Cooling device and cooling unit utilizing latent heat of vaporization

Abstract

To provide a cooling device and cooling unit that utilize latent heat of vaporization, enabling miniaturization of the entire device. [Solution] The system includes a metal heat receiving body 14 that receives heat from a heating element 21 on one side and has multiple fins 14a erected on the other side to vaporize the working fluid supplied to the base of each erected fin, a metal slit electrode having multiple electrode plates 15b that are inserted in a non-contact state between the multiple fins formed on the heat receiving body, the base end of each electrode plate being open in a slit shape to form a passage 15c for the working fluid, and a DC power supply 17 that generates an electric field between the alternately adjacent fins 14a of the heat receiving body and the electrode plates 15b of the slit electrode by applying a DC voltage between the heat receiving body 14 and the slit electrode 15.

Description

Technical Field

[0001] The present invention relates to a cooling device and a cooling unit using latent heat of vaporization, which can be suitably employed for cooling, for example, laser diodes used as light sources for large-screen projection in projection mapping.

Background Art

[0002] In response to the demand for large-screen projection by the aforementioned projection mapping, the output power of laser diodes used as the light source has been increasing, and cooling design accompanying this has been regarded as important. Conventionally, this type of large-sized projector employs a so-called water-cooling cooling device, in which heat received from a laser diode raises the temperature of a fluid, the temperature-raised fluid is cooled by a radiator, and the cooled fluid is returned to the heat-receiving portion again to circulate the fluid.

[0003] Furthermore, similar water-cooling cooling devices are also employed in power semiconductors used for travel control of fuel cell vehicles and electric vehicles, as well as in various industrial equipment such as laser processing machines and exposure machines. However, along with the further increase in output power of power devices including the aforementioned laser diodes in recent years, the heat generation density from power devices and the like has been increasing more and more, which makes the increase in size of cooling devices a problematic issue.

[0004] Under such circumstances, insufficient cooling capacity occurs in the aforementioned water-cooling method, which dominates the mainstream of conventional cooling devices. For this reason, the inventor of the present application has previously proposed a cooling device that can cool heat-generating bodies such as the aforementioned power devices with high efficiency by utilizing the latent heat of vaporization generated when a working fluid as a cooling medium changes from a liquid phase (liquid) to a gas phase (gas), which is disclosed in Patent Document 1.

[0005] Figures 11 and 12 show the cooling unit portion that constitutes the cooling device disclosed in Patent Document 1. Specifically, Figure 11 is a longitudinal cross-sectional view of the cooling unit 91, and Figure 12 is a partially enlarged cross-sectional view showing the relationship between the heat receiving plate 94 and the electrode 95 with a slit 95a that constitutes the cooling unit 91. As shown in Figure 11, the cooling unit 91 disclosed in Patent Document 1 has a rectangular conductive heat receiving plate 94 and an electrode 95 having a plurality of slits 95a attached to a frame-shaped lower case 92 equipped with a spacer 92a at predetermined intervals, with the back surface of the heat receiving plate 94 forming the bottom surface of the lower case 92.

[0006] A rectangular upper case 93 is mounted on the lower case 92 so as to cover the electrode 95 which has multiple slits 95a, and a DC power supply 97 is provided for applying a predetermined voltage (several kV) between the electrode 95 and the heat receiving plate 94. A working fluid inlet 92b is formed in a part of the lower case 92 for introducing working fluid as a cooling medium into the lower case 92, and a working fluid outlet 93a is formed in a part of the upper case 93 for discharging the working fluid. A heat-generating element 99, such as a laser diode, which is to be cooled by this cooling unit 91, is attached in close contact to the back surface of the heat receiving plate 94.

[0007] The working fluid is introduced into the working fluid inlet 92b, which boils and vaporizes at a temperature below the upper limit of the allowable temperature of the heating element 99. Therefore, the working fluid introduced into the lower case 92 from the working fluid inlet 92b boils and vaporizes upon receiving heat from the heating element 99 via the heat receiving plate 94, and is sent into the upper case 93 in a mixed state of liquid and gas phases through the multiple slits 95a formed in the electrode 95. The working fluid in the upper case 93 is then sent to the heat sink from the working fluid outlet 93a of the upper case 93, where it is liquefied and condensed, and then introduced again into the working fluid inlet 92b of the cooling unit 91 by a pump. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6603895 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Incidentally, according to the cooling unit 91 disclosed in Patent Document 1, as shown in Figure 11, a configuration is employed in which a DC voltage is applied between an electrode 95 having a plurality of slits 95a and a heat receiving plate 94 facing it, and this is called the microslit channel method (MSC method). According to this, as shown in Figure 12, an electric field is applied between each electrode 95 and the heat receiving plate 94, as indicated by the dashed electric field lines. The details of the effects of applying this electric field will be explained later, but in the area where the electric field is formed, the heat transfer coefficient to the working fluid can be improved, which reduces the thermal resistance and is expected to increase the cooling effect on the heat-generating element 99. However, the cooling effect on the heat-generating element 99 by the MSC method described above occurs only in the local area between the tip of each electrode 95 and the heat receiving plate 94 facing it, as shown in Figure 12. For this reason, the cooling effect obtained by adopting the MSC method cannot be fully realized, and there is room for improvement.

