U.S. patent application number 12/155614 was filed with the patent office on 2008-12-11 for evaporative cooling system.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Naoki Hamanaka, Takeshi Kato, Yoshihiro Kondo, Tatsuya Saito.
Application Number | 20080302505 12/155614 |
Document ID | / |
Family ID | 40094774 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080302505 |
Kind Code |
A1 |
Kato; Takeshi ; et
al. |
December 11, 2008 |
Evaporative cooling system
Abstract
The evaporative cooling system comprises: evaporative cooling
modules, a liquid supply system which comprises a liquid supply
pump and a tube, and which supplies a refrigerant liquid to the
evaporative cooling modules; an air supply system which comprises
air supply tubes, and which supplies warm air to the evaporative
cooling modules; an exhaust system which comprises an exhaust pump
and a tube, and which exhausts air containing a refrigerant vapor
from the evaporative cooling modules; a reflux system which
comprises a primary heat exchanger and a reflux tube, and which
condenses the refrigerant vapor to return the condensed refrigerant
liquid to the liquid supply system; and a heat exhaust system which
comprises a secondary heat exchanger and tubes, and which
discharges heat absorbed from the primary heat exchanger.
Inventors: |
Kato; Takeshi; (Akishima,
JP) ; Kondo; Yoshihiro; (Tsuchiura, JP) ;
Saito; Tatsuya; (Kunitachi, JP) ; Hamanaka;
Naoki; (Tokyo, JP) |
Correspondence
Address: |
Stanley P. Fisher;Reed Smith Hazel & Thomas LLP
Suite 1400, 3110 Fairview Park Drive
Falls Church
VA
22042-4503
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
40094774 |
Appl. No.: |
12/155614 |
Filed: |
June 6, 2008 |
Current U.S.
Class: |
165/61 ;
165/104.26; 165/104.33; 165/108 |
Current CPC
Class: |
F25B 25/005 20130101;
H01L 23/427 20130101; F25B 23/006 20130101; H05K 7/20809 20130101;
H01L 2924/0002 20130101; F28D 15/0266 20130101; H01L 2924/0002
20130101; B60K 2001/003 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/61 ;
165/104.33; 165/104.26; 165/108 |
International
Class: |
F25B 29/00 20060101
F25B029/00; F28D 15/00 20060101 F28D015/00; F28D 15/04 20060101
F28D015/04; F28F 13/06 20060101 F28F013/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2007 |
JP |
2007-149882 |
Claims
1. An evaporative cooling system for cooling a heating element by
using heat of evaporation of a refrigerant, comprising: a
vaporizing plate having an area larger than a heat generating
portion of the heating element, and configured to dissipate heat by
being brought into contact with the heat generating portion and to
evaporate the refrigerant liquid into a refrigerant vapor; a liquid
supply system to supply the refrigerant liquid to the vaporizing
plate; an air supply system to supply air to the vaporizing plate;
an exhaust system to exhaust air containing the refrigerant vapor
around the vaporizing plate; and a reflux system to condense the
refrigerant vapor of the exhaust system to collect the condensed
refrigerant liquid, and to return the collected refrigerant liquid
to the liquid supply system.
2. The evaporative cooling system according to claim 1, wherein the
vaporizing plate has one surface in contact with the heat
generating portion of the heating element and the other surface
having affinity with the refrigerant liquid or covered with
capillaries.
3. The evaporative cooling system according to claim 1, wherein the
air supply system supplies, to the vaporizing plate, warm air at a
temperature lower than the upper limit temperature of the heating
element.
4. The evaporative cooling system according to claim 1, wherein the
liquid supply system supplies, to the vaporizing plate, the
refrigerant liquid at a temperature lower than the upper limit
temperature of the heating element.
5. The evaporative cooling system according to claim 1, wherein the
air supply system supplies air to the vaporizing plate from a
direction different from a direction in which the refrigerant
liquid is supplied to the vaporizing plate by the liquid supply
system.
6. An evaporative cooling system for cooling a first and a second
heating element, comprising: a vaporizing plate to be brought into
contact with the first heating element and to evaporate a
refrigerant liquid into a refrigerant vapor; a liquid supply system
to supply the refrigerant liquid to the vaporizing plate; an intake
and exhaust system to intake air in the vicinity of the heating
elements to supply the air to the vaporizing plate, and to exhaust
air containing the refrigerant vapor from the vaporizing plate; and
a reflux system to condense the refrigerant vapor from the
exhausted air to collect the refrigerant liquid, and to return the
collected refrigerant liquid to the liquid supply system.
7. The evaporative cooling system according to claim 6, wherein the
liquid supply system supplies the refrigerant liquid to the
vaporizing plate from a place higher in level than the vaporizing
plate by using the weight of the refrigerant liquid itself.
8. The evaporative cooling system according to claim 6, wherein the
exhaust system includes a pump for, by performing a forced exhaust,
setting a side of the vaporizing plate to a negative pressure and
setting a side of the reflux system to a positive pressure.
9. An evaporative cooling system comprising: holding means to hold
a planar heating element in a substantially vertical state; a
vaporizing plate to be brought into contact with the heating
element and to evaporate a refrigerant liquid into a refrigerant
vapor; a liquid supply system to supply the refrigerant liquid to
the vaporizing plate; an air supply system to supply air to the
vaporizing plate; an exhaust system to exhaust air containing the
refrigerant vapor from the vaporizing plate; and a reflux system to
condense the refrigerant vapor of the exhaust system to collect the
condensed refrigerant liquid, and to return the collected
refrigerant liquid to the liquid supply system.
10. The evaporative cooling system according to claim 9, wherein
the exhaust system discharges a residual liquid of the refrigerant
liquid from the vaporizing plate, together with air containing the
refrigerant vapor.
11. An evaporative cooling system for cooling a heating element by
using heat of evaporation of a refrigerant, comprising: a
vaporizing plate to be brought into contact with the heating
element and to evaporate a refrigerant liquid into a refrigerant
vapor; a liquid supply system to-supply the refrigerant liquid to
the vaporizing plate; an air supply system to intake air from
ambient air and to send the air to the vaporizing plate; an exhaust
system to exhaust air containing the refrigerant vapor from the
vaporizing plate; and a reflux system to condense the refrigerant
vapor from the exhaust air to return the condensed refrigerant
liquid to the liquid supply system, and to discharge residual air
to ambient air, wherein the refrigerant is circulated in a closed
circuit which is configured by the liquid supply system, the
exhaust system, and the reflux system, and wherein air is
circulated in an open circuit which is configured by the air supply
system, the exhaust system, and the reflux system.
