A solar heat collecting tube and its collector

Abstract

The present invention provides a solar heat collecting tube, which comprises a heat collecting tube body. The fluid in the heat collecting tube body is a vapor-liquid two-phase flow. A fin is arranged inside the heat collecting tube body. The fin is a cone, which extends from the inner wall towards the center of the heat collecting tube body. The cone includes a bottom and a tip. The bottom of the cone is arranged on the inner wall of the heat collecting tube body, and the tip of the cone extends towards the center. The present invention provides a heat collecting tube with a new structure. By arranging the conical fins, when the vapor-liquid two-phase flow flows in the heat collecting tube, the bubbles in the fluid are punctured, thereby realizing the rapid heat exchange of the fluid and achieving the effect of enhancing heat transfer.

Description

Technical Field

[0001] The present invention belongs to the field of heat exchange, and particularly relates to an internally finned heat collecting tube and a heat collector thereof. Background Art

[0002] With the rapid development of the modern social economy, the demand for energy by human beings is increasing. However, the reserves of traditional energy sources such as coal, oil, and natural gas are continuously decreasing and becoming increasingly scarce, resulting in continuous price increases. At the same time, the environmental pollution problems caused by conventional fossil fuels are becoming more and more serious, which greatly restricts the development of society and the improvement of the quality of human life. The energy problem has become one of the most prominent problems in the contemporary world. Therefore, seeking new energy sources, especially pollution-free clean energy, has become a research hotspot for people now.

[0003] Solar energy is a clean energy source that is inexhaustible and has a huge amount of resources. The total amount of solar radiation energy received by the earth's surface every year is 1×10 18 kW·h, which is more than ten thousand times the total annual energy consumption of the world. All countries in the world have regarded the utilization of solar energy as an important item in the development of new energy. However, due to the small energy density of solar radiation reaching the earth (about one kilowatt per square meter) and its discontinuity, it brings certain difficulties to large-scale development and utilization. Therefore, in order to widely utilize solar energy, not only technical problems need to be solved, but also it must be economically competitive with conventional energy sources.

[0004] A solar energy utilization device converts solar light energy into heat energy, and heats water from a low temperature to a high temperature through the heat energy to meet the hot water usage requirements of people in life and production. Utilizing this clean energy source of solar energy is beneficial to reducing the use of non-renewable energy sources and reducing carbon emissions.

[0005] Two-phase flow heat transfer widely exists in heat collecting tubes. In the heat transfer process of two-phase flow, due to the existence of the vapor phase, the heat transfer efficiency is low, the heat transfer deteriorates, the fluid flow process is unstable, and the occurrence of water hammer phenomenon will be caused. When the vapor-liquid phases of the two-phase working fluid are not evenly mixed and do not flow continuously, large-sized liquid masses will rapidly occupy the vapor mass space, resulting in unstable two-phase flow, thereby violently impacting the equipment and the heat collecting pipeline, generating strong vibrations and noises, and seriously threatening the safe operation of the equipment.

[0006] In the prior art, there are also corresponding solutions. For example, a solution is proposed in CN109654917A. A plurality of radially extending radial rods are arranged in the heat collecting pipe body. A plurality of fins extending in a direction opposite to the fluid flow are arranged on the radial rods. The fins have tips, and the tips extend in a direction opposite to the fluid flow. The problems existing in the gas-liquid two-phase flow are solved by the tips. However, the above solution adopts the method of radial rods, which makes its manufacturing difficult. Moreover, because the radial rods and their fins are arranged in the middle, the flow resistance is increased. And because the fins are far from the inner wall of the heat collecting pipe, the heat exchange effect of the fin heat collecting pipe is not good, thus affecting the heat exchange of the fluid and unable to play a good role in stabilizing the flow.

[0007] Therefore, in view of the above problems, the present invention provides an inner fin heat collecting pipe with a new structure, which solves the water hammer phenomenon existing in the gas-liquid two-phase flow, and also solves the problems of low heat transfer coefficient and difficult manufacturing in the case of heat exchange of the heat collecting pipe. Summary of the Invention

[0008] The present invention provides a new inner fin heat collecting pipe to solve the above-mentioned technical problems.

