US20080179046A1

US20080179046A1 - Water cooling apparatus

Info

Publication number: US20080179046A1
Application number: US11/858,174
Authority: US
Inventors: Katsumi Hisano; Hideo Iwasaki; Tomonao Takamatsu
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2007-01-31
Filing date: 2007-09-20
Publication date: 2008-07-31
Also published as: JP2008187116A; JP4231081B2

Abstract

In a cooling apparatus, a heating element is thermally connected to a container that defines a first channel through which a coolant flows. A porous block having a large number of pores is accommodated in the container so as to block the first channel. The porous block has second channels formed in the porous block along the first channel and each having an opening on an upstream side of the first channel. Further, third channels are formed in the porous block along the first channel, each have an opening on an upstream side of the first channel, and communicate with the second channels via the pores.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-021125, filed Jan. 31, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a cooling apparatus, and in particular, to a cooling apparatus having a porous block.
2. Description of the Related Art
A year-on-year increase in the amount of heat generated by semiconductor devices has been making it increasingly difficult to cool the semiconductor devices. Air cooling apparatuses are conventionally used to cool the semiconductor devices. However, owing to the insufficient cooling capacity of the air cooling apparatus, liquid cooling apparatuses using an antifreeze solution or the like as a coolant have been developed. The liquid cooling apparatus using the antifreeze solution or the like as a coolant employs a technique for enhancing heat transfer from a solid wall surface to the coolant to cool semiconductor devices. One type of such a technique is a cooling apparatus utilizing micro-channels, which was described by D. B. Tuckerman in the early 1980s, in D. B. Tuckerman, R. F. Pease, High-Performance Heat Sinking for VLSI, 1981, IEEE EDL-2(5), pp. 126-129. In this cooling apparatus, a semiconductor device as a heating element is placed on a heat receiving block to which heat from the semiconductor element is transferred. A channel is defined in the heat receiving block such that a coolant can flow through the channel. Comb-shaped fins formed by etching Si or the like are arranged parallel to one another in the channel. In this structure, micro-channels of width several tens of micrometers to several hundred micrometers are defined among the fins such that the coolant can flow through the micro-channels. It is known that in such a structure, narrower channels reduce the thickness of a temperature boundary layer to provide improved heat transfer performance.
On the other hand, the reduced thickness of the thermal boundary layer is associated with the reduced thickness of a velocity boundary layer. Accordingly, it can be easily expected that the improved heat transfer performance based on the miniaturized channels may increase pressure loss of the coolant.
It is also well known that the thermal boundary layer becomes progressively thicker with a downstream distance from the inlets of the channels. Thus, the increased length of the channels increases heat transfer area but unfortunately fails to correspondingly improve the heat transfer performance.
In the design of the cooling apparatus, the width or length of the channels is determined taking into account the tradeoff between the heat transfer performance and the pressure loss. If very high heat transfer performance is demanded, practical design solutions may not be obtained from the above structure only by dimensional adjustments. That is, increased pressure loss results from an increase in the length of the channels in an attempt to increase the contact area between the coolant and the solid wall surface. However, the heat transfer performance is not improved in proportion to the increase in the channel length. Further, a reduction in the length of the channels in an attempt to reduce the pressure loss may directly decrease heat transfer area.
As a method for solving this problem, a structure has been proposed in which serpentine fins are arranged in the channels. This structure is adopted for a heat exchanger disclosed in JPA 2005-123496 (KOKAI). Further, instead of the cooling apparatus, some filters have adopted structures similar to the serpentine fins. The fins comprising plates with a large number of through-holes are expected to improve the heat transfer performance of the micro-channels at the through-hole portions. The serpentine of the plates increases the area of the plates with the through-holes in the cooling apparatus, that is, the number of through-holes, to ensure both improved heat transfer performance and reduced pressure loss. However, with the structure adopting the serpentine fins, a reduction in the diameter of the through-holes and an increase in the flow rate of the coolant, both carried out to improve the heat transfer performance, may increase the difference in pressure between the front and back surfaces of the thin plate. This may prevent the fins from being made sufficiently strong.
Another problem is how to mount the thin plates for the fins on the wall surfaces of the channels. For example, the channels in which the serpentine fins are provided are each formed to be a substantially rectangular cavity enclosed by six wall surfaces. With this cooling structure, the cooling performance is intended to be improved by reducing the thickness of the walls defining the cavity portion to increase the number of turnups. Thus, in design, the walls are desirably thinner. However, in actuality, the reduced thickness of the walls is expected to make it difficult to mount the end surfaces of the walls on a container.
As described above, with the cooling apparatus using the micro-channels, disclosed in D. B. Tuckerman, R. F. Pease, High-Performance Heat Sinking for VLSI, 1981, IEEE EDL-2(5), pp. 126-129, the improved heat transfer performance based on the miniaturized channels may worsen the pressure loss of the coolant. Another problem with this cooling apparatus is that the increase length of the channels increases the heat transfer area but fails to correspondingly improve the heat transfer performance.
With the heat exchanger having the serpentine fins, disclosed in JPA 2005-123496 (KOKAI), a reduction in the diameter of the through-holes and an increase in the flow rate of the coolant, both carried out to improve the heat transfer performance, may prevent the fins from being made sufficiently strong. Another problem is how to mount the thin plates for the fins on the wall surfaces of the channels.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention provides a cooling apparatus comprising:
a heating element;
a container thermally connected to the heating element to define a first channel through which a coolant flows;
a porous block having a large number of pores formed in the container so as to block the first channel;
second channels formed in the porous block along the first channel and each having an opening on the upstream side of the first channel; and
third channel formed in the porous block along the first channel and each having an opening on the upstream side of the first channel, the third channel communicating with the second channels via the pores.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view schematically showing a cooling apparatus in accordance with an embodiment;