12. An evaporative cooling system for cooling a heating element by
using heat of evaporation of a refrigerant, comprising: a
vaporizing plate to be brought into contact with the heating
element and to evaporate a first refrigerant liquid into a first
refrigerant vapor; a liquid supply system to supply the first
refrigerant liquid to the vaporizing plate; an air supply system to
send air to the vaporizing plate; an exhaust system to exhaust air
containing the first refrigerant vapor from the vaporizing plate; a
primary heat exchange system to cool air of the exhaust system by a
second refrigerant liquid to condense the first refrigerant vapor,
and to collect the condensed first refrigerant liquid; a reflux
system to return the first refrigerant liquid from the primary heat
exchange system to the liquid supply system; and a secondary heat
exchange system to discharge heat absorbed by the second
refrigerant liquid from the first refrigerant vapor.
13. An evaporative cooling system for cooling a heating element by
using heat of evaporation of a refrigerant, comprising: a
vaporizing plate to be brought into contact with the heating
element and to evaporate a refrigerant liquid into a refrigerant
vapor; a liquid supply system to supply the refrigerant liquid to
the vaporizing plate; an air supply system to supply air to the
vaporizing plate; an exhaust system to exhaust air containing the
refrigerant vapor in the vicinity of the vaporizing plate; and a
reflux system to condense the refrigerant vapor of the exhaust
system to collect the refrigerant liquid, and to return the
collected refrigerant liquid to the liquid supply system, wherein
the liquid supply amount, the liquid supply temperature, the air
supply amount, or the air supply temperature is controlled
according to the heat generation amount, the power consumption, the
operation rate, or the temperature, of the heating element.
Description
INCORPORATION BY REFERENCE
[0001] The present application claims priority from Japanese
application JP 2007-149882 filed on Jun. 6, 2007, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a cooling system for a
heating element, and more particularly to an evaporative cooling
system suitable for information platform apparatuses such as a
server, a network, and a storage which are required to have higher
performance and higher density.
[0003] Conventionally, evaporative cooling is known as means for
efficiently cooling heating elements, such as a processor, an LSI,
electronic devices, power devices, and dynamic devices. The
evaporative cooling utilizing latent heat of refrigerant is
considered promising for improving the cooling efficiency and
reducing the weight and size of cooling system, as compared with
air cooling and liquid cooling which utilize heat conduction and
heat transfer from a heating element to refrigerant.
[0004] For example, air cooling, water cooling, and evaporative
cooling are compared with each other in the case where a heating
element of 100 W is cooled. It is assumed that the specific heat
and density of air are 1.0 J/gK, and 0.0012 g/cm.sup.3, that the
specific heat, density, and heat of evaporation of water are 4.2
J/gK, 1 g/cm.sup.3, and 2300 J/g, and that the temperature rise of
refrigerant in air cooling and water cooling is 30 K. The weight
ratio between the refrigerants necessary for cooling the heating
element on this assumed condition is given as air cooling:water
cooling:evaporative cooling=3.3 g/s:0.79 g/s:0.043 g/s=77:18:1, and
the volume ratio between the refrigerants is given as air
cooling:water cooling:evaporative cooling=2800 cm.sup.3/s:0.79
cm.sup.3/s:0.043 cm.sup.3/s=64000:18:1. Thus, it is seen that
evaporative cooling has extraordinarily high potential performance
in comparison with air cooling and water cooling. However, the
practical cooling performance largely depends on supply means,
evaporation condition, and the like, of the refrigerant.
[0005] There are several known examples as the evaporative cooling
means.
[0006] U.S. Pat. No. 6,085,831 discloses that a semiconductor chip
which is a heating element is covered with a jacket, and a
refrigerant is circulated in the inside of the jacket. The
refrigerant is circulated in the inside of the jacket in such a
manner that the refrigerant liquid is evaporated by the heating
element, that the refrigerant vapor is cooled and condensed by the
air cooling fins outside the jacket, and that the condensed
refrigerant liquid is again returned to the heating element.
[0007] JP-A-2000-252671 discloses that a circulatory pipe is
attached to a microprocessor which is a heating element. The
circulatory system is configured in such a manner that a
refrigerant vapor evaporated by the heating element is moved in the
inside of the pipe, that the refrigerant vapor is condensed in a
heat exchanging section configured by air cooling fins, and is
separated into a refrigerant liquid and air, that the refrigerant
liquid and air are respectively fed to a nozzle by separate pipes,
and the refrigerant liquid is sprayed to the surface of the heating
element by a piezoelectric film from the nozzle, and that the
refrigerant liquid is again evaporated by the heating element.
[0008] U.S. Pat. No. 6,205,799 discloses that a circuit board with
a semiconductor device which is a heating element mounted thereon
is housed in a case, and a refrigerant liquid is sprayed to the
heating element from a sprayer in the case. The refrigerant liquid
is circulated in such a manner that an evaporated refrigerant vapor
is fed to a heat exchanger through a pipe connected to the case,
and that the condensed refrigerant liquid is fed to a reservoir by
a pump, and is again fed to the sprayer from the reservoir. The
sprayer is configured by a heater, a chamber, an opening, and the
like, which are formed in a silicon substrate in accordance with a
thermal ink jet system which is a printing technique for a
printer.
[0009] U.S. Pat. No. 6,889,515 discloses that a spray module is
attached to a semiconductor which is a heating element, and a
coaxial tube is connected to the module. A refrigerant liquid is
circulated in such a manner that the refrigerant liquid is sprayed
to the heating element through the inner tube of the coaxial tube
from a pump, that a refrigerant vapor is collected from an opening
in the module, and fed to a condenser through the outer tube of the
coaxial tube, and that the liquefied refrigerant is fed to a
reservoir from the condenser, and is again sprayed to the heating
element by the pump.
