JP6329064B2 - Heat spreader - Google Patents

Description

  The present invention relates to a heat diffusion device using an EHD fluid that flows as a cooling medium by an electrohydrodynamic phenomenon.

2. Description of the Related Art Conventionally, a thermal diffusion device (cooling device) that cools a heating element using an EHD fluid that flows due to an electrohydrodynamics phenomenon as a cooling medium is known.
The cooling device disclosed in Patent Document 1 uses an electrically sensitive working medium, which is a kind of EHD fluid, as a cooling medium, and applies voltage to at least a pair of electrodes, thereby making the electrically sensitive working medium a heat absorbing part and a heat radiating part. The pump mechanism that moves between them is realized with a simple configuration.

JP 2000-2222072 A

The cooling device of Patent Document 1 improves the cooling efficiency of a CPU or the like of a personal computer and contributes to a reduction in thickness. However, the electrically sensitive working medium used for this cooling device has a problem that the heat transfer coefficient is low.
The present invention has been made in view of the above-described problems, and an object thereof is to provide a thermal diffusion device that improves the heat transfer coefficient between an insulating substrate or electrode in contact with a heating element and an EHD fluid.

The thermal diffusion device of the present invention includes an EHD fluid, a flow path forming member, at least a pair of electrodes including a first electrode and a second electrode, an alternating voltage supply device, and dielectric fine particles.
The EHD fluid can flow as a cooling medium by an electrohydrodynamic phenomenon.
The flow path forming member forms a flow path in which the EHD fluid is filled so as to be flowable.
The at least one pair of electrodes includes a first electrode that is disposed in the flow path along the flow path direction and has a sharp tip in the flow path direction, and a second electrode that has a gap penetrating in the flow path direction. When voltages having different polarities are applied to the first electrode and the second electrode, an EHD fluid flow is generated from the tip of the first electrode toward the gap between the second electrodes.

  The alternating voltage supply device can apply a voltage whose polarity is alternately reversed over time to the first electrode and the second electrode. The alternating voltage supply device may be configured by combining a DC power source and a polarity inverting device that reverses the voltage application direction of the DC power source, or may be configured by an AC power source.

The charged dielectric fine particles are added so as to float in the EHD fluid.
For example, the dielectric fine particles are resin or ceramic particles. The size of the dielectric fine particles is preferably smaller than the narrowest gap of the gap between the second electrodes, and the specific gravity of the dielectric fine particles is 0.5 to 2.0 times the specific gravity of the EHD fluid. preferable.

  With the above configuration, in the thermal diffusion device of the present invention, there are a first voltage mode in which the first electrode is a negative electrode and the second electrode is a positive electrode, and a second voltage mode in which the first electrode is a positive electrode and the second electrode is a negative electrode. Repeated alternately. Then, the charged dielectric fine particles added to the EHD fluid repeatedly adhere to the first electrode and the second electrode and release to the EHD flow. As a result, the heat transfer rate between the insulating substrate and the electrode and the EHD fluid can be improved by making the EHD flow around the electrode pair that also functions as a heat radiation fin a turbulent flow.

1 is an overall configuration diagram of a thermal diffusion device according to an embodiment of the present invention. The II-II sectional view taken on the line of FIG. 1 which shows the internal structure of a thermal-diffusion apparatus. The III-III sectional view taken on the line of FIG. 2 which shows the internal structure of a thermal-diffusion apparatus. The figure which shows the structure of the EHD pump in the flow path of the thermal diffusion apparatus of FIG. The elements on larger scale of FIG. 4 explaining the flow of the EHD fluid in a 1st voltage mode. The elements on larger scale of FIG. 4 explaining the flow of the EHD fluid in 2nd voltage mode. The figure which shows the preferable specific gravity ratio of a dielectric microparticle and an EHD fluid. The figure explaining the heat transfer rate improvement effect in the thermal diffusion apparatus by one Embodiment of this invention.

  Hereinafter, a thermal diffusion device according to an embodiment of the present invention will be described with reference to the drawings. The figure used here is a schematic diagram for facilitating understanding of the features of the present invention. For this reason, the size and the like of some components are exaggerated and do not accurately reflect the dimensional ratios in actual products. Moreover, illustrations of parts other than the characteristic configuration of the present invention are omitted or simplified.

