US20130020058A1

US20130020058A1 - Cooling unit

Info

Publication number: US20130020058A1
Application number: US13/533,043
Authority: US
Inventors: Masumi Suzuki; Michimasa Aoki; Yosuke Tsunoda; Masaru Sugie; Shinichirou Kouno; Kenji Katsumata
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2011-07-22
Filing date: 2012-06-26
Publication date: 2013-01-24
Also published as: JP2013026526A; JP5760796B2

Abstract

A cooling unit includes: at least one pump that circulates coolant; a tank having a first inlet through which coolant is caused to flow in and at least one first outlet through which the coolant is expelled to the at least one pump; and an air bubble accumulating portion provided in an upper part of the tank, wherein the first inlet is disposed at a position such that the coolant is caused to flow into the air bubble accumulating portion, and the at least one first outlet is provided below the air bubble accumulating portion.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-161356, filed on Jul. 22, 2011, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments disclosed herein are related to a cooling unit that cools electronic components mounted in an electronic device, using coolant.

BACKGROUND

In recent years, in PC servers, the rack-mount system has become mainstream. In the rack-mount system, a plurality of server modules are mounted so that they are stacked on top of each other in a rack cabinet. One or more integrated circuit elements (LSIs) typified by processors (CPUs) are mounted on each server module. In a server or a personal computer, a dedicated fan is placed immediately above a component that generates a large amount of heat, such as a CPU or an LSI, and the component is air-cooled so as to stabilize the operation. However, in the rack mount system, in order to improve performance and to save space, as many server modules as possible have to be stacked in a rack cabinet. For this reason, the thickness of individual server modules has to be reduced. Thus, in rack-mounted server modules, it is difficult to attach a fan directly to a component that generates a large amount of heat, such as a CPU or an LSI. In addition, since the server modules are stacked, it is difficult to release the heat generated in individual server modules to the outside. In order to solve these problems, there is a method to cool a CPU, an LSI, or the like, including circulating coolant over a heat-generating component, such as a CPU or an LSI, circulating the coolant that has absorbed heat from the CPU, LSI, or the like to a radiator with a pump, and cooling the coolant with a cooling fan
The following is reference documents:

[Document 1] Japanese Laid-open Patent Publication No. 2004-319628

[Document 2] Japanese Laid-open Patent Publication No. 2005-26498

SUMMARY

According to an aspect of the invention, a cooling unit includes: at least one pump that circulates coolant; a tank having a first inlet through which coolant is caused to flow in and at least one first outlet through which the coolant is expelled to the at least one pump; and an air bubble accumulating portion provided in an upper part of the tank, wherein the first inlet is disposed at a position such that the coolant is caused to flow into the air bubble accumulating portion, and the at least one first outlet is provided below the air bubble accumulating portion.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the structure of a server module employing a cooling unit;

FIG. 2 illustrates a tank of a first embodiment;

FIGS. 3A and 3B illustrate the structure of the tank of the first embodiment;

FIG. 4 illustrates the advantageous effect of the tank of the first embodiment;

FIG. 5 illustrates a tank of a second embodiment;

FIGS. 6A and 6B illustrate the structure of the tank of the second embodiment; and

FIG. 7 illustrates the advantageous effect of the tank of the second embodiment.

