Cooling device

Abstract

To provide a cooling device which can significantly obtain an improved effect in cooling efficiency enabled by adding a plasma actuator.SOLUTION: A cooling device comprises: a heat sink which has a base plate with a plurality of fins erected thereon, and which is provided with a flow path formed between the fins; a fan for flowing a main air current in the flow path; a plasma actuator which discharges electricity between electrodes separated by a dielectric so as to generate an induction flow in a flow direction of the main air current; and an additional fin. The additional fin and the plasma actuator are disposed upstream the heat sink in the flow direction of the main air current in the flow path. The additional fin and the plasma actuator face each other so as to form an extension flow path. A generation surface of the induction flow is flush with main surfaces of the fins. The additional fin is thicker than the fins. The extension flow path is narrower than the flow path. With such a configuration, it becomes possible to provide the cooling device which has a significantly great improvement effect in cooling efficiency enabled by adding a plasma actuator.SELECTED DRAWING: Figure 2

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.

[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, there has been a demand for miniaturization and high power of power conversion devices. When electronic components are arranged densely to reduce the size, 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, so it is necessary to improve the performance of the heat sink for cooling them.

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

[0005] Patent Document 1 discloses a cooling device in which an electrode is provided on a fin of a heat sink to serve as a plasma actuator, and an induced flow is generated between the fins.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the cooling device described in Patent Document 1, the fins of the heat sink are provided with the function of the plasma actuator, and the heat sink itself has to be processed, resulting in low versatility. In addition, since a part of the fins is covered with an insulator to reduce the heat dissipation area, a significant improvement in the cooling efficiency by providing the plasma actuator cannot be expected.

[0008] 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 in which the effect of improving the cooling efficiency by adding a plasma actuator can be remarkably obtained.

Means for Solving the Problems

[0009] As a result of intensive studies to achieve the above object, the present inventor has found that by disposing a plasma actuator separate from the heat sink on the end side of the heat sink, narrowing the flow path width to increase the flow velocity of the main air flow from the fan, and generating an induced flow here, the above object can be achieved, and the present invention has been completed.

[0010] That is, the cooling device of the present invention includes a heat sink having a plurality of fins erected on a base plate and forming a flow path between the fins, a fan that allows a main air flow to flow in the flow path, and discharges between electrodes separated by a dielectric to generate an induced flow in the flow direction of the main air flow. A plasma actuator, and additional fins, wherein the additional fins and the plasma actuator are arranged upstream of the heat sink in the flow direction of the main air flow in the flow path, and these face each other to form an extended flow path. And the generation surface of the induced flow is flush with the main surface of the fin, the thickness of the additional fin is thicker than that of the fin, and the width of the extended flow path is narrower than the width of the flow path.

Effects of the Invention

[0011] According to the present invention, since an induced flow is generated at a location where the main airflow is accelerated, it is possible to provide a cooling device having an extremely large effect of improving the cooling efficiency by adding a plasma actuator.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

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

[0014] 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 (cooled body) 5 is in contact with the other main surface of the base plate 22. The fan promotes heat dissipation from the heat sink by flowing a main airflow through the flow path of the heat sink.

[0015] In FIG. 1, the X-axis direction is the length direction of the flow path and the flow direction of the main airflow. 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.

[0016] As shown in FIG. 2, in the plasma actuator 1, a covered electrode 12 and an exposed electrode 11 separated by a dielectric 13 are arranged 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.

[0017] The induced flow 15 of the plasma actuator accelerates the main airflow 41 and thins the boundary layer generated by the friction between the main airflow and the fins 21, thereby improving the cooling efficiency.

[0018] Such a plasma actuator can generate a strong induced flow by increasing the voltage applied between its electrodes.

[0019] However, the voltage cannot be increased beyond the voltage withstand of the plasma actuator itself. In addition, the heat sink is often formed of a metal material to enhance thermal conductivity, and when the applied voltage is increased, undesired discharge occurs between the heat sink and the plasma actuator, so there is a limit to generating a strong induced flow.

