heat transfer tube.

Step 4, performing hydrophobic modification coating on the surface of the heat transfer tube. Put the sealed heat transfer tube into the hydrophobic layer vapor deposition system, and then seal the sealing cover used by the system. At this time, choose the mode of hydrophobic layer deposition, in order to make the hydrophobic coating on the outer surface of the heat transfer tube more durable First, the outer surface of the heat transfer tube is plated with a first hydrophobic layer, and then a second hydrophobic layer is plated on the basis of the first hydrophobic layer. The thickness of the second hydrophobic layer is smaller than the thickness of the first water transfer layer (thinner The hydrophobic layer has a larger surface contact angle), that is, two layers of hydrophobic films are deposited on the three-dimensional reinforced tube by vapor deposition equipment:

The vapor deposition system is evacuated. When the vacuum degree reaches the coating conditions, vapor deposition is performed on the surface of the heat transfer tube, and the first hydrophobic layer is plated on the outer surface of the heat transfer tube. The process parameters are: power 105W, pressure 200mTorr, time 15min ; Then vacuumize the vapor deposition system, when the vacuum degree reaches the coating conditions, carry out vapor deposition, and coat the second hydrophobic layer on the first hydrophobic layer, the process parameters are: power 90W, pressure 400mTorr, time 20min; second hydrophobic layer After the coating is completed, the pressure in the system is restored to atmospheric pressure, and the hydrophobic modification of the outer surface of the heat transfer tube is completed when the temperature of the heat transfer tube is cooled to room temperature.

The hydrophobic layer can also be formed by chemical etching.

The heat transfer coefficient of condensation of the composite modified surface heat transfer tube used in the present invention can be further greatly improved. Specifically, an example sample tube is used to introduce the enhancement effect of its condensation heat transfer. The example sample tube is for three typical refrigerants. The coefficient can be increased by at least 70%. Taking the machined three-dimensional heat transfer tube listed in Table 1 as an example to illustrate the implementation process, enhanced heat transfer principle and implementation effect of the invention.

Table 1 Test and compare the geometric parameters of heat exchange tubes

The coating of the surface-modified tube is based on copper machining of three-dimensional finned tubes, which are characterized by further processing three-dimensional fins on the basis of two-dimensional low-finned tubes to obtain a heat exchange surface with a higher condensation heat transfer coefficient. The three-dimensional finned tube can enhance heat transfer through different three-dimensional structures. On the basis of the three-dimensional reinforced heat transfer tube, different surface coatings or modification methods are used for treatment. Compared with the mechanical processing of three-dimensional finned tubes, the condensation heat transfer coefficient is greatly improved.

As shown in Figure 1 (d _i and d _o in the figure are the inner diameter and outer diameter of the tube, respectively), the outer surface of the conventional light pipe without surface hydrophobic modification is plated with relatively The thick first hydrophobic layer 41 and the relatively thin second hydrophobic layer 42, the reason for plating the first hydrophobic layer 41 first is mainly to enhance the adhesion strength of the second hydrophobic layer 42, so that the second hydrophobic layer 42 can be more sustainable. Strengthen the condensation heat transfer outside the tube. Using single or multi-layer coating, if the adhesion strength is high and can promote the thinning of the liquid film, this coating method can also be used. The coating material is a polymer material or plasma. This coating method is effective for the three-dimensional reinforced tube, but the effect of enhancing the condensation heat transfer of the refrigerant is not obvious for the bare tube coating. The present invention also compares the effect of the smooth surface coating on the condensation heat transfer of different refrigerants with a light pipe. The process of surface hydrophobic modification of smooth pipe is similar to that of reinforced pipe. The main difference is that there is a mechanically processed three-dimensional rib reinforced structure outside the reinforced pipe. The smooth pipe is directly coated on the smooth surface without any fins.

