U.S. patent application number 13/323973 was filed with the patent office on 2012-05-31 for loop heat pipe and startup method for the same.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Shigenori Aoki, Takeshi Shioga, Hiroki Uchida.
Application Number | 20120132402 13/323973 |
Document ID | / |
Family ID | 43449214 |
Filed Date | 2012-05-31 |
United States Patent
Application |
20120132402 |
Kind Code |
A1 |
Aoki; Shigenori ; et
al. |
May 31, 2012 |
LOOP HEAT PIPE AND STARTUP METHOD FOR THE SAME
Abstract
A loop heat pipe includes: a first evaporator and a second
evaporator each of which vaporizes a liquid-phase working fluid and
converts the liquid-phase working fluid to a vapor-phase working
fluid; a first condenser and a second condenser each of which
condenses the vapor-phase working fluid and converts the
vapor-phase working fluid back to the liquid-phase working fluid; a
first vapor line through which the working fluid converted to the
vapor phase is transported to the first condenser; a first liquid
line through which the working fluid converted to the liquid phase
is transported to the second evaporator; a second vapor line
through which the working fluid converted to the vapor phase is
transported to the second condenser; and a second liquid line
through which the working fluid converted to the liquid phase is
transported to the first evaporator.
Inventors: |
Aoki; Shigenori; (Kawasaki,
JP) ; Shioga; Takeshi; (Kawasaki, JP) ;
Uchida; Hiroki; (Kawasaki, JP) |
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
43449214 |
Appl. No.: |
13/323973 |
Filed: |
December 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2010/056093 |
Apr 2, 2010 |
|
|
|
13323973 |
|
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Current U.S.
Class: |
165/104.21 |
Current CPC
Class: |
H05K 7/20809 20130101;
H01L 23/427 20130101; F28F 2250/06 20130101; H01L 2924/0002
20130101; H01L 2924/0002 20130101; F28D 15/0266 20130101; F28D
15/06 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/104.21 |
International
Class: |
F28D 15/02 20060101
F28D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2009 |
JP |
2009-164960 |
Claims
1. A loop heat pipe comprising: a first evaporator and a second
evaporator each of which vaporizes a liquid-phase working fluid by
receiving heat from a heat source and thereby converts the
liquid-phase working fluid to a vapor-phase working fluid; a first
condenser and a second condenser each of which condenses the
vapor-phase working fluid by giving off heat and thereby converts
the vapor-phase working fluid back to the liquid-phase working
fluid; a first vapor line through which the working fluid converted
to the vapor phase by the first evaporator is transported to said
first condenser; a first liquid line through which the working
fluid converted to the liquid phase by the first condenser is
transported to said second evaporator; a second vapor line through
which the working fluid converted to the vapor phase by the second
evaporator is transported to said second condenser; and a second
liquid line through which the working fluid converted to the liquid
phase by the second condenser is transported to said first
evaporator.
2. The loop heat pipe as claimed in claim 1, further comprising a
bypass line which connects between said first vapor line and said
second vapor line.
3. The loop heat pipe as claimed in claim 2, wherein said bypass
line connects between a portion of said first vapor line in the
vicinity of said first condenser and a portion of said second vapor
line in the vicinity of said second condenser.
4. The loop heat pipe as claimed in claim 2, wherein the
cross-sectional area of a working fluid flow section of said bypass
line is not larger than the cross-sectional area of a working fluid
flow section of said first vapor line or said second vapor
line.
5. The loop heat pipe as claimed in claim 4, wherein the ratio of
said cross-sectional area of said bypass line to said
cross-sectional area of said first vapor line or said second vapor
line is in the range of 0.1 to 1.
6. The loop heat pipe as claimed in claim 1, wherein said first
evaporator is located upwardly of said second evaporator as viewed
along a plumbline direction.
7. The loop heat pipe as claimed in claim 1, wherein said first
condenser and said second condenser are constructed in integral
fashion.
8. The loop heat pipe as claimed in claim 7, wherein said first
condenser includes a first condenser line and said second condenser
includes a second condenser line, and wherein a plurality of heat
sinking plates are coupled in common to both said first condenser
line and said second condenser line.
9. A method for starting up a loop heat pipe which comprises: a
first evaporator and a second evaporator each of which vaporizes a
liquid-phase working fluid by receiving heat from a heat source and
thereby converts the liquid-phase working fluid to a vapor-phase
working fluid; a first condenser and a second condenser each of
which condenses the vapor-phase working fluid by giving off heat
and thereby converts the vapor-phase working fluid back to the
liquid-phase working fluid; a first vapor line through which the
working fluid converted to the vapor phase by the first evaporator
is transported to said first condenser; a first liquid line through
which the working fluid converted to the liquid phase by the first
condenser is transported to said second evaporator; a second vapor
line through which the working fluid converted to the vapor phase
by the second evaporator is transported to said second condenser;
and a second liquid line through which the working fluid converted
to the liquid phase by the second condenser is transported to said
first evaporator, wherein said first evaporator is located upwardly
of said second evaporator as viewed along a plumbline direction,
and said first evaporator is started to receive heat after a
predetermined length of time has elapsed from the time said second
evaporator began to receive heat.
10. The loop heat pipe startup method as claimed in claim 9,
wherein said predetermined length of time is determined based on
the time taken for the liquid-phase working fluid to begin to flow
into said first evaporator.
11. The loop heat pipe startup method as claimed in claim 9,
wherein said loop heat pipe comprises a bypass line which connects
between said first vapor line and said second vapor line.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2009-164960,
filed on Jul. 13, 2009, and International Patent Application
PCT/JP2010/056093, filed on Apr. 2, 2010, the entire contents of
which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention is related to a loop heat pipe and a
startup method for the same.
BACKGROUND ART
[0003] Heat pipes are used for cooling electronic devices. A heat
pipe is a heat transfer device that transports heat by utilizing
the phase change of the working fluid sealed therein.
[0004] In order to enhance the cooling capability for cooling
electronic devices, a heat pipe known as a loop heat pile has been
developed that can transport a larger heat load over a longer
distance.
[0005] The loop heat pipe includes an evaporator which receives
heat from a heat source and vaporizes a liquid-phase working fluid,
and a condenser which condenses the vapor-phase working fluid by
giving off heat. The loop heat pipe further includes a vapor line
through which the working fluid converted to the vapor phase by the
evaporator is transported to the condenser, and a liquid line
through which the working fluid converted to the liquid phase by
the condenser is transported to the evaporator. The loop heat pipe
has a loop structure in which the evaporator, the evaporator line,
the condenser, and the liquid line are connected in series, and the
working fluid is sealed therein.
[0006] In recent years, a blade server of the type that has two
CPUs on one blade has been developed in order to enhance the
processing capability of the server.
[0007] If two CPUs are to be cooled during operation by using a
loop heat pipe, there arises a need to provide two evaporators in
order to receive heat from the respective CPUs, which means that
two loop heat pipes have to be incorporated into the blade
server.
[0008] In order to incorporate two loop heat pipes into the blade
server, an area for accommodating the two loop heat pipes needs to
be provided on the substrate.