[0010] JP-A-2006-39916 discloses that a vapor generator is attached
to a CPU which is a heating element. A circulation cycle of a
refrigerant is formed in such a manner that a refrigerant is
evaporated in the generator, and a refrigerant vapor is fed to a
condenser connected to the generator, that the refrigerant is
cooled by an air cooling fan to be liquefied and sent to a
receiving tank, and that the liquefied refrigerant is again fed to
the generator from the receiving tank.
[0011] JP-A-11-26665 discloses an example in which a hollow heat
sink is attached to a case of a CPU which is a heating element, and
a refrigerant is supplied to the inner surface of the heat sink
brought into contact with the heating element, from a water storage
pit inside the heat sink on the basis of a capillary phenomenon. A
circulatory system is configured in such a manner that the
refrigerant is evaporated inside the heat sink, and air containing
a refrigerant vapor is fed to a heat exchanger and a dehumidifier
through a pipe by a fan, that the refrigerant liquefied by the heat
exchanger is again returned to the water storage pit of the heat
sink by a pump, and that the air dried by the dehumidifier is
returned to the heat sink by a compressor.
[0012] In U.S. Pat. No. 6,085,831 and JP-A-2000-252671, the
refrigerant is enclosed in the jacket and the circulatory pipe, and
the refrigerant vapor and liquid are mixed in the same space. Thus,
there is a problem that vapor pressure of the refrigerant in the
vicinity of the heating element is increased to make it difficult
to evaporate. Further, the jacket and the circulatory pipe are
integrated with the air cooling fins, and thereby the mounting area
of such integrated components need to be provided around the
heating element. Thus, there is also a problem that the mounting
density of the heating element cannot be increased.
[0013] In U.S. Pat. No. 6,205,799 and U.S. Pat. No. 6,889,515, the
cooling system is configured by the sprayer and the spray module
which spray the refrigerant liquid to the heating element, the heat
exchanger and the condenser which condense the refrigerant, the
reservoir which stores the refrigerant, the pump which feeds the
refrigerant liquid to the spray, and the like. Since the
refrigerant vapor and liquid are mixedly fed similarly to U.S. Pat.
No. 6,085,831 and JP-A-2000-252671, a spray mechanism based on a
thermal ink jet and a compressor, needs to be provided, in order to
destroy the saturated vapor layer in the vicinity of the heating
element in order to promote evaporation of the refrigerant. Thus,
there is a problem that these components hinder the miniaturization
and the improvement of reliability of the cooling system.
[0014] In JP-A-2006-39916, the cooling system is configured by the
vapor generator attached to the heating element, the condenser
based on air cooling, the receiving tank, and the like. However,
the refrigerant vapor and liquid are enclosed in the same
circulatory system similarly to U.S. Pat. No. 6,085,831 to U.S.
Pat. No. 6,889,515. Thus, there is a problem that the vapor
pressure of the refrigerant is increased in the circulatory system
and thereby the vaporization efficiency is lowered.
[0015] In JP-A-11-26665, the cooling system is configured by the
hollow heat sink having a substantially same area as that of the
heating element, the heat exchanger which cools and liquefies the
refrigerant vapor evaporated in the hollow heat sink by the air
cooling fan, the dehumidifier which dries the air exhausted from
the heat sink, the pump which returns the refrigerant liquid from
the heat exchanger to the heat sink, the compressor which sends the
dry air from the dehumidifier to the heat sink, and the like. In
the same closed circulatory system as those in U.S. Pat. No.
6,085,831 to JP-A-2006-39916, the dehumidifier is provided so that
the vapor pressure inside the heat sink is reduced to promote the
evaporation of the refrigerant. However, such configuration
prevents the miniaturization and weight reduction of the cooling
system. Further, the refrigerant liquid and the dry air are
supplied to the heat sink in the same direction with respect to the
heat sink. Thus, there is a problem that as the evaporation is
performed on the front side, the vapor pressure is increased on the
back side to thereby make it difficult to evaporate the
refrigerant.
[0016] As described above, the conventional techniques have
problems that the evaporative cooling efficiency is low and the
miniaturization and weight reduction of the cooling system is
difficult. An object of the present invention is to effect
miniaturization and weight reduction of the cooling system by
making evaporative cooling efficiently performed, and to realize
high performance of the cooling system by improving the mounting
density of the information platform devices. To this end, according
to the present invention, there is provided an evaporative cooling
system in which the supply of the refrigerant and atmosphere and
the evaporation condition are optimized on the basis of the
principle of evaporative cooling, and which is suitable for the
high mounting density.
BRIEF SUMMARY OF THE INVENTION
[0017] An evaporative cooling model can be obtained, on the basis
of the Penman-Monteith method, by assuming that an evaporation
amount is proportional to a difference between saturated vapor
pressure and vapor pressure of an atmosphere. When latent heat flux
(heat removal density from a heating element) is set as L.sub.a
(W/cm.sup.3), heat of evaporation of a refrigerant is set as
.epsilon. (J/g), saturated vapor pressure is set as e.sub.s (hPa),
vapor pressure of atmosphere is set as e.sub.a (hPa), and a
coefficient is set as k (g/cm.sup.2shPa), the relation between
these parameters is expressed by Expression 1.
L.sub.a=k.epsilon.(e.sub.s-e.sub.a) (1)
[0018] The latent heat flux L.sub.a is proportional to the heat of
evaporation .epsilon. and to the difference between the saturated
vapor pressure and the vapor pressure of atmosphere
(e.sub.s-e.sub.a). When the percentage .phi. (%) of the vapor
pressure e.sub.a of atmosphere with respect to the saturated vapor
pressure e.sub.s, that is, the so-called relative humidity is used,
Expression 1 is rewritten as Expression 2. In order to increase the
latent heat flux L.sub.a, it is important that a refrigerant having
a large heat of evaporation .epsilon. is used, that the refrigerant
is evaporated in a condition of high saturated vapor pressure
e.sub.s, and that the vapor pressure e.sub.a of atmosphere in the
vicinity of the cooling object is reduced to lower the relative
humidity .phi..
