Cooling device

Abstract

To provide a cooling device which can improve cooling efficiency by causing an induction flow to reach the downstream of a flow path even if a heat sink has a long flow path length.SOLUTION: A cooling device comprises: a heat sink which has a flow path 23 formed between fins 21; a fan 4 for flowing a main air current 41 in the flow path 23; a plasma actuator which discharges electricity between electrodes 11 and 12 separated by a dielectric 13 so as to generate an induction flow 15 in a flow direction of the main air current 41; and an additional fin 3. The additional fin 3 and the plasma actuator are disposed upstream the heat sink in the flow direction of the main air current 41 in the flow path 23. The additional fin and the plasma actuator face each other so as to form an extension flow path 31. The plasma actuator is configured such that: the dielectric 13 is thicker than the fins 21; and a generation surface of the induction flow 15 is further offset to the center side in the width direction of the flow path 23 than main surfaces of the fins 21. The extension flow path 31 is narrower than the flow path 23.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] 2. Description of the Related Art Power conversion devices such as converters include electronic components that generate heat, such as semiconductors, capacitors, and coils, and are equipped with heat sinks to cool these electronic components.

[0003] In recent years, there has been a demand for power conversion devices to be smaller and have higher power. When electronic components are arranged densely to reduce size, the density of heat-generating elements within the power conversion device increases. In addition, increasing power output increases the amount of heat generated by the heat-generating elements, so the performance of the heat sinks that cool these elements must also 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 the 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, 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] JP 2014-183175 A Summary of the Invention [Problem to be solved by the invention]

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

[0008] Rather than forming a plasma actuator in the heat sink itself, a plasma actuator that is separate from the heat sink is placed on the end side of the heat sink and an induced flow is generated toward the flow path of the heat sink, thereby improving versatility and cooling efficiency.

[0009] In such a cooling device, since the plasma actuator is provided outside the flow path of the heat sink, if the flow path is long, the induced flow will lose speed on the downstream side, and the improvement of the cooling efficiency on the downstream side will decrease.

[0010] The present invention has been made in consideration of the problems associated with such conventional technology, and its purpose is to provide a cooling device that can improve cooling efficiency by making the induced flow reach the downstream side of the flow path, even in a heat sink with a long flow path length. [Means for solving the problem]

[0011] As a result of extensive research into achieving the above-mentioned objective, the inventors discovered that the above-mentioned objective could be achieved by positioning the plasma actuator so that its induced flow generation surface was offset toward the center of the width of the flow path from the main surface of the fin, and thus completed the present invention.

[0012] That is, the cooling device of the present invention comprises a heat sink having a plurality of fins standing on a base plate and forming a flow path between the fins, a fan for causing a main airflow to flow through the flow path, a plasma actuator for discharging between electrodes separated by a dielectric to generate an induced flow in the flow direction of the main airflow, and additional fins; The additional fin and the plasma actuator are disposed upstream of the heat sink in the flow direction of the main airflow of the flow path, and are opposed to each other to form an extended flow path. The plasma actuator is characterized in that the thickness of its dielectric is thicker than that of the fin, the generation surface of the induced flow is offset toward the center in the width direction of the flow path from the main surface of the fin, and the width of the extension flow path is narrower than the width of the flow path. Effect of the Invention

[0013] According to the present invention, the plasma actuator is provided at a position where the induced flow generation surface is offset toward the center of the width of the flow path from the main surface of the fin, thereby reducing friction between the induced flow and the fin and providing a cooling device with improved cooling efficiency. [Brief description of the drawings]

[0014] [Figure 1] 1 is a perspective view showing an example of a cooling device according to the present invention; [Diagram 2] FIG. 2 is a diagram illustrating the flow of a main airflow and an induced airflow in the cooling device of the present invention. [Diagram 3] FIG. 1 is a diagram showing an example of a single-sided plasma actuator. [Figure 4] FIG. 4 is a diagram showing the wind speed distribution of the cooling device of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The cooling device of the present invention will now be described in detail. The cooling device of the present invention comprises a heat sink, a fan, a plasma actuator, and additional fins.

[0016] The heat sink 2 has a plurality of fins 21 standing on one main surface of a base plate 22, and a flow path 23 is formed between the fins. A heat generating body (body to be cooled) 5 is in contact with the other main surface of the base plate 22. The fan promotes heat dissipation from the heat sink by causing a main airflow to flow through the flow path of the heat sink.

