JPS6259889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiling cooling device that cools a heating element, such as a power semiconductor element, by applying boiling heat transfer, and an object thereof is to improve the cooling characteristics thereof. It is in.

FIG. 1 is a sectional view showing a conventional evaporative cooling device 100, in which 1 is a heating element such as a semiconductor element, 2 is a refrigerant liquid, and 3 is a container.

Now, when the heating element 1 generates heat due to electricity, etc.
Bubbles 4 are generated from the surface of the heating element 1 that is in contact with the refrigerant liquid 2 (heat transfer surface). The bubbles or steam generated are
The gas rises through the gas phase space 5 in the container 3 as shown by the solid arrow, and is condensed and liquefied on the inner wall surface of the container 3, which is being cooled. At this time, the heat generated by the heating element 1 is radiated to the outside of the container 3 as latent heat of condensation. The condensed and liquefied refrigerant liquid 2A descends under the action of gravity along the inner wall surface of the container and flows back into the refrigerant liquid 2. At this time, the refrigerant liquid 2 is disturbed by the rising bubbles 4, and therefore, the portion of the inner wall surface of the container 3 that is in contact with the refrigerant liquid 2 also has a heating element due to convective heat transfer of the refrigerant liquid 2. 1
A part of the heat generated is transferred and radiated out of the container 3 through the wall of the container 3.

However, in the conventional evaporative cooling device 100, the disturbance of the refrigerant liquid 2 by the rising bubbles 4
Since it was uncertain, the convective heat transfer coefficient was extremely small.

In fact, in the case of the configuration shown in Figure 1,
The disturbance caused by the bubbles 4 is limited to the area in the refrigerant liquid 2 near the surface of the heating element 1 where the bubbles 4 are generated, and depending on the disturbance of the bubbles, the bubbles 4 may reach the lower part of the container 3. It is recognized that the convection caused by the disturbance has not reached the area. Therefore, the heat dissipation effect by convective heat transfer was extremely small.

An object of the present invention is to provide a boiling cooling device with improved cooling characteristics by actively utilizing the flow of the refrigerant liquid 2 induced by the rising bubbles 4.

Figure 2 shows the prior art (Japanese Patent Application No. 56-053466 =
57-167663) is a sectional view showing a boiling cooling device. In the figure, numerals 1 to 5 indicate devices completely similar to the conventional device described above. Reference numeral 6 denotes a flow path for the refrigerant liquid 2 formed inside the heating element 1, which extends downward from the heating element 6 in this example. Reference numeral 7 denotes a rectifier plate that forms a flow path through which the refrigerant liquid 2 flows downward along the inner wall surface of the container 3. When the heating element 1 generates heat, the bubbles 4 generated in the flow path, that is, the duct 6 rise, and a frictional force based on viscosity acts between the bubbles 4 and the refrigerant liquid 2, which scrapes the refrigerant liquid 2 in the flow path 6. The so-called bubble pump effect works to raise the temperature. Furthermore, when the heat generated from the heating element 1 is small and no bubbles are generated within the flow path 6, the refrigerant liquid 2 within the flow path 6 is heated, its density is reduced, and buoyancy is generated. Therefore, in any case, when the heating element 1 generates heat, an upward flow occurs in the flow path 6. The driving force for raising the refrigerant liquid 2 is determined by the average density of the gas (indicated by bubbles 4) and liquid in the flow path 6 and the refrigerant liquid 2 outside the flow path 6.
It is known that the larger the difference from the average density, or the larger the height of the flow path 6 in the vertical direction, the larger the difference.

Therefore, if the baffle plate 7 and flow path 6 are configured in the boiling cooling device 100 as shown in FIG. 2, the refrigerant liquid 2 will circulate as shown by the solid arrows. That is, due to the driving force generated in the flow path 6 in the heating element 1, the refrigerant liquid 2 flows into the flow path 6 from the lower part of the flow path 6 and flows out from the upper part of the flow path 6. The outflowing refrigerant liquid 2 flows downward through a channel 8 formed between the inner wall surface of the container 3 and the baffle plate 7, and flows into the lower part of the channel 6. Therefore, the refrigerant liquid 2 induced in the heating element 1 flows through the flow path 8 in an orderly manner, increasing the convective heat transfer characteristics between the refrigerant liquid 2 in the flow path 8 and the inner wall surface of the container 3.