L a = k e s ( 1 - .psi. 100 ) ( 2 ) ##EQU00001##
[0019] The coefficient k which is the first term of the right side
of Expression 2, is considered to depend on refrigerant supply
means (volume, film thickness, thermal conductivity, heat
resistance, and the like, of refrigerant), air supply means
(density, specific heat, wind velocity, wind direction, and the
like, of air), and the state of the evaporating surface of the
heating element (refrigerant affinity, surface shape, surface
treatment, and the like). It is necessary to increase the
coefficient k by facilitating the evaporation of the refrigerant
from the heating element in such a way that the effective area of
the evaporating surface is increased and the refrigerant is
uniformly and thinly supplied.
[0020] When water having a relatively large heat of evaporation is
taken as an example of the refrigerant, the heat of evaporation
.epsilon. of the second term can be expressed by an approximate
expression with respect to temperature t (.degree. C.) as given by
Expression 3. Even when the temperature t is changed in a range
from normal temperature to (.degree. C.) to the boiling point of
100.degree. C., the temperature dependency of the heat of
evaporation .epsilon. is relatively small.
.epsilon.=2502.3-2.4794t (3)
[0021] When the refrigerant is water, the saturated vapor pressure
e.sub.s of the third term is expressed by the Tetens formula as
given by Expression 4. When the temperature t is elevated, the
saturated vapor pressure e.sub.s is almost exponentially increased.
In order to increase the latent heat flux L.sub.a, it is effective
to increase the ambient temperature t in the vicinity of the
cooling object.
e s = 6.11 .times. 10 7.5 t t + 237.3 ( 4 ) ##EQU00002##
[0022] Similarly, when the refrigerant is water, the fourth term
(1-.phi./100) is expressed by using the relative humidity
.phi..sub.o (%) and the Tetens formula as given by Expression 5. In
order to increase the value of the fourth term, it is necessary
that the ambient temperature t is set higher than the normal
temperature t.sub.o, so as to lower the relative humidity .phi. at
temperature t, and to lower the vapor pressure e.sub.a of
atmosphere.
1 - .psi. 100 = 1 - .psi. .omicron. 100 .times. 10 7.5 t .omicron.
t .omicron. + 237.3 - 7.5 t t + 237.3 ( 5 ) ##EQU00003##
[0023] FIG. 13 shows the dependency of the latent heat flux L.sub.a
on the temperature t when water is used as the refrigerant. In the
drawing, the calculation is performed by such a way that Expression
3 to Expression 5 are substituted in Expression 2, and that the
normal temperature t.sub.o is set to 20.degree. C., the relative
humidity .phi..sub.o is set to 60% RH, and the coefficient k is set
as a parameter. It is seen from FIG. 13 that the latent heat flux
L.sub.a is increased as the temperature t is elevated.
[0024] In the evaporative cooling, a cooling temperature is
determined in an equilibrium state between the heat generation
density per unit area of the heating element and the latent heat
flux L.sub.a (heat removal density). In order to increase the
amount of heat removed from the heating element and to increase the
evaporative cooling efficiency, it is necessary to use a
refrigerant having a large heat of evaporation e and to increase
the area, from which the refrigerant is evaporated, so that the
latent heat flux L.sub.a is increased on the basis of the above
described method.
[0025] A feature of a typical embodiment according to the present
invention is that the area where the latent heat flux L.sub.a is
obtained and the total amount of heat removed from the heating
element are increased by attaching a vaporizing plate having an
area larger than that of a heat generating portion of the heating
element.
[0026] Another feature of the typical embodiment according to the
present invention is that the coefficient k and the latent heat
flux L.sub.a are increased by supplying the refrigerant liquid in a
thin film manner and by increasing the effective area of the
vaporizing plate in such a way that the surface treatment and the
shape processing, for increasing affinity with the refrigerant, are
performed to the surface of the vaporizing plate brought into
contact with the heating element, or that capillaries are provided
to the surface of the vaporizing plate.
[0027] Further, another feature is that the latent heat flux
L.sub.a is increased by such a way that the saturated vapor
pressure e.sub.s in the vicinity of the vaporizing plate is
increased and the relative humidity .phi. is reduced by supplying
to the vaporizing plate warm air at the upper limit temperature or
below of the heating element. It is also possible to obtain the
effect of increasing the latent heat flux L.sub.a by similarly
supplying to the vaporizing plate the refrigerant liquid at the
upper limit temperature or below of the heating element.
[0028] Further, another feature is that the latent heat flux
L.sub.a is increased in such a way that the refrigerant liquid and
air are respectively supplied from different directions with
respect to the vaporizing plate, to thereby remove the saturated
vapor layer on the surface of the vaporizing plate while
maintaining the relative humidity .phi. at low, and to lower the
vapor pressure e.sub.a of atmosphere.
[0029] Further, another feature is that the size of the air supply
system is reduced by eliminating the warm air generating mechanism
in such a way that in a configuration having first and second
heating elements, warm air generated in the second heating element
is supplied to the vaporizing plate of the first heating
element.
[0030] Further, another feature is that the liquid supply system of
the refrigerant is simplified in such a way that the refrigerant is
supplied to the vaporizing plate from a position higher than the
heating element by utilizing the weight of the refrigerant
itself.
[0031] Further, another feature is that components of the liquid
supply system or the air supply system and the reflux system are
reduced in such a way that the liquid supply or the air supply is
performed, by an exhaust system which forcibly exhausts the air
containing the refrigerant vapor from the vaporizing plate, in the
state where the pressure of the vaporizing plate side is made
negative with respect to the normal pressure, and in such a way
that the reflux is performed in the state where the pressure of the
reflux side, in which the refrigerant vapor is condensed from the
exhaust and the condensed refrigerant liquid is returned to the
liquid supply system, is made positive.
[0032] Further, another feature is that the planar heating element
is substantially vertically arranged, and that the refrigerant
liquid is supplied to the upper part of the vaporizing plate, and
the air containing the refrigerant vapor and the residual
refrigerant liquid are discharged from the lower part of the
vaporizing plate. Thereby, it is possible to configure the liquid
supply system or the discharge system which is suitable for the
vertical heating element, and in which the cooling system can be
miniaturized.
[0033] Further, another feature is that the closed circuit system
is configured by the liquid supply system for supplying the
refrigerant to the vaporizing plate, the exhaust system, and the
reflux system which returns the refrigerant to the liquid supply
system, and that the open circuit system is configured by the air
supply system for intaking air from ambient air, the exhaust
system, and the reflux system for discharging the air to ambient
air. Thereby, it is possible to increase the latent heat flux
L.sub.a by supplying air of a low vapor pressure e.sub.a to the
vaporizing plate by the use of ambient air in the simple open loop
system, while circulating the refrigerant in the closed circuit
system.