(One embodiment)
About the thermal diffusion apparatus by one Embodiment of this invention, after describing the whole structure first with reference to FIGS. 1-3, the characteristic structure and effect of a detailed part are demonstrated with reference to FIGS. To do. This heat diffusing device is a device that cools a heating element using an EHD fluid that flows due to an electrohydrodynamics phenomenon as a cooling medium, and is applied to, for example, a CPU of a personal computer or an electronic control unit (ECU) for a vehicle. The
In this embodiment, it is assumed that an electric field conjugate fluid (Electro-Conjugate Fluid, ECF) which is a kind of EHD fluid is used. A specific example of the ECF is described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-222072) and the like, and thus description thereof is omitted here.

FIG. 1 shows an external configuration of the thermal diffusion device of the present embodiment. 2 shows the internal configuration of the II-II cross section of FIG. 1, and FIG. 3 shows the internal configuration of the III-III cross section of FIG.
As shown in FIG. 1, the heat diffusing device 31 includes a cooling unit 32 for cooling the heating element 36, a heat radiating unit 33 for releasing heat transmitted from the cooling unit 32 using the EHD fluid as a medium, And the connection part 35 which connects between the cooling part 32 and the thermal radiation part 33 is included.

The cooling unit 32, the heat radiating unit 33, and the connecting unit 35 are each formed with a flow path for carrying an EHD fluid. In the following, the reference numeral including the EHD fluid flow paths is “14”, and the reference numerals 141 to 145 are assigned to the respective flow paths (see FIGS. 2 and 3).
The EHD fluid in the flow path 14 flows in a predetermined direction by applying a voltage from the power source 38 to the electrode pair 15 shown in FIGS. Therefore, the electrode pair 15 is regarded as one pump mechanism and is also referred to as “EHD pump (or ECF pump) 15”. The number and arrangement of the EHD pumps 15 shown in FIG. 2 and FIG. 3 are examples, and in practice, an appropriate number of EHD pumps 15 are installed at appropriate locations in the flow path 14.
Further, the power source 38 of the present embodiment is configured by combining the DC power source 18 and the polarity inverting device 19. Detailed configurations and operations of the electrode pair 15 and the power source 38 will be described later.

As shown in FIG. 1, communication channels 141 and 142 are formed inside the connecting portion 35 so that the EHD fluid is bidirectionally transferred between the cooling portion 32 and the heat radiating portion 33.
The cooling unit 32 and the heat radiating unit 33 each include a plurality of casings 34 in which flow paths 143 to 145 (see FIGS. 2 and 3) through which EHD fluid is carried are formed. A heating element 36 to be cooled is inserted between the plurality of casings 34 of the cooling unit 32. Air cooling fins 37 are installed between the plurality of casings 34 of the heat radiating portion 33. The number of casings 34 can be determined as appropriate depending on the number of heating elements 36 and air-cooling fins 37, the amount of heat generation, the device scale, and the like.

  The configuration of the flow path 14 in the casing 34 will be described with reference to FIGS. The casing 34 is configured using an external plate 41 that forms the outside and an internal plate 42 that partitions the space inside the external plate 41. As shown in FIG. 2, the flow path 14 in the casing 34 includes vertical flow paths 143 and 145 and a horizontal flow path 144.

  In FIG. 2, the EHD fluid that has flowed in from the flow path 142 of the connecting portion 35 flows upward in the vertical flow path 143 on the left side of the drawing as indicated by an arrow fu, and is divided to flow into a plurality of horizontal flow paths 144. And flows sideways as indicated by arrow fh. The flows of the plurality of lateral flow paths 144 merge, and the EHD fluid flows downward in the vertical flow path 145 on the right side of the figure as indicated by an arrow fd and is discharged to the communication flow path 141 of the connecting portion 35. .

