A leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs

Abstract

This invention discloses a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs, belonging to the field of heat sink technology, and solving the problems of poor temperature uniformity and additional pumping costs in microchannel heat sinks. The invention features a primary leaf vein flow channel located at the center of the microchannel heat sink, with a heat plate at the bottom. The microchannel heat sink includes two heat sinks (first and second), which are mirror-symmetrical to the first heat sinks. Each heat sink contains several secondary and tertiary leaf vein flow channels and several rib arrays. The secondary leaf vein flow channels are inclined and connected to the primary leaf vein flow channels. The tertiary leaf vein flow channels are evenly spaced between the secondary leaf vein flow channels. The rib arrays are located at the inner ends of the secondary leaf vein flow channels, each rib being an arc-shaped plate. This invention features high heat dissipation efficiency, good temperature uniformity, low flow resistance, and low pressure drop, thereby ensuring the efficient and stable operation of high-power micro-devices.

Description

Technical Field

[0001] This invention relates to the field of radiator technology, specifically to a leaf vein-shaped composite bionic microchannel radiator with petal-shaped ribs. Background Technology

[0002] Currently, rapid technological advancements have significantly increased the integration of devices in fields such as microelectronics, laser equipment, aerospace, and advanced semiconductor manufacturing processes. This has led to a surge in system power density and consequently, a dramatic increase in heat generation. To prevent thermal runaway, a thermal management system with high heat dissipation efficiency and excellent performance is needed. Microchannel heat exchangers, with channel equivalent diameters ranging from 10 to 1000 μm, contain dozens of tiny flow channels within their flat tubes. Due to their large heat transfer area and high heat transfer coefficient within these tiny channels, microchannel heat exchangers outperform large-scale heat exchangers and have broad application prospects in high-power, highly integrated, and micro-device heat dissipation applications.

[0003] Currently used microchannel heat sinks are mostly direct-flow (DC) and manifold microchannels, but several problems remain: DC microchannels have limited cooling capacity, poor cooling at the channel ends, a large temperature gradient along the channel direction, and poor heat dissipation uniformity. Furthermore, DC microchannels have a large internal pressure drop, unstable flow, are prone to minor vibrations, and consume significant pumping power. Manifold microchannels have multiple branch ports, and differences in flow velocity within each channel lead to varying heat transfer efficiencies and uneven temperature distribution in the cooled devices. On the other hand, manifold microchannels suffer from uneven working fluid distribution and are prone to flow blockages, potentially creating "localized hot spots" that affect the performance of the cooled devices. Therefore, poor temperature uniformity in the heat dissipation area, mechanical vibrations caused by large flow pressure drops, and additional pumping power consumption limit the practical application of microchannel heat sinks. Summary of the Invention

[0004] To address the aforementioned problems of poor temperature uniformity and additional pumping costs in microchannel heat sinks, this invention proposes a leaf-vein-shaped composite biomimetic microchannel heat sink with petal-shaped fins. This invention features high heat dissipation efficiency, good temperature uniformity, low flow resistance, and low pressure drop, thereby ensuring the efficient and stable operation of high-power micro-devices.

[0005] This invention proposes a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs, specifically comprising a microchannel heat sink and a primary leaf vein flow channel. The primary leaf vein flow channel is located at the center of the microchannel heat sink, and a heat plate is located at the bottom of the microchannel heat sink. The microchannel heat sink includes two heat sinks (first and second). The two heat sinks (first and second) are arranged in a matrix, with the two heat sinks (first and second) diagonally opposite each other. Each heat sink (first) contains several secondary leaf vein flow channels, several tertiary leaf vein flow channels, and several rib groups. The secondary leaf vein flow channels are inclined and connected to the primary leaf vein flow channels. The tertiary leaf vein flow channels are evenly spaced between the secondary leaf vein flow channels. The rib groups are located at the inner ends of the secondary leaf vein flow channels. Each rib group includes two ribs, and each rib is an arc-shaped plate. The second heat sink and the first heat sink are mirror-symmetrical.

[0006] Furthermore, the edges of the ribs are Fibonacci spirals.

[0007] Furthermore, the angle between the secondary leaf vein channel and the primary leaf vein channel is 10 degrees.

[0008] Furthermore, the two secondary vein channels near the upper edge of the microchannel heat sink in the secondary vein channel have their ends turned to be perpendicular to the upper edge of the microchannel heat sink.