[0009] However, since the blade server was originally developed as
a server more compact in volume than the conventional server,
electronic devices including CPUs are packed at high density on the
substrate.
[0010] There are therefore cases in which it is difficult to secure
an area for accommodating two loop heat pipes on the substrate.
[0011] On the other hand, a loop heat pipe equipped with two
evaporators has been proposed. A loop heat pipe of this type is
depicted in FIG. 1.
[0012] The loop heat pipe 110 includes a first evaporator 111A and
a condenser 112. The loop heat pipe 110 further includes a first
liquid line 114A through which the working fluid converted to the
liquid phase by the condenser 112 is transported to the first
evaporator 111A, and a vapor line 113 through which the working
fluid converted to the vapor phase by the first evaporator 111A is
transported to the condenser 112.
[0013] Further, as depicted in FIG. 1, the loop heat pipe 110
includes a second evaporator 111B which assists in transporting the
liquid-phase working fluid into the first evaporator 111A at the
time of startup. A portion of the liquid-phase working fluid passed
through the first liquid line 114A flows into the second evaporator
111B through a second liquid line 114B and through the condenser
112. The working fluid converted to the vapor phase by the second
evaporator 111B merges with the working fluid flowing in the vapor
line 113 and is transported to the condenser 12. The working fluid
transported through the second liquid line 114B is passed through
the condenser 12 and flows into the second evaporator 111B without
merging with the working fluid flowing in the first liquid line
114A.
[0014] When starting up the loop heat pipe 110, the liquid-phase
working fluid is quickly fed into the second evaporator 111B
disposed near the condenser 112, thus starting the circulation of
the working fluid through the loop and causing the liquid-phase
working fluid to flow into the first evaporator 111A. The second
evaporator 111B is an auxiliary evaporator provided to assist the
startup of the loop heat pipe 110. Therefore, the second evaporator
111B has a smaller size and lower cooling capacity than the first
evaporator 111A.
[0015] If such a loop heat pipe 110 having two evaporators 111A and
111B is used for cooling two CPUs substantially equal in heat load,
the circulation of the working fluid through the loop tends to
become unsteady because of the difference in cooling capacity
between the two evaporators 111A and 111B and because of the
arrangement of the fluid lines. [0016] [Patent Document 1] Japanese
Unexamined Patent Publication No. 2008-85112 [0017] [Patent
Document 2] U.S. Patent Application No. 2004/0182550
SUMMARY
[0018] According to an aspect of the embodiment disclosed in this
specification to solve the above problem, there is provided a loop
heat pipe which includes: a first evaporator and a second
evaporator each of which vaporizes a liquid-phase working fluid by
receiving heat from a heat source and thereby converts the
liquid-phase working fluid to a vapor-phase working fluid; a first
condenser and a second condenser each of which condenses the
vapor-phase working fluid by giving off heat and thereby converts
the vapor-phase working fluid back to the liquid-phase working
fluid; a first vapor line through which the working fluid converted
to the vapor phase by the first evaporator is transported to the
first condenser; a first liquid line through which the working
fluid converted to the liquid phase by the first condenser is
transported to the second evaporator; a second vapor line through
which the working fluid converted to the vapor phase by the second
evaporator is transported to the second condenser; and a second
liquid line through which the working fluid converted to the liquid
phase by the second condenser is transported to the first
evaporator.
[0019] The object and advantages of the embodiments will be
realized and attained by means of the elements and combinations
particularly pointed out in the claims.
[0020] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram illustrating a loop heat pipe according
to the related art;
[0022] FIG. 2 is a diagram illustrating a first embodiment of a
loop heat pipe disclosed in this specification;
[0023] FIG. 3 is a diagram illustrating a blade server in which the
loop heat pipe of FIG. 2 is incorporated;
[0024] FIG. 4 is an enlarged longitudinal cross-sectional view of
an evaporator in the loop heat pipe of FIG. 2;
[0025] FIG. 5 is an enlarged lateral cross-sectional view of the
evaporator in the loop heat pipe of FIG. 2;
[0026] FIGS. 6(A) to 6(D) are diagrams illustrating the operation
of the loop heat pipe of FIG. 2;
[0027] FIG. 7 is a diagram illustrating how the amount of received
heat becomes unbalanced;
[0028] FIG. 8 is a diagram illustrating a second embodiment of the
loop heat pipe disclosed in this specification;
[0029] FIGS. 9(A) to 9(D) are diagrams illustrating the operation
of the loop heat pipe of FIG. 8;
[0030] FIG. 10 is a diagram illustrating a third embodiment of the
loop heat pipe disclosed in this specification;
[0031] FIG. 11 is a diagram illustrating a blade server in which a
fourth embodiment of the loop heat pipe disclosed in this
specification is incorporated;
[0032] FIG. 12 is a diagram illustrating Working Examples 1 to 14
of the loop heat pipe disclosed in this specification;
[0033] FIG. 13 is a diagram illustrating Working Example 15 of the
loop heat pipe disclosed in this specification;
[0034] FIG. 14 is a diagram illustrating Working Example 16 of the
loop heat pipe disclosed in this specification;
[0035] FIG. 15 is a diagram illustrating Working Example 17 of the
loop heat pipe disclosed in this specification; and
[0036] FIG. 16 is a diagram illustrating Working Example 18 of the
loop heat pipe disclosed in this specification.
DESCRIPTION OF EMBODIMENTS
[0037] A first preferred embodiment of a loop heat pipe disclosed
in this specification will be described below with reference to
drawings. It will, however, be noted that the technical scope of
the present invention is not limited to the specific embodiments
disclosed herein, but extends to the inventions described in the
appended claims and their equivalents.
[0038] FIG. 2 is a diagram illustrating the first embodiment of the
loop heat pipe disclosed in this specification. FIG. 3 is a diagram
illustrating a blade server in which the loop heat pipe of FIG. 2
is incorporated. FIG. 4 is an enlarged longitudinal cross-sectional
view of an evaporator in the loop heat pipe of FIG. 2. FIG. 5 is an
enlarged lateral cross-sectional view of the evaporator in the loop
heat pipe of FIG. 2.
[0039] As illustrated in FIG. 2, the loop heat pipe 10 of the
present embodiment includes a first evaporator 11A and a second
evaporator 11B each of which vaporizes a liquid-phase working fluid
16 by receiving heat from a heat source and thereby converts the
liquid-phase working fluid 16 to a vapor-phase working fluid 16.
The loop heat pipe 10 further includes a first condenser 12A and a
second condenser 12B each of which condenses the vapor-phase
working fluid 16 by giving off heat and thereby converts the
vapor-phase working fluid 16 back to the liquid-phase working fluid
16. Further, the loop heat pipe 10 includes a first vapor line 13A
through which the working fluid 16 converted to the vapor phase by
the first evaporator 11A is transported to the first condenser 12A,
and a first liquid line 14A through which the working fluid 16
converted to the liquid phase by the first condenser 12A is
transported to the second evaporator 11B. Furthermore, the loop
heat pipe 10 includes a second vapor line 13B through which the
working fluid 16 converted to the vapor phase by the second
evaporator 11B is transported to the second condenser 12B, and a
second liquid line 14B through which the working fluid 16 converted
to the liquid phase by the second condenser 12B is transported to
the first evaporator 11A.