The direct effect on the heat transfer tube after the hydrophobic coating is applied is the change of the surface contact angle. Here, a smooth heat transfer tube and a three-dimensional mechanically enhanced heat transfer tube are selected as examples to illustrate the effects of coating on the surface contact angle and condensation heat transfer before and after coating. The parameters of the two heat transfer tubes are shown in Table 1. The reinforced pipe is a double-sided reinforced pipe, the inner part of the pipe is reinforced with internal threads, and the reinforced structure outside the pipe is rib 2. Due to the soft material of the copper pipe, it can be processed into different three-dimensional rib geometric structures. The density of the fins outside the tube is higher. Figures 4a to 4l show the comparison of the contact angle of water on the surface of the three-dimensional reinforced fins before and after the modified coating. For smooth surfaces, the contact angle of water on the surface of the heat transfer tube further increases after coating. For the smooth heat transfer tubes tested experimentally, the contact angle increased from 88° to 121°. In order to check whether the organic refrigerant of the refrigerant corrodes the coating in the experiment, after a month of the condensation heat transfer experiment of the refrigerant at a saturation temperature of 40°C, the static and dynamic contact angle tests were carried out. It can be seen from the figure that the contact angle The angle did not decrease, and even increased to some extent. It can be seen that the cooling medium has no effect on the surface heat transfer effect of the modified light pipe. For the surface of the three-dimensional reinforced finned tube, the surface where the rib top is located is the reference surface. Before the modified coating is applied, when the droplet drops on the reinforced heat transfer surface, a part of the liquid enters the interior of the rib, and the liquid wraps part of the rib top section. The contact angle was measured to be 122°. After modification, the droplets stay on the reinforced surface. When the droplets are small, the droplets are suspended on the top of the reinforced fins, and no liquid enters between the fins. At this time, the contact angle is 152°, which has reached superhydrophobicity. The contact angle of the surface has almost no change after a one-month condensation heat transfer experiment of the refrigerant at a saturation temperature of 40°C. The actual test result is a static contact angle of 154 degrees. The dynamic contact angle includes advancing and receding contact angles. Similar to the static contact angle, before the unmodified coating, the advancing and receding contact angles are close to the static contact angles. After surface modification, the contact angles all increased to more than 150°. It can be seen that in the process of condensation heat exchange, the condensate flows on the heat transfer surface, and its contact angle is still large. With the progress of condensation heat transfer, the modification effect will not change, and the heat exchange effect of the heat exchanger is still very good. After a month of condensation heat transfer experiments at 40°C saturation temperature of the refrigerant, the dynamic and static contact angles did not change much. The contact angle changes of the two example heat exchange tubes before and after the coating modification and before and after the experiment are shown in Table 2.

Table 2

The morphology of the strengthened surface also changed microscopically after coating. Figures 5a to 5i are the changes of the heat transfer surface under the microscope before and after the surface coating of the three-dimensional reinforced tube and after the condensation heat transfer experiment is performed. It can be seen from the figure that after coating, the rough unit on the surface of the reinforced pipe due to mechanical processing is smoother, and the mechanical chamfering is changed from sharp to smooth. The photo at 5000x magnification shows that the surface structure is more uniform. After the condensation heat transfer test for one month, the structure and smoothness of the surface of the three-dimensional reinforced tube coating did not change much, which is the reason why the surface contact angle did not change much after the condensation heat transfer.

Figures 6a-11b show the comparison of the refrigerant condensation heat transfer coefficients before and after the two example heat transfer tubes are coated. In order to study whether the coating surface still works on different refrigerants, the representative R134a (hydrofluorocarbons), R1234ze(E) (hydrofluoroolefins, new environmentally friendly refrigerants) and R290 (hydrofluorocarbons) were selected. ) The effect of coating on its condensation heat transfer coefficient was studied for three refrigerants. The experimental results before and after the surface hydrophobic modification are shown in Figures 6a-11b, in which Figures 6a-8b are the effects of the surface hydrophobic modification of the light pipe on the condensation heat transfer coefficient of R134a, R1234ze(E) and R290 outside the light pipe at different saturation temperatures . Figures 9a to 11b show the effect of hydrophobic modification of the surface of the machined three-dimensional fins on the condensation heat transfer coefficients of R134a, R1234ze(E) and R290 enhanced tubes at different saturation temperatures. The saturation temperature of the condensation heat transfer test is 40°C and 30°C.

It can be seen from Figures 6a to 8b that the hydrophobic modification of the outer surface of the light pipe can improve the coagulation coefficients of R134a, R1234ze(E) and R290 at different saturation temperatures. Since the thermophysical parameters of R134a and R1234ze(E) at different saturation temperatures are relatively similar, it can also be seen from Fig. 6a, Fig. 6b, Fig. 7a and Fig. 7b that the condensation heat transfer coefficients of the two are similar. When the heat flux density reaches the minimum, the strengthening effect is not very obvious, but the enhanced condensation heat transfer effect of the surface hydrophobic modification increases continuously with the decrease of the heat flux density, and the strengthening effect reaches the maximum when the heat flux density reaches the minimum. And R1234ze(E) the outer condensation heat transfer coefficient of the light pipe increased by 16.5% and 12.3% respectively. The enhancement effect of surface hydrophobic modification on the heat transfer coefficient of condensation outside the R290 light pipe is more significant than that of R134a and R1234ze(E). The thermophysical parameters of R290 and R134a and R1234ze(E) are quite different, especially in density and viscosity. These differences make the enhancement effect of surface hydrophobic modification on the condensation heat transfer coefficient outside the R290 tube stronger, and the maximum enhancement effect can reach 19.7%.

