heat exchanger

Abstract

To provide a heat exchanger with high heat exchange efficiency. [Solution] The heat exchanger 1 includes a heat exchange section 10 in which a first flow path 40 through which a first fluid P flows and a second flow path 50 through which a second fluid Q flows are adjacent to each other and extend along the axial direction. Within the first flow path 40, at a position where the first fluid P flows without changing its velocity in the axial direction, the region in the flow path area perpendicular to the axial direction in which the absolute value of the flow velocity of the first fluid P along the axial direction corresponds to the top 20% is defined as the high-velocity region H. In this flow path region, the normalized heat exchange distance L', defined as L'=L / D, where L is the shortest distance from the wall surface defining the first flow path 40 to the high-velocity region H and D is the diameter of the smallest circle C that can include the entire cross-sectional shape of the first flow path 40, is less than 0.15.

Description

Technical Field

[0001] The present invention relates to a heat exchanger.

Background Art

[0002] Conventionally, in order to improve the heat exchange efficiency of a heat exchanger, a plurality of flow paths are formed, and for example, the cross-sectional shape and position of these flow paths are adjusted so as to form a geometric pattern as a whole (see, for example, Patent Document 1). In recent years, there has been a demand for further increasing the heat exchange efficiency of heat exchangers.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a heat exchanger with high heat exchange efficiency.

Means for Solving the Problems

[0006] [Figure 1] Figure 1 is a conceptual diagram showing the configuration of a heat exchanger in one embodiment of the present invention. [Figure 2] Figure 2 is a schematic perspective view showing the heat exchange section of the heat exchanger shown in Figure 1. [Figure 3] Figure 3 is a partially enlarged cross-sectional view showing the shapes of the first and second flow channels of the heat exchange section shown in Figure 2. [Figure 4] Figure 4 shows the velocity distribution along the axial direction of the first fluid flowing through the first channel shown in Figure 3. [Figure 5] Figure 5 is a diagram illustrating the normalized heat exchange distance in the first flow path shown in Figure 4. [Figure 6] Figure 6 is a partially enlarged cross-sectional view showing the shapes of the first and second channels in another embodiment of the present invention. [Figure 7] Figure 7 is a schematic perspective view showing an example of a model for evaluating the normalized heat exchange distance according to the present invention. [Figure 8A] Figure 8A shows the cross-sectional shape of the first channel of Model A. [Figure 8B] Figure 8B shows the cross-sectional shape of the first channel of Model B. [Figure 8C] Figure 8C shows the cross-sectional shape of the first channel of Model C. [Figure 8D] Figure 8D shows the cross-sectional shape of the first channel of Model D. [Figure 8E] Figure 8E shows the cross-sectional shape of the first channel of Model E. [Figure 8F] Figure 8F shows the cross-sectional shape of the first channel of model F. [Figure 8G] Figure 8G shows the cross-sectional shape of the first channel of model G. [Figure 9A] Figure 9A shows the velocity distribution along the axial direction of the first fluid flowing through the first channel of Model A. [Figure 9B] FIG. 9B is a diagram showing the distribution of the flow velocity along the axial direction of the first fluid flowing through the first flow path of Model B. [Figure 9C] FIG. 9C is a diagram showing the distribution of the flow velocity along the axial direction of the first fluid flowing through the first flow path of Model C. [Figure 9D] FIG. 9D is a diagram showing the distribution of the flow velocity along the axial direction of the first fluid flowing through the first flow path of Model D. [Figure 9E] FIG. 9E is a diagram showing the distribution of the flow velocity along the axial direction of the first fluid flowing through the first flow path of Model E. [Figure 9F] FIG. 9F is a diagram showing the distribution of the flow velocity along the axial direction of the first fluid flowing through the first flow path of Model F. [Figure 9G] FIG. 9G is a diagram showing the distribution of the flow velocity along the axial direction of the first fluid flowing through the first flow path of Model G. [Figure 10] FIG. 10 is a graph showing the relationship between the normalized heat exchange distance and the heat exchange amount in Models A to G. [Figure 11] FIG. 11 is a graph showing the in-plane average temperature in the axial direction of the first fluid and the second fluid in Model A. [Figure 12] FIG. 12 is a graph showing the in-plane average temperature in the axial direction of the first fluid and the second fluid in Model F. [Figure 13] FIG. 13 is a graph showing the in-plane average temperature in the axial direction of the first fluid and the second fluid in Model G.