[0009] Furthermore, the first and second secondary vein channels near the upper edge of the heat sink are not connected.

[0010] Furthermore, the secondary leaf vein flow channel near the lower edge of the heat sink has its root parallel to the lower edge of the heat sink.

[0011] Furthermore, no rib group is provided in the first secondary leaf vein flow channel near the upper edge of the heat sink.

[0012] Furthermore, the three-stage leaf vein flow channel is an arc-shaped flow channel.

[0013] Furthermore, the curvature center of the leftmost third-level leaf vein channel in the first heat sink coincides with the left boundary of the first heat sink.

[0014] Furthermore, the tertiary vein channels on both sides of the secondary vein channel are symmetrical about the secondary vein channel.

[0015] The beneficial effects of the leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs described in this invention are as follows:

[0016] (1) The leaf vein-shaped composite bionic microchannel heat sink with petal-shaped ribs described in this invention has excellent heat dissipation performance and good temperature uniformity. In the thermal management application of laser crystals in solid-state lasers, compared with a DC microchannel with the same heat exchange area, when the laser crystal thermal power is 20 W and the working fluid flow rate is 12 ml / min, the highest temperature on the crystal surface is 305.7043 K, which is 3.1368 K lower than that of the DC microchannel; the maximum temperature difference on the crystal surface is 1.4819 K, which is 69.38% lower than that of the DC microchannel. At higher power, the heat dissipation capacity is further enhanced compared with the DC microchannel. Keeping the flow rate constant, when the power is increased to 30 W, the highest temperature on the crystal surface is 4.7687 K lower than that of the DC microchannel, and the maximum temperature difference on the crystal surface is only 2.2145 K. It can be seen that this structure still has excellent heat dissipation performance under high heat load.

[0017] (2) The leaf vein-shaped composite biomimetic microchannel radiator with petal-shaped ribs described in this invention has a small flow pressure drop, reduces pumping power consumption, has excellent topology, small inlet and outlet pressure drop, low flow resistance, and strong heat exchange capacity. Compared with a direct-flow microchannel with the same heat exchange area, at a flow rate of 12 ml / min, the flow pressure drop of this biomimetic structure is only 33.09 Pa, which is only 51.53% of that of the direct-flow microchannel. When the flow rate increases to 24 ml / min, the pressure drop of this structure is 71.43 Pa, which is 51.87% of that of the direct-flow microchannel. It can be seen that with the continuous increase of the flow rate, the relative pressure drop remains almost unchanged. This structure has the characteristics of small pressure drop, low pumping power consumption, and stable flow.

[0018] (3) The leaf vein-shaped composite bionic microchannel heat sink with petal-shaped ribs described in this invention can meet the unique heat dissipation requirements of high-power micro devices and can be applied to the heat dissipation field of high-power micro devices. It has the characteristics of high heat dissipation efficiency, strong temperature uniformity, stable heat dissipation and low flow pressure drop. In the thermal management application of laser crystals in solid-state lasers, it can ensure that the surface temperature difference of the laser crystal is maintained within 1-3℃ in the power range of 10-30 W, which significantly reduces the problems of thermal lensing effect, thermal stress and crystal breakage caused by thermal effect and uneven temperature distribution during the operation of the laser crystal. The bionic microchannel has excellent performance. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] In the attached diagram:

[0021] Figure 1This is a schematic diagram of the structure of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0022] Figure 2 This is a schematic diagram of the flow channel structure of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0023] Figure 3 This is a schematic diagram of the structure of a heat sink of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0024] Figure 4 This is a schematic diagram of the heat sink and flow channel structure of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0025] Figure 5 This is a top view of the flow channel of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0026] Figure 6 This is a schematic diagram of the rib assembly of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0027] Figure 7 This is a side view of the rib assembly of a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to the present invention.

[0028] Figure 8 This is a comparison diagram of the heat dissipation effect of the leaf vein-shaped composite bionic microchannel heat sink with petal-shaped ribs described in this invention and other microchannel heat sinks.

[0029] Figure 9 This is a diagram of a mesh-like leaf vein structure that mimics the leaf vein-like composite biomimetic microchannel heat sink with petal-shaped ribs described in this invention.

[0030] Figure 10 This is a diagram of an irregularly shaped petal structure, which is based on the leaf vein-like composite bionic microchannel heat sink with petal-shaped ribs described in this invention.

