A heat collecting tube with fin spacing arrangement and heat collecting device thereof

Abstract

The present invention provides a heat collecting tube with fin spacing arrangement and a heat collector thereof, comprising a tube body, wherein the inner wall of the tube body is provided with fins, the fins have a tip extending toward the center of the tube body, and in the direction of fluid flow, the fins are arranged in multiple rows, and the rows are arranged along the circumference of the tube body; the fluid in the heat collecting tube is a cold source, and the distance from the entrance of the heat collecting tube is S, and the distance between adjacent rows is D, D=Y1(S), that is, D is a function with the distance S as a variable, and D' is the first derivative of D, satisfying the following requirement: D'<0. The present invention provides a heat collecting tube with a new structure, which continuously separates the vapor phase and the liquid phase during the fluid transportation process, thereby reducing vibration and noise and enhancing heat transfer.

Description

Technical Field

[0001] The invention belongs to the field of solar energy, and in particular relates to an inner fin heat collecting tube and a heat collector thereof. Background Art

[0002] Solar energy is an inexhaustible clean energy source with huge resources. The total amount of solar radiation energy received by the earth’s surface each year is 1×10 18 kW·h, which is more than 10,000 times the world's total annual energy consumption. Countries around the world have already regarded the use of solar energy as an important part of new energy development. However, since the energy density of solar radiation reaching the earth is low (about 1 kilowatt per square meter) and it is discontinuous, this brings certain difficulties to large-scale development and utilization. Therefore, in order to widely use solar energy, not only technical problems must be solved, but also it must be able to compete with conventional energy in terms of economy.

[0003] Solar energy utilization devices convert sunlight into heat energy, and use the heat energy to heat water from low temperature to high temperature to meet people's demand for hot water in life and production. Using solar energy, a clean energy, is conducive to reducing the use of non-renewable energy and reducing carbon emissions.

[0004] In solar collectors, the fluid in the heat collecting tube forms a vapor-liquid two-phase flow due to heat. The presence of the vapor phase in the vapor-liquid two-phase flow during the heat exchange process will lead to low heat exchange efficiency, deterioration of heat exchange, unstable fluid flow process, and water hammer. When the vapor and liquid phases of the two-phase working fluid are not evenly mixed and flow discontinuously, large-sized liquid masses will occupy the vapor mass space at a high speed, resulting in unstable two-phase flow, which will severely impact the equipment and pipelines, generate strong vibration and noise, and seriously threaten the safety of equipment operation.

[0005] There are corresponding solutions in the prior art. For example, a solution is proposed in CN109654917A. A plurality of radial rods extending radially are arranged in the tube body, and a plurality of fins extending from the radial rods to a direction opposite to the fluid flow are arranged on the radial rods. The fins have a tip, and the tip extends in a direction opposite to the fluid flow. The problem of vapor-liquid two-phase flow is solved by the tip. However, the above solution adopts the method of radial rods, which makes it difficult to manufacture. Moreover, because the radial rods and their fins are arranged in the middle, the flow resistance is increased. Moreover, because the fins are far away from the inner wall of the heat collecting tube, the heat exchange effect of the finned tube is not good, which affects the heat exchange of the fluid and cannot play a good flow stabilization role.

[0006] Therefore, in order to solve the above problems, the present invention provides a new structure of internal fin heat collecting tube, which solves the water hammer phenomenon existing in the vapor-liquid two-phase flow, and also solves the problem of low heat transfer coefficient and difficult manufacturing of heat collecting tube in the case of heat exchange. Summary of the invention

[0007] The present invention provides a new inner fin heat collecting tube, thereby solving the above-mentioned technical problems.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] A cold source heat collecting pipe comprises a pipe body, wherein the inner wall of the pipe body is provided with fins, the fins have a tip extending toward the center of the pipe body, and in the direction of fluid flow, the fins are arranged in multiple rows, and the rows are arranged along the circumference of the pipe body; the fluid in the heat collecting pipe is a cold source, and the distance from the entrance of the heat collecting pipe is S, and the distance between adjacent rows is D, D=Y1(S), that is, D is a function with the distance S as a variable, and D' is a first derivative of D, which satisfies the following requirements:

[0010] D'<0.

