CN101644545B - Air-cooled condenser - Google Patents

Abstract

The invention relates to the field of air-cooling technology, and relates to an air-cooled condenser, which has a heat dissipation pipe for conveying a cooling medium, and a piezoelectric fan is arranged along the heat dissipation pipe. Compared with the prior art, the invention has the advantages of low power consumption, low noise, strong heat exchange capacity and the like.

Description

an air-cooled condenser

technical field

The invention relates to the technical field of air cooling, in particular to an air cooling condenser using a piezoelectric fan.

Background technique

As an economical and relatively environmentally friendly water-saving approach, air-cooling technology has become an important choice to solve the construction of thermal power plants in "coal-rich and water-shortage" areas or arid areas. However, the direct air-cooling units so far mainly rely on large axial flow fans to generate forced convection, which consumes a lot of energy, is noisy, and is easily affected by ambient wind.

The piezoelectric effect is a physical phenomenon known more than one hundred years ago. Through this effect, certain special ceramic materials can generate large mechanical stress under the excitation of an external electric field. However, the deformation or displacement directly produced by the piezoelectric effect is usually very small, so it has been mainly used as a pressure sensor and an actuator for micro-nano devices for a long time. The use of the piezoelectric effect to generate significant air flow was developed in the past 10 years in response to the cooling needs of microelectronic devices to solve the noise problem of cooling fans for sound-sensitive devices such as smartphones and DVD players. So far, it has not been applied in air cooling technology.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology, and provide a condenser that uses the inverse piezoelectric effect of functional ceramics to drive the vibrating plate to replace the air-cooling fan to make the air oscillate and exchange heat, which has low power consumption and low noise. Strong heat capacity.

The object of the present invention is achieved through the following technical measures: an air-cooled condenser has a heat dissipation pipe for conveying a cooling medium, and a piezoelectric fan is arranged along the heat dissipation pipe.

In the above technical solution, the piezoelectric fan includes blades made of thin metal sheets and piezoelectric ceramic sheets fixed on the edges of the blades, and the other end of the piezoelectric ceramic sheets is fixed on a support frame adjacent to the heat dissipation pipe, Each piezoelectric ceramic sheet is connected in parallel with an alternating current power supply.

In the above technical solution, the piezoelectric ceramic sheet on the piezoelectric fan is one or a plurality of stacked ones with the same thickness.

In the above technical solution, the distance between the blade and the heat pipe is 0.05 to 0.15 meters, the distance between each piezoelectric ceramic sheet is 0.1 to 0.3 meters, and the extension length of the blade from the piezoelectric ceramic sheet (that is, the length described below) Leaf length) is 0.3 to 0.7 meters.

In the above technical solution, the piezoelectric ceramic sheet is a solid solution of lead niobium nickel zirconate titanate (PZT) as the main component.

The invention uses the inverse piezoelectric effect of functional ceramics to convert electrical energy into mechanical energy, and at the same time converts the micro-scale vibration generated by the piezoelectric effect into macro-scale vibration with very low energy consumption through the resonance between the piezoelectric ceramic sheet and the blade. The air flow that generates enough flow can achieve the purpose of air cooling and heat exchange, and the frequency of resonance is selected outside the frequency that can be felt by hearing, which can almost completely eliminate the influence of noise. Compared with the prior art, the invention has the advantages of low power consumption, low noise and strong heat exchange capacity.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of the piezoelectric fan in the embodiment.

Fig. 3 is a block diagram of a piezoelectric air cooling system applying the present invention.

Fig. 4 is an arrangement diagram of an air-cooled condenser based on the present invention.

Fig. 5 is a graph showing the relationship between the distance from the blade to the heat pipe and the heat transfer coefficient of the pipe wall surface.

Fig. 6 is a graph showing the relationship between the blade pitch and the heat transfer coefficient of the tube wall surface.

Fig. 7 is a graph showing the relationship between the blade length and the heat transfer coefficient of the tube wall surface.

Fig. 8 is a graph showing the relationship between the operating frequency of the blade and the heat transfer coefficient of the tube wall surface.

Fig. 9 is a graph showing the relationship between the arrangement of blades and the heat transfer coefficient of the tube wall surface.

Among them, 1 is the cooling pipe, 2 is the piezoelectric ceramic sheet, 3 is the blade, 4 is the support frame, 5 is the boiler, 6 is the superheater, 7 is the steam turbine, 8 is the generator, 9 is the exhaust pipe of the steam turbine, 10 is Radiation pipe, 11 is cooling element, 12 is small motor, 13 is condensate tank, 14 is condensate pump, 15 is condensate polishing device, 16 is condensate pump, 17 is low pressure heater, 18 is deaerator, 19 is Feedwater pump, 20 is a high-pressure heater.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in FIG. 1 , the air-cooled condenser in this embodiment has a heat dissipation pipe 1 for conveying a cooling medium, and a piezoelectric fan is arranged along the heat dissipation pipe 1 .