FIG. 2 is a sectional view of the cooling apparatus shown in FIG. 1, the view being taken along line II-II in FIG. 1;

FIG. 3A is a perspective view showing a fin block incorporated into the cooling apparatus shown in FIG. 1 as viewed from a downstream side of a flow passage for a coolant;

FIG. 3B is a perspective view showing the fin block incorporated into the cooling apparatus shown in FIG. 1 as viewed from the upstream side of the flow passage for the coolant;

FIG. 4 is a sectional view schematically showing a fin block incorporated into a cooling apparatus in accordance with another embodiment;

FIG. 5 is a sectional view schematically showing a fin block incorporated into a cooling apparatus in accordance with yet another embodiment; and

FIG. 6 is a sectional view schematically showing a cooling apparatus in accordance with still another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A cooling apparatus in accordance with an embodiment of the present invention will be described below with reference to the drawings as required.
FIGS. 1 and 2 show a cooling apparatus in accordance with the embodiment of the present invention. FIG. 1 is a sectional view of a cooling apparatus taken along a coolant flow passage. FIG. 2 shows a cross section of the cooling apparatus shown in FIG. 1, the cross section being taken along line II-II in FIG. 1.
In the cooling apparatus in FIGS. 1 and 2, a heating element 1 is mounted on a wall surface of a heat receiving block 2 having an external shape substantially like a rectangular parallelepiped. A channel 3 is formed in the heat receiving block 2. As a coolant 4, water or an antifreeze solution is allowed to flow through the channel 3. A fin block 5 is mounted on an inner surface of the heat receiving block 2 in proximity to the wall surface of the heat receiving block 2 on which the heating element 1 is mounted. Heat generated by the heating element 1 is transmitted to the coolant via the fin block 5 and discharged to the exterior of the heat receiving block 2 as the coolant flows through the channel.
The fin block 5 is made of an anisotropic porous material with a large number of pores 6. The pores 6 penetrate the fin block 5 and have a diameter of several μm to several tens of μm. The pores 6 are formed in the fin block 5 so as to extend through the block 5 along a Y direction in FIGS. 1 and 2. The fin block 5 has an upstream side surface 5 a that faces the upstream side of the coolant channel 3 and a downstream side surface 5 b that faces the downstream side of the coolant channel 3. The upstream side surface 5 a and the downstream side surface 5 b are located opposite each other.
A plurality of coolant introduction holes 7 and a plurality of coolant discharge holes 8 are formed in a grid in the YZ surface of each of the upstream side surface 5 a and the downstream side surface 5 b. In the arrangement shown in FIGS. 1 and 2, the coolant introduction holes 7 and the coolant discharge holes 8 are alternately arranged along the Y direction. The coolant introduction holes 7 and the coolant discharge holes 8 are arranged in respective lines along the Z direction. As shown in FIGS. 3A and 3B, the coolant introduction holes 7 and the coolant discharge holes 8 have a diameter of, for example, 100 to 1,000 μm, which is sufficiently larger than that of the pores 6. The coolant introduction holes 7 and the coolant discharge holes 8 are arranged to cross the pores 6, for example, to extend substantially orthogonally to the pores 6. The coolant introduction holes 7 and the coolant discharge holes 8 are further arranged so as not to cross one another or communicate directly with one another. The coolant introduction holes 7 and the coolant discharge holes 8 extend through the fin block 5 so that the inner diameter of each hole decreases progressively. In FIGS. 3A and 3B, the direction in which the pores 6 extend is shown by arrow A, and the direction in which the coolant 4 flows is shown by arrow B. The coolant introduction holes 7 extend from the upstream side surface 5 a along arrow B and do