JP2017009239A - Liquid transport device and heat pipe using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid transport device that efficiently transports liquid by using capillary force, and a heat pipe using the same.SOLUTION: A heat pipe 10 moves liquid enclosed in a hollow container 11, to an evaporation part 13 from a condensation part 12 by using capillary force. A plurality of minute grooves 20 that reach the evaporation part 13 from the condensation part 12 are provided in an inside surface 19 of the hollow container 11. The width of the minute grooves 20 is formed so as to become narrower toward the region of the evaporation part 13 from the region of the condensation part 12. The liquid is efficiently moved by the capillary force of the minute grooves 20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a liquid transport apparatus that transports a liquid using capillary force and a heat pipe using the same.

Heat pipes for cooling small electronic devices, microdevices that send, separate, and mix liquid samples, and drainage mechanisms that discharge water generated during power generation by the fuel cell to the outside, are energy-saving. From the viewpoint and the like, it is desirable to employ an apparatus that moves the liquid using capillary force. This is because the capillary force is used as a driving force for moving the liquid, so that an external driving source such as a pump or a motor is not required. Specific examples of transporting the liquid using the capillary force are described in Patent Documents 1 to 3, for example.

By the way, when liquid is transported by capillary force, it is known that as the capillary (including a groove capable of moving the liquid by capillary action) becomes thinner, the capillary force increases, but the pressure loss due to flow resistance also increases. ing. For this reason, in order to secure the transportation force of a liquid having a predetermined size, it is necessary to consider pressure loss in addition to capillary force.
When the liquid transport capacity is insufficient, for example, in a heat pipe, there is a problem that dryout occurs in the evaporation section and a necessary cooling capacity cannot be obtained.

JP 2001-296093 A Japanese Patent Laid-Open No. 2003-090688 JP 2013-032904 A

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid transport apparatus that efficiently transports a liquid using capillary force and a heat pipe using the same.

In the liquid transport apparatus according to the first aspect of the present invention, the liquid transport apparatus moves the liquid in the fine groove by capillary force, and the width of the fine groove becomes narrower toward the downstream side.

In the liquid transport apparatus according to the first invention, it is preferable that the wettability of the fine groove is higher on the downstream side than on the upstream side.

In the liquid transport device according to the first aspect of the present invention, the fine groove is preferably branched on the downstream side.

In the liquid transport device according to the first aspect of the present invention, it is preferable that there are a plurality of the fine grooves, and each of them is formed in parallel.

The heat pipe according to the second invention that meets the above-mentioned object is a heat pipe that moves the liquid sealed in the hollow container from the condensing part to the evaporation part by the capillary force of the fine groove. A plurality of the fine grooves extending from the condensing part to the evaporation part are provided, and the width of the fine groove becomes narrower from the condensation part region toward the evaporation part region.

In the heat pipe according to the second aspect of the present invention, it is preferable that the wettability of the fine groove is higher in the area of the evaporation section than in the area of the condensation section.

In the heat pipe according to the second aspect of the present invention, the fine groove is preferably branched in the region of the evaporation portion.

In the liquid transport device according to the first invention and the heat pipe according to the second invention, the width of the fine groove is narrowed toward the downstream side (the region of the evaporation section), so that the liquid is transported efficiently. It is possible. This effect has been confirmed as a result of various verifications.

(A), (B) is the longitudinal cross-sectional view of the heat pipe which concerns on one embodiment of this invention, respectively, and the top view of the base board used with the same heat pipe. It is explanatory drawing of the fine groove | channel provided in the heat pipe. It is an enlarged plan view of a fine groove. It is an expansion perspective view of a fine groove. (A), (B) is a graph which shows the relationship between the width | variety of a fine groove | channel, and the liquid transport force in the case where a groove width is constant and the case where a groove width increases / decreases, respectively. It is a graph which shows the transport power of the liquid of an Example and each comparative example. It is a graph which shows the measurement result of a heat flux and effective thermal conductivity about an Example and each comparative example.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIGS. 1A, 1B, and 2, the heat pipe 10 according to the embodiment of the present invention condenses the liquid sealed in the hollow container 11 by the capillary force of the fine groove 20. It is moved from the unit 12 to the evaporation unit 13. Details will be described below.

As shown in FIGS. 1A, 1 </ b> B, and 2, the hollow container 11 includes a rectangular heat-resistant glass plate 14 and a rectangular base plate 15 provided below the heat-resistant glass plate 14. (1 to 5 mm in this embodiment) and are arranged to face each other. A rectangular frame 16 is provided between the heat-resistant glass plate 14 and the base plate 15. In the present embodiment, the main component of the frame body 16 is silicon, but it goes without saying that the present invention is not limited to this.
Pure water, which is an example of a liquid, is sealed in a sealed space 17 that is covered by the heat-resistant glass plate 14 and the base plate 15 and is surrounded by the frame body 16.

