Ebullient cooling device   

Abstract: An ebullient cooling device having a simple structure and capable of limiting the bubbles to an appropriate volume. The ebullient cooling device for cooling a heat generating element is provided with a plurality of vertically arranged cooling channels comprising a lower channel (2), a middle channel (3) and un upper channel (4). Each cooling channel has cooling fins (12) for guiding a refrigerant to flow in a vertical direction, and a vapor discharge path (16) formed at the side of the cooling fins (12) that is opposite the side in contact with the heat generating element. Furthermore, flow path partition/vapor discharge guiding plates (18) are provided between the cooling channels so that the bubbles that have been generated are guided to the vapor discharge path (16) and prevented from moving into the subsequent cooling channel.

TECHNICAL FIELD

The present invention relates to an ebullient cooling device, and more particularly to an improvement in cooling performance of a cooling device using boiling two-phase flow (gas-liquid two-phase flow).

BACKGROUND ART

Conventionally, cooling devices using boiling two-phase flow under a forced flow have been developed and applied to inverter cooling systems of hybrid vehicles and others.

Patent Document 1 discloses a power semiconductor module which is structured with a cooling base including a coolant flow path and a plurality of power semiconductors mounted on the base. The cooling efficiency is improved by determining an appropriate mounting position of power semiconductor element to optimize the temperature increase of coolant.

Patent Document 2 discloses an ebullient cooling device which prevents deterioration of heat dissipation performance at an upper portion (downstream region) of a module. Vapor generated at a lower portion (upstream region) of the module due to heat received from a power semiconductor is prevented from entering into the upper portion (downstream region) of the module by a partition or the like.

Patent Document 1: JP 2007-12722A

Patent Document 2: JP 9-23081A

DISCLOSURE OF THE INVENTION

It is required for cooling devices using boiling two-phase flow to be designed not only to restrict a decrease of critical heat flux and heat transfer coefficient at the time of boiling, but also to be compact as possible. Generally, the heat transfer performance during boiling is determined based on gas-liquid behavior at the bottom-of bubbles. More specifically, two types of regions coexist, one region where the heat transfer is enhanced because a thin liquid film is formed, and the other region where the heat transfer is deteriorated due to a development of dried portions. The size of the area where bubbles are attached significantly influences which of the regions will be dominating. When the size of the bubble attaching area is enlarged as the bubbles grow, the dominating region may be changed from the heat transfer enhancing region to the deteriorating region.

FIGS. 8A and 8B show a heat transfer manner when a heat transfer enhancement is low in a nucleate boiling heat transfer as a small bubble grows. Shown is a case where an open flow path is used and the size of a bubble is small. FIG. 8(A) is a plan view; and FIG. 8(B) is a side view. When the pressure is lower, the size of a bubble is larger. The lower the temperature of ambient fluid is than the saturation temperature (sub-cool state), the smaller the size of a bubble. When the size of a bubble is small, although the area of dried portion 50 is accordingly small, the area occupied by a thin liquid film 52 also becomes small. As a result, the boiling heat transfer effect is weakened, while a heat transfer applied to a liquid single-phase flow surrounding the bubble remains large. Therefore, the ratio of heat transfer enhancement is smaller than the heat transfer to the liquid single-phase flow.

FIGS. 9A and 9B show a heat transfer manner when the heat transfer enhancement is high in a nucleate boiling heat transfer as a large bubble grows. Shown is a case where an open flow path is used and the size of a bubble is middle to large. When the bubble size becomes larger, although the area of the dried portion 50 becomes large, the area occupied by the thin liquid film 52 also becomes large. As a result, the effect of the boiling heat transfer becomes significant, and as a result the ratio of heat transfer enhancement is larger than the heat transfer to the liquid single-phase flow.