[0010] This invention has been made in view of the aforementioned problems, and aims to further increase the cooling efficiency for the heat-generating element by increasing the surface area on the heat-receiving plate side where the electric field is formed. The objective is to provide a cooling device and cooling unit that utilize latent heat of vaporization, enabling miniaturization of the entire device. [Means for solving the problem]

[0011] The cooling device according to this invention, made to solve the aforementioned problems, comprises a cooling unit that cools a heat-generating element by receiving heat from the heat-generating element and causing at least a portion of the working fluid to change from a liquid phase to a gas phase; a heat sink in the cooling unit that receives and cools the working fluid that has undergone the phase change, thereby liquefying and condensing the working fluid; and a pump that sends the working fluid liquefied by the heat sink to the cooling unit, thereby circulating the working fluid between the cooling unit and the heat sink, wherein the cooling unit has, on one side, the heat-generating element The system includes a metal heat receiver that receives heat from one side and has multiple fins erected on the other side to vaporize the working fluid supplied to the base of each erected fin; a metal slit electrode having multiple electrode plates inserted in a non-contact manner between the multiple fins formed on the heat receiver, with the base end of each electrode plate being slit-shaped to form a passage for the working fluid; and a DC power supply that generates an electric field between the alternately adjacent fins of the heat receiver and the electrode plates of the slit electrode by applying a DC voltage between the heat receiver and the slit electrode.

[0012] Furthermore, the cooling unit according to this invention, which was made to solve the aforementioned problems, is a cooling unit that cools a heating element by receiving heat from the heating element and causing at least a portion of the working fluid to change from a liquid phase to a gas phase, and the cooling unit has a metal heat receiving body that receives heat from the heating element on one side and has a plurality of fins erected on the other side to vaporize the working fluid supplied to the base portion of each erected fin, and a plurality of electrode plates that are inserted in a non-contact state between the plurality of fins formed on the heat receiving body, and the base end of each electrode plate is The device comprises a metal slit electrode that is slit-shaped and forms a passage for the working fluid, a first case that holds the heat receiving body and the slit electrode, with one side of the heat receiving body as the bottom surface and forming an inlet for the working fluid, a second case that covers the slit electrode and is superimposed on the first case or molded integrally with the first case to form an outlet for the working fluid, and a DC power supply that generates an electric field between the fins of the heat receiving body and the electrode plate of the slit electrode by applying a DC voltage between the heat receiving body and the slit electrode.

[0013] In this case, the first embodiment of the cooling unit is characterized in that the plurality of fins formed on the heat receiving body are each formed in the shape of a flat plate with equal thickness and arranged at equal intervals, and the plurality of electrode plates formed on the slit electrode are each formed in the shape of a flat plate with equal thickness and arranged at equal intervals, so that each fin and each electrode plate inserted between each fin in a non-contact state are arranged parallel to each other and at equal intervals.

[0014] Furthermore, in the second embodiment of the cooling unit, the plurality of fins formed on the heat receiving body are arranged at equal intervals with their thickness gradually decreasing from the base to the other end, and the plurality of electrode plates formed on the slit electrode are each formed as flat plates of equal thickness and arranged at equal intervals, so that the distance between each fin and each electrode plate inserted between each fin in a non-contact state gradually increases from the base to the other end of each fin.

[0015] Furthermore, in the third embodiment of the cooling unit, the plurality of fins formed on the heat receiving body are arranged at equal intervals with their thickness gradually decreasing from the base to the other end, and the plurality of electrode plates formed on the slit electrode are formed as flat plates of equal thickness and arranged at equal intervals, so that the distance between each fin and each electrode plate inserted between each fin in a non-contact state gradually increases from the base to the other end of each fin, and an arc-shaped groove is formed along the base between the bases of adjacent fins.