[0040] In the loop heat pipe 10, a loop flow passage is formed by
connecting in series the first evaporator 11A, the first vapor line
13A, the first condenser 12A, the first liquid line 14A, the second
evaporator 11B, the second vapor line 13B, the second condenser
12B, and the second liquid line 14B.
[0041] The working fluid is hermetically sealed in the loop flow
passage. The working fluid 16 transports heat while undergoing a
phase change between the liquid phase and the vapor phase in the
loop heat pipe 10. The working fluid 16 is hermetically sealed in
the loop heat pipe 10 at saturated vapor pressure.
[0042] As the working fluid 16, for example, water, alcohol,
ammonia, fluorocarbon, or the like, may be used.
[0043] In use, the loop heat pipe 10 is incorporated, for example,
in a blade server 20, as illustrated in FIG. 3.
[0044] The blade server 20 is equipped with two CPUs 21A and 21B.
The first evaporator 11A of the loop heat pipe 10 is disposed in
thermal contact with the CPU 21A. The second evaporator 11B is
disposed in thermal contact with the CPU 21B.
[0045] In many cases, the blade server 20 has an elongated
rectangular shape as depicted in FIG. 3. The blade server 20 is
usually oriented in such a manner that its width direction
extending at right angles to its longitudinal direction coincides
with the plumbline direction. Typically, the CPU 21A is located
upwardly of the CPU 21B, as viewed along the plumbline
direction.
[0046] Accordingly, in the loop heat pipe 10, the first evaporator
11A that receives heat from the CPU 21A is located upwardly of the
second evaporator 11B that receives heat from the CPU 21B, as
viewed along the plumbline direction.
[0047] A main fan 22 delivers air to the first and second
condensers 12A and 12B to promote heat dissipation.
[0048] While FIG. 3 has depicted an example in which the loop heat
pipe 10 is incorporated in the blade server, the loop heat pipe 10
may be incorporated in other electronic apparatus having a heat
source to be cooled.
[0049] Next, the first evaporator 11A will be described in further
detail below with reference to FIGS. 4 and 5. Since the second
evaporator 11B is identical in structure to the first evaporator
11A, the description hereinafter given of the first evaporator 11A
applies as well to the second evaporator 11B.
[0050] As illustrated in FIG. 4, the first evaporator 11A has a
longitudinally extending shape. The longitudinal direction of the
first evaporator 11A coincides with the direction in which the
working fluid 16 flows through the flow passage of the loop heat
pipe 10. In FIG. 4, the flow direction of the working fluid 16 is
indicated by arrows.
[0051] As illustrated in FIGS. 4 and 5, the first evaporator 11A
includes a longitudinally extending housing 30, a metal block 31
centrally located within the housing 30, a metal tube 32 located in
a hollow space within the metal block 31, and a wick 33 located
within the metal tube 32.
[0052] The housing 30, the metal block 31, and the metal tube 32
are each formed from a metal having high thermal conductivity such
as copper.
[0053] The longitudinal direction of the housing 30 coincides with
the longitudinal direction of the first evaporator 11A. The second
liquid line 14B is connected to one longitudinal end of the housing
30. The first vapor line 13A is connected to the other longitudinal
end of the housing 30.
[0054] The heat source such as the CPU 21A is thermally coupled to
the housing 30 by means of a thermal bonding material such as
thermal grease (not depicted).
[0055] The metal block 31 is in intimate contact with the inner
surface of the housing 30 and is thus thermally coupled to the
housing 30. The metal block 31 has a cylindrically shaped hollow
core. The longitudinal direction of the hollow core coincides with
the longitudinal direction of the first evaporator 11A. The metal
block 31 quickly conducts the heat, received from the heat source
21A via the housing 30, to the metal tube 32 located in the hollow
core.
[0056] The metal tube 32 has a longitudinally elongated cylindrical
shape. The metal tube 32 is located in the hollow core of the metal
block 31. The longitudinal direction of the metal tube 32 coincides
with the longitudinal direction of the first evaporator 11A. The
outer surface of the metal tube 32 is in intimate contact with the
inner surface of the hollow core of the metal block 31, and thus
the metal tube 32 is thermally coupled to the metal block 31.
[0057] As illustrated in FIG. 5, a plurality of projections 34a and
depressions 34b are formed on the inner surface of the metal tube
32 at a prescribed pitch in the circumferential direction thereof.
The projections 34a and depressions 34b are formed along the entire
longitudinal direction of the metal tube 32. The groove-like space
formed between the wick 33 and the depressions 34b provides a
passage for the working fluid 16.
[0058] The wick 33 has a longitudinally elongated cylindrical
shape, as depicted in FIG. 4. The wick 33 is open at one end
thereof that faces the second liquid line 14B and closed at the
other end thereof that faces the first vapor line 13A.
[0059] The wick 33 is inserted in the metal tube 32 with its closed
end facing toward the first vapor line 13A. As illustrated in FIG.
5, the outer surface of the wick 33 contacts the tips of the
plurality of projections 34a formed on the inner surface of the
metal tube 32, and thus the wick 33 is thermally coupled to the
metal tube 32.
[0060] The wick 33 is formed of a porous material. For example, the
wick 33 is constructed from a porous member formed by sintering
copper powder. Preferably, the hollow interior space of the wick 33
is made to communicate with the exterior thereof by means of
numerous fine pores of diameters about 10 .mu.m to 50 .mu.m.
[0061] When the liquid-phase working fluid 16 flows into the first
evaporator 11A from the second liquid line 14B, the working fluid
16 infiltrates into the wick 33 by capillary action, and the wick
33 is thus wetted with the working fluid 16. The liquid-phase
working fluid 16 infiltrated into the wick 33 is heated and
vaporized by the heat received from the heat source such as the CPU
21A.
[0062] The vapor-phase working fluid 16 existing in the wick 33
itself or on its surface or in the hollow interior space of the
wick 33 is vented from the hollow interior space to the outside
through the fine pores formed in the wick 33.
[0063] The housing 30 of the first evaporator 11A having the above
structure may be chosen to have dimensions measuring 50 mm
vertically, 50 mm horizontally, and 20 mm in height, compared with
the CPU as the heat source which measures, for example, 30 mm
vertically and 30 mm horizontally. The metal block 31 may be chosen
to have dimensions measuring 40 mm vertically, 40 mm horizontally,
and 20 mm in height. The metal tube 32 may be chosen to have an
outer diameter of 14 mm and an inner diameter of 10 mm (tube wall
thickness of 2 mm). The depressions 34b of depth 1 mm are formed in
the inner surface of the metal tube 32, for example, at a pitch of
2 mm. The wick 33 may be chosen to have an outer diameter of 10 mm
and an inner diameter of 4 mm.
[0064] Next, the first condenser 12A will be described in further
detail below with reference to FIGS. 2 and 3. Since the second
condenser 12B is identical in structure to the first condenser 12A,
the description hereinafter given of the first condenser 12A
applies as well to the second condenser 12B.
[0065] As depicted in FIG. 2, the first condenser 12A includes a
first condenser line 40A and a plurality of first heat sinking
plates 41A coupled to the first condenser line 40A.