not penetrate the fin block 5 or open in the downstream side surface 5 b. The coolant introduction holes 7 communicate with the large number of pores 6, crossing the coolant introduction holes 7, and communicate with the coolant discharge holes 8, with which the large number of pores 6 communicate. Similarly, the coolant discharge holes 8 extend from the downstream side surface 5 b in a direction opposite to that of arrow B and do not penetrate the fin block 5 or open in the upstream side surface 5 a. The coolant discharge holes 8 communicate with the large number of pores 6, crossing the coolant discharge holes 8, and communicate with the coolant introduction holes 7, with which the large number of pores 6 communicate. The coolant introduction holes 7 and the coolant discharge holes 8 are further arranged so as not to cross one another or communicate directly with one another. Consequently, a coolant flowing into the fin block 5 through the upstream side surface 5 a flows out through the downstream side surface 5 b of the fin block 5 via the coolant introduction holes 7, the pores 6, and the coolant discharge holes 8.
The anisotropic porous material as the fin block 5 is produced by, for example, one of the methods shown in Jpn. Pat. Appln. No. P2005-322629 and Jpn. Pat. Appln. No. P2006-121730. That is, molten metal is poured into a mold in which carbon fibers are arranged parallel to one another. After the metal is solidified, the carbon fibers are oxidized and removed to form the pores 6; the material thus becomes porous. With the carbon fibers remaining in the solidified metal, the coolant introduction holes 7 and the coolant discharge ports 8 are formed in the fin block 5 by machining. The carbon fibers are then removed. This manufacturing method enables the production of a cooling apparatus that prevents the pores from being crushed during machining to avoid obstructing the flow of the coolant.
The coolant flows from the coolant introduction holes 7 through the pores 6 and flows out from the coolant discharge holes 8. As previously described, the inner walls of the small-diameter pores 6 contribute to improving the heat transfer performance. Further, the possible pressure loss between the inlet and outlet of each pore 6 is imposed on the inner walls of the corresponding coolant introduction holes 7 and coolant discharge holes 8, which constitute curved surfaces. Accordingly, the increased flow rate of the coolant and the reduced diameter of the pores make it possible to maintain sufficient strength even with an increase in pressure loss.
Moreover, the entire bottom surface of the fin block 5 can be utilized to mount the fin block 5 on the wall of the channel in the heat receiving block. This facilitates production.
FIG. 4 is a sectional view showing the fin block 5 in accordance with another embodiment of the present invention. As shown in FIG. 4, the coolant introduction holes 7 and the coolant discharge holes 8 are arranged in a zigzag. Two lines of coolant introduction holes 7 and two lines of the coolant discharge holes 8 are alternately formed in each of the upstream side surface 5 a and the downstream side surface 5 b. It is assumed that the surface shown in FIG. 4 is the upstream side surface 5 a. Then, given that in the first line from the left end of the drawing, one line of the three coolant introduction holes 7 are formed, in the third line, one line of the coolant discharge holes 8 are formed. In the fifth line, one line of the three coolant introduction holes 7 are formed, and in the seventh line, one line of the coolant discharge holes 8 are formed. Further, given that in the second row from the left end of the drawing, the coolant introduction channel 7 and the coolant discharge channel 8 are formed, in both the fourth and sixth lines, the coolant introduction channel 7 and the coolant discharge channel 8 are formed. Inside the fin block 5, the pores 6 are arranged so that their axes extend in a horizontal direction (Y direction). When the coolant introduction holes 7 and discharge holes 8 are arranged in a grid as shown in FIGS. 1 and 2, that is, the coolant introduction holes 7 and discharge holes 8 are arranged in respective lines in the Y direction, the coolant does not flow in some of the pores 6. However, when the coolant introduction holes 7 and discharge holes 8 are arranged in a zigzag as shown in FIG. 4, the coolant flows as shown by arrow 4 in FIG. 4. This makes it possible to improve the utilization of the pores and thus the cooling performance.