[0016] Furthermore, the first case has guide passages formed to lead the working fluid from the working fluid inlet to both ends of the base portions of the multiple fins erected on the heat receiving body. Furthermore, the slit electrode is formed from aluminum, and an anodized insulating layer is formed on the entire surface of the slit electrode. In this case, it is desirable that the positive electrode voltage of the DC power supply is applied to the electrode plate of the slit electrode, and the negative electrode voltage is applied to the fins of the heat receiving body. [Effects of the Invention]

[0017] According to the cooling device and cooling unit of this invention, the heat receiving body that receives heat from the heat-generating element is provided with a slit electrode having a plurality of fins erected on it, and a plurality of electrode plates that are inserted between the plurality of fins in a non-contact manner. In addition, a DC voltage is applied between the heat receiving body and the slit electrode, and an electric field is formed between the alternately adjacent fins of the heat receiving body and the electrode plates formed on the slit electrode. In the area where this electric field is formed, the supply effect of the working fluid in liquid phase is enhanced, which in turn improves the heat transfer coefficient to the working fluid and contributes to reducing thermal resistance.

[0018] Therefore, according to the cooling device and cooling unit of the present invention, the increase in heat dissipation area achieved by the plurality of fins provided upright on the heat receiving body and the aforementioned effect of increasing the electric field formation area act synergistically, whereby high cooling efficiency for a heating element can be achieved. This makes it possible to provide a cooling device and a cooling unit that enable size reduction of the entire device. Other characteristic functions and effects of the cooling unit according to the present invention will be described as they arise in the description of the embodiments below. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [Figure 1] FIG. 1 is a schematic diagram showing the basic configuration of the cooling device according to the present invention. [Figure 2] FIG. 2 is a perspective view showing the external configuration of a cooling unit included in the cooling device shown in FIG. 1. [Figure 3] FIG. 3 is a longitudinal cross-sectional view of the cooling unit according to a first embodiment. [Figure 4] FIG. 4 is a perspective view showing the relationship between a heat receiving body and slit electrodes in the cooling unit according to the first embodiment. [Figure 5] FIG. 5 shows the configuration of an individual slit electrode, wherein (A) is a top view, (B) is a perspective view, and (C) is a partial enlarged cross-sectional view. [Figure 6] FIG. 6 is a cross-sectional view of a first case taken along line I-I of FIG. 3 as viewed in the direction of the arrow. [Figure 7] FIG. 7 is a schematic diagram for explaining the functional effect obtained by the electric field applied between the fins of the heat receiving body and the electrode plates of the slit electrodes. [Figure 8] FIG. 8 is a partially enlarged cross-sectional view of the cooling unit according to the first embodiment. [Figure 9] FIG. 9 is a partially enlarged cross-sectional view of the cooling unit according to a second embodiment. [Figure 10] FIG. 10 is a partially enlarged cross-sectional view of the cooling unit according to a third embodiment. [Figure 11] FIG. 11 is a longitudinal cross-sectional view showing an example of a conventional cooling unit. [Figure 12]Figure 11 is a partially enlarged cross-sectional view showing the relationship between the heat receiving plate and the electrodes of the cooling unit. [Modes for carrying out the invention]

[0020] Embodiments of the cooling device and the cooling unit used in the cooling device according to this invention will be described with reference to the figures. Note that the figures described below are schematic representations of embodiments of this invention, with appropriate emphasis, omissions, and adjustments to proportions, and may differ from the actual shapes, positions, and proportions.

[0021] Figure 1 shows the basic configuration of the cooling device according to this invention. As shown in Figure 1, the cooling device 10 is configured to cool the heat-generating element 21, such as a laser diode, by receiving the heat emitted from the heat-generating element 21 with a cooling unit 11 and dissipating the heat with a heat sink 31. This system includes a cooling unit 11, a heat sink 31, a pump 41, and a tubular member 51 that circulates the working fluid in the direction of the arrow. The working fluid is a fluid for transporting heat, and in this specification and claims, it includes liquids, gases, and fluids in which liquids and gases are mixed.

[0022] The cooling unit 11 has the function of cooling the heat-generating element 21, such as the laser diode, by utilizing the latent heat of vaporization that occurs when at least a portion of the working fluid undergoes a phase change from the liquid phase to the gaseous phase in response to heat from the heat-generating element 21. In this embodiment, the outer casing of the cooling unit 11 is constructed by stacking a second case 13 on top of a rectangular first case 12. The internal configuration of the cooling unit 11 will be described later based on Figures 2 to 6.