As shown in FIG. 3, the EHD fluid discharged from the longitudinal flow paths 145 of the plurality of casings 34 of the cooling unit 32 merges and flows through the communication flow path 141 in the direction of the arrow fa.
Thus, the heat radiated from the heating element 36 in the cooling section 32 passes through one communication flow path (outward path) 141 of the connecting section 35 from the cooling section 32 to the heat radiating section 33 by the EHD fluid. Carried.

The flow path 14 in the casing 34 of the heat radiating part 33 is configured similarly to the flow path 14 of the cooling part 32 shown in FIG. The heat of the heating element 36 carried from the cooling unit 32 is released into the air by the air cooling fins 37 installed between the casings 34 of the heat radiating unit 33.
The cooled EHD fluid is conveyed to the cooling unit 32 through the other communication channel (return channel) 142 of the connecting unit 35 as indicated by an arrow fb. The heat diffusion device 31 cools the heating element 36 adjacent to the casing 34 of the cooling unit 32 by the EHD fluid performing such a circulation operation.

Next, a detailed configuration of the electrode pair (EHD pump) 15 will be described with reference to FIG. FIG. 4A is a schematic view viewed from above the flow path 14, and FIG. 4B is a schematic cross-sectional view viewed from the side of the flow path 14.
Assuming that the lower side of FIG. 4B is the lower side in the gravity direction, the bottom surface of the flow path 14 is constituted by the insulating substrate 13. The insulating substrate 13 is in direct contact with the electrode pair 15 on the flow path 14 side, and has an insulating property so that the voltage applied to the electrode pair 15 does not short-circuit. The insulating substrate 13 is in contact with the heating element 36 on the side opposite to the flow path 14. For example, a grease-like or sheet-like heat conducting material may be interposed between the insulating substrate 13 and the heating element 36.

The side surface and the ceiling surface of the flow channel 14 are constituted by the flow channel wall 12. Since the flow path wall 12 has a function as a heat radiating fin, the flow path wall 12 is formed of a material having a high thermal conductivity such as a metal similar to the electrode pair 15. The flow path wall 12 is electrically insulated from the electrode pair 15 via the insulating substrate 13.
Here, the flow path wall 12 and the insulating substrate 13 correspond to a “flow path forming member” recited in the claims, and constitute the casing 34 in relation to FIGS. 1 to 3. The flow path 14 is partitioned into a width Wp and a height Hp by the flow path wall 12 and the insulating substrate 13.

The pair of electrodes 15 includes a needle electrode 16 and a slit electrode 17 disposed on the insulating substrate 13. The needle-like electrode 16 as the “first electrode” has a sharp tip in the flow path direction. The slit electrode 17 as the “second electrode” has a slit-like gap penetrating in the flow path direction.
The slit electrode 17 may be divided into two pillar portions 171 and 172 facing each other with a gap (denoted only by the left electrode pair 15 in FIG. 4A). Or two pillar parts may be connected by the bottom, for example. Hereinafter, the form of division or connection of the two pillar portions 171 and 172 is not referred to, and is simply described as “slit electrode 17”.
Further, the needle-like electrode 16 and the slit electrode 17 also function as a heat radiating fin.

  As shown in FIG. 4B, the needle electrode 16 and the slit electrode 17 are applied with the voltage of the DC power source 18 through the polarity inversion device 19. In the present embodiment, the DC power supply 18 and the polarity reversing device 19 are combined to form an “alternating voltage supply device” described in the claims, and in FIG. .

  Here, the voltage of the DC power supply 18 is a high voltage of, for example, several tens of volts to several tens of kV. The polarity inverting device 19 inverts the voltage polarity output to the output terminals OA and OB by switching the connection between the input terminals IA and IB on the DC power supply 18 side and the output terminals OA and OB on the electrode pair 15 side. In the present embodiment, the polarity reversing device 19 reverses the voltage polarity periodically (for example, at intervals of several seconds) during the operation of the thermal diffusion device 31.

  The needle electrodes 16 of the plurality of electrode pairs 15 are connected to one output end OA of the polarity inverting device 19, and the slit electrode 17 of the plurality of electrode pairs 15 is connected to the other output end OB of the polarity inverting device 19. . As a result, voltages having different polarities are applied to the needle electrode 16 and the slit electrode 17 of each electrode pair. In addition, voltages having the same polarity are applied to the needle electrodes 16 of the plurality of electrode pairs 15 and the slit electrode 17.