[0011] As an improvement, D" is the second derivative of D, satisfying the following requirements:

[0012] D”>0.

[0013] As an improvement, the fin is a cone, and the cone extends from the inner wall to the center of the tube body.

[0014] A solar collector comprises a heat collecting tube, the heat collecting tube comprises a tube body, the inner wall of the tube body is provided with fins, the fins have a tip extending toward the center of the tube body, and in the direction of fluid flow, the fins are arranged in multiple rows, and the rows are arranged along the circumference of the tube body; the fluid in the heat collecting tube is a cold source, and the distance from the entrance of the heat collecting tube is S, and the distance between adjacent rows is D, D=Y1(S), that is, D is a function with the distance S as a variable, and D' is a first derivative of D, which satisfies the following requirements:

[0015] D'<0.

[0016] As an improvement, D" is the second derivative of D, satisfying the following requirements:

[0017] D”>0.

[0018] As an improvement, the fin is a cone, and the cone extends from the inner wall to the center of the tube body.

[0019] As an improvement, the heat exchanger is a horizontal shell and tube heat exchanger, the shell side includes a shell, and a baffle is arranged inside the shell.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The present invention provides a new type of heat collecting pipe structure, which continuously separates the vapor phase and the liquid phase during the vapor-liquid two-phase flow fluid transportation process, thereby reducing vibration and noise and enhancing heat transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the cross-sectional structure of the heat collecting tube of the present invention;

[0023] Figure 2 It is a schematic diagram of the longitudinal interface structure of the heat collecting tube;

[0024] Figure 3 A heat collecting pipe connecting the components is provided. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention are described in detail below with reference to the accompanying drawings.

[0026] Figure 1-2 An internal fin solar collector tube is shown. Figure 1 As shown, the finned heat collecting tube comprises a heat collecting tube body 1 , the fluid in the heat collecting tube body is a vapor-liquid two-phase flow, and fins 2 are arranged inside the heat collecting tube body 1 .

[0027] As an improvement, in the fluid flow direction, the fins are arranged in multiple rows, and the rows are arranged along the circumference of the heat collecting tube body.

[0028] Along the flow direction of the fluid in the heat collector, the distance between adjacent rows becomes shorter and shorter. Let the distance from the heat collector inlet be S, the distance between adjacent rows be D, D=Y1(S), that is, D is a function with distance S as the variable, D' is the first derivative of D, and meets the following requirements:

[0029] D'<0;

[0030] The main reason is that during the flow of fluid in the heat collecting tube, the heat collecting tube is constantly heated, resulting in more and more gas in the gas-liquid two-phase flow. As the gas phase in the gas-liquid two-phase flow increases, the heat exchange capacity in the heat collecting tube will be relatively weakened as the gas phase increases, and the vibration and noise will also increase as the gas phase increases. Therefore, the distance between adjacent rows needs to be set shorter and shorter.

[0031] In addition, from the outlet of the heat collector to the heat exchanger header, because the space in this section suddenly becomes larger, the change in space will cause the gas to flow out and gather quickly upward. Therefore, the change in space will cause the gathered vapor phase to enter the heat exchanger header from the collector position. Due to the difference in vapor-liquid density, the vapor group will quickly move upward after leaving the collector position, and the liquid pushed away from the wall by the vapor group in the original spatial position will also quickly rebound and hit the wall, forming a collision phenomenon. The more discontinuous the vapor-liquid phase is, the larger the vapor group gathers, and the greater the water hammer energy. The collision phenomenon will cause greater noise, vibration and mechanical shock, causing damage to the equipment. Therefore, in order to avoid this phenomenon, the distance between adjacent flow stabilization devices 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.

[0032] Further preferably, from the inlet of the heat collecting tube 1 to the outlet of the heat collecting tube 1, the distance between adjacent rows is getting shorter and shorter, and the amplitude is increasing. That is, D" is the second derivative of D, which meets the following requirements:

[0033] D”>0;

[0034] Through experiments, it was found that such a setting can further reduce vibration and noise while improving the heat exchange effect.