[0023] The heat exchanger 31 receives the working fluid supplied from the cooling unit 11 and exchanges heat between the working fluid circulating inside the heat exchanger and the fluid in contact with the outside. Furthermore, since the vaporized working fluid liquefies inside the heat exchanger 31, the heat exchanger 31 also functions as a condenser. The heat sink 31 shown in this example comprises, for example, a plurality of thin tubes (not shown) arranged at predetermined intervals, and a fan 32 that circulates air between the thin tubes. It has the function of cooling the working fluid by exchanging heat between the working fluid flowing inside the thin tubes and the air, thereby liquefying the working fluid that has been vaporized.

[0024] The pump 41 performs the function of forcibly sending the working fluid from the heat sink 31 to the cooling unit 11 via the tubing member 51. In Figure 1, the pump 41 is provided in the tubing member 51 that sends the working fluid from the heat sink 31 to the cooling unit 11, but this pump 41 may also be provided in the tubing member 51 that sends the working fluid from the cooling unit 11 to the heat sink 31.

[0025] Figures 2 to 6 show the configuration of the cooling unit 11. As mentioned above, the cooling unit 11 is constructed by stacking a second case 13 on top of a rectangular first case 12, and Figure 3 shows a vertical cross-sectional view of the cooling unit 11. As shown in Figure 3, the cooling unit 11 consists of a rectangular conductive heat receiving body 14 on which a heat-generating element 21 such as a laser diode is mounted, and a metal slit electrode 15 having a plurality of electrode plates 15b, which are mounted at predetermined intervals in a frame-shaped first case 12 equipped with spacers 12a, with one side of the heat receiving body 14 on which the heat-generating element 21 is mounted forming the bottom surface of the first case 12.

[0026] Furthermore, a rectangular second case 13 is mounted on the first case 12 so as to cover the slit electrode 15. Furthermore, a DC power supply 17 for applying a predetermined voltage is provided between the slit electrode 15 and the heat receiving body 14, which are located in the first case 12. In this embodiment, as shown in Figure 2, the working fluid inlet 12b is formed on the side wall of the first case 12. The working fluid outlet 13a is formed on the upper surface of the second case 13, but it can also be formed on the side surface of the second case 13.

[0027] As shown in Figures 3 and 4, on the other surface of the rectangularly shaped heat receiving body 14, i.e., the upper surface of the heat receiving body 14, a plurality of fins 14a are erected perpendicular to the surface of the heat receiving body 14, and each fin 14a is formed into a rectangular plate shape that is parallel to each other at the same interval and has the same thickness. The materials constituting the heat receiving body 14 and the plurality of fins 14a are preferably materials with high electrical and thermal conductivity, and metals such as copper and aluminum, or other alloys can be used. In this embodiment, copper is used for the heat receiving body 14 and the plurality of fins 14a. Furthermore, the multiple fins 14a face the multiple electrode plates 15b arranged on the slit electrode 15, which will be described later, and function as electrodes on the heat receiving body 14 side.

[0028] Furthermore, it is desirable that the upper surface of the heat receiving body 14 on which the fins 14a are formed, and the entire surface of each fin 14a, be subjected to a rough surface treatment with minute irregularities. This makes it easier for bubbles to be generated from the working fluid, thereby promoting the vaporization of the working fluid. In this case, a means of roughening the surface can be employed, such as coating (electrodeposition) with a powder such as diamond, which has high thermal conductivity.

[0029] Figure 5 shows the individual components of the slit electrode 15. This slit electrode 15 is constructed by attaching the ends of multiple electrode plates 15b to two opposing sides in the longitudinal direction of a rectangular support frame 15a. The base end of each electrode plate 15b on the support frame 15a side is open in a slit shape to form a passage 15c for the working fluid. As shown in Figure 5(B), one of the electrode plates 15b has a gripping portion 15d that protrudes upward integrally molded into it.

[0030] Each of the aforementioned electrode plates 15b is attached to the support frame 15a so as to be parallel to each other at equal intervals, and each electrode plate 15b is formed into a rectangular plate shape with the same thickness. The material constituting the electrode plates 15b is not particularly limited as long as it is a conductive material, and metals or alloys such as copper or aluminum can be used, similar to the materials of the heat receiving body 14 and fins 14a. In this embodiment, the entire slit electrode 15, including the electrode plate 15b and support frame 15a, is made of aluminum. The reason for this will be explained later.