[0034] Further, another feature is that the system for effecting
reflux from exhaust system through the primary heat exchange system
is miniaturized in such a way that the primary refrigerant vapor
with heat taken from the heating element in the primary heat
exchange system is cooled and condensed by the secondary
refrigerant, and that the heat absorbed by the secondary
refrigerant from the primary refrigerant vapor is discharged in the
secondary heat exchange system, and is that the cooling efficiency
is improved by keeping the heat exhaust place in the secondary heat
exchange system away from the vicinity of the heating element.
[0035] Further, another feature is that the evaporative cooling is
efficiently performed in such a way that a required amount of the
refrigerant and air is supplied to the vaporizing plate by
controlling the supply liquid amount, the supply liquid
temperature, the supply air amount or the supply air temperature
according to the heat generation amount, the power consumption, the
operation rate, or the temperature of the heating element.
[0036] According to claims 1-5 of the present application, it is
possible to efficiently perform the evaporative cooling even for a
heating element with high heat generation density by increasing the
latent heat flux L.sub.a. According to claims 6-13 of the present
application, it is possible to effect the reduction in size and
weight of the cooling system configured by the liquid supply
system, the air supply system, the exhaust system, the reflux
system, and the like. The present invention is particularly
effective to increase the mounting density and to improve
performance of major devices, such as a processor and an LSI in
information platform devices, such as a server, a network, and a
storage.
[0037] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0038] FIG. 1 is a view showing a configuration of an evaporative
cooling system of a first embodiment according to the present
invention;
[0039] FIG. 2 is a view showing a configuration of an evaporative
cooling module of the first embodiment according to the present
invention;
[0040] FIG. 3 is a sectional view of the evaporative cooling module
of the first embodiment according to the present invention;
[0041] FIG. 4 is a view showing a configuration of a primary and a
secondary heat exchanger of the first embodiment according to the
present invention;
[0042] FIG. 5 is a view showing a configuration of an evaporative
cooling system of a second embodiment according to the present
invention;
[0043] FIG. 6 is a view showing a configuration of an evaporative
cooling system of a third embodiment according to the present
invention;
[0044] FIG. 7 is a view showing a function of the evaporative
cooling system of the first embodiment according to the present
invention;
[0045] FIG. 8 is a view showing a function of the evaporative
cooling system of the second embodiment according to the present
invention;
[0046] FIG. 9 is a view showing a function of the evaporative
cooling system of the third embodiment according to the present
invention;
[0047] FIG. 10 is a view showing a function of an evaporative
cooling system of a fourth embodiment according to the present
invention;
[0048] FIG. 11 is a view showing a function of an evaporative
cooling system of a fifth embodiment according to the present
invention;
[0049] FIG. 12 is a view showing a function of an evaporative
cooling system of a sixth embodiment according to the present
invention; and
[0050] FIG. 13 is an illustration of an evaporative cooling model
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0051] In the following, embodiments of evaporative cooling systems
according to the present invention will be described with reference
to the accompanying drawings.
[0052] FIG. 1 is a view showing a configuration of an evaporative
cooling system of a first embodiment according to the present
invention, and an example in which the present invention is applied
to a blade server system. The blade server system comprises a
plurality of blade servers 40, a back plane connected to the
plurality of blade servers 40, an I/O module, a switch module, a
storage module, a management module, a power supply module, an air
cooling fan module, and the like, and a server chassis 41 for
housing these components. The blade server 40 comprises a processor
to which evaporative cooling modules 10 and 11 are attached, a chip
set 20, a memory module 21, a mother board 30, a connector 31 for
effecting connection with the back plane, and the like, and a case
for covering these components.
[0053] The evaporative cooling system comprises the evaporative
cooling modules 10 and 11 in contact with the processor which is a
heating element, a liquid supply system which includes a liquid
supply pump 50 and a liquid supply tube 51, and which supplies a
refrigerant liquid to the evaporative cooling modules 10 and 11, an
air supply system which includes an air supply tubes 60 and 61, and
which supplies air to the evaporative cooling modules 10 and 11, an
exhaust system which includes an exhaust pump 70 and an exhaust
tube 71, and which exhausts air containing a refrigerant vapor from
the evaporative cooling modules 10 and 11, a reflux system which
includes a primary heat exchanger 80, a reflux tube 81, and an
exhaust port 82, and which condenses the refrigerant vapor and
returns the condensed refrigerant liquid to the liquid supply
system, and a heat exhaust system which includes a secondary heat
exchanger 90, a water conveyance tube 91, and a water returning
tube 92, and which discharges the heat absorbed from the primary
heat exchanger.
[0054] FIG. 2 is a view showing a configuration of the evaporative
cooling module 10, and FIG. 3 is a sectional view of the
evaporative cooling module 10. A processor package 100, to which
the evaporative cooling module 10 is mounted, comprises a processor
chip 101 which is a heating element, a cap 102 in close contact
with the chip 101, and a package substrate 103 to which the chip
101 is connected. The processor package 100 is connected to the
mother board 30 via a socket 104. The evaporative cooling module 10
comprises a vaporizing plate 110 in contact with the cap 102 via a
heat conducting material 105, a wick 111 formed on a surface of the
vaporizing plate 110, and a jacket 109 to which the liquid supply
tube 51, the air supply tube 60, and the exhaust tube 71 are
connected.
[0055] The heat generated by the processor chip 101 is conducted to
the vaporizing plate 110 via the cap 102 and the heat conducting
material 105. The refrigerant liquid supplied from the liquid
supply tube 51 is spread on the surface of the vaporizing plate 110
by a capillary phenomenon of the wick 111 as shown by a liquid
supply flow 112. Air warmed by the heat generated by the chip set
20 and the memory module 21 is sucked into an inside of the jacket
109 from the air supply tube 60 by the exhaust pressure of the pump
70 as shown by an air supply flow 113. The refrigerant liquid
spread on the surface of the vaporizing plate 110 is evaporated
into the warm air inside the jacket by the heat from the processor
chip 101 as shown by an evaporative flow 115. The air containing
the refrigerant vapor and the residual liquid of the unevaporated
refrigerant liquid are discharged from the exhaust tube 71 by the
pump 70 as shown by an exhaust air and liquid flow 115.