As shown in Figure 2, the piezoelectric fan includes a blade 3 made of metal sheet and a piezoelectric ceramic sheet 2 fixed on the edge of the blade 3, and the other end of the piezoelectric ceramic sheet 2 is fixed adjacent to the cooling pipe 1. On the support frame 4, each piezoelectric ceramic sheet 2 is connected in parallel with an alternating power supply, and its power supply wiring is installed along the metal support frame 4, and the voltage placed at both ends of the piezoelectric fan is controlled by a transformer and a resistor R.

The piezoelectric ceramic sheet 2 is a solid solution with niobium nickel lead zirconate titanate (PZT) as the main component. Electrodes are formed on both sides, and the polarization direction is perpendicular to the electrodes. If a voltage is applied between the electrodes of the piezoelectric ceramic sheet 2, due to the inverse piezoelectric effect, the vibrator of the piezoelectric ceramic sheet 2 will be displaced in the longitudinal direction. The multi-layer piezoelectric ceramic sheet 2 structure is made by stacking several layers of piezoelectric ceramic sheets 2 with the same thickness to form a laminate, which is electrically connected in parallel and mechanically connected in series, and is elongated in the length direction when an electric field is applied. Its total displacement is several times the displacement of each layer. The thrust of this structure is very large, and due to the mechanical gain, their displacement is greater than the expansion and contraction displacement of the block, so there is a large deflection displacement.

This patent is to use the inverse piezoelectric effect of the piezoelectric ceramic sheet 2, adopt the method of resonance amplification between the piezoelectric ceramic sheet 2 and the blade 3, and amplify the micro-scale vibration of the piezoelectric ceramic sheet 2 by 2-3 orders of magnitude to generate large-scale vibration. Air flow, thereby replacing the driving fan in the traditional direct air cooling unit, to achieve the purpose of heat dissipation, energy saving and noise reduction. Driven by an external electric field, the inverse piezoelectric effect of the piezoelectric ceramic sheet 2 drives the large blade 3 to oscillate, and this oscillating motion drives the surrounding air to oscillate, just like a fan, thereby enabling forced convection heat exchange on the heat sink 1 .

In practical application, the piezoelectric air cooling system using this embodiment is shown in FIG. 3 .

Further, for the air-cooled condenser part, the 600MW direct air-cooled condenser is taken as the research object, and the existing "∧" shaped condenser is changed to a vertical arrangement in consideration of the fixing of the piezoelectric fan. As shown in Figure 4, the exhaust steam discharged from the low-pressure cylinder of the steam turbine 7 is led out of the main workshop through the exhaust pipeline 9, and the exhaust steam is introduced into the steam distribution header on the top of the air-cooled condenser through the steam distribution pipe. The direct air-cooled condenser is divided into several units, and each unit is composed of several groups of cooling pipes 1 . After adopting this embodiment, since a number of piezoelectric fans are arranged on the sides of the vertically arranged cooling pipes 1, after a weak voltage is applied to the piezoelectric ceramic sheet 2, it will drive the blades 3 to vibrate, and the piezoelectric ceramic sheet 2 can be driven to vibrate. Small-scale vibrations of sheet 2 are converted into large-scale resonances of blade 3 . This can replace the axial flow fan in the existing direct air cooling system, thereby realizing a new energy-saving system with "low energy consumption" and "low noise".

In the above-mentioned technical scheme, according to the relevant data of the characteristics of the piezoelectric fan blade 3, the distance d between the blade 3 and the heat dissipation pipe 1 when there is no ambient wind speed, the distance m between the blades 3, the length l of the blade 3, Vibration frequency f, arrangement of blades 3, and the influence of these parameters on the heat dissipation effect when these parameters change. The temperature gradient in the normal direction of the wall surface of the heat dissipation pipe 1 is obtained through simulation, and the corresponding surface heat transfer coefficient is obtained. The research results are shown in Figure 5 to Figure 9.

It can be seen from Fig. 9 that the difference in surface heat transfer coefficient between the leeward side and the windward side under two different arrangements of blades 3 on one side and symmetrically.

When the blade 3 is arranged on one side, the surface heat transfer coefficient of the leeward side is very small, only about 1/2 of that of the windward side. In the figure, A is the surface heat transfer coefficient of the leeward side, and B represents the surface heat transfer coefficient of the windward side. . C in the figure is the surface heat transfer coefficient of the heat pipe 1 wall when symmetrically arranged. The surface heat transfer coefficient under the symmetrical arrangement is smaller than that on the windward side when arranged on one side, but it is only reduced by 0.17W/(m2 K). This is because when the symmetrical arrangement is adopted, the two blades will affect each other, which hinders the air diffusion around the heat dissipation pipe 1 and reduces the flow velocity, thereby deteriorating the heat exchange effect.