[0031] Figure 4 shows the state in which each electrode plate 15b of the slit electrode 15 is inserted between a plurality of fins 14a formed on the heat receiving body 14. In this embodiment, when the distance between each fin 14a formed on the heat receiving body 14 is a, the thickness of each fin 14a is b, the distance between the fin 14a and the electrode plate 15b is c, and the distance between the lower end of the electrode plate 15b and the heat receiving body 14 is d, The dimensions are set to a=1.7mm, b=0.5mm, c=0.6mm, and d=0.6mm. Furthermore, when the distance between each electrode plate 15b in the slit electrode 15 shown in Figure 5(C) is e and the thickness of each electrode plate 15b is f, e=1.7mm and f=0.5mm are set.

[0032] In this embodiment, the plurality of fins 14a formed on the heat receiving body 14 are each formed in the shape of a flat plate with equal thickness (b) and are arranged at equal intervals (a), and the plurality of electrode plates 15b formed on the slit electrode 15 are each formed in the shape of a flat plate with equal thickness (f) and are arranged at equal intervals (e), and each fin 14a and each electrode plate 15b inserted between each fin 14a in a non-contact state are arranged parallel to each other and at equal intervals (c).

[0033] The values ​​a to e mentioned above are not particularly limited, as the optimal values ​​will differ depending on factors such as the voltage applied between the slit electrode 15 and the heat receiving body 14, and the flow velocity of the working fluid. However, in this embodiment, the values ​​were selected based on the values ​​that are currently machinable when the fins 14a of the heat receiving body 14 are formed by machining. Then, as shown in Figure 4, the output voltage from the DC power supply 17 is applied between the electrode plate 15b of the slit electrode 15 and the fin 14a of the heat receiving body 14, thereby creating an electric field as shown by the dashed electric field lines.

[0034] Figure 6 is a cross-sectional view of the first case 12, as seen in the direction of the arrow from line II in Figure 3. As shown in Figure 6, the first case 12 has guide passages 12c formed from the working fluid inlet 12b to both ends of the base portion of the multiple fins 14a erected on the heat receiving body 14, respectively, for guiding the working fluid. Therefore, the working fluid supplied to the working fluid inlet 12b splits into left and right channels as shown by the dashed line and is guided to both ends of each fin 14a via the guide passage 12c. The working fluid is then supplied along the base of each fin 14a toward the central part of each fin 14a, as shown by the arrows. As a result, the working fluid receives heat from the heat receiving element 14 and each fin 14a, boils, and vaporizes. The latent heat of vaporization at this time can be used to effectively cool the heat generating element 21.

[0035] The working fluid is preferably one that boils below the upper limit of the allowable temperature of the heating element 21. For example, if it is desired to maintain the heating element 21 at 60°C or below, a working fluid with a boiling point below 60°C is used. Furthermore, considering safety, a working fluid that is non-flammable or has low flammability is preferred, as is one that is low in toxicity and has low conductivity. In this embodiment, AGC refrigerant code HCFO-1224yd can be suitably used as the working fluid. This is an organic solvent with hydrochlorofluoroolefin (specifically, (Z)-1-chloro-2,3,3,3-tetrafluoropropene) as a single component, and has a low standard boiling point of 15°C and high thermal and chemical stability.

[0036] It is desirable that the aforementioned DC power supply 17 be configured so that its output voltage can be switched in stages from 500V to 3000V. Furthermore, in order to generate an electric field using the DC power supply 17, it is sufficient to create a potential difference between the electrode plate 15b of the slit electrode 15 and the fin 14a of the heat receiving body 14. Therefore, it is generally not necessary to distinguish and connect the positive (+) and negative (-) terminals of the DC power supply 17.

[0037] However, in this embodiment, the electrode plate 15b of the slit electrode 15 is prone to electric field concentration and therefore poses a high risk of discharge. For this reason, the entire slit electrode 15 is made of aluminum, and an anodized treatment is applied to the entire surface of the slit electrode 15 to form an electrically insulating layer. In this case, since the anodized aluminum may have its oxide film peeled off when a negative potential (-) is applied, the positive (+) terminal of the DC power supply 17 is connected to the slit electrode 15, and the negative (-) terminal is connected to the heat receiving body 14, while the negative (-) terminal is also connected to the reference potential point (ground) of the cooling unit 11.