MODE FOR CARRYING OUT THE INVENTION

[0007] Hereinafter, embodiments of the heat exchanger according to the present invention will be described in detail with reference to Figures 1 to 13. In Figures 1 to 13, identical or corresponding components are denoted by the same reference numerals, and redundant descriptions are omitted. Also, in Figures 1 to 13, the scale and dimensions of each component may be exaggerated, or some components may be omitted. In the following description, unless otherwise specified, terms such as "first" and "second" are used only to distinguish components from one another and do not represent a specific rank or order.

[0008] Figure 1 is a conceptual diagram showing the configuration of a heat exchanger 1 in one embodiment of the present invention. In this embodiment, the heat exchanger 1 performs heat exchange between a first fluid P (e.g., oil) and a second fluid Q (e.g., water), but the present invention can also be applied when heat exchange is performed between three or more types of fluids. As shown in Figure 1, the heat exchanger 1 includes a heat exchange section 10 in which heat exchange is performed between the first fluid P and the second fluid Q, a first header 20 provided at one end of the heat exchange section 10, and a second header 30 provided at the other end of the heat exchange section 10.

[0009] The heat exchange section 10 is formed with one or more first channels 40 through which a first fluid P flows, and one or more second channels 50 through which a second fluid Q flows, each extending along the axial direction. The axial length of the channels 40 and 50 is such that the flow of the first fluid P and the second fluid Q develops sufficiently and the flow velocity no longer changes in the axial direction. In Figure 1, one first channel 40 and one second channel 50 are typically shown, but multiple first channels 40 and multiple second channels 50 may be formed in the heat exchange section 10. A heat exchanger 1 having such a channel structure can be manufactured, for example, by additive manufacturing using a 3D printer.

[0010] In the heat exchange section 10 of this embodiment, the direction of the first fluid P flowing through the first channel 40 and the direction of the second fluid Q flowing through the second channel 50 are opposite to each other, so the heat exchanger 1 of this embodiment is a counterflow type heat exchanger. However, it is also possible to configure the heat exchanger 1 as a parallel flow type heat exchanger by making the direction of the first fluid P flowing through the first channel 40 and the direction of the second fluid Q flowing through the second channel 50 the same.

[0011] In this embodiment, the first header 20 is configured to introduce a first fluid P into the heat exchange section 10 from the outside and discharge a second fluid Q from the heat exchange section 10 to the outside, while the second header 30 is configured to discharge the first fluid P from the heat exchange section 10 to the outside and introduce the second fluid Q into the heat exchange section 10 from the outside. When a plurality of first flow paths 40 and a plurality of second flow paths 50 are formed in the heat exchange section 10, the first header 20 is configured to branch the first fluid P into the plurality of first flow paths 40 and to merge the second fluid Q from the plurality of second flow paths 50, while the second header 30 is configured to merge the first fluid P from the plurality of first flow paths 40 and to branch the second fluid Q into the plurality of second flow paths 50. Known structures can be used as such first headers 20 and second headers 30, and their details will not be described.

[0012] The details of the heat exchange section 10 will be described below. Figure 2 is a schematic perspective view of the heat exchange section 10. In the example shown in Figure 2, a plurality of first flow channels 40 and a plurality of second flow channels 50 are formed adjacent to each other in the rectangular parallelepiped heat exchange section 10. These flow channels 40 and 50 extend along the axial direction (Z direction) and penetrate the heat exchange section 10.

[0013] Figure 3 is a partially enlarged cross-sectional view showing the shapes of the first channel 40 and the second channel 50. As shown in Figures 2 and 3, in the XY plane perpendicular to the axial direction (Z direction), each of the first channels 40 has a roughly X-shaped cross-section, and each of the second channels 50 has a square cross-section. The cross-sectional shapes of both the first channel 40 and the second channel 50 are symmetrical with respect to the Y and X axes.

[0014] As shown in Figures 2 and 3, the first channel 40 and the second channel 50 are arranged alternately at a constant interval in the X direction, and also alternately at a constant interval in the Y direction. The distance W between the centers of adjacent first channel 40 and second channel 50 in the X direction is... X The distance W is the distance between the center of the adjacent first channel 40 and the center of the second channel 50 in the Y direction. Y It is equal to this.