The heat-resistant glass plate 14 is provided with an introduction portion 18 used when pure water is injected into the sealed space 17. The introduction portion 18 is closed after the insertion portion that has been opened is injected with pure water into the sealed space 17 and the pressure of the sealed space 17 is reduced by a vacuum pump via the insertion portion.
The condensing unit 12 and the evaporating unit 13 are on the front side (one side) and the rear side (the other side) in the sealed space 17 of the box-shaped hollow container 11 that is long in the front and rear, and the evaporating unit 13 absorbs heat from the outside. The condensing part 12 functions as a part that radiates heat to the outside.

On the upper surface 19 (an example of the inner surface of the hollow container 11) 19 of the base plate 15, there are a plurality of fine grooves 20 along the longitudinal direction (front-rear direction) of the base plate 15 in a rectangular region surrounded by the frame body 16. They are formed in parallel (the center lines of the plurality of fine grooves 20 are parallel). Each fine groove 20 extends from the condenser 12 to the evaporator 13.
As shown in FIGS. 1B and 2, a plurality of long protruding pieces 21 are formed in parallel on the upper surface 19 of the base plate 15, and one fine groove 20 is provided between adjacent protruding pieces 21. Is provided.

The fine groove 20 and the protruding piece 21 are formed by etching, and a nitride film (Si) functioning as a mask during the etching process is formed on the protruding piece 21 as shown in FIGS. ₃ N ₄₎ 22 is arranged. The base plate 15 is formed using silicon (Si) as a raw material except for the nitride film 22, and a plurality of protruding pieces 21 and a plurality of fine grooves 20 are formed on the upper surface 19 by etching using potassium hydroxide (KOH) as an etching solution. Is formed.
Due to the anisotropy of potassium hydroxide, the cross section of the fine groove 20 has a reverse isosceles trapezoidal shape in which the isosceles trapezoid is turned upside down as shown in FIG.

In the present embodiment, the depth H of the fine groove 20 is in the range of 50 to 200 μm, and is constant (substantially constant) in the front-rear direction. The inclination angle γ of the protruding piece 21 with respect to the bottom surface of the fine groove 20 is 54.7 °, the arrangement pitch D of the fine grooves 20 is 100 to 800 μm, and the width of the fine grooves 20 (representative length in this embodiment). Is 1 to 500 μm. Note that the inclination angle γ is not limited to 54.7 ° because it is determined by the etching solution, the base material, and the like.

Further, as shown in FIG. 3, each fine groove 20 has a narrow width toward the rear (downstream side) (that is, toward the evaporation unit 13). In the present embodiment, the reduction rate of the width per unit length of the fine groove 20 is constant, but the reduction rate may be different in the front-rear direction.
As described above, the process of making the depth of the fine groove 20 constant in the front-rear direction and narrowing the fine groove 20 from the region of the condensation unit 12 toward the region of the evaporation unit 13 is, for example, the above-described etching process. Can be carried out more stably.

The width of the fine groove 20 is narrowed from the region of the condensation unit 12 toward the region of the evaporation unit 13 compared to the fine groove whose width is constant from the region of the condensation unit to the region of the evaporation unit. This is because various verifications have revealed that the liquid can be moved efficiently.
The angle φ at which the width of the fine groove 20 decreases is 5 degrees or less, preferably 1 degree or less, more preferably 0.3 degrees or less. This is because, when the reduction angle φ increases, the arrangement pitch D of the fine grooves 20 needs to be increased, and the number of fine grooves 20 provided per unit area decreases.

Hereinafter, the relationship between the width of the fine groove 20 and the movement amount of the liquid will be described.
σ is the surface tension of the liquid, θ is the contact angle of the liquid (angle formed by the tangent of the liquid dropped on the horizontal surface of the fine groove and the horizontal surface), W is the width of the fine groove, and h is the depth of the fine groove (See FIG. 4), the capillary force Δp _ca of the fine groove can be expressed by the following formula (1).

In addition, the subscript e and the subscript c in the formula mean the evaporation portion and the condensation portion, respectively, and as shown in FIG. 4, W _c is one end of the fine groove (in the region of the condensation portion, the furthest away from the evaporation portion region). W _e means the width of the other end of the fine groove (the portion farthest from the condensing part region in the evaporation part region).
According to Formula (1), it turns out that capillary force becomes large, so that the width | variety of the evaporation part of a fine groove is narrow.
On the other hand, it can be said that most of the pressure loss caused when the liquid moves through the fine groove is flow resistance. Therefore, when the pressure loss is regarded as the flow resistance, the pressure loss Δp ₁ can be expressed by the following equation (2).