  Next, the operation of this embodiment will be described with reference to FIGS. Each of FIG. 5 and FIG. 6 (a) is a schematic view seen from above the flow path 14, and each (b) is a schematic cross-sectional view seen from the side of the flow path 14, respectively. This corresponds to a partially enlarged view of FIG.

  FIG. 5 shows a state in which the voltage of the DC power source 18 is applied by switching the polarity reversing device 19 so that the needle electrode 16 is a negative electrode and the slit electrode 17 is a positive electrode. This state is referred to as a “first voltage mode”. That's it. FIG. 6 shows a state in which the voltage of the DC power source 18 is applied by switching the polarity reversing device 19 so that the needle electrode 16 is a positive electrode and the slit electrode 17 is a negative electrode. This state is referred to as a “second voltage mode”. That's it.

  In FIG. 5 and FIG. 6, the broken line arrow f indicates the flow of the EHD fluid F. The EHD fluid F passes from the upstream side (the left side in the figure) to the center of the flow path 14 along the tapered shape at the tip of the needle electrode 16 after passing through both the left and right sides of the needle electrode 16, and the slit electrode 17 Pass the gap toward the downstream side (right side in the figure). That is, the direction in which the EHD fluid F flows is constant in both the first voltage mode and the second voltage mode.

In the present embodiment, the charged dielectric fine particles D are added to the EHD fluid F in advance. The dielectric fine particles D are dielectric particles, and for example, resin such as PMMA (polyethyl methacrylate) or ceramic particles can be used. The dielectric fine particles D preferably have a thermal conductivity equal to or higher than that of the EHD fluid F.
In FIGS. 5 and 6, the negatively charged dielectric fine particles D are suspended in the EHD fluid F within the flow path 14. The number of dielectric fine particles D in the figure is for schematically representing the distribution of positions in the flow path and the relative relationship between FIG. 5 and FIG. 6, and reflects the actual number. is not.

In the first voltage mode shown in FIG. 5, the negatively charged dielectric fine particles D do not adhere to the needle-like electrode 16 that is the negative electrode, but adhere to the slit electrode 17 that is the positive electrode.
On the other hand, in the second voltage mode shown in FIG. 6, the negatively charged dielectric fine particles D adhere to the needle-like electrode 16 that is the positive electrode. Further, the dielectric fine particles D adhering to the slit electrode 17 in the first voltage mode are discharged into the EHD fluid F from the slit electrode 17 turned to the negative electrode, and flow downstream through the gap of the slit electrode 17.
Thereafter, when the first voltage mode is entered again, the dielectric fine particles D adhering to the needle electrode 16 in the second voltage mode are released into the EHD fluid F from the needle electrode 16 turned to the negative electrode.

  In this way, by applying a voltage whose polarity is alternately reversed to the needle-like electrode 16 and the slit electrode 17, the charged dielectric fine particles D adhere to the electrodes 16 and 17 and enter the EHD fluid F. The release is repeated. Thereby, a turbulent flow is generated in the EHD flow around the electrode pair 15, and the temperature boundary layer is disturbed. In other words, the temperature boundary layer is destroyed and reduced. As a result, the heat transfer coefficient between the insulating substrate 13 and the electrodes 16 and 17 and the EHD fluid F is improved.

Next, preferable conditions for the size and specific gravity of the dielectric fine particles D will be described.
The size of the dielectric fine particle D is larger than the narrowest interval We (see FIGS. 5A and 6A) of the gap of the slit electrode 17 so that the dielectric fine particle D can flow through the gap of the slit electrode 17. Small is preferable. For example, when the minimum dimension of the slit that can be processed at the time of manufacturing the slit electrode 17 is 200 μm, the size (particle diameter) of the dielectric fine particles D is preferably defined to be less than 200 μm.