[0035] like Figure 1 As shown, the fin 1 is a cone, which extends from the inner wall of the heat collector body to the center of the heat collector 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 collector body, and the tip 22 of the cone extends to the center of the heat collector body.

[0036] The present invention increases the heat exchange area of ​​the inner wall of the heat collecting tube by arranging conical inner fins on the inner wall of the heat collecting tube, compared with the prior art in which a pointed fin is arranged in the center of the circular heat collecting tube, thereby achieving the purpose of enhancing heat transfer. At the same time, because the tip of the cone is toward the center of the heat collecting tube, the bubbles in the vapor-liquid two-phase flow are punctured when they contact the tip of the inner fin, so that the vapor phase is divided into small bubbles, avoiding the generation of large bubbles, and also reducing the heat exchange deterioration caused by the bubbles on the inner wall, promoting the smooth flow of the vapor phase, playing a role in stabilizing the flow rate, avoiding the occurrence of water hammer phenomenon, having the effect of reducing vibration and noise, and improving the heat exchange effect.

[0037] As an improvement, the length of the fins extending toward the center of the heat collecting tube body (cone height) is 0.2-0.4 times, preferably 0.25-0.35 times, the diameter of the heat collecting tube body.

[0038] As an improvement, the diameter of the cylindrical bottom 21 is 0.15-0.35 times, preferably 0.20-0.30 times, the height of the cone.

[0039] The above dimensions are optimized designs that can maximize heat transfer while achieving the best vibration and noise reduction effects.

[0040] As an improvement, the heat collecting tubes are arranged horizontally, and reflectors are arranged at the lower part, which reflect the solar energy to the lower part of the heat collecting tubes.

[0041] As an improvement, the heat collecting tube is arranged horizontally, and a convex lens is arranged on the upper part, and the convex lens collects solar energy to the upper part of the heat collecting tube.

[0042] As an improvement, the heat collecting tube is arranged horizontally, with a reflector arranged at the lower part and a convex lens arranged at the upper part, the reflector reflects the solar energy to the lower part of the heat collecting tube, and the convex lens collects the solar energy to the upper part of the heat collecting tube, so that both the upper part and the lower part can exchange heat.

[0043] As an improvement, Figure 2 As shown, the fins at different positions of the heat collecting tube body 1 are arranged at different positions, for example Figure 2 The middle fins are arranged at the lower part and the upper part respectively. Along the flow direction of the fluid, the fins arranged at the upper part of the heat collecting tube body and the fins arranged at the lower part of the heat collecting tube body are arranged at intervals. By arranging the upper part and the lower part with fins at intervals, a baffle-like effect can be formed to avoid short-circuiting of the flow of the fluid, and at the same time, the fluid can continuously change direction during the flow, increase the disturbance of the fluid, and further realize the enhancement of heat transfer.

[0044] As an improvement, Figure 2 As shown in the figure, along the flow direction of the fluid in the heat collector, the spacing between adjacent fins increases from the heat collector inlet to the middle of the heat collector. Then, from the middle of the heat collector to the heat collector outlet, the spacing between adjacent fins decreases. Because during the heat collection process, the heat absorption of the heat collector per unit length along the flow of the fluid is relatively uniform, which makes the overall heat exchange effect the best. However, it was found in experiments and simulations that the heat collection in the middle is significantly greater than the heat collection at the inlet and outlet of the heat collector. Therefore, the heat exchange area of ​​the heat collector fluid in the fins changes by changing the fin spacing. Therefore, the uneven heat exchange is compensated by the change in area, thereby further improving the heat exchange efficiency.

[0045] As an improvement, along the flow direction of the fluid in the heat collecting tube, the amplitude of the increasing distance between the fins increases from the heat collecting tube entrance to the middle of the heat collecting tube. Then, from the middle of the heat collecting tube to the heat collecting tube exit, the amplitude of the decreasing distance between the fins decreases. The above amplitude changes can make the heat exchange per unit length of the entire fluid movement more uniform, further improving the heat collection efficiency.