[0056] FIG. 4 is a view showing a configuration of the primary heat
exchanger 80 and the secondary heat exchanger 90. The primary heat
exchanger 80 comprises a condenser which includes an insertion pipe
120 connected to the exhaust tube 71 and a mantle pipe (cooling
pipe) 121, and which condenses the refrigerant vapor in the exhaust
air, a liquid tank 122 which stores the condensed refrigerant
liquid, a chamber 123 which stores the residual air after
condensation, and the exhaust port 82. The secondary heat exchanger
90 comprises a radiator 130 and a fan 131 which air-cools the
radiator. The cooling water is supplied from the secondary heat
exchanger 90 to the mantle pipe (cooling pipe) 121 by a water
conveyance pump 93 and the water conveyance tube 91, so as to cool
the refrigerant vapor passing through the insertion pipe 120. The
warm water into which the heat is absorbed from the refrigerant
vapor is refluxed to the radiator 130 by the water returning tube
92, so as, to be cooled. The heat exhausted from the warm water is
discharged to ambient air as shown by an exhaust heat flow 132.
[0057] FIG. 7 is a view showing a function of the evaporative
cooling system of the first embodiment. The refrigerant liquid is
fed to the evaporative cooling module 10 from the liquid supply
system which comprises the liquid supply pump 50 and the liquid
supply tube 51, and is evaporated into a refrigerant vapor inside
the evaporative cooling module 10. The refrigerant vapor is fed to
the primary heat exchanger 80 from the exhaust system which
comprises the exhaust pump 70 and the exhaust tube 71, together
with the residual liquid. The refrigerant vapor is condensed in the
heat exchanger 80, so as to be changed back to the refrigerant
liquid. The refrigerant liquid is again fed to the liquid supply
system from the reflux system which comprises the primary heat
exchanger 80 and the reflux tube 81. Thus, the refrigerant forms a
closed circuit circulatory system. The ambient air warmed by the
chip set 20 is fed into the evaporative cooling module 10 from the
air supply system including the air supply tube 60. The air
containing the refrigerant vapor is fed to the primary heat
exchanger 80 from the exhaust system, and the refrigerant vapor is
condensed. The residual dry air is discharged from the exhaust port
82 to ambient air. Thus, the air system forms an open circuit
system.
[0058] In the first embodiment configured as described above, the
evaporative cooling is performed by obtaining the latent heat flux
of about 4 W/cm.sup.2, for a processor having a maximum power
consumption of about 100 W, the upper limit operating temperature
of 65.degree. C., and a package size of approximately 4 cm square,
in such a way that water is used as a refrigerant liquid, the size
of vaporizing plate 110 made of copper is set to about 5 cm square,
and the supply air temperature is set to around 40.degree. C.,
under an atmosphere condition set at a usual room air temperature
of 25.degree. C. and the indoor humidity of 60% RH. It is
considered to use water or a fluorochemical inert fluid as the
refrigerant material, but in the first embodiment, water having a
relatively large heat of evaporation is used. In the first
embodiment, the operation rate, the power consumption, the package
temperature, or the like, of the processor is monitored in
correspondence with the variation in the power consumption, that
is, the heat generation amount of the processor. Thereby, the
supply liquid amount and the supply air amount (exhaust air amount)
are controlled according to these values. However, in addition to
these, the supply liquid temperature and the supply air temperature
can also be used as the control factors. When a processor of
different specifications about the maximum power consumption, the
package size, and the like, is used, the refrigerant material and
the material, size, and the like, of the vaporizing plate are
correspondingly designed in addition to the control factors. As
shown in FIG. 13, the supply liquid temperature and the supply air
temperature relate to the temperature t represented along the
horizontal axis, while the supply liquid amount and the supply air
amount relate to the coefficient k. The control and design may be
performed in consideration of these relationships.
[0059] In the first embodiment, the vaporizing plate 110 having an
area larger than that of the processor chip 101 which is the
heating element is used. Thus, the heat is spread to the vaporizing
plate, so as to increase the region in which the latent heat flux
can be obtained. Thereby, the evaporation can be promoted and the
amount of removed heat can be increased as compared with the case
where the refrigerant is directly evaporated from the surface of
the heating element 101 and the cap 102. In order to efficiently
spread the evaporation region, a heat pipe and a vapor chamber may
also be used as the vaporizing plate. Further, the wick 111 is
stuck on the surface of the vaporizing plate 110. The wick 111 is
capillaries formed by fibers in a mesh form. The refrigerant liquid
is spread thinly and uniformly on the surface of the vaporizing
plate 110 by the capillary phenomenon of the wick 111. Thereby, the
heat resistance of the refrigerant liquid is reduced and the
effective area of the evaporation region is increased, so that the
latent heat flux can be increased. In order to obtain the same
effect, instead of using the capillaries, an affinity coating and
fine uneven processing may also be applied to the surface of the
vaporizing plate 110.
[0060] In the first embodiment, the intake ports of the air supply
tubes 60 and 61 are provided in the vicinity of the chip set 20 or
the memory module 21 around the processor chip 101. That is, the
air supplied to the evaporative cooling modules 10 and 11 is the
air subjected to the heat exchange with the chip set 20 or the
memory module 21. Thereby, it is possible to obtain the effect of
cooling the memory module and the chip set, and the warmed air is
supplied to the vaporizing plate 110. When the temperature of air
is elevated, the saturated vapor pressure is increased. Thereby,
the relative humidity is reduced and the latent heat flux is
increased. Further, the heat generation in the chip set 20 and the
memory module 21 is utilized, and hence a heating mechanism
exclusively used for warming the air need not be provided. The air
is taken at a negative pressure from the air supply tubes 60 and 61
by the suction of the exhaust pump 70, and thereby the air supply
system can be simplified. Note that the temperature of the warm air
does not exceed the upper limit temperature of the processor chip
101, and hence there is no problem for the operation and the
reliability of the processor chip 101.