In equation (2), μ is the viscosity coefficient of the liquid, u is the average flow velocity of the liquid, and L is the length of the fine groove. Equation (2) assumes that the width of the fine groove is constant along the longitudinal direction of the fine groove. From equation (2), if L is constant, the more W is small (narrow width of the fine groove), it can be said that the pressure loss of the liquid △ p _l increases.
Here, as shown in FIG. 4, when the width of the fine groove is gradually narrowed at a constant rate from the condensing unit to the evaporating unit, the pressure loss Δp ₁ is expressed by the following equation (3). .

It can also be seen from equation (3) that if L is constant, the pressure loss Δp ₁ increases as W _c and W _e are smaller (the width of the fine groove is narrower).
Since it can be said that the liquid transport force by the fine groove is obtained by subtracting the pressure loss Δp ₁ from the capillary force Δp _ca , (liquid transport force) = (capillary force Δp _ca ) − (pressure loss Δp ₁ ) It can obtain | require by the calculation formula of.

Next, assuming that the liquid is pure water and the width of the fine groove is unchanged along the longitudinal direction (hereinafter also referred to as “the case where the groove width is constant”), the width of the fine groove is changed from the condensing part to the evaporation part. When the pressure gradually changes (widens or narrows) at the same rate (hereinafter also referred to as “increase / decrease in groove width”), the capillary force Δp _ca , pressure loss Δp _1, and liquid The transport force (Δp _{ca −Δp 1} ) was calculated. When the groove width was constant, the capillary force Δp _ca and the pressure loss Δp ₁ were calculated using the equations (1) and (2). If the groove width increase or decrease, the _{W e} were fixed with 100 [mu] m, by varying the _{W c,} using equation (1) and (3) to calculate capillary force △ _{p ca} and pressure loss △ _{p l,} respectively.
In both cases where the groove width is constant and the groove width is increased or decreased, θ _c = 80 ° and θ _e = 0 °.

From the graph of FIG. 5 (A), when the groove width constant, the width of the fine groove is in 50μm or less, the pressure loss △ p _l is a capillary force △ p _ca above, transport capacity of the liquid is next zero, capillary limit It becomes. When the groove width is constant, the liquid transport force increases with the width of the fine groove being 50 to 100 μm, and the width of the fine groove is widened, and becomes the maximum value when the width of the fine groove is 100 μm. As the width becomes wider than 100 μm, it gradually decreases.

On the other hand, from the graph of FIG. 5 (B), when the groove width increase or decrease, in _{W c} is 50 [mu] m or less, it becomes capillary limit as in the case of groove width fixed, when _{W c} is more than 50 [mu] m, the _{W c} is increased At the same time, the liquid transport capacity increases. The reason _{why the} liquid transport force increases as W _c increases is the same as the width of the evaporation part of the fine groove becomes narrower than the width of the condensation part of the fine groove, that is, even in a region where W _c is larger than 100 μm. This point is different in the graphs of FIGS.
Therefore, it is understood that the fine groove whose groove width becomes narrower from the condensing part toward the evaporation part has a larger liquid transporting force than the fine groove having a constant groove width.

Further, in this embodiment, as shown in FIG. 1B, each fine groove 20 is formed without branching in the middle, but instead of the fine groove 20, the fine groove branched in the region of the evaporation portion. A groove may be employed. Even in the branched portion of the fine groove, the groove width is preferably narrower toward the downstream side. By branching the fine groove in the region of the evaporation section, a plurality of transport paths can be secured, and the amount of liquid that can be transported by one fine groove can be increased. In the branched fine groove, the unbranched region is parallel to the unbranched region of the other fine groove.
From Equation (1), when cos θ _e > cos θ _c , the capillary force is larger than when cos θ _e <cos θ _c , and therefore, the wettability of the fine groove 20 is reduced in the region of the evaporation portion 13. It is preferably higher than the area of the portion 12.

Next, a liquid transport device according to an embodiment of the present invention will be described. The liquid transport device is a base plate 15 in which the fine grooves 20 in the heat pipe 10 shown in FIGS. 1A, 1B, and 2 are formed, and moves the liquid in the fine grooves 20 by capillary force. is there. The width of the fine groove 20 is narrowed from the upstream side toward the downstream side, with the condensation unit 12 side being the upstream side and the evaporation unit 13 side being the downstream side.