[0017] 1, the X-axis direction is the length direction of the flow passage and the direction of the main airflow, the Y-axis direction is the width direction of the flow passage, and the Z-axis direction is the height direction of the flow passage.

[0018] 2, the plasma actuator 1 has a covered electrode 12 and an exposed electrode 11 separated by a dielectric 13, which are offset in the in-plane direction of the main surface of the dielectric. A barrier discharge occurs by applying a voltage between the electrodes, generating an induced flow 15 in the in-plane direction of the main surface of the dielectric 13.

[0019] As shown in FIG. 2, the plasma actuator 1 and additional fin 3 are arranged facing each other on the upstream side of the heat sink in the flow direction of the main airflow, with their respective fins parallel to the main surfaces of the fins, forming an extended flow path 31 that is continuous with the flow path 23 of the heat sink.

[0020] The induced flow 15 of the plasma actuator improves the cooling efficiency by accelerating the main airflow 41 and thinning the boundary layer generated by friction between the main airflow and the fins 21. However, like the main airflow, the induced flow also loses speed downstream due to friction with the fins 21, resulting in a difference in cooling efficiency between the upstream and downstream sides.

[0021] In the cooling device of the present invention, the plasma actuator has a dielectric 13 whose thickness is greater than that of the fin 21, and the main surface of the dielectric 13 where an induced flow is generated (hereinafter sometimes referred to as the "induced flow generation surface") is offset toward the center in the width direction of the flow path from the main surface of the fin 21, and the induced flow generation surface is separated from the main surface of the fin in the width direction (Y direction) of the flow path 21. Therefore, friction between the induced flow 15 and the fin 21 is suppressed.

[0022] Furthermore, since the thickness of the dielectric 13 is large, it is possible to increase the pressure resistance of the plasma actuator, and a strong induced flow can be generated. In addition, since the width of the extension flow passage 31 where the induced flow occurs is narrower than the width of the flow passage 23 of the heat sink, the flow velocity of the main airflow 41 in the extension flow passage becomes faster, and the induced flow 15 is generated here, so that an even stronger induced flow is generated and the induced flow reaches the downstream side.

[0023] Therefore, the boundary layer can be made thin even on the downstream side of the flow path 23, and the difference in cooling efficiency between the upstream side and the downstream side is reduced, thereby improving the cooling efficiency of the entire cooling device.

[0024] Furthermore, as shown in Figure 1, when the height (Z-axis direction) of the plasma actuator and the additional fin are the same as the height of the fins, the boundary layer can be made thin throughout the entire height direction (Z-axis direction) of the flow path, all the way to the downstream side, thereby further improving the cooling efficiency.

[0025] The width of the extension flow passage 31 is preferably ½ or more of the width of the flow passage 23 . By making the width of the extension flow passage 14 at least half the width of the flow passage, the flow velocity of the main airflow 15 flowing through the extension flow passage 31 can be increased without significantly increasing the pressure loss of the main airflow from the fan.

[0026] The width of the extension flow passage 31 can be adjusted by the thickness of the additional fins and the thickness of the dielectric of the plasma actuator, but it is preferable to narrow the width of the extension flow passage by making the thickness of the additional fins the same as the thickness of the fins of the heat sink and increasing the thickness of the dielectric. In the present invention, the "width of the extension flow passage" refers to the width of the thickest part of the dielectric.

[0027] The additional fins are made of an insulating material, so that even if the electrodes of the plasma actuator and the additional fins are close to each other, no discharge occurs between them, making it possible to narrow the width of the extension flow path and increase the thickness of the dielectric, thereby generating a strong induced flow.

[0028] It is preferable that the thickness of the dielectric be thinner on the upstream side in the flow direction of the main airflow than on the downstream side. Since the upstream side of the dielectric is thin, the main airflow can easily enter the extension flow passage, and the width of the extension flow passage is partially widened, thereby reducing an increase in pressure loss.

[0029] The above-mentioned plasma actuator may be a single-sided plasma actuator having a covered electrode 12 on one main surface of a dielectric and an exposed electrode 11 on the other main surface, as shown in FIG. 3, but it is preferable that it is a double-sided plasma actuator having two exposed electrodes 11 sandwiching a dielectric, as shown in FIG. 2, and capable of generating an induced flow on both sides of the main surface of the above-mentioned dielectric 13.

