US20080302505A1

US20080302505A1 - Evaporative cooling system

Info

Publication number: US20080302505A1
Application number: US12/155,614
Authority: US
Inventors: Takeshi Kato; Yoshihiro Kondo; Tatsuya Saito; Naoki Hamanaka
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2007-06-06
Filing date: 2008-06-06
Publication date: 2008-12-11
Also published as: JP2008304093A

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.

Description

INCORPORATION BY REFERENCE

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

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.
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.
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/g·K, and 0.0012 g/cm³, that the specific heat, density, and heat of evaporation of water are 4.2 J/g·K, 1 g/cm³, 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 cm³/s:0.79 cm³/s:0.043 cm³/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.
There are several known examples as the evaporative cooling means.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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_a(W/cm³), heat of evaporation of a refrigerant is set as ε (J/g), saturated vapor pressure is set as e_s(hPa), vapor pressure of atmosphere is set as e_a(hPa), and a coefficient is set as k (g/cm²·s·hPa), the relation between these parameters is expressed by Expression 1.
L _a =k·ε·(e _s −e _a) (1)
The latent heat flux L_ais proportional to the heat of evaporation ε and to the difference between the saturated vapor pressure and the vapor pressure of atmosphere (e_s−e_a). When the percentage φ (%) of the vapor pressure e_aof atmosphere with respect to the saturated vapor pressure e_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_a, it is important that a refrigerant having a large heat of evaporation ε is used, that the refrigerant is evaporated in a condition of high saturated vapor pressure e_s, and that the vapor pressure e_aof atmosphere in the vicinity of the cooling object is reduced to lower the relative humidity φ.
$\begin{matrix} L_{a} = k \cdot ɛ \cdot e_{s} \cdot (1 - \frac{ψ}{100}) & (2) \end{matrix}$
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.
When water having a relatively large heat of evaporation is taken as an example of the refrigerant, the heat of evaporation ε of the second term can be expressed by an approximate expression with respect to temperature t (° C.) as given by Expression 3. Even when the temperature t is changed in a range from normal temperature to (° C.) to the boiling point of 100° C., the temperature dependency of the heat of evaporation ε is relatively small.
ε=2502.3−2.4794t (3)
When the refrigerant is water, the saturated vapor pressure e_sof 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_sis almost exponentially increased. In order to increase the latent heat flux L_a, it is effective to increase the ambient temperature t in the vicinity of the cooling object.
$\begin{matrix} e_{s} = 6.11 \times 10^{\frac{7.5 t}{t + 237.3}} & (4) \end{matrix}$
Similarly, when the refrigerant is water, the fourth term (1−φ/100) is expressed by using the relative humidity φ_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_o, so as to lower the relative humidity φ at temperature t, and to lower the vapor pressure e_aof atmosphere.
$\begin{matrix} 1 - \frac{ψ}{100} = 1 - \frac{ψ_{ο}}{100} \times 10^{\frac{7.5 t_{ο}}{t_{ο} + 237.3} - \frac{7.5 t}{t + 237.3}} & (5) \end{matrix}$
FIG. 13 shows the dependency of the latent heat flux L_aon 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_ois set to 20° C., the relative humidity φ_ois 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_ais increased as the temperature t is elevated.
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_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_ais increased on the basis of the above described method.
A feature of a typical embodiment according to the present invention is that the area where the latent heat flux L_ais 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.
Another feature of the typical embodiment according to the present invention is that the coefficient k and the latent heat flux L_aare 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.
Further, another feature is that the latent heat flux L_ais increased by such a way that the saturated vapor pressure e_sin the vicinity of the vaporizing plate is increased and the relative humidity φ 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_aby similarly supplying to the vaporizing plate the refrigerant liquid at the upper limit temperature or below of the heating element.
Further, another feature is that the latent heat flux L_ais 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 φ at low, and to lower the vapor pressure e_aof atmosphere.
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.
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.
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.
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.
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_aby supplying air of a low vapor pressure e_ato the vaporizing plate by the use of ambient air in the simple open loop system, while circulating the refrigerant in the closed circuit system.
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.
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.
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_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.
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

FIG. 1 is a view showing a configuration of an evaporative cooling system of a first embodiment according to the present invention;

FIG. 2 is a view showing a configuration of an evaporative cooling module of the first embodiment according to the present invention;

FIG. 3 is a sectional view of the evaporative cooling module of the first embodiment according to the present invention;

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;

FIG. 5 is a view showing a configuration of an evaporative cooling system of a second embodiment according to the present invention;

FIG. 6 is a view showing a configuration of an evaporative cooling system of a third embodiment according to the present invention;

FIG. 7 is a view showing a function of the evaporative cooling system of the first embodiment according to the present invention;

FIG. 8 is a view showing a function of the evaporative cooling system of the second embodiment according to the present invention;

FIG. 9 is a view showing a function of the evaporative cooling system of the third embodiment according to the present invention;

FIG. 10 is a view showing a function of an evaporative cooling system of a fourth embodiment according to the present invention;

FIG. 11 is a view showing a function of an evaporative cooling system of a fifth embodiment according to the present invention;

FIG. 12 is a view showing a function of an evaporative cooling system of a sixth embodiment according to the present invention; and

FIG. 13 is an illustration of an evaporative cooling model according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of evaporative cooling systems according to the present invention will be described with reference to the accompanying drawings.
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.
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.
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.
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.
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.
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.
In the first embodiment configured as described above, the evaporative cooling is performed by obtaining the latent heat flux of about 4 W/cm², for a processor having a maximum power consumption of about 100 W, the upper limit operating temperature of 65° 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° C., under an atmosphere condition set at a usual room air temperature of 25° 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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;

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;

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

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 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;

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:

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.