[0031] Wherein: 1-Microchannel heat sink, 2-Fluid inlet, 3-Cooling medium, 4-Fin assembly, 5-Fluid outlet, 6-Primary blade channel, 7-Secondary blade channel, 8-Tertiary blade channel, 9-Fin, 10-Heat sink one, 11-Heat sink two. Detailed Implementation

[0032] The technical solution of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of, and not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0033] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Specific implementation method one: See Figures 1-10 This embodiment is described in detail. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs described in this embodiment specifically includes a microchannel heat sink 1 and a primary leaf vein flow channel 6. The primary leaf vein flow channel 6 is located at the center of the microchannel heat sink 1. The overall dimensions of the microchannel heat sink 1 are 14 mm × 14 mm × 1 mm. A heat plate is provided at the bottom of the microchannel heat sink 1, and the primary leaf vein flow channel 6 is perpendicular to the heat plate. The width of the primary leaf vein flow channel 6 is 0.3 mm, the depth is 1 mm, and the upper and lower ends are 0.5 mm away from the edge of the microchannel heat sink 1. The microchannel heat sink 1 includes two heat sinks 10 and two heat sinks 11. The two heat sinks 10 and two heat sinks 11 are arranged in a matrix around the primary leaf vein flow channel 6, with the two heat sinks 10 and two heat sinks 11 diagonally opposite each other. The structures of the heat sinks 11 and the heat sinks 10 are mirror images of each other.

[0037] Taking heat sink 10 as an example, the structure is described as follows: heat sink 10 is provided with several secondary blade vein channels 7, several tertiary blade vein channels 8 and several rib groups 4. The several secondary blade vein channels 7 are inclined and connected to the primary blade vein channels 6. The included angle between the secondary blade vein channels 7 and the primary blade vein channels 6 is 10 degrees. The width of the secondary blade vein channels 7 is 0.3 mm, the depth of the channels is 0.5 mm, and the spacing between the channels is 0.3 mm.

[0038] Several tertiary leaf vein channels 8 are equally spaced between secondary leaf vein channels 7, with six arranged along the direction of the secondary leaf vein channels 7 and nine groups arranged perpendicular to the direction of the secondary leaf vein channels 7. No tertiary leaf vein channels 8 are placed between the first and second secondary leaf vein channels 7 near the upper edge of the heat sink 10. Rib groups 4 are located at the inner end of the secondary leaf vein channels 7. No rib groups 4 are placed in the first secondary leaf vein channel 7 near the upper edge of the heat sink 10. Except for the rib group 4 in the second secondary leaf vein channel 7 near the upper edge of the heat sink 10, the center line of the remaining rib groups 4 is perpendicular to the secondary leaf vein channels 7. The rib group 4 is shaped like a petal and includes two ribs 9, which are arc-shaped plates. The upper end of one rib 9 is connected to the upper surface of the interior of the secondary leaf vein channel 7, and the lower end of the other rib 9 is connected to the heat plate. The two ribs 9 are interlocked but do not contact each other. Figures 6-7 As shown.

[0039] The edge of the rib 9 is a Fibonacci spiral, the length of the rib 9 is 1 mm, and the thickness is 0.01 mm; the radii of curvature of the constituent lines of the Fibonacci spiral are 0.1 mm and 0.2 mm, respectively; to ensure reasonable processing, the rib 9 of the upper rib 9 is cut at a point 0.02 mm perpendicular to the upper surface of the secondary blade channel 7, so that a right-angle structure is formed at the connection position; the rib 9 of the lower rib 9 is cut at a point 0.02 mm perpendicular to the hot plate, so that a right-angle structure is formed at the connection position, as shown below. Figure 7 As shown.

[0040] The two secondary vein channels 7 near the upper edge of the heat sink 10 have their ends bend at a position 0.3 mm from the upper edge of the heat sink 10, forming a direction perpendicular to the upper edge of the heat sink 10. Figure 5 As shown.

[0041] The secondary leaf vein flow channel 7 inside the heat sink 10 near the lower edge has its root parallel to the lower edge of the heat sink 10.

[0042] The three-stage leaf vein flow channel 8 is an arc-shaped flow channel with a radius of curvature of 0.9 mm. The spacing between the three-stage leaf vein flow channels 8 in the same group is 1 mm, and the channel depth is 0.5 mm.