FIGS. 10A and 10B show a manner in which a heat transfer is deteriorated in a nucleate boiling heat transfer as a massive bubble grows. Shown is a case where an open flow path is used and the size of a bubble is significantly large. When a bubble becomes excessively large, the area occupied by the dried portion 50 expands. Thus, the heat transfer deterioration of this area becomes more significant than the heat transfer enhancement achieved by the evaporation of the thin liquid film 52. As a result, an aspect of deterioration of heat transfer becomes obvious in the heat transfer area as a whole.

FIGS. 11A and 11B show a manner in which a heat transfer is enhanced in a nucleate boiling heat transfer as a flattened bubble grows between cooling fins 12 (hereinafter to referred simply as “fins”). Shown is a case where a narrow flow path between fins is used and the size of a bubble is medium. Increase of both the heat transfer area and heat transfer coefficient with the fins 12 can be achieved by generating and growing a flattened bubble of a sufficient size.

FIG. 12 shows a relationship between a bubble volume and heat transfer enhancement/deterioration. The horizontal axis shows a bubble volume, while the vertical axis shows the heat transfer characteristics. The arrow P of the vertical axis indicates enhancement of the heat transfer, while the arrow Q indicates deterioration of the heat transfer. Both in an open flow path (indicated by sign “a” in the drawing) and a narrow flow path between fins (indicated by sign “b” in the drawing), heat transfer enhancement cannot be expected when the bubble volume is either too small or too large. It is necessary to maintain bubbles at a sufficient size (the optimum volume is shown by “OPT” in the drawing). Therefore, it is important to control a time duration when a bubble contacts with a heat transfer surface in order to prevent the contact time from being excessively long.

An object of the present invention is to provide a cooling device which maintains a bubble volume at a sufficient size with a simple structure, and thereby enhances heat transfer characteristics.

The present invention is characterized by an ebullient cooling device for cooling a heating body, comprising: at least first and second cooling channel blocks, both arranged in a vertical direction, comprising: a cooling fin that causes coolant to flow in the vertical direction; and a vapor discharge path formed on a side of the cooling fin that is opposite to a side in contact with a heating body; and a guiding portion provided between the first and second cooling channel blocks, the guiding portion guiding a bubble generated in the first cooling channel block to the vapor discharge path by preventing the bubble from proceeding into the second cooling channel block.

In one embodiment of the present invention, the ebullient cooling device further comprises a partition positioned between the cooling fin and the vapor discharge path, and the guiding portion is formed as a portion of the partition.

In another embodiment of the present invention, the partition has an opening portion at a position between the first and second cooling channel blocks, and the guiding portion is formed to project from an edge of the opening portion towards the heating body contacting side of the cooling fin.

In yet another embodiment, the ebullient cooling device further comprises a fluid supply pipe that is provided between the first and second cooling channel blocks, the fluid supply pipe supplying the coolant to the second cooling channel block, and a front edge of the guiding portion contacts with the fluid supply pipe.

In yet another embodiment, the first cooling channel block is positioned vertically beneath the second cooling channel block, and the guiding portion is formed, from the cooling fin of the second cooling channel block, to be tilted towards the cooling fin of the first cooling channel block.

The present invention can improve heat transfer characteristics by maintaining a bubble volume at a sufficient size with a simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front view of a cooling device according to an embodiment of the present invention.

FIG. 1B is a side view of a cooling device according to an embodiment of the present invention.

FIG. 1C is a cross-sectional view taken along the line B-B′ of a cooling device according to an embodiment of the present invention.

FIG. 1D is a cross-sectional view taken along the line A-A′ of a cooling device according to an embodiment of the present invention.

FIG. 2A is a design diagram of a fluid supply pipe.

FIG. 2B is another design diagram of a fluid supply pipe.

FIG. 3A is a front view of a flow path partition/vapor discharge guiding plate.

FIG. 3B is a side view of a flow path partition/vapor discharge guiding plate.

FIG. 4 is an exploded perspective view of fins and a flow path partition/vapor discharge guiding plate.

FIG. 5 is an overall design diagram of a cooling device according to an embodiment of the present invention.