[0009] In order to achieve the above object, the technical solution of the present invention is as follows:

[0010] An inner fin heat collecting pipe includes a heat collecting pipe body. The fluid in the heat collecting pipe body is a gas-liquid two-phase flow. Fins are arranged inside the heat collecting pipe body. It is characterized in that the fins are cones, and the cones extend from the inner wall towards the center of the heat collecting pipe body. The cone includes a bottom and a tip. The bottom of the cone is arranged on the inner wall of the heat collecting pipe body, and the tip of the cone extends towards the center.

[0011] As an improvement, the fins are respectively arranged in the lower part and the upper part; along the fluid flow direction, the fins arranged in the upper part of the heat collecting pipe body and the fins arranged in the lower part of the heat collecting pipe body are arranged at intervals.

[0012] As an improvement, along the fluid flow direction in the heat collecting pipe, the distribution density of the fins in the upper part of the heat collecting pipe body is greater than that in the lower part.

[0013] As an improvement, the length of the fin extending towards the center of the heat collecting pipe body is 0.2 - 0.4 times the diameter of the heat collecting pipe body.

[0014] As an improvement, the length of the fin extending towards the center of the heat collecting pipe body is 0.25 - 0.35 times the diameter of the heat collecting pipe body.

[0015] As an improvement, the diameter of the bottom of the cylinder is 0.15 - 0.35 times the height of the cone.

[0016] As an improvement, the diameter of the bottom of the cylinder is 0.20 - 0.30 times the height of the cone.

[0017] A solar collector, comprising a heat collecting pipe, and the heat collecting pipe is an inner finned heat collecting pipe as claimed in any one of claims 1-7.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention is equivalent to arranging a conical inner fin on the inner wall of the heat collecting pipe, which increases the heat transfer area of the inner wall of the heat collecting pipe and achieves the purpose of strengthening heat transfer. At the same time, because the tip of the cone faces the center of the heat collecting pipe, the bubbles in the vapor-liquid two-phase flow are punctured when they come into contact with the tip of the inner fin, so that the vapor phase is divided into small bubbles, avoiding the generation of large bubbles. At the same time, it also reduces the heat transfer deterioration caused by bubbles on the inner wall, promotes the smooth flow of the vapor phase, plays a role in stabilizing the flow rate, avoids the occurrence of water hammer phenomenon, has the effect of reducing vibration and noise, and improves the heat transfer effect. Brief Description of the Drawings

[0020] Figure 1 is a schematic cross-sectional structure view of the heat collecting pipe of the present invention;

[0021] Figure 2 is a schematic longitudinal sectional structure view of the heat collecting pipe. Detailed Description of the Invention

[0022] The following will make a detailed description of the specific embodiments of the present invention with reference to the drawings.

[0023] Figure 1-2 Disclosed is an inner finned heat collecting pipe. As Figure 1 shown, the finned heat collecting pipe includes a heat collecting pipe body 1, and the fluid in the heat collecting pipe body is a vapor-liquid two-phase flow. A fin 2 is arranged inside the heat collecting pipe body 1. As Figure 1 shown, the fin 1 is a cone, and the cone extends from the inner wall of the heat collecting pipe body towards the center of the heat collecting pipe body. The cone includes a bottom 21 and a tip 22. The bottom 21 of the cone is arranged on the inner wall of the heat collecting pipe body, and the tip 22 of the cone extends towards the center of the heat collecting pipe body.

[0024] By arranging a conical inner fin on the inner wall of the heat collecting pipe, compared with the prior art in which a tip fin is arranged at the center of a circular heat collecting pipe, the present invention increases the heat transfer area of the inner wall of the heat collecting pipe and achieves the purpose of strengthening heat transfer. At the same time, because the tip of the cone faces the center of the heat collecting pipe, the bubbles in the vapor-liquid two-phase flow are punctured when they come into contact with the tip of the inner fin, so that the vapor phase is divided into small bubbles, avoiding the generation of large bubbles. At the same time, it also reduces the heat transfer deterioration caused by bubbles on the inner wall, promotes the smooth flow of the vapor phase, plays a role in stabilizing the flow rate, avoids the occurrence of water hammer phenomenon, has the effect of reducing vibration and noise, and improves the heat transfer effect.