[0020] In the cooling device of the present invention, the plasma actuator 1 and the additional fins 3 are arranged opposite to the upstream side of the heat sink in the flow direction of the main airflow so as to be parallel to the main surfaces of the fins as shown in FIG. 2, and form an extended flow path 31 continuous with the flow path 23 of the heat sink.

[0021] And, since the thickness of the additional fins is thicker than that of the fins and the width of the extended flow path 31 where the induced flow is generated is narrower than the width of the flow path 23 of the heat sink, the flow velocity of the main airflow 41 in the extended flow path becomes faster, and since the induced flow 15 is generated here, a strong induced flow can be generated.

[0022] Furthermore, since the main surface of the dielectric 13 of the plasma actuator, that is, the surface for generating the induced flow (hereinafter sometimes referred to as the "induced flow generation surface") is provided flush with the main surface of the fin 21, the induced flow flows along the main surface of the fin and thins the boundary layer near the main surface of the fin 21, so that the effect of improving the cooling efficiency by the plasma actuator can be maximally obtained.

[0023] Further, as shown in FIG. 1, when the height (in the Z-axis direction) of the plasma actuator and the additional fins is the same as the height of the fins respectively, the boundary layer can be thinned up to the downstream side over the entire height direction (Z-axis direction) of the flow path, so that the cooling efficiency is further improved.

[0024] The width of the extension flow path 31 is preferably 1 / 2 or more of the width of the flow path 23. When the width of the extension flow path is 1 / 2 or more of the width of the flow path, the flow velocity of the main air flow 15 flowing in the extension flow path 31 can be increased without significantly increasing the pressure loss of the main air flow from the fan. In the present invention, the "width of the extension flow path" refers to the width of the portion where the thickness of the additional fins is the thickest.

[0025] The additional fins are formed of an insulating material. Thereby, even when the electrode of the plasma actuator and the additional fins are close to each other, discharge does not occur between the electrode of the plasma actuator and the additional fins, so that the width of the extension flow path can be narrowed.

[0026] The thickness of the additional fins is preferably thin on either the upstream side or the downstream side in the flow direction of the main air flow, or on both the upstream side and the downstream side. Since the thickness of the additional fins varies in the flow direction of the main air flow, the width of the extension flow path becomes wider in part, so that an increase in pressure loss can be reduced. In particular, when the upstream side of the additional fins is thin, the main air flow can easily enter the extension flow path.

[0027] The plasma actuator may be a single-sided plasma actuator having a coated electrode 12 on one main surface of a dielectric and an exposed electrode 11 on the other main surface as shown in FIG. 3. However, as shown in FIG. 2, it is preferably a double-sided plasma actuator having two exposed electrodes 11 sandwiching a dielectric and capable of generating an induced flow on both sides of the main surface of the dielectric 13.

[0028] Since the above-described double-sided plasma actuator can cause an induced flow to flow toward two adjacent flow paths with a single plasma actuator, by arranging the actuators every other fin, the induced flow can be caused to flow through all the flow paths of the heat sink, improving the cooling efficiency.

[0029] The above plasma actuator is preferably driven in bursts. Burst driving is a driving method in which the application and interruption of an alternating voltage applied between electrodes are periodically switched.

[0030] 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 is generated in the flow direction of the induced flow, and a flow in the direction opposite to the induced flow is generated, generating a vortex.

[0031] Due to the generation of this vortex, the main airflow oscillates in the Y-axis direction while hitting the fins on both sides forming the flow path, thinning the boundary layers on both sides of the flow path generated near the fins, and improving the cooling performance.

[0032] In addition, since no power is consumed when the voltage applied between the electrodes is off, power consumption can be reduced.

[0033] 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, since the fins standing on the base plate are straight fins and are flat, the induced flow flows along the fins, reducing the pressure loss and thinning the boundary layer away from the plasma actuator, and improving the cooling performance.

[0034] As the above fan, an axial flow fan or a blower fan (centrifugal fan) can be used.

[0035] 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.

[0036] When the fan is provided on the upstream side of the heat sink, the main airflow is pushed into the flow path, increasing the pressure inside the flow path and making it difficult for dust and dirt to enter the flow path.