[0066] The first vapor line 13A is connected to one end of the
first condenser line 40A. The first liquid line 14A is connected to
the other end of the first condenser line 40A.
[0067] The plurality of first heat sinking plates 41A are thermally
coupled to the first condenser line 40A, and the heat of the
working fluid 16 passing through the first condenser line 40A is
dissipated via the plurality of first heat sinking plates 41A.
[0068] As depicted in FIG. 3, it is preferable to blow air over the
plurality of first heat sinking plates 41A of the first condenser
12A by means of the main fan 22 or the like in order to dissipate
heat and facilitate the phase change of the working fluid 16 from
the vapor phase to the liquid phase.
[0069] Next, the first vapor line 13A will be described in further
detail below with reference to FIGS. 2 and 3. Since the second
vapor line 13B is identical in structure to the first vapor line
13A, the description hereinafter given of the first vapor line 13A
applies as well to the second vapor line 13B.
[0070] One end of the first vapor line 13A is connected to the
first evaporator 11A. The other end of the first vapor line 13A is
connected to the first condenser 12A.
[0071] All of the working fluid 16 flowing in the first vapor line
13A is not necessarily in vapor phase. Depending on the operating
conditions or installation environment of the loop heat pipe 10,
the working fluid 16 may turn into liquid phase during passage
between the first evaporator 11A and the first condenser 12A, so
that the working fluid 16 partly in liquid phase and partly in
vapor phase may flow in the first vapor line 13A.
[0072] The first vapor line 13A is formed from a metal having high
thermal conductivity such as copper.
[0073] Next, the first liquid line 14A will be described in further
detail below with reference to FIGS. 2 and 3. Since the second
liquid line 14B is identical in structure to the first liquid line
14A, the description hereinafter given of the first liquid line 14A
applies as well to the second liquid line 14B.
[0074] One end of the first liquid line 14A is connected to the
first condenser 12A. The other end of the first liquid line 14A is
connected to the second evaporator 11B.
[0075] All of the working fluid 16 flowing in the first liquid line
14A is not necessarily in liquid phase. Depending on the operating
conditions or installation environment of the loop heat pipe 10,
the working fluid 16 may turn into vapor phase during passage
between the first condenser 12A and the second evaporator 11B, so
that the working fluid 16 partly in liquid phase and partly in
vapor phase may flow in the first liquid line 14A.
[0076] The first liquid line 14A is formed from a metal having high
thermal conductivity such as copper.
[0077] The working fluid 16 is sealed in the loop heat pipe 10
preferably in such an amount that the liquid-phase working fluid 16
fills the first evaporator 11A, the second liquid line 14B, the
second evaporator 11B, and the first liquid line 14A. Also
preferably, the volume of this working fluid 16 is a little larger
than one half of the volume of the flow passage in the loop heat
pipe 10. If the volume of the working fluid 16 is larger than this
specific volume, the flow resistance increases, and the thermal
resistance thus increases. On the other hand, if the volume of the
working fluid 16 is smaller than this specific volume, the
operation of the loop heat pipe 10 may become unstable.
[0078] Next, the operation of the loop heat pipe 10 will be
described below with reference to FIGS. 6(A) to 6(D). FIGS. 6(A) to
6(D) are diagrams illustrating the operation of the loop heat
pipe.
[0079] First, as illustrated in FIG. 6(A), in the loop heat pipe
10, the first evaporator 11A is located upwardly of the second
evaporator 11B, as viewed along the plumbline direction.
Accordingly, in the pre-startup stage, the liquid-phase working
fluid 16 is collected in the lower part of the loop heat pipe 10,
and the inside of the second evaporator 11B is filled with the
liquid-phase working fluid 16. The fine pores of the wick 33 inside
the second evaporator 11B are thus impregnated with the
liquid-phase working fluid 16.
[0080] The upper part of the loop heat pipe 10 is filled with the
vapor-phase working fluid 16. Accordingly, the inside of the first
evaporator 11A is filled with the vapor-phase working fluid 16.
That is, the wick 33 inside the first evaporator 11A is in a dry
condition, and the first evaporator 11A is thus in the so-called
dry-out condition.
[0081] When starting up the loop heat pipe 10, first the second
evaporator 11B is started to receive heat. In the example
illustrated in FIG. 3, only the CPU 21B is put into operation, and
the second evaporator 11B begins to receives heat from the CPU 21B
which is the heat source.
[0082] The first evaporator 11A is started to receive heat after a
predetermined length of time has elapsed from the time the second
evaporator 11B began to receive heat. This predetermined length of
time is determined based on the time taken for the liquid-phase
working fluid 16 to begin to flow into the first evaporator
11A.
[0083] In the second evaporator 11B that received heat from the
heat source, first the housing 30 is heated by the heat from the
heat source, and the heat thus applied to the housing 30 is
transferred to the metal block 31. The heat transferred to the
metal block 31 is then transferred to the metal tube 32, and the
heat transferred to the metal tube 32 is further transferred via
the projections 34a of the metal tube 32 to the wick 33 which is
thus heated.
[0084] When the temperature of the wick 33 rises as it is heated,
the liquid-phase working fluid 16 filled into the fine pores of the
wick 33 boils and vaporizes. Since the pressure inside the fine
pores increases as the working fluid 16 in the fine pores of the
wick 33 turns into vapor phase, the vapor-phase working fluid 16 is
forced out onto the outer surface of the wick 33.
[0085] The vapor-phase working fluid 16 forced out onto the outer
surface of the wick 33 passes, for example, through the space
formed by the depressions 34b of the metal tube 32 and flows into
the interior space of the housing 30 on the second evaporator 13B
side. The vapor-phase working fluid 16 then flows into the second
vapor line 13B.
[0086] In the operating condition after the startup of the loop
heat pipe 10, some of the vapor-phase working fluid 16 may remain
inside the metal tube 32 of the second evaporator 11B. This
vapor-phase working fluid 16 is also forced out onto the outer
surface of the wick 33 as the pressure increases due to the
vaporization of the working fluid 16.
[0087] Next, as illustrated in FIG. 6(B), as the pressure rises
inside the housing 30 of the second evaporator 11B, the
liquid-phase working fluid 16 remaining in the second evaporator
line 13B is forced into the second condenser 12B. The liquid-phase
working fluid 16 is further forced from the second condenser 12B
into the second liquid line 14B, and the fluid level in the second
liquid line 14B thus rises.
[0088] Then, the vapor-phase working fluid 16 pushed by the
liquid-phase working fluid 16 is forced to pass through the first
evaporator 11A and then through the first vapor line 13A, and
finally flows into the first condenser 12A. The vapor-phase working
fluid 16 flowing into the first condenser 12A is condensed by
giving off heat and changes to the liquid phase. The heat contained
in the working fluid 16 is transferred via the first condenser line
40A to the first heat sinking plates 41A from which the heat is
dissipated.
[0089] In this way, in the first condenser 12A, the vapor-phase
working fluid 16 is cooled, and all or part of it changes to the
liquid phase. As a result, the liquid-phase working fluid 16
accumulates in the first condenser 12A and the first vapor line
13A, and the fluid level thus rises.