FIG. 6 is a system configuration diagram according to an embodiment of the present invention.

FIG. 7 is a system configuration diagram according to another embodiment of the present invention.

FIG. 8A is a plan view showing heat transfer characteristics when an open flow path is used and the size of a bubble is small.

FIG. 8B is a side view showing heat transfer characteristics when an open flow path is used and the size of a bubble is small.

FIG. 9A is a plan view showing heat transfer characteristics when an open flow path is used and the size of a bubble is medium.

FIG. 9B is a side view showing heat transfer characteristics when an open flow path is used and the size of a bubble is medium.

FIG. 10A is a plan view showing heat transfer characteristics when an open flow path is used and the size of a bubble is excessively large.

FIG. 10B is a side view showing heat transfer characteristics when an open flow path is used and the size of a bubble is excessively large.

FIG. 11A is a plan view showing heat transfer characteristics when a narrow flow path between fins is used and the size of a bubble is medium.

FIG. 11B is a side view showing heat transfer characteristics when a narrow flow path between fins is used and the size of a bubble is medium.

FIG. 12 is a graph showing a relationship between a bubble volume and heat transfer characteristics.

1 ebullient cooling device, 2 lower channel block, 3 middle channel block, 4 upper channel block, 10 fluid supply pipe, 12 fins, 13 fin base, 14 cooling surface, 16 vapor discharge path, 18 flow path partition/vapor discharge guiding plate, 19 guiding portion, 20 partition.

Embodiments according to the present invention are described below by referring to the attached drawings.

FIGS. 1A to 1D show a structure of main elements of an ebullient cooling device according to an embodiment of the present invention. FIG. 1 is a plan view; FIG. 1B is a side view; FIG. 1C is a cross-sectional view taken along the line B-B′; and FIG. 1D is a cross-sectional view taken along the line A-A′.

The ebullient cooling device 1 comprises a fluid supply pipe 10, fins 12, fin base 13, cooling surface 14, vapor discharge path 16, and flow path partition/vapor discharge guiding plate 18.

A plurality of the fins 12 are provided to stand on the fin base 13 at predetermined intervals. A multi-channel system is provided in which fins 12 form cooling channels. As shown in the front view in FIG. 1A, the ebullient cooling device 1 is installed in a vertical direction (vertical installation) with each fin 12 arranged to extend in the vertical direction. FIG. 1A shows an example structure in which a lower channel block 2, middle channel block 3, and upper channel block 4 are provided, each of which is further divided by a partition 20 into right and left blocks, resulting in 6 channel blocks in total. However, the prevent invention is not limited to this example. Each fin 12 is made of, for example, aluminum having a high heat conductivity. Coolant flow paths are formed in a vertical direction. The coolant is force-circulated upward in the vertical direction by a pump. The fins 12 expand the surface area of the fin base 13 which forms the cooling surface 14 and also enhances the heat conductivity. The cooling surface 14 of the fins 12 is contacted by, for example, a power device unit (IGBT module) of a hybrid vehicle.

Being positioned between blocks of fins 12, the fluid supply pipe 10 supplies cooling fluid as coolant to the fins 12. As shown in FIG. 1A, the fluid supply pipe 10 is provided, in a horizontal direction, for each of the channel blocks. To the lower channel block 2, the coolant is supplied upward from the fluid supply pipe 10 positioned beneath the lower channel block 2; to the middle channel block 3, the coolant is supplied upward from the fluid supply pipe 10 positioned beneath the middle channel block 3, that is between the middle channel block 3 and the lower channel block 2; and to the upper channel block 4, the coolant is supplied upward from the fluid supply pipe 10 positioned beneath the upper channel block 4, that is between the upper channel block 4 and the middle channel block 3. As described above, the fluid supply pipe 10 is positioned in a horizontal direction. The coolant is supplied from the right side as shown by arrows in FIG. 1A to each of fluid supply pipes 10 which are positioned on the right side of the partition 20, while the coolant is supplied from the left side to each of fluid supply pipes 10 which are positioned on the left side of the partition 20. The coolant is heated and boiled by the fins 12 of each channel block and bubbles are generated.