[0025] As an improvement, the length (height of the cone) that the fin extends towards the center of the heat collecting pipe body is 0.2 - 0.4 times the diameter of the heat collecting pipe body, preferably 0.25 - 0.35 times.

[0026] As an improvement, the diameter of the bottom 21 of the cylinder is 0.15 - 0.35 times the height of the cone, preferably 0.20 - 0.30 times.

[0027] The above dimensions are optimized designs, which can maximize heat transfer while achieving the best vibration reduction and noise reduction effects.

[0028] As an improvement, the heat collecting pipe is horizontally arranged, and a reflector is arranged at the lower part. The reflector reflects solar energy to the lower part of the heat collecting pipe.

[0029] As an improvement, the heat collecting pipe is horizontally arranged, and a convex lens is arranged at the upper part. The convex lens collects solar energy to the upper part of the heat collecting pipe.

[0030] As an improvement, the heat collecting pipe is horizontally arranged, a reflector is arranged at the lower part, and a convex lens is arranged at the upper part. The reflector reflects solar energy to the lower part of the heat collecting pipe, and the convex lens collects solar energy to the upper part of the heat collecting pipe. Heat exchange can be carried out in both the upper and lower parts.

[0031] As an improvement, as Figure 2 shown, the positions of the fins at different positions of the heat collecting pipe body 1 are different. For example, Figure 2 the fins are respectively arranged at the lower part and the upper part. Along the flow direction of the fluid, the fins arranged at the upper part of the heat collecting pipe body and the fins arranged at the lower part of the heat collecting pipe body are arranged at intervals. By arranging the fins at intervals in the upper and lower parts, the effect similar to that of a baffle can be formed, avoiding the short - circuit of the fluid flow, and at the same time enabling the fluid to continuously change direction during the flow, increasing the disturbance of the fluid, and further realizing enhanced heat transfer.

[0032] As an improvement, as Figure 2 shown, along the flow direction of the fluid in the heat collecting pipe, from the inlet of the heat collecting pipe to the middle position of the heat collecting pipe, the distance between adjacent fins continuously increases. Then from the middle position of the heat collecting pipe to the outlet of the heat collecting pipe, the distance between adjacent fins continuously decreases. Because during the heat collection process, the heat absorption amount of the heat collecting pipe per unit length along the fluid flow process is relatively uniform, the overall heat exchange effect is the best. However, it is found in experiments and simulations that the heat collection amount in the middle is significantly greater than that at the inlet and outlet of the heat collecting pipe. Therefore, by changing the fin spacing, the heat exchange area of the fluid in the finned heat collecting pipe also changes. Therefore, by compensating for the non - uniformity of the heat exchange amount through the area change, the heat exchange efficiency can be further improved.

[0033] As an improvement, along the flow direction of the fluid in the heat collecting pipe, from the inlet of the heat collecting pipe to the middle position of the heat collecting pipe, the increasing amplitude of the fin spacing continuously increases. Then, from the middle position of the heat collecting pipe to the outlet of the heat collecting pipe, the decreasing amplitude of the fin spacing continuously decreases. The change of the above amplitude can make the heat exchange amount per unit length of the whole fluid motion more uniform, and further improve the heat collection efficiency.

[0034] The fins are arranged in the vertical direction and include upper fins and lower fins, and the upper fins and the lower fins are arranged at intervals; along the flow direction of the fluid in the heat collecting pipe, the height of the lower fins extending upward from the inner wall of the bottom shell side gradually increases, and the length of the upper fins extending downward from the inner wall of the upper shell side gradually decreases.

[0035] During the research process, it is found that the heat exchange on the cross-section of the fins of the traditional heat exchanger is uneven in the fluid flow direction. The closer to the inlet, the greater the density of the heat exchange liquid at the lower part of the shell side. Therefore, the liquid flows downward, resulting in a significant increase in the lower heat exchange liquid. Therefore, it is necessary to design a heat exchange structure for improvement. Along the flow direction of the fluid in the present invention, the height changes of the upper fins and the lower fins make the liquid in the pipe gradually move closer to the center as it flows, strengthening the heat exchange of the heat collecting pipes around the center of the shell, changing the past heat exchange method, enhancing the heat exchange efficiency at different positions, making the overall heat exchange uniform, and further achieving the purpose of strengthening heat transfer.

