WO2024069203A1

WO2024069203A1 - Cooling device

Info

Publication number: WO2024069203A1
Application number: PCT/IB2022/000568
Authority: WO
Inventors: 淳平新井田; 健太江森; 滋春山上; 瑛美高橋
Original assignee: 日産自動車株式会社; ルノーエス．ア．エス．
Priority date: 2022-09-29
Filing date: 2022-09-29
Publication date: 2024-04-04

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

Cooling system

The present invention relates to a cooling device, and more specifically, to a cooling device having a heat sink and a plasma actuator.

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

In recent years, there has been a demand for smaller power conversion devices with higher power output. When electronic components are arranged densely to reduce 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 as the power increases, so the performance of the heat sinks that cool these components must also be improved.

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.

Patent Document 1 discloses a cooling device in which electrodes are provided on the fins of a heat sink to act as a plasma actuator, generating an induced flow between the fins.

Japanese Patent Publication No. 2014-183175

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

The present invention was made in consideration of the problems with the conventional technology, and its purpose is to provide a versatile, inexpensive cooling device that does not require machining of the heat sink itself.

As a result of extensive research into achieving the above objective, the inventors have completed the present invention by arranging the plasma actuator on the upstream side of the heat sink so that the main surface of the dielectric is parallel to the main surface of the fin, and by generating an induced flow in the direction of the main airflow.

That is, the cooling device of the present invention comprises a heat sink having a plurality of fins erected on a base plate with a flow path formed between the fins, a fan that directs a main airflow through the flow path, and a plasma actuator that discharges 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 to each other, and the flow direction of the induced flow is the same as the flow direction of the main airflow.

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, making 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.

1 is a cross-sectional view showing a main part of an example of a plasma actuator. FIG. 1 is a perspective view showing an example of a cooling device of the present invention. 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. FIG. 4 is a diagram showing the distance between an exposed electrode and a covered electrode. FIG. 13 is a diagram showing a distance between an exposed electrode and a covered electrode that can be substituted for the distance in the flow path direction only. 1 is a cross-sectional view of a main portion of a plasma actuator that generates an induced flow on both sides of a dielectric body. FIG. 1 is an XY plan view of a cooling device in which plasma actuators and additional fins are provided alternately. 4 is a diagram illustrating the intake and exhaust directions of air by a blower fan. FIG. FIG. 1 is an XY plan view of a cooling device in which a plasma actuator is arranged in accordance with the rotor blades of a blower fan. FIG. 13 is a diagram showing a state in which the flow of an induced flow is changed by a gap. FIG. 13 is a diagram showing a state in which the induced flow flows linearly without being changed by a gap.

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.

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

As shown in Figure 1, the plasma actuator has electrodes separated by a plate-shaped dielectric, which are offset in the in-plane direction of the main surface of the dielectric. A voltage is applied between the electrodes to generate a barrier discharge, generating an induced flow in the in-plane direction of the main surface of the dielectric.

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

In FIG. 2, the X-axis direction (length 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.

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 itself is endowed with the function of a plasma actuator. Since the heat sink and the plasma actuator are separate components, there is no need to process the heat sink, and commercially available products can be used, making it highly versatile and inexpensive.

In addition, because the plasma actuator is not attached to 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 and ensures the withstand voltage of the dielectric without the need to thin the dielectric to ensure the flow path width.

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 over the entire height direction (Z-axis direction) of the fin.

As a result, 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, improving cooling efficiency.

Such a plasma actuator can be arranged upright on a support member that is arranged parallel to the main surface of the base plate of the heat sink.

It is preferable that the thickness of the dielectric of the plasma actuator is the same as the thickness of the heat sink fins, and that the main surface of the dielectric and the main surface of the fins are arranged on the same plane.

As a result, there is no step between the dielectric and the fin, and the pressure loss of the induced flow near the main surface of the fin can be reduced, making it possible to make the boundary layer thinner further, improving cooling performance. Note that the above "same thickness" does not exclude manufacturing errors.

It is preferable that the cooling device has a gap between the plasma actuator and the fins of the heat sink, as shown in Figure 3.

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

However, heat sinks are often made of metals such as aluminum that have high thermal conductivity, and if the plasma actuator and heat sink are in close proximity, undesirable discharges can occur between the plasma actuator's electrode and the heat sink.

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 that gap, preventing undesired discharge in the direction of the heat sink.