The vapor discharge path 16 is provided on the top surface side of the fins, that is, the surface opposite to the cooling surface 14 of the fins 12 in contact with a heating body. Being commonly provided for all of the cooling channel blocks, the vapor discharge path 16 discharges bubbles generated in each of the cooling channel blocks.

The flow path partition/vapor discharge guiding plate 18 is provided on the top surface of the fins 12, that is the surface opposite to the fin base 13. In other words, the flow path partition/vapor discharge guiding plate 18 is provided to contact with the surface opposite to the cooling surface of the fins 12 in order to partition between the fins 12 and the vapor discharge path 16. Further, the flow path partition/vapor discharge guiding plate 18 is provided with an opening portion between the fins 12 of the lower channel block 2 and fins 12 of the middle channel block 3, and the other opening portion between the fins 12 of the middle channel block 3 and the fins 12 of the upper channel block 4. Furthermore, the flow path partition/vapor discharge guiding plate 18 includes, at the edge of the opening portion, a guiding portion 19 which projects to be tilted at a certain angle towards the fin base 13. As shown in FIG. 1B, it should be noted that between the lower channel block 2 and the middle channel block 3, the guiding portion 19 of the flow path partition/vapor discharge guiding plate 18 projects towards the fin base 13 from the vertically lower portion of the fins 12 of the middle channel block so as to contact with the fluid supply pipe 10. Similarly, between the middle channel block 3 and the upper channel block 4, the guiding portion 19 projects towards the fin base 13 from the vertically lower portion of the fins 12 of the upper channel block 4 so as to contact with the fluid supply pipe 10. The guiding portion 19 may be formed separately from the flow path partition/vapor discharge guiding plate 18 and joined to the flow path partition/vapor discharge guiding plate 18. The guiding portion 19 may also be formed by bending a portion of the flow path partition/vapor discharge guiding plate 18 towards the fin base 13. The guiding portion 19 projects to be tilted at a certain angle towards the fin base 13 from the vertically lower portion of the fins 12 of the middle channel block 3 so as to contact with the fluid supply pipe 10. Therefore, bubbles which were generated from the fins 12 of the lower channel block 2 and have passed the fins 12 are prevented from flowing into the middle channel block 3 because of the guiding portion 19 which works as an obstacle, and guided into the vapor discharge path 16. Similarly, because the guiding portion 19 projects at a certain angle towards the fin base 13 from the vertically lower portion of the fins 12 of the upper channel block 4 so as to contact with the fluid supply pipe 10, bubbles which were generated from the fins 12 of the middle channel block 3 and have passed the fins 12 are prevented from flowing into the upper channel block 4 because of the guiding portion 19 which works as an obstacle, and guided into the vapor discharge path 16.

FIGS. 2A and 2B show an example of a structure of the fluid supply pipe 10. FIG. 2A shows a fluid supply pipe 10 which includes, at a certain interval on the side surface, a plurality of coolant supply holes having diameters which are gradually enlarged. Further, FIG. 2B shows another case where the fluid supply pipe 10 includes, on its side surface, a coolant supply slit having an opening area which is gradually enlarged. In either case, the opening diameter and the opening area are arranged to be larger at a further downstream side of the coolant.

FIGS. 3A and 3B shows a structure of the flow path partition/vapor discharge guiding plate 18. FIG. 3A shows a front view and FIG. 3B shows a side view. The flow path partition/vapor discharge guiding plate 18 is formed by a pressed metal plate. Opening portions 18a and 18b are respectively formed between the lower channel block 2 and the middle channel block 3 and between the middle channel block 3 and the upper channel block 4. Bubbles generated and growing in the lower channel block 2 are discharged from the opening portion 18a into the vapor discharge path 16. Similarly, bubbles generated and growing in the middle channel block 3 are discharged from the opening portion 18b into the vapor discharge path 16.