[0030] The above-mentioned double-sided plasma actuator can direct induced flow toward two adjacent flow paths with a single plasma actuator, so by placing them alternately on the fins, induced flow can be directed into all flow paths in the heat sink, improving cooling efficiency.

[0031] 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.

[0032] By cyclically switching 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, creating a pressure difference in the direction of the induced flow, which in turn creates a flow in the opposite direction to the induced flow, generating a vortex.

[0033] 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 are generated near the fins, thereby improving cooling performance.

[0034] Furthermore, since no power is consumed when the voltage applied between the electrodes is off, power saving is achieved.

[0035] The heat sink may be made of a metal material having high thermal conductivity, such as aluminum or an alloy thereof. In addition, since the fins erected on the base plate are straight fins and 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.

[0036] As the fan, an axial fan or a blower fan (centrifugal fan) can be used.

[0037] The fan may be provided on the upstream side or downstream side of the heat sink in the flow direction of the main airflow, and this can be selected depending on the location where the cooling device is to be installed.

[0038] 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, making it difficult for dust and dirt to enter the flow path.

[0039] 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, making it less likely to be disrupted than when the fan is located upstream, and the main airflow can be straightened from near the entrance of the flow path. EXAMPLES

[0040] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0041] [Experimental Example 1] A plasma actuator and additional fins with different dielectric thicknesses were placed opposite a heat sink with a flow path 65 mm long and 5 mm wide, and an extension flow path 10 mm long was added to create a cooling device with a total length of 75 mm. The main airflow was passed through the cooling devices with different widths of the extension passages, and the pressure loss of the main airflow was measured from the difference between the inlet and outlet of the extension passage + passage. The measurement results are shown in Table 1.

[0042] [Table 1] From the results in Table 1, it can be seen that if the width of the extended flow passage is 1 / 2 or more of the width of the above flow passage, the pressure loss does not increase significantly and the cooling efficiency by the main airflow does not decrease.

[0043] [Experimental Example 2] The main airflow was applied in the same manner as in Experimental Example 1, and the plasma actuator was burst-driven at 100 Hz, duty 50%, and 18.5 mN / m to measure the average Nusselt number on the flow path wall surface. The measurement results are shown in Table 2 and the wind speed distribution in Figure 4. The Nusselt number is the ratio of the thermal conduction and heat transfer of a convecting fluid, and the higher the Nusselt number, the higher the heat transport effect due to convection.

[0044] [Table 2] The results in Table 2 show that if the width of the extended flow path is half or more of the flow path width, the improvement factor of the cooling efficiency by the plasma actuator is high. As described above, from Tables 1 and 2, it can be seen that if the width of the extended flow path is half or more of the flow path width, the pressure loss of the main airflow does not increase significantly, and the improvement factor of the cooling efficiency by the plasma actuator becomes high, thereby improving the cooling efficiency of the entire cooling device. [Explanation of symbols]

[0045] 1 Plasma Actuator 11 Exposed electrode 12 Coated electrode 13 Dielectrics 14 AC power supply 15 Induced flow 2 Heat sink 21 Finn 22 Base plate 23 Flow Path 3 Additional fins 31 Extension channel 4 Fans 41 Main airflow 5 Heating element

Claims

1. a heat sink having a plurality of fins standing on a base plate and forming flow paths between the fins; A fan for blowing a main airflow through the flow path; a plasma actuator that generates an induced flow in the direction of the main airflow by discharging between electrodes separated by a dielectric; and an additional fin; a cooling device in which the additional fin and the plasma actuator are disposed opposite each other on an upstream side of the heat sink in a flow direction of the main airflow of the flow path, forming an extension flow path, the plasma actuator has a dielectric thickness greater than that of the fin, and the induced flow generation surface is offset toward the center in the width direction of the flow path from the main surface of the fin; A cooling device characterized in that the width of the extension flow passage is narrower than the width of the flow passage.

2. 2. The cooling device according to claim 1, wherein the width of the extension flow passage is at least half the width of the flow passage.

3. 2. The cooling device according to claim 1, wherein the thickness of the dielectric body is thinner on the upstream side in the flow direction of the main airflow than on the downstream side.

4. 2. The cooling device according to claim 1, wherein the plasma actuator generates the induced flow toward each of the adjacent flow paths across the fin.

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

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