According to the similarity principle, the experimental data of convective heat transfer should be expressed as a functional relationship between the similarity criterion numbers. According to the above simulation results, the dimensionless temperature gradient of the fluid on the wall surface of heat pipe 1 can be fitted. It can be seen from the above results that the temperature gradient of a single tube is related to l/d and Re.

Linear regression is performed on the above calculation results, and the dimensionless criterion relationship of the influence of the vibration of the blade 3 on the heat transfer of the heat pipe 1 can be obtained, where Nu is the Nusselt number and Re is the Reynolds number:

$\mathrm{Nu}=1.7R{e}^{0.47}{\left(\frac{l}{d}\right)}^{-0.44}$ (l/d≥5)

$\mathrm{Nu}=63.4{\mathrm{Re}}^{0.13}{\left(\frac{l}{d}\right)}^{0.02}$ (l/d≤5)

Using the fluid analysis software Fluent to simulate the influence of different blade 3 parameters on the heat transfer effect of the air-cooled heat pipe 1, and analyzing the numerical simulation results under different working conditions, the following conclusions can be obtained:

1. The distance d between the blade 3 and the heat pipe 1 will affect the heat exchange effect, and its value ranges from 0.05 to 0.15 meters. When the distance is less than 0.1 meters, the surface heat transfer coefficient increases with the increase of the distance , when the distance is greater than 0.1 meters, the disturbance effect of the blade 3 on the air near the wall of the heat pipe 1 is reduced, resulting in a decrease in heat transfer performance. Therefore, it is recommended to take a distance of 0.1 meters as the optimal value.

2. The arrangement distance m of the blades 3 will also affect the heat transfer performance, and its value ranges from 0.1 to 0.3 meters. The general trend is that the surface heat transfer coefficient decreases with the increase of the distance, but the reduction rate is different. When the spacing is between 0.1m and 0.2m, the decrease is relatively gentle; after 0.2m, the surface heat transfer coefficient decreases greatly.

3. The length l of the blade 3 will also affect the heat transfer performance, and its value ranges from 0.3 to 0.7 meters. With the increase of the length l of the blade 3, the heat transfer effect of the heat dissipation pipe 1 generally increases, but the increase rate gradually increases. Slow down, when the length is less than 0.5 meters, the surface heat transfer coefficient increases faster with the increase of length, and when the length is greater than 0.5 meters, the effect of length on heat transfer performance is basically negligible. Considering the fixation of the blade 3, it is recommended to take 0.5 meters.

4. Increasing the vibration frequency f of the blade 3 can also improve heat dissipation, but within a certain range, the effect on heat dissipation is not large, showing a similar effect to the length of the blade 3 . Considering that the power frequency in our country is 50Hz, it is recommended to take 50Hz. To minimize noise, frequencies can be taken outside the range that the human ear can perceive.

5. The layout of the blades 3 affects the heat transfer performance of the heat pipe 1. When the blades 3 are arranged on one side of the heat pipe 1, the surface heat transfer coefficient of the windward side is about twice that of the leeward side; When the pipe 1 is on both sides, the surface heat transfer coefficients on both sides are basically the same, which is lower than the surface heat transfer coefficient on the windward side when one side is arranged, but the reduction is not much. Therefore, it is recommended to adopt a form in which the blades 3 are arranged symmetrically on both sides.

In summary, compared with the traditional air-cooled condenser, the air-cooled condenser of the present invention has the advantages of strong heat transfer capacity, low energy consumption, no noise, etc. environment is widely used.

Claims (4)

1. an air-cooled condenser has the radiating tube of carrying coolant, it is characterized in that: be furnished with the piezoelectric type fan along radiating tube; Described piezoelectric type fan comprises blade made from sheet metal and the piezoelectric ceramic piece that is fixed on the blade edge, and the other end of piezoelectric ceramic piece is fixed on the bracing frame that is close to radiating tube, and each piezoelectric ceramic piece and an alternating source are in parallel.

2. air-cooled condenser according to claim 1 is characterized in that: the piezoelectric ceramic piece on the described piezoelectric type fan is one or is identical be superimposed together a plurality of of thickness.

3. air-cooled condenser according to claim 1, it is characterized in that: the blade of described piezoelectric type fan and the distance of radiating tube (d) are 0.05～0.15 meter, distance between each piezoelectric ceramic piece (m) is 0.1～0.3 meter, and blade is 0.3～0.7 meter from the development length (1) of piezoelectric ceramic piece.

4. air-cooled condenser according to claim 1 is characterized in that: described piezoelectric ceramic piece is that niobium nickel lead zirconate titanate (PZT) is the solid solution of main component.

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