Cooling device

Abstract

A cooling device according to the present invention comprises: a heatsink in which a plurality of fins are installed upright on a base plate and a flow path is formed between the fins; a fan that causes a main air stream to flow into the flow path; and a plasma actuator that discharges electricity between electrodes separated by a plate-shaped dielectric body and generates an induced flow. The plasma actuator is such that the main face of the dielectric body and the main faces of the fins are disposed upstream of the heatsink in the flow direction of the main air stream so as to be parallel to each other, and the flow direction of the induced flow is set to be the same as the flow direction of the main air stream; and therefore it is possible to provide a cooling device which is inexpensive due to machining of a heatsink not being necessary, and which can improve cooling efficiency by the thinning a boundary layer near the fins.

Description

[Technical Field]

[0001] The present invention relates to a cooling device, and more particularly to a cooling device including a heat sink and a plasma actuator. [Background technology]

[0002] 2. Description of the Related Art A power conversion device such as a converter includes electronic components that generate heat, such as semiconductors, capacitors, and coils, and a heat sink is attached to cool these electronic components.

[0003] In recent years, there has been a demand for smaller power conversion devices with higher power output. When electronic components are densely packed together to reduce size, the density of heat-generating elements within the power conversion device increases. In addition, the amount of heat generated by the heat-generating elements increases as the power increases, so the performance of the heat sinks that cool these elements also needs to be improved.

[0004] The cooling performance of a heat sink generally depends on its volume (heat capacity), material (thermal conductivity), and surface area (heat transfer area) depending on its shape. Therefore, if the heat sink itself is enlarged to improve its cooling performance, the entire power conversion device will become larger, making it difficult to miniaturize the power conversion device.

[0005] Patent Document 1 discloses a cooling device in which electrodes are provided on the fins of a heat sink to serve as plasma actuators, and an induced flow is generated between the fins. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2014-183175 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the cooling device described in Patent Document 1, the fins are given the function of a plasma actuator, which means that the heat sink itself must be processed, making it less versatile. In addition, part of the fins must be covered with an insulator, which reduces the heat dissipation area.

[0008] The present invention was made in consideration of the problems associated with the prior art, and its purpose is to provide a versatile, inexpensive cooling device that does not require processing of the heat sink itself. [Means for solving the problem]

[0009] As a result of extensive research into achieving the above-mentioned objective, the inventors have completed the present invention by positioning the plasma actuator upstream of the heat sink so that the main surface of the dielectric and the main surface of the fin are parallel, thereby generating an induced flow in the direction of the main airflow.

[0010] That is, the cooling device of the present invention comprises a heat sink having a plurality of fins standing on a base plate with flow paths formed between the fins, a fan that directs a main airflow through the flow path, and a plasma actuator that discharges electricity between electrodes separated by a plate-shaped dielectric to generate an induced flow. The plasma actuator is arranged upstream of the heat sink in the flow direction of the main airflow, with the main surface of the dielectric and the main surface of the fin parallel, and the flow direction of the induced flow is the same as the flow direction of the main airflow. [Effects of the Invention]