[0015] As shown in Figure 3, the cross-sectional shape of the first channel 40 is approximately X-shaped, as described above, and includes a central portion 41 and four arm portions 42 extending outward from the central portion 41. The four arm portions 42 are arranged at equal intervals around the central portion 41, i.e., at 90-degree intervals. In this embodiment, the arm portions 42 extend at angles of 45 degrees with respect to the X and Y axes, respectively. The cross-sectional shape of the second channel 50 is square, as described above, and this square has sides parallel to the direction in which the arm portions 42 of the first channel 40 extend (i.e., in directions of 45 degrees with respect to the X and Y axes, respectively).

[0016] The inventors have diligently researched the cross-sectional shape of a flow path that can improve the heat exchange efficiency of a heat exchanger, and have found that the heat exchange efficiency can be improved by bringing the high-velocity region where the fluid flows at high speed as close as possible to the wall surface of the flow path. More specifically, the inventors introduced the concept of a normalized heat exchange distance L' as an index representing the distance from the high-velocity region to the wall surface of the flow path, and discovered that the normalized heat exchange distance L' that can achieve high heat exchange efficiency is less than 0.15, preferably less than 0.13, more preferably less than 0.08, and even more preferably less than 0.05.

[0017] Here, the high-velocity region is defined as the region in the flow path perpendicular to the axial direction where the fluid flows without changing velocity in the axial direction, and where the absolute value of the fluid velocity along the axial direction is in the top 20%. The normalized heat exchange distance L' is defined as the shortest distance from the wall surface defining the flow path to the high-velocity region in the flow path region, with L being the shortest distance and D being the diameter of the smallest circle that can encompass the entire cross-sectional shape of the flow path. L'=L / D It is defined as follows.

[0018] Figure 4 shows the velocity distribution of the first fluid P flowing through the first channel 40 along the axial direction (Z direction). In this channel region, the first fluid P flows at a constant velocity in the axial direction, but at different velocities in the XY plane. As shown in Figure 4, in this channel region, the velocity of the first fluid P flowing through the central part 41 is faster than the velocity of the first fluid P flowing through the arm part 42. As described above, the high-velocity region is defined as the region where the absolute value of the velocity of the first fluid P along the axial direction is in the top 20%, and in the channel region shown in Figure 4, the dark-colored region H in the range of velocity ratio from 0.8 to 1.0 is the high-velocity region. This high-velocity region H is located in the central part 41 of the first channel 40.

[0019] Therefore, as shown in Figure 5, the normalized heat exchange distance L' of the first channel 40 is, in the channel region, where L is the shortest distance from the wall surface defining the first channel 40 to the high-velocity region H, and D is the diameter of the smallest circle C that can encompass the entire cross-sectional shape of the first channel 40, L'=L / D This is determined by [formula]. Furthermore, this normalized heat exchange distance L' is less than 0.15.

[0020] As long as the normalized heat exchange distance L' is less than 0.15, the cross-sectional shape of the first channel 40 can be anything. For example, instead of the first channel 40 having a roughly X-shaped cross-section, a first channel 140 having an asterisk-shaped cross-section as shown in Figure 6 may be used. The cross-sectional shape of the first channel 140 shown in Figure 6 includes a central portion 141 and six arm portions 142 extending outward from the central portion 141. The six arm portions 42 are arranged at equal intervals around the central portion 141, i.e., at 60-degree intervals. Also, in the example shown in Figure 6, instead of the second channel 50 having a square cross-section, a second channel 150 having a triangular cross-section may be used, in this example where six second channels 150 are arranged to surround one first channel 140. The triangular cross-sectional shape of the second channel 150 has sides parallel to the direction in which the arm portions 142 of the first channel 140 extend.