In addition, the gap cuts off the heat transfer path from the heat sink to the plasma actuator, making it difficult for heat to be transferred from the heat sink to the plasma actuator, preventing the temperature of the plasma actuator from becoming too high, improving the durability and reliability of the plasma actuator.

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

If a gap is provided between the plasma actuator and the heat sink, the induced flow flowing over the dielectric surface creates a negative pressure in the gap compared to the dielectric surface, and the induced flow is pulled inward in the thickness direction of the fin in the gap, disrupting the flow. The induced flow then collides with the edge of the fin and flows out toward the center of the flow path, making it impossible to thin the boundary layer and reducing cooling efficiency.

By setting the distance d between the plasma actuator and the heat sink to less than three times the thickness t of the fin, disturbance of the induced flow caused by the gap is suppressed, and the induced flow flows in a straight line, just as if there was 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 generate vortexes caused by hitting the ends of the fins.

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 passage formed between the fins.
This makes it possible to further suppress turbulence of the induced flow.

The plasma actuator is preferably a combination of electrodes separated by a plate-shaped dielectric, the electrodes being an exposed electrode with its surface exposed, and a covered electrode entirely covered by a dielectric, the exposed electrode having a ground potential and the covered electrode having a high potential.

These electrodes are arranged so that the exposed electrode is on the upstream side and the covered electrode is on the downstream side in the main airflow direction, i.e., the covered electrode is offset toward the heat sink from the exposed electrode.

The exposed electrode has a low potential, and the high potential electrode is a covered electrode, which prevents discharge from the high potential electrode to the heat sink. This allows the plasma actuator and the heat sink to be placed close to each other, improving cooling efficiency and enabling the cooling device to be made smaller.

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.

It is preferable that the exposed electrode and the covered electrode are arranged so that the distance between them is narrower than the distance between the covered electrode and the fin.

By arranging them in this way, it is possible to suppress discharge between the covered electrode, which is a high-potential electrode, and the fins. Even if an undesired discharge occurs between the covered electrode and the fins, the discharge between the exposed electrode and the covered electrode is strong, and the desired induced flow is strong, so that the overall flow of the induced flow is directed toward the heat sink.

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 Figure 4, but it may also be substituted with the distance component only in the flow path direction, as shown in Figure 5.

The plasma actuator can also have two of the above-mentioned exposed electrodes, which can be arranged in opposing positions with a dielectric between them, as shown in Figure 6.

Since 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, making it possible for a single plasma actuator to generate an induced flow in two adjacent flow paths.

Therefore, it is only necessary to place plasma actuators on every other fin, which reduces the number of plasma actuators and reduces costs.

In this case, it is preferable to alternately provide the plasma actuators and the additional fins. As shown in FIG. 7, the additional fins are in contact with the fins of the heat sink and have a plate shape extending from the fins of the heat sink to the upstream side in the flow direction of the main airflow, and are positioned opposite the exposed electrode of the plasma actuator across the flow path.

In the above 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 opposite the exposed electrode, no discharge will occur toward this additional fin.

The additional fins are in contact with the fins of the heat sink, so they can dissipate heat transferred from the heat sink, increasing the surface area of the fins per unit volume of the cooling device and improving the cooling process.

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

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, creating a pressure difference in the direction of the induced flow, which creates a flow in the opposite direction to the induced flow and generates a vortex.

The generation of these vortices 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, improving cooling performance.

In addition, no power is consumed when the voltage applied between the electrodes is off, which helps save energy.

The heat sink preferably has straight fins that are erected on the base plate. 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, improving cooling performance.

The heat sink preferably also has a lid on the side (top) of the fin opposite the base plate. Providing a lid on the top of the fin prevents leakage of the main airflow through the flow path, and allows the main airflow through the flow path to flow to the outlet of the flow path, improving cooling performance.

Furthermore, by extending the lid to the upstream end of the plasma actuator in the direction of the main airflow, and 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.

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 having a plasma actuator in the middle of the flow path, the boundary layer that develops downstream can be made thinner, improving cooling efficiency even if the flow path is long.

The fan may be installed either upstream or downstream of the heat sink in the direction of the main airflow, depending on where the cooling device is installed.

If the fan is placed upstream 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 get into the flow path.

In addition, 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, so the flow of the main airflow is less likely to be disturbed than when the fan is located upstream, and the main airflow can be straightened from near the entrance of the flow path.

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

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

In contrast, unlike axial fans, blower fans have a rotational axis direction, i.e., the air intake and exhaust directions, that 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 match the shape of the main airflow discharged to the shape of the flow path inlet face without using a nozzle, and it is possible to reduce the height of the cooling device and make it more compact.