Similarly, from Figures 9a to 11b, it can be seen that the enhancement effect of surface hydrophobic modification on the coagulation coefficient of R134a, R1234ze(E) and R290 strengthened tubes at different saturation temperatures is much more significant than that of bare tubes. As mentioned above, the thermophysical parameters of R134a and R1234ze(E) are relatively similar, and the effect of surface hydrophobic modification on R134a and R1234ze(E) enhanced condensation heat transfer coefficient is also similar. When the heat flux density is high, due to the thick condensate outside the tube, the heat transfer enhancement effect tends to a constant value as the heat flux density decreases. When the heat flux density is less than 60kW·m ^-2 , the strengthening effect obviously increases continuously with the decreasing heat flux density. The surface hydrophobic modification has the greatest effect on strengthening the heat transfer coefficient of condensation outside the R134a and R1234ze(E) three-dimensional strengthened tubes. up to 112.4% and 186.3%. Also for R290, the enhancement effect of surface hydrophobic modification on R290 three-dimensionally strengthened tube condensation heat transfer coefficient is more significant than that of R134a and R1234ze(E). When the heat flux density is as high as 150kW·m ^-2 , the surface hydrophobic modification can still enhance the condensation heat transfer system outside the R290 tube by about 70%.

It can be seen from the condensation heat transfer experiments of the above two heat transfer tubes that the surface hydrophobically modified composite tube can strengthen the condensation heat transfer coefficient of R134a, R1234ze(E) and R290 outside the plain tube and the three-dimensional strengthened tube, and its strengthening effect is intensified. The performance on the tube is more pronounced. If this type of heat transfer tube equipment is used to manufacture an air conditioner condenser, the heat exchange area can be reduced by more than one third, which has good application prospects and economic value.

The heat transfer tube prepared by the present invention can be used in refrigeration, air conditioning and HVAC equipment using shell-and-tube condensers, and the surface hydrophobically modified heat transfer tube can conduct heat transfer for condensation in the range of large heat flux density and small heat flux density The heat transfer performance of the device is permanently enhanced. After using the surface hydrophobically modified heat transfer tube, since it can enhance the heat exchange performance of the heat exchanger, the size of the condenser can be reduced, thereby reducing the hardware cost of the system.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the scope of the claims of the present invention. within the scope of protection.

Claims (10)

1. A surface hydrophobically modified composite condensation-enhanced heat transfer tube is characterized in that, comprising a tube wall (1), the tube wall (1) is provided with a fin (2) outside, and the fin (2) comprises The rib root (21), the root of the rib root (21) is connected to the pipe wall (1), and the end of the rib root (21) extends outward with a first tip (22) and a second tip (23) , the first tip (22) and the lower part of the second tip (23) are in contact with each other, and the angles at the tips of the first tip (22) and the second tip (23) are both less than 30°; the pipe wall (1 ) and the outer surfaces of the fins (2) are covered with a hydrophobic layer (4). 2 . The surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 1 , wherein the hydrophobic layer ( 4 ) comprises a first hydrophobic layer ( 41 ) and a surface covered on the first hydrophobic layer ( 41 ). 3 . ) on the second hydrophobic layer (42), the thickness of the hydrophobic layer (4) is less than 0.1 micron; the thickness of the first hydrophobic layer (41) is greater than the thickness of the second hydrophobic layer (42). 3 . The surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 2 , wherein the material of the hydrophobic layer ( 4 ) is a polymer material or plasma. 4 . 4 . The surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 1 , characterized in that, the tube wall ( 1 ) is provided with an internal thread strengthening structure ( 3 ). 5 . 5 . The surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 1 , wherein the angle of the interface between the first tip ( 22 ) and the second tip ( 23 ) is ≥90°. 6 . 6. A surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 1, wherein the height of the fin root (21) is 2H/3, and the height of the first tip (22) is 2H/3. The height is 1H/3, the height of the second tip (23) is 1H/9, and H is the height of the rib (2). 7 . The surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 1 , wherein the fins ( 2 ) have a rib density of 38 fpi to 50 fpi, and a rib height of 0.5 mm to 0.9 mm. 8 . 8. the preparation method of the surface hydrophobically modified composite condensation strengthening heat transfer tube of claim 1, is characterized in that, comprises the following steps: Step 1, processing the rib (2) outside the pipe wall (1); Step 2, remove the lubricating oil remaining on the surface of the heat transfer tube during the process of processing the fins (2) from the heat transfer tube; Step 3, drying the surface of the heat transfer tube; Step 4, seal both ends of the heat transfer tube: In step 5, hydrophobic modification coating is performed on the outer surface of the heat transfer tube, and a hydrophobic layer (4) is formed on the outer surface of the heat transfer tube. 9. The preparation method of a surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 8, wherein in step 1, the heat transfer tube is surface rinsed with isoacetone, isopropanol and clear water successively, Then use a spray gun to blow off the water droplets on the surface of the heat transfer tube. 10. The preparation method of a surface hydrophobically modified composite condensation-enhanced heat transfer tube according to claim 8, wherein the specific process of step 5 is: vacuumize the vapor deposition system, and when the vacuum degree reaches the coating conditions During the process, vapor deposition is performed on the surface of the heat transfer tube, and the outer surface of the heat transfer tube is coated to form a hydrophobic layer (4); after the coating is completed, the pressure in the vapor deposition system is restored to atmospheric pressure, and the temperature of the heat transfer tube is cooled to room temperature That is, the hydrophobic modification of the outer surface of the heat transfer tube is completed.

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