[0090] Next, as illustrated in FIG. 6(C), the liquid-phase working
fluid 16 forced into the second liquid line 14B by being pushed
from the second condenser 12B side begins to flow into the first
evaporator 11A.
[0091] At this point in time, the first evaporator 11A starts to
receive heat. For example, as illustrated in FIG. 3, the CPU 21A is
put into operation, and the first evaporator 11A begins to receive
heat from the CPU 21A which is the heat source.
[0092] The liquid-phase working fluid 16 flowing into the first
evaporator 11A changes to the vapor phase, and the vapor-phase
working fluid 16 flows into the first vapor line 13A.
[0093] Next, as illustrated in FIG. 6(D), the interior space of the
wick 33 in the first evaporator 11A is substantially filled with
the liquid-phase working fluid 16, and the operation of the loop
heat pipe 10 thus becomes stable. When the operation of the loop
heat pipe 10 becomes stable, the first evaporator 11A, the second
evaporator 11B, the first liquid line 14A, and the second liquid
line 14B are substantially filled with the liquid-phase working
fluid 16. The other portions of the loop heat pipe 10 are filled
with the vapor-phase working fluid 16.
[0094] In this way, the two heat sources are cooled stably by the
loop heat pipe 10.
[0095] According to the loop heat pipe 10 described above, since
the loop heat pipe is constructed from a single loop flow passage,
the overall dimensions of the structure can be reduced.
Furthermore, because of the provision of two evaporators, the loop
heat pipe 10 can cool two heat sources.
[0096] According to the startup method of the loop heat pipe 10
described above, since the evaporator filled with the liquid-phase
working fluid 16 is first started to receive heat, the loop heat
pipe 10 can be started up in a reliable manner.
[0097] For example, in the case of a blade server equipped with two
CPUs, if the two CPUs can both be mounted in the lower part of the
substrate (lower as viewed along the plumbline direction), the two
evaporators can both be filled with the liquid-phase working fluid
at the time of the loop heat pipe startup. However, such an
arrangement greatly constrains the blade server construction, and
is therefore difficult to implement in practice.
[0098] Further, in the case of a blade server equipped with two
CPUs, the two CPUs are often mounted in different positions as
viewed along the plumbline direction. In this case, if different
loop heat pipes are provided for the two respective CPUs, the
evaporator thermally coupled to the CPU mounted in the upper
position as viewed along the plumbline direction may not be able to
be filled with the liquid-phase working fluid at the time of
startup. If the loop heat pipe is to be started up with no
liquid-phase working fluid in the evaporator, the loop heat pipe
will not start up because the evaporator is in the dry-out
condition and is therefore unable to cause the liquid-phase working
fluid to change to the vapor phase.
[0099] By contrast, according to the loop heat pipe 10 described
above, since two evaporators are provided within a single loop, the
evaporator located in the lower part as viewed along the plumbline
direction can be easily filled with the liquid-phase working fluid
at the time of startup. Further, according to the loop heat pipe
startup method described above, the evaporator located in the lower
part as viewed along the plumbline direction is first started to
receive heat, and after the liquid-phase working fluid has begun to
flow into the evaporator located in the upper part as viewed along
the plumbline direction, the evaporator located in the upper part
is started to receive heat. In this way, the loop heat pipe 10 can
be started up in a reliable manner.
[0100] The loop heat pipe 10 described above operates stably when
the amount of received heat is equal between the first evaporator
11A and the second evaporator 11B. However, if the amount of
received heat is not equal between the first evaporator 11A and the
second evaporator 11B, the amount of the working fluid 16 that
changes from liquid phase to vapor phase becomes different between
the first evaporator 11A and the second evaporator 11B; as a
result, the distribution of the working fluid 16 in the flow
passage becomes uneven, and the circulation of the working fluid 16
may become unstable or may stop.
[0101] An example of this will be described with reference to FIG.
7. FIG. 7 is a diagram illustrating how the amount of received heat
becomes unbalanced.
[0102] In the loop heat pipe 10 depicted in FIG. 7, the amount of
received heat in the first evaporator 11A has increased, and on the
other hand, the amount of received heat in the second evaporator
11B has decreased, resulting in a situation where the amount of
received heat is unbalanced. In the example of the blade server
depicted in FIG. 3, this corresponds to the situation where the
usage rate of the CPU 21A has increased and its temperature has
risen, while the usage rate of the CPU 21B has decreased and its
temperature has decreased.
[0103] In the loop heat pipe 10, the vaporization rate of the
working fluid 16 is higher in the first evaporator 11A where the
amount of received heat has increased than in the second evaporator
11B where the amount of received heat has decreased.
[0104] As a result, the amount of the liquid-phase working fluid 16
in the second liquid line 14B decreases, while the amount of the
liquid-phase working fluid 16 in the first liquid line 14A
increases. FIG. 7 shows the condition in which the fluid level of
the liquid-phase working fluid 16 has risen into the first vapor
line 13A.
[0105] If this condition further continues, the first evaporator
11A eventually runs out of the liquid-phase working fluid 16 and is
forced into the dry-out condition, and the circulation of the
working fluid 16 stops.
[0106] Such a phenomenon tends to occur, in particular, when the
flow resistance of the working fluid 16 is relatively large, for
example, when the distance between the evaporator and the condenser
is large or when the evaporator is located in a position lower than
the condenser.
[0107] It is therefore preferable to design the loop heat pipe so
that it can operate stably even when the amount of received heat
becomes unbalanced between the two evaporators.
[0108] In view of the above, loop heat pipes according to second to
fourth embodiments will be described below with reference to
drawings as examples of the loop heat pipe that can operate stably
even when the amount of received heat becomes unbalanced between
the two evaporators. The detailed description of the first
embodiment given above essentially applies to those parts of the
second to fourth embodiments that are not specifically described
herein. Further, in FIGS. 8 to 11, the same component elements as
those in FIGS. 2 to 7 are designated by the same reference
numerals.
[0109] FIG. 8 is a diagram illustrating the loop heat pipe 50 of
the second embodiment disclosed in this specification.
[0110] The loop heat pipe 50 includes a bypass line 15 which
connects between the first vapor line 13A and the second vapor line
13B. The bypass line 15 has the function of diverting the flow of
the working fluid 16 and thereby bringing the loop heat pipe 50
back into the stable operating condition when the distribution of
the working fluid 16 in the flow passage has become uneven because,
for example, the amount of received heat has become unbalanced
between the two evaporators.
[0111] It is preferable for the bypass line 15 to be provided so as
to connect between a portion of the first vapor line 13A in the
vicinity of the first condenser 12A and a portion of the second
vapor line 13B in the vicinity of the second condenser 12B. For
example, it is preferable for the bypass line 15 to connect between
the portion of the first vapor line 13A that is located 1 to 3 cm
away from the first condenser 12A and the portion of the second
vapor line 13B that is located 1 to 3 cm away from the second
condenser 12B.
[0112] Preferably, the cross-sectional area of the section of the
bypass line 15 through which the working fluid 16 passes is not
larger than the cross-sectional area of the section of the first
vapor line 13A or the second vapor line 13B through which the
working fluid 16 passes. Also preferably, the pressure'loss of the
working fluid 16 in the bypass line 15 is larger than that in the
liquid line or the vapor line.