[0036] As an improvement, along the flow direction of the fluid in the heat collecting pipe, the increasing amplitude of the height of the lower fins extending upward from the inner wall of the bottom shell side continuously increases, and the decreasing amplitude of the length of the upper fins extending downward from the inner wall of the upper shell side continuously decreases. Through the change of the above amplitude, the overall heat exchange can be further made uniform, and the purpose of strengthening heat transfer is further achieved.

[0037] As an improvement, along the flow direction of the fluid in the heat collecting pipe, the distribution density of the fins on the upper part of the heat collecting pipe body is greater than that on the lower part. This is mainly because the bubbles are easy to flow upward due to their small density, and at the same time, because the bubbles are easy to accumulate in the upper part, it is also easy to cause deterioration of heat exchange in the upper part. Therefore, by setting the fin density on the upper part to be larger, the bubbles can be pierced more quickly, and by setting the fin density on the upper part to be larger, the enhanced heat transfer in the upper part can be increased, realizing uniform overall heat exchange.

[0038] As an improvement, along the flow direction of the fluid in the heat collecting pipe, the distribution density of the fins gradually increases. Because as the fluid continuously flows, the liquid is converted into bubbles, making the number of bubbles in the fluid more and more. Therefore, by increasing the fin density, heat exchange deterioration can be prevented and the water hammer phenomenon can be avoided.

[0039] As an improvement, along the flow direction of the fluid in the heat collecting pipe, the distribution density of the fins gradually increases with an increasing amplitude. The above-mentioned amplitude change also conforms to the actual situation. Through actual observation, as the fluid in the heat collecting pipe continuously flows, the generation speed of bubbles also becomes faster and faster. Therefore, through the above settings, heat transfer deterioration can be further prevented and the water hammer phenomenon can be avoided.

[0040] As an improvement, along the flow direction of the fluid, the fins, preferably the fins arranged on the upper part of the heat collecting pipe body, have a decreasing height extending from the inner wall of the heat collecting pipe body towards the center. The main reason is that as the fluid continuously flows, the bubbles, due to their low density, increasingly gather upwards. By setting the height to decrease, the bubbles constantly touch the tips of the fins during the upward flow, preventing the bubbles from directly entering the gaps between the fins and hindering heat transfer, and thus being continuously punctured, further preventing heat transfer deterioration and avoiding the water hammer phenomenon.

[0041] Along the flow direction of the fluid, the fins, preferably the fins arranged on the upper part of the heat collecting pipe body, have an increasing amplitude of decreasing height extending from the inner wall of the heat collecting pipe body towards the center. The above-mentioned amplitude change also conforms to the law of bubble rising, and can further prevent heat transfer deterioration and avoid the water hammer phenomenon.

[0042] As an improvement, in the fluid flow direction, the fins are arranged in multiple rows. The rows are arranged circumferentially along the heat collecting pipe body.

[0043] Along the flow direction of the fluid in the heat collecting pipe, the distance between adjacent rows becomes shorter and shorter. Let the distance from the inlet of the heat collecting pipe be S, and the distance between adjacent rows be D. D = Y1(S), that is, D is a function with the distance S as a variable. D' is the first derivative of D, and it satisfies the following requirements:

[0044] D' < 0;

[0045] The main reason is that during the flow of the fluid in the heat collecting pipe, the heat collecting pipe is continuously heated, resulting in an increasing amount of gas in the gas-liquid two-phase flow. Because the gas phase in the gas-liquid two-phase flow is increasing, the heat transfer capacity in the heat collecting pipe will relatively decrease as the gas phase increases, and the vibration and noise will also continuously increase as the gas phase increases. Therefore, it is necessary to set the distance between adjacent rows to be shorter and shorter.