DESCRIPTION OF EMBODIMENTS

The preferred embodiments of the present disclosure will be described in detail with reference to the drawings.
FIG. 1 illustrates the configuration of the inside of a server module employing a cooling unit to which the disclosed technique is applied. A circuit board 95 on which a plurality of CPUs 90 are mounted is disposed inside the server module 100. Cooling jackets 92 for transferring heat from the CPUs to coolant are attached to the CPUs 90. The cooling jackets 92 are made of metal having good thermal conductivity, for example, copper or aluminum.
A radiating fin 10 is disposed at an end of the inside of the server module 100 (in the upper part of FIG. 1). On the inner side of the radiating fin 10, a plurality of fans 70 are disposed. The plurality of fans 70 rotate in a direction such that air is blown toward the radiating fin 10. Air heated by the radiating fin 10 is discharged from the end of the server module 100 to the outside of the server module 100.
The server is usually installed in a temperature controlled room. Thus, the plurality of fans 70 may be rotated in the opposite direction to suck in outside air through the end of the server module 100 to cool the radiating fin 10 with the outside air. Also in this case, a cooling effect is achieved.
A tank 40 that stores coolant is disposed inside the server module 100. In the case of this embodiment, in order to save space, the tank 40 is disposed on the top of the cooling jacket 92 on the top of one of the CPUs 90. A plurality of pumps 80 are connected to a side surface of the tank 40. Coolant pressurized by the pumps 80 is sent out from the tank 40 to a pipe 60.
In this embodiment, in order to improve reliability, not only a single pump but a plurality of pumps are provided. If one of the pumps brakes down and stops working, the flow of coolant may be maintained by the other pump, and the temperature rise of heat-generating components such as CPUs 90 may be suppressed. It is also possible to control the number of working pumps to change the flow rate of coolant to adjust the cooling effect according to the operating conditions of the CPUs 90.
Coolant sent out from the tank 40 absorbs heat from the CPUs 90 in the cooling jackets 92 and is sent to the radiating fin 10 through a pipe 61. Coolant is cooled in the radiating fin 10 by the fans 70 and is returned to the tank 40 by a pipe 62. The cooling unit includes the tank 40, the pipe 60, the cooling jackets 92, the pipe 61, the radiating fin 10, and the pipe 62. Coolant circulates through these components, which form a radiating circulation loop. By arranging this radiating circulation loop linearly and setting the route short, coolant may be returned in a short time and the heat radiating efficiency may be improved. The circuit board 95 is designed centering around the CPUs 90, which are the nerve centers of the circuit, and thus the CPUs 90 are often disposed in the center of the circuit board 95. Thus, the radiating circulation loop is also often disposed across the center of the circuit board 95.
For example, a propylene glycol based antifreeze is used as coolant. However, examples of coolant are not limited to this. Parts of the pipes 60, 61, and 62 are made of a flexible heat-insulating material such as rubber or resin. Parts of the pipes 60, 61, and 62 near the cooling jackets 92 are made of a material having good thermal conductivity such as metal in order to efficiently transfer heat from the CPUs 90 to coolant.
Next, with reference to FIG. 2, a tank 40 of a first embodiment will be described. FIG. 2 is a transparent perspective view of the tank 40. The pipe 62 is connected to an inlet 50 in one of the side surfaces of the tank 40. Coolant cooled in the radiating fin 10 is caused to flow through the pipe 62 into the tank 40. A plurality of pumps 80 are connected to the other side surface of the tank 40. The pumps 80 suck out coolant from the tank 40 and expel coolant to the tank 40, thereby producing a flow of coolant. Coolant expelled from the pumps 80 is returned to the radiating circulation loop through an outlet 52 provided in the surface of the tank 40 to which the pumps 80 are connected, and the pipe 60.
Next, with reference to FIGS. 3A and 3B, the structure of the tank 40 will be described in detail. FIG. 3A is a sectional view of the tank 40 and the pumps 80 in FIG. 2 taken along line IIIA-IIIA and in the direction of the arrows. FIG. 3B is a sectional view of the tank 40 and the pumps 80 in FIG. 2 taken along line IIIB-IIIB and in the direction of the arrows.
With reference to FIG. 3A, the inside of the tank 40 is partitioned by a partition plate 46 into two sections: a coolant storing chamber 42 that stores coolant flowing in through the inlet 50 in the upper-left part of FIG. 3A, and a coolant mixing chamber 44 in which coolant expelled from the plurality of pumps 80 is mixed and that is located in the upper-right part in FIG. 3A. If the cooling unit includes only a single pump, the pump is provided in the radiating circulation loop, and coolant is sucked out from the radiating circulation loop and is turned to the radiating circulation loop. However, as described above, in this embodiment, a plurality of pumps 80 are provided in order to improve reliability. For this reason, the coolant mixing chamber 44 for collecting coolant expelled from the plurality of pumps 80 and returning the collected coolant to the radiating circulation loop has to be used. The plurality of pumps 80 are connected in parallel to the coolant mixing chamber 44 so that if one of the pumps 80 brakes down, the flow of coolant of the other pump 80 is not stopped.
Coolant cooled by the radiating fin 10 is caused to flow through the pipe 62 and the inlet 50 into the coolant storing chamber 42. The pumps 80 suck coolant through pump suction ports 54 of the coolant storing chamber 42 located below the coolant mixing chamber 44, and pump suction pipes 82, and then expel coolant through pump expelling pipes 84 and pump expelling ports 56 into the coolant mixing chamber 44.
With reference to FIG. 3B, coolant expelled from the plurality of pumps 80 is collected in the coolant mixing chamber 44 and is then discharged to the pipe 60 through the outlet 52 located at the bottom of FIG. 3B.
In addition to coolant flowing through the radiating circulation loop, coolant for replacing coolant lost through the surface of rubber that makes up the pipes and the surface of resin that makes up the pumps is stored in the tank 40.
At the stage of manufacturing the server module 100, the radiating circulation loop is filled with coolant. The coolant storing chamber 42 and the coolant mixing chamber 44 in the tank 40 are also filled with coolant. Coolant filling is usually performed at room temperature. At this time, air is dissolved in coolant.
When the server module 100 operates and the cooling of the CPUs 90 starts, the temperature of coolant rises, and air dissolved in coolant at room temperature vaporizes to become air bubbles. The air bubbles move through the radiating circulation loop with the flow of coolant. If the air bubbles accumulate in the pumps 80, air locks may arise in the pumps 80, and the ability to expel coolant may decrease significantly.