[0021] In the above embodiment, the normalized heat exchange distance L' of the first flow path 40 is set to less than 0.15. However, the normalized heat exchange distance L' of the second flow path 50 may be set to less than 0.15 without setting the normalized heat exchange distance L' of the first flow path 40 to less than 0.15. Alternatively, both the normalized heat exchange distance L' of the first flow path 40 and the normalized heat exchange distance L' of the second flow path 50 may be set to less than 0.15. In this case, it is preferable to preferentially select the flow path through which the fluid with a small heat transfer coefficient α to the flow path wall flows, and to set its normalized heat exchange distance L' to less than 0.15. Here, the heat transfer coefficient α to the flow path wall can be calculated using the following formula. α = Nu × λ / d Here, Nu is the Nusselt number, λ is the thermal conductivity, and d is the hydraulic diameter. The Nusselt number Nu is given by Hausen's equation when the flow is laminar (Reynolds number Re is less than 2300).

number

number

[0022] The inventors evaluated a suitable range for the normalized heat exchange distance L' of the first flow path 40 described above by the following simulation. In this simulation, a double-walled pipe 230 as shown in Figure 7 was used as a model. This double-walled pipe 230 includes an outer pipe 210 and an inner pipe 220 arranged radially inward of the outer pipe 210. A first flow path 240 extending in the axial direction is formed in the center of the inner pipe 220, and an annular second flow path 250 is formed between the outer pipe 210 and the inner pipe 220 so as to extend in the axial direction.

[0023] For double-walled pipe 230, the density is 7910 kg / m³. 3 Stainless steel pipe components with a specific heat of 469 J / kg·K and a thermal conductivity of 13 W / m·K were used. The length of the double-walled pipe 230 was 200 mm, the outer diameter of the outer pipe 210 was 9 mm, and the inner diameter was 8 mm. The outer diameter of the inner pipe 220 was 6 mm. The diameter D of the smallest circle C that can contain the entire cross-sectional shape of the first flow path 240 was set to 5 mm.

[0024] The first fluid P flowing through the first channel 240 has a density of 782 kg / m³. 3 Specific heat 2269 J / kg·K, thermal conductivity 0.15 W / m·K, kinematic viscosity 1.93 × 10 -5 The oil used was a second fluid Q with a density of 998 kg / m³. 3 Specific heat 4182 J / kg·K, thermal conductivity 0.5975 W / m·K, kinematic viscosity 1.00 × 10 -6 Water was used. The flow direction of the first fluid P and the flow direction of the second fluid Q were reversed. The oil inlet temperature was 80°C, the oil flow rate was 0.1 L / min, the water inlet temperature was 10°C, and the water flow rate was 0.5 L / min.

[0025] Model A was created by applying the cross-sectional shape shown in Figure 8A to the first channel 240, Model B by applying the cross-sectional shape shown in Figure 8B, Model C by applying the cross-sectional shape shown in Figure 8C, Model D by applying the cross-sectional shape shown in Figure 8D, Model E by applying the cross-sectional shape shown in Figure 8E, Model F by applying the cross-sectional shape shown in Figure 8F, and Model G by applying the cross-sectional shape shown in Figure 8G. For these Models A to G, the flow velocity distribution along the axial direction of the first fluid P flowing through the first channel 240 was calculated, resulting in the distributions shown in Figures 9A to 9G. From these flow velocity distributions, the normalized heat exchange distance L' of the first channel 240 was obtained as follows. Model A: L' = 0.315 Model B: L' = 0.194 Model C:L'=0.142 Model D:L'=0.112 Model E:L'=0.074 Model F:L'=0.015 Model G:L'=0.014

[0026] Furthermore, when the amount of heat exchange between the first fluid P and the second fluid Q was calculated for these models A to G, the results were as follows. Model A: 42.21W Model B: 43.62W Model C: 46.53W Model D: 53.86W Model E: 66.55W Model F: 117.35W Model G: 141.86W

[0027] These results are summarized in the graph shown in Figure 10. In the graph in Figure 10, the horizontal axis represents the normalized heat exchange distance L', and the vertical axis represents the heat exchange rate. From the graph in Figure 10, it can be seen that if the normalized heat exchange distance L' is less than 0.15, the heat exchange rate increases compared to the conventional flow path (Figures 8A and 8B), if it is less than 0.13, the heat exchange rate increases further, if it is less than 0.08, the heat exchange rate increases further, and if it is less than 0.05, the heat exchange rate increases even further. Therefore, in order to achieve high heat exchange efficiency, it is preferable that the normalized heat exchange distance L' is less than 0.15, more preferably less than 0.13, even more preferably less than 0.08, and most preferably less than 0.05.