  Further, it is preferable that the dielectric fine particles D float in the liquid without sinking downward in the direction of gravity in the flow of the EHD fluid F or floating on the liquid surface. Therefore, a preferable condition is defined using a specific gravity ratio, which is “the specific gravity of the dielectric fine particles D relative to the specific gravity of the EHD fluid F”, as a parameter. It is clear that ideally, the specific gravity ratio is closer to 1 and better.

  As shown in FIG. 7, a peak-shaped characteristic diagram can be obtained by plotting the “sustainable continuation time of the dielectric fine particles D” against the specific gravity ratio in consideration of the assumed flow velocity. That is, the smaller the specific gravity ratio is, the easier it is to float on the liquid surface, and the larger the specific gravity ratio is, the easier it is to settle down in the direction of gravity. Then, it can be seen that when the specific gravity ratio is in the range of “0.5 or more and 2.0 or less”, the floating continuation time of the dielectric fine particles D is not less than the minimum time Tmin that can be used in this embodiment. Therefore, it is preferable that the specific gravity of the dielectric fine particles D is defined to be not less than 0.5 times and not more than 2.0 times the specific gravity of the EHD fluid.

  By the way, the prior invention by the inventor of the present application disclosed in Japanese Patent Application Laid-Open No. 2013-18789 is to separate the fine particles, which are foreign matters attached to the electrode of the EHD pump, by reversing the polarity of the voltage applied to the electrode. is there. For example, it may seem that the prior invention and the present invention are common in that the polarity of the voltage is reversed. Therefore, differences between the prior invention and the present invention will be described.

  First, with respect to the fine particles in the EHD fluid, the fine particles of the prior invention are “foreign substances” which are naturally generated after the intention as a result of the flow of the EHD fluid over a certain period of time. The foreign fine particles are naturally charged by friction during flow, and the size and specific gravity are likely. Of course, it is unknown whether the heat transfer coefficient is large or small with respect to the EHD fluid. And it should be removed in order to prevent it from adhering to the electrode and having an adverse effect.

  On the other hand, the dielectric fine particles D used in the present invention are intentionally charged in advance and added to the EHD fluid F. The dielectric fine particles D preferably have a large heat transfer coefficient with respect to the EHD fluid, and the size and specific gravity are defined within a preferable range as described above. Of course, it is not positively removed like the foreign particle of the prior invention.

  Next, with respect to voltage polarity reversal, in the prior invention, in order to peel off the foreign particles from the electrode, the voltage polarity is reversed only for a short time at a certain time interval (for example, during operation, it is reversed for 3 seconds at 1 hour intervals). Yes, and the voltage polarity during other operations is constant.

On the other hand, in the present invention, the voltage polarity applied to the electrodes 16 and 17 is always reversed during operation. For example, the voltage polarity is periodically reversed at 10-second intervals. Thereby, the turbulent flow generation effect by the desorption of the dielectric fine particles D to the electrodes 16 and 17 can be effectively maintained.
Thus, the prior invention and the present invention are clearly different in technical idea.

Next, the effect of this embodiment will be described with reference to FIG. Here, the heat transfer coefficient in the laminar flow state and the turbulent flow state at the same flow velocity is estimated by calculation. The flow rate is 0.07 m / s.
First, as a comparative example, the heat transfer coefficient is calculated when only the EHD fluid flows in a laminar flow without performing “addition of dielectric fine particles D” and “polarity inversion of applied voltage to electrodes”. Calculation is performed with a circular tube having an inner diameter of 10 mm so that the Reynolds number Re satisfies the laminar flow condition (Re = 1066 <2300). From the laminar heat transfer equation, the heat transfer coefficient α = 230.1 [W / (m ² · K)] is calculated.

On the other hand, the heat transfer coefficient in the present embodiment in which a turbulent flow state is generated by alternating the applied voltage of the electrode pair 15 and repeatedly attaching and detaching the dielectric fine particle D to the electrode pair 15 is calculated. Calculation is performed with a circular tube having an inner diameter of 50 mm so that the Reynolds number Re satisfies the turbulent flow condition (Re = 5332> 2300). From the turbulent heat transfer equation, the heat transfer coefficient α = 557.1 [W / (m ² · K)] is calculated.
As a result of the calculation, as shown in FIG. 8, it can be seen that the heat transfer coefficient differs by two times or more depending on whether the flow is laminar or turbulent at the same flow rate. Thus, the heat diffusing device 31 of this embodiment can remarkably improve a heat transfer rate with respect to the comparative example corresponding to a prior art.