[0046] The fins are arranged in the vertical direction, including fins located at the upper part and fins located at the lower part, and the upper fins and the lower fins are arranged at intervals; along the flow direction of the fluid in the heat collecting tube, the height of the lower fins extending upward from the inner wall of the bottom shell gradually increases, and the length of the upper fins extending downward from the inner wall of the upper shell gradually decreases.

[0047] During the research, it was found that the fins of the traditional heat exchanger have uneven heat exchange in the cross section in the direction of fluid flow. As the distance from the inlet increases, the heat exchange liquid density in the lower part of the shell is large, so the liquid flows downward, which significantly increases the heat exchange liquid in the lower part. Therefore, it is necessary to design a heat exchange structure for improvement. The present invention changes the height of the upper and lower fins along the flow direction of the fluid, so that the liquid in the tube gradually moves closer to the center as it flows, so that the center of the shell strengthens the heat exchange of the heat collection tube around the heat collection tube shell, changes the previous heat exchange method, enhances the heat exchange efficiency at different positions, makes the overall heat exchange uniform, and further achieves the purpose of enhanced heat transfer.

[0048] As an improvement, along the flow direction of the fluid in the heat collecting tube, the vertical height of the lower fin extending upward from the bottom shell inner wall gradually increases, and the vertical length of the upper fin extending downward from the upper shell inner wall gradually decreases. Through the above-mentioned amplitude changes, the overall heat exchange can be further uniform, further achieving the purpose of enhancing heat transfer.

[0049] As an improvement, along the flow direction of the fluid in the heat collecting tube, the fin distribution density of the upper part of the heat collecting tube body is greater than that of the lower part. This is mainly because bubbles tend to flow upward due to their low density, and because bubbles tend to gather at the upper part, it is also easy to cause the upper heat exchange to deteriorate. Therefore, by setting the upper fin density to be higher, the bubbles can be further punctured faster, and by setting the upper fin density to be higher, the enhanced heat transfer of the upper part can be increased, and the overall heat exchange can be uniform.

[0050] As an improvement, the distribution density of the fins gradually increases along the flow direction of the fluid in the heat collecting tube. As the fluid continues to flow, the liquid is converted into bubbles, making the bubbles in the fluid more and more. Therefore, by increasing the density of the fins, the heat exchange deterioration and water hammer phenomenon can be prevented.

[0051] As an improvement, along the flow direction of the fluid in the heat collecting tube, the distribution density of the fins gradually increases. The above amplitude change is also in line with the actual situation. Through actual observation, as the fluid in the heat collecting tube continues to flow, the speed of bubble generation is also getting faster and faster. Therefore, the above setting can further prevent heat exchange deterioration and avoid water hammer phenomenon.

[0052] As an improvement, along the flow direction of the fluid, the fins, preferably the fins arranged on the upper part of the heat collecting tube body, extend from the inner wall of the heat collecting tube body to the center with decreasing height. The main reason is that as the fluid continues to flow, the bubbles gather more and more upwards due to their low density. By setting the height smaller and smaller, the bubbles continuously touch the tip of the fins during the upward flow process, avoiding the bubbles directly entering the gaps of the fins to hinder heat exchange, and thus being continuously punctured, thereby further preventing the deterioration of heat exchange and avoiding water hammer phenomenon.

[0053] Along the flow direction of the fluid, the fins, preferably the fins arranged on the upper part of the heat collector tube body, extend from the inner wall of the heat collector tube body to the center with a decreasing amplitude. The above amplitude change is also in line with the law of bubble rise, which can further prevent heat exchange deterioration and avoid water hammer phenomenon.

[0054] As an improvement, in the fluid flow direction, the fins are arranged in multiple rows, and the rows are arranged along the circumference of the heat collecting tube body.

[0055] Preferably, multiple rows of fins are arranged in the heat collecting tube 1 along the height direction of the heat collecting tube 1, and the distribution density of the fins in the rows increases from the inlet to the outlet of the heat collecting tube 1. That is, the distribution density of the fins in each row is V, V=Y2(S), V' is the first derivative of V, and meets the following requirements:

[0056] V'>0;

[0057] As a preference, from the inlet to the outlet of the heat collecting tube, that is, the distribution density of the fins in each row increases continuously. That is, V" is the second derivative of V, which meets the following requirements:

[0058] V ”>0.