[0028] Figures 11, 12, and 13 are graphs showing the in-plane average temperatures in the axial direction of the first fluid P and the second fluid Q in models A, F, and G, respectively. As shown in Figure 11, in model A, which has a normal first flow path with a circular cross-sectional shape, the outlet temperature of the first fluid P can only be reduced to 65.7°C. However, in model F, where the normalized heat exchange distance L' is less than 0.05, it can be reduced to 40.3°C, and in model G, to 32.0°C. This shows that models with a lower normalized heat exchange distance L' have higher heat exchange efficiency.

[0029] In particular, despite the similar cross-sectional shapes of the first channel 240 in Model F and Model G, the heat exchange rate in Model G increases sharply compared to that of Model F, as shown in Figure 10. This is thought to be because, as shown in Figure 8G, the cross-sectional shape of the first channel 240 in Model G has folds F that increase the surface area of ​​the first channel 240.

[0030] As described above, the heat exchanger according to the present invention can employ the following configuration. [Configuration 1] The device comprises a heat exchange section in which a first fluid flows and a second fluid flows, with the first flow path and the second flow path being adjacent to each other and extending along the axial direction. Within the first flow path described above, the region in the flow path area perpendicular to the axial direction where the first fluid flows without changing velocity in the axial direction is defined as the high-velocity region H, and within the flow path region, the normalized heat exchange distance L' defined as L' = L / D is defined as the shortest distance from the wall surface defining the first flow path to the high-velocity region H, and the diameter of the smallest circle that can include the entire cross-sectional shape of the first flow path D. L'<0.15 That is, heat exchanger.

[0031] [Configuration 2] The cross-sectional shape of the first channel described above is The central region including the high flow velocity region H, Three or more arm sections extending outward from the central part mentioned above including, The heat exchanger described in Configuration 1.

[0032] [Configuration 3] The heat exchanger according to configuration 2, wherein the three or more arm sections are arranged at equal intervals around the central section.

[0033] [Structure 4] The heat exchanger according to configuration 2 or 3, wherein the cross-sectional shape of the second flow path is a polygon having sides parallel to the direction in which the three or more arm portions extend.

[0034] [Composition 5] The heat exchanger according to any one of configurations 1 to 4, wherein the cross-sectional shape of the first flow channel includes folds that increase the surface area of ​​the first flow channel.

[0035] [Composition 6] A heat exchanger according to any one of configurations 1 to 5, wherein the heat transfer coefficient of the first fluid to the wall surface of the first flow path is smaller than the heat transfer coefficient of the second fluid to the wall surface defining the second flow path.

[0036] Although preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the embodiments described above and may be implemented in various different forms within the scope of its technical concept. [Explanation of Symbols]

[0037] 1 heat exchanger 10 Heat exchange section 40,140,240 First channel 41,141 central part 42,142 Arm section 50,150,250 Second channel C Minimum Circle F fold H High flow rate region P 1st fluid Q 2nd fluid

Claims

1. The device comprises a heat exchange section in which a first fluid flows and a second fluid flows, the first and second flow channels being adjacent to each other and extending along the axial direction. Within the first flow path, at a position where the first fluid flows without changing velocity in the axial direction, the region perpendicular to the axial direction in which the absolute value of the flow velocity of the first fluid along the axial direction is defined as the high-velocity region H, and within the flow path region, the shortest distance from the wall surface defining the first flow path to the high-velocity region H is L, and the diameter of the smallest circle that can include the entire cross-sectional shape of the first flow path is D, and the normalized heat exchange distance L' defined as L' = L / D is L' < 0.15 That is, heat exchanger.

2. The cross-sectional shape of the first flow path is The central portion including the high flow velocity region H, Three or more arm portions extending outward from the central portion and including, The heat exchanger according to claim 1.

3. The heat exchanger according to claim 2, wherein the three or more arm portions are arranged at equal intervals around the central portion.

4. The heat exchanger according to claim 2, wherein the cross-sectional shape of the second flow path is a polygon having sides parallel to the direction in which the three or more arm portions extend.

5. The heat exchanger according to claim 1, wherein the cross-sectional shape of the first flow channel includes folds that increase the surface area of ​​the first flow channel.

6. The heat exchanger according to any one of claims 1 to 5, wherein the heat transfer coefficient of the first fluid to the wall surface of the first flow path is smaller than the heat transfer coefficient of the second fluid to the wall surface defining the second flow path.

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