FIG. 5 is a sectional view showing the fin block 5 in accordance with another embodiment of the present invention. The fin block 5 shown in FIGS. 1 and 2 is made of the anisotropic porous member having the pores extending linearly inside the material in the Y direction. In contrast, the fin block 5 shown in FIG. 5 is made of a porous member having pores extending in a plurality of directions in the YZ surface. The coolant is allowed to flow in the respective axial directions. Since the pores do not extend in any single direction inside the fin block 5, the coolant flows between the coolant introduction holes 7 and the coolant discharge holes 8 wherever the coolant introduction holes and discharge holes are arranged in the YZ surface. To clarify the arrangement of the coolant introduction holes 7 and the arrangement of the coolant discharge holes 8, the coolant discharge holes 8 are marked with reference character x so as to be distinguished from the coolant introduction holes 7.
FIG. 6 shows a cooling apparatus in accordance with another embodiment of the present invention. The coolant introduction holes 7 and discharge holes 8 formed close to the heating element 1 are set to have a smaller diameter, whereas the coolant introduction holes 7 and discharge holes 8 formed away from the heating element 1 are set to have a smaller diameter. In the thus configured cooling apparatus, the inner surfaces of the pores 6 have a larger surface area in an area in the fin block 5 which is closer to the heating element 1 and which thus has a higher temperature. This improves radiating performance.
As described above, the cooling apparatus in accordance with the present invention makes it possible to effectively cool a heating element with a large heating value.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A cooling apparatus comprising:

a heating element;

a container thermally connected to the heating element to define a first channel through which a coolant flows;

a porous block having a large number of pores formed in the container so as to block the first channel;

second channels formed in the porous block along the first channel and each having an opening on the upstream side of the first channel; and

third channels formed in the porous block along the first channel and each having an opening on an upstream side of the first channel, the third channel communicating with the second channels via the pores.

2. The apparatus according to claim 1, wherein the porous block is made of an anisotropic porous material, and the pores are formed in the anisotropic porous material so as to extend in a direction crossing the first channel, and

the second channels and the third channels are substantially arranged in a grid in a cross section of the first channel.

3. The apparatus according to claim 1, wherein the porous block is made of an anisotropic porous material, and the pores are formed in the anisotropic porous material so as to extend in a direction crossing the first channel, and

the second channels and the third channels are substantially arranged in a zigzag in a cross section of the first channel.

4. The apparatus according to claim 1, wherein each of the pores has a diameter of several μm to tens of μm.

5. The apparatus according to claim 1, wherein each of the second and third channels has a diameter of 100 μm to 1000 μm.

6. The apparatus according to claim 1, wherein the second and third channels have a first diameter at a side of the heating element and a second diameter at a opposite side of the heating element, the second diameter being larger than the first diameter.