[0046] In addition, from the outlet of the heat collecting pipe to the header of the heat exchanger, since the space in this section suddenly becomes larger, the change in space will cause the vapor to flow out and accumulate upward rapidly. Therefore, the change in space will cause the accumulated vapor phase to enter the header of the heat exchanger from the position of the heat collecting pipe. Due to the vapor-liquid density difference, the vapor mass will move upward rapidly when leaving the position of the heat collecting pipe, and the liquid that is pushed away from the wall surface by the vapor mass at the original space position of the vapor mass will also rebound rapidly and impact the wall surface, forming an impact phenomenon. The more discontinuous the vapor-liquid phase is, the larger the vapor mass accumulation is, and the greater the water hammer energy is. The impact phenomenon will cause relatively large noise, vibration and mechanical shock, and damage the equipment. Therefore, in order to avoid the occurrence of this phenomenon, the distance between adjacent flow stabilizing devices set at this time is getting shorter and shorter, so as to continuously separate the vapor phase and the liquid phase during the fluid transportation process, thereby minimizing vibration and noise to the greatest extent.

[0047] Further preferably, from the inlet of the heat collecting pipe 1 to the outlet of the heat collecting pipe 1, the amplitude of the distance between adjacent rows is continuously increasing. That is, D” is the second derivative of D, and it meets the following requirements:

[0048] D”>0;

[0049] Through experiments, it is found that by setting in this way, the vibration and noise can be further reduced, and at the same time, the heat exchange effect can be improved.

[0050] Preferably, along the height direction of the heat collecting pipe 1, multiple rows of fins are arranged inside the heat collecting pipe 1. From the inlet of the heat collecting pipe 1 to the outlet of the heat collecting pipe 1, the distribution density of the fins of each row is increasing. That is, the distribution density of the fins of each row is V, V = Y2(S), and V’ is the first derivative of V, and it meets the following requirements:

[0051] V’>0;

[0052] Preferably, from the inlet of the heat collecting pipe to the outlet of the heat collecting pipe, that is, the amplitude of the increasing distribution density of the fins of each row is continuously increasing. That is

[0053] V” is the second derivative of V, and it meets the following requirements:

[0054] V ”>0.

[0055] For the specific reasons, refer to the changes of each row.

[0056] A solar collector includes the internally finned heat collecting pipe described above.

[0057] Although the present invention has been disclosed above with preferred embodiments, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A solar heat collecting tube, comprising a heat collecting tube body, wherein the fluid inside the heat collecting tube body is a vapor-liquid two-phase flow, and fins are arranged inside the heat collecting tube body, and it is characterized in that, The fins are conical bodies that extend from the inner wall towards the center of the heat collecting tube body. The conical body includes a bottom and a tip. The bottom of the conical body is provided on the inner wall of the heat collecting tube body, and the tip of the conical body extends towards the center; the fins are respectively provided in the lower part and the upper part; along the flow direction of the fluid, the fins provided in the upper part of the heat collecting tube body and the fins provided in the lower part of the heat collecting tube body are arranged at intervals; along the flow direction of the fluid in the heat collecting tube, the distribution density of the fins in the upper part of the heat collecting tube body is greater than that in the lower part; along the flow direction of the fluid in the heat collecting tube body, from the inlet of the heat collecting tube body to the middle position of the heat collecting tube body, the distance between adjacent fins continuously increases, and then from the middle position of the heat collecting tube body to the outlet of the heat collecting tube body, the distance between adjacent fins continuously decreases.

2. The solar heat collecting tube according to claim 1, characterized in that, The length that the fin extends towards the center of the heat collecting tube body is 0.2 - 0.4 times the diameter of the heat collecting tube body.

3. The solar heat collecting tube according to claim 2, characterized in that, The length that the fin extends towards the center of the heat collecting tube body is 0.25 - 0.35 times the diameter of the heat collecting tube body.

4. The solar heat collecting tube according to claim 1, characterized in that, The diameter of the bottom of the conical body is 0.15 - 0.35 times the height of the conical body.

5. The solar heat collecting tube according to claim 4, characterized in that, The diameter of the bottom of the conical body is 0.20 - 0.30 times the height of the conical body.

6. A solar heat collector, comprising a heat collecting tube, and the heat collecting tube is the solar heat collecting tube according to any one of claims 1-5.

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