With reference to FIG. 4, the air bubbles generated in the radiating circulation loop move with the flow of coolant and flow into the coolant storing chamber 42 in the tank 40. Since the air bubbles have a lower specific gravity than coolant, the air bubbles accumulate in a region (hereinafter referred to as air bubble accumulating portion 48) in the upper part of the coolant storing chamber 42 and beside the coolant mixing chamber 44. Air bubbles accumulated in the air bubble accumulating portion 48 form an air layer 49. Since air bubbles accumulate in the air bubble accumulating portion 48, air bubbles are not sucked into the pumps 80 together with coolant through the pump suction ports 54 in the lower part of the coolant storing chamber 42. Thus, according to this embodiment, air locks of the pumps 80 may be suppressed. Since air bubbles generated in the radiating circulation loop finally accumulate in the coolant storing chamber 42, the amount of coolant flowing through the radiating circulation loop is substantially stable, and a decrease in cooling efficiency may be suppressed.
Turning to FIG. 1, the flow of coolant discharged from the tank 40 is divided into two flows and sent through the pipe 60 to each of the cooling jackets 92 for cooling two CPUs 90 in this embodiment. The flows of coolant that has absorbed heat from each CPU 90 are merged in the pipe 61 on the opposite side of the cooling jackets 92 and sent to the radiating fin 10. Coolant cooled in the radiating fin 10 is returned through the pipe 62 to the tank 40.
Next, with reference to FIG. 5, a tank 40A of a second embodiment will be described. FIG. 5 is a transparent perspective view of the tank 40A. Unlike the tank 40 according to the first embodiment, the tank 40A of this embodiment has a structure such that a plurality of pumps 80 are disposed on the left and right sides of the tank 40A. By disposing a plurality of (six in this case) pumps 80 on the left and right sides of the tank 40A, the flow rate of coolant is increased and the cooling efficiency is improved. The pipe 62 is connected to an inlet 50 in one of the side surfaces of the tank 40A. Coolant cooled in the radiating fin 10 is caused to flow through the pipe 62 into the tank 40A. Three pumps 80 are connected to each of other two side surfaces of the tank 40A. In order to reduce the mounting height in the height direction in the server module 100, the pumps 80 connected to the tank 40A are inclined. In this embodiment, the pumps 80 on the left side are inclined in a direction opposite to that of the inclination of the pumps 80 on the right side.
The pumps 80 suck out coolant from the tank 40A and expel coolant to the tank 40A, thereby producing a flow of coolant. Coolant expelled from the pumps 80 is returned to the radiating circulation loop through an outlet 52 provided in one of the surfaces of the tank 40A to which the pumps 80 are connected, and the pipe 60.
Next, with reference to FIGS. 6A and 6B, the structure of the tank 40A will be described in detail. FIG. 6A is a sectional view of the tank 40A and the pumps 80 in FIG. 5 taken along line VIA-VIA of FIG. 5 and in the direction of the arrows (since the pumps 80 on the left side are inclined in a direction opposite to that of the inclination of the pumps 80 on the right side, the sectional direction is changed). FIG. 6B is a sectional view of the tank 40A and the pumps 80 in FIG. 5 taken along line VIB-VIB of FIG. 5 and in the direction of the arrows.
With reference to FIG. 6A, the inside of the tank 40A is partitioned by partition plates 46 into three sections: a coolant storing chamber 42 that stores coolant flowing in through the inlet 50 in the center of FIG. 6A, and two coolant mixing chambers 44 in which coolant expelled from the pumps 80 on the left and right sides is mixed and that are located in the upper-left part and upper-right part in FIG. 6A.
In this embodiment, six pumps 80 are provided in order to improve reliability and cooling efficiency. For this reason, the coolant mixing chambers 44 for collecting coolant expelled from the plurality of pumps 80 and returning the collected coolant to the radiating circulation loop are used. In order not to stop the flow of coolant even if one of the pumps 80 brakes down, three pumps 80 are connected in parallel to one coolant mixing chamber 44. Three pumps 80 are connected in parallel to one coolant mixing chamber 44 so that if one of the pumps 80 brakes down, the flows of coolant of the other pumps 80 are not stopped.
Coolant cooled by the radiating fin 10 is caused to flow through the pipe 62 and the inlet 50 into the coolant storing chamber 42. The pumps 80 on the left and right sides suck coolant through pump suction ports 54 of the coolant storing chamber 42 located below the coolant mixing chambers 44, and pump suction pipes 82, and then expel coolant through pump expelling pipes 84 and pump expelling ports 56 into the left and right coolant mixing chambers 44.
With reference to FIG. 6B, the left and right coolant mixing chambers 44 communicate with each other at the bottom of FIG. 6B. This part will hereinafter be referred to as second coolant mixing chamber 45. Coolant expelled from the plurality of pumps 80 to the left and right coolant mixing chambers 44 is collected in the second coolant mixing chamber 45 and is then discharged to the pipe 60 through the outlet 52 located at the bottom of FIG. 6B.
With reference to FIG. 7, the air bubbles generated in the radiating circulation loop move with the flow of coolant and flow into the coolant storing chamber 42 in the tank 40A. Since the air bubbles have a lower specific gravity than coolant, the air bubbles accumulate in a region (hereinafter referred to as air bubble accumulating portion 48) in the upper part of the coolant storing chamber 42 and between the two coolant mixing chambers 44. Air bubbles accumulated in the air bubble accumulating portion 48 form an air layer 49. Since air bubbles accumulate in the air bubble accumulating portion 48, air bubbles are not sucked into the pumps 80 together with coolant through the pump suction ports 54 in the lower part of the coolant storing chamber 42. In this embodiment, the left and right coolant mixing chambers 44 have a cross-sectional shape inclined downward toward the inside of the tank 40A. Since the flow path to the pump suction ports 54 becomes narrower downward, air bubbles are kept from being sucked into the pumps 80 even if air bubbles flow forcefully into the coolant storing chamber 42 together with coolant owing to an increase in the flow rate of coolant.
Owing to the above-described structure, also in this embodiment, air locks of the pumps 80 may be suppressed. Since air bubbles generated in the radiating circulation loop finally accumulate in the coolant storing chamber 42, the amount of coolant flowing through the radiating circulation loop is substantially stable, and a decrease in cooling efficiency may be suppressed.
Turning to FIG. 1, the flow of coolant discharged from the tank 40 is divided into two flows and sent through the pipe 60 to each of the cooling jackets 92 for cooling two CPUs 90 in this embodiment. The flows of coolant that has absorbed heat from each CPU 90 are merged in the pipe 61 on the opposite side of the cooling jackets 92 and sent to the radiating fin 10. Coolant cooled in the radiating fin 10 is returned through the pipe 62 to the tank 40A.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims

1. A cooling unit comprising:

at least one pump that circulates coolant;

a tank having a first inlet through which coolant is caused to flow in and at least one first outlet through which the coolant is expelled to the at least one pump; and

an air bubble accumulating portion provided in an upper part of the tank,

wherein the first inlet is disposed at a position such that the coolant is caused to flow into the air bubble accumulating portion, and

the at least one first outlet is provided below the air bubble accumulating portion.

2. The cooling unit according to claim 1, wherein

the at least one pump comprises a plurality of pumps,

the at least one first outlet comprises a plurality of first outlets, and

the tank further has at least one mixing chamber having a plurality of second inlets connected to outlets of the plurality of pumps.

3. The cooling unit according to claim 2, wherein

the at least one mixing chamber has a second outlet through which the coolant flowing in through the plurality of second inlets is expelled, and

a circulation loop that leads from the second outlet to the first inlet and circulates the coolant is connected to the at least one mixing chamber.

4. The cooling unit according to claim 3, wherein

a radiating fin that cools the coolant, and

a cooling member that absorbs heat from a heat-generating component with the coolant are connected to the route of the circulation loop.

5. The cooling unit according to claim 2, wherein

the at least one mixing chamber comprises a plurality of mixing chambers, and

the tank further has a second mixing chamber in which the coolant from the plurality of mixing chambers is mixed.