A guiding portion 19 is formed at the edge of the opening portion 18a, more specifically, at a vertically lower edge portion of the fins 12 of the middle channel block 3. Similarly, a guiding portion 19 is formed at the edge of the opening portion 18b, more specifically, at a vertically lower edge portion of the fins 12 of the upper channel block 4. The guiding portion 19 may be formed by bending a portion of the flow path partition/vapor discharge guiding plate 18.

FIGS. 4A and 4B show an exploded perspective view of fins 12 and flow path partition/vapor discharge guiding plate 18. Bubbles which are generated at the fins 12 in the lower channel block 2 collide into the guiding portion 19 and thereby, instead of proceeding into the middle channel block 3, the bubbles are discharged from the opening portion 18a into the vapor discharge path 16. Bubbles which are generated at the fins 12 in the upper channel block 4 are directly discharged into the vapor discharge path 16.

FIG. 5 shows an overall structure of the ebullient cooling device 1. The cooling portion 28, a main portion, is sandwiched between heating bodies 26 such as a power device unit. Provided vertically beneath the cooling portion 28 are a coolant supply jacket 22 and a fluid distribution plate 24. Coolant which is supplied from vertically below by a pump is stored and distributed in a sufficient amount to each fluid supply pipe 10 of the cooling portion 28. On the other hand, provided vertically above the cooling portion 28 is a vapor discharge jacket 30 which is connected to the vapor discharge path 16 of the cooling portion 28. The bubbles discharged into the vapor discharge path 16 by the guiding portion 19 are collected at the vapor discharge jacket 30 to be discharged to the outside.

By sandwiching the flow path partition/vapor discharge guiding plate 18 between the fins 12 and vapor discharge path 16 in such a manner, the present embodiment can avoid the deterioration of heat transfer performance and reduction of the critical heat flux by preventing bubbles generated by each cooling channel block from proceeding into and growing excessively in the subsequent cooling channel block.

Further, in the present embodiment, as the vapor discharge path 16 is provided on the top surface side of the fins 12, that is the opposite side to the power device unit which is a heating body, the width of the cooling device can be shortened.

Furthermore, because the flow path partition/vapor discharge guiding plate 18 in the present embodiment can be simply positioned on the fins 12, a simplification of the structure and enhancement of assemblability at the time of manufacturing can be achieved.

Further, the bubble discharging performance can be enhanced because of buoyancy by vertically installing the ebullient cooling device 1 and fins 12 as in the present embodiment.

It should be noted that an ebullient cooling device according to the present embodiment can be applied not only to inverter cooling devices of hybrid vehicles but also to any heating bodies. Although the system configuration of a cooling device according to the present embodiment can be freely decided, examples are shown in FIGS. 6 and 7.

In FIG. 6, the gas-liquid two-phase flow discharged from the ebullient cooling device 1 is supplied to the gas-liquid separator 106. Connected to the gas-liquid separator 106 is a condensor 108, which is further connected to a second gas-liquid separator 110. The cooling fluid from the gas-liquid separators 106, 110 is supplied to a supercooler 102 via an adjusting valve 112 and circulated to the ebullient cooling device 1 by a pump 104. Connected between the adjusting valve 112 and the supercooler 102 is an accumulator 100 which supplies the cooling fluid to the supercooler 102 by using a gas pressure.

In FIG. 7, the gas-liquid two-phase flow which is discharged from the ebullient cooling device 1 is supplied to a condenser 108, to which the gas-liquid separator 116 is connected. The cooling fluid from the gas-liquid separator 116 is circulated to the ebullient cooling device 1 by a pump 104. Connected between the pump 104 and the gas-liquid separator 116 is an accumulator 100 which supplies the cooling fluid to the pump 104 by using gas pressure.