[0011] According to the present invention, the plasma actuator is provided upstream of the heat sink so that the main surface of its dielectric is parallel to the main surface of the heat sink fins. This makes it possible to provide a cooling device that does not require processing of the heat sink, is inexpensive, and can improve cooling efficiency by thinning the boundary layer near the fins. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view showing a main part of an example of a plasma actuator. [Figure 2] 1 is a perspective view showing an example of a cooling device of the present invention. [Figure 3] FIG. 1 is an XY plan view of a cooling device with a gap between the plasma actuator and the fins of the heat sink. [Figure 4] FIG. 10 is a diagram showing the distance between the exposed electrode and the covered electrode. [Figure 5] FIG. 10 is a diagram showing the distance between the exposed electrode and the covered electrode in terms of only the component in the flow path direction, which can be used as a substitute for the distance between the exposed electrode and the covered electrode. [Figure 6] FIG. 1 is a cross-sectional view of a main part of a plasma actuator that generates an induced flow on both sides of a dielectric body. [Figure 7] FIG. 1 is an XY plan view of a cooling device in which plasma actuators and additional fins are provided alternately. [Figure 8] 4A and 4B are diagrams illustrating the intake and discharge directions of air from a blower fan. [Figure 9] This is an XY plan view of a cooling device in which a plasma actuator is arranged in accordance with the rotating blades of a blower fan. [Figure 10] FIG. 10 is a diagram showing a state in which the flow of an induced flow is changed by a gap. [Figure 11] FIG. 10 is a diagram showing a state in which the induced flow flows linearly without being changed by the gap. DETAILED DESCRIPTION OF THE INVENTION

[0013] The cooling device of the present invention will now be described in detail. The cooling device of the present invention includes a heat sink, a fan, and a plasma actuator.

[0014] The heat sink has a plurality of fins standing on one main surface of a base plate, with flow paths formed between the fins. The fan directs a main airflow through the flow paths to promote heat dissipation from the heat sink.

[0015] In addition, the plasma actuator has electrodes separated by a plate-like dielectric and arranged offset in the in-plane direction of the main surface of the dielectric, as shown in Figure 1. A barrier discharge occurs when a voltage is applied between the electrodes, generating an induced flow in the in-plane direction of the main surface of the dielectric.

[0016] As shown in Figure 2, the plasma actuator is positioned upstream of the heat sink in the direction of the main airflow, with the main surface of its dielectric parallel to the main surfaces of the fins of the plasma actuator, and generates the induced flow in the same direction as the direction of the main airflow, thereby thinning the boundary layer created by friction between the main airflow and the fins and improving cooling efficiency.

[0017] 2, the X-axis direction (lengthwise direction of the heat sink) is the flow direction of the main airflow, the Y-axis direction is the width direction of the heat sink, and the Z-axis direction is the height direction of the heat sink. A heat-generating body (body to be cooled) is in contact with the other main surface of the base plate.

[0018] The cooling device of the present invention is not a cooling device in which the heat sink and plasma actuator are integrated, but rather the heat sink and plasma actuator are separate components, so there is no need to process the heat sink and commercially available products can be used, making it highly versatile and inexpensive.

[0019] Furthermore, since the plasma actuator is not installed on the fins of the heat sink, the flow path width (Y-axis direction) of the heat sink is not narrowed by the plasma actuator, which suppresses pressure loss of the main airflow.In addition, there is no need to thin the dielectric to ensure the flow path width, and the dielectric's withstand voltage can be ensured.

[0020] Furthermore, in the cooling device of the present invention, the plasma actuator is arranged so that the main surface of its dielectric is parallel to the main surface of the fin, and by matching the height of the plasma actuator to the height of the fin, an induced flow can be generated across the entire height direction (Z-axis direction) of the fin.

[0021] Therefore, the boundary layer can be made thin over the entire height direction (Z-axis direction) of the flow passage formed between the fins of the heat sink, thereby improving the cooling efficiency.

[0022] Such a plasma actuator can be arranged upright on a support member provided parallel to the main surface of the base plate of the heat sink.

[0023] In the plasma actuator, it is preferable that the thickness of the dielectric is the same as the thickness of the fins of the heat sink, and that the main surface of the dielectric and the main surface of the fins are arranged on the same plane.

[0024] This eliminates any step between the dielectric and the fin, reducing the pressure loss of the induced flow near the main surface of the fin, making it possible to make the boundary layer thinner further, improving cooling performance. Note that the "same thickness" does not exclude manufacturing errors.

[0025] The cooling device preferably has a gap between the plasma actuator and the fins of the heat sink, as shown in FIG.