[0038] Figure 7 illustrates the effect of reducing thermal resistance due to the electric field generated by applying a DC voltage between the fins 14a of the heat receiving body 14 and the electrode plate 15b of the slit electrode 15. In Figure 7, the electric field lines representing the electric field are shown as dashed lines. In Figure 7, the parts corresponding to those shown in Figure 4 are indicated by the same reference numerals, and therefore, a detailed explanation of them is omitted.

[0039] The working fluid supplied by the pump 41 is delivered to the base of a plurality of fins 14a erected on the heat receiving body 14, as indicated by the symbol F in Figure 7, via the working fluid conduit 12c shown in Figure 6. Meanwhile, heat from the heat generating element 21 is transferred to the base of the fins 14a, causing the working fluid to immediately boil and evaporate, forming a vaporization space at the base of the fins 14a. The vapor B generated by boiling tries to remain between the fin 14a and the electrode plate 15b due to surface tension. However, due to the action of the electric field generated between the fin 14a and the electrode plate 15b, an electrostatic pressure, indicated by arrow P, is generated at the gas-liquid interface between the vapor and liquid of the working fluid, i.e., on the surface of the vapor B.

[0040] In this state, the pump 41 also applies pressure to deliver the working fluid, so the vapor B of the working fluid is transported from the vaporization space at the base of the fin 14a through the slit of the slit electrode 15 (working fluid passage 15c) into the second case 13 shown in Figure 3, together with the liquid working fluid. As a result, the working fluid (liquid) is constantly drawn and supplied to the surface (boiling surface) at the base of the fin 14a facing the electrode plate 15b due to the action of the electric field described above, promoting boiling and improving the heat transfer coefficient (h). The gas and liquid working fluid transported into the second case 13 are then sent to the radiator 31 as a gas-liquid two-layer flow, where they condense and are returned to a liquid working fluid state.

[0041] Incidentally, the cooling effect of the cooling unit 11 on the aforementioned heat-generating element 21 depends on the degree to which the thermal resistance (R) decreases when heat is transferred from the boiling surface to the working fluid. The thermal resistance (R) can be determined by the reciprocal of the heat transfer coefficient (h) due to the application of an electric field and the heat dissipation area (Aw) of the fins 14a of the heat receiving element 14. R = 1 / hAw …… Equation 1

[0042] Therefore, according to the cooling device and cooling unit of this invention, the increase in the heat dissipation area (Aw) due to the multiple fins 14a erected on the heat receiving body 14 and the improvement in the heat transfer coefficient (h) due to the increase in the area where the electric field is formed work synergistically, and the effect of reducing thermal resistance (R) can be fully demonstrated. This enables high cooling efficiency for the heat-generating element 21, making it possible to provide a cooling device and cooling unit that allows for miniaturization of the entire device.

[0043] The examples shown in Figures 8 to 10 represent the first to third embodiments of the cooling unit 11 described above, with further consideration given to the heat transfer coefficient (h). Figures 8 to 10, which show the first to third embodiments, illustrate the relationship between a pair of fins 14a established on the heat receiving body 14 and the electrode plate 15b of the slit electrode 15 inserted between them, in partially enlarged cross-sectional views. Electric field lines indicating the electric field are shown as dashed lines. Furthermore, the first embodiment shown in Figure 8 has already been explained based on Figures 3 and 4, etc., and therefore Figure 8 is provided as an example to illustrate the technical issues regarding the heat transfer coefficient (h) in the first embodiment.

[0044] Furthermore, regarding the effect of improving the heat transfer coefficient (h) according to the first to third embodiments shown in Figures 8 to 10, it is necessary to understand that dielectrophoretic force is at work, causing liquid to be attracted and move to areas with a strong electric field, and vapor to be attracted and move to areas with a weak electric field. Therefore, in the first embodiment shown in Figure 8, as already explained, the multiple fins 14a formed on the heat receiving body 14 are each formed in the shape of a flat plate with equal thickness and are arranged at equal intervals, and the multiple electrode plates 15b formed on the slit electrode 15 are each formed in the shape of a flat plate with equal thickness and are arranged at equal intervals. Thus, each fin 14a and the electrode plates 15b inserted between each fin 14a in a non-contact state are arranged parallel to each other and at equal intervals.

[0045] According to the configuration shown in Figure 8, the rising portion of the fin 14a erected on the heat receiving body 14 (near the corner at the base) is a region where the electric field is weaker compared to other parts because the distance from the electrode plate 15b of the slit electrode 15 is larger. According to this, because a dielectrophoretic force acts on the boiling working fluid vapor B in the direction indicated by the white arrow, vapor B tends to accumulate near the upper surface of the heat receiving body 14, including the rising portion of the fins 14a. Depending on the amount of working fluid introduced by the pump 41, for example, there is a concern that dryout may occur at the rising portion of the fins 14a. Therefore, in the event that dryout actually occurs, the upper surface portion of the heat receiver 14, indicated by the symbol D in Figure 8, carries the risk of hindering the effect of improving the heat transfer coefficient (h) by the working fluid.