When using a blower fan 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 rotor 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.

Furthermore, an additional fin can be provided between the plasma actuator, which is arranged along the arc of the blower fan's rotor blades, and the heat sink fin, which abuts against the fin and extends from the fin upstream of the main airflow.

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

By providing an additional fin between the plasma actuator and the fin that comes into contact with the fin, the heat from the heat sink is transferred to the additional fin, maintaining the effect of thinning the boundary layer provided by the plasma actuator, and coupled with the increased heat dissipation area provided by the additional fin, the cooling efficiency can be improved.

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

[Example 1]
The thickness of the fin and plasma actuator was changed in the range of 0.5 mm to 3.0 mm to form a flow path with a flow path width (Y-axis direction) of 5 mm, and an induced flow was generated from the plasma actuator with a volume force of 3,700 N/ ^m3 . 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.

FIG. 10 shows the case where the fin thickness is 1 mm and the gap is 4 mm, and FIG. 11 shows the case where the fin thickness is 1 mm and the gap is 3 mm.
In FIG. 10, the flow of the induced flow changes and flows toward the center of the flow channel, whereas in FIG. 11, the induced flow flows linearly.

As in Table 1, when there is no gap, the induced flow flows in a straight line, and when the induced flow hits the edge of the fin and becomes turbulent, it is indicated with an "O" and an "X."

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

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 induced flow changed and flowed away from the fins.

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

[Example 2]
Using a fin and plasma actuator with a thickness of 1 mm, a flow path was formed by changing the flow path width (Y-axis direction) in the range of 2 mm to 5 mm, and an induced flow was generated from the plasma actuator with a volume force of 3700 N/ ^m3 . 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.
It should be noted that no effect was obtained from the plasma actuator when the flow path width was 1 mm or less.

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 linearly.

In addition, when the distance between the heat sink fins was 4.0 mm and the flow path width was 5 mm, the induced flow changed and flowed away from the fins.

These results show that if the distance between the plasma actuator and the fins of the heat sink is 0.75 times or less than the flow path width, the induced flow will flow linearly, making the boundary layer near the fin surface thinner, and preventing undesired discharges while improving cooling efficiency.

REFERENCE SIGNS LIST 1 plasma actuator 11 exposed electrode 12 covered electrode 13 dielectric 14 AC power supply 15 induced flow 2 heat sink 21 fin 22 base plate 23 lid 3 fan 31 main air flow 32 rotor 33 air intake direction 34 air discharge direction 4 additional fin 5 heating element

Claims

a heat sink having a plurality of fins standing on a base plate and a flow path formed between the fins;
A fan for blowing a main airflow through 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 flow 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.
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.
The cooling device according to claim 2, characterized in that there is a gap between the plasma actuator and the fins of the heat sink.
The cooling device according to claim 3, characterized in that the distance between the plasma actuator and the fins of the heat sink is less than three times the thickness of the fins.
The cooling device according to claim 4, characterized in that 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.
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.
The cooling device according to claim 6, characterized in that the gap between the exposed electrode and the covered electrode is narrower than the gap between the covered electrode and the fin.
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.
an additional fin abutting the fin of the heat sink and extending from the fin of the heat sink;
The cooling device according to claim 1 , wherein the additional fins and the plasma actuators are arranged alternately.
The cooling device according to claim 1, characterized in that the fan is disposed upstream of the plasma actuator in the flow path direction.
The cooling device according to claim 10, characterized in that the fan is a blower fan.
The cooling device according to claim 11, characterized in that the tips of the plasma actuators on the upstream side of the main airflow are arranged along the arc described by the rotor blades of the blower fan.
The cooling device according to claim 11, characterized in that it has additional fins at least between the plasma actuator and the fins at both ends of the width of the heat sink, which abut the fins and extend from the fins upstream of the main airflow.
The cooling device according to claim 1, characterized in that the fan is disposed downstream of the plasma actuator in the flow path direction.
The cooling device according to claim 1, characterized in that the fins of the heat sink are straight fins.
The cooling device according to claim 1, characterized in that it has multiple combinations of the plasma actuator and the heat sink in the flow path direction.
The cooling device according to claim 1, characterized in that the heat sink is covered with a lid on the opposite side of the base plate, sandwiching the fins.
The cooling device according to claim 1, characterized in that the plasma actuator is burst driven.