[0026] In order to thin the boundary layer by the induced flow, it is advantageous to place the plasma actuator close to the heat sink and to cause a strong induced flow near the main surface of the fin.

[0027] However, heat sinks are often made of metals such as aluminum, which have high thermal conductivity, and if the plasma actuator and the heat sink are close to each other, undesired discharges may occur between the electrode of the plasma actuator and the heat sink.

[0028] If there is a gap between the plasma actuator and the heat sink, air, which has a smaller dielectric constant than the dielectric, will be present in the gap, preventing undesired discharge in the direction of the heat sink.

[0029] In addition, the gap disrupts the heat transfer path from the heat sink to the plasma actuator, making it difficult for heat from the heat sink to be transferred to the plasma actuator, preventing the temperature of the plasma actuator from rising and improving the durability and reliability of the plasma actuator.

[0030] The distance d between the plasma actuator and the heat sink is preferably three times or less the thickness t of the fins.

[0031] If a gap is provided between the plasma actuator and the heat sink, the induced flow flowing on the dielectric surface will cause the gap to have a negative pressure relative to the dielectric surface, and the induced flow will be pulled inward in the thickness direction of the fin in the gap, causing the flow to become turbulent.The induced flow will then collide with the edge of the fin and will flow out toward the center of the flow path, making it impossible to thin the boundary layer and reducing cooling efficiency.

[0032] By making the distance d between the plasma actuator and the heat sink no more than three times the thickness t of the fin, the turbulence of the induced flow caused by the gap is suppressed, and the induced flow flows in a straight line, just as if there were no gap, thereby preventing a decrease in cooling efficiency. In the present invention, the phrase "the induced flow flows linearly" refers to a state in which the induced flow does not hit the end of the fin and generate a vortex.

[0033] Furthermore, it is preferable that the distance d between the plasma actuator and the heat sink is 0.75 times or less the width w of the flow path formed between the fins. This makes it possible to further suppress turbulence of the induced flow.

[0034] In the plasma actuator, the electrodes separated by a plate-like dielectric are a combination of an exposed electrode whose surface is exposed and a covered electrode whose entire surface is covered by a dielectric, and it is preferable that the potential of the exposed electrode is ground potential and the potential of the covered electrode is high potential.

[0035] These electrodes are arranged such that the exposed electrode is on the upstream side and the covered electrode is on the downstream side in the direction of the main airflow, that is, the covered electrode is offset closer to the heat sink than the exposed electrode.

[0036] Since the exposed electrode has a low potential and the high-potential electrode is a covered electrode, discharge from the high-potential electrode to the heat sink is prevented, and the plasma actuator and the heat sink can be placed close to each other, improving cooling efficiency and enabling the cooling device to be made smaller.

[0037] The exposed electrode may have a portion exposed on the surface of the dielectric, or may be partially buried in the dielectric so that the surface of the dielectric and the surface of the exposed electrode are flush with each other.

[0038] The exposed electrode and the covered electrode are preferably arranged so that the distance between them is smaller than the distance between the covered electrode and the fin.

[0039] This arrangement can suppress discharge between the fin and the covered electrode, which is a high-potential electrode. Even if an undesired discharge occurs between the covered electrode and the fin, the discharge between the exposed electrode and the covered electrode is strong, and the desired induced flow is strong, so that the overall induced flow is directed toward the heat sink.

[0040] In the present invention, the "distance between the exposed electrode and the covered electrode" refers to the distance between the exposed electrode and the covered electrode at their closest points, as shown in FIG. 4, but may also be substituted by the distance component in the flow path direction only, as shown in FIG. 5.

[0041] Furthermore, the plasma actuator can have two of the above-mentioned exposed electrodes, and these exposed electrodes can be arranged at opposing positions with a dielectric interposed therebetween, as shown in FIG.

[0042] Because the plasma actuator has two exposed electrodes of the same potential, a barrier discharge occurs on both main surfaces of the plasma actuator, and an induced flow occurs on both main surfaces of the plasma actuator, so that a single plasma actuator can generate an induced flow in two adjacent flow paths.

[0043] Therefore, since it is sufficient to arrange the plasma actuators on every other fin, the number of plasma actuators can be reduced, leading to cost reduction.

[0044] In this case, it is preferable to alternately provide the plasma actuators and additional fins. As shown in Fig. 7, the additional fins are in contact with the fins of the heat sink, have a plate-like shape that extends from the fins of the heat sink to the upstream side in the direction of the main airflow, and are positioned opposite the exposed electrodes of the plasma actuators across the flow path.

[0045] In the above-mentioned plasma actuator, the high-potential electrode is covered with a dielectric and the exposed electrode is at ground potential, so even if an additional metal fin is provided in a position opposite the exposed electrode, no discharge will occur toward this additional fin.

[0046] Furthermore, since the additional fins are in contact with the fins of the heat sink, they can dissipate the heat transferred from the heat sink, increasing the surface area of ​​the fins per unit volume of the cooling device and improving the cooling efficiency.

[0047] The plasma actuator is preferably burst driven, which is a driving method in which an AC voltage applied between the electrodes is periodically switched on and off.

[0048] By periodically turning the voltage applied between the electrodes on and off, an induced flow occurs when the voltage is on and stops when the voltage is off, which creates a pressure difference in the direction of the induced flow, causing a flow in the opposite direction to the induced flow and generating a vortex.

[0049] The generation of this vortex causes the main airflow to oscillate in the Y-axis direction as it hits the fins on both sides that form the flow path, thinning the boundary layers on both sides of the flow path that form near the fins, thereby improving cooling performance.

[0050] Furthermore, when the voltage applied between the electrodes is off, no power is consumed, which contributes to power saving.

[0051] In the heat sink, it is preferable that the fins erected on the base plate are straight fins. If the fins are flat, the induced flow flows along the fins, reducing pressure loss and thinning the boundary layer away from the plasma actuator, thereby improving cooling performance.

[0052] The heat sink preferably has a cover on the top of the fin opposite the base plate, which prevents leakage of the main airflow through the flow path and ensures that the main airflow through the flow path reaches the outlet of the flow path, improving cooling performance.

[0053] Furthermore, by extending the lid to the upstream end of the plasma actuator in the direction of the main airflow, and by providing a support member on which the plasma actuator is erected so that it is flush with the base plate of the heat sink on the opposite side of the lid, it is possible to prevent leakage of the main airflow from the location where the plasma actuator is installed.

[0054] The cooling device can have multiple combinations of plasma actuators and heat sinks in the flow path direction. As the flow path becomes longer, a boundary layer is more likely to develop downstream, but by providing a plasma actuator midway through the flow path, the boundary layer that develops downstream can be made thinner, thereby improving cooling efficiency even if the flow path is long.

[0055] The fan may be provided on the upstream side or downstream side of the heat sink in the direction of the main airflow, and this can be selected depending on the location where the cooling device is to be installed.

[0056] When the fan is provided upstream of the heat sink, the main airflow is forced into the flow path, increasing the pressure within the flow path and making it difficult for dust and dirt to enter the flow path.

[0057] Furthermore, when the fan is installed downstream of the heat sink, the main airflow is generated by drawing in the surrounding air into the flow path, which makes it less likely to disrupt the main airflow than when the fan is located upstream, and the main airflow can be rectified from near the entrance of the flow path.

[0058] The fan may be an axial fan, but is preferably a blower fan (centrifugal fan).

[0059] In an axial flow fan, the direction of the fan's rotation axis and the discharge direction are the same, and the shape of the main airflow discharged is approximately cylindrical, which differs from the shape of the flow path inlet surface of the heat sink. Therefore, it is necessary to straighten the airflow using a nozzle or the like and make the shape of the main airflow rectangular to match the shape of the flow path inlet surface.

[0060] In contrast, a blower fan differs from an axial fan in that the direction of the fan's rotation axis, i.e., the air intake and discharge directions, are perpendicular to each other, as shown in Figure 8. Therefore, by aligning the height of the blower fan with the height of the heat sink, it is possible to align the shape of the main airflow discharged with the shape of the flow path inlet face without using a nozzle, and it is also possible to reduce the height of the cooling device and make it more compact.

[0061] When a blower fan is used as the fan, it is preferable to arrange multiple plasma actuators so that their tips on the upstream side of the main airflow follow the arc described by the rotating blades of the blower fan, as shown in Figure 9. This allows the main airflow generated by the blower fan to flow through the flow path between the fins without diffusing to the surrounding area.

[0062] In addition, an additional fin can be provided between the plasma actuator, which is arranged along the arc of the rotating blades of the blower fan, and the fin of the heat sink, so as to abut against the fin and extend from this fin upstream of the main airflow.

[0063] If the plasma actuators are arranged along the arc described by the rotating blades of the blower fan, the plasma actuators at both ends of the width of the heat sink will be farther away from the heat sink, making it difficult to thin the boundary layer.

[0064] By providing additional fins that abut against the fins between the plasma actuator and the fins, the heat from the heat sink is transferred to the additional fins, thereby maintaining the effect of thinning the boundary layer provided by the plasma actuator and, combined with the increased heat dissipation area provided by the additional fins, improving cooling efficiency. [Example]

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0066] [Example 1] The thickness of the fins and plasma actuators was changed in the range of 0.5mm to 3.0mm to form a flow path with a width (Y-axis direction) of 5mm, and the volume force was 3700N / m 3 An induced flow was generated from the plasma actuator, and the flow pattern of the induced flow was investigated by changing the gap between the plasma actuator and the fin and the thickness of the fin.

[0067] Figure 10 shows the case where the fin thickness is 1 mm and the gap is 4 mm, and Figure 11 shows the case where the fin thickness is 1 mm and the gap is 3 m. In Figure 10, the induced flow changes direction and flows outward toward the center of the channel, while in Figure 11, the induced flow flows in a straight line.

[0068] As in the case of no gap in Table 1, cases where the induced flow flows in a straight line are indicated by a circle, and cases where the induced flow hits the edge of the fin and becomes turbulent are indicated by an x.

[0069] [Table 1]

[0070] As shown in Table 1, when the distance between the heat sink fins is 3.0 mm, the fin thickness is 1.0 mm, and the distance between the plasma actuator and the heat sink fins is three times the fin thickness, the induced flow remains unchanged and flows in a straight line.

[0071] In addition, when the distance between the heat sink and the fins was 4.0 mm and the fin thickness was 1.0 mm, and when the distance between the heat sink and the fins was 2.0 mm and the fin thickness was 0.5 mm, the flow of the induced flow changed and became a flow away from the fins.

[0072] These results show that if the distance between the plasma actuator and the fins of the heat sink is three times the thickness of the fins or less, the induced flow will flow linearly, making it possible to thin the boundary layer near the fin surface, thereby preventing undesired discharges and improving cooling efficiency.

[0073] [Example 2] Using fins with a thickness of 1 mm and plasma actuators, the flow path width (in the Y-axis direction) was changed in the range of 2 mm to 5 mm to form a flow path, and the volume force was 3700 N / m 3 The induced flow was generated from the plasma actuator, and the flow pattern of the induced flow was investigated by changing the gap between the plasma actuator and the fin and the flow path width (Y-axis direction). The results are shown in Table 2. Furthermore, the plasma actuator was not effective when the flow path width was 1 mm or less.

[0074] [Table 2]

[0075] As shown in Table 2, when the distance between the heat sink fins is 3.0 mm, the flow path width is 4 mm, and the distance between the plasma actuator and the heat sink fins is 0.75 times the flow path width, the induced flow remains unchanged and flows in a straight line.

[0076] Furthermore, when the distance between the heat sink and the fins was 4.0 mm and the flow path width was 5 mm, the induced flow changed and became a flow away from the fins.

[0077] These results show that if the distance between the plasma actuator and the fins of the heat sink is 0.75 times the flow path width or less, the induced flow will flow linearly, making it possible to thin the boundary layer near the fin surface, thereby preventing undesired discharges and improving cooling efficiency. [Explanation of symbols]

[0078] 1. Plasma Actuator 11 Exposed electrode 12 Coated electrode 13 Dielectrics 14 AC power supply 15 Induced flow 2 heat sinks 21 Finn 22 Base plate 23 Lid 3 Fans 31 Main airflow 32 Rotor 33 Air intake direction 34 Air discharge direction 4 additional fins 5 Heating element

Claims

1. a heat sink having a plurality of fins standing on a base plate and channels formed between the fins; a fan for causing a main airflow to flow within the flow path; A cooling device comprising: a plasma actuator that generates an induced flow by discharging between electrodes separated by a plate-shaped dielectric; the plasma actuator is disposed upstream of the heat sink in the direction of the main airflow, with a main surface of the dielectric body and a main surface of the fin being parallel to each other; A cooling device characterized in that the flow direction of the induced flow is the same as the flow direction of the main air flow.

2. the thickness of the dielectric and the thickness of the fin are the same; 2. The cooling device according to claim 1, wherein a main surface of the dielectric body and a main surface of the fin are on the same plane.

3. The cooling device according to claim 2, wherein a gap is provided between the plasma actuator and the fins of the heat sink.

4. 4. The cooling device according to claim 3, wherein the distance between the plasma actuator and the fin of the heat sink is three times or less the thickness of the fin.

5. 5. The cooling device according to claim 4, wherein the distance between the plasma actuator and the fins of the heat sink is 0.75 times or less the width of the flow path formed between the fins.

6. the electrodes of the plasma actuator are a combination of an exposed electrode having at least a surface exposed and a covered electrode covered with the dielectric; 2. The cooling device according to claim 1, wherein the exposed electrode has a ground potential and the covered electrode has a high potential.

7. 7. The cooling device according to claim 6, wherein the exposed electrode and the covered electrode are disposed at a distance smaller than the distance between the covered electrode and the fins.

8. the plasma actuator has two exposed electrodes; 2. The cooling device according to claim 1, wherein the two exposed electrodes are disposed at positions facing each other with the dielectric interposed therebetween.

9. additional fins abutting the fins of the heat sink and extending from the fins of the heat sink; The cooling device according to claim 1, wherein the additional fins and the plasma actuators are arranged alternately.

10. 2. The cooling device according to claim 1, wherein the fan is disposed upstream of the plasma actuator in the flow path direction.

11. 11. The cooling device according to claim 10, wherein the fan is a blower fan.

12. 12. The cooling device according to claim 11, wherein the plurality of plasma actuators are arranged such that their tips on the upstream side of the main airflow are aligned along an arc described by the rotating blades of the blower fan.

13. 12. The cooling device according to claim 11, further comprising additional fins at least at both widthwise ends of the heat sink between the plasma actuator and the fins, the additional fins abutting the fins and extending from the fins upstream of the main airflow.

14. 2. The cooling device according to claim 1, wherein the fan is disposed downstream of the plasma actuator in the flow path direction.

15. 2. The cooling device according to claim 1, wherein the fins of the heat sink are straight fins.

16. 2. The cooling device according to claim 1, wherein a plurality of combinations of the plasma actuator and the heat sink are provided in the flow path direction.

17. The cooling device according to claim 1 , wherein the heat sink is covered with a lid on the opposite side of the base plate with the fins interposed therebetween.

18. 2. The cooling device according to claim 1, wherein the plasma actuator is burst-driven.

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