[0046] Next, in the second embodiment shown in Figure 9, the multiple fins 14a formed on the heat receiving body 14 are arranged at equal intervals with their thickness gradually decreasing from the base to the other end, and the multiple electrode plates 15b formed on the slit electrode 15 are formed as flat plates of equal thickness and arranged at equal intervals. Therefore, the distance between each fin 14a and each electrode plate 15b inserted between each fin 14a in a non-contact state is configured to gradually increase from the base to the other end of each fin 14a.

[0047] In this configuration, the region where the fin 14a and the electrode plate 15b face each other increases in distance towards the top, so the electric field in this upper region is distributed in such a way that it transitions from strong to weak. Therefore, the dielectrophoretic force indicated by the upward-pointing white arrow acts on the boiling working fluid vapor B, promoting the exhaust effect of vapor B and improving the heat transfer coefficient (h) of the working fluid.

[0048] On the other hand, in the second embodiment shown in Figure 9, the rising portion of the fin 14a erected on the heat receiving body 14, i.e., the portion indicated by the symbol C, is far from the electrode plate 15b of the slit electrode 15, similar to the first embodiment shown in Figure 8, and this is a region where the electric field is weaker compared to other parts. Therefore, the dielectrophoretic force acts on the boiling working fluid vapor B in the direction indicated by the white arrow, resulting in a low vapor discharge effect and insufficient improvement in the heat transfer coefficient (h) by the working fluid.

[0049] In the third embodiment shown in Figure 10, the multiple fins 14a formed on the heat receiving body 14 are arranged at equal intervals, with their thickness gradually decreasing from the base to the other end, and the multiple electrode plates 15b formed on the slit electrode 15 are formed as flat plates of equal thickness and are arranged at equal intervals. Therefore, the distance between each fin 14a and each electrode plate 15b inserted between each fin 14a in a non-contact state gradually increases from the base of each fin 14a to the other end (upper part). In addition, a configuration is adopted in which an arc-shaped groove R is formed along the base of each adjacent fin 14a.

[0050] With this configuration, the distance between the fin 14a and the electrode plate 15b increases towards the top in the region where they face each other. As a result, similar to the second embodiment shown in Figure 9, the steam B discharge effect is promoted, and the heat transfer coefficient (h) by the working fluid can be improved. Furthermore, since an arc-shaped groove R is formed along the base of each adjacent fin 14a, the distance between the heat receiving body 14 and the electrode plate 15b at the bottom inevitably decreases. As a result, the electric field near the arc-shaped groove R becomes stronger and more uniform than in the upper region where the fins 14a and electrode plate 15b face each other.

[0051] Therefore, as indicated by the white arrow, a dielectrophoretic force acts upward on the vapor B of the working fluid generated near the arc-shaped groove R, enabling efficient discharge of vapor B. This makes it possible to further improve the heat transfer coefficient (h) of the working fluid and achieve a high reduction in thermal resistance (R).

[0052] In the first to third embodiments shown in Figures 8 to 10, each has the advantages and disadvantages described above when comparing the effect of improving the heat transfer coefficient (h). However, in the cooling units 11 of these first to third embodiments, the effect of improving the heat transfer coefficient (h) by increasing the heat dissipation area (Aw) and the electric field formation area can be greatly improved compared to the cooling unit disclosed in Patent Document 1, which was cited as a prior example. As described above, this makes it possible to miniaturize the entire device and to provide a cooling device and cooling unit that have high cooling efficiency for heat-generating elements.