[0061] The refrigerant liquid is supplied to the vaporizing plate
110 from the direction of the supply liquid flow 112, while the air
is supplied to the vaporizing plate 110 from the direction of the
supply air flow 113. By supplying the air and the refrigerant
liquid from the different directions, the relative humidity of the
air can be kept low till the surface of the vaporizing plate 110.
Further, the saturated vapor layer on the surface of the vaporizing
plate 110 is removed by the wind pressure, and thereby the
evaporation can be promoted. The refrigerant liquid is supplied to
an upper part of the vaporizing plate 110 which is vertically
erected. Thus, by the flow caused by the weight of the refrigerant
liquid itself, and also by the capillary effect of the wick 111,
the refrigerant liquid is spread on the surface of the vaporizing
plate 110, so as to be efficiently evaporated. Further, the
unevaporated residual liquid is also automatically discharged by
the weight of the refrigerant liquid itself, together with the
refrigerant vapor, from a lower part of the vaporizing plate 110.
Thus, the liquid supply system and the exhaust system can be
simplified.
[0062] The refrigerant liquid is circulated through the closed
circuit system which is configured by the liquid supply system, the
exhaust system, and the reflux system, while the air is passed
through the open circuit system in such a manner that the air taken
from ambient air is passed through the air supply system, the
exhaust system, the reflux system, and is then returned to ambient
air. The air with low vapor pressure is supplied to the vaporizing
plate 110 by using ambient air, and thereby the evaporation is
promoted. The exhaust air with increased vapor pressure is fed to
the reflux system, and the refrigerant vapor is condensed. Thus,
the air with reduced vapor pressure is returned to ambient air. The
refrigerant is circulated and hence need not be frequently
replenished. When the refrigerant vapor is slightly leaked from the
exhaust port 82 and thereby the volume of refrigerant in the liquid
tank 122 is reduced, then the refrigerant for evaporative cooling
may be automatically replenished to the liquid tank 122 from the
water conveyance tube 91 or the water returning tube 92 through a
bypass pipe, by utilizing that the refrigerant for evaporative
cooling is the same as the refrigerant of the secondary heat
exchanger.
[0063] The heat flow is in such a manner that the heat generated
from the processor chip 101 is successively conducted to the cap
102, the heat conducting material 105, and the vaporizing plate
110, and is transferred to the refrigerant vapor as the latent
heat, that the refrigerant vapor is fed through the exhaust system
and is condensed in the condenser of the primary heat exchanger 80,
and that the latent heat is transferred to the cooling water in the
secondary heat exchanger 90, and is discharged to ambient air as
the exhaust heat flow 132 from the radiator 130. The refrigerant
vapor is cooled and condensed by the water cooling using the
condensers 120 and 121 more efficiently than the air cooling. Thus,
the primary heat exchanger 80 is miniaturized, so as to be able to
be provided, for example, in a part of a server rack, a side panel,
a back panel, or the like. Further, the primary heat exchanger 80
is separated from the secondary heat exchanger 90 which is the
place where the heat is discharged to ambient air. Thus it is
possible that a server rack in which a server chassis 41 and the
primary heat exchanger 80 are housed is installed in an indoor
place, such as in a room of data center, and the secondary heat
exchanger 90 is installed in an outdoor place. As a result, the
indoor air conditioning load, that is, the air conditioning power
can be reduced without raising the temperature in the room.
[0064] FIG. 5 is a view showing a configuration of an evaporative
cooling system of a second embodiment according to the present
invention. FIG. 8 is a view showing a function of the evaporative
cooling system of the second embodiment. Here, the present
invention is applied to the blade server system is shown similarly
to the case of the first embodiment. The evaporative cooling system
of the second embodiment is different from the first embodiment in
that the air supply system is configured by a warm air blower 62
and the air supply tubes 60 and 61, and that the exhaust system is
configured by the exhaust tube 71.
[0065] In the second embodiment, the evaporative cooling modules 10
and 11 are attached to the processor, the refrigerant liquid is
evaporated from the vaporizing plate having an area larger than
that of the processor chip and having capillaries on the surface
thereof. The refrigerant liquid is supplied from an upper part of
the evaporative cooling modules 10 and 11 via the liquid supply
tube 51. The warm air is supplied to the modules 10 and 11 via the
air supply tubes 60 and 61 from the direction different from the
direction in which the refrigerant liquid is supplied. The
refrigerant vapor and the residual liquid are discharged from a
lower part of the modules 10 and 11. The condensed refrigerant
liquid collected by the primary heat exchanger 80 is again returned
to the modules 10 and 11 through the liquid supply pump 50. The
refrigerant is circulated in the closed circuit circulatory system,
while the air is passed through in the open circuit system from the
warm air blower 62 to the discharge opening 82 of the primary heat
exchanger 80. In the secondary heat exchanger 90, the heat absorbed
by the refrigerant vapor from the processor is eventually
discharged to ambient air via the cooling water and the
radiator.
[0066] According to the second embodiment, the warm air at the
upper limit operating temperature or below of the processor chip
which is the heating element is supplied to the evaporative cooling
modules 10 and 11 from the warm air blower 62. Thereby, the
saturated vapor pressure inside the modules is increased, so as to
facilitate the evaporation of the refrigerant liquid supplied from
the liquid supply pump 50. The air containing the refrigerant vapor
and the unevaporated residual liquid are discharged from the
evaporative cooling modules 10 and 11 by the air supply pressure of
the warm air blower 62, and hence the exhaust pump 70 can be
eliminated from the exhaust system. The latent heat flux, that is,
the cooling capacity is accurately controlled to the variation in
the heat generation amount of the processor, in such a way that the
supply air temperature and the supply air amount (wind velocity) of
the warm air blower 62 are changed according to the operation rate,
the power consumption, the package temperature, or the like, of the
processor.
[0067] FIG. 6 is a view showing a configuration of an evaporative
cooling system of a third embodiment according to the present
invention. FIG. 9 is a view showing a function of the evaporative
cooling system. In the third embodiment, a blade chassis 42 is
provided inside the server chassis 41, and the plurality of blade
boards 30 is enclosed in the inside of the blade chassis 42. The
evaporative cooling is performed inside the blade chassis 42, and
hence liquid-proof treatment against the refrigerant liquid, which
treatment also serves as the affinity coating, is applied to the
surfaces of the board 30, the vaporizing plates 110 and 116
attached to the processor, the chip set 20, the memory module 21,
the connector 31, and the like.