The base plate 15 that is a liquid transport device is not used only in the heat pipe 10, but is used in, for example, a device for feeding a sample or as a discharge mechanism that discharges water generated in a fuel cell. It can also be used.
Further, in the base plate 15 that is a liquid transport device, the wettability of the fine groove 20 is higher in the region of the evaporation unit 13 (downstream side) than in the region of the condensation unit 12 (upstream side). Then, instead of the fine groove 20, a fine groove branched in the area of the evaporation portion can be adopted.
In the base plate 15, a plurality of fine grooves 20 are provided. However, one fine groove may be provided depending on an object for which the liquid transport apparatus is used.

Hereinafter, in order to confirm the effect of this invention, the experiment conducted on the heat pipe is demonstrated.
In the experiment, the first and second heat pipes having a base plate in which 33 fine grooves having a depth of 100 ± 4 μm were formed in parallel in a region having a width of 15 mm and a length of 70 mm on the upper surface were used. Water was transported.

In the first heat pipe (example), the width of each fine groove is narrowed at a constant rate from the condensing part to the evaporation part, and W _e = 200 μm, W _c = 400 μm, In the heat pipe (comparative example), the width of the fine groove is constant at 300 μm along the fine groove.
The first and second heat pipes have different surface treatments in the condensation area and the evaporation area, and the contact angles of pure water are θ _e = 10 ° and θ _c = 92 ° for the first heat pipe. Yes, the second heat pipe has θ _e = 0 ° and θ _c = 80 °. Note that the contact angle of pure water in the first and second heat pipes is measured under conditions of room temperature of 25 ° C. and humidity of 40 RH%.

The graph of FIG. 6 shows the results of simulation measurement of the capillary force Δp _ca , the pressure loss Δp _1, and the liquid transport force (Δp _ca −Δp ₁ ) for each of the first and second heat pipes. In the graph of FIG. 6, the first and second heat pipes are shown as Cases 1 and 2, respectively. The difference between θ _c and θ _e is as small as 2 ° between the first and second heat pipes (that is, the difference in wettability is small), but the liquid transport force is that the first heat pipe is the second heat pipe. The difference was about 1.7 times that of the pipe.

Further, the first and second heat pipes are cooled by a Peltier element attached to the lower side of the base plate, and the evaporation part is heated by a heater attached to the lower side of the base plate to be hollow. After making heat transfer in the container, heat quantity is measured by using 11 thermocouples embedded in a heat-resistant glass plate and heat flux sensors provided in the evaporator and condenser. The relationship of thermal conductivity was obtained.
The relationship between the obtained heat flux and effective thermal conductivity is shown in the graph of FIG. In the graph of FIG. 7, the horizontal axis is the heat flux, the vertical axis is the effective thermal conductivity, and the first and second heat pipes are shown as Cases 1 and 2, respectively.

When comparing the first and second heat pipes having a small difference in wettability, the maximum value of the effective thermal conductivity is about 1.5 times that of the second heat pipe in the first heat pipe, It was confirmed that the heat pipe is superior in thermal conductivity to the second heat pipe.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.
For example, the heat pipe may have fine grooves formed on the entire inner surface in the hollow container.
Moreover, the hollow container of a heat pipe does not need to be a box shape, For example, a vertically long capsule shape may be sufficient.
In the heat pipe and the liquid transport apparatus, the plurality of fine grooves do not need to be parallel and need not be formed in a straight line.
Furthermore, the liquid transported by the liquid transport apparatus is not limited to pure water, and may be, for example, an antifreeze liquid.

10: Heat pipe, 11: Hollow container, 12: Condensing part, 13: Evaporating part, 14: Heat-resistant glass plate, 15: Base plate, 16: Frame body, 17: Sealed space, 18: Introduction part, 19: Upper surface, 20: fine groove, 21: protruding piece, 22: nitride film

Claims (7)

In the liquid transport device that moves the liquid in the fine groove by capillary force,
The width of the fine groove is narrower toward the downstream side. 2. The liquid transport apparatus according to claim 1, wherein the wettability of the fine groove is higher on the downstream side than on the upstream side. 3. The liquid transport apparatus according to claim 1, wherein the fine groove is branched on the downstream side. 3. The liquid transport apparatus according to claim 1, wherein there are a plurality of the fine grooves, and each of them is formed in parallel. In the heat pipe that moves the liquid sealed in the hollow container from the condensing part to the evaporation part by the capillary force of the fine groove,
A plurality of the fine grooves extending from the condensing part to the evaporation part are provided on the inner surface of the hollow container, and the width of the fine groove is from the condensation part region toward the evaporation part region. Heat pipe characterized by narrowing. 6. The heat pipe according to claim 5, wherein the wettability of the fine groove is higher in the area of the evaporation section than in the area of the condensation section. The heat pipe according to claim 5 or 6, wherein the fine groove is branched in a region of the evaporation section.

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