[0043] The curvature center of the leftmost tertiary vein flow channel 8 in the group of tertiary vein flow channels 8 near the lower edge of the heat sink 10 coincides with the left boundary of the heat sink 10, and the curvature center of the leftmost tertiary vein flow channel 8 is 0.1 mm away from the left end of the rib group 4 near the lower edge.

[0044] The two sets of tertiary vein channels 8 adjacent to the secondary vein channel 7 are symmetrical about the secondary vein channel 7.

[0045] The specific working process of the leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs described in this invention is as follows:

[0046] The cooling medium 3 inside the microchannel heat sink 1 flows in along the fluid inlet 2 perpendicular to the hot plate and enters the primary blade channel 6; the cooling medium 3 flows into the secondary blade channel 7 through the primary blade channel 6, and the secondary blade channel 7 achieves uniform delivery of the cooling medium 3.

[0047] Tertiary vein channels 8 are interspersed at equal intervals between adjacent secondary vein channels 7. The tertiary vein channels 8 are arc-shaped channels, which have a larger heat exchange area and lower flow resistance compared to straight channels. The primary, secondary, and tertiary channels form a vein-like network structure, which enables rapid and uniform delivery of the cooling medium 3 in the heat dissipation area.

[0048] Cooling medium 3 flows through the mesh-like leaf veins to the edge of the microchannel heat sink 1. At this time, the temperature of cooling medium 3 increases, the temperature difference with the heat source decreases, and the heat dissipation capacity decreases. In order to enhance the heat exchange capacity at the edge of the microchannel heat sink, a petal-shaped fin assembly 4 is designed and installed to increase the heat exchange area at the edge, add flow disturbance, and destroy the thermal boundary layer, so as to ultimately enhance the heat exchange capacity, make up for the performance loss caused by the decrease in temperature difference, and ensure the temperature uniformity of the entire heat dissipation area.

[0049] Figure 8 Three examples of microchannels with the same heat transfer area applied to the thermal management system of laser crystals in solid-state lasers are provided: a direct-flow microchannel, a biomimetic lung-like microchannel, and a leaf-vein-shaped composite biomimetic microchannel with petal-shaped ribs. The surface temperature difference of the laser crystal and the convective heat transfer coefficient at the fluid-structure interaction interface are also given. Figure 8As can be seen, under a constant flow rate, the surface temperature difference of the laser crystals in all three microchannel cooling methods increases linearly with increasing thermal power. The DC-cooled microchannel exhibits the largest surface temperature difference and the greatest increase, with its maximum surface temperature difference exceeding that of the other two microchannels at the same power. The biomimetic lung-type and composite biomimetic microchannels show similar increases in temperature difference and exhibit more uniform temperature distribution compared to the DC-cooled microchannel. At a thermal power of 30 W, the maximum surface temperature difference of the DC-cooled microchannel laser crystal is 7.2441 K, while that of the composite biomimetic microchannel is 2.2145 K, representing a 69.43% reduction compared to the DC-cooled type, demonstrating good temperature uniformity. The convective heat transfer coefficients of all three increase with increasing thermal power, but the rate of increase gradually decreases. The convective heat transfer coefficient is mainly affected by the channel structure and fluid velocity; after the power increases to a certain level, the change in the convective heat transfer coefficient gradually stabilizes. Figure 8 The composite biomimetic microchannel shown exhibits the highest convective heat transfer coefficient at the same thermal power, reaching 3615.528 W / (m²) at a thermal power of 30 W. 2 ·K), significantly higher than that of bionic lungs and direct current microchannels.