[0068] The refrigerant liquid is supplied to an upper surface of
the blade chassis 42 from the liquid supply system which is
configured by the liquid supply pump 50 and the liquid supply tube
51. The air warmed by the heat generated by the components (an I/O
module, a switch module, a storage module, a management module, a
power supply module, and the like) other than the blade server is
taken into the inside of the blade chassis 42 from an air supply
port 63 by the exhaust pressure of the exhaust pump 70. The
refrigerant liquid is evaporated from the vaporizing plates 110 and
116, the chips 20 and 21, and the like, which are mounted on the
board 30. The refrigerant vapor and the unevaporated residual
liquid are discharged from the lower surface of the evaporative
cooling chassis 42 by the exhaust system which is configured by the
exhaust pump 70 and the exhaust tube 71. The refrigerant liquid is
circulated to the liquid supply system through the primary heat
exchanger 80 and the reflux tube 81. The residual air is exhausted
from the exhaust port 82.
[0069] According to the third embodiment, the evaporative cooling
can be performed not only to the processor but also to the
peripheral chips on the board 30. Thus, it is not necessary to
provide the evaporative cooling module, the liquid supply tube, and
the air supply tube for each processor. Also, the air cooling fan
for cooling the peripheral chips can be eliminated. As a result, it
is possible to reduce the weight of the blade server system. Note
that the vaporizing plate is attached to the processor in the third
embodiment, but the vaporizing plate may be attached to the
peripheral chip according to the heat generation amount of the
peripheral chip. Further, it is possible to attach a common
vaporizing plate over a plurality of chips, and also possible to
provide a vaporizing plate serving as a liquid-proof cover.
[0070] FIG. 10 is a view showing a function of the evaporative
cooling system of a fourth embodiment according to the present
invention. The basic configuration of the fourth embodiment is the
same as that of the second embodiment. But the configuration of
embodiment 4 is different that of the second embodiment in that the
warm air blower 62 intakes warm air from the chamber of the primary
heat exchanger 80 via a suction tube 64, and feeds the warm air
from the air supply tube 60 to the evaporative cooling module 10.
The primary heat exchanger 80 has no exhaust port. Thus, there are
configured a closed circuit circulatory system for circulating air
through the warm air blower 62, the air supply tube 62, the
evaporative cooling module 10, the exhaust tube 71, the primary
heat exchanger 80, and the suction tube 64, and a closed circuit
circulatory system for circulating the refrigerant through the air
supply pump 50, the air supply tube 51, the module 10, the exhaust
tube 71, the primary heat exchanger 80, and the reflux tube 81.
[0071] According to the fourth embodiment, closed circuit systems
are configured for both the refrigerant and air. Thus, even when
the refrigerant vapor is slightly mixed in the air after the
refrigerant vapor is condensed in the primary heat exchanger 80, it
is possible to prevent the loss of the refrigerant as compared with
the cases in the first embodiment and the second embodiment. The
residual air after the refrigerant vapor is condensed is fed to the
warm air blower 62. Thus, the dry air whose saturated vapor
pressure is increased and whose relative humidity is reduced, is
supplied to the evaporative cooling module 10, so as to thereby
promote the evaporation.
[0072] FIG. 11 is a view showing a function of an evaporative
cooling system of a fifth embodiment according to the present
invention. The basic configuration of the fifth embodiment is
similar to that of the first embodiment. However, the configuration
of the fifth embodiment is different from that of the first
embodiment in that the refrigerant liquid is warmed by a liquid
warming heater 52 in the liquid supply system, and that the warm
liquid at the upper limit temperature or below of the processor is
supplied to the evaporative cooling module 10. Similarly to the
effect obtained by supplying the warm air and warm wind in the
first embodiment and the second embodiment, by supplying the warm
liquid, the saturated vapor pressure is increased and also the
relative humidity is reduced in the vicinity of the vaporizing
plate inside the module 10, so that the vaporization efficiency is
improved.
[0073] The liquid warming heater 52 may be provided side by side
with the liquid supply pump 50. In the air supply system, the air
warmed by the heat generated by the peripheral chip may be supplied
in a manner similarly to the case of the first embodiment. However,
when the effect to promote the evaporation by the warm liquid is
enough for the heat generation amount, it is not necessary to warm
the air by the heat generated by the peripheral chip. That is, it
is also possible to change the direction of the intake port of the
air supply tube 60.
[0074] FIG. 12 is a view showing a function of an evaporative
cooling system of a sixth embodiment according to the present
invention. In the sixth embodiment, the pressure on the side of the
evaporative cooling module 10 is made negative by using the exhaust
pressure of the exhaust pump 70, and thereby the warm air is
supplied to the vaporizing plate from the air supply tube 60. Also,
the pressure on the side of the primary heat exchanger 80 is made
positive, and thereby the refrigerant liquid is fed to a liquid
supply tank 53 from the reflux tube 80. In the primary heat
exchanger 80, when the valve of the exhaust port 82 is set in the
closed state, the internal pressure of the chamber is increased by
the exhaust air and the exhaust liquid, so as to make the
refrigerant liquid flow into the reflux tube 81 from the liquid
tank. The liquid supply tank 53 is placed higher in level than the
evaporative cooling module 10. Thus, the refrigerant liquid is made
to flow down from the liquid supply tank 53 to the module 10 by the
weight of the refrigerant liquid itself, so as to be supplied to
the vaporizing plate brought in contact with the processor 100.
[0075] According to the sixth embodiment, the liquid supply pump
can be eliminated from the liquid supply system by using the
exhaust pressure of the exhaust pump and the weight of the
refrigerant liquid itself. Thus, it is possible to reduce the power
required for the cooling system, and also possible to reduce the
size of the blade server system.
[0076] The evaporative cooling system according to the present
invention is suitable for information platform devices, such as a
server, a network, and a storage which are required to have higher
performance and higher density. The evaporative cooling system
according to the present invention can be widely applied to cool an
apparatus having a heating element, such as, for example,
electronic devices such as a PC and a portable telephone, power
devices such as a generator and a fuel cell, and dynamic devices
such as a motor vehicle and a railroad vehicle.
[0077] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *