Cooling device

Abstract

To provide a cooling device that can improve cooling efficiency over the entire area from the upstream area to the downstream area of a flow path of a heat sink.SOLUTION: A cooling device according to the present invention includes a heat sink having a plurality of fins standing on a base plate with a flow path formed between the fins, and a plasma actuator arranged upstream of the heat sink in the airflow direction. The induced flow generating surface and its back surface of the plasma actuator are located in the middle of the width direction of the flow path, such that the cooling device can be provided that can improve cooling efficiency throughout the entire area of the flow path from the upstream area to the downstream area.SELECTED DRAWING: Figure 1

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 Art

[0002] Power conversion devices such as converters include electronic components that generate heat, such as semiconductors, capacitors, and coils, and heat sinks are attached to cool these electronic components.

[0003] In recent years, miniaturization and high power of power conversion devices have been required. When electronic components are arranged densely for miniaturization, the density of heat-generating elements in the power conversion device increases. In addition, the amount of heat generated by the heat-generating elements increases due to high power. Therefore, it is necessary to improve the performance of the heat sink for cooling these.

[0004] Patent Document 1 describes a cooling device provided with a surface plasma actuator of a heat sink to generate an induced flow on the surface of the heat sink.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the cooling device described in Patent Document 1 generates an induced flow in a direction intersecting the main air flow from the fan, and does not accelerate the main air flow flowing in the length direction of the flow path with the induced flow. Therefore, the main air flow stalls in the downstream region and the cooling efficiency decreases.

[0007] The present invention has been made in view of the problems of such prior art, and an object thereof is to provide a cooling device capable of improving the cooling efficiency throughout the entire region from the upstream side to the downstream side of the flow path formed in the heat sink.

Means for Solving the Problems

[0008] As a result of intensive studies to achieve the above object, the present inventor has found that by arranging a plasma actuator in the middle part in the width direction of the flow path and accelerating the main air flow flowing on both sides of the plasma actuator with the induced flow and flowing it into the flow path, the above object can be achieved, and the present invention has been completed.

[0009] That is, the cooling device of the present invention includes a heat sink in which a plurality of fins are erected on a base plate and a flow path is formed between the fins, and a plasma actuator disposed at an upstream portion in the air flow direction of the heat sink. And the induced flow generation surface and the back surface of the plasma actuator are located in the middle part in the width direction of the flow path.

Effects of the Invention

[0010] According to the present invention, since the induced flow is generated in the middle part in the width direction of the flow path and the main air flow flowing on both sides of the plasma actuator is accelerated, it is possible to provide a cooling device capable of improving the cooling efficiency throughout the entire region from the upper stream region to the lower stream region of the flow path.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying out the Invention

[0012] The cooling device of the present invention will be described in detail. As shown in FIG. 1, the cooling device of the present invention includes a heat sink and a plasma actuator, and has a fan for generating a main air flow as needed.

[0013] In the heat sink 2, a plurality of fins 21 are erected on one main surface of the base plate 22, and a flow path 23 is formed between the fins. Further, a heat generating body (body to be cooled) 5 is in contact with the other main surface of the base plate 22.

[0014] In FIG. 1, the X-axis direction is the length direction of the flow path and the flow direction of the main air flow. The Y-axis direction is the width direction of the flow path, and the Z-axis direction is the height direction of the flow path.

[0015] The plasma actuator 1 is a single-sided type plasma actuator as shown in FIG. 2, and a covered electrode 12 and an exposed electrode 11 separated by a plate-like dielectric 13 are offset in the in-plane direction of the main surface of the dielectric. Then, by applying a voltage between the electrodes, barrier discharge occurs, and an induced flow 15 is generated in the in-plane direction of the main surface of the dielectric 13.

[0016] The plasma actuator is arranged such that the flow direction of the main air flow is located at the upstream portion of the heat sink, and the width direction of the flow path is located at the middle portion in the width direction of the flow path, that is, between adjacent fins where the induced flow generation surface and its back surface are adjacent.

[0017] In the present invention, "being located at the upstream portion of the heat sink" means that at least a part of the plasma actuator covers the upstream end of the heat sink as shown in FIG. 3, and the upstream end or the downstream end of the plasma actuator may be at a position that coincides with the upstream end of the heat sink.

[0018] In particular, as shown in FIG. 3, between the downstream end of the exposed electrode and the upstream end of the covering electrode, that is, since the induced flow generation position is located at the upstream end of the heat sink, the cooling capacity by the induced flow is exhibited from the upstream end of the heat sink.

[0019] Further, except when the upstream end of the plasma actuator coincides with the upstream end of the heat sink, that is, when the plasma actuator is completely inserted into the flow path, as shown in FIG. 4, additional fins flush with the fins can be provided.

[0020] By providing additional fins at positions facing the plasma actuator, leakage of the induced flow outside the flow path is prevented and the cooling performance is improved.

[0021] The thickness of the plasma actuator is formed to be thinner than the width of the flow path so as not to block the opening of the flow path, and the main air flow flowing in the flow path flows into the flow path through both the induced flow generation surface side and the back surface side of the plasma actuator.

[0022] In the cooling device of the present invention, since the induced flow generation surface of the plasma actuator is located at a position separated from the fins, the friction between the induced flow and the fins is reduced and a strong air flow reaches the downstream region.

[0023] Furthermore, compared with the case where the plasma actuator is provided on the fins, the distance between the plasma actuator and the fins becomes narrower and the thickness of the induced flow becomes thinner, so that a strong induced flow is generated even with the same body force.

[0024] In this way, the reduction of the friction and the strong induced flow act together to suppress the decrease in the cooling capacity in the downstream region.

[0025] Also, on the back surface side of the plasma actuator, the main air flow is pulled and accelerated by the induced flow, and this accelerated main air flow flows near the fins to thin the boundary layer on the upstream region back surface side, thus not only improving the cooling capacity in the upstream region but also contributing to the suppression of the decrease in the cooling capacity in the downstream region.

[0026] In addition, when accelerating the main airflow on the back side, the induced airflow generates a velocity difference in the width direction of the flow path due to friction with the main airflow on the back side with a slow velocity, and instead of flowing straight downstream in the flow path, it bends towards the fins on the induced airflow generation surface side. Therefore, this induced airflow can also thin the boundary layer near the fins on the induced airflow generation surface side in the upper flow region.

[0027] Thus, the cooling device of the present invention can thin the boundary layers near the fins on both the induced airflow generation surface side and the back side in the upper flow region. Furthermore, since the momentum of the induced airflow is strong enough to reach the lower flow region and thin the boundary layer, the cooling capacity can be improved throughout the entire region from the upper flow region to the lower flow region.

[0028] The thickness of the plasma actuator described above depends on the shape of the heat sink such as the length of the flow path, but is preferably 25% or less of the flow path width.

[0029] If the thickness of the plasma actuator is 25% or less of the flow path width, the pressure loss of the main airflow can be suppressed to a few percent, and the improvement in the cooling capacity due to the induced airflow exceeds the pressure loss of the main airflow, resulting in an improvement in the cooling capacity.

[0030] The thickness of the induced airflow described above can be adjusted according to the position of the induced airflow generation surface in the width direction of the flow path. The distance between the induced airflow generation surface of the plasma actuator and the fin or additional fin facing it is preferably 1 / 2 or more of the flow path width. Also, the distance between the back surface of the plasma actuator and the fin or additional fin facing it only needs to be able to introduce the main airflow into the flow path from the back side, and there is no particular limitation, but the substantial lower limit is 0.5 mm.

[0031] The plasma actuator described above is preferably driven in bursts. Burst driving is a driving method that periodically switches the on and off of the alternating voltage applied between the electrodes.

[0032] By periodically turning on and off the voltage applied between the electrodes, an induced flow is generated when it is on and stops when it is off. Therefore, a pressure difference occurs in the flow direction of the induced flow, and a flow in the direction opposite to the induced flow occurs, generating vortices.

[0033] Due to the generation of these vortices, the main airflow oscillates in the Y-axis direction while hitting the fins on both sides forming the flow path, and the boundary layers on both sides of the flow path generated near the fins are thinned, improving the cooling performance.

[0034] Also, when the voltage applied between the electrodes is off, no power is consumed, so power consumption can be reduced.

[0035] As the above heat sink, those formed of a metal material such as aluminum or its alloy with high thermal conductivity can be used. In addition, when the fins erected on the base plate are straight fins and flat plates, the induced flow flows along the fins, so the pressure loss is reduced, and the boundary layer away from the plasma actuator can also be thinned, improving the cooling performance.

[0036] As the above additional fins, in addition to the above metal materials, they can be formed of an insulating material such as ceramics. In particular, when formed of an insulating material, even if the electrodes of the plasma actuator and the additional fins are close to each other, no discharge occurs between the electrodes of the plasma actuator and the additional fins, so the width of the flow path can be narrowed, and a strong induced flow can be generated.

[0037] As the above fan, an axial flow fan or a blower fan (centrifugal fan) can be used.

[0038] The above fan may be provided on the upstream side of the heat sink in the flow direction of the main airflow, or may be provided on the downstream side, and can be selected according to the installation location of the cooling device.

[0039] When the fan is provided on the upstream side of the heat sink, the main airflow is pushed into the flow path, so the pressure in the flow path increases, and it becomes difficult for dust and dirt to enter the flow path.

[0040] Also, when the fan is provided on the downstream side of the heat sink, the main air flow is generated by drawing the surrounding air into the flow path. Therefore, compared with the case where the fan is on the upstream side, the flow of the main air flow is less likely to be disturbed, and the main air flow can be rectified from the vicinity of the entrance of the flow path.

[0041] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0042] [Example 1] An additional fin with a length of 10 mm was provided flush with the fins of a heat sink having a flow path with a length of 65 mm and a width of 5 mm at the upstream end of the fins. A plasma actuator with a thickness of 1 mm and a length of 10 mm was placed between adjacent additional fins such that its downstream end was located at the upstream end of the fins, and a cooling device was fabricated with the flow path width on the back side of the plasma actuator being 1 mm and the flow path width on the induced flow generation surface side being 3 mm.

[0043] [Comparative Example 1] A cooling device was fabricated in the same manner as in Example 1, except that a plasma actuator was provided flush with the fins instead of the additional fins.

[0044] [Comparative Example 2] A cooling device was fabricated in the same manner as in Comparative Example 1, except that a plasma actuator with a thickness changed so that the flow path width on the induced flow generation surface side was 3 mm was provided and the flow path on the back side was blocked.

[0045] While flowing the main air flow through the above cooling device, the plasma actuator was driven in burst mode at 100 Hz Duty 50% and 18.5 mN / m, and the average Nusselt number of the flow path wall surface was measured.

[0046] The measurement results are shown in Table 1, and the wind speed distribution is shown in FIG. 5. Note that the Nusselt number is the ratio of the heat conduction to the heat transfer of the convective fluid, and the larger the Nusselt number, the higher the heat transport effect by convection.

[0047]

Table 1

[0048] In Comparative Example 1, the induced flow was bent due to the friction with the fins, and the boundary layer on the surface facing the plasma actuator could be thinned, but the flow velocity of the air flow decreased in the downstream region.

[0049] In Comparative Example 2, the friction with the fins was reduced, and the decrease in the flow velocity in the downstream region could be suppressed, but in the upstream region, the boundary layer could not be thinned.

[0050] In Example 1, the boundary layer could be thinned from the upstream region, and the decrease in the flow velocity of the air flow in the downstream region could also be suppressed, and the cooling efficiency could be improved throughout the entire region from the upstream region to the downstream region.

Explanation of Reference Numerals

[0051] 1 Plasma actuator 11 Exposed electrode 12 Coated electrode 13 Dielectric 14 AC power supply 15 Induced flow 2 Heat sink 21 Fins 22 Base plate 23 Flow path 3 Additional fins 4 Fan 41 Main air flow 5 Heating element

Claims

1. A heat sink having a plurality of fins standing upright on a base plate and forming a flow path between the fins, and a plasma actuator disposed upstream in the air flow direction of the heat sink, the cooling device comprising: The cooling device is characterized in that the induced flow generation surface and the back surface of the plasma actuator are located at the middle part in the width direction of the flow path.

2. The cooling device according to claim 1, wherein the plasma actuator is characterized in that the induced flow generation position thereof is located at the upstream end in the air flow direction of the fin.

3. The cooling device according to claim 2, characterized in that it has an additional fin flush with the fin at a position facing the plasma actuator.

4. The cooling device according to claim 1, wherein the plasma actuator is characterized by burst driving.

5. The cooling device according to claim 1, further comprising a fan for flowing the main air flow into the flow path.

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