[0050] In summary, the leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs described in this invention exhibits excellent heat dissipation performance and good temperature uniformity. In the thermal management application of laser crystals in solid-state lasers, compared to a DC-type microchannel with the same heat exchange area, at a laser crystal thermal power of 20 W and a working fluid flow rate of 12 ml / min, the highest crystal surface temperature is 305.7043 K, a decrease of 3.1368 K compared to the DC-type microchannel; the maximum temperature difference on the crystal surface is 1.4819 K, a decrease of 69.38% compared to the DC-type microchannel. At higher power, the heat dissipation capacity is further enhanced compared to the DC-type microchannel. Maintaining a constant flow rate, when the power increases to 30 W, the highest crystal surface temperature is 4.7687 K lower than the DC-type, and the maximum temperature difference on the crystal surface is only 2.2145 K. This demonstrates that this structure still possesses excellent heat dissipation performance under high heat loads. The present invention discloses a leaf vein-shaped composite biomimetic microchannel radiator with petal-shaped fins, exhibiting low flow pressure drop, reduced pumping power consumption, excellent topology, low inlet and outlet pressure drop, low flow resistance, and strong heat exchange capacity. Compared with a direct-flow microchannel with the same heat exchange area, at a flow rate of 12 ml / min, the flow pressure drop of this biomimetic structure is only 33.09 Pa, which is only 51.53% of that of the direct-flow microchannel. When the flow rate increases to 24 ml / min, the pressure drop of this structure is 71.43 Pa, which is 51.87% of that of the direct-flow microchannel. It can be seen that with further increasing the flow rate, the relative pressure drop remains almost unchanged. This structure has the characteristics of low pressure drop, low pumping power consumption, and stable flow. The present invention discloses a leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs, which can meet the unique heat dissipation requirements of high-power micro-devices and can be applied to the field of heat dissipation of high-power micro-devices. It features high heat dissipation efficiency, strong temperature uniformity, stable heat dissipation, and low flow pressure drop. In the thermal management application of laser crystals in solid-state lasers, it can ensure that the surface temperature difference of the laser crystal is maintained within 1-3℃ in the power range of 10-30 W, significantly reducing the problems of thermal lensing effect, thermal stress and crystal breakage caused by thermal effects and uneven temperature distribution during the operation of the laser crystal. This biomimetic microchannel structure has excellent performance.

[0051] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the invention. They can also be reasonable combinations of the features described in the above embodiments. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs, characterized in that: It includes a microchannel heat sink (1) and a primary leaf vein channel (6). The primary leaf vein channel (6) is located at the center of the microchannel heat sink (1). A heat plate is provided at the bottom of the microchannel heat sink (1). The microchannel heat sink (1) includes two heat sinks (10) and two heat sinks (11). The two heat sinks (10) and two heat sinks (11) are arranged in a matrix. The two heat sinks (10) are diagonally opposite each other, and the two heat sinks (11) are diagonally opposite each other. The heat sink (10) is provided with several secondary blade flow channels (7), several tertiary blade flow channels (8) and several rib groups (4). The several secondary blade flow channels (7) are inclined and connected to the primary blade flow channels (6); the several tertiary blade flow channels (8) are equally spaced between the secondary blade flow channels (7); the rib group (4) is located at the end of the secondary blade flow channel (7); the rib group (4) includes two ribs (9), which are arc-shaped plates; the upper end of one rib (9) is connected to the upper surface of the secondary blade flow channel (7), and the lower end of the other rib (9) is connected to the heat plate. The two ribs (9) are interlocked but do not contact each other. Heat sink 2 (11) and heat sink 1 (10) are mirror symmetric.

2. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 1, characterized in that: The edge of the rib (9) is a Fibonacci spiral.

3. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 1, characterized in that: The angle between the secondary leaf vein channel (7) and the primary leaf vein channel (6) is 10 degrees.

4. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 3, characterized in that: The two secondary vein channels (7) near the upper edge of the heat sink (10) in the secondary vein channel (7) have their ends turned to be perpendicular to the upper edge of the heat sink (10).

5. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 4, characterized in that: The first secondary vein flow channel (7) and the second secondary vein flow channel (7) near the upper edge of the heat sink (10) are not connected.

6. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 3, characterized in that: The secondary leaf vein flow channel (7) is located near the lower edge of the heat sink (10), and its root is parallel to the lower edge of the heat sink (10).

7. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 1, characterized in that: The first secondary leaf vein flow channel (7) near the upper edge of the heat sink (10) is not equipped with rib group (4).

8. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 1, characterized in that: The third-level leaf vein flow channel (8) is an arc-shaped flow channel.

9. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 8, characterized in that: The curvature center of the leftmost third-order leaf vein channel (8) in the heat sink (10) coincides with the left boundary of the heat sink (10).

10. The leaf vein-shaped composite biomimetic microchannel heat sink with petal-shaped ribs according to claim 1, 8 or 9, characterized in that: The tertiary vein channels (8) on both sides of the secondary vein channel (7) are symmetrical about the secondary vein channel (7).

Images