(Other embodiments)
(Overall configuration of thermal diffusion device)
The whole structure shown in FIGS. 1-3 in the said embodiment is an example to the last. For example, the number of channels and the size of the channels can be determined by several conditions such as the type of EHD fluid, the material of the casing, the amount of heat generated by the heating element, and the capability of the EHD pump. Further, the number and arrangement interval of EHD pumps installed in the flow path can be set in consideration of these conditions.

(EHD fluid, dielectric fine particles)
The EHD fluid F used in the heat diffusion device of the present invention is not limited to the ECF, and any EHD fluid may be used. Further, the dielectric fine particles D can be charged and float in the EHD fluid F, and any material and type can be used as long as they satisfy the conditions described in the above-described embodiment with respect to size and specific gravity.

(First electrode, second electrode)
In the above embodiment, the needle electrode 16 is exemplified as the “first electrode having a sharp tip in the flow path direction”, and the slit electrode 17 is illustrated as the “second electrode having a gap penetrating in the flow path direction”. As an example of the first electrode and the second electrode, electrodes having the shapes disclosed in FIGS. 6 and 7 of JP2013-18789A may be employed.

(Alternating voltage supply device)
As an “alternating voltage supply device capable of applying a voltage whose polarity is alternately reversed over time with respect to the first electrode and the second electrode”, the DC power source 18 and the polarity reversing device 19 are used as in the above embodiment. It is not limited to a combination of the above and an AC power source may be used. In this case, the AC waveform may be a rectangular wave, a sine wave, or any other waveform. Further, in the configuration in which the DC power supply 18 and the polarity inverting device 19 are combined, the inversion period is not necessarily constant, and the inversion period may be variable based on some variable.

(Use of heat diffusion equipment)
The heat diffusing device of the present invention is not limited to a personal computer CPU or an on-vehicle electronic control unit (ECU), and can be applied to any device that requires excellent heat dissipation, particularly with downsizing and higher output. is there.
As mentioned above, this invention is not limited to such embodiment, In the range which does not deviate from the meaning of invention, it can implement with a various form.

12 ... flow path wall (flow path forming member),
13 ... Insulating substrate (flow path forming member),
14 (141-145) ... flow path,
15 ... Electrode pair, EHD pump,
16 ... acicular electrode (first electrode),
17 ... slit electrode (second electrode),
18 ... DC power supply (alternating voltage supply device),
19: Polarity reversing device (alternating voltage supply device),
31 ... Thermal diffusion device,
34 ... casing,
F: EHD fluid,
D: Dielectric fine particles.

Claims (4)

An EHD fluid (F) that can flow as a cooling medium by an electrohydrodynamic phenomenon;
A flow path forming member (12, 13) that forms a flow path (14) filled with the EHD fluid in a flowable manner;
A first electrode (16) disposed along the flow path direction in the flow path and having a sharp tip in the flow path direction, and a second electrode (17) having a gap penetrating in the flow path direction, At least a pair of electrodes (15) that generate a flow of the EHD fluid from the tip of the first electrode toward the gap of the second electrode when voltages having different polarities are applied to the one electrode and the second electrode When,
An alternating voltage supply device (18, 19) capable of applying a voltage whose polarity is alternately reversed over time with respect to the first electrode and the second electrode;
Charged dielectric fine particles (D) added to float in the EHD fluid;
A thermal diffusion device comprising:   The thermal diffusion apparatus according to claim 1, wherein the dielectric fine particles are resin or ceramic particles.   The thermal diffusion device according to claim 1 or 2, wherein the size of the dielectric fine particles is smaller than the narrowest gap of the gap between the second electrodes. 4. The thermal diffusion device according to claim 1, wherein a specific gravity of the dielectric fine particles is 0.5 to 2.0 times a specific gravity of the EHD fluid.

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