[0113] The reason is that the flow resistance of the working fluid
16 through the bypass line 15 needs to be increased to prevent the
working fluid 16 from easily flowing into the bypass line 15 when
the loop heat pipe 50 is operating stably.
[0114] Next, a description will be given of the preferred
relationship between the cross-sectional area of the fluid flow
section of the bypass line 15 and the cross-sectional area of the
fluid flow section of the first vapor line 13A or the second vapor
line 13B.
[0115] That is, the ratio of the cross-sectional area of the fluid
flow section of the bypass line 15 to the cross-sectional area of
the fluid flow section of the first vapor line 13A or the second
vapor line 13B is preferably in the range of 0.1 to 1, and more
preferably in the range of 0.4 to 0.6.
[0116] The cross-sectional area ratio of 0.1 or larger is
preferable from the standpoint of quickly diverting the flow of the
working fluid 16 and bringing the loop heat pipe back into the
stable operating condition when the distribution of the working
fluid 16 in the flow passage has become uneven. If the
cross-sectional area ratio is smaller than 0.1, the pressure loss
through the bypass line 15 becomes too large, and the flow of the
working fluid 16 through the bypass line 15 is impeded.
[0117] On the other hand, the cross-sectional area ratio of 1 or
smaller is preferable from the standpoint of preventing the working
fluid 16 from preferentially flowing into the bypass line 15 when
the loop heat pipe 50 is operating stably. Further, when the
cross-sectional area ratio is 1 or smaller, the liquid-phase
working fluid 16 can be caused to flow into the bypass line 15 by
utilizing capillary forces.
[0118] The length of the bypass line 15 is suitably chosen
according to the configuration of the loop heat pipe 50.
[0119] The bypass line 15 may be provided with a loop section, a
bent section, etc. in order to increase the pressure loss of the
working fluid 16.
[0120] The structure of the other portions of the loop heat pipe 50
is the same as that of the foregoing first embodiment.
[0121] Next, the operation of the loop heat pipe 50 will be
described below with reference to FIGS. 9(A) to 9(D). FIGS. 9(A) to
9(D) are diagrams illustrating the operation of the loop heat pipe
50.
[0122] First, in FIG. 9(A), the loop heat pipe 50 is operating in a
stable condition. The process from the time the loop heat pipe 50
is started up until it reaches the stable operating condition is
the same as that described in the first embodiment.
[0123] Next, suppose that the amount of received heat in the first
evaporator 11A has increased and the amount of received heat in the
second evaporator 11B has decreased, thus putting the loop heat
pipe 50 in a situation where the amount of received heat is
unbalanced, as illustrated in FIG. 9(B).
[0124] In the loop heat pipe 50, the vaporization rate of the
working fluid 16 is higher in the first evaporator 11A where the
amount of received heat has increased than in the second evaporator
11B where the amount of received heat has decreased.
[0125] As a result, the amount of the liquid-phase working fluid 16
in the second liquid line 14B decreases. Here, since the amount of
the working fluid 16 in the flow passage is constant, the amount of
the liquid-phase working fluid 16 in the first liquid line 14A
increases. FIG. 9(B) shows the condition in which the fluid level
of the liquid-phase working fluid 16 has risen into the first
condenser 12A.
[0126] As a result, the pressure of the vapor phase portion of the
working fluid 16 in the second liquid line 14B decreases, while the
pressure in the first vapor line 13A increases. As the pressure in
the second liquid line 14B decreases, the pressure in the second
condenser 12B as well as the pressure in the second vapor line 13B
decreases.
[0127] Thereupon, the vapor-phase working fluid 16 in the first
vapor line 13A flows through the bypass line 15 into the second
vapor line 13B. The working fluid 16 flowing into the second vapor
line 13B enters the second condenser 12B where it is converted to
the liquid-phase working fluid 16 which then flows into the second
liquid line 14B. If any liquid-phase working fluid 16 exists in the
first vapor line 13A, the liquid-phase working fluid 16 may also
flow into the bypass line 15.
[0128] As a result, the amount of the liquid-phase working fluid 16
in the second liquid line 14B increases, while the amount of the
liquid-phase working fluid 16 in the first liquid line 14A
decreases. In this way, the distribution of the working fluid 16 in
the loop heat pipe 50 is automatically brought back to the
condition illustrated in FIG. 9(A). The loop heat pipe 50 is thus
restored to the stable operating condition.
[0129] However, if the rate of increase in the amount of received
heat in the first evaporator 11A and the rate of decrease in the
amount of received heat in the second evaporator 11B are large, the
amount of received heat becomes further unbalanced, and the
distribution of the working fluid 16 in the loop heat pipe 50
changes to the condition illustrated in FIG. 9(C).
[0130] FIG. 9(C) illustrates the condition in which the amount of
the liquid-phase working fluid 16 in the second liquid line 14B has
further decreased and the amount of the liquid-phase working fluid
16 in the first liquid line 14A has further increased. In the
condition illustrated in FIG. 9(C), the fluid level of the
liquid-phase working fluid 16 has risen into the first vapor line
13A.
[0131] When the fluid level of the working fluid 16 thereafter
reaches the portion connected to the bypass line 15, the
liquid-phase working fluid 16 in the first vapor line 13A flows
through the bypass line 15 into the second vapor line 13B due to
the pressure difference and capillary forces, as illustrated in
FIG. 9(D).
[0132] The working fluid 16 flowing into the second vapor line 13B
is passed through the second condenser 12B and flows into the
second liquid line 14B.
[0133] As a result, the amount of the liquid-phase working fluid 16
in the second liquid line 14B increases, while the amount of the
liquid-phase working fluid 16 in the first liquid line 14A
decreases. In this way, the distribution of the working fluid 16 in
the loop heat pipe 50 is automatically brought back to the
condition illustrated in FIG. 9(A). The loop heat pipe 50 is thus
restored to the stable operating condition.
[0134] The operation of the loop heat pipe 50 has been described
above by taking as an example the case where the amount of received
heat in the first evaporator 11A increases and the amount of
received heat in the second evaporator 11B decreases. However, when
the amount of received heat increases only in the first evaporator
11A and the amount of received heat remains unchanged in the second
evaporator 11B, or when the amount of received heat remains
unchanged in the first evaporator 11A but the amount of received
heat decreases in the second evaporator 11B, the loop heat pipe 50
can also be restored to the stable operating condition.
[0135] In this way, when a relative change occurs in the amount of
received heat between the first evaporator 11A and the second
evaporator 11B, the distribution of the working fluid 16 in the
flow passage is brought back to the normal condition, and the loop
heat pipe 50 is thus restored to the stable operating
condition.
[0136] Further, when a relative change occurs in cooling capability
between the first condenser 12A and the second condenser 12B, the
distribution of the working fluid 16 in the flow passage is also
brought back to the normal condition, and the loop heat pipe 50 is
thus restored to the stable operating condition.
[0137] According to the loop heat pipe 50 described above, when the
distribution of the working fluid 16 in the flow passage becomes
uneven, the working fluid 16 is caused to flow from the first vapor
line 13A to the second vapor line 13B through the bypass line 15,
so that the loop heat pipe 50 can be restored to the stable
operating condition.
[0138] Accordingly, even when the amount of received heat becomes
unbalanced between the two evaporators, the loop heat pipe 50 can
be made to operate stably.
[0139] Furthermore, since any uneven distribution of the working
fluid 16 occurring in the flow passage can be resolved without
using external energy such as electric power, the loop heat pipe 50
is of an energy saving design.
[0140] Next, the loop heat pipe of the third embodiment will be
described below with reference to FIG. 10. FIG. 10 is a diagram
illustrating the loop heat pipe 60 of the third embodiment
disclosed in this specification.
[0141] In the loop heat pipe 60, the first evaporator 11A and the
second evaporator 11B are differently sized. For example, the
second evaporator 11B may be made two times as long as the first
evaporator 11A.
[0142] The loop heat pipe 60 can be used to cool two heat sources
having different heat loads. The loop heat pipe 60 can also be used
to cool two heat sources having different sizes.
[0143] For example, the loop heat pipe 60 can be used to cool a CPU
and a chip controller mounted in a server.
[0144] Generally, the CPU has a larger size and a larger heat load
that the chip controller.
[0145] The metal block 31 in the first evaporator 11A may be chosen
to have dimensions measuring 30 mm vertically, 30 mm horizontally,
and 20 mm in height, compared with the chip controller as one heat
source which measures, for example, 20 mm vertically and 20 mm
horizontally. On the other hand, the metal block 31 in the second
evaporator 11B may be chosen to have dimensions measuring 50 mm
vertically, 50 mm horizontally, and 20 mm in height, compared with
the CPU as the other heat source which measures, for example, 30 mm
vertically and 30 mm horizontally.
[0146] The structure of the other portions of the loop heat pipe 60
is the same as that of the foregoing second embodiment.
[0147] According to the loop heat pipe 60 described above, the heat
sources can be efficiently cooled by using the evaporators each
designed to match the size and heat load of the heat source to be
cooled.
[0148] Next, the loop heat pipe of the fourth embodiment will be
described below with reference to FIG. 11. FIG. 11 is a diagram
illustrating a blade server 80 in which the loop heat pipe 70 of
the fourth embodiment disclosed in this specification is
incorporated.
[0149] In the loop heat pipe 70, the first and second condensers
are constructed in integral fashion, as illustrated in FIG. 11.
[0150] More specifically, a plurality of heat sinking plates 41 are
coupled in common to both the first condenser line 40A in the first
condenser and the second condenser line 40B in the second
condenser.
[0151] The structure of the other portions of the loop heat pipe 70
is the same as that of the earlier described second embodiment.
[0152] According to the loop heat pipe 70 described above, the
overall dimensions can be further reduced because the first and
second condensers are constructed in integral fashion.
[0153] In the present embodiment, the loop heat pipe of each of the
above embodiments and its startup method can be modified in various
ways without departing from the spirit and purpose of the present
invention.
[0154] For example, while the first evaporator 11A has been
described in each of the above embodiments as being disposed
upwardly of the second evaporator 11B as viewed along the plumbline
direction, the second evaporator 11B may be disposed upwardly of
the first evaporator 11A as viewed along the plumbline
direction.
[0155] In this case, if it is not possible to identify, at the time
of manufacture of the loop heat pipe, the plumbline direction by
reference to which the loop heat pipe 10 is to be oriented for use,
a component element such as described below may be provided. 1. An
acceleration sensor is attached to the loop heat pipe 10 so that
the plumbline direction can be identified. 2. Upon startup of the
loop heat pipe 10, the temperatures of the two heat sources such as
CPUs are monitored, and the heat source whose temperature rise is
larger is identified. Then, power supply to the heat source whose
temperature rise is larger is slowed down for a prescribed period
of time, to provide a startup time difference between the two heat
sources. By providing such a component element, the evaporator
located in the lower part as viewed along the plumbline direction
can be started to receive heat earlier than the other.
[0156] In each of the above embodiments, the first vapor line 13A,
the second vapor line 13B, the first liquid line 14A, and the
second liquid line 14B have been described as having the same
diameter, but each line may have a different diameter.
[0157] Each of the above embodiments has been described based on
the schematically illustrated loop heat pipe, and it will be
recognized that each component element is not limited in its
structure, arrangement, configuration, etc. to the specific example
illustrated herein. For example, the arrangement of the evaporators
or condensers and the configuration (layout) of the vapor lines and
liquid lines connecting between them can be modified as desired
according to the internal configuration of the electronic device in
which the loop heat pipe is to be incorporated. Further, other
component elements such as startup radiating fins or a startup fan
may be provided as desired according to the arrangement and
configuration of the evaporators, condensers, vapor lines, or
liquid lines.
[0158] Next, the operation and effect of the loop heat pipe
disclosed in this specification will be further described below
with reference to working examples. However, the present invention
is not limited by the working examples described herein.
WORKING EXAMPLES
Working Example 1
[0159] First, a loop heat pipe of the structure depicted in FIG. 8
was fabricated. Then, the loop heat pipe was assembled into a blade
server such as depicted in FIG. 3. The blade server was set with
its substrate surface oriented perpendicularly to the plumbline
direction so that the two evaporators were arranged in a horizontal
plane. The heat load of the CPU A whose heat was to be transferred
to the first evaporator was 0 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator was 60 W;
the loop heat pipe thus fabricated was taken as Working Example
1.
Working Example 2
[0160] Working Example 2 was fabricated in the same manner as
Working Example 1, except that the heat load of the CPU A whose
heat was to be transferred to the first evaporator was 20 W, and
the heat load of the CPU B whose heat was to be transferred to the
second evaporator was 60 W.
Working Example 3
[0161] Working Example 3 was fabricated in the same manner as
Working Example 1, except that the heat load of the CPU A whose
heat was to be transferred to the first evaporator was 40 W, and
the heat load of the CPU B whose heat was to be transferred to the
second evaporator was 60 W.
Working Example 4
[0162] Working Example 4 was fabricated in the same manner as
Working Example 1, except that the heat load of the CPU A whose
heat was to be transferred to the first evaporator was 60 W, and
the heat load of the CPU B whose heat was to be transferred to the
second evaporator was 60 W.
Working Example 5
[0163] Working Example 5 was fabricated in the same manner as
Working Example 1, except that the heat load of the CPU A whose
heat was to be transferred to the first evaporator was 60 W, and
the heat load of the CPU B whose heat was to be transferred to the
second evaporator was 40 W.
Working Example 6
[0164] Working Example 6 was fabricated in the same manner as
Working Example 1, except that the heat load of the CPU A whose
heat was to be transferred to the first evaporator was 60 W, and
the heat load of the CPU B whose heat was to be transferred to the
second evaporator was 20 W.
Working Example 7
[0165] Working Example 7 was fabricated in the same manner as
Working Example 1, except that the heat load of the CPU A whose
heat was to be transferred to the first evaporator was 60 W, and
the heat load of the CPU B whose heat was to be transferred to the
second evaporator was 0 W.
Working Example 8
[0166] The blade server was set with its substrate surface oriented
in parallel to the plumbline direction so that the two evaporators
were arranged in a vertical plane. Further, the heat load of the
CPU A whose heat was to be transferred to the first evaporator
located in the upper part as viewed along the plumbline direction
was 0 W, and the heat load of the CPU B whose heat was to be
transferred to the second evaporator located in the lower part as
viewed along the plumbline direction was 60 W. Otherwise, Working
Example 8 was fabricated in the same manner as Working Example
1.
Working Example 9
[0167] The heat load of the CPU A whose heat was to be transferred
to the first evaporator located in the upper part as viewed along
the plumbline direction was 20 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator located
in the lower part as viewed along the plumbline direction was 60 W.
Otherwise, Working Example 9 was fabricated in the same manner as
Working Example 8.
Working Example 10
[0168] The heat load of the CPU A whose heat was to be transferred
to the first evaporator located in the upper part as viewed along
the plumbline direction was 40 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator located
in the lower part as viewed along the plumbline direction was 60 W.
Otherwise, Working Example 10 was fabricated in the same manner as
Working Example 8.
Working Example 11
[0169] The heat load of the CPU A whose heat was to be transferred
to the first evaporator located in the upper part as viewed along
the plumbline direction was 60 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator located
in the lower part as viewed along the plumbline direction was 60 W.
Otherwise, Working Example 11 was fabricated in the same manner as
Working Example 8.
Working Example 12
[0170] The heat load of the CPU A whose heat was to be transferred
to the first evaporator located in the upper part as viewed along
the plumbline direction was 60 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator located
in the lower part as viewed along the plumbline direction was 40 W.
Otherwise, Working Example 12 was fabricated in the same manner as
Working Example 8.
Working Example 13
[0171] The heat load of the CPU A whose heat was to be transferred
to the first evaporator located in the upper part as viewed along
the plumbline direction was 60 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator located
in the lower part as viewed along the plumbline direction was 20 W.
Otherwise, Working Example 13 was fabricated in the same manner as
Working Example 8.
Working Example 14
[0172] The heat load of the CPU A whose heat was to be transferred
to the first evaporator located in the upper part as viewed along
the plumbline direction was 60 W, and the heat load of the CPU B
whose heat was to be transferred to the second evaporator located
in the lower part as viewed along the plumbline direction was 0 W.
Otherwise, Working Example 14 was fabricated in the same manner as
Working Example 8.
[0173] Working Examples 1 to 14 were operated as described below,
and the temperatures of the CPUs A and B were measured.
[0174] First, power was turned off to the blade server, and the
blade server, including the CPUs and the loop heat pipe, was
allowed to cool down for a sufficient period of time until the
entire structure reached room temperature. Next, power was turned
on to the blade server, and the temperatures that the CPUs A and B
finally reached were measured.
[0175] The results of the measurements are given in FIG. 12.
[0176] In Working Example 14, the temperature of the CPU A reached
80.degree. about one minute after power was turned on to the blade
server. It was found that when the evaporators were vertically
arranged, the loop heat pipe did not start up if the second
evaporator located in the lower part as viewed along the plumbline
direction did not receive heat.
[0177] On the other hand, in Working Examples 1 to 13, the final
temperatures of the CPUs A and B were both lower than 60.degree. C.
That is, it was found that even when the two evaporators were
vertically arranged, if the second evaporator located in the lower
part as viewed along the plumbline direction received heat, the
loop heat pipe started up to cool the CPUs A and B. It was also
found that when the two evaporators were horizontally arranged, the
loop heat pipe started up to cool the CPUs A and B, even if one or
the other of the evaporators did not receive heat.
[0178] Further, using the loop heat pipe of the structure depicted
in FIG. 11, measurements similar to those of Working Examples 1 to
14 were made; in this case also, similar results were obtained.
[0179] Next, using a two-phase fluid simulator, computer
experiments were conducted to simulate the operation of the loop
heat pipes having the structures depicted in FIGS. 2 and 8,
respectively, and Working Examples 15 to 18 were obtained.
SINDA/FLUINT (available from C&R TECHNOLOGIES) was used as the
two-phase fluid simulator.
Working Example 15
[0180] The loop heat pipe of the structure depicted in FIG. 2 was
used. A non-CFC refrigerant R141b, or more specifically, HCFC
(hydrochlorofluorocarbon), was used as the refrigerant. The first
and second liquid lines and the first and second vapor lines were
each 4.5 mm in inner diameter. The first and second liquid lines
were each 1.0 m in length. The first and second vapor lines were
each 1.0 m in length. The first and second condensers were each 1.0
m in length. The first and second evaporators were each heated by a
heat source having an output of 150 W. The first and second
evaporators were arranged horizontally relative to the plumbline
direction. The loop heat pipe had a first set formed by the second
condenser, the second liquid line, the first evaporator, and the
first vapor line, and a second set formed by the first condenser,
the first liquid line, the second evaporator, and the second vapor
line. In each set, the liquid line was divided into eight grids,
the evaporator was divided into two grids, the vapor line was
divided into 12 grids, and the condenser was divided into eight
grids. Then, in the steady-state condition of the loop heat pipe,
the proportion of the vapor phase of the working fluid was
calculated for each grid in each set. The results of the
calculations are given in FIG. 13.
Working Example 16
[0181] Working Example 16 was obtained in the same manner as
Working Example 15, except that the loop heat pipe of the structure
depicted in FIG. 8 was used. The inner diameter of the bypass line
was 4.5 mm, and the length of the bypass line was 1.4 mm. The
results of the calculations are given in FIG. 14.
Working Example 17
[0182] Working Example 17 was obtained in the same manner as
Working Example 15, except that the first evaporator in the first
set was heated by a heat source having an output of 50 W and the
second evaporator in the second set was heated by a heat source
having an output of 150 W. The results of the calculations are
given in FIG. 15.
Working Example 18
[0183] Working Example 18 was obtained in the same manner as
Working Example 16, except that the loop heat pipe of the structure
depicted in FIG. 8 was used and that the first evaporator in the
first set was heated by a heat source having an output of 50 W and
the second evaporator in the second set was heated by a heat source
having an output of 150 W. The results of the calculations are
given in FIG. 16.
[0184] As can be seen from FIGS. 13 and 14, in Working Examples 15
and 16 in which the two evaporators were equally heated, all of the
working fluid in each vapor line was in vapor phase, and all of the
working fluid in each liquid line was in liquid phase.
[0185] As can be seen from FIG. 15, in Working Example 17, the
circulation of the working fluid did occur in the loop heat pipe,
but in the first vapor line in the first set, about 40% of the
working fluid was in vapor phase and about 60% was in liquid phase.
On the other hand, in the second set, all of the working fluid in
the second vapor line was in vapor phase.
[0186] As can be seen from FIG. 16, in Working Example 18, all of
the working fluid in each vapor line was in vapor phase, and all of
the working fluid in each liquid line was in liquid phase. It was
thus found that when the bypass line was added in the loop heat
pipe structure of Working Example 17, all of the working fluid
flowing in the vapor line of the first set also was maintained in
vapor phase.
[0187] 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 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.
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