[0053] In the embodiments described above, the outer casing of the cooling unit 11 is constructed by stacking a second case 13 on top of a first case 12. However, the first case 12 and the second case 13 can also be integrally molded. [Industrial applicability]

[0054] Because the cooling device and cooling unit according to this invention have high cooling efficiency, they can be suitably used for cooling electronic components with high heat density, such as laser diodes used as light sources for large projectors as exemplified at the beginning, power semiconductors used for driving control in electric vehicles, or highly integrated microprocessing units (MPUs) used in computers. [Explanation of Symbols]

[0055] 10 Cooling device 11 Cooling Unit 12. First Case 12a Spacer 12b Working fluid inlet 12c Working fluid conduit 13. Second Case 13a Working fluid outlet 14 Heat receiver 14a Fin 15 Slit electrode 15a Support frame 15b Electrode plate 15c slit (working fluid passage) 15d grip part 17 DC power supply 21 Heating element 31 Heat radiator (heat exchanger) 32 Fans 41 pumps 51 Pipe members B. Working fluid vapor R-shaped arc groove

Claims

1. A cooling unit that cools a heat-generating element by receiving heat from the element and causing at least a portion of the working fluid to change from the liquid phase to the gas phase, The cooling unit includes a heat sink that cools the working fluid by receiving it after it has undergone a phase change, thereby liquefying and condensing the working fluid, A pump that sends the working fluid liquefied by the heat sink to the cooling unit, A cooling device comprising a cooling unit and a heat sink, wherein the working fluid is circulated between the cooling unit and the heat sink, The cooling unit includes a metal heat receiver that receives heat from the heating element on one side and vaporizes the working fluid supplied to the base of each of the fins by having a plurality of fins erected on the other side, A metal slit electrode having a plurality of electrode plates inserted in a non-contact state between a plurality of fins formed on the heat receiving body, with the base end of each electrode plate open in a slit shape to form a passage for the working fluid, A DC power supply is used to generate an electric field between the fins of the heat receiving body and the electrode plate of the slit electrode by applying a DC voltage between the heat receiving body and the slit electrode, respectively, by alternately applying a DC voltage between the heat receiving body and the slit electrode. A cooling device characterized by being equipped with [a certain feature].

2. A cooling unit that cools a heat-generating element by receiving heat from the element and causing at least a portion of the working fluid to undergo a phase change from the liquid phase to the gas phase, The cooling unit includes a metal heat receiver that receives heat from the heating element on one side and vaporizes the working fluid supplied to the base of each of the fins by having a plurality of fins erected on the other side, A metal slit electrode having a plurality of electrode plates inserted in a non-contact state between a plurality of fins formed on the heat receiving body, with the base end of each electrode plate open in a slit shape to form a passage for the working fluid, A first case holds the heat receiving element and the slit electrode, with one side of the heat receiving element serving as the bottom surface and forming an inlet for the working fluid, A second case that covers the slit electrode and is superimposed on the first case, or molded integrally with the first case, and forms the outlet for the working fluid, A DC power supply is used to generate an electric field between the fins of the heat receiving body and the electrode plate of the slit electrode by applying a DC voltage between the heat receiving body and the slit electrode, respectively, by alternately applying a DC voltage between the heat receiving body and the slit electrode. A cooling unit characterized by having the following features.

3. The plurality of fins formed on the heat receiving body are each formed in the shape of a flat plate with equal thickness and arranged at equal intervals, and the plurality of electrode plates formed on the slit electrode are each formed in the shape of a flat plate with equal thickness and arranged at equal intervals, The cooling unit according to claim 2, characterized in that each of the fins and each electrode plate inserted between each of the fins in a non-contact state are arranged parallel to each other and at equal intervals.

4. The plurality of fins formed on the heat receiving body are arranged at equal intervals, with their thickness gradually decreasing from the base to the other end, and the plurality of electrode plates formed on the slit electrode are each formed as flat plates of equal thickness and arranged at equal intervals. The cooling unit according to claim 2, characterized in that the distance between each fin and each electrode plate inserted between each fin in a non-contact state is gradually increased from the base of each fin toward the other end.

5. The plurality of fins formed on the heat receiving body are arranged at equal intervals, with their thickness gradually decreasing from the base to the other end, and the plurality of electrode plates formed on the slit electrode are each formed as flat plates of equal thickness and arranged at equal intervals. The distance between each fin and each electrode plate inserted between each fin in a non-contact state is gradually increased from the base of each fin toward the other end. Furthermore, the cooling unit according to claim 2, characterized in that an arc-shaped groove is formed between the base portions of adjacent fins, along the base portions.

6. The cooling unit according to claim 2, wherein the first case has guide passages formed to lead the working fluid from the working fluid inlet to both ends of the base portions of a plurality of fins erected on the heat receiving body.

7. The slit electrode is made of aluminum, and an anodized insulating layer is formed on the entire surface of the slit electrode. The cooling unit according to any one of claims 2 to 6, wherein the positive electrode voltage of the DC power supply is applied to the electrode plate of the slit electrode, and the negative electrode voltage is applied to the fins of the heat receiving body.

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