[0037] Also, when the fan is provided on the downstream side of the heat sink, a main airflow is generated by drawing in the surrounding air into the flow path. Therefore, compared to the case where the fan is on the upstream side, the flow of the main airflow is less likely to be disturbed, and the main airflow can be rectified from near the entrance of the flow path.

Example

[0038] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0039] [Experimental Example] A cooling device with a total length of 75 mm, having an additional fin of different thicknesses and a plasma actuator arranged opposite to each other on a heat sink having a flow path with a length of 65 mm and a width of 5 mm, and an extension flow path with a length of 10 mm was fabricated. The main airflow was passed through the cooling devices with different widths of the above extension flow paths, and the pressure loss of the main airflow was measured from the difference between the inlet and outlet of the extension flow path + flow path. The measurement results are shown in Table 1.

[0040]

Table 1

[0041] [Example 1] An additional fin with a constant thickness of 2 mm and a plasma actuator were arranged opposite to each other to form an extension flow path. While passing the main airflow in the same manner as in Experimental Example 1, the plasma actuator was further driven in burst mode at 100 Hz Duty 50% and 18.5 mN / m to measure the average Nusselt number on the flow path wall surface.

[0042] [Example 2] The average Nusselt number of the channel wall was measured in the same manner as in Example 1, except that an additional fin having a wedge shape with a thin upstream side was used, where the thickness at the upstream end was 0 mm and the thickness at the location where the induced flow occurred was the thickest at 2 mm.

[0043] [Example 3] The average Nusselt number of the channel wall was measured in the same manner as in Example 1, except that an additional fin having a wedge shape with a thin downstream side was used, where the thickness at the upstream end was the thickest at 2 mm and the thickness at the location where the induced flow occurred was 0 mm.

[0044] [Comparative Example 1] The average Nusselt number of the channel wall was measured in the same manner as in Example 1, except that an additional fin having a main surface flush with the main surface of the fin was used.

[0045] The measurement results are shown in Table 2, and the wind speed distribution is shown in FIG. 4. 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.

[0046]

Table 2

[0047] In Example 1, the flow velocity of the main airflow at the location where the induced flow occurred was high, and the magnification of the improvement in the cooling performance by the plasma actuator was the highest. In Example 2, the flow velocity of the main airflow was not sufficiently accelerated up to the location where the induced flow occurred. In Example 3, the flow velocity of the main airflow decreased at the location where the induced flow occurred, and the magnification of the improvement in the cooling performance was not as high as that in Example 1.

[0048] From the results of Table 1 and Table 2 above, it can be seen that by setting the width of the extended channel to be 1 / 2 or more and less than 1 times the width of the above channel, the pressure loss of the main airflow does not increase significantly, and the magnification of the improvement in the cooling efficiency by the plasma actuator becomes high.

Description of Reference Numerals

[0049] 1 Plasma actuator 11 Exposed electrode 12 Coated electrode 13 Dielectric 14 AC power supply 15 Induced current 2 Heat sink 21 Fin 22 Base plate 23 Flow path 3 Additional fin 31 Extended flow path 4 Fan 41 Main air flow 5 Heating element

Claims

1. A heat sink having a plurality of fins erected on a base plate and forming a flow path between the fins, a fan that causes a main air flow to flow in the flow path, a plasma actuator that discharges between electrodes separated by a dielectric and generates an induced flow in the flow direction of the main air flow, and additional fins, wherein the additional fins and the plasma actuator are arranged upstream of the heat sink in the flow direction of the main air flow in the flow path, and they face each other to form an extended flow path, and the cooling device is characterized in that, the generation surface of the induced flow is flush with the main surface of the fins, the thickness of the additional fins is thicker than that of the fins, and the width of the extended flow path is narrower than the width of the flow path.

2. The cooling device according to claim 1, characterized in that the width of the extended flow path is 1 / 2 or more of the width of the flow path.

3. The cooling device according to claim 1, characterized in that the additional fins have different thicknesses in the flow direction of the main air flow.

4. The cooling device according to claim 1, characterized in that the plasma actuator generates the induced flow toward each adjacent flow path sandwiching the fins.

5. The cooling device according to claim 1, characterized in that the plasma actuator is driven in burst mode.

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