[0059] See the changes in each row for specific reasons.

[0060] A solar thermal collector comprises the internal fin thermal collecting tube mentioned above.

[0061] like Figure 3 As shown, the heat collecting tubes 1 are multiple and arranged side by side, and the adjacent heat collecting tubes are connected by connecting tubes 3. During the operation of the heat collector, there is uneven fluid distribution, and because different heat collecting tubes absorb different amounts of heat during the heat collection process, the fluid temperatures in different heat collecting tubes are different, resulting in different pressures. By setting connecting tubes between the heat collecting tubes, the fluids can flow mutually in the heat collecting tubes, so that the pressure distribution in all the heat collecting tubes is balanced, and the fluid distribution can also be promoted to be balanced.

[0062] Preferably, along the flow direction of the fluid in the heat collecting tube, the distance between adjacent connecting tubes 3 is continuously reduced. Because as the fluid flows, the fluid is continuously heated, and as the fluid is continuously heated, the heating in different heat collecting tubes becomes increasingly uneven. Therefore, through the above arrangement, it is possible to ensure that pressure balance is achieved as soon as possible during the fluid flow process.

[0063] Preferably, along the flow direction of the fluid in the heat collecting tube, the distance between adjacent connecting tubes 3 is reduced to a greater and greater extent. It is found through experiments that the above arrangement can ensure that pressure balance is achieved better and faster during the fluid flow process.

[0064] Although the present invention has been disclosed as 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, so the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A heat collecting tube with fin spacing arrangement, comprising a tube body, wherein fins are arranged on the inner wall of the tube body, wherein the fins have a tip extending toward the center of the tube body, and in the direction of fluid flow, the fins are arranged in multiple rows, wherein the rows are arranged along the circumference of the tube body; the fluid in the heat collecting tube is a cold source, and the distance from the entrance of the heat collecting tube is S, and the distance between adjacent rows is D, wherein D=Y1(S), i.e., D is a function with the distance S as a variable, and D' is a first derivative of D, which satisfies the following requirements: D’<0； The heat collecting tube is arranged horizontally, and the fins of the heat collecting tube body 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 tube body and the fins arranged at 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 height of the lower fin extending upward from the bottom shell inner wall gradually increases, and the length of the upper fin extending downward from the upper shell inner wall gradually decreases; along the flow direction of the fluid in the heat collecting tube, the height of the lower fin extending upward from the bottom shell inner wall gradually increases, and the length of the upper fin extending downward from the upper shell inner wall gradually decreases.

2. The heat collecting tube as claimed in claim 1, wherein D" is the second derivative of D and satisfies the following requirements: D”>0。 3. The heat collecting tube according to claim 1, characterized in that: The fin is a cone, and the cone extends from the inner wall to the center of the tube body.

4. A heat collector, comprising a heat collecting tube, the heat collecting tube comprising a tube body, the inner wall of the tube body is provided with fins, the fins have a tip extending toward the center of the tube body, and in the direction of fluid flow, the fins are arranged in multiple rows, and the rows are arranged along the circumference of the tube body; the fluid in the heat collecting tube is a cold source, and the distance from the entrance of the heat collecting tube is S, and the distance between adjacent rows is D, D=Y1(S), that is, D is a function with the distance S as a variable, and D' is a first derivative of D, which meets the following requirements: D’<0； The heat collecting tube is arranged horizontally, and the fins of the heat collecting tube body 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 tube body and the fins arranged at 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 height of the lower fin extending upward from the bottom shell inner wall gradually increases, and the length of the upper fin extending downward from the upper shell inner wall gradually decreases; along the flow direction of the fluid in the heat collecting tube, the height of the lower fin extending upward from the bottom shell inner wall gradually increases, and the length of the upper fin extending downward from the upper shell inner wall gradually decreases.

5. The heat collector according to claim 4, characterized in that: D" is the second derivative of D, satisfying the following requirements: D”>0。 6. The heat collector according to claim 4, characterized in that: The fin is a cone, and the cone extends from the inner wall to the center of the tube body.

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