However, in the prior art, as shown in FIG. 2, the cross-sectional area S of the flow path between the current plate 7 and the container 3 is almost uniform in this example, so The refrigerant liquid 2 at the bottom 9 of the container 3 stagnates, resulting in a drawback that heat dissipation in this portion 9 is hindered. According to experiments,
It was confirmed that this area accounts for more than 20% of the total heat dissipation area. As shown in FIG. 4, this tendency becomes more pronounced as the bottom portion 9 of the heating element 1 becomes larger, in other words, as the distance H between the lower end of the heating element 1 and the lower end of the container 3 becomes larger. .

This invention has been made to improve the drawbacks of the prior art described above.

FIGS. 5 and 6 are sectional views showing one embodiment of the present invention, respectively. The cross-sectional area S of the flow path 8 formed between the rectifying plate 7 and the container 3 gradually becomes smaller toward the lower part of the container 3, and the distance H becomes smaller. In this way, the flow rate of the refrigerant liquid 2 flowing through the flow path 8 becomes faster toward the lower part of the container 3, and the heat transfer coefficient increases. Furthermore, stagnation of the refrigerant liquid at the bottom of the container 3 is reduced. This is extremely effective, for example, when the boiling cooling device 100 is installed under the floor of a train or the like, since the bottom of the container 3 particularly contributes to heat radiation. That is, as shown in FIG. 7, various electrical devices 1 are installed under the floor of the vehicle 10.
1 is equipped, and the running wind under the floor generated when the vehicle 10 moves is larger at the bottom of the boiling cooling device 100, and smaller at the top because it is obstructed by other electrical equipment 11. Therefore,
It is advantageous to increase the heat transfer coefficient toward the bottom of the boiling cooling device 100 and increase heat dissipation in order to suppress the temperature rise of the heating element 1. 12 is the railway line,
13 is a wheel.

FIG. 8 shows another embodiment of the invention. The end of the current plate 7 near the bottom of the container 3 is smoothly bent. By doing so, the flow of the refrigerant liquid 2 through the flow path 8 becomes smooth, and the pressure loss is reduced.

9 and 10 are sectional views showing other embodiments of the present invention, in which the container 3 is a hexagonal cylinder and a square cylinder, respectively. In FIG. 10, the terminal end of the second flow path 8 is the second
It corresponds to the lower part of the flow path 8, and the cross-sectional area of this part is smaller than the cross-sectional area of the upper part.

As explained above, the present invention provides the second flow path 8
Since the lower cross-sectional area is smaller than the upper cross-sectional area of
The flow rate of the refrigerant liquid flowing through the channel 8 at the bottom of the container becomes faster, and the stagnation of the refrigerant liquid at the bottom of the container becomes smaller, so that the heat dissipation effect at the bottom of the container can be extremely enhanced.

Furthermore, when the second flow path 8 is connected to the lower part of the first flow path 6, a desired circulation path for the refrigerant liquid is formed, and the entrainment flow outside the desired circulation path is reduced, so that the heat dissipation effect is further promoted. be done.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional evaporative cooling device, FIG. 2 is a sectional view showing a prior art evaporative cooling device, and FIGS. 3 to 6 each show an embodiment of the evaporative cooling device of the present invention. FIG. FIG. 7 is a schematic front view showing an application example of the present invention, and FIGS. 8 to 10 are sectional views showing one embodiment of the invention. In the figure, 1 is a heating element, 2 is a refrigerant liquid, 3 is a container, 4 is an air chamber, 6 is a first flow path, 7 is a rectifying plate,
8 is a second flow path, and 10 is a vehicle. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A refrigerant liquid, a heating element immersed in the refrigerant liquid, a container containing the refrigerant liquid and the heating element, and a structure in which air bubbles in the refrigerant liquid generated by the heat of the heating element flow upward. The refrigerant liquid flows downward in contact with the inner wall surface of the container due to the driving force generated by the upward flow of the air bubbles in the first flow path formed in the heating element, and the refrigerant liquid that has descended flows into the first flow path. 1. A boiling cooling device having a second flow path formed to be guided to the first flow path, wherein the second flow path has a lower cross-sectional area smaller than an upper cross-sectional area. 2. In what is stated in claim 1,
The second flow path is formed by the inner wall surface of the container and a rectifying plate, and the lower end of the rectifying plate is smoothly curved. 3. The boiling cooling device according to claim 1 or 2, wherein the second